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Demography, dispersal and colonisation of larvae of Pacific giant salamanders (dicamptodon tenebrosus… Ferguson, Heather Margaret 1998

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DEMOGRAPHY, DISPERSAL A N D COLONISATION OFL A R V A E OF P A C I F I C G I A N T S A L A M A N D E R S (DICAMPTODON  TENEBROSUS,  GOOD)  AT T H E NORTHERN EXTENT OFTHEIR R A N G E by Heather M a r g a r e t F e r g u s o n  H o n s . B . S c , T h e U n i v e r s i t y o f T o r o n t o 1995 A THESIS S U M B I T T E D I NP A R T I A L F U L F I L M E N T O F THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OFGRADUATE  STUDIES  Department o f Z o o l o g y  v  W e accept this thesis as c o n f o r m i n g Jx> the(TeT3t}hpd standard  THE UNIVERSITY OFBRITISH  COLUMBIA  N o v e m b e r 1998 © Heather M a r g a r e t F e r g u s o n , 1998  In presenting  this thesis  in partial fulfilment of  the  requirements  for  an  advanced  degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. copying  I further agree that permission for  of this thesis for scholarly purposes  department  or  by  his  or  her  may be granted by the head of  representatives.  It  is  understood  that  publication of this thesis for financial gain shall not be allowed without permission.  Department of  zealot  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  extensive  copying  my or  my written  Abstract T h e P a c i f i c G i a n t Salamander, (Dicamptodon  tenebrosus G o o d ) is red-listed i n B r i t i s h  C o l u m b i a , the northern extent o f the species' range. L i t t l e is k n o w n about the demography o f these populations and their ability to recover f r o m disturbance b y r e c o l o n i s a t i o n . I c o n d u c t e d a f i e l d experiment to measure the c o l o n i s i n g ability o f l a r v a l P a c i f i c G i a n t Salamanders at 4 streams w i t h i n the C h i l l i w a c k V a l l e y o f B r i t i s h C o l u m b i a . I also estimated basic s u r v i v a l , g r o w t h a n d dispersal rates f o r these larvae. These rates were c o m p a r e d to others f r o m O r e g o n where this species i s not considered threatened. M a r k - r e c a p t u r e i n 120 m reaches i n four streams i n 1996 a n d 1997 revealed (a) l o w e r larval densities, (b) l o w e r annual g r o w t h rates and (c) s i m i l a r annual s u r v i v a l o f these larvae i n c o m p a r i s o n to those i n s i m i l a r O r e g o n streams. D u e to s l o w e r g r o w t h rates, I hypothesise the the larval p e r i o d i n B r i t i s h C o l u m b i a is 2-3 times longer than i n O r e g o n . T o study c o l o n i s a t i o n , larvae were r e m o v e d f r o m a 2 5 - 4 0 m section w i t h i n each 120 m reach and the recolonisation o f each section was m o n i t o r e d f o r 13 m o n t h s . D e p l e t e d reaches were repopulated s l o w l y b y l a r v a l dispersal and m o r e q u i c k l y b y adult r e p r o d u c t i o n . F e w larvae m o v e d m o r e than 4 m . F u l l r e c o l o n i s a t i o n o f these reaches was p r e d i c t e d to take 6-42 months. P r o v i d e d terrestrial adults are available, l o c a l r e p r o d u c t i o n appears to b e a m o r e effective means o f repopulating an area than l a r v a l i m m i g r a t i o n . L a r v a l dispersal was not influenced b y l a r v a l density, b i o m a s s , substrate, wetted w i d t h , depth, or pool-riffle c o m p o s i t i o n . L o g g i n g - i n d u c e d habitat shifts m a y thus have little consequence to l a r v a l dispersal as m o v e m e n t was u n i f o r m l y l o w t h r o u g h a variety o f m i c r o habitats.  A l t h o u g h l o g g i n g and other disturbances m a y increase the rate o f l o c a l e x t i n c t i o n o f D. tenebrosus'm B r i t i s h C o l u m b i a , these populations are not unusually susceptible to disturbance. D e s p i t e h a v i n g l o w e r density and growth rates than i n other parts o f their range, larvae i n B r i t i s h C o l u m b i a exist w i t h i n the s u r v i v a l and g r o w t h bounds o f other non-threatened s t r e a m - d w e l l i n g salamanders. M o r e importantly, recruitment can facilitate r a p i d recovery f r o m small-scale disturbances. C o n s e r v a t i o n efforts s h o u l d focus on terrestrial as w e l l as aquatic habitat a n d dispersal routes.  Table of Contents Abstract  ii  T a b l e o f Contents  iv  L i s t o f Tables  vi  L i s t o f Figures  x  Acknowledgements  xiv  Dedication  xv  CHAPTER 1  General Introduction  C H A P T E R 2 Life history and demography of Pacific Giant Salamander larvae in five streams at the northern limit of its range  1  7  Introduction  7  Methods  11  Results  17  Discussion  ;  Conclusions  CHAPTER 3  Determinants of Dispersal in Pacific Giant Salamander larvae  . 2 0 26  45  Introduction  45  Methods  49  Results  54  Discussion  58  Conclusions  60  C H A P T E R 4 Colonising ability of Pacific Giant Salamander larvae  78  Introduction  78  Methods  81  Results  89  Discussion  92  Conclusions  99  iv  C H A P T E R 5 General Conclusions  116  Bibliography  123  Appendix 1  132  Appendix 2  133  Appendix 3  134  List of Tables Table 2.1  Page A g e and category o f forest surrounding streams used i n d e m o g r a p h i c analysis o f larval D. tenebrosus populations.  2.2  27  D u r a t i o n and frequency o f s a m p l i n g o f five sites used i n demographic study. Sites were s a m p l e d once a week.  2.3  28  Dates o f sampling for estimation o f l a r v a l abundance and s u r v i v a l . O n l y one sampling p e r i o d was possible at F o l e y R as the efficiency o f capture became so l o w i n A u g u s t o f 1996 that m o n i t o r i n g was discontinued. L a r v a e were still present i n this site i n 1997 but at v e r y l o w density.  2.4  29  M e a n l a r v a l abundance and density at the f i v e study sites. N u m b e r s i n brackets represent the n u m b e r o f density estimates used to calculate the mean value.  2.5  30  M e a n larval density i n streams r u n n i n g through different forest types. Clearcut sites h a d significantly l o w e r density than those r u n n i n g through y o u n g second g r o w t h ( A N O V A , F , i = 4 . 5 9 3 , 2  4  p= 0..029). 2.6  31  M e a n b o d y length ( + S D ) o f larvae at each site. T u k e y ' s H S D test was used to c o m p a r e sites. Sites that share the same H S D letter are statistically indistinguishable at p = 0.05.  2.7  32  J o l l y - S e b e r (J-S) estimates o f D. tenebrosus l a r v a l s u r v i v a l and disappearance rates ( + S E ) . J - S s u r v i v a l estimates are for one m o n t h i n the s u m m e r o f 1996 a n d for 9 m o n t h s (September - June) o v e r the winter o f 1996-1997. D i s a p p e a r a n c e rates have been scaled to reflect change over a m o n t h p e r i o d i n b o t h s u m m e r and winter.  2.8  33  T h e relationship between change i n snout-vent length a n d n u m b e r o f days between capture o f D. tenebrosus larvae d u r i n g the active season. P-values are the p r o b a b i l i t y that the slope o f the change i n length vs. time relationship is indistinguishable f r o m zero.  34  vi  Page  Table 2.9  T a b l e 2.9: D e m o g r a p h i c variables collected for l a r v a l D. tenebrosus and the c l o s e l y related D. ensatus throughout their range.  Subscripts  represent the source o f i n f o r m a t i o n : a) this study, b) K e l s e y 1995, c) C o r n & B u r y 1989, d) N u s s b a u m & C l o t h i e r 1973, e) K e s s e l & K e s s e l 1943 & f) H a y c o c k 1991. W h e r e possible, data are stratified b y forest type w i t h l o g g e d sites b e i n g less than 10 years o l d a n d forested sites older than 10 years. D a t a presented i n the m i d d l e o f a b o x are not habitat specific.  2.10  35  S u m m a r y table o f demographic variables and their relationship to larval density and l o g g i n g history. F o r each variable, sites are r a n k e d f r o m highest value to lowest (highest = left, l o w e s t = right). O f the four d e m o g r a p h i c variables, time since harvest correlates o n l y w i t h d a i l y g r o w t h rate (negative). L a r v a l density correlates w i t h none o f the four d e m o g r a p h i c variables. P r o B H = P r o m o n t o r y B H , P r o 3 a = P r o m o n t o r y 3a, C e n = Centre H F , F o l R = F o l e y R a n d T a m C = Tamihi C - D S .  3.1  36  N a m e and location o f four D. tenebrosus larvae streams used i n study. A l l populations were studied f r o m J u n e to O c t o b e r i n 1996,  3.2 3.3  and i n June and September o f 1997.  62  M a c r o h a b i t a t and e n v i r o n m e n t a l features measured at each site.  63  Substrate definition and size classes. S i z e designation refers t o the longest l o n g i t u d i n a l axis o f the stone.  3.4'  64  Percentage o f m o v e r s and n o n - m o v e r s at each site. T h e larvae at Centre H F were significantly more l i a b l e to m o v e than those at a l l other sites ( C h i - s q u a r e d test f o r t w o w a y tables, % = 10.348, 2  p < 0.025). 3.5  65  M e d i a n distance m o v e d b y larvae at each site. T h e m e d i a n c u m u l a t i v e distance m o v e d at Centre H F was s i g n i f i c a n t l y h i g h e r than at any other site ( B r o w n - M o o d M e d i a n test, % = 18.42, d f = 3, p < 0 . 0 0 1 ) . 2  66  vii  Table 3.6  Page M o v e m e n t b e h a v i o u r and habitat properties o f four D. tenebrosus larvae populations. V a l u e s i n brackets (x,y) represent the n u m b e r o f samples used i n each analysis, w i t h " x " indicating the n u m b e r o f times the site was visited and " y " the number o f samples taken o n each visit. T h e s y m b o l denotes w h i c h habitat variables were +  significantly different between sites., w i t h different letter superscripts being significantly different f r o m one another ( T u k e y ' s H S D test). T h e * s y m b o l indicates w h i c h habitat properties distinguish the most m o b i l e p o p u l a t i o n , Centre H F , f r o m a l l the others. 3.7  67  A n a l y s i s o f covariance results f r o m study of l o c a l m o v e m e n t (10 m reach scale), habitat characteristics and site effects. S i x t e e n data points were used i n each A N C O V A (4 f r o m each site). M a i n effect results refer to the relationship between a continuous habitat variable and the l o g ( x + l ) transformed n u m b e r o f i m m i g r a n t s and emigrants respectively. Interaction effects test the hypothesis that the slopes o f the relationship between a habitat variable and movement are s i m i l a r at a l l sites.  68  4.1  Periods w h e n c o l o n i s a t i o n b y D. tenebrosus larvae were m o n i t o r e d .  101  4.2  S i z e and location o f r e m o v a l zones w i t h i n the 120 m study reach.  102  4.3  N u m b e r o f larvae detected and r e m o v e d f r o m experimental stream reaches. T h e n u m b e r o f detected larvae does not i n c l u d e i n d i v i d u a l s - that were k n o w n to have dispersed out o f the r e m o v a l zone before the start o f the e x p e r i m e n t based o n their l o c a t i o n s i n subsequent w e e k l y surveys, or those o n the verge o f t r a n s f o r m a t i o n . R e m o v a l efficiency is the total n u m b e r r e m o v e d d i v i d e d b y the total n u m b e r detected.  4.4  103  N u m b e r s o f D. tenebrosus larvae estimated to have c o l o n i s e d each r e m o v a l zone annually under the C o n s e r v a t i v e , Statistically P r o b a b l e and L i b e r a l M o d e l s .  4.5  104  N u m b e r o f larvae captured i n 120 m study area and the percentages o f these that were c o l o n i s e r s .  105  viii  M a g n i t u d e o f l o c a l density reduction caused b y experimental r e m o v a l o f larvae i n four study reaches and the expected times f o r these depletions to be replenished by colonisation. T h i s prediction o f r e c o l o n i s a t i o n time is based on the assumption that rates measured d u r i n g the 13 m o n t h s o f this experiment w o u l d remain constant through t i m e . I d i v i d e d the total length o f the depleted reaches b y their estimated recovery time to predict the rate at w h i c h stream reaches w i t h s i m i l a r density reductions w o u l d be recolonised.  List of Figures Figure 2.1  Page E s t i m a t e d abundance o f D. tenebrosus larvae at four study sites i n 1996 and 1997. B a r s represent one standard error  2.2  37  S i z e frequency distributions o f D. tenebrosus larvae at 5 sites. Distributions are p o o l e d over a l l captures f r o m June-September 1996, a n d June and September 1997 (one record per i n d i v i d u a l ) .  2.3a  38  Seasonal changes i n size structure o f larvae at the Centre H F site. T h e x-axis represents total b o d y length ( m m ) and the y - a x i s is proportion i n sample.  2.3b  Seasonal changes i n size structure o f larvae at the P r o m o n t o r y 3 a site. A x e s are the same as i n F i g u r e 2.3a.  2.3c  42  Seasonal changes i n l a r v a l size structure i n 4 D. tenebrosus populations i n 1997. A x e s are the same as i n F i g u r e 2.3a.  2.5  41  Seasonal changes i n size structure o f larvae at the T a m i h i C - D S site. A x e s are the same as i n F i g u r e 2.3a.  2.4  40  Seasonal changes i n size structure o f larvae at the P r o m o n t o r y B H site. A x e s are the same as i n F i g u r e 2.3a.  2.3d  39  43  P r e d i c t e d change i n snout-vent length ( m m ) i n D. tenebrosus larvae f r o m four different streams. T h e s e rates a p p l y o n l y between June and September (active season). T h e slope o f these relationships d i d not significantly differ between sites ( A N C O V A , Site effects F , i o = 0 . 3 3 2 , p = 0 . 8 0 2 ) . 3  3.1  2  44  Seasonal differences i n the average v o l u m e o f each 120 m reach . T h e error bars represent one standard error. A v e r a g e water v o l u m e was significantly higher i n the early season at C e n t r e H F (T-test, t = 2.814, p = 0 . 0 0 2 , d f = 8), P r o m o n t o r y 3 a (t = 4 . 1 4 6 , p = 0 . 0 0 4 , d f = 8) and P r o m o n t o r y B H (T-test, t= 3 . 3 3 4 , p = 0 . 0 1 2 5 , d f =7). N = 6 for dark bar, N = 4 f o r l i g h t bar.  3.2a 3.2b  Seasonal changes i n wetted w i d t h at f o u r streams. Seasonal changes i n depth at f o u r streams.  69 70 70  x  Figure 3.3  Page Seasonal differences i n the m e a n percentage o f p o o l habitat i n each stream w i t h standard errors. T h e transformed values o f mean percentage o f p o o l habitat were significantly different between the late season 1996 a n d early season 1997 at C e n t r e H F (T-test, t = - 3 . 9 2 4 , p = 0 . 0 0 6 , df=7) a n d at T a m i h i C - D S (T-test, t= - 4 . 0 8 2 , p = 0.004, d f = 8 ) . S a m p l e sizes as i n F i g . 3.1.  3.4a  Differences i n mean air temperature between late season 1996 and early season 1997. E a c h site m e a n was based o n 8-18 observations.  3.4b  72  Differences i n mean water temperature between late season 1996 a n d early season 1997- E a c h site m e a n was based o n 8-18 observations.  3.5  71  72  C u m u l a t i v e distance traveled b y D. tenebrosus larvae early and late i n their active season. T h e s e data are p o o l e d f r o m a l l o f the f o u r streams. E a r l y season refers to m o v e m e n t s made i n June and J u l y 1997 (n = 30) and late season to m o v e m e n t s made i n A u g u s t a n d September 1996 (n = 76). T h e r e w a s n o significant difference between these t w o distributions ( K o l m o g o r o v - S m i r n o v test, p = 0.985).  3.6  73  P r o p o r t i o n o f larvae that m o v e d (displacement greater than 0.5 m ) and d i d not m o v e at t w o different p e r i o d s throughout the active season. T h e proportion o f movers was not s i g n i f i c a n t l y different between these two periods.  3.7  74  M e a n l a r v a l density and standard error at f o u r D. tenebrosus larvae streams.  3.8  75  R e l a t i o n s h i p between the n u m b e r o f larvae m o v i n g into and out o f a 1 0 m reach o f stream d u r i n g a 13 m o n t h experiment. The, n u m b e r o f larvae m o v i n g into a zone was not significantly/related to the number m o v i n g out ( A N C O V A , , i m m i g r a t i o n effect F i , n = 3.201, p = 0.101). T h e r e were n o interactions between site interactions ( A N C O V A , site effects F , n = 0 . 6 1 8 , p = 0.618). 3  3.9  76  T h e relationship between b o d y length and c u m u l a t i v e distance traveled, p o o l e d over all sites (n = 2 4 1 ) . T h e dark l i n e is the l i n e o f best fit between these t w o v a r i a b l e s . T h i s regression was not significant (r = 0 . 0 0 7 , p = 0.192). T h e r e l a t i o n s h i p between these 2  variables is described as : D i s t a n c e traveled (m) = 0 . 0 6 1 * B o d y length(mm) + 4.81. 4.1  77  Steps taken to determine the n u m b e r o f l a r v a l D. tenebrosus colonists under the Statistically P r o b a b l e M o d e l .  107  xi  Figure 4.2  Page Percent recovery o f artificially depleted stream reaches one year after disturbance under 3 different c o l o n i s a t i o n models. Percent recovery is the n u m b e r of colonists after one year d i v i d e d b y the n u m b e r o f larvae detected i n each r e m o v a l zone before m a n i p u l a t i o n . R e c o v e r y values greater than 1 0 0 % indicate that the pre-disturbance abundance was exceeded.  4.3  Percentage of colonisers i n 120 reach as a f u n c t i o n o f m e a n larval density.  4.4a  108  109  Percentage of in-stream colonisers i n source areas as a f u n c t i o n o f m e a n p o p u l a t i o n density. A n in-stream c o l o n i s e r is one that was o r i g i n a l l y captured i n the source areas a n d then dispersed i n t o the r e m o v a l zone.  4.4b  Percentage of recruits i n the r e m o v a l z o n e as a f u n c t i o n o f m e a n p o p u l a t i o n density i n the source areas.  4.5  110  110  O r i g i n o f colonists that c o l o n i s e d the r e m o v a l zone. In-stream dispersers are larvae that entered the r e m o v a l z o n e f r o m up or d o w n stream. R e c r u i t s are young-of-the-year larvae that w e r e l i k e l y deposited into the r e m o v a l z o n e b y adult dispersal and oviposition.  4.6  Ill  E x p e c t e d distribution o f m e a n snout-vent length ( S V L ) i n a r a n d o m l y selected group o f 37 n o n - c o l o n i s i n g larvae and the observed m e a n S V L i n 37 k n o w n colonisers.  4.7  112  E x p e c t e d distribution o f m e a n snout-to-ventral length ( S V L ) i n a r a n d o m l y selected group o f 7 n o n - c o l o n i s i n g larvae and the observed mean S V L i n 7 k n o w n in-stream c o l o n i s e r s . T h e r e is n o significant difference i n the mean length o f larvae that a c t i v e l y c o l o n i s e d the r e m o v a l zone and those that d i d not.  4.8  113  D i s t r i b u t i o n o f mean c u m u l a t i v e distance travelled b y 7 n o n - c o l o n i s i n g larvae f r o m the source areas o f each site (based o n 1000 trials). T h e mean v a l u e o f this d i s t r i b u t i o n , 10.7m, was l o w e r than the m e a n v a l u e m o v e d b y the 7 c o l o n i s i n g larvae : 26.1 m (p = 0.056).  114  Figure 4.9  Page D i s t r i b u t i o n o f the expected number o f downstream m o v e m e n t s i n a r a n d o m l y selected group o f 7 n o n - c o l o n i s i n g larvae (all sites p o o l e d , based o n 1000 trials). T h e mean o f the expected d i s t r i b u t i o n , 3.1 , was not significantly different f r o m the observed n u m b e r o f downstream movements made i n the group o f 7 c o l o n i s i n g  .  larvae, p = 0.224.  115  xiii  Acknowledgments I cannot imagine a more supportive, i n s i g h t f u l and h e l p f u l supervisor than I f o u n d i n D r . William Neill.  I thank h i m for our many hours o f discussion regarding m y thesis a n d the  wonders o f nature i n general, his patience and b e l i e f i n m e w h e n I encountered challenges w i t h m y w o r k , and his sense o f h u m o u r . It has truly been a pleasure to w o r k w i t h D r . N e i l l a n d his advice has been invaluable. I w o u l d also l i k e to thank m y c o m m i t t e e members D r . J a m i e S m i t h and D r . J o h n R i c h a r d s o n . T h e i r careful r e v i e w o f m y research has been instrumental i n shaping m y i n i t i a l l y rough tangle o f ideas into coherency. I greatly appreciate their help. I w o u l d also l i k e to thank D r . D a n H a y d o n for his statistical advice. I w a s very p r i v i l e g e d to have an excellent team o f dedicated f i e l d assistants: D i a n e Casimir, Leonardo Frid, M a r k Krause, Shelagh Parken, A l e x Skrepnik, and C a r o l y n n Stephenson. M a n y thanks to t h e m for their h a r d w o r k and u n f l a g g i n g pursuit o f salamanders i n rain o r shine. A very special thanks goes to K a r l M a l l o r y for his advice o n site selection, capturing techniques, and assistance w i t h f i e l d supplies and h o u s i n g . A d d i t i o n a l thanks g o to the m a n y other volunteers w h o c a m e out to C h i l l i w a c k for a f e w days to h e l p w i t h m y f i e l d w o r k . T h i s project w o u l d not have been p o s s i b l e w i t h o u t the generous f i n a n c i a l support o f Forest R e n e w a l B . C . and the W o r l d W i l d l i f e F u n d o f C a n a d a . I w o u l d also l i k e to thank N . S . E . R . C . w h o p r o v i d e d personal f i n a n c i a l support through a P G S A s c h o l a r s h i p . I must also thank the m a n y people w h o s e friendship and sense o f h u m o u r kept m e o n track. S p e c i a l thanks go to C h r i s t i n e , A n n e , B e a , Christiarine, K r i s t a , Stephanie, M i c h e l l e , < T o n y , D a v i d C . and W e n d y for " d r a g g i n g " m e f o r a beer, k e e p i n g m e c o m p a n y at the R a i l w a y C l u b , and e n d u r i n g Braveheart a r e c o r d 10 times. F i n a l l y , I w o u l d l i k e to each and every o n e o f the 600+ P a c i f i c G i a n t Salamanders that had to endure m y h a n d l i n g throughout the course o f this experiment. I sincerely hope the information I gained through this endeavour w i l l p r o v e useful to the maintenance o f this e l u s i v e and beautiful creature w i t h i n the C h i l l i w a c k V a l l e y .  xiv  For Irene and Tom,  Dulcius ex Asperis  Chapter 1: General Introduction  In 1989, the P a c i f i c G i a n t Salamander {Dicamptodon tenebrosus G o o d ) w a s d e c l a r e d vulnerable b y the C o m m i t t e e o n the Status o f E n d a n g e r e d W i l d l i f e i n C a n a d a ( C O S E W I C ) . T h i s species is red-listed and classified as "at r i s k " b y the p r o v i n c i a l government o f B r i t i s h C o l u m b i a . Despite this designation o f the highest l e v e l o f risk ( B r i t i s h C o l u m b i a M i n i s t r y o f E n v i r o n m e n t , L a n d s & P a r k s 1993), the true status o f this species i n C a n a d a and the extent to w h i c h it is threatened are u n k n o w n . M u c h o f the evidence supporting D. tenebrosus' l i s t i n g c o m e s f r o m observation o f perceived threats such as l o g g i n g ( H a y c o c k 1991), a n d the a s s u m p t i o n that b e i n g on the m a r g i n o f the species' range makes populations i n B r i t i s h C o l u m b i a inherently more vulnerable to extirpation. T h i s assumption is based o n field evidence f r o m other taxa that s h o w s peripheral populations have a greater p r o b a b i l i t y o f l o c a l e x t i n c t i o n ( L o m o l i n o & C h a n n e l 1995, N a t h a n et a l . 1996) than those i n the centre due to l o w e r p o p u l a t i o n densities ( H e n g e v e l d 1990, L a w t o n 1993), l o w e r s u r v i v a l ( R a n d a l l 1982, R o g e r s & R a n d o l p h 1986), a n d l o w e r fecundity ( C a u g h l e y et a l . 1 9 8 6 ) . W h i l e these factors m a y warrant c o n c e r n , there has been n o thorough demographic examination o f D. tenebrosus populations i n B r i t i s h C o l u m b i a to demonstrate that they are truly i m p e r i l l e d . T h e scientific criteria required to assess whether a species is at r i s k are not w e l l defined. M a n y different schemes o f assessment have been p r o p o s e d ( A y e n s u 1981, M a c e 1 9 9 1 , Spellerberg 1992, P r i m a c k 1993, C a u g h l e y & G u n n 1996), but n o standard m e t h o d o l o g y has been adopted. It i s generally agreed h o w e v e r , that e v a l u a t i o n o f requires k n o w l e d g e o f l o c a l demography, the impact o f h u m a n activities a n d the general a b i l i t y o f the species to respond to disturbance (Soule & K o h n 1989, P r i m a c k 1993, E l l i s & S e a l 1995). U s i n g these issues as a  guide, several k e y questions c a n be f o r m u l a t e d to assess whether D. tenebrosus populations i n B r i t i s h C o l u m b i a merit special conservation attention:  a) Local  Demography  • A r e population densities significantly reduced i n regions where the species is c o n s i d e r e d threatened i n c o m p a r i s o n to areas where they are not? • A r e populations d e c l i n i n g i n regions where they are considered threatened? • A r e vital demographic rates such as s u r v i v a l , fecundity and/or g r o w t h s i g n i f i c a n t l y l o w e r i n regions where the species is c o n s i d e r e d threatened i n c o m p a r i s o n to areas where it i s not? • A r e D. tenebrosus' vital d e m o g r a p h i c rates uncharacteristically l o w i n c o m p a r i s o n to other non-threatened stream d w e l l i n g salamanders?  b) Impact of human activities • A r e p o p u l a t i o n densities, s u r v i v a l , f e c u n d i t y and/or g r o w t h rates r e d u c e d i n regions that have been logged, the p r i m a r y f o r m o f h u m a n disturbance i n D. tenebrosus'  range?  • D o the specific habitat changes caused b y l o g g i n g c o m p r o m i s e D. tenebrosus' dispersal and recolonisation ability?  c) General ability to recover from  disturbance  • H o w q u i c k l y can D. tenebrosus r e c o l o n i s e sites o f l o c a l extinctions?  S o m e o f these questions are addressed i n this thesis. term population trends cannot be assessed.  I n a t w o year study such as this one, l o n g  H o w e v e r , basic life history i n f o r m a t i o n a n d seasonal  demographic rates can be estimated. T h i s i n f o r m a t i o n is a c r u c i a l first step f o r i d e n t i f y i n g whether these allegedly vulnerable populations behave differently f r o m those i n O r e g o n , W a s h i n g t o n and C a l i f o r n i a where the species is not a major c o n s e r v a t i o n c o n c e r n . T h e s e basic rates c a n also be c o m p a r e d to those i n other, non-threatened s t r e a m - d w e l l i n g salamanders to reveal whether this salamander is intrinsically less viable than other species. S u c h f r a g i l i t y w o u l d indicate an increased susceptibility to extinction, even i n the absence o f disturbance.  2  T o obtain reliable demographic estimates, I repeatedly sampled a f e w populations (5) instead o f less intensively s a m p l i n g a large n u m b e r o f sites. T h i s study is the first to p r o d u c e robust estimates of larval density, s u r v i v a l , g r o w t h , dispersal and c o l o n i s i n g ability f o r several p o p u l a t i o n s o f D. tenebrosus. M a n y of these parameters such as s u r v i v a l a n d g r o w t h have n e v e r before been rigorously estimated for D. tenebrosus i n B r i t i s h C o l u m b i a . Others such as c o l o n i s i n g ability have never been measured for this species anywhere i n its range. In addition to the estimation of basic v i t a l rates, I e x a m i n e d i f the m o r e recently l o g g e d sites d i s p l a y e d distinct demographic properties. A l t h o u g h not rigorous, this qualitative analysis m a y generate preliminary hypotheses o f h o w habitat influences l a r v a l persistence. T h i s species' general ability to recover f r o m disturbance, a f i n a l indicator o f v u l n e r a b i l i t y , was studied experimentally. In B r i t i s h C o l u m b i a , l o g g i n g is presumed to increase the frequency o f l o c a l e x t i n c t i o n ( F a i r 1989, H a y c o c k 1991), yet almost n o t h i n g is k n o w n o f  Dicamptodon's  ability to recover by colonisation. I simulated p o i n t extinctions w i t h i n l a r v a l populations a n d m o n i t o r e d the speed of recolonisation. I also studied l a r v a l dispersal i n d i f f e r i n g stream m i c r o habitats to determine i f recolonisation is habitat-dependent.  I) N a t u r a l H i s t o r y P a c i f i c G i a n t Salamanders are an i m p o r t a n t c o m p o n e n t o f the vertebrate fauna i n the forests o f the P a c i f i c Northwest. In the streams w h e r e it occurs, this salamander is often the dominant predator and can constitute up to 9 9 % o f the total vertebrate b i o m a s s ( M u r p h y & H a l l 1981). L a r v a e prey p r i m a r i l y upon benthos ( P a r k e r 1994) although large i n d i v i d u a l s c a n also eat T a i l e d F r o g (Ascaphus truei) larvae, s m a l l fish a n d s m a l l e r c o n s p e c i f i c s ( N u s s b a u m et a l . 1983). A d u l t salamanders consume large prey i n c l u d i n g m i c e , shrews and l i z a r d s ( B u r y 1972). W i t h  3  larvae o c c u r r i n g at densities o f up to 3 per m  2  i n some P a c i f i c N o r t h w e s t streams ( K e l s e y 1995),  they m a y regulate numbers o f their prey species. In B r i t i s h C o l u m b i a , these animals spend at least t w o years as aquatic larvae ( R i c h a r d s o n & N e i l l 1995). L a r v a e reside p r i m a r i l y i n c o o l , fast f l o w i n g headwater streams although s o m e have been f o u n d i n larger streams and lakes. A f t e r the l a r v a l p e r i o d , D. tenebrosus either transform into sexually mature terrestrials or r e m a i n i n streams i n neotenic f o r m . A d u l t s c a n g r o w up to 35 c m i n total length, m a k i n g this species the largest semi-aquatic salamander i n N o r t h A m e r i c a ( N u s s b a u m et a l . 1983).  II) D i s t r i b u t i o n P a c i f i c G i a n t Salamanders are f o u n d a l o n g the western coast o f N o r t h A m e r i c a f r o m northern C a l i f o r n i a to southern B r i t i s h C o l u m b i a . In C a n a d a , D. tenebrosus is f o u n d only i n the C h i l l i w a c k R i v e r drainage basin and a few adjacent s m a l l tributaries that d r a i n directly into the Fraser R i v e r . W i t h i n the C h i l l i w a c k V a l l e y watershed, D. tenebrosus i s distributed patchily w i t h many u n e x p l a i n e d gaps i n its distribution. S u r v e y w o r k i n C h i l l i w a c k detected D. tenebrosus i n only 21 o f 59 seemingly habitable streams ( R i c h a r d s o n & N e i l l 1995). It is possible that m a n y o f these currently barren streams have experienced l o c a l e x t i n c t i o n .  III) R o l e o f larvae i n U r o d e l e p o p u l a t i o n d y n a m i c s M y research was conducted solely o n larvae o f D. tenebrosus. W h i l e no concrete prediction o f species' persistence can be d r a w n f r o m the study o f one life history stage, l a r v a l e c o l o g y is an essential component o f p o p u l a t i o n b i o l o g y . F u r t h e r m o r e , there is reason to b e l i e v e that larvae m a y be the o n l y stage i n recently d i s t u r b e d habitats. Terrestrial adults m a y suffer great mortality i n clearcuts due to increased d e s i c c a t i o n a n d f r e e z i n g i n exposed habitats ( R i c h a r d s o n  4  1994). Under such a scenario, depopulated areas would rely on larval propagules from undisturbed stream reaches for recolonisation. Although this hypothesis has not yet been tested, it suggests that studies of larvae are vital to judge the recovery potential of this species.  IV) Organisation of Thesis This thesis is composed of three research chapters and a general conclusions section. The research chapters will address the following three topics: 1) D. tenebrosus larval demographic rates in British Columbia, 2) habitat-dispersal associations and 3) recolonising ability. In combination, these studies will provide new insights into the resilience of this species and whether it is currently compromised in British Columbia. Each chapter is based on two summers of research within the Chilliwack Valley. The major goals and hypotheses of each chapter are outlined below.  1) Life history and demography of Pacific Giant Salamander larvae infivestreams at the northern limit of its range The primary aim of this chapter is to provide base-line demographic information on larval D. tenefcrosw^populations in British Columbia and compare rates with those collected in more southerly, non threatened populations. I also examine the influence of forest age from 5 to 60 years on demography and the impact of larval population density on survival and growth.  2) Determinants of Dispersal in Pacific Giant Salamander Larvae In this chapter, I examine the influence of abiotic and biotic factors on dispersal of D. tenebrosus larvae. A s dispersal is the key means by which populations re-establish in disturbed  5  areas, a k n o w l e d g e o f the environmental a n d demographic factors that l i m i t m o v e m e n t m a y b e useful f o r management.  3) Colonising Ability of Pacific Giant Salamander  larvae  In this experiment I measured h o w q u i c k l y artificially depleted stream reaches w e r e recolonised b y D. tenebrosus larvae. I tested whether larvae are capable o f r e c o v e r i n g f r o m s m a l l disturbances w i t h i n a short p e r i o d o f t i m e (< 1 year). I also tested whether this r e c o l o n i s a t i o n is l i m i t e d b y source p o p u l a t i o n density, size structure a n d l o c a t i o n .  4) General  Conclusions  T h e general conclusions section summarises the major f i n d i n g s o f this research. T h i s section discusses the i m p l i c a t i o n s o f this research to the evaluation o f D. tenebrosus'' current status a n d future persistence i n B r i t i s h C o l u m b i a .  6  Chapter 2: Life history and demography of Pacific Giant Salamander larvae in five streams at the northern limit of its range Introduction: A s the number o f species exposed to h u m a n disturbance increases, there is a great need to assess the potential impacts o n p o p u l a t i o n persistence. A l t h o u g h n o d e f i n i t i v e c r i t e r i a exist, i t is w i d e l y accepted that information o n l o c a l demography is v i t a l to evaluate the v i a b i l i t y o f populations (Soule & K o h n 1989, C a u g h l e y & G u n n 1996, P r i m a c k 1993). B a s i c life history i n f o r m a t i o n is useful both to understand habitat requirements a n d suggest the m e c h a n i s m s that l i m i t populations i n different areas. R e d u c t i o n s i n d e m o g r a p h i c rates such as s u r v i v a l , reproduction and growth between habitats c a n also suggest causes o f d e c l i n e and l o c a l e x t i n c t i o n (Caughley & G u n n 1993). C o n v e r s e l y i f demography is unaffected b y habitat change, there is little reason f o r concern about the persistence o f such p o p u l a t i o n s u n d e r s i m i l a r events. In this chapter I present detailed d e m o g r a p h i c analyses o f l a r v a l P a c i f i c G i a n t Salamanders (Dicamptodon tenebrosus) i n five sites i n the C h i l l i w a c k V a l l e y o f B r i t i s h C o l u m b i a , the northern extent o f this species' range. I n B r i t i s h C o l u m b i a , populations o f this red-listed species are thought to be l i m i t e d b y c o o l temperatures a n d threatened b y l o g g i n g ( H a y c o c k 1991). V e r y little demographic analysis has been c o n d u c t e d to support these c l a i m s . I e x a m i n e d l a r v a l s u r v i v a l , recruitment, m e t a m o r p h o s i s a n d g r o w t h . M y a i m s were to:  1) P r o v i d e base-line demographic i n f o r m a t i o n for larvae i n B r i t i s h C o l u m b i a ; 2) E x a m i n e the relationship between l o g g i n g history a n d l a r v a l d e m o g r a p h i c parameters; 3) E x a m i n e the relationship between s u r v i v a l , g r o w t h a n d l a r v a l density.  7  1) P a c i f i c G i a n t Salamander life history - a review G i v e n the secretive nature o f D. tenebrosus, m u c h o f the basic l i f e history o f this a n i m a l remains u n k n o w n . W h a t is k n o w n about this species' e c o l o g y and response to disturbance comes f r o m studies i n W a s h i n g t o n , O r e g o n , and C a l i f o r n i a . V e r y little research has been conducted i n B r i t i s h C o l u m b i a . T h e f o l l o w i n g summarises what is k n o w n about D. tenebrosus' life history and the major questions that r e m a i n .  a) Reproduction W h e r e a s D. tenebrosus i n O r e g o n and C a l i f o r n i a are b e l i e v e d to have distinct breeding periods i n S p r i n g and F a l l ( N u s s b a u m et al. 1983), p r e l i m i n a r y evidence f r o m B r i t i s h C o l u m b i a suggests the t i m i n g o f breeding is variable ( H a y c o c k 1991). I f this is true, D. tenebrosus i n B r i t i s h C o l u m b i a w o u l d be one o f the few temperate a m p h i b i a n species to display asynchronous breeding. ( D u e l l m a n & T r u e b 1986). A l t h o u g h the t i m i n g of breeding m a y be variable, it is potentially concentrated i n specific months or seasons. In this study, mark-recapture throughout the active seasons o f 1996 and 1997 was u s e d to test for seasonality i n recruitment o f D.  tenebrosus. Observations i n aquaria and the f i e l d s h o w that eggs take a p p r o x i m a t e l y 2 0 0 days to hatch ( N u s s b a u m et a l . 1983) into larvae 33-35 m m i n total length ( N u s s b a u m & C l o t h i e r 1973). N e w l y hatched larvae r e m a i n b u r i e d i n the substrate a n d attached to their y o l k sac for three to four months before appearing i n streams at 45-51 m m i n length ( N u s s b a u m & C l o t h i e r 1973). C o m b i n i n g these periods, I assume that larvae are first detectable 9-11 months after they are spawned. U s i n g this c r i t e r i o n , the t i m i n g o f b r e e d i n g i n m y streams w a s back-calculated as 9-11 months f r o m the first appearance o f s m a l l , 4 5 - 5 0 m m l o n g larvae.  8  b) Transformation A f t e r 2-4 years as larvae, D. tenebrosus either transform into terrestrial adults or r e m a i n i n the stream i n neotenic f o r m ( D u e l l m a n & T r u e b 1986). T h e t i m i n g o f transformation varies considerably between populations ( N u s s b a u m & C l o t h i e r 1973), but is b e l i e v e d to o c c u r between June and A u g u s t . I f so, the frequency o f large larvae s h o u l d d e c l i n e o v e r this p e r i o d . I tracked c h a n g i n g size structure throughout the active season to p i n p o i n t the t i m i n g o f transformation i n C h i l l i w a c k streams. D e s c r i b i n g the c h r o n o l o g y o f natural abundance fluctuations i n larval populations, either b y recruitment or metamorphosis, w i l l h e l p b i o l o g i s t s distinguish change caused b y life history processes a n d change caused b y extrinsic factors.  c) Survival L i t t l e is k n o w n about larval s u r v i v a l i n D. tenebrosus and h o w it varies seasonally a n d spatially. Scientists have identified several sources o f mortality i n D. tenebrosus, but not their net effect on s u r v i v a l . C h i e f agents o f m o r t a l i t y i n this species are thought to be c a n n i b a l i s m , predation, and desiccation ( N u s s b a u m & C l o t h i e r 1973). P r e l i m i n a r y research i n the C h i l l i w a c k region suggests that l a r v a l s u r v i v a l varies throughout the year. M o r e larvae " d i s a p p e a r " o v e r the s u m m e r than they do over the winter ( N e i l l & R i c h a r d s o n 1998). It is unclear whether this increased s u m m e r loss rate is due to t r a n s f o r m a t i o n or h i g h e r m o r t a l i t y . I attempted to separate these alternatives b y correcting s u m m e r s u r v i v a l rates for loss due to transformation. Seasonal differences i n s u r v i v a l were then assessed b y c o m p a r i n g this less biased s u m m e r rate to the winter disappearance rate.  9  d) Growth Working in one British Columbia stream, Haycock (1991) found that first year larvae increased between 0.5 to 3.2 mm in snout-vent length ( S V L ) per month during the active season. It is unclear whether these rates vary between streams, habitats and regions. I measured larval growth at four sites within the Chilliwack Valley. Mean growth at these sites was compared to estimates from larvae in Oregon, the centre of D. tenebrosus' range, to examine i f northern populations showed signs of depressed growth  2) The Impact of Logging on Life History Parameters Most studies of D. tenebrosus in the Pacific Northwest have inferred logging effects by correlating larval density to the age of the surrounding forest. Results of these studies have been mixed, with some finding reduced density in logged stands (Bury 1983, Bury & Corn 1988, Connor et al. 1988, Corn & Bury 1989, Cole et al. 1997), others finding no effect (Hawkins et al. 1983, Kelsey 1995) and still others finding increased density in logged areas (Murphy et al. 1981, Murphy & Hall 1981). Without examining demographic rates, it is difficult to interpret why abundance varies, increasing or decreasing, in logged areas. I investigated growth and survival in different aged stands in addition to larval density to determine i f they varied with forest age. Only a small number of sites were investigated in this analysis so my ability to detect habitat-specific population trends is low. However i f recently logged habitat is of poorer quality to D. tenebrosus larvae than mature forest, I expected to find some correlation between larval demographic rates and forest practices. If logging is highly detrimental to these animals, I predicted that either larval density, survival and/or growth should increase with forest age.  10  D e m o g r a p h i c analysis m a y also reveal whether one o f the p r o p o s e d benefits o f l i v i n g i n a recently l o g g e d stream, increased growth ( M u r p h y et al. 1 9 8 1 , M u r p h y & H a l l 1981, H a w k i n s et al. 1983), is v a l i d . Temperature and p r i m a r y p r o d u c t i v i t y o f streams often rise after l o g g i n g , p o s s i b l y enhancing the f o o d supply and length o f g r o w i n g season o f D. tenebrosus ( M u r p h y et al. 1981, C o r n & B u r y 1989). H i g h e r g r o w t h rates c o u l d increase the fitness o f larvae i n clearcut streams b y shortening the length o f time they spend e x p o s e d to size-dependent c a n n i b a l i s m and predation. I tested whether forest age related to l a r v a l g r o w t h rate.  3) B i o t i c R e g u l a t i o n i n D. tenebrosus L a r v a l P o p u l a t i o n s In addition to forest habitat, I also e x a m i n e d the influence o f l a r v a l density o n demography. S o m e studies o f l a r v a l salamanders indicate s u r v i v a l and g r o w t h are p r i m a r i l y a f u n c t i o n o f p o p u l a t i o n density ( K u s a n o 1981, P e t r a n k a & S i h 1986, B u s k i r k & S m i t h 1991). It is therefore possible that larval demography is more i n f l u e n c e d b y density than forest habitat. I e x a m i n e d whether s u r v i v a l and growth decreased w i t h increasing l a r v a l density at four sites. A l t h o u g h the n u m b e r o f sites used i n this analysis is l o w , i f strong density dependence w a s acting these trends s h o u l d be evident.  Methods:  Site Selection F i v e headwater streams i n four watersheds o f the C h i l l i w a c k R i v e r drainage basin were selected f o r study. Sites were selected both o n the basis o f a c c e s s i b i l i t y b y l o g g i n g r o a d and larval abundance. O n l y sites at w h i c h at least o n e larvae w a s detected w i t h i n a p r e l i m i n a r y thirty minute searching p e r i o d were used. Sites differed i n their l o g g i n g history (Table 2.1). F o u r o f  11  the five sites were used i n a colonisation experiment (Chapter 4) a n d were s a m p l e d intensively throughout the active season i n 1996 and 1997. A t these sites, larvae w e r e r e m o v e d f r o m a central p o r t i o n o f the stream. T h i s manipulation s h o u l d not influence this analysis as a l l d e m o g r a p h i c estimates were gathered f r o m larvae l i v i n g outside o f the r e m o v a l zone. T h e fifth site, F o l e y R, was studied o n l y for a f e w months i n s u m m e r 1996. A s a consequence o f reduced s a m p l i n g frequency at this site, estimates o f s u r v i v a l and g r o w t h w e r e not c o m p a r e d to those at other sites. A b u n d a n c e was calculated for this site and used i n the analysis o f l o g g i n g history and l a r v a l density.  Mark-Recapture A 120 m reach o f stream was selected at each site. L a r v a e l i v i n g w i t h i n these reaches were routinely sampled u s i n g mark-recapture. Partial r e m o v a l s o f 2 5 - 4 0 m i n length were conducted o n four o f these five streams. O n l y the r e m a i n i n g 8 0 to 95 m o f u n m a n i p u l a t e d (noncleared) reach was used i n this analysis (Table 2.1)  S a m p l i n g was c o n d u c t e d w e e k l y (Table  2.2). W i t h the exception o f F o l e y R, a l l sites were s a m p l e d at least twenty times. T h i s frequency o f s a m p l i n g ensured that the opportunity to recapture a n i m a l s was h i g h . O n each visit, the entire 120 m reach was systematically searched. A l l large r o c k s and debris were turned over and the substrate inspected f o r larvae. A l l o v e r t u r n e d material was returned to its o r i g i n a l p o s i t i o n . L a r v a e were detected b y sight or t o u c h a n d captured i n s m a l l d i p nets. T h e i r l o c a t i o n was recorded to the nearest h a l f meter and m a r k e d b y t y i n g fluorescent flagging tape to a rock. C a p t u r e d larvae were h e l d i n d i v i d u a l l y i n 1 L plastic jars d u r i n g subsequent processing.  12  U n m a r k e d larvae were anaesthetised i n a 0.33g L "  1  solution o f M S 2 2 2 (tricaine  methanesulfonate). W h i l e anaesthetised, larvae were m a r k e d either b y toe c l i p p i n g o r the insertion o f a P a s s i v e l y Induced T r a n s d u c e r (P.I.T.) tag ( A V I D M i c r o c h i p s , M U S I C C 21-23). E a c h tag emits a distinct electromagnetic field w h i c h c a n be p i c k e d u p b y a h a n d h e l d reader ( A V I D P o w e r T r a c k e r II) and translated into a unique identity code. A n i m a l s w i t h a total length < 100 m m were toe c l i p p e d . A unique c o m b i n a t i o n o f one or t w o toes was r e m o v e d f r o m these animals w i t h a s c a l p e l . T o e s that appeared to b e r e g r o w i n g on subsequent capture were c l i p p e d again. L a r v a e > 100 m m were g i v e n a P . I . T . tag. T o insert a tag, a s m a l l i n c i s i o n was made anterior to the h i n d l e g o n the a n i m a l ' s side. A disinfected tag was then inserted b y hand (wearing m e d i c a l gloves) under the first layer o f s k i n . T h e w o u n d was disinfected w i t h antibacterial ointment a n d sealed w i t h V e t B o n d ™ , a veterinary surgical adhesive. O n recapture, a l l larvae were e x a m i n e d f o r toe loss a n d scanned w i t h a h a n d - h e l d P . I . T . tag reader. T h e total b o d y and snout-vent length o f each l a r v a were r e c o r d e d to the nearest m i l l i m e t r e . A n i m a l s were also w e i g h e d o n a portable electronic balance (Ohaus Inc.) accurate to 0.1 g . A n i m a l s were returned to their i n i t i a l point o f capture after they h a d regained their s w i m m i n g ability.  Larval Abundance and Density  Estimation  I used a c l o s e d mark-recapture m o d e l to estimate l a r v a l density throughout this study. C l o s e d m o d e l s assume that no birth, death o r d i s p e r s a l i n t o o r out o f the study area have o c c u r r e d d u r i n g the p e r i o d w h e n the mark-recapture data were c o l l e c t e d . A s s u c h , data must be gathered over a short p e r i o d o f time to m i n i m i s e bias due to n o n - c l o s u r e ( P o l l o c k et a l . 1990).  13  M a r k - r e c a p t u r e data were split i n t o four periods: S p r i n g 1996, F a l l 1996, S p r i n g 1997 and F a l l 1997 (Table 2.3). W i t h the e x c e p t i o n o f F a l l 1997, each p e r i o d consisted o f data f r o m f o u r mark-recapture episodes over four w e e k s . A f o u r - w e e k p e r i o d was thought to be the longest span of time that w o u l d meet the assumptions o f a c l o s e d p o p u l a t i o n m o d e l . In F a l l 1997, density was estimated on the basis o f t w o instead o f four s a m p l i n g periods. T h e p r o g r a m C A P T U R E ( B u r n h a m et a l . 1994) was used to calculate l a r v a l abundance d u r i n g each 4 week interval ( S p r i n g 9 6 , F a l l 9 6 , S p r i n g 97). F r o m i n s p e c t i o n o f capture records, it was evident that some animals were m o r e l i k e l y to be caught than others. A s a consequence, the assumption o f equal p r o b a b i l i t y . o f capture was v i o l a t e d . T o account f o r this, the data w e r e fitted to a specific m o d e l w i t h i n C A P T U R E ( B u r n h a m & O v e r t o n 1979) k n o w n as M ( h ) that compensates for heterogeneity i n capture p r o b a b i l i t y ( B u r n h a m & O v e r t o n 1979). T h i s m o d e l requires more than t w o s a m p l i n g occasions to determine the amount o f variation i n capture p r o b a b i l i t y between animals. W i t h o n l y t w o s a m p l i n g intervals, F a l l 1997 abundance c o u l d not be estimated by the M ( h ) m o d e l . A b u n d a n c e at this t i m e was calculated u s i n g the L i n c o l n Peterson method ( L i n c o l n 1930). C h a p m a n ' s M o d i f i c a t i o n o f the L i n c o l n - P e t e r s o n m e t h o d was used to offset bias caused b y l o w recapture p r o b a b i l i t y ( C h a p m a n 1951) ( A p p e n d i x 1).  By  i g n o r i n g heterogeneity i n capture probabilities between i n d i v i d u a l s , this m o d e l m a y underestimate abundance i n c o m p a r i s o n to M ( h ) ( P o l l o c k et a l . 1990). L a r v a l density (individuals per m ) was estimated at each site b y d i v i d i n g the estimated abundance b y the area 2  o f the study reach (length o f u n m a n i p u l a t e d stream searched m u l t i p l i e d b y the average wetted w i d t h ) (Table 2.1).  14  Size Structure Variation: Recruitment, metamorphosis and logging impacts Measurements of total length on first capture were pooled over all time periods and used to generate a cumulative length-frequency histogram at all five sites. I used KolmogorovSmirnov tests to examine i f larval size-frequency distributions varied between sites with different logging history. Additionally I examined the mean body size of larvae at each site. Statistical differences in larval size between sites were evaluated using a Kruskal-Wallis test. To investigate temporal trends in recruitment and metamorphosis, I examined how size structure changed throughout the larval active season at four sites. A t each site, histograms of larval total length were computed for each month of the study period: June - September 1996, June and September 1997. Kolmogorov-Smirnov tests were used to determine whether the shape of the length distribution changed significantly through time. The data were examined for evidence of a sudden appearance of larval recruits at some point during the active season and for a sudden disappearance of large larvae due to transformation.  Larval Disappearance Rates and Survival Open population mark-recapture models give relatively robust, unbiased estimates of disappearance rates between sampling intervals (Pollock et al. 1990). Disappearance does not necessarily reflect the amount of death, as animals may also leave the study area by dispersal. From this point forward, I will use the term "disappearance" to refer to the percentage of animals that leave the study area over a given period, while "mortality" is used only when the actual death rate is implied. I calculated and compared larval disappearance rates over one  15  m o n t h i n the active season ( m i d J u l y to m i d A u g u s t ) and over w i n t e r (September - M a y ) at f o u r sites. T h e P r o g r a m J O L L Y was used to estimate these rates ( H i n e s 1991). I also recorded i n f o r m a t i o n o n dispersal and transformation to assess h o w strongly these processes i n f l u e n c e d s u m m e r disappearance rates. B y m e a s u r i n g distances t r a v e l l e d b e t w e e n captures, I was able to characterise l a r v a l dispersal distances a n d estimate the p r o b a b i l i t y o f m i g r a t i o n i n t o o r out o f the study z o n e between s a m p l i n g p e r i o d s . C a l c u l a t i n g the percentage of loss due to transformation was more difficult. F r o m m y observations i n the C h i l l i w a c k area, most larvae > 130 m m i n total length s h o w e d signs o f i m m i n e n t t r a n s f o r m a t i o n , i.e. considerable reduction o f g i l l size and the appearance o f m a r b l i n g o n the s k i n . U s i n g a cut-off o f 130 m m total length, I c a l c u l a t e d the percentage o f larvae large e n o u g h to be o n the verge o f transformation i n each S p r i n g sample. I f this fraction was h i g h , I interpreted disappearance rates f r o m S p r i n g to F a l l as b e i n g significantly influenced b y metamorphosis.  Growth G r o w t h between captures was defined as the change i n snout-vent length ( S V L ) .  As  m a n y larvae lose part o f their tail, p o s s i b l y as a result o f fights, S V L i s a m o r e accurate measure of skeletal growth than total b o d y length. T h e difference i n S V L length between first and last capture d u r i n g the active season (June - September) was p l o t t e d as a f u n c t i o n o f the n u m b e r o f days between captures. A linear regression was used to d e t e r m i n e the strength o f this relationship. A m p h i b i a n g r o w t h is p r o b a b l y best described b y a c u r v i l i n e a r rather than linear relationship, w i t h rates s l o w i n g d o w n w i t h age. H o w e v e r I w a s e x a m i n i n g s i z e changes o n l y over a f e w months o f the active season a n d not between years. I assume l i n e a r analysis is sufficient to describe this short t e r m g r o w t h .  16  T o e x a m i n e h o w age influences g r o w t h , I calculated d a i l y g r o w t h rates f o r larvae < 100 m m (small) i n total length and > 100 m m ( l a r g e ) . A l t h o u g h there is n o d e f i n i t i v e means o f ageing larvae, m y successive 1996-1997 mark-recapture suggests larvae 100 m m i n length are at least one year o l d . T h u s this analysis attempts to l o o k at differences between larvae i n their first year, and those older (2-4 years?). I used analysis o f covariance to determine i f d a i l y g r o w t h was affected b y b o d y size. I f b o d y size strongly affected g r o w t h rate, c o m p a r i s o n s b e t w e e n sites were stratified b y size.  Results Abundance and Density Estimation L a r v a l density i n the five study streams v a r i e d between 0.46 a n d 1.31  larvae m " ( T a b l e 2  2.4). W i t h the exception o f F o l e y R , m e a n density at each site was based o n f o u r estimates o f abundance. A s o n l y one measurement o f density was taken at F o l e y R , this site was e x c l u d e d f r o m statistical analysis o f between-site density differences. M e a n density v a r i e d s i g n i f i c a n t l y between the r e m a i n i n g four sites but not between S p r i n g a n d F a l l ( T w o - w a y A N O V A ,  site  effects: F , = 9.642 p = 0.005, season effects: F i , = 0.419, p = 0.535). L a r v a l density w a s 3  8  8  highest i n the y o u n g second g r o w t h site, but not s i g n i f i c a n t l y so ( T a b l e 2.5). In the four sites m o n i t o r e d f o r t w o s u m m e r s , l a r v a l abundance s h o w e d moderate seasonal and annual fluctuations ( F i g u r e 2.1). S p r i n g densities i n 1997 were a l w a y s s l i g h t l y l o w e r than F a l l 1997 estimates. S i m i l a r l y i n 1996, almost a l l S p r i n g density estimates w e r e equal or less than the F a l l values.  17  Size Structure S u m m e d across a l l s a m p l i n g dates, larval body length at a l l sites varied f r o m 4 0 - 1 6 0 m m (Figure 2.2). M e a n larval size v a r i e d significantly between sites (Table 2.6). L a r v a l size w a s significantly higher i n the y o u n g second growth site ( K r u s k a l - W a l l i s , % = 2 9 . 1 5 2 , p < 0 . 0 0 1 ) . 2  G i v e n that o n l y one site was i n this habitat category, this result c o u l d be due to r a n d o m site v a r i a t i o n a n d not to forestry treatment. Size-structure fluctuated between months i n the s u m m e r o f 1996 ( F i g u r e 2.3 a,b,c,d) a n d 1997 ( F i g u r e 2.4). In F a l l 1997, the size structure at P r o m o n t o r y 3 a a n d T a m i h i C - D S w a s significantly shifted towards s m a l l larvae i n the 4 0 - 5 0 m m length range ( K o l m o g o r o y - S m i r n o v test, p < 0.001). A s i m i l a r influx o f s m a l l larvae appeared at the P r o m o n t o r y B H a n d P r o m o n t o r y 3a i n A u g u s t 1996. T h e p r o p o r t i o n o f larvae larger than 130 m m T L consistently d e c l i n e d f r o m June to September at P r o m o n t o r y B H a n d P r o m o n t o r y 3a. I n 1996, significant decreases i n large larvae were evident as early as J u l y ( K o l m o g o r o v - S m i r n o v test, p < 0.01). S i m i l a r decreases were seen i n 1997, but as n o J u l y sample was taken i n this year it is difficult to p i n p o i n t the start o f this decline.  Larval Disappearance  Rates and Survival  B e f o r e s u m m e r a n d winter rates were c o m p a r e d , they w e r e scaled to the same time p e r i o d . A one-month w i n t e r disappearance rate w a s extrapolated f r o m the n i n e m o n t h rate i n the f o l l o w i n g w a y : 1 M o n t h W i n t e r Disappearance R a t e = (9 m o n t h W i n t e r D i s a p p e a r a n c e R a t e ) ' 1  9  B a c k calculated m o n t h l y winter disappearance rates were not consistently h i g h e r or l o w e r than m o n t h l y s u m m e r rates (Table 2.7). S u m m e r disappearance rates d i d not appear to be related to  18  forest practices, w i t h rates being s i m i l a r l y l o w i n the oldest and youngest site ( P r o m o n t o r y B H and T a m i h i C - D S ) . T h e same is true for w i n t e r rates that h a d no specific association w i t h the l o g g i n g history o f sites. S u m m e r and w i n t e r disappearance rates were not c l e a r l y associated w i t h larval density, w i t h the two streams most s i m i l a r i n density (Centre H F a n d P r o m o n t o r y B H ) h a v i n g the most divergent rates. O n average, larval disappearance over a one m o n t h p e r i o d i n the s u m m e r was about 12%. A s D. tenebrosus larvae are p o o r dispersers ( C h a p t e r 3), I have a s s u m e d dispersal does not s i g n i f i c a n t l y impact m o n t h to m o n t h disappearance rates i n a 120 m reach. T r a n s f o r m a t i o n , however, c o u l d account for a more significant loss o f i n d i v i d u a l s o v e r the s u m m e r m o n t h s . F o r e x a m p l e , i n the first s a m p l i n g p e r i o d o f 1996, 1 8 % (34/192) o f a l l larvae were large e n o u g h to be close to transformation and 8 0 % o f these same i n d i v i d u a l s (n = 34) were never caught again. T h e mean capture probability at a l l sites v a r i e d between 1 5 - 2 0 % per o c c a s i o n . G i v e n that each stream was s a m p l e d an additional 15 times, these large i n d i v i d u a l s s h o u l d have been recaptured at least once d u r i n g the remainder o f the study i f they were still i n the reach i n l a r v a l f o r m . T h e fraction o f the m o n t h l y s u m m e r disappearance due to transformation can be a p p r o x i m a t e d as the percentage o f larvae >130 m m i n an area at the start o f a s u m m e r m o n t h m u l t i p l i e d b y their observed disappearance rate o v e r the same one m o n t h p e r i o d . C o m b i n i n g data f r o m a l l m y study sites, this value equals a p p r o x i m a t e l y 1 0 % ( 1 3 % o f larvae > 130 m m T L x 8 0 % disappearance rate o f these larvae). T h e percent o f larvae that actually die over a one m o n t h p e r i o d i n the s u m m e r can be estimated as the percentage o f total disappearances m i n u s the percentage o f disappearances due to m e t a m o r p h o s i s : 1 2 % - 1 0 % = 2 % . T h i s value s l i g h t l y underestimates mortality as it assumes a l l disappearance o f larvae > 130 m m was due to transformation and not death. T a k i n g this v a l u e as a l o w e r e x t r e m e , I assume that between 2 % -  19  5 % o f larvae die over a one m o n t h p e r i o d i n the summer, the rest o f the loss b e i n g d u e to transformation. A s transformation does not o c c u r i n winter, w i n t e r disappearance rates are l i k e l y to be a g o o d reflection o f m o r t a l i t y . I thus c o n c l u d e that l a r v a l m o r t a l i t y is l o w e r throughout the s u m m e r ( 2 - 5 % per m o n t h ) than it is i n w i n t e r (mean disappearance o f 1 2 % per m o n t h ) . C o m b i n i n g these estimates o f summer mortality w i t h winter disappearances rates, m e a n annual s u r v i v a l o f larvae w a s approximated to be between 3 0 % and 3 5 % .  Growth In the 4 sites where growth w a s studied, s m a l l larvae (< 100 m m total length) g r e w faster than large larvae ( > 100 m m total length) but not s i g n i f i c a n t l y so ( A N C O V A , F i  > 2  n = 1.485, p  = 0.224). P o o l i n g ; a c r o s s a l l b o d y sizes, g r o w t h was d e s c r i b e d at a l l sites ( T a b l e 2.8). M e a n d a i l y l a r v a l g r o w t h rate throughout the active season w a s 0.06 m m ( 9 5 % C L : 0 . 0 4 - 1.11 m m per day). G r o w t h at the o n l y clearcut site, T a m i h i C - D S , w a s almost t w i c e as fast as other sites (Figure 2.5) although the trend w a s not significant. L a r v a l density d i d not influence v a r i a t i o n i n growth.  Discussion: Larval Demography in British  Columbia  a) L a r v a l D e n s i t y In this study, m e a n l a r v a l density w a s 0.88 + 0.09 i n d i v i d u a l s per square meter o f stream. M y study sites were chosen because they h a d relatively h i g h l a r v a l densities and therefore they reflect m a x i m u m densities w i t h i n the C h i l l i w a c k area.  20  b) R e p r o d u c t i o n T w o sites experienced a sharp increase i n young-of-the-year larvae ( P r o m o n t o r y 3 a & T a m i h i C - D S ) i n the late active season ( A u g u s t - September). U s i n g N u s s b a u m et a l . ' s (1983) developmental data as a guide, breeding at these t w o sites must have been concentrated i n September-October o f 1996 to g i v e rise to a recruitment pulse i n the F a l l o f 1997. A t the other t w o sites, density increased i n A u g u s t and September but there was n o increase i n the frequency o f s m a l l larvae. It is difficult to interpret this m i x t u r e o f results. A t b o t h T a m i h i C - D S a n d P r o m o n t o r y 3a, the increase o f recruits i n F a l l o f 1997 c o u l d have been the result o f a s i n g l e c l u t c h hatching. In both cases, the appearance o f hatchlings was concentrated w i t h i n a 10 m reach o f stream. M y results c o u l d thus be e x p l a i n e d b y the existence o f one female at each o f the t w o sites l a y i n g eggs at approximately the same t i m e , and not seasonally restrictive breeding. D i r e c t study o f adults at m a n y different streams is needed to* c l a r i f y seasonal trends i n reproduction. U n f o r t u n a t e l y r a d i o - t r a c k i n g o f 2 0 + adult D. tenebrosus i n the C h i l l i w a c k region b y Johnston (1998) and L . F r i d (pers. c o m m ) have f a i l e d to y i e l d any i n f o r m a t i o n o n reproduction.  c) T r a n s f o r m a t i o n T h e size structure throughout 1996 ( F i g u r e 9a) s h o w s a loss o f large larvae ( > 130 m m T L ) between June and A u g u s t at b o t h the P r o m o n t o r y 3a a n d P r o m o n t o r y B H site. N o c h a n g e i n the frequency o f large larvae was f o u n d at either T a m i h i C - D S o r C e n t r e H F . It is p o s s i b l e that larvae i n the latter sites were m o r e p r o n e to neoteny than those at P r o m o n t o r y 3 a a n d B H .  21  Losses at the Promontory sites were most visible between June and July, suggesting that transformation may peak in the early stages of the active season.  d) Survival After correcting the mean survival rate across all sites for transformation loss, monthly survival of larvae was found to be higher in summer than in winter. Harsh climatic conditions over the winter, including snowfall and the freezing of streams, may be responsible for reduced survival during this season. Extrapolated over a year, these mean survival rates suggest that only 30-35% of larvae survive each year. Survival throughout a 2-4 year larval period (as suggested by Duellman & Trueb (1986) for this species) could thus vary from 1-12%.  e) Growth Larval D. tenebrosus in my study sites grew between 1.3 mm and 3.2 mm in SVL per month from June through September. I found no significant difference between the growth of larvae < 100 mm TL and > 100 mm TL, and thus estimate and all subsequent values were based on the pooled set of all larvae, regardless of body size. My growth rates are similar to those reported by Haycock (1991) who found that first year larvae in one Chilliwack stream grew between 0.5 mm and 3.2 mm SVL per month (mean = 1.3 mm). The above growth calculations are for the active season only (June - September). As rates likely slow during winter months, theseestimates cannot be extrapolated to predict annual growth. At each site, a few larvae were recaptured in successive summers and their annual growth could be calculated. These individuals were not used in my growth analysis as their inclusion would have violated the assumption of linear regression that every value on the x-axis  22  has a measurable value o f y (Zar 1984). A s larvae were o n l y s a m p l e d i n s u m m e r , t i m e (the x axis) w a s a continuous variable o n l y throughout the active season and not between years. T e m p o r a r i l y i g n o r i n g this statistical c o n c e r n , I i n c l u d e d annual g r o w t h i n f o r m a t i o n f r o m these larvae c a l c u l a t e d a growth rate o f 7.3-10.6 m m S V L a year. A s s u m i n g the same amount o f length is added every year, it c o u l d take 4 - 6 years f o r larvae i n m y study areas to g r o w f r o m their S V L w h e n first detectable (= 2 5 m m ) to their S V L at m e t a m o r p h i c size (70 m m +).  Comparison of Demographic Rates with other areas in D . tenebrosus' Range G i v e n the paucity o f data f r o m other parts o f D. tenebrosus' range, it is d i f f i c u l t to m a k e robust geographic c o m p a r i s o n between l a r v a l demography i n B r i t i s h C o l u m b i a and d e m o g r a p h y i n W a s h i n g t o n , O r e g o n and C a l i f o r n i a where the species is not c o n s i d e r e d threatened. k n o w n about this species and its closest relative, Dicamptodon  W h a t is  ensatus, i s presented i n T a b l e  2.9. A f e w general geographic trends i n d e m o g r a p h y are evident, although i n a l l instances these patterns require m o r e replication to be c o n f i r m e d . M e a n density o f larvae i n forested streams i n O r e g o n w a s 2.3 larvae per square meter ( C o r n & B u r y 1989), a l m o s t three times the m a x i m u m density recorded i n this study. T h e difference i n l a r v a l density between W a s h i n g t o n a n d B r i t i s h C o l u m b i a is not nearly so pronounced. T h e m e a n density o f larvae reported i n this study exceeded that f r o m W a s h i n g t o n . H o w e v e r the data f r o m W a s h i n g t o n w a s based o n a r a n d o m s a m p l i n g o f sites whereas data i n this study w a s d r a w n f r o m streams k n o w n to have reasonably h i g h densities o f larvae. A s such it s h o u l d not be c o n c l u d e d that abundance is generally higher i n B r i t i s h C o l u m b i a , but rather that these areas l i k e l y d o not differ greatly i n l a r v a l density. N u s s b a u m & C l o t h i e r (1973) estimated annual s u r v i v a l o f first year D. tenebrosus larvae i n one O r e g o n stream to be 4 3 % , s l i g h t l y greater than the 3 0 - 3 5 % estimated i n this study.  23  A n n u a l s u r v i v a l does not appear to vary m u c h between these regions, h o w e v e r the length o f the l a r v a l p e r i o d does. A c c o r d i n g to m y analysis, larvae i n m y four study streams c o u l d take 4 - 6 years to reach m e t a m o r p h i c size (130 m m T L +). L a r v a e i n t w o O r e g o n streams were estimated to g r o w 2-3 times faster than larvae i n m y study, and are b e l i e v e d to have a l a r v a l p e r i o d o f o n l y t w o years ( N u s s b a u m & C l o t h i e r 1973). E v e n i f annual s u r v i v a l was the same i n O r e g o n a n d B r i t i s h C o l u m b i a , net s u r v i v a l through the l a r v a l p e r i o d w i l l be l o w e r i n B r i t i s h C o l u m b i a . F o r e x a m p l e i f annual s u r v i v a l was 4 0 % i n both regions, s u r v i v a l throughout the entire l a r v a l p e r i o d w o u l d be 1 6 % i n O r e g o n (2 year l a r v a l period), a n d o n l y 0 . 5 - 3 % i n B r i t i s h C o l u m b i a (4-6 year larval period). T h i s difference i n net l a r v a l s u r v i v a l m a y help e x p l a i n w h y densities o f D. tenebrosus are l o w e r i n B r i t i s h C o l u m b i a than i n the centre o f its range. H o w e v e r , m a n y m o r e populations i n both B r i t i s h C o l u m b i a and O r e g o n need to be studied before any geographic trends i n s u r v i v a l c a n be c o n f i r m e d .  The Impact of Logging on Life History  Parameters  T h e l o w number o f sites used i n this study makes it d i f f i c u l t to e x a m i n e the influence o f l o g g i n g on D. tenebrosus. A l t h o u g h m y sites differed i n l o g g i n g history f r o m recently clearcut (< 5 years) to mature second g r o w t h (+ 6 0 years), there w a s almost n o r e p l i c a t i o n o f p a r t i c u l a r forest age classes. A s s u c h , I cannot ascertain whether v a r i a t i o n i n d e m o g r a p h i c rates is due to l o g g i n g effects or r a n d o m site variation. H o w e v e r even w i t h a s m a l l n u m b e r o f sites, it is useful to e x a m i n e i f the more recently l o g g e d sites d i s p l a y distinct d e m o g r a p h i c properties. A c r o s s m y f i v e study streams, o n l y l a r v a l g r o w t h appeared to be associated w i t h forest practices (Table 2.10). A l t h o u g h not statistically s i g n i f i c a n t , l a r v a l g r o w t h rate at the clearcut site was almost t w i c e as fast as i n any o f the c l o s e d c a n o p y sites. T h i s observation is c o m m o n i n  24  fisheries research, where growth i s frequently f o u n d to increase i n clearcut streams ( H a r t m a n & S c r i v e n e r 1990). M y results suggest this p h e n o m e n o n also occurs i n D. tenebrosus larvae. I f both larvae and adults o f D. tenebrosus have greater fitness i n clearcut streams due to increased g r o w t h however, it is unclear w h y these areas are sometimes f o u n d to have the l o w e s t densities o f larvae ( C o r n & B u r y 1989, W e l s h 1991, C o l e et a l . 1997). F u r t h e r research i n recently l o g g e d and unharvested areas is needed to determine whether g r o w t h enhancement i s a constant feature o f larvae i n streams d r a i n i n g clearcuts. It is possible that this p h e n o m e n o n occurs o n l y under certain altitude, p r o d u c t i v i t y and c l i m a t i c conditions. R e g i o n a l differences i n these variables m a y e x p l a i n w h y studies o f D. tenebrosus throughout its range h a v e f o u n d v a r i e d associations between l o g g i n g history and l a r v a l density ( M u r p h y et a l . 1981, M u r p h y & H a l l 1981, B u r y 1983, H a w k i n s et a l . 1983, B u r y & C o r n 1988, C o n n o r et a l . 1988, C o r n & B u r y 1989, K e l s e y 1995, C o l e e t a l . 1997).  Biotic Regulation  o / D i c a m p t o d o n tenebrosus  Larvae  P o p u l a t i o n density w a s not correlated w i t h i n d i v i d u a l g r o w t h o r s u r v i v a l across m y four study sites. G i v e n that D. tenebrosus are aggressive and c a n n i b a l i s t i c , the l a c k o f a relation between density and s u r v i v a l is surprising, especially as density-dependent s u r v i v a l has been . f o u n d i n other stream d w e l l i n g salamanders ( S h o o p 1974, P e t r a n k a & S i h 1986). It is p o s s i b l e that cooler c l i m a t i c conditions experienced b y larvae l i v i n g i n B r i t i s h C o l u m b i a l i m i t populations f r o m attaining densities at w h i c h resources b e c o m e scarce and c o m p e t i t i o n / c a n n i b a l i s m occur.  Conclusions:  25  The mode of larval regulation in my study areas still remains uncertain. There is weak evidence that logging may influence larval growth but not density or annual survival. O n the basis of my investigation, I propose that D. tenebrosus larvae living at the northern extent of their range in British Columbia are limited by regional climatic conditions. This is supported by reduced growth, density and survival (as a consequence of a longer larval period) at my sites in comparison to those from Oregon, the centre of the species' range. B y elevating stream temperature, logging may enhance larval growth rates. Studies of more clearcut areas are required to confirm i f growth enhancement is a universal feature of these habitats, and i f so, what the long term implications of this phenomenon are on population processes.  26  c« CM  S W  o J:  -  G  u  eu  o  sa 5I e £ CB  -M  o  H  •M EC  2  o  Mil T3 C  a, O>-'. W)|  o  X) T3 C C O o  o CD  to bJQ|  o  C 3 O  CD  o CD  c/2  TJ  M  Cfl V  >•  M  «  JS  CN  cu CJ  C cu  E H 03  CD C O CD  u  $  u  o  Ui  53  fc  da  c  o  s  CL,  o  6 o  00  00  CN  ON  CM  co CN  CN  ©  '1  s  rON ON  r-  VO  VO ON ON  ON ON  155  X> h  ,2  ON  ON ON  0) <  e  CN CN CM c or 3 .3 *2 oo  o IK  K  a e U  ON  VO  5T O N oo •4-* 3 bO a 3  oo r-  ON ON  ON ON  U  Pi >~. Oi  1——I  O fc  ON  2 <1> 00  3  c3 CO  CN  ON ON ON  o  c  o  gC CD  CN CD  in 5P CN oo  5T oo  e  CD  CN X) rON .  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C/l CU U  E  c  E  ca  U  ca H  H  CD  X  PQ PQ  o  o u  cn o u  CM CM  CD  s .S3 ca  X!  51 'fc  3  co| u  CD  C CD p-J X! -u» "•*-» ca O o u H  IQ  ca CD 'ca  fc  c  o  Q  U'  CO  CD  ca CO  C  la  , ca  M  CD O  e co CD  E 3 X>  co ca  CU  Centre HF  • •• Spring 1997  Spring 1996  Promontory BH  100 •  50  Spring 1997  Spring 1996  Promontory 3a 250 • 200 • 150 • 100 • 50 • 0 • Spring 1997  Spring 1996  Tamihi C-DS 250 • 200 • 150 • 100 • 50 • 0 • Spring 1997  Spring 1996  Figure 2.1:  E s t i m a t e d abundance o f D. tenebrosus larvae at f o u r study sites  i n 1996 and 1997. B a r s represent o n e s t a n d a r d error. 5  Foley  SO  R  100  120  Total Length  T a m ih i C  140  160  180  (m m )  - D S  0 .3 0 .2  +  0.1 0 60  80  100  B  l  |  |  120  Total Length  C e n tre  1 n  Pro mi realfeeji  |  f  140  |  160  180  (m m )  H F  0 .4  ti g  3 I  it  0.3  0 2  80  100  120  Total Length P r o m o n to ry  80  100  ontory  16 0  140  160  18 0  BH  120  Total Length  Prom  140  (m m )  3a  (m m )  180  Centre H F  June 1996 0.5 0.4 0.3  --  0.2  --  0.1  -I | O •3-  0  |  O  |  co  | | "a | ™ | | | m | m | m \ m \ | O O O O + oo o CMTJco o  O  T -  T—  T—  T—  00  July 1996 0.5 0.4  --  0.3  --  0.2  -  0.1 |M  o  |  —  |B  o  o  o  CO  CO  O  .  o  o ,  OJ  T -  oo  CO  T C O-  + 00 o  August 1996  September 1 996 0.5  T  40  Figure 2.3a:  60  80  100  120  140  160  Seasonal changes i n size structure o f l a r v a e at the C e n t r e H F site.  T h e x-axis represents total b o d y length ( m m ) a n d the y - a x i s i s p r o p o r t i o n i n s a m p l  Promontory 3a  June 1 996  July 1996 0.5 -r0.4 - 0.3 -  o  o  CO  o  CO  o  O  o  CM  o  o  +  O  CD  August 1 996 0.5  H o co  H + o oo  September 1 996  H  h o co  + o oo  Figure 2.3b: Seasonal changes in size structure of larvae at the Promontory 3a site. Axes are the same as in Figure 2.3a.  40  Promontory B H June 1996  July 1 9 9 6  August 1 996 0.5  +—H  o  H  H  CM  o  1  o CO  h  + o oo  September 1 996  Figure 2.3c: Seasonal changes in size structure of larvae at the Promontory B H site. Axes are the same as in Figure 2.3a.  Tamihi C-DS  July 1996 0.5 0.4 0.3 0.2 0.1  H—I—H  0  o  H  o  1—H  o  CO  CD  + o CO  August 1996 0.4 0.3 0.2 0.1 0  o ^r  H—I—H  ^—i—h + o o CO oo  o  CD  September 1996 0.5 0.4 0.3 + 0.2 0.1  +  H—I—I—h  0  o  o CD  O CO  + o CO  Figure 2.3d: Seasonal changes in size structure of larvae at the Tamihi C-DS site. Axes are the same as in Figure 2.3a.  J  -  091 s"  oei.  O)  fgi 02 E_ , ™. Si ni'  T—  CO CD  \_ CD n  CD C 3  E  0) Q.  CD CO  — i — i — i — i — Ofr 10  CO CM  i -  d d d d d  O  LO  CO CM  T-_  d d d d d  o 091-  021.  CD  o  CD  c 3  LO •>3- CO CM  O  i -  •d d d d  d  *  ffl  N  i-.O  d  d  d  d  -o- CO CM . i - o d o d o d LO  LO  ^n  CM  d d d d  td  H—I—I—h  cq CM t - ; o  d d d  d  o  10 cq ou o d d d d d  c .u 3  .o  PH  O c_o O ' X2 4-*  ca <D  o  E— 1  u-  OO  2 o3  ^ CD § -cs CD 5a •xs 2? w M  „ <  O y CO  I  cj to >S oo  i  x! -a  CD C CD CD  £> £ X) Ci „^  >H  •—i c .<D •s ^ > = *n CD C S CD ca co JO O  .5 ,>» its CD C bfl O . c ca x>oo X!  DH  ca  CD co ti cuia CJ CD  a  PH  in  CD  CO CD  H  cu g fa 3 cE a  T3 TJ  X!  O 00  § d "3  11  co m  •8f> S CD m to tS -C <-s  Chapter 3: Determinants of Dispersal in Pacific Giant Salamander Larvae Introduction: T h e p r i n c i p a l a i m o f this study was to examine the influence o f abiotic a n d biotic factors on the dispersal and movement o f D. tenebrosus larvae. A s dispersal is a k e y means b y w h i c h populations c a n re-establish i n sites o f l o c a l extinctions, a k n o w l e d g e o f the e n v i r o n m e n t a l a n d d e m o g r a p h i c factors that enhance movement m a y be useful for management. I studied movement b y D. tenebrosus larvae at t w o different spatial scales i n four streams i n the C h i l l i w a c k V a l l e y . A t each scale I e x a m i n e d the relationships between l a r v a l dispersal, habitat, and p o p u l a t i o n density. T h i s two-tiered approach w a s taken to determine whether m i c r o - h a b i t a t features (< 10 m ) o r the general state o f the stream (mean c o n d i t i o n i n 120 m reach) were a better predictor o f l a r v a l movements. In a d d i t i o n to addressing spatial v a r i a t i o n , I also tested f o r temporal shifts i n m o b i l i t y i n response to seasonal changes i n stream temperature, water v o l u m e and abundance o f p o o l habitat. S o m e scientists have argued that habitat disturbance, s p e c i f i c a l l y b y l o g g i n g , is particularly detrimental to P a c i f i c G i a n t Salamanders as they are adapted to the h i s t o r i c a l l y stable, temperate rainforests o f the P a c i f i c N o r t h w e s t ( W e l s h 1991). H o w e v e r very little is k n o w n about D. tenebrosus' a b i l i t y to survive through disturbance and/or disperse i n response to l o c a l l y adverse conditions. In this study, I describe the m e d i a n values a n d general range o f distances D. tenebrosus larvae are capable o f m o v i n g over t w o s u m m e r s and e x a m i n e whether dispersal is elevated i n habitats w i t h p h y s i c a l attributes s i m i l a r to l o g g e d streams (i.e. open canopy, h i g h silt). T h i s i n f o r m a t i o n w i l l demonstrate the capacity o f larvae to respond to disturbance b y dispersal.  45  Components of larval habitat and their potential impacts on dispersal A l m o s t nothing is k n o w n about the stream attributes that influence dispersal b y D. tenebrosus and facilitate its re-entry into streams after l o c a l e x t i r p a t i o n . I n this study, I e x a m i n e d 13 different environmental factors that m i g h t influence l a r v a l dispersal ( T a b l e 3.2). These variables are frequently referred to i n the literature as important c o m p o n e n t s o f streamd w e l l i n g a m p h i b i a n and fish habitat (Southerland 1986, T u m l i n s o n et a l . 1990, W a l l s et a l . 1992, M u r p h y 1995, W e l s h & L i n d 1996, Slaney & M a r t i n 1997). T h e variables f a l l into five categories: 1) H y d r o l o g y (stream depth, w i d t h , v o l u m e a n d percent p o o l ) , 2) G e o m o r p h o l o g y (slope and substrate c o m p o s i t i o n ) , 3) C l i m a t e (mean air and water temperature), 4) D i s t u r b a n c e history (time since harvest and percent c a n o p y coverage) and 5) F o o d a v a i l a b i l i t y (average macrobenthos abundance). Possible effects o f these variable p h l a r v a l e c o l o g y a n d dispersal are discussed b e l o w .  1) Hydrology L a r v a l P a c i f i c G i a n t Salamanders are p r e d o m i n a n t l y f o u n d i n p o o l s ( H a y c o c k 1991). It is unclear whether higher abundance i n p o o l s is due to l o w e r m o r t a l i t y , increased i m m i g r a t i o n , or adult preference for o v i p o s i t i o n i n these areas. S t r e a m depth a n d w i d t h are also g o o d predictors o f larval salamander abundance, w i t h abundance frequently decreasing w i t h increasing wetted w i d t h ( R i c h a r d s o n & N e i l l 1995) and increased stream depth ( S o u t h e r l a n d 1986, T u m l i n s o n 1990). B y f o l l o w i n g m o v e m e n t i n t o a n d out o f reaches o f different w i d t h , depth a n d p o o l c o m p o s i t i o n , I tested whether dispersal c o u l d account for abundance patterns associated w i t h these variables.  46  2) Geomorphology The abundance of stream dwelling salamanders is often correlated with substrate type (Tumlinson 1990, Welsh & L i n d 1996). In Western Washington and Oregon, the abundance of D. tenebrosus was positively correlated with the number of substrate crevices and cover objects available (Hall et al. 1978, Murphy & Hall 1981, Connor et al. 1988). T o maintain their position against a current, D. tenebrosus larvae must be able to grip the substrate. Gravel and pebble substrates are easier for larval salamanders to grip onto than fine sediment (Holomuzki 1991). Thus alteration of stream sediment size may change displacement rates. In the field I tracked movement rates of larvae on a variety of different substrate types. If displacement increases on silty substrates, influxes of fine sediment into streams after logging (Murphy 1995) may trigger a net loss of larvae from these reaches.  3) Climate Larval activity is often reduced at high temperatures (Maurer & Sih 1996). In Chilliwack, D. tenebrosus larvae become sluggish and easy to catch at stream temperatures > 20 C (W. Neill, pers. comm.). In this study, I compared movements by larvae at four sites differing in mean air and water temperature. If increasing temperature reduces movements, warming of streams may significantly lower dispersal between stream reaches and connected tributaries. Summer water temperatures in streams draining clear cuts in coastal Oregon were up to 1 0 C higher than in those under a closed canopy (Beschta et al. 1987). Even in the absence of other habitat change, increased temperature in logged streams could limit larval dispersal.  47  4) Food avaUabUity The abundance of aquatic invertebrates in streams often increases for a few years after logging. Clearcut sites in Oregon had an average of 1.5 to 2.3 times as many benthic invertebrates in June and August as those in forested sites (Murphy et al., 1983). Such increases may reduce the need to make extended foraging trips in recently logged streams. I thus predicted larval salamanders should move more frequently and perhaps over greater distances in sites with low aquatic invertebrate abundance.  Density Dependent Determinants of Movement and Dispersal In my second analysis, I investigated whether the density of resident larvae influences the number of dispersers an area produces or absorbs. If it does, the reduction or removal of one high density population could alter the flow of individuals to or from surrounding areas. A s D. tenebrosus larvae interact aggressively and prey on smaller conspecifics (Nussbaum et al. 1983, Connor et al. 1988, Mallory 1996), I predicted that greater mortality and/or emigration should occur from high density reaches, and that movement frequency should increase within high density areas. These predictions are based on the assumption that neighbour-neighbour physical contacts increase with density, and should trigger agonistic displacements to other areas of the stream. I tested these predictions at two scales. The first prediction was tested by studying dispersal in and out of a series of 10 m reaches with differing densities, and the second by monitoring the numbers and lengths of movements made within four 120 m reaches of different density.  48  Body size and dispersal A final factor that m a y influence larval m o b i l i t y is b o d y size. B o d y size determines h o w easily a l a r v a can be d i s p l a c e d either b y the stream current or other c o n s p e c i f i c s ( B r u c e 1986, M a l l o r y 1996). In a stream m e s o c o s m experiment, l a r v a l b o d y size was the most important determinant o f displacement probability ( M a l l o r y 1996). S m a l l larvae w e r e routinely d i s p l a c e d or eaten b y larger larvae i n M a l l o r y ' s experiment. C o n s e q u e n t l y I p r e d i c t e d that m o v e m e n t w o u l d decrease w i t h increasing b o d y size.  Methods: Abiotic Determinants of Dispersal I) Habitat and Movement: 120 m Reach Scale L a r v a l m o v e m e n t and habitat associations were studied at f o u r streams differing i n l o g g i n g history i n the s u m m e r o f 1996 and 1997 ( T a b l e 3.1). A t each stream a 120 m reach was chosen and thirteen measures o f stream habitat w e r e c o l l e c t e d ( T a b l e 3.2). A f t e r appropriate statistical transformation, the mean value o f each variable was c o m p u t e d f o r each site. O n e w a y analysis o f variance was then e m p l o y e d to test for between-site differences i n habitat. A l l percentages (i.e. % p o o l habitat, canopy c o v e r a n d substrate c o m p o s i t i o n ) w e r e arcsine square root transformed and a l l counts (i.e. n u m b e r o f benthic invertebrates i n one sample) w e r e square root transformed to better approximate a n o r m a l d i s t r i b u t i o n before analysis. M a r k - r e c a p t u r e censuses were c o n d u c t e d w e e k l y at each site f r o m June to O c t o b e r 1996, and i n June and September 1997 to study l a r v a l m o v e m e n t (see C h a p t e r 2). A l l larvae were u n i q u e l y m a r k e d , either b y toe c l i p p i n g or a P . I . T . tag. O n each v i s i t , the l o c a t i o n o f every l a r v a was recorded to the nearest 0.5 m . L a r v a l dispersal w i t h i n each 120 m reach was  49  characterised by t w o variables: 1) the p r o p o r t i o n of m o v i n g and stationary larvae a n d 2) the c u m u l a t i v e length o f movements. A m o v e m e n t was considered to be any displacement > 0.5 m f r o m the capture point. Information on altitude and time since harvest was taken f r o m forest c o v e r maps o f the C h i l l i w a c k A r e a (1: 250000). A l l other variables were measured i n the f i e l d . B e n t h i c invertebrate abundance was assessed f r o m approximately twelve samples c o l l e c t e d at each site i n J u l y and A u g u s t 1996. Samples were collected i n riffles every 2 0 to 3 0 m a l o n g the study reach using a 3 0 c m x 3 0 c m Surber sampler (250 u.m mesh). T h e substrate w i t h i n the 9 0 0 c m  2  quadrat  was v i g o r o u s l y raked for one minute. A l l material drifting up f r o m the substrate was captured i n the drift net and stored i n 3 3 % ethanol. In the lab, this material was sorted through a 1 m m sieve and counted under a dissecting m i c r o s c o p e . T h e percent o f p o o l habitat i n each 10 m section o f the 120 m study reach was estimated v i s u a l l y o n four occasions in the F a l l o f 1996 (August-September) and o n s i x occasions i n the S p r i n g o f 1997 ( M a y - J u n e ) . P o o l s were i d e n t i f i e d as areas o f stream a p p r o x i m a t e l y 9 0 0 c m or 2  greater i n area o f still water. T h e percent p o o l habitat i n the entire 120 m reach was calculated b y averaging a l l estimates f r o m the 12 consecutive 10 m estimates. These means were averaged over all s a m p l i n g days to give a grand m e a n for the percent o f p o o l habitat i n each site over the course o f the study. T h e percent o f canopy c l o s u r e w i t h i n each o f 12 consecutive 10 m sections was estimated u s i n g a hand h e l d densiometer w i t h a 10 x 10 g r i d . A s c a n o p y c o v e r a g e d i d not vary m u c h throughout the study, this variable was measured o n l y once. T h e slope f r o m the start o f each 10 m reach to the e n d was estimated u s i n g a c l i n o m e t e r . T h e s e t w e l v e estimates were averaged to give the mean slope o f each stream reach.  50  O n the first day o f habitat s a m p l i n g , the widest point i n each 10 m s a m p l i n g reach w a s determined and m a r k e d with a w o o d e n stake. W e e k l y measurements o f wetted w i d t h , m a x i m u m and mean depth were taken at these points (one per 10 m reach) i n A u g u s t - S e p t e m b e r 1996 a n d June 1997. M e a n depth was based o n the average o f s i x e q u a l l y spaced measurements o f depth taken a l o n g a transect perpendicular to the stream b a n k . W e t t e d w i d t h a n d depth measurements were c o m b i n e d to estimate the v o l u m e o f water i n each 10 m section u s i n g the f o l l o w i n g equation:  Vol. of Water in 10m Reach (m) = (Wetted Width at Point) x (Mean Depth at Point) x 10  F o r each s a m p l i n g day, the total water o f v o l u m e i n the study site w a s c a l c u l a t e d as the s u m o f volumes f r o m a l l twelve 10 m reaches. Substrate c o m p o s i t i o n at each site was described i n four r a n d o m l y chosen 10 m reaches. Stream substrate was classified into f i v e different categories o n the basis o f particle size (Table 3.3). F i n a l l y , a i r and water temperatures were m e a s u r e d at each 120 m reach o n every s a m p l i n g occasion.  JJ) Habitat and L o c a l D i s p e r s a l : 10 m R e a c h S c a l e F o u r non-contiguous 10 m segments were r a n d o m l y c h o s e n f r o m each 120 m reach. Seven e n v i r o n m e n t a l variables that v a r i e d between segments were measured i n each 10 m zone: percent coarse substrate (substrate > 6 4 m m across the longest l o n g i t u d i n a l axis), percent silt substrate, percent canopy coverage, percent p o o l habitat, slope, m a x i m u m wetted w i d t h a n d m a x i m u m stream depth. M e a s u r e m e n t s w e r e taken at each reach o n several occasions  51  throughout the summer of 1996 and 1997. All percentages were arcsine square root transformed for analysis. I used analysis of covariance to determine if there was a relationship between each habitat variable and the number of larvae moving into or out of a reach (log(x + 1) transformed) and whether this relationship varied between sites.  Seasonality and Movement: Variation in Time  Water volume, percent pool and temperature (air and water) show strong seasonal fluctuations in streams. Mean values of these variables were computed for August-September 1996 (late active season) and May-June 1997 (early active season). I examined whether seasonal changes in these variables were mirrored by corresponding differences in larval movement.  Biotic Determinants of Dispersal  I) Larval Density and Movement: 120 m Reach Scale In this analysis I examined the association of movement frequency, movement length to larval density within the four 120 m study reaches. Mark-recapture data collected in 1996 and 1997 were used to estimate the larval density at each of the four study streams. I calculated the mean density of larvae at each site throughout two summers of study (see chapter 2 for estimation methods). I assessed whether the frequency and median length of movements made at each site increased with larval density.  52  II) L a r v a l D e n s i t y and L o c a l D i s p e r s a l : 10 m R e a c h Scale F o u r non-contiguous 10 m reaches were r a n d o m l y chosen f r o m each o f the four study sites. F r o m repeated mark-recapture s a m p l i n g , the total n u m b e r o f resident animals l i v i n g i n each reach f r o m June 1996 to September 1997 w a s recorded. A resident w a s d e f i n e d as a n animal that w a s only ever caught w i t h i n the 10 m reach. O v e r this same p e r i o d , the n u m b e r o f immigrants a n d emigrants into each zone w a s recorded. A n i m m i g r a n t w a s a l a r v a i n i t i a l l y caught outside the 10 m focal reach that subsequently dispersed into it. A n emigrant w a s a l a r v a initially f o u n d w i t h i n the 10 m reach that dispersed out. A per capita i m m i g r a t i o n rate f o r each 10 m reach w a s c a l c u l a t e d f o r the 13 m o n t h period f r o m June 1996 t i l l September 1997 b y d i v i d i n g the n u m b e r o f larvae that m o v e d i n t o the zone b y the size o f the resident p o p u l a t i o n . A per capita e m i g r a t i o n rate w a s s i m i l a r l y calculated b y d i v i d i n g the number o f larvae that left each reach b y the n u m b e r o f residents. I used analysis o f covariance to test i f l o c a l i m m i g r a t i o n and e m i g r a t i o n rates depended o n resident density,.and whether these relationships v a r i e d between sites. A s i m i l a r analysis w a s used to determine i f the biomass o f resident larvae w i t h i n a 10 m reach w a s related to l o c a l i m m i g r a t i o n and e m i g r a t i o n .  Body size and dispersal F i n a l l y I tested the hypothesis that l a r v a l dispersal is negatively related to b o d y size. I used a linear regression to relate l a r v a l b o d y size and distance travelled b y larvae w i t h i n a 120 m study reach at a l l sites. A t the 10 m scale, I u s e d a c h i - s q u a r e d test to c o m p a r e the proportions o f large (> 100 m m total length) v s . s m a l l larvae (< 100 m m total length) that dispersed.  53  Results: Abiotic Determinants of Dispersal I) Habitat a n d M o v e m e n t : 120 m R e a c h S c a l e L a r v a e at 3 o f the 4 study sites were h i g h l y sedentary. L a r v a e at C e n t r e H F h a d the highest p r o b a b i l i t y o f m o v i n g (Table 3.4). N i n e t y three percent o f larvae m o v e d at this site i n c o m p a r i s o n to 7 1 - 8 0 % at the other streams. T h e m e d i a n distance m o v e d b y C e n t r e H F larvae, 8 m , was also greatest ( T a b l e 3.5), f o l l o w e d b y T a m i h i C - D S , P r o m o n t o r y B H a n d P r o m o n t o r y 3a. T h e distribution o f distances travelled b y larvae at Centre H F w a s s i g n i f i c a n t l y different f r o m the t w o P r o m o n t o r y sites ( K o l m o g o r o v - S m i r n o v test, p < 0.01), but not f r o m the T a m i h i C - D S site ( K o l m o g o r o v - S m i r n o v test, p = 0.34). F o u r habitat variables distinguished Centre H F : percent p e b b l e , percent g r a v e l , water v o l u m e and wetted w i d t h (Table 3.6). Centre H F h a d less gravel a n d pebble than any o f the : other three sites. Substrate at this site w a s m a i n l y c o m p o s e d o f sand/silt ( 3 3 % ) a n d large boulders (37.2%). Centre H F was also the narrowest stream w i t h a m e a n m a x i m u m wetted w i d t h o f just over 1 m (Table 3.6). W a t e r depth was s l i g h t l y but not s i g n i f i c a n t l y l o w e r at this site. T h e total water v o l u m e contained i n the 120 m reach was also s i g n i f i c a n t l y l o w e r at Centre H F , l i k e l y as a result o f its narrow m e a n wetted w i d t h .  II) Habitat and L o c a l D i s p e r s a l : 10 m R e a c h S c a l e N o n e o f the 7 measured microhabitat variables were, related to l a r v a l dispersal i n 10 m stream reaches (Tables 3.7a, b). In every case, there w a s a significant interaction between the slope o f movement-habitat relationship a n d the site at w h i c h data w e r e c o l l e c t e d . A l t h o u g h  54  reach scale attributes m a y influence l a r v a l dispersal, the nature o f this relationship l i k e l y varies between sites and no general p r e d i c t i o n c a n be made f r o m k n o w l e d g e o f the selected habitat variables alone.  Seasonality in Dispersal Stream h y d r o l o g y and temperature v a r i e d significantly between the late active season i n 1996 and the early active season i n 1997. A t three sites, water v o l u m e i n the early season w a s d o u b l e or m o r e o f that i n late season ( F i g u r e 3.1) and b o t h wetted w i d t h a n d depth decreased (Figures 3.2 a & b ) . T h e amount o f p o o l habitat also increased throughout the active season ( F i g u r e 3.3). W i t h the exception o f T a m i h i C - D S , a i r and water temperature changes between s a m p l i n g periods i n the late season 1996 a n d early season 1997 were modest (Figures 3.4 a & b). T h e mean difference i n water temperature between these t w o periods d i d not e x c e e d 3 C at any site. M e a n air temperature at T a m i h i C - D S f e l l b y 8.3 C between s a m p l i n g periods i n the late season o f 1996 and early season o f 1997. Despite large h y d r o l o g i c a l changes a n d moderate temperature changes, there w e r e n o differences i n l a r v a l movement between early a n d late season. T h e distribution o f distances travelled b y larvae i n the early s u m m e r w a s s i m i l a r to that i n late s u m m e r ( K o l m o g o r o v - S m i r n o v test, p = 0.985) (Figure 3.5), and the frequencies o f m o v e m e n t s w e r e nearly i d e n t i c a l between the t w o periods ( F i g u r e 3.6). Peak flow i n s m a l l headwater streams o f the C h i l l i w a c k v a l l e y u s u a l l y occurs w i t h snow melt i n A p r i l or M a y . Capture efficiency is v e r y l o w at these times because o f c o o l water temperatures ( < 5 C ) and p o o r v i s i b i l i t y o f larvae i n fast f l o w i n g currents. L a r v a l dispersal  55  c o u l d increase d u r i n g this time i n response to f l o w , but this p o s s i b i l i t y w a s not tested i n this study. If l a r v a l dispersal fluctuates seasonally, it does so outside o f the June - September active season.  Biotic Determinants of Dispersal I) L a r v a l D e n s i t y a n d M o v e m e n t M e a n larval density varied significantly over the four study sites ( F i g u r e 3.7) but this variation was not related to either measurement o f m o v e m e n t . L a r v a l densities at P r o m o n t o r y B H and Centre H F were significantly higher than the t w o other sites. D e s p i t e this s i m i l a r i t y i n larval density, these t w o streams d i s p l a y e d v e r y different m o v e m e n t patterns. A l m o s t a l l larvae at Centre H F m o v e d at least once and w h e n they d i d , h a l f t r a v e l l e d at least 8 m . In contrast m o r e than a quarter o f the larvae at P r o m o n t o r y B H f a i l e d to m o v e a n d those that d i d g e n e r a l l y stayed w i t h i n 2-3 m o f their o r i g i n a l point o f capture. A c r o s s these f o u r streams, there is n o evidence that  D. tenebrosus' density influenced m o v e m e n t .  II) L a r v a l D e n s i t y a n d L o c a l D i s p e r s a l T h e number o f resident larvae i n a 10 m reach d i d not s i g n i f i c a n t l y affect l o c a l immigration ( F  U 1  = 1.683, p = 0 . 1 0 1 , r = 0 . 1 8 0 ) o r e m i g r a t i o n ( F i = 1.576, p = 0 . 2 3 5 , r = 2  2  U  0.153). T h e r e were no were n o interactions between site and l o c a l i m m i g r a t i o n or e m i g r a t i o n ( A N C O V A , i m m i g r a t i o n site effects: F n = 0 . 3 2 9 , p = 0 . 8 0 4 ; e m i g r a t i o n site effects: F 3 i  3 i U  =  0.199, p = 0.895). There was almost an i d e n t i c a l n u m b e r o f i m m i g r a n t s and emigrants i n each reach (Figure 3.8). T h i s correlation suggests that the tendencies to i m m i g r a t e and emigrate at the 10 m scale are not independent. L a r v a e that i m m i g r a t e d into a reach were m o r e l i k e l y to  56  leave it after a f e w months than those that were established i n the area at the b e g i n n i n g o f the experiment. F r o m a total o f 41 l a r v a l i m m i g r a n t s , 14 later emigrated ( 3 4 % o f total) whereas o n l y 15 % o f larvae i n each reach at the start o f the study later emigrated. T h e total biomass o f resident larvae had n o effect o n i m m i g r a t i o n ( A N C O V A F i , n = 1.878, p = 0.198, r = 0.0217) or e m i g r a t i o n rates ( A N C O V A F i = 1.381, p = 0 . 2 6 5 , r = 2  2  U  0.155) and there were n o significant site effects ( i m m i g r a t i o n site effects F , n = 6 0 6 , p = 0 . 6 2 5 ; 3  emigration site effects F , ] i = 0.350, p = 0.790). A s i m m i g r a t i o n and e m i g r a t i o n rate were not 3  related to either the density or biomass o f residents i n 10 m reaches o f stream, it seems u n l i k e l y that biotic interactions have a strong influence o n l o c a l dispersal o f larvae.  Body Size and Dispersal L a r v a l b o d y size was not strongly correlated to dispersal distance w i t h i n a 120 m reach o f s t r e a n r . B o d y size w a s positively, but not s i g n i f i c a n t l y , correlated w i t h c u m u l a t i v e distance travelled b y larvae (Figure 3.9). A t the 10 m scale, the p r o p o r t i o n o f large larvae (> 100 m m total length) dispersing was significantly greater than f o r s m a l l larvae ( x = 4 . 8 3 1 , p < 0 . 0 5 , 1 2  df). C o n t r a r y to m y p r e d i c t i o n , s m a l l larvae were s l i g h t l y m o r e sedentary than their larger conspecifics. A s s u m i n g that size is the most important p r e d i c t o r o f l a r v a l displacement, these results suggest dispersal was not due to the i n v o l u n t a r y d i s p l a c e m e n t o f s m a l l larvae b y larger i n d i v i d u a l s o r a strong current.  57  Discussion Abiotic Determinants of Movement A c r o s s m y 3 o f m y 4 study sites, the rates and lengths o f l a r v a l m o v e m e n t were s i m i l a r . O n l y one site exhibited different m o v e m e n t behaviour, Centre H F , where larvae tended to m o v e more frequently and further than at the other three streams. C e n t r e H F differed i n substrate a n d wetted w i d t h f r o m the other sites, but w i t h such little variation i n m o v e m e n t amongst streams there is n o w a y o f correlating these habitat differences to v a r i a t i o n i n d i s p e r s a l . I n fact, the l a c k o f association between these variables and m o v e m e n t at the 10 m scale suggests they have n o effect o n movement. A t the 10 m reach scale, none o f the 7 measured habitat variables w a s associated w i t h larval m o b i l i t y i n D. tenebrosus. T h i s pattern suggests that the p o s i t i v e a s s o c i a t i o n between larval density and p o o l habitat, decreasing wetted w i d t h a n d s o m e substrate classes is not created .by dispersal into preferred areas. I f larvae are f o u n d at higher densities i n p o o l s o r n a r r o w reaches, it is because either adults selectively o v i p o s i t and/or larvae s u r v i v e better i n these areas. If shifts i n the habitat variablesT studied affect l a r v a l demography, they d o so b y c h a n g i n g s u r v i v a l and not dispersal. T h e lack o f association between l a r v a l m o v e m e n t a n d a l l other measured habitat variables c o u l d also be a f u n c t i o n o f inappropriate measurement scale. P r i o r to this study, little was k n o w n about larval dispersal b y D. tenebrosus. F i e l d study o f other stream d w e l l i n g larval salamanders f o u n d that they can m o v e u p to 10 m i n o n e day ( H o l o m u z k i 1991). I thus chose to partition and describe habitat i n 10 m units, a s s u m i n g that larvae were capable o f m o v i n g between reaches of this length i n response to l o c a l c o n d i t i o n s . H o w e v e r , most larvae m o v e d less than 5 m oyer a season. Consequently, larvae m a y be capable o f selecting o n l y amongst habitats w i t h i n a few  58  meters o f their o r i g i n . Therefore I c a n o n l y c o n c l u d e that p o o l habitat, water depth a n d v o l u m e do not e x p l a i n movement between r e a c h e s o f 10 m or greater.  Density Dependent Determinants of Dispersal L a r v a l density had n o influence o n m o v e m e n t b y D. tenebrosus larvae at 10 m a n d 120 m reach scales.  T h i s observation contradicts m y o r i g i n a l p r e d i c t i o n o f density-dependent  regulation as a result o f intraspecific aggression and c a n n i b a l i s m . G i v e n the h o s t i l i t y that characterises most larval interactions i n the laboratory ( M a l l o r y 1996), it i s s u r p r i s i n g that density h a d n o impact o n m o v e m e n t . It is possible h o w e v e r that m y study w a s c o n d u c t e d o n t o o large a scale to detect l o c a l effects o f density. M a l l o r y ' s (1996) study o f l a r v a l interactions w a s conducted i n pools and riffles a f e w metres i n length. Results observed at the 1-5 m scale m a y not e x p l a i n movement over larger areas. A l t e r n a t i v e l y the c a n n i b a l i s m a n d a n t a g o n i s m noted b y M a l l o r y m a y not reflect interactions i n natural settings. It is also possible that density m a y b e l more important i n more southerly parts o f the range where l a r v a l densities a n d b i o m a s s are higher than i n B r i t i s h C o l u m b i a ( M u r p h y & H a l l 1981, K e l s e y 1995).  Body size and dispersal T h e fact that one third o f a l l i m m i g r a n t s i n t o 10 m reaches later became emigrants suggests that a sub-section o f larvae are m o r e m o b i l e than the rest o f the p o p u l a t i o n . I f this is so, one m i g h t ask what differentiates a disperser f r o m a resident. I i n i t i a l l y expected s m a l l e r i n d i v i d u a l s to be more vulnerable to d i s p l a c e m e n t b y the stream current or other larvae ( B r u c e 1986, M a l l o r y 1996). C o n t r a r y to this e x p e c t a t i o n , I f o u n d that large larvae were s l i g h t l y m o r e m o b i l e than smaller individuals, perhaps because large larvae face l o w e r risks w h e n travelling.  59  C a n n i b a l i s m risk decreases w i t h body size and large larvae m a y be less l i k e l y to be attacked w h i l e m o v i n g than their smaller conspecifics. These results suggest that m o v e m e n t s throughout the stream are not forced b y dominant conspecifics.  Conclusions M y m a i n c o n c l u s i o n is that  D. tenebrosus larvae exhibit h i g h site fidelity and extremely  l i m i t e d dispersal. M o s t larvae f a i l e d to m o v e more than 5 m over 13 m o n t h s . O f those that d i d m o v e , ninety percent stayed w i t h i n 2 0 meters o f their o r i g i n a l capture point. A l t h o u g h v a r i a t i o n existed between sites, m o v e m e n t was generally conservative i n time and space. T h e correlation between i m m i g r a t i o n and e m i g r a t i o n at the 10 m scale suggests that although most larvae are sedentary, a s m a l l number o f transient animals travel frequently throughout the stream. It is unclear w h y these i n d i v i d u a l s are transient. A s size was a w e a k p r e d i c t o r o f m o v e m e n t length, this b e h a v i o u r cannot be ascribed to a p a r t i c u l a r age group o r to d o m i n a n c e interactions. L a r v a e seem i l l - e q u i p p e d to disperse i n response to habitat changes. A n y l o c a l and lethal impact that c o u l d not be a v o i d e d by a m o v e m e n t o f less than 2 0 m w o u l d l i k e l y k i l l 9 0 % o f a l l larvae. It s h o u l d be cautioned, h o w e v e r , that is c o n c l u s i o n is based o n the o b s e r v a t i o n o f larvae w i t h i n relatively stable environments. Other than m y mark-recapture surveys a n d seasonal shifts i n c l i m a t e and stream f l o w , there were n o disturbances or drastic habitat changes w i t h i n each stream d u r i n g this study. It is possible that l a r v a l dispersal is elevated i n m o r e r a p i d l y c h a n g i n g or h i g h l y disturbed environments than u s e d i n this study. P o o r l a r v a l dispersal ability is not u n i q u e to d w e l l i n g salamanders exhibit similar behaviour.  D. tenebrosus. O t h e r species o f stream-  Desmognathus fuscus, Desmognathus  ochrophaeus and Ambystoma barbouri have s m a l l h o m e ranges o f 1.44, 1, a n d 1 m  2  60  respectively ( A s h t o n 1975, H o l o m u z k i 1982, 1991). W h i l e larvae o f D. tenebrosus certainly have l i m i t e d dispersal capabilities, this trait does not d i s t i n g u i s h the species. L o w dispersal o f larvae does not necessarily m a k e this species vulnerable to e x t i n c t i o n . Recent evidence suggests that adults are not s i m i l a r l y l i m i t e d i n m o v e m e n t .  Seasonal dispersal  distances > 100 m were recorded i n some radio-tracked adults i n the C h i l l i w a c k drainage (Johnston 1998). H o w e v e r disturbances such as l o g g i n g m a y put adults at greater risk than larvae b y increasing their probability o f desiccation w h i l e on l a n d ( B l a u s t e i n et a l . 1994). If adult mortality is h i g h , the site fidelity o f larvae m a y hasten l o c a l e x t i n c t i o n . U n t i l the exact d e m o g r a p h i c effects o f l o g g i n g on both adults and larvae are k n o w n , the consequences o f l o w larval m o b i l i t y o n p o p u l a t i o n persistence are u n k n o w n . H o w e v e r this study suggests that logging-associated habitat changes such as increased silt, temperature a n d riffle habitat d o not trigger l o c a l e m i g r a t i o n .  61  co  c o OH  o p3  o  3  l-l  O C o o co  .52  lc t— ON — OS c —«  00  cn  rt  3 O  T3 O & «~ S2  co  §e  fa < D OJ u.  0>rt  to <*>  CO C T3 > rt jo  ca rt co 3 C £  3  c 3 > c-> -  s  rt  v ov" O O v c  O rt  < * < l_ rt  rt  co  .Si -4—»  c o o 6 o  t/3  40  o x> c 2 .2 ^ o o o rt m •a e c 3  rt — !>  E o rt  z.. 0rt, 0  ^  rt  H  I  3 03  o  o  O  £3 CD 1/3  03  CO  <U E .S c/3  «  O O  CM  3  > u  CU  t5  o l-P  O  E  E H ID cu u,  a  H I-  CU  o  c 03  TJ  c  " 53 3 > CU »  03  >TJ X) O cu >  u. cu r^: CU O. C M CO O t £ t £ c£ CO  u& o  03  i£  cu  rs  | 2  E  <  CU  X i OS 3 +-» C/3 V* CO co co •3 C x = ".£ .S 3> CU CO  X)  o  «i  03  Substrate Class Boulder Cobble Pebble Gravel Sand/Silt  Size Designation > 256 mm 64 mm - 256 mm 16mm- 64mm 2 mm- 16 mm < 2 mm  Table 3.3: Substrate definition and size classes. Size designation refers to the longest longitudinal axis of the stone.  64  a o  o  'c 60  co  a  CD  >  O  6  o  o  o  ^  o  .v C »5  o\ r-  (N N  H  |S  CO e  Ti  O  CO  o m TJ- TJON m ON m  CO ON CN  oo  ON CO f-  tf O  <n O <—• "t3  IS  CU  ca ca  -4—*  IES  c^ O CD  tf  cSpQg CU 4 •— »  a  & o c o  & o  6 G o CU  U  CM CM  ,  u  ca  o H  Site Centre HF Promontory 3 a Promontory B H Tamihi C-DS All sites combined  Median distance moved (m) 8.0 1.5 2.0 4.0 3.8  Range(m) 0.5 - 111.5 0.5 - 62.5 0.5 - 104.0 0 - 34.0 0.5- 111.5  n 83 44 70 45 231  Table 3.5: Median distance moved by larvae at each site. The median cumulative distance moved at Centre HF was significantly higher than at any other site (Brown-Mood Median test, X = 18.42, df= 3, p < 0.001). 2  66  m o o VO o O o d  + „ o-  o m  o o  CN o d  00 o m •* d  ho VO  o o o d  o o o  |tn| o o  CN VO^ CN CN o PQ o PQ o  Ov CN  o CN  CN  CN  rt  co  X  S x  03  CO CN  CN  Iqi CN  |oq  ti CO  X  CN  + O O VO VO Ov cn co in VO od K ho  vo o o  CO  CO VO in in CN CO  Ov  03 i  03 m  O CN  ho  Q l  o  U ,  Ov  VO  d  >n  U  in  q  13 u £  o o  ^  vo d CN  d  §T  bp ,  CO  co  e * » Q M  S ° £ 00 to CO CO ffi rt X no  co  rt 3 B rt S co  CN- CN  O  co  •i-"  1  CN  in  VO 00 CO CN CN  CN  w  *••»  • *-«  Q  .5  . 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K  CD CDuCDV o' X i 03 03 CH lo  « H  d  CO  o d  6  c  Tt  o  S  O  ca Tt  © <  CO  CM2  ca  G  co O  PH  co  'o3  'o3  ta  o 'ii u  (50  '•9  0 i-3 cn  Xi 3  CO (U  03 > u 03  J  la  «  5T  CL)  Q > o  u  Tj C C  u  CD »  o Ui  00  03  Xi T3  CM  TJ  CD>  CD >  ^—» CD  O  U  £  P-l  co — i03 cT  "ca  i3  3  I*  £ 03  >  13 CO  CD|.£  CO  0 3  -2 xi .2 >  E .ti 3 C  X) 03  CD  ca  E  3  <£3 CD +  1  CD  «>  •c *  TJ  03 C  c  xi  p  u  c  00  2  CD  X!  I  £ TJ  CD CD  £  x: U  O  3 U  , £ .c &0 0 -5§ o ca 3CD T3 t- co CD g  o fe  c  CN'I  «  a  PH  PH  C  O  CO < ,  CD »  co  ! CD X C D1 E .£ CD <~ > CD  C  00  o fe W  O0  '£  C  o PH 03 u CD» ^—  |M3  c  o  u  TJ  9 I?  PH  oo  <D  CO  rt  U  ™ 3  fe  »  ^  -ti  CD  © & .£ £ 03 «  pq  o PH o 3 u  *H  Xi  o fe  _o  CD  c. ca ca '—' co " x: 3 2 3 CD  c  CO  .ti  X!  ~ cD £  u  ) CM ca co Xca o o .£ H co o o o ca .2 ta 03 CO co -rj ri co ^ C "ca CD X! ca CD co O  C CD O 3 • • co  X)  CM  £ ^  o  r- fe CD  CO  <D  § 5 ca CD  3 ~ co CD CD ^ 03 TCJ  H ca  CD  X)  fe  CD  68  c o CO ca  c o 00 CD CO CD  CO  C3  LU  5 -° £  CO  CO  •  I * U  X3  ,o  CL,  HH  ^  Tj-  & °°  II  d IS <A - ca o p -is  t=: o §  8I-,  J3  II  &  OO CN  u  £  Z  iS I 5Q -C c-i >n  • xCD P  c  CD  6 u  o  CN  ©  CM  *8 £  CD  q  •4)  ii  co  "ftO x> S CD  s  3  > CD  ca CD  ~c PQ CD  O  00  ca ^ CD  ti  .5 CD c/3  p  ,4>  ca  co II CO c+_  ^  * ""3  TJ  TT  fe £  -  ~ 2 © C D T f C v J O C O C D T j - O J O  S £ co  CD ca CO  i p e e y WQZl UJ aiun|OA Jeie/w eBejeAV  9  O  CD  cn v  >H  s  CD >  ca  cn  t  250  TJ  a)  > 200  |  150  g  100 -- ^ ^ " ^  © 5  • Early Season @ Late Season  I * CD o 2  n  .  _  u  Centre HF  Promontory 3a  Promontory BH  Tamihi CDS  Site  Q. CU  Q E  £ 55 0> O) CD w CU  > <  18 16 14 . . 12 10 -• 8 6 4 2 0  b) I Early Season I Late Season  Centre HF  Promontory 3a  Promontory BH  Tamihi CDS  Site  Figures 3.2a & b: Seasonal changes i n wetted w i d t h and depth i n f o u r streams containing D. tenebrosus larvae. E a r l y season measurements were c o l l e c t e d i n June and J u l y 1997. L a t e season measurements were taken i n A u g u s t a n d S e p t e m b e r 1996. S a m p l e sizes as i n F i g . 3.1.  70  co *L  c c o o CO CO CD  13 tu  CO CO CO  -a co E £ U CO  (fi ty) >^ TZ CO  LU  CD  CO I  co  C 03  •  c  cn  +2 03  tu  ^  ON  H  B-S co  O  co  o 8 IH s o b 8 JS S3 * co rt  CO  N  T3 CO  'co hj  T3  o 3 CO  "3 NO ON  ON 03 CO  X  X O CO  o  OO  B  o  co 03 CO co CO rt  "St  O O  rt d CO  X  E o  03 rt  i  Q_  03  CO  o  1  ~ rt CO C N  co oo  X  £ q o rt Bco t-i  co  00 C3 rt B co  .CO  II.  CO  rt  00  ~ Q  ' B S rj & rt co l » B ts x 'S o3  03 CO  c  E ba co  B 03  X  T3  S  03  co CO  x rx <a o o vo -a C M rt q 13 co  s  co I—  .CO  ©  O CD  O  O  O CO  O  OJ  ipeey LUQI. u; |ood juaojad sBejaAV  B O  O  CO  o II  co 03 CO  s °<  PH  < ?  CU  §  II  oo  u co rt S  OB  co  co J— HH 1  tu  o  a)  Centre HF  Pro3a  ProBH  TamC-DS  ProBH  TamC-DS  10  £ o  8 +  fl) O)  i = 11  CD ca  2 +  3 fc a> <s ^a> ca. u _oi  0  H  < 1 c cs a  °2  SI  -8 +  -10  o  Site  b)  Centre HF  Pro3a  5i  o u _ 5 :§  a) a. •9 E  4 3 +  4) CO 1 + = £ 0+  II  I  H.  HI  -2 +  > co C 10  -3  — =cn -4 + 0) O) Ol Tc 5 co =  o  Site  Figure 3.4a& b: Differences in the mean air and water temperature between late season 1996 and early season 1997 sampling. Each site mean was based on 8-18 observations.  72  Cumulative Distance Travelled by Pacific Giant Salamander Larvae (m)  Figure 3.5: Cumulative distance travelled by D. tenebrosus larvae early and late in their active season. These data are pooled from all of the four streams. Early season refers to movements made in June and July 1997 (n = 30) and late season to movements made in August and September 1996 (n = 76). There was no significant difference between these two distributions (Kolmogorov-Smirnov test, p = 0.985).  73  • Movers ID Non Movers  Early Season  Late Season  Time during the active s e a s o n  Figure 3.6: Proportion of larvae that moved (displacement greater than 0.5 m) and did not move at two different periods throughout the active season. The proportion of movers was not significantly different between these two periods.  J  74  I  Figure 3.7: Mean larval density and standard error at four D. tenebrosus larvae streams.  75  CO C O  E in  14.0i 12.0.  T—  c  10.0.  o CQ CD  cr E o  CO  o o  8.0. 6.0. SITE  4.0.  * TamC-DS  CD  c o E  •>  2.0.  CO CO  0.0.  £  CO  -J  *  • ProBH  *  -2.0, -2.0 .  * Pro3a  * •  • CenHF 0.0  2.0  4.0  6.0  8.0  10.0  12.0  # Larvae moving into a 10 m Reach in 15 months  Figure 3.8: Relationship between the number of larvae moving into and out of a 10 m reach of stream during a 13 month experiment. The log (x + 1) transformed number of larvae moving into a zone was significantly related to the log (x + 1) transformed number moving out ( A N C O V A , F i = 5.619, p = 0.037). There were no site interactions ( A N C O V A , site effects F , = 0.333, p = 0.802). U  3  u  76  C  'S O  +  CD c«  •  E S en  a  <u  o • •  o H  o CN  o  CN  —I—I—I—I—h-  o  O  o  00  o  VO  o  o  "3- CN  (UI)  H  x  E  .22 X  UIB3JJS UI p3||3ABJX 33UBJSIQ  77  Chapter 4: Colonising Ability of Pacific Giant Salamander Larvae Introduction: T h e ability o f salamander populations to recover f r o m l o c a l disturbances has been debated b y conservation biologists (Petranka et al. 1993, A s h & B r u c e 1994, P e t r a n k a 1994). S p e c i f i c a l l y , herpetologists have argued over whether amphibians c a n compensate f o r increased rates o f habitat disturbance b y r a p i d recolonisation. In the P a c i f i c N o r t h w e s t , habitat loss is p r i m a r i l y due to l o g g i n g and development. S e v e r a l studies have f o u n d that p o p u l a t i o n densities o f aquatic salamanders are l o w e r i n streams d r a i n i n g through clearcuts than i n undisturbed stands ( B u r y & C o r n 1988, C o n n o r et a l . 1988, C o r n & B u r y 1989, W e l s h 1991, C o l e et a l . 1997). T h e s m a l l p o p u l a t i o n p a r a d i g m tells us that s m a l l populations are more vulnerable to l o c a l e x t i n c t i o n than large p o p u l a t i o n s ( C a u g h l e y 1994). T h u s b y decreasing p o p u l a t i o n density, l o g g i n g m a y increase the p r o b a b i l i t y o f l o c a l extinction. I f dispersal c a n facilitate r a p i d r e c o l o n i s a t i o n o f disturbed areas, an increased frequency o f l o c a l extinction m a y have n o l o n g term affect o n salamander persistence.  However,  i f l a r v a l and adult dispersal are weak, r e g i o n a l extinction m a y ensue w h e n entire landscapes are disturbed. It is generally b e l i e v e d that a m p h i b i a n s are p o o r dispersers ( D u e l l m a n & T r u e b 1986, B l a u s t e i n et a l . 1994) and it has even been suggested that a m p h i b i a n c o m m u n i t i e s are i n f l u e n c e d more b y dispersal ability than b y specific habitat tolerances o r c o m p e t i t i v e interactions ( C o r t w r i g h t 1986). A twenty year translocation study i n western I n d i a n a f o u n d that the s e m i aquatic T w o - L i n e d Salamander, Eurycea cirrigera,  c o u l d s u r v i v e i n m a n y areas outside its  traditional range, but it h a d been e x c l u d e d f r o m those areas b y p o o r dispersal a b i l i t y ( T h u r o w  78  1996). Thus even within undisturbed, tolerable habitat, dispersal may limit amphibian distribution and community composition.  Pacific Giant Salamanders and disturbance  In this study, I used experimental techniques to measure the colonising ability of larval Pacific Giant Salamanders (Dicamptodon tenebrosus). In Canada, this provincially red-listed species is restricted to the Chilliwack River drainage basin where it is distributed patchily. Survey work in this area detected D. tenebrosus in only 22 of 59 seemingly habitable streams within this area (Richardson & Neill 1995). It is possible that many of these currently barren streams experienced local extinction in the past. Logging has occurred on much of D. tenebrosus' Canadian range, and may increase the frequency of local extinction (Haycock 1991). Though little is known of this species' ability to respond to local extinction by colonisation, larvae reappeared in one Washington stream only two years after it had temporarily dried (Nussbaum & Clothier 1973). It is unknown whether these animals were dispersers from nearby areas or survivors that took refuge in subsurface waters during the drought. I tested the hypothesis that colonisation of barren stream reaches by D. tenebrosus is rapid (< 1 year) and is accomplished by larval dispersal. I did this by simulating reach extinctions at four stream sites. I removed larvae from 25-40 m stream sections and then monitored recolonisation of these areas for a year. As colonisation implies the establishment of animals in an unoccupied habitat, this phenomena could not be studied by monitoring immigration into populated reaches. If movements are influenced by the presence of conspecifics, as found in D. tenebrosus larvae in the lab by Mallory (1996), dispersal rates into  79  populated and depopulated reaches will vary significantly (Stenseth & Lidicker 1992). Thus to model the natural process of colonisation, experimental removals had to be conducted. In addition to measuring the speed of recolonisation, this experiment yielded information about the relative contribution of larval dispersal and adult reproduction to the repopulation of barren areas. Both larvae and terrestrial adults are potential dispersal agents in this species. Terrestrial adults are more mobile than larvae, with some radio-tracked individuals travelling up to 305 m from their capture site between July and October (Johnston 1998). Although larvae are more limited in their dispersal capabilities, they are much more numerous than adults and can move > 50 m during the active season (Neill 1998). Consequently they may be the most efficient colonisers in stream reaches experiencing frequent, small-scale disturbances due to debris torrents or rock slides. Such disturbances are relatively common in headwater streams of the Pacific Northwest and their frequency is increased by logging (Lamberti 1991). I examined the size structure of the colonists of my removal zones to assess which life history stage, adult or larvae, had added the most individuals. Even if larvae are not efficient colonisers, there are reasons for studying their movements. Larvae may be the only viable dispersal stage in logged habitats, because terrestrial adults may suffer high mortality in clearcuts due to an increased risk of desiccation and freezing. (Richardson 1994). Under such a scenario, depopulated areas could be recolonised only by larval propagules from undisturbed stream reaches. It has not yet been tested, however this hypothesis suggests studies of larvae are vital forjudging recovery potential. Although removal studies have been widely used to estimate dispersal rates in other taxa (Stenseth & Lidicker 1992), these methods have seldom been used on amphibians (Bruce 1995). My study is one of the first to use removal techniques to estimate colonisation in salamanders.  80  Removal techniques have several shortcomings (Appendix 2). In this experiment I have employed a mixture of field and statistical techniques to reduce the impact of the five most serious biases noted by Stenseth and Lidicker (1992) (Appendix 2). Although none of these corrections completely eliminates bias, they provide more accurate measures of colonisation. Because conservation decisions often rely upon the recovery potential of a species, it is essential that these estimates be as accurate as possible.  Methods: Measuring Colonisation in the Field  The colonising ability of D. tenebrosus larvae was studied in four headwater streams in the Chilliwack River Valley: Centre HF, Promontory 3a, Promontory BH and Tamihi C-DS. The location and age of surrounding forest habitat at each site is detailed in Chapter 2 (Table 2.1). At each site, a 120 m long reach of stream was set aside for study. Colonisation was studied by removing all larvae from a 25-40 m central section of this study reach  1) Pre-Removal Sampling Each 120 m reach was searched intensively each week in June and July 1996 (Table 4.1) to identify all larvae that might later act as colonists. Larvae were captured by hand and individually marked (see Chapter 2) before being returned to their location of capture. All sites were sampled between 5 to 8 times to enumerate the larval population before removals began (Table 4.1). Even after this effort, some unmarked individuals were found within the study reach suggesting not all resident larvae may have been marked or some dispersal from beyond the study reach took place.  81  2) C r e a t i n g R e m o v a l Zones A f t e r the initial m a r k i n g p e r i o d , r e m o v a l zones were created i n the m i d d l e o f each 120 m reach. T h e length and area o f the r e m o v a l zone at each site varied between 2 5 - 4 0 m l o n g a n d 26-75 m ( T a b l e 4.2). T h e size o f the r e m o v a l zones v a r i e d because o f a p r i o r d e c i s i o n not to 2  r e m o v e more than one third o f the l a r v a l p o p u l a t i o n at any site. T h i s f r a c t i o n was chosen to ensure that there were more than enough i n d i v i d u a l s i n the adjacent reaches to f u l l y r e c o l o n i s e m y r e m o v a l areas. In two sites, larvae were h e a v i l y clustered i n the m i d d l e o f the study reach and o n l y 25 m c o u l d be cleared w h i l e at the other t w o sites, larvae w e r e distributed m o r e u n i f o r m l y and the m i d d l e 4 0 m was cleared. R e m o v a l s were conducted o n a d a i l y basis at each site i n late J u l y and early A u g u s t 1996. M e s h fences (1 m m ) were b u i l t to obstruct dispersal into or out o f the area d u r i n g the r e m o v a l 2  p e r i o d . A l l captured salamanders (larvae, neotene or adults) were taken out o f the stream and housed i n artificial stream channels. T h e n u m b e r o f larvae r e m o v e d v a r i e d between sites (Table 4.3). S e a r c h i n g was stopped w h e n n o larvae were captured i n the r e m o v a l z o n e o n t w o consecutive days.  A t this time the dispersal fences w e r e r e m o v e d and the reach was opened f o r  colonisation.  3) M o n i t o r i n g C o l o n i s a t i o n E a c h 120 m site, i n c l u d i n g a r e m o v a l zone a n d up and d o w n s t r e a m source reaches, was m o n i t o r e d on a w e e k l y basis u n t i l late September 1996, w h e n water temperature d r o p p e d b e l o w 6 C and larvae c o u l d no longer be detected. W e e k l y s a m p l i n g resumed f r o m June to m i d J u l y 1997 and again for t w o w e e k s i n S e p t e m b e r 1997. N o further r e m o v a l s o c c u r r e d after m o n i t o r i n g started i n 1996. T h e identity a n d l o c a t i o n o f each l a r v a f o u n d inside a n d outside o f  82  the r e m o v a l zone were recorded. A l l n e w l y f o u n d larvae were u n i q u e l y m a r k e d so that their future dispersal c o u l d be f o l l o w e d . A l l larvae captured w i t h i n the r e m o v a l zone after c l e a r i n g were categorised as potential colonists. B y c o n t i n u i n g to m a r k i n d i v i d u a l s i n areas outside the r e m o v a l zone, I estimated l a r v a l abundance i n the adjacent reaches. I used the p r o g r a m C A P T U R E to calculate l a r v a l abundance i n the source areas i n September 1996 a n d June 1997 ( B u r n h a m et a l . , 1994). Estimates f o r these periods were based on four w e e k l y mark-recapture surveys. P o p u l a t i o n sizes i n the adjacent areas were also calculated i n September 1997. A s o n l y t w o surveys per site w e r e conducted i n this m o n t h , p o p u l a t i o n size c o u l d not be estimated b y C A P T U R E  (insufficient  s a m p l i n g intervals). Instead a s i m p l e L i n c o l n - P e t e r s o n m o d e l was used to estimate the size o f the September 1997 p o p u l a t i o n . D e t a i l s o f both this m o d e l a n d the C A P T U R E estimate are i n c l u d e d i n Chapter 2.  Statistical Models of  Colonisation  C o l o n i s a t i o n was f o l l o w e d for just over a year at a l l sites. A l l c o l o n i s a t i o n rates represent the number o f colonists entering the r e m o v a l zone i n a one year p e r i o d (the exact p e r i o d that each site was m o n i t o r e d is s h o w n i n T a b l e 4.1). T w o issues m a d e the e n u m e r a t i o n o f colonists difficult. T h e first p r o b l e m was that not a l l animals f o u n d i n the r e m o v a l z o n e after clearing were m a r k e d . It was thus u n c l e a r whether these larvae h a d dispersed into the zone or were residents that h a d not been r e m o v e d .  S e c o n d , m a n y potential colonists were captured  only once i n the r e m o v a l zone; G i v e n the l o w capture p r o b a b i l i t y o f these animals, it is uncertain whether these i n d i v i d u a l s were transients or colonists that r e m a i n e d undetected i n the zone. I dealt w i t h these p r o b l e m s b y c a l c u l a t i n g c o l o n i s a t i o n under three different models: a)  83  Conservative b) Liberal and c) Statistically probable. The conservative and liberal rates were calculated to establish the range of values within which the true per annum colonisation rate of larvae lies. The statistically probable model incorporates information on site-specific trapping efficiency and capture history to estimate a likely number of colonists. The assumptions and methods used to derive each estimate are detailed below:  a) Conservative Colonisation Only larvae that were initially marked outside the removal zone and then captured within it were considered colonists. Unmarked animals found within the zone were considered missed residents except for several small, unmarked larvae ( < 60 mm total length) found in the removal zone in September 1997. These animals were too young to have been present in the stream when the manipulations were taking place. They were considered to be colonists as their presence was most likely due to post-removal reproduction. These animals will be referred to as recruited colonists. To separate transient dispersers from true colonists, this model also required evidence that dispersing larvae had settled in the removal zone. All larvae dispersing into the zone had to be captured at least twice in the zone to be considered colonists.  b) Liberal Colonisation Under this model, all larvae captured within the removal zone after clearing were counted as colonists. Any animal that was caught once within the removal zone, whether marked or not, was added to the coloniser pool. This method definitely overestimates colonisation as removals were not 100% successful at any site. Several larvae were found in each removal zone that had been marked prior to manipulation but had not been successfully  84  cleared. Although these animals were excluded from this estimate of colonisation rate, their presence indicates that at least some of the unmarked larvae found in the removal zone were missed residents.  c) Statistically Probable Colonisation Unmarked larvae found in the removal zone after clearing were divided into two categories: those hatched before the manipulation and those that hatched after it. Any small larvae (< 60 mm total length) found in the removal zone in September 1997 were considered recruited colonists as described above. As I could not determine the origin of the other unmarked larvae in the removal zone, I used a site-specific removal efficiency rate to infer how many were likely missed residents. To do this I compiled a list of all larvae captured in the removal zone before manipulation. I subtracted from this list the number of larvae known to have dispersed out of the zone or that I suspected to have transformed before clearing. Larvae larger than 130 mm in total length that showed signs of gill resorption or skin mottling were classified as probable transformers. I divided the number of larvae that were removed at each site by the corrected number detected before clearing to obtain a removal efficiency rate for each stream. I used this efficiency index to calculate the number of unmarked larvae found in the removal zone that were likely missed residents. For example if the efficiency rate of a particular clearing was 75%, then 25% of larvae known to be present in the removal zone prior to manipulation were not successfully cleared. Thus if 20 unmarked larvae were later found in the removal zone, I inferred that 25% of them (5 larvae) had been present before the clearing and were not true colonists. By applying this correction, I divided the total number of unmarked  85  larvae into missed residents and immigrants. The number of unmarked larvae inferred to be immigrants was added to the number of marked animals known to have immigrated to calculate the total number of larvae that dispersed into the removal zone over the course of the experiment. The number of dispersers does not necessarily equal the number of colonists as some dispersers may have later emigrated or died. For each disperser into the removal zone, I calculated its probability of remaining undetected in the area for the balance of the experiment. If this probability was greater than 50%, I assumed this animal was still within the zone. These animals were designated as colonists. If the probability of non-detection was less than 50% and I never caught it again, I assumed it had died or dispersed. The specific methodology used to estimate this probability is described in Appendix 3. A schematic diagram detailing the steps taken in the model is given in Figure 4.1.  Percent replacement of removed individuals by colonists  The number of colonists predicted under each of the three models was calculated. These numbers were divided by the number of animals initially taken out of the removal zone to estimate what percent of the removed individuals were replaced by colonists in a year.  Density Dependent  Colonisation  A per capita colonisation rate was calculated for each site by dividing the predicted number of colonists by the total number of larvae marked in the source areas above and below the removal zone. This rate represents the proportion of larvae in an undisturbed reach that  86  were capable o f local recolonisation. O n l y the n u m b e r o f colonists estimated under the Statistically Probable M o d e l was used i n this and a l l further analyses. T h i s per capita colonisation rate w a s also used to e x a m i n e the relationship between larval density i n source areas and speed o f recolonisation. I f density dependence w a s operating on dispersal, I predicted that per capita c o l o n i s a t i o n at each o f four sites w o u l d increase w i t h increasing density o f the source p o p u l a t i o n .  Origin of Colonists T h e c o l o n i s i n g group at each site was c o m p o s e d o f t w o types o f a n i m a l s : second year o r older larvae and young-of-the-year recruits. Y o u n g - o f - t h e - y e a r recruits were < 6 0 m m total b o d y length i n the second year o f the experiment. These animals were the product o f b r e e d i n g i n F a l l 1996 and w o u l d not have hatched u n t i l the s u m m e r o f 1997. A l l other c o l o n i s i n g larvae w o u l d have been i n the stream at the t i m e o f the r e m o v a l s and w o u l d o n l y b e f o u n d i n the r e m o v a l zone i f they had dispersed i n . B y c o m p a r i n g the n u m b e r o f i n d i v i d u a l s i n each category, I c o u l d infer the relative contributions o f r e p r o d u c t i o n versus l a r v a l dispersal to the c o l o n i s a t i o n process.  Body Size and Colonisation I w i s h e d to determine whether c o l o n i s i n g larvae were a r a n d o m sub-set o f i n d i v i d u a l s f r o m the source areas o r a unique size class. T o d o this I s u m m e d the total n u m b e r o f k n o w n colonists (37) f r o m all sites, i n c l u d i n g both l a r v a l colonists and adult-dispersed recruited colonists. A n equal number o f i n d i v i d u a l s w a s then r a n d o m l y selected f r o m the set o f a l l larvae that d i d not colonise the r e m o v a l zone d u r i n g the year o f m o n i t o r i n g (pooled across a l l sites, n = 619). T h e mean snout-vent length ( S V L ) o f these i n d i v i d u a l s was calculated. T h i s procedure  87  was repeated 1000 times to generate a distribution o f the expected m e a n snout-vent length i n a group o f 37 r a n d o m l y selected n o n - c o l o n i s i n g larvae. I then c o m p a r e d the observed m e a n S V L o f c o l o n i s i n g larvae to this distribution. If the observed value fell w i t h i n the outer five percent o f values i n the expected distribution, the b o d y size o f colonisers was c o n s i d e r e d significantly different f r o m resident larvae (alpha = 0.05). A Pascal-based r a n d o m i s a t i o n test p r o g r a m was written b y D r . D . H a y d o n for this and all subsequent r e s a m p l i n g analyses.  Distance Travelled By Colonisers A n o t h e r resampling analysis was conducted to determine i f l a r v a l colonisers e x h i b i t e d distinct m o v e m e n t distances f r o m non-colonisers. T h e c u m u l a t i v e distance travelled b y a l l n o n c o l o n i s i n g larvae throughout the experiment was calculated, after e x c l u d i n g larvae that d i d not m o v e . N o n - m o v e r s were e x c l u d e d as a c o m p a r i s o n o f i n d i v i d u a l s that b y d e f i n i t i o n must m o v e (colonisers) w i t h those that often d o not ( 8 - 2 5 % o f larvae r e m a i n e d stationary, C h a p t e r 3) w i l l y i e l d the o b v i o u s result that colonisers are m o r e m o b i l e . Instead, I w i s h e d to k n o w whether c o l o n i s a t i o n proceeded b y the short-distance dispersal characteristic o f most larvae (Chapter 3), or long-distance dispersal o f a few atypically m o b i l e i n d i v i d u a l s . F r o m the p o o l e d data set o f a l l n o n - c o l o n i s i n g yet m o b i l e larvae (those that m o v e d > 0 . 5 m , n = 213), a number o f i n d i v i d u a l s equal to the n u m b e r o f in-stream l a r v a l colonisers (n = 7) was r a n d o m l y selected 1000 times. A f t e r each selection, the m e a n c u m u l a t i v e distances travelled b y the group was c o m p u t e d . A n expected d i s t r i b u t i o n o f c u m u l a t i v e distance travelled b y n o n - c o l o n i s i n g larvae was generated f r o m these values. T h e o b s e r v e d m e a n distance travelled b y c o l o n i s i n g larvae was c o m p a r e d to this d i s t r i b u t i o n to determine i f they were m a k i n g statistically longer m o v e m e n t s than those i n the source areas.  88  Direction of  Colonisation  A final analysis was undertaken to determine i f colonisation w a s d i r e c t i o n a l l y b i a s e d . T o do this I first examined the net d i r e c t i o n of movements made b y n o n - c o l o n i s i n g larvae i n the source areas o f each stream. E a c h l a r v a that made a net d o w n s t r e a m m o v e m e n t o v e r the course o f the experiment was assigned a d i r e c t i o n c o d e o f " 0 " , and each larvae that m o v e d upstream received a "1". L a r v a e that made n o net movements were not i n c l u d e d i n the analysis. D i r e c t i o n records f r o m a l l four sites were p o o l e d into one data set (n = 213). F r o m this data set, a n u m b e r o f i n d i v i d u a l s equal to the number o f in-stream l a r v a l colonisers (n = 7) was r a n d o m l y selected 1000 times. A f t e r each selection, the n u m b e r o f upstream m o v e m e n t s i n the g r o u p was calculated b y s u m m i n g direction codes o f a l l i n d i v i d u a l s to produce an expected d i s t r i b u t i o n o f the n u m b e r o f upstream movements.  I then s u m m e d the net d i r e c t i o n c o d e s o f in-stream l a r v a l  colonisers and c o m p a r e d it to the expected d i s t r i b u t i o n .  Results: T h e numbers o f colonists at each site was calculated under 3 different c o l o n i s a t i o n models (Table 4.4). Conservative estimates o f c o l o n i s a t i o n v a r i e d between 0 a n d 5 larvae per year. These estimates are l o w because at least 10 unique i n d i v i d u a l s w e r e detected i n each r e m o v a l zone after disturbance. B y a s s u m i n g that none o f the u n m a r k e d a n i m a l s f o u n d i n the removal zone were colonisers, this estimator excludes a significant p r o p o r t i o n o f dispersal. T h e liberal m o d e l predicted f u l l replacement o f r e m o v e d larvae at three o f f o u r sites ( F i g u r e 4.2). T h e liberal estimates undoubtedly overestimated c o l o n i s a t i o n . T h e biggest f l a w i n this m o d e l is the assumption that a l l u n m a r k e d i n d i v i d u a l s f o u n d i n the r e m o v a l zone p o s t - m a n i p u l a t i o n were  89  dispersers. F r o m the efficiency index, I estimated that at least 2 5 % o f larvae i n i t i a l l y detected i n the r e m o v a l zone post-clearing were m i s s e d residents. A n y l o c a l recovery predictions b a s e d o n this m o d e l w i l l be optimistic. T h e Statistically Probable m o d e l consistently p r o d u c e d estimates m i d w a y between the conservative and liberal models.  Percent replacement of removed individuals by colonists T h e percentage o f r e m o v e d i n d i v i d u a l s that were replaced b y c o l o n i s a t i o n v a r i e d amongst sites (Figure 4.2). U n d e r the Statistically P r o b a b l e M o d e l , 29 to 2 1 0 % o f the larvae r e m o v e d f r o m each site were replaced i n one year. W h i l e T a m i h i C - D S recovered f u l l y , c o l o n i s a t i o n h a d replenished o n l y 2 9 - 7 7 % o f the r e m o v e d p o o l at the other three sites.  Per Capita Colonisation O n l y a s m a l l percentage o f a l l larvae caught w i t h i n each 120 m s t u d y zone were colonists (Table 4.5). A c r o s s the three forested sites, (Centre H F , P r o m o n t o r y 3a a n d P r o m o n t o r y B H ) , the  per capita c o l o n i s a t i o n rate was r e m a r k a b l y u n i f o r m , r a n g i n g between 3 to 5 percent o f a l l  captured i n d i v i d u a l s per year. In contrast, 1 3 % percent o f captures at T a m i h i - C D S were colonists. A s w i l l be discussed b e l o w , the h i g h  per capita rate at T a m i h i C - D S is l i k e l y due to  l o c a l l y higher recruitment at this site.  Density Dependent Colonisation There was no relation between the  per capita c o l o n i s a t i o n rate at a site and the m e a n  larval density o f larvae i n the source reaches ( F i g u r e 4.3). A possible density association was observed w h e n the  per capita rate was split into t w o values, one f o r c o l o n i s a t i o n b y l a r v a l  90  dispersal a n d another f o r c o l o n i s a t i o n b y recruitment (Figures 4 . 4 a & b). T h e r e w a s a trend f o r colonisation b y l a r v a l dispersal to increase w i t h density. H o w e v e r this trend is based o n differences o f one or t w o dispersing i n d i v i d u a l s between sites and c o u l d easily be due to chance.  Origin of Colonists T h e percentage o f c o l o n i s a t i o n that w a s due to reproduction v a r i e d c o n s i d e r a b l y between sites. C o l o n i s e r s were p r i m a r i l y dispersing larvae at t w o sites, and p r i m a r i l y recruits at the r e m a i n i n g t w o (Figure 4.5). T h e o n l y site to c o m p l e t e l y recover f r o m the r e m o v a l , T a m i h i C - D S , was restocked entirely b y recruits. A t this site, sexually mature animals must have bred i n the r e m o v a l zones a f e w months after the r e m o v a l h a d taken place. P r o m o n t o r y 3 a w a s also e x c l u s i v e l y c o l o n i s e d b y recruits, but h a d o n l y replaced 2 9 % o f its previous inhabitants b y the end o f the experiment.  Body Size and  Colonisation  T h e expected distribution o f mean S V L s i n 37 n o n - c o l o n i s i n g larvae is s h o w n i n F i g u r e 4.6. C o l o n i s i n g larvae were significantly smaller than n o n - c o l o n i s i n g i n d i v i d u a l s . T h i s result is not due to greater dispersal b y s m a l l larvae, b u t to h i g h e r recruitment i n the depopulated zones. A s s h o w n i n Chapter 3 , b o d y size h a d little i n f l u e n c e o n m o v e m e n t i n any o f the four study streams. T h e only w e a k trend observed w a s an increase i n m o v e m e n t w i t h b o d y size, contradicting the notion that recruits are the m o s t m o b i l e . I f the r e m o v a l zones h o l d m o r e recruits than the source areas, it is because m o r e eggs w e r e deposited and/or successfully hatched w i t h i n them.  91  E x c l u d i n g recruits f r o m the sample, I tested whether the b o d y s i z e o f l a r v a l c o l o n i s e r s was significantly different f r o m n o n - c o l o n i s i n g individuals. T h e mean S V L o f in-stream colonisers, 53.6 m m , was not significantly different f r o m the m e a n S V L o f 7 r a n d o m l y selected non-colonisers (expected mean = 53.4 m m , p = 0.446, F i g u r e 4.7).  Distance Travelled By  Colonisers  T h e expected mean distance travelled b y n o n - c o l o n i s i n g larvae was l o w e r than that m o v e d b y the in-stream colonists, but not significantly so (Figure 4.8). T h e m e a n distance travelled b y in-stream c o l o n i s i n g larvae was more than twice the m e a n recorded i n the source areas.  Direction of  Colonisation  P o o l i n g across a l l sites, the ratio o f d o w n s t r e a m to upstream m o v e m e n t s was 4 2 : 5 8 . j  T h i s slight preference for upstream m o v e m e n t was reflected i n the r a n d o m i s a t i o n tests, w h i c h predicted an average o f 3.9 net upstream m o v e m e n t s i n a group o f 7 d i s p e r s i n g larvae; In contrast w i t h this value, six out o f seven c o l o n i s i n g larvae m o v e d upstream into the r e m o v a l zone. A l t h o u g h this result is not significantly different f r o m expected (p = 0.224, F i g u r e 4.8), it proves larvae are capable o f m o v i n g upstream against the current into a n e w area.  Discussion L o c a l recovery i n D. tenebrosus populations was variable d u r i n g the first year f o l l o w i n g a disturbance. F u l l recovery o c c u r r e d i n o n l y 1 o f 4 sites w i t h c o l o n i s a t i o n r e p l e n i s h i n g o n l y 2 9 7 7 % o f r e m o v e d i n d i v i d u a l s at the r e m a i n i n g three streams. G i v e n the s m a l l area o f these  92  removals and the h i g h abundance o f larvae i n nearby source reaches, it is s u r p r i s i n g that f u l l recovery d i d not o c c u r at all sites. It is unclear whether larvae l a c k e d the a b i l i t y to c o l o n i s e at a faster rate or s i m p l y h a d no cause to m o v e f r o m where their i n i t i a l l o c a t i o n (i.e. no density dependence o r destructive habitat change f o r c i n g m o v e m e n t ) . F u l l repopulation w i t h i n a year after r e m o v a l was a c h i e v e d o n l y at T a m i h i C - D S , the sole stream r u n n i n g through a recent clear cut. M e a n air temperature at this site was h i g h e r than at the other three streams (Table 3.6). T h e m e a n abundance o f macrobenthos at this site was less than h a l f that o f the forested sites. It is not k n o w n h o w or i f these variables affect c o l o n i s a t i o n speed, but they d i d not appear to e x p l a i n the v a r i a t i o n i n dispersal rates b e t w e e n f o u r unmanipulated streams i n C h a p t e r 3. W i t h n o replicate clear cut sites, it is i m p o s s i b l e to determine whether this is a habitat or site effect. A s m y study is one o f the first r e m o v a l experiments to be c o n d u c t e d o n a m p h i b i a n s , the closest t a x o n o m i c c o m p a r i s o n I can m a k e is to other aquatic vertebrates. S u c h c o m p a r i s o n s show the recolonisation ability o f D. tenebrosus larvae to be p o o r . F o r e x a m p l e , several species o f fish r e m o v e d f r o m 4 0 - 1 0 0 m reaches i n an I l l i n o i s stream regained 9 0 % o f their o r i g i n a l abundance w i t h i n 10 days (Peterson & B a y l e y 1993). M u c h v a r i a t i o n , h o w e v e r , exists a m o n g fish species, w i t h some predicted to r e c o l o n i s e w i t h i n a f e w w e e k s ( L a r i m o r e 1959), others a few months ( M a t t h e w s 1986) a n d others u p to a year ( G u n n i n g & B e r r a 1969). In almost a l l o f these studies, the experimental reaches cleared were larger than i n m y experiment. I f recolonisation proceeds at the rates observed i n m y experiment, f u l l n u m e r i c a l recovery at the three unsaturated sites s h o u l d take 6-42 m o n t h s ( T a b l e 4.6). I d i v i d e d the total length o f each depleted reach b y its p r e d i c t e d recovery t i m e to estimate h o w fast reaches experiencing s i m i l a r reductions c o u l d be replenished (Table 4.6). F o r e x a m p l e , m i l d  93  disturbances that caused density reductions o f 0.1 larvae m (magnitude o f m y depletion at 2  P r o m o n t o r y 3a) w o u l d be recolonised at a rate o f 2 0 m per year. A l t e r n a t i v e l y , severe disturbances that caused depletions o f 1.1 larvae m " (Centre H F ) , a value w h i c h w o u l d cause 2  complete extirpation at many streams, w o u l d be r e c o l o n i s e d at a s l o w e r rate o f 7.1 m p e r year. I n o w use these simple predictions to estimate the t i m e required f o r r e c o l o n i s a t i o n i n stream reaches running through a clearcut ( m a x i m u m length o f 4 0 0 m ) . I f l o g g i n g triggered o n l y moderate depletions o f 0.1-0.3 larvae m " , l a r v a l recolonisation o f a 4 0 0 m x 1 m reach c o u l d 2  take 8-20 years. H o w e v e r i f l o g g i n g triggered an almost f u l l extirpation o f larvae (depletion o f > 1.1 larvae m" ), recolonisation o f this stream reach c o u l d take m o r e than 5 5 years. 2  E i g h t to fifty five years f o r the f u l l r e c o l o n i s a t i o n o f a stream r u n n i n g through a c u t b l o c k agrees w i t h other estimates f o r salamanders i n l o g g e d habitats. P l e t h o d o n t i d salamanders i n eastern N o r t h A m e r i c a were estimated to take 2 0 - 2 5 to 5 0 - 7 0 years to return to pre-harvest density i n cutblocks ( A s h & B r u c e 1997). H o w e v e r other species o f a m p h i b i a n s are faster colonisers. In S p a i n , an o l d lignite m i n e site w a s r e c o l o n i s e d b y several a m p h i b i a n species w i t h i n o n l y t w o years o f abandonment ( G a l a n 1997). S i m i l a r l y artificial ponds i n a B a v a r i a n experiment were c o l o n i s e d b y the newt  Triturus alpestris w i t h i n a year ( J o l y & G r o l e t 1997).  V a r i a t i o n i n recovery speed is l i k e l y a result o f species-specific c o l o n i s a t i o n ability, the magnitude o f depletion caused b y the disturbance, a n d dispersal barriers i n the landscape. A l t h o u g h the above extrapolation o f m y s m a l l - s c a l e results to larger areas p r o v i d e s a q u i c k c o m p a r i s o n to other species, these c a l c u l a t i o n s are not accurate e n o u g h to i n f o r m management decisions. M y study provides a detailed description o f l a r v a l c o l o n i s a t i o n , but there was n o study o f adults. I have s h o w n that r e p r o d u c t i o n increases l o c a l density m o r e r a p i d l y than  94  larval dispersal. T h u s , understanding the c o l o n i s i n g a b i l i t y o f adults is p i v o t a l to estimating the speed o f recovery by D. tenebrosus  after large disturbances.  E x t r a p o l a t i o n o f small-scale results to large areas is also r i s k y as rates measured at one scale d o not always predict b e h a v i o u r at another. T h r u s h et a l . (1997) f o u n d that c o l o n i s a t i o n speed for some benthic marine organisms decreases significantly w i t h increasing plot size. R e a l disturbances often act over a m u c h w i d e r area than any experimental plots a n d must be restocked b y a proportionately smaller colonist p o o l . A s a consequence, c o l o n i s a t i o n rates measured i n s m a l l areas w i l l l i k e l y overestimate the recovery speed o f large areas. T h e type o f disturbance applied i n this experiment m a y also y i e l d o v e r l y optimistic c o l o n i s a t i o n rates. D e p o p u l a t i o n was achieved b y r e m o v i n g i n d i v i d u a l s e x p e r i m e n t a l l y and not b y destructive habitat change. T h i s experiment d i d not e x p l i c i t l y c o n s i d e r the role o f habitat on c o l o n i s a t i o n . A s larvae were f o u n d i n a l l sites p r i o r to m a n i p u l a t i o n , the habitat was suitable to larvae. Habitat clearly affects a m p h i b i a n c o l o n i s a t i o n i n addition to intrinsic dispersal a b i l i t y (Hecnar & M c C l o s k e y 1997, S k e l l y & M e i r 1997). M y experiment has s h o w n o n l y h o w q u i c k l y larvae can recolonise acceptable habitat. In the field, even i f D. tenebrosus  c a n reach a  depopulated area q u i c k l y , they m a y a v o i d settling i n it or die w i t h i n it i f the habitat is unsuitable. It is thus uncertain h o w m u c h or i f m y rates w o u l d v a r y under different types o f habitat change. H o w e v e r , the h i g h speed o f c o l o n i s a t i o n i n the one clearcut site suggests l o g g i n g does not necessarily deter movement. F i n a l l y i n m y study, recolonisation refers o n l y to the n u m e r i c a l replacement o f i n d i v i d u a l s and not to biomass recovery. P r e and p o s t - r e m o v a l l a r v a l b i o m a s s c o u l d not be c o m p a r e d as the number o f colonists was statistically inferred and hot d i r e c t l y enumerated. A s such, the precise identity o f each colonist was not k n o w n a n d thus their total b i o m a s s c o u l d not be calculated.  95  T h i s o m i s s i o n may optimistically bias the rate o f recovery at the T a m i h i C - D S . A l t h o u g h this site exceeded its pre-removal abundance w i t h i n a year, the colonisers w e r e p r i m a r i l y s m a l l i n d i v i d u a l s (< 6 0 m m T L ) . L a r v a e f o u n d i n the r e m o v a l zone o f this site before clearing w e r e generally large i n d i v i d u a l s (> 100 m m T L ) . T h e discrepancy i n size between the pre a n d postr e m o v a l occupants o f this zone suggests f u l l b i o m a s s recovery was not a c h i e v e d at this site.  Life History and Colonisation A s mentioned above, full recolonisation occurred o n l y at T a m i h i C - D S where colonists were e x c l u s i v e l y recruits. T h i s colonisation was l i k e l y achieved entirely b y adults breeding i n the r e m o v a l zone. C o l o n i s a t i o n b y larval dispersal o c c u r r e d at t w o sites, but never added as m a n y i n d i v i d u a l s to the r e m o v a l zone as reproduction. L a r v a l dispersal never c o n t r i b u t e d m o r e than 13 i n d i v i d u a l s to any r e m o v a l zone. A d u l t females can carry between 8 5 - 2 0 0 eggs ( N u s s b a u m 1969). U n l e s s egg-to-larvae mortality is greater than 9 0 % , one c l u t c h o f eggs c o u l d p r o v i d e just as m a n y colonists to a stream reach as l o c a l l a r v a l dispersal. E g g - t o - l a r v a e s u r v i v a l i n D. tenebrosus is u n k n o w n , but was 2 2 % i n one p o p u l a t i o n o f the related Ambystoma  maculatum  (Shoop 1974). I f this rate is s i m i l a r to that i n D. tenebrosus, one r e p r o d u c t i v e event c o u l d increase l o c a l density i n depopulated areas m u c h m o r e effectively than l a r v a l i m m i g r a t i o n f r o m adjacent reaches. A l t h o u g h m y one-year study is i n f o r m a t i v e , the final o u t c o m e o f the c o l o n i s a t i o n process cannot be j u d g e d f r o m observation on this t i m e scale. Re-establishment o f D. tenebrosus i n m y r e m o v a l zones w i l l depend on the s u r v i v a l o f larvae to sexual m a t u r i t y , a process that c o u l d take 2-6 years (Chapter 2). S t u d y i n g o n l y l a r v a l c o l o n i s t s w i t h o u t c o n s i d e r a t i o n o f their s u r v i v a l to sexual maturity m a y overestimate the speed o f c o l o n i s a t i o n . A l t h o u g h i n d i v i d u a l s m a y have  96  higher s u r v i v a l and/or growth i n the absence o f conspecifics, it is still p r o b l e m a t i c to assume a l l larval colonisers w i l l survive to a d u l t h o o d . F o r e x a m p l e , one intertidal study f o u n d that defaunated areas were q u i c k l y r e c o l o n i s e d b y a polychaete w o r m species. M o s t c o l o n i s i n g polychaetes, however, d i e d w i t h o u t c o n t r i b u t i n g to the l o n g t e r m r e c o v e r y o f the plots ( T h r u s h et al. 1996). A l t h o u g h the n u m b e r o f l a r v a l colonists entering a d e p o p u l a t e d area m a y b e a g o o d indicator o f future occupancy, c o n t i n u e d m o n i t o r i n g is required to ensure their presence leads to the long-term survival of i n d i v i d u a l s .  Size of Colonisers T h e mean size o f larvae w i t h i n the r e m o v a l zones was s i g n i f i c a n t l y l o w e r than outside, reflecting that most n e w recruits were located i n the r e m o v a l zones. R e c r u i t s at P r o m o n t o r y 3 a and T a m i h i C - D S were clustered h e a v i l y i n and around the r e m o v a l z o n e a n d were not spread evenly throughout the rest o f the stream. T h i s m a y be the r a n d o m o u t c o m e o f a s i n g l e c l u t c h at each site being c o i n c i d e n t a l l y deposited i n or i m m e d i a t e l y adjacent to the r e m o v a l zone. A l t e r n a t i v e l y there m a y be a selective advantage to b e i n g hatched i n depopulated areas. I n support o f the latter hypothesis, C o n n o r et a l . (1988) f o u n d densities o f first a n d second year D. tenebrosus larvae to be twenty times greater i n stream sections i n w h i c h o l d e r salamanders a n d fish were absent. Recruits c o u l d be selectively concentrated i n the r e m o v a l zone i f adults chose to l a y eggs in areas o f l o w l a r v a l density, or i f hatchlings were more successful i n the absence o f conspecifics. T h e first o f these scenarios, selective o v i p o s i t i o n , has been r e c o r d e d i n other species o f stream d w e l l i n g salamanders ( K a t s & S i h 1992). T h e second hypothesis, that hatchling survival is greater i n l o w density areas, is also feasible for D. tenebrosus. P a c i f i c G i a n t  97  Salamanders are k n o w n to prey on s m a l l conspecifics i n the lab ( M a l l o r y 1996) a n d I o b s e r v e d some instances o f c a n n i b a l i s m i n the field. N e w recruits are the most vulnerable to intraspecific predation and conceivably m a y survive best i n the absence o f conspecifics. I f this hypothesis is true, this benefit may favour dispersing adults and promote recolonisation i n disturbed landscapes.  Dispersal Behaviour of Larval  Colonists  O b v i o u s l y larval colonisers had to m o v e some distance to enter the r e m o v a l zone, h o w e v e r their mean dispersal distance was t w i c e that o f m o b i l e , n o n - c o l o n i s i n g larvae. M a n y potential colonists w e r e clustered just o n the b o u n d a r y o f the r e m o v a l z o n e (1-5 m a w a y ) . H a d they dispersed into the r e m o v a l zone, the m e a n distance travelled b y c o l o n i s i n g i n d i v i d u a l s w o u l d be no different f r o m that o f non-colonisers. H o w e v e r c o l o n i s a t i o n d i d not p r o c e e d b y gradual range expansions o f these fringe animals but b y a few l o n g distance m o v e m e n t s (4 - 63 m , mean = 26.1 m ) b y h i g h l y m o b i l e i n d i v i d u a l s . C o l o n i s e r s m a y have been b e h a v i o u r a l l y predisposed to m o v e m e n t and encountered the r e m o v a l zone b y chance. T h i s i d e a is supported b y findings i n Chapter 3 that suggest i n p o p u l a t e d stream reaches, the l a r v a l p o p u l a t i o n is c o m p o s e d of a large n u m b e r o f h i g h l y sedentary larvae and a s m a l l n u m b e r o f transient individuals. O f the seven c o l o n i s i n g larvae, s i x m o v e d upstream into the zone. T h e d o m i n a n t upstream direction o f c o l o n i s a t i o n suggests that it was not a l w a y s f o r c e d b y the stream current. T h i s contradicts previous c l a i m s that most c o l o n i s a t i o n occurs b y d o w n s t r e a m drift o f larvae ( B r u c e 1985, 1986). S e c o n d g r o w t h forest d o w n s t r e a m o f d i s t u r b e d reaches m a y therefore be a more important source o f colonists than o l d g r o w t h stands l o c a t e d upstream. T h e s e s e c o n d  98  growth areas m a y be more vulnerable to forest harvest and development than upstream sources. T h i s activity c o u l d have more a destructive influence o n D. tenebrosus metapopulation d y n a m i c s than the harvest o f o l d growth.  Conclusions: M y experiment provides n e w insights into the response o f the P a c i f i c G i a n t S a l a m a n d e r to disturbance i n B r i t i s h C o l u m b i a . N u m e r i c a l recovery f r o m small-scale " e x t i r p a t i o n s " occurs between 6-42 months after disturbance. E x t i r p a t i o n s throughout streams the length o f clearcuts ( m a x i m u m length o f 4 0 0 m ) l i k e l y take significantly longer to be f u l l y recolonised. T h i s suggests that D. tenebrosus i n recent clearcuts (< 5 years) are m o r e apt to have s u r v i v e d t h r o u g h the l o g g i n g event than to have r e c o l o n i s e d after a l o c a l extirpation. T h e i r presence suggests s u r v i v a l through l o g g i n g i s possible p r o v i d e d the stream remains intact. A l t h o u g h depopulated areas can be restocked b y both in-stream dispersal o f larvae and adults, dispersal and o v i p o s i t i o n b y adults appears to be the most r a p i d means o f r e c o l o n i s a t i o n . C o n s e r v a t i o n efforts s h o u l d therefore be directed p r i m a r i l y at adult dispersal capabilities and habitat requirements. F i n a l l y , it i s obvious f r o m the above d i s c u s s i o n that the measurement o f c o l o n i s a t i o n i n the f i e l d is c o m p l i c a t e d . A c c u r a t e estimates are hampered b y biases due to s m a l l sample size, l o w recapture rates, and restricted spatial scales. W h i l e the c o l o n i s a t i o n rates I have p r o v i d e d are a potentially useful management t o o l , they s h o u l d be u s e d w i t h c a u t i o n . I have incorporated uncertainty into m y estimates and generated a c o l o n i s a t i o n rate based o n the probable n u m b e r o f colonists and not direct enumeration. U n d e r different assumptions o f capture detection a n d r e m o v a l efficiency, slightly different estimates c o u l d be d r a w n f r o m the same data. W h i l e I  99  believe m y methods to be b i o l o g i c a l l y realistic, other estimations are possible. F o r this reason I advocate the use o f m y conservative and liberal rates presented as l i m i t s for what is p o s s i b l e i n the  field.  100  c o co  '2 ^  O co 7v 173>» r9 U T3 •fi  .a  rt  tu  •fi k  £ 2 | S o tN  CN  CN  CN  T3  o CO  VO VO VO VO  .fi  cd  1  >-1  c4  > <*>  a co  VO oo Ov  £ c  CO >  X  c o  o S to  CN  co  00 rt  Pi  c  co  3, 3  < 03  cn  rt  $ rt c o  '2 o  "oo c CD X!  & co  T3 O 'C  1)  OH  Tf  3  H  101  CU  fi O O fi N  CM  .2 -a  CS  > o  a  £  x  *!« 2 § £ N  73 o H  X ! CD  ca •'fi" >.  T3 3  £ S £ fi  -o g  O.  E «  CD  CU  CN  >  to CD  C o  cu fi o N  73 >  >  £  N  o  73  S £  c o  *-4—'  ca o  o T3 C 1—1  ca  CS CO  cu  t/3  o e o £ o  CD N  CO CN Tt  Qi  3  ca  H  102  CO  rt  cu  T3 O  C  B t-  CU  r-m  IS  73 > © £  o o  d  cn cn vo m  CO c3 ^ to tl_^  rt  O co  • rt  03  CO .  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CO co  CO u-  co  c3 rt  a) xx  X  g « _ E3  03 Js  § ^ >© *1  * •£• s cs  rt  —  1  C  CO  03  .3  CO  o  <rt CO O T3 tH 3 3 O c3  |cn CU  & o  rt IK <D irt  ,  c  o £ <u o  c  U  PH  00  Q U  co co 3 cci o a Xco C « e co  E Z  ..  rri  •  x,  S  CO  T3  t-  O CO T3 g  £  .2 % « ° 5  > el B  H  ^2 cd Pi  CS )-. rr co 1  103  0) 0) c 3 cS 3  a c  03 <D 3 O N  > o  £  8 XI  of  JH  -a  3  es Xi © ON  73  OO  oo  aj CO '£ o 73 o > o3 XI  "2 £  a OJ 2 T3 £  '£  O  ^  2 OJ > X) oj 03  J3 J 5  3  Co  l i Q x? .O  -° -a~ £ 3 w  03  cn  •4—»  C  o  s o  CM  g  Z o  OJ" >  e  •o  s  o  V  —  OJ CO  H  U  X! 8J  C O  104  Site  # Unique Larvae Caught  % Captures that Were  in 120 m Study Reach  Colonists  Centre H F  162  4.9  Promontory 3 a  133  3.0  Promontory B H  239  5.4  Tamihi C-DS  145  13.0  Table 4.5: N u m b e r o f larvae c a p t u r e d i n 120 m study area and the percentages o f these that were colonisers.  105  b 2 ca  T3 c"b a  CO  ~3  ca  C D a  Pi  C D u  col onise  4J  Cu O  c o -a  C CD CD  *4J  x!  ~3  CD CD C XJ  E,  due  whi  o  4->  ^ >  den  3  CD  U  o O d vd dvn CN CN  3 O £ co  X 3 CD CM O CD E o '•u> X! 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CM '-r.  o  uo!)esjuo|oo  Aq 3BAJB|  paAouiaj | o  CU  £ 8 S S3  CD  tr  }uaiuaoe|dau %  9* .6  .. e  CN  cu  O  CO  £ -a  £  .3 u  rt fi T3 CO CU X)  ^ '3 O  11  to u  C  cu  3  3  ID .52 -p  T3  108  c  CD "c3 T3  >  c <D  C  _o  "4—» CD  C  a  a ccj  JS CD  a CD  1-1  o  C N  CD  c/>  'S o "o  CD 1)  OO cS  4->  c CD CD  PH  m CU '  Ui  9 DC  109  Colonisation due to larval dispersal 0.06 Promontory BH  E <o v  0.05  (A  0.04  I  g >  Centre HF  0)  |1  0.03  <2 o 6 O o.02 (4) n  j;  Promontory 3a  0.01  Tamihi C-DS -+-  0.2  0.4  0.6  0.8  1  1.2  1.4  Mean Larval Density of Source A r e a s (larvae/m)  Colonisation due to recruitment  ^ c  0.15  •5  c o o  • Tamihi C-DS  0.12  " Si 0.09 a> S  a  <D  a 2 a  1 S. 0  0.06 Promontory 3a  •  0.03 00  Centre HF Promontory BH  1  1  1  i  1  0.2  0.4  0.6  0.8  1  -  A  1  1.2  .*....  1.4  Mean Larval Density of Source A r e a s (larvae/ m)  Figures 4.4a & b: Larval density in source areas and rate of in-stream and recruitment colonisation. a) (Top): Percentage of in-stream colonisers in source areas as a function of mean population density. A n in-stream coloniser is one that was originally captured in the source areas and then dispersed into the removal zone. b) (Bottom): Percentage of recruits in the removal zone as a function of mean population density in the source areas.  110  CO CD ® , CO  d E  CO CD  Ct •  6  0)  c  £  1  CD >  o E  0>  tr  c o o  o  CO  "co >  CO  co £• o  o  o  C  O O  l  I O  O N I O O  D  I O  f l O  ^ n C O O  l  I  r  O  O  |OOd jazjuo|oo IBJOJ. jo uoijjodojd  11  113  T3  CD >  o  I co  6 J  cd >  o 1— C s 03 CD  o CO  1Z X! 2 e i_i  03  CD  X *-  ^ 0 3  Jo  I %  £  O  CO  ^  '2 J2 2  o i> V o c ^ § c  i-  -2  >, g x x T3 CD  TJ  'S to  ^  >  CO  CD O  o  C  03  •«—» CO  CD >  CD  3  > C  VD  c3 CD  2 3  2 CD X  °*  CJ  c  a  CD  CO  "c3  VO CN  8 § 2 "5 C rt  o ~c5 .52 "3 co Q x '2 w o x rt  CD  CD N, bi  CO  "o  8  3  CD  c3  CD X  1— *<  rt O  X  a « ~  114  'cO  CO  °  ca  ,2  "  CM  O  o m'r> T3  CD  O  ^  \Q  CM  Si I 13 is  •a g d  6 0  c  1 5c o  cD  o £ •~  - -1 * s  *> «  <u  ti  CO  <MJ 3  E CD >> o O  O  CD  e  E Cca CD CD C > FJ 2 E e  sag  r CD E H ia ca • co —  I 1  o  S3 2 8  2 CD  2g1 CD  1 a  O  =  "I "o  co  « " -e CD  O  O  ^ CD  O CD  cD  E •S "a o P o 3 co f—I  CD c  ca"  u,W  ca  •3 C N  bQ  CN  CO  fic  •• 'E c dII ©\ o 'E CM T t o bo 'co ca  >  no lar  .1. §  4^  r-  1  Chapter 5: General conclusions T w o categories o f risk must be addressed w h e n e v a l u a t i n g a species' status: the l i k e l i h o o d s o f stability and o f persistence. Stability refers to the p r o b a b i l i t y that abundance w i l l remain constant, and persistence to the probability o f extinction w i t h i n a g i v e n t i m e p e r i o d ( C o n n e l l & S o u s a 1983). G i v e n the difficulty o f identifying 'stable' e q u i l i b r i a and distinguishing uncharacteristic declines f r o m natural v a r i a t i o n , it is often most useful t o study factors w h i c h influence extinction probability and recovery potential ( C o n n e l l & S p u s a 1983). B y e x a m i n i n g the short-term population b i o l o g y o f larvae, m y thesis has f o c u s e d o n factors that m a y influence D. tenebrosus persistence i n B r i t i s h C o l u m b i a . O n l y l o n g t e r m m o n i t o r i n g o f p o p u l a t i o n trends w i l l s h o w whether this species is n u m e r i c a l l y stable i n this p r o v i n c e . In the introductory chapter, I presented three general areas o f i n v e s t i g a t i o n f r o m w h i c h information o n D. tenebrosus p o p u l a t i o n v i a b i l i t y and c o n t i n u e d persistence can be d r a w n : studies o f l o c a l demography, the i m p a c t o f h u m a n activities, and the a b i l i t y to recover f r o m disturbance. A l t h o u g h I d i d not r i g o r o u s l y explore a l l o f these issues i n this thesis, m y research on larval demography and c o l o n i s i n g ability bears o n each issue. A f t e r b r i e f l y r e v i e w i n g m y findings as they relate to these three areas, I w i l l discuss whether the s u m total o f m y research supports the notion that this species is at risk i n B r i t i s h C o l u m b i a .  I. R e v i e w o f major results a) L o c a l demography  Comparison of larval demography between threatened and non-threatened areas I f o u n d the mean larval density i n m y 5 sites, 0.88 + 0.09 m ' , w a s j u s t o v e r a t h i r d o f 2  that reported i n O r e g o n , the centre o f the species' range ( C o r n & B u r y 1989). T h e difference  116  between m y density estimates and those f r o m Western W a s h i n g t o n , a n e i g h b o u r i n g r e g i o n where they are not endangered, is not nearly so pronounced. K e l s e y (1995) c a l c u l a t e d the m e a n l a r v a l density i n unharvested stands i n W e s t e r n W a s h i n g t o n to be 1.1 m " , o n l y s l i g h t l y greater than i n 2  this study. L o w e r densities i n B r i t i s h C o l u m b i a suggests that these p o p u l a t i o n s differ i n o n e or more k e y demographic rates f r o m those i n O r e g o n . A n n u a l s u r v i v a l does not appear to vary m u c h between these regions, h o w e v e r the length o f the l a r v a l p e r i o d does. N u s s b a u m & C l o t h i e r (1973) estimated annual l a r v a l s u r v i v a l i n one O r e g o n stream to be 4 3 % , o n l y slightly higher than the 3 0 - 3 5 % m e a n annual rate I estimated. A c c o r d i n g to m y analysis, larvae i n m y four study streams c o u l d take 4 - 6 years to reach m e t a m o r p h i c size (130 m m T L +). L a r v a e i n t w o O r e g o n streams w e r e estimated to g r o w 2-3 times faster than larvae i n m y study, a n d are b e l i e v e d to have a l a r v a l p e r i o d o f o n l y t w o years ( N u s s b a u m & C l o t h i e r 1973). E v e n i f annual s u r v i v a l was the same i n O r e g o n and B r i t i s h C o l u m b i a , net s u r v i v a l through the l a r v a l p e r i o d w i l l be l o w e r i n B r i t i s h C o l u m b i a . F o r e x a m p l e i f annual s u r v i v a l was 4 0 % i n both regions, s u r v i v a l throughout the entire l a r v a l p e r i o d w o u l d be 16% i n O r e g o n (2 year l a r v a l period), a n d o n l y 0 . 5 - 3 % i n B r i t i s h C o l u m b i a (4-6 year l a r v a l period). T h i s difference i n net l a r v a l s u r v i v a l m a y help e x p l a i n w h y densities o f D. tenebrosus are l o w e r i n B r i t i s h C o l u m b i a than i n the centre o f its range. H o w e v e r , m a n y more populations i n both B r i t i s h C o l u m b i a and O r e g o n need to be studied before any geographic trends i n s u r v i v a l can be c o n f i r m e d .  Comparison of D . tenebrosus larval demography with other salamanders L a r v a l s u r v i v a l varies m a r k e d l y between species and habitats and n o t y p i c a l value c a n be identified for stream d w e l l i n g salamanders. H o w e v e r it is useful to note that l a r v a l s u r v i v a l i n D.  117  tenebrosus is s i m i l a r to that i n other species. I a p p r o x i m a t e d annual s u r v i v a l o f D. tenebrosus larvae to be 3 0 - 3 5 % (corrected for transformation loss). B a s e d o n these rates, s u r v i v a l o f D. tenebrosus through a 4-6 year l a r v a l p e r i o d w o u l d b e 0 . 5 - 3 % . T h i s range is s i m i l a r to that o f both Ambystoma barbouri and Ambystoma texanum whose s u r v i v a l through a 6 0 day l a r v a l p e r i o d is 0 . 5 - 1 2 . 5 % and 1-4% respectively (Petranka & S i h 1986, H o l o m u z k i 1991). I n one N o r t h C a r o l i n a stream, Gyrinophilus porphyriticus  was f o u n d to have an annual s u r v i v a l o f 2 1 %  ( B e a c h y 1997), w h i c h w o u l d y i e l d a net s u r v i v a l o f 0 . 2 % through its 4 year l a r v a l p e r i o d . T h u s s u r v i v a l o f D. tenebrosus larvae i n B r i t i s h C o l u m b i a is s i m i l a r to that o f other s t r e a m - d w e l l i n g species. T h e g r o w t h rates I f o u n d for D. tenebrosus larvae are slightly l o w e r than recorded i n other temperate aquatic salamander species. I estimated D. tenebrosus larvae i n m y study streams w o u l d grow between 7.3-10.6 m m S V L per year. A t s i m i l a r latitudes i n A l b e r t a a n d Quebec, larvae o f the p o n d d w e l l i n g Ambystoma macrddactylum and Ambystoma  maculatum  g r o w approximately 15 m m S V L although there is considerable variation ( F l a g e o l e & L e C l a i r 1992, R u s s e l l et al. 1996). Y e a r l y increases o f 12-20 m m S V L have been reported i n stream d w e l l i n g Eurycea wilder ae and Hynobius kimurae larvae ( B e a c h y 1997, M i s a w a & M a t s u i 1997), but as these studies were c o n d u c t e d i n m o r e southern l o c a t i o n s , c o m p a r i s o n c o u l d b e c o n f o u n d e d b y latitude effects.  A l t h o u g h these between-species c o m p a r i s o n s are u s e f u l , they  may be confounded by differences i n b o d y size. B i g g e r species w i l l l i k e l y have greater absolute growth even though their proportionate rate o f increase c o u l d be l o w e r than i n s m a l l species. T h e species I have discussed here have s l i g h t l y s m a l l e r larvae (1-2 c m ) than D. tenebrosus. I have s h o w n that despite h a v i n g r e d u c e d g r o w t h rates i n c o m p a r i s o n to p o p u l a t i o n s i n the centre o f the species' range, D. tenebrosus i n B r i t i s h C o l u m b i a has l a r v a l demography s i m i l a r  118  to other stream d w e l l i n g salamanders. A n n u a l s u r v i v a l and g r o w t h rates i n D. tenebrosus larvae are c o m p a r a b l e to those i n other, non-threatened species. A l t h o u g h g r o w t h m a y not be m a x i m a l i n B r i t i s h C o l u m b i a , larvae i n these populations are not unusual w i t h respect other streamd w e l l i n g species.  b) T h e impact o f h u m a n activities T h e l o w number o f sites used i n this study makes it difficult to e x a m i n e the influence o f l o g g i n g on D. tenebrosus. W i t h almost h o r e p l i c a t i o n o f forest age classes, I c o u l d not test whether variation i n l a r v a l demography was due to l o g g i n g or r a n d o m site v a r i a t i o n . H o w e v e r I f o u n d no relation between forest age and l a r v a l density across m y f i v e study sites. T h i s neutral result has also be f o u n d b y H a w k i n s (1983) and K e l s e y (1995), but contradicts the p o s i t i v e association between density and forest age f o u n d b y B u r y (1983), C o n n o r et a l . (1988), C o r n & B u r y (1989), ( C o l e et a l . 1997) and the negative association f o u n d b y M u r p h y et a l . (1981) a n d •; M u r p h y & H a l l (1981). I also noted that l a r v a l g r o w t h i n m y o n l y clearcut site was t w i c e as fast as i n m y second growth sites. F r o m these observations, I speculate that c l e a r c u t t i n g c a n reduce the density o f larvae but that survivors m a y benefit f r o m increased g r o w t h i n disturbed habitats. F i n a l l y I found that l o c a l l a r v a l dispersal (more than 10 m ) was not influenced b y any o f 7 stream habitat variables i n c l u d i n g substrate type, p o o l - r i f f l e c o m p o s i t i o n , wetted w i d t h and depth. D i s p e r s a l was u n i f o r m l y l o w through a w i d e variety o f micro-habitats. M o v e m e n t i n m y clearcut site was indistinguishable f r o m that i n m y second g r o w t h sites. B l a u s t e i n et. a l . (1994) suggested that anthropogenic habitat alteration exacerbates a m p h i b i a n p o p u l a t i o n e x t i n c t i o n b y hampering recolonisation. M y results suggest that l o g g i n g - i n d u c e d habitat shifts i n streams have  119  little consequence for the l o c a l dispersal o f D. tenebrosus larvae. It is not k n o w n , h o w e v e r , whether these habitat changes influence the longer distance movements o f larvae between confluent streams or the o v e r l a n d m o v e m e n t o f terrestrial adults.  c) G e n e r a l ability to recover disturbance T o predict the l i k e l i h o o d o f persistence, it is necessary to have i n f o r m a t i o n o n a p o p u l a t i o n ' s capacity to increase f r o m l o w numbers either b y recruitment or i m m i g r a t i o n (Blaustein et a l . 1994). T h e speed o f r e c o l o n i s a t i o n v a r i e d between sites but w a s p r e d i c t e d to take 6-42 months to repopulate reaches o f 2 5 - 4 0 m (26-75 m ) . A s s u m i n g the rates I o b s e r v e d 2  i n 13 months o f study r e m a i n e d constant through t i m e , moderate depletions o f 0.1-0.3 larvae m"" i n headwater streams r u n n i n g through clearcuts (approximately 4 0 0 m x l m ) c o u l d take 8-20 years to be fully recolonised b y larvae. A l t e r n a t i v e l y i f l o g g i n g caused an almost complete extirpation o f larvae, f u l l r e c o l o n i s a t i o n o f reaches r u n n i n g through a 4 0 0 m c u t b l o c k c o u l d take approximately 55 years. T h e average life span o f D. tenebrosus i n the w i l d is not k n o w n , h o w e v e r s i m i l a r l y s i z e d aquatic salamanders can l i v e approximately 25 years i n captivity ( D u e l l m a n & T r u e b 1986). I f this value obtains i n the f i e l d , recolonisation o f stream reaches < 4 0 0 m after moderate to severe disturbances c o u l d be a c h i e v e d i n one or t w o p o p u l a t i o n turnovers. T h u s p r o v i d e d source populations are nearby and habitat is suitable for breeding, n u m e r i c a l recovery can o c c u r over short e c o l o g i c a l time spans (less than 2 generations). E x p e r i m e n t a l l y defaunated stream reaches were repopulated both b y l a r v a l dispersal and adult reproduction. L o c a l reproduction appears to be a m u c h m o r e efficient means o f repopulating an area than l a r v a l i m m i g r a t i o n . O n l y 4 - 5 % o f larvae i n reaches adjacent to m y  120  r e m o v a l zones became colonists and this dispersal never contributed m o r e than 13 i n d i v i d u a l s to any o f m y plots i n 13 months. In contrast, c l u m p s o f 15-20 young-of-the-year, p o s s i b l y a l l f r o m the same c l u t c h , were f o u n d at t w o sites i n the s u m m e r o f 1997. T h i s suggests that i n one breeding attempt, an adult female c o u l d p r o v i d e an equal or greater n u m b e r o f c o l o n i s t s than supplied b y n e i g h b o u r i n g reaches w i t h 100-200 larvae.  II. Implications for assessment o f D. tenebrosus' status i n B r i t i s h C o l u m b i a A l t h o u g h l o g g i n g and other disturbances m a y increase the rate o f l o c a l e x t i n c t i o n , m y research suggests that D. tenebrosus populations i n B r i t i s h C o l u m b i a are not u n u s u a l l y susceptible to disturbance. A l t h o u g h they are f o u n d at l o w e r densities than i n other parts o f the species' range, larvae i n these populations exist w e l l w i t h i n the s u r v i v a l a n d g r o w t h b o u n d s o f other non-threatened s t r e a m - d w e l l i n g salamanders. F u r t h e r m o r e , the c o m b i n e d influences o f recruitment and l a r v a l recolonisation can facilitate r a p i d recovery f r o m small-scale disturbances. Consequently, any argument o f v u l n e r a b i l i t y must be based on the action o f e x t r i n s i c factors such as l o g g i n g . In the absence o f c o n c l u s i v e p r o o f that l o g g i n g increases l o c a l e x t i n c t i o n rate b e y o n d that w h i c h can be balanced b y r e c o l o n i s a t i o n , it is uncertain whether D. tenebrosus i n B r i t i s h C o l u m b i a are truly i m p e r i l l e d . I c a u t i o n , h o w e v e r , that m y results are d r a w n f r o m small-scale manipulations w i t h l i m i t e d r e p l i c a t i o n . T h e i r ability to describe the d y n a m i c s o f a l l populations o f D. tenebrosus i n B r i t i s h C o l u m b i a a n d their response to disturbance i s therefore l i m i t e d . M y colonisation rates were measured under o p t i m a l habitat c o n d i t i o n s a n d i n the presence o f source areas containing m a n y potential c o l o n i s t s . T h i s situation is not l i k e l y to o c c u r i n the f i e l d , especially i f potential disturbances s u c h as l o g g i n g o c c u r frequently enough to d i m i n i s h source  121  populations. T o c o n f i r m m y conclusions about the status o f D. tenebrosus i n B r i t i s h C o l u m b i a , future research should examine the colonisation o f larger areas w i t h a l o w e r a v a i l a b i l i t y o f potential dispersers and the c o l o n i s i n g ability o f terrestrial adults.  Bibliography A s h , A . N . 1997. Disappearance and return o f P l e t h o d o n t i d Salamanders t o clearcut plots i n the Southern B l u e R i d g e M o u n t a i n s . C o n s e r v a t i o n B i o l o g y 11: 9 8 3 - 9 8 9 . A s h , A . N . & R . C . B r u c e . 1994. Impacts o f t i m b e r harvesting o n salamanders. C o n s e r v a t i o n B i o l o g y 8: 3 0 0 - 3 0 1 . A s h t o n , R . E . 1975. A study o f m o v e m e n t , h o m e range, a n d winter b e h a v i o r o f Desmognathus fuscus (Rafinesque). Journal o f H e r p e t o l o g y 9: 85-91. A y e n s u , E . S . 1981. Assessment o f threatened plant species i n the U n i t e d States. I n H . S y n g e (editor): T h e b i o l o g i c a l aspects o f rare plant conservation. J o h n W i l e y & S o n s , Chichester. B e a c h y , C . K . 1997. Effect o f predatory l a r v a l Desmognathus s u r v i v a l , and metamorphosis o f larval Eurycea wilderae.  quadramaculatus  on growth,  C o p e i a 1997: 131-137.  B e r y e n , K . A . I 9 9 0 . Factors affecting p o p u l a t i o n fluctuations i n l a r v a l a n d adult stages o f the w o o d f r o g (Rana sylvaticd). E c o l o g y 7 1 : 1599-1608. B e s c h t a , R . L . , R . E . B i l b l y , G . W . B r o w n , L . B . H o l t b y & T . D . H o f s t r a . 1987. S t r e a m temperature and aquatic habitat: fisheries and forestry interactions. In E . O . S a l o & T . W . C u n d y (editors): Streamside management: forestry and fishery interactions. C o n t r i b u t i o n N o . 7, Institute o f Foresty Resources, U n i v e r s i t y o f W a s h i n g t o n , Seattle. B l a u s t e i n , A . R., D . B . W a k e & W . P . Sousa. 1994. A m p h i b i a n D e c l i n e s : J u d g i n g stability, persistence, and susceptibility o f populations to l o c a l a n d g l o b a l extinctions. C o n s e r v a t i o n B i o l o g y 8: 60-71. B l a u s t e i n , A . R . & D . B . W a k e . 1995. T h e p u z z l e o f d e c l i n i n g a m p h i b i a n populations. S c i e n t i f i c A m e r i c a n 272: 52-57. B o u t i n , S., B . S . G i l b e r t , C . J . K r e b s , A . R . E . S i n c l a i r & J . N . M . S m i t h . 1 9 8 5 . T h e role o f dispersal i n the p o p u l a t i o n d y n a m i c s o f snowshoe hares. C a n a d i a n J o u r n a l o f Z o o l o g y 6 3 : 106- 115. B o u t i n , S. 1980. Effect o f spring r e m o v a l experiments o n the spacing b e h a v i o u r o f female S n o w s h o e Hares. C a n a d i a n J o u r n a l o f Z o o l o g y 5 8 : 2 1 6 7 - 2 1 7 4 . B r i t i s h C o l u m b i a M i n i s t r y o f the E n v i r o n m e n t , L a n d s & P a r k s . 1993. P a c i f i c G i a n t Salamander: W i l d l i f e species at risk. Pamphlet. B r u c e , R . C . 1985. L a r v a l periods, p o p u l a t i o n structure a n d the effects o f stream drift i n larvae o f the salamanders Desmognathus quadramaculatus  a n d Leurognathus  marmoratus i n a Southern  A p p a l a c h i a n stream. C o p e i a 4: 8 4 7 - 8 5 4 .  123  B r u c e , R . C . 1986. U p s t r e a m and downstream m o v e m e n t s o f Eurycea bislineata a n d other salamanders i n a southern A p p a l a c h i a n stream. H e r p e t o l o g i c a 4 2 : 149-155. B r u c e , R . C . 1995. T h e use o f temporary r e m o v a l s a m p l i n g i n a study o f p o p u l a t i o n d y n a m i c s o f the salamander Desmognathus monticola.  Australian Journal o f E c o l o g y  20:403-412.  B u r n h a m , K . P . & W . S . O v e r t o n . 1979. R o b u s t estimation o f p o p u l a t i o n size w h e n capture probabilities vary a m o n g animals. E c o l o g y 60: 927-936. Burnham, K . P , E . A . Rexstad, G . C . White & D . R . Anderson. Program C A P T U R E . V e r s i o n J u l y 18, 1994. C o l o r a d o Cooperative Fisheries and W i l d l i f e R e s e a r c h U n i t . B u r y , R . B . 1972. S m a l l m a m m a l s and other prey i n the diet o f the P a c i f i c G i a n t S a l a m a n d e r (Dicamptodon  ensatus). A m e r i c a n M i d l a n d N a t u r a l i s t 87: 5 2 4 - 5 2 5 .  B u r y , R . B . 1983. Differences i n a m p h i b i a n populations i n l o g g e d a n d o l d g r o w t h r e d w o o d forest. N o r t h w e s t S c i e n c e 57: 167-178. B u r y , R . B . & P . S . C o r n . 1988. D o u g l a s - f i r forests i n the O r e g o n a n d W a s h i n g t o n Cascades: R e l a t i o n o f H e r p e t o f a u n a to stand age and moisture. I n : R . E . S z a r o , K . E . S e v e r s o n & D . R . Patton (eds.), M a n a g e m e n t o f A m p h i b i a n s , R e p t i l e s , a n d S m a l l M a m m a l s i n N o r t h A m e r i c a . P r o c . S y m p . , 19-21 J u l y 1988, Flagstaff, A r i z o n a . B u s k i r k , J . V . & D . C . S m i t h . 1991. Density-dependent p o p u l a t i o n regulation i n a salamander. E c o l o g y 7 2 : 1747-1756. 1  C a u g h l e y , G . 1995. D i r e c t i o n s i n conservation b i o l o g y . J o u r n a l o f A n i m a l E c o l o g y .  63:214-244.  C a u g h l e y , G . & A . G u n n . 1996. C o n s e r v a t i o n b i o l o g y i n theory a n d practice. B l a c k w e l l S c i e n c e , Massachusetts. C h a m b e r l i n , T . W . , R . D . H a r r & F . H . Everest. 1991. T i m b e r harvesting, s i l v i l c u l t u r e and watershed processes. In W . R . M e e h a n (editor): Influences o f forest and rangeland management on s a l m o n i d fishes and their habitat. S p e c i a l p u b l i c a t i o n N o . 19, A m e r i c a n Fisheries Society, Betheseda, M D . C h a p m a n , D . G . 1951. S o m e properties o f the h y p e r g e o m e t r i c d i s t r i b u t i o n w i t h applications to z o o l o g i c a l censuses. U n i v e r s i t y o f C a l i f o r n i a P u b l i c a t i o n o n Statistics 1: 131-160. C o l e , E . C , W . C . M c C o m b , M . N e w t o n , C L . C h a m b e r s & J . P . L e e m i n g . 1997. R e s p o n s e o f amphibians to clearcutting, b u r n i n g and glyphosate a p p l i c a t i o n i n the O r e g o n Coast R a n g e . Journal o f W i l d l i f e M a n a g e m e n t 6 1 : 656-664. C o n n e l l , J . H . & W . P . Sousa. 1983. O n the evidence needed to j u d g e e c o l o g i c a l stability o r persistence. A m e r i c a n Naturalist 121: 7 8 9 - 8 2 4 .  124  C o n n o r , E . J . , W . J . T r u s h & A . W . K n i g h t . 1988. Effects o f l o g g i n g o n P a c i f i c G i a n t Salamanders: influence o f age-class c o m p o s i t i o n and habitat c o m p l e x i t y . B u l l e t i n o f the E c o l o g i c a l S o c i e t y o f A m e r i c a 69: 104-105. C o r n , P . S . & R . B . B u r y . 1989. L o g g i n g i n western O r e g o n : responses o f headwater habitats and stream a m p h i b i a n s . Forest E c o l o g y and M a n a g e m e n t 2 9 : 39-57 C o r t w r i g h t , S . A . 1986. T h e roles o f dispersal and history i n A m p h i b i a n c o m m u n i t i e s . Indiana A c a d e m y o f S c i e n c e 9 5 : 187. D a v i e s , P . E . & M . N e l s o n . 1994. R e l a t i o n s h i p s between r i p a r i a n buffer w i d t h s a n d the effects o f l o o g i n g o n stream habitat, invertebrate c o m m u n i t y c o m p o s i t i o n arid f i s h abundance. A u s t r a l i a n Journal o f M a r i n e and Freshwater R e s e a r c h 4 5 : 1289-305. D u e l l m a n , W . & L . Trueb. 1986. T h e B i o l o g y o f A m p h i b i a n s . M c - G r a w H i l l Inc., U . S . A . D u p u i s , L . A . , J . N . M . S m i t h & F . B u n n e l l . 1995. R e l a t i o n o f terrestrial-breeding a m p h i b i a n abundance to tree-stand age. C o n s e r v a t i o n B i o l o g y 9: 6 4 5 - 6 5 3 . E l l i s , S. & U . S . S e a l . 1995. T o o l s o f the trade to a i d d e c i s i o n - m a k i n g for species s u r v i v a l . B i o d i v e r s i t y and C o n s e r v a t i o n 4: 553-572. F a r r , A . C M . 1985. Status report on the P a c i f i c G i a n t S a l a m a n d e r i n C a n a d a . P r e p a r e d for the C o m m i t t e e on the status o f endangered w i l d l i f e i n C a n a d a . F a r r , A . C . M . 1989. Status report o n the P a c i f i c G i a n t S a l a m a n d e r Dicamptodon  tenebrosus i n  C a n a d a . Prepared for the C o m m i t t e e on the Status o f E n d a n g e r e d W i l d l i f e i n C a n a d a (COSEWIC). F l a g e o l e , S. & R . L e c l a i r . 1992. E t u d e d e m o g r a p h i q u e d ' u n e p o p u l a t i o n de salamandres (Ambystoma maculatum) a l ' a i d e de l a methode squeletto-chronologique.  Canadian Journal o f  Z o o l o g y 70: 7 4 0 - 7 4 0 . G a l a n , P . 1997 C o l o n i z a t i o n o f spoil benches o f an opencast lignite m i n e i n northwest S p a i n b y A m p h i b i a n s and Reptiles. B i o l o g i c a l C o n s e r v a t i o n 79:  187-195.  G i l l , D . E . 1978. T h e metapopulation e c o l o g y o f the R e d - S p o t t e d N e w t ,  Notophthalmus  viridescens (Rafinesque). E c o l o g i c a l M o n o g r a p h s 4 8 : 145-166. G o l d i n g , D . L . 1987. Changes i n streamflow peaks f o l l o w i n g t i m b e r harvest o f a coastal B r i t i s h C o l u m b i a watershed. Internationational association o f h y d r o l o g i c a l sciences 167: 509-517. G u n n i n g , G . E . & T . M . B e r r a . 1969. F i s h r e p o p u l a t i o n o f e x p e r i m e n t a l l y decimated segments i n the headwaters o f t w o streams. Transactions o f the A m e r i c a n F i s h e r i e s S o c i e t y 2: 3 0 5 - 3 0 8 .  125  H a n s k i , I. & M . G i l p i n . 1991. M e t a p o p u l a t i o n d y n a m i c s : b r i e f history and conceptual d o m a i n . Pages 3-16 i n M . G i l p i n and I. H a n s k i , (eds). M e t a p o p u l a t i o n d y n a m i c s : e m p i r i c a l and theoretical investigations. A c a d e m i c Press, L o n d o n . H a r t m a n G . F . & J . C . Scrivener. 1990. Impacts o f forestry practices o n a coastal stream ecosystem Carnation Creek, B r i t i s h C o l u m b i a , C a n a d a . C a n a d i a n B u l l e t i n o f Fisheries a n d A q u a t i c Sciences 223: 1-148. H a w k i n s , C P . , M L . M u r p h y , N . H . A n d e r s o n , & M . A . W i l z b a c h . 1983. D e n s i t y o f fish a n d salamanders i n relation to riparian canopy a n d p h y s i c a l habitat i n streams o f the northwestern U n i t e d States. C a n a d i a n Journal o f Fisheries a n d A q u a t i c Sciences 4 0 : 1173-1185. H a y c o c k , R . A . 1991. P a c i f i c G i a n t Salamander Dicamptodon  tenebrosus Status R e p o r t . U n p u b l .  report to the B r i t i s h C o l u m b i a M i n i s t r y o f E n v i r o n m e n t , W i l d l i f e B r a n c h . . H e c n a r , S . J . & R . T . M c C l o s k e y . 1997. Spatial scale a n d determination o f species status o f the G r e e n F r o g . C o n s e r v a t i o n B i o l o g y 11: 6 7 0 - 6 8 2 . H e y e r , W . R . et al. 1994. M e a s u r i n g and M o n i t o r i n g B i o l o g i c a l D i v e r s i t y : Standard M e t h o d s f o r A m p h i b i a n s . Smithsonian Institution Press, W a s h i n g t o n . H i n e s , J . E . 1991. P r o g r a m J O L L Y , V e r s i o n 01/24/91, M B . H o l o m u z k i , J . R . I 9 9 1 . M a c r o h a b i t a t effects o n e g g d e p o s i t i o n and l a r v a l g r o w t h , s u r v i v a l , a n d instream dispersal i n Ambystoma barbouri. C o p e i a 3: 6 8 7 - 6 9 4 . H o l o m u z k i , J . R . 1982. H o m i n g behavior o f Desmognathus  ochrophaeus a l o n g a stream. J o u r n a l  o f H e r p e t o l o g y 16: 3 0 7 - 3 0 9 . J o h n s o n , M L . & M . S . G a i n e s . 1985. Selective basis f o r e m i g r a t i o n o f the P r a i r i e V o l e , Microtus ochrogaster. O p e n f i e l d experiment. J o u r n a l o f A n i m a l E c o l o g y 54: 3 9 9 - 4 1 0 . Johnston, B . 1998. Terrestrial P a c i f i c G i a n t S a l a m a n d e r s {Dicamptodon tenebrosus G o o d ) : N a t u r a l history a n d their response to forest practices. M . S c . T h e s i s . D e p a r t m e n t o f Z o o l o g y , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 98 pgs. J o l y , P . & O . Grolet. 1996. C o l o n i z a t i o n d y n a m i c s o f n e w ponds a n d the age structure o f c o l o n i z i n g A l p i n e newts, Triturus alpestris  Acta Oecologica  17: 5 9 9 - 6 0 8 .  K a t s , L . B . & A . S i h . 1992. O v i p o s i t i o n site selection a n d avoidance o f f i s h b y streamside salamanders (Ambystoma barbouri).  C o p e i a 1992: 468-473.  K e l s e y , K . A . 1995. Responses o f headwater stream a m p h i b i a n s to forest practices i n W e s t e r n W a s h i n g t o n . P h . D . Thesis, U n i v e r s i t y o f W a s h i n g t o n , 164 pgs.  126  K e s s e l , E . L . & B . B . K e s s e l . 1943. T h e rate o f g r o w t h o f the y o u n g larvae o f the P a c i f i c G i a n t Salamander, Dicamptodon ensatus ( E s c h s c h o l t z ) . W a s m a n n C o l l e c t o r 5:  108-111.  K r e b s , C . J . , J . A . R e d f i e l d & M . J . Taitt. 1978. A p u l s e d - r e m o v a l experiment o n the v o l e townsendii.  C a n a d i a n Journal o f Z o o l o g y  Microtus  56: 2253-2263.  K u s a n o , T . 1981. G r o w t h and s u r v i v a l rate o f the larvae o f Hynobius nebulosus tokyoensis T a g o ( A m p h i b i a , H y n o b i d a e ) . Researches o n P o p u l a t i o n E c o l o g y 2 3 : 360-378. L a m b e r t i , G . A . , S . V . G r e g o r y , L . R . A s h k e n a s , R . C . W i l d m a n & K . M . S . M o o r e . 1991. S t r e a m ecosystem recovery f o l l o w i n g . a catastrophic debris f l o w . C a n a d i a n Journal o f F i s h e r i e s a n d A q u a t i c Sciences 4 8 : 196-208. L a r i m o r e , R . W . , W . F . C h i l d e r s & C . Ffeckrotte. 1959. D e s t r u c t i o n and re-establishment o f stream f i s h and invertebrates affected b y drought. Transactions o f the A m e r i c a n Fisheries S o c i e t y 88:  261-285.  L i n c o l n , F . C . 1930. C a l c u l a t i n g w a t e r f o w l abundance on the basis o f b a n d i n g returns. U . S . Department o f A g r i c u l t u r e C i r c u l a t i o n . 118: 1-4. L i s l e , T . E . & S. H i l t o n . 1992. T h e v o l u m e o f fine sediment i n pools: an i n d e x o f sediment supply in gravel bed streams. W a t e r Resources B u l l e t i n 2 8 :  371-383.  L o m o l i n o , M . V . & R . C h a n n e l l . 1995. S p l e n d i d isolation: patterns o f geographic range collapse i n endangered m a m m a l s . Journal o f M a m m a l o g y 76:  335-347.  M a c e , G . M . & R . L a n d e . 1991. A s s e s s i n g e x t i n c t i o n threats t o w a r d a reevaluation o f I U C N threatened species categories.  C o n s e r v a t i o n B i o l o g y 5: 148-157.  M a l l o r y , K . T . 1996. Size-dependent interactions i n l a r v a l Dicamptodon  tenebrosus a n d their  effects on spatial distributions i n streams. H o n o r s B . S c . T h e s i s . T h e U n i v e r s i t y o f B r i t i s h Columbia. M a t t h e w s , W . J . 1986. F i s h faunal structure i n on O z a r k S t r e a m : S t a b i l i t y , persistence a n d a catastrophic f l o o d . C o p e i a 1986: 3 8 8 - 3 9 6 . M e h l m a n , D . W . 1997. Change i n a v i a n abundance across the geographic range i n response to environmental change. E c o l o g i c a l A p p l i c a t i o n s 7: 6 1 4 - 6 2 4 . M i s a w a , Y . & M . M a t s u i . 1997. L a r v a l l i f e history v a r i a t i o n i n t w o populations o f the Japanese salamander Hynobius kimurae ( A m p h i b i a , U r o d e l a ) . Z o o l o g i c a l S c i e n c e 14: 2 5 7 - 2 6 2 . M o n k o n n e n , M . 1990. R e m o v a l o f territory holders causes i n f l u x o f s m a l l - s i z e d intruders i n passerine b i r d communities i n N o r t h e r n F i n l a n d . O i k o s 2 8 1 - 2 8 8 .  127  Murphy, M . L , C P . Hawkins & N . H . Anderson. 1981. Effects of canopy modification and accumulated sediment on stream communities. Transactions of the American Fisheries Society 110:469-478. Murphy, M . L . & J.D. Hall. 1981. Varied effects of clear-cut logging on predators and their habitat in small streams of the Cascade Mountains, Oregon. Canadian Journal of Fisheries and Aquatic Sciences. 38: 147-145. Murphy, M . L . & K . V . Koski. 1989. Input and depletion of large woody debris in Alaskan streams and implications for management. North American Journal of Fisheries Management 9: 427-436. Murphy, M . L . 1995. Forestry impacts on freshwater habitat and anadromous salmonids in the Pacific Northwest and Alaska - requirements for protection and restoration. N O A A Coastal Ocean Program Decision Analysis series No. 7. N O A A Coast Ocean Office, Silver Spring M D . 156 pp. Primack, R . B . 1993. Essentials of conservation biology. Sinauer Associates Inc., Massachussetts. Nathan, R., U . N . Safriel & H . Shrihai. 1996. Extinction and vulnerability to extinction at distribution peripheries: an analysis of Israeli breeding avifauna. Israel Journal of Zoology 42: 361-383. Neill, W . E . 1998. Recovery of Pacific Giant Salamander populations threatened by logging. Unpubl. report to World Wildlife Fund, Canada. Neill, W . E . & J. S. Richardson. 1998. Persistence of threatened of Pacific Giant Salamander populations under forest harvesting. Forest Renewal British Columbia Final Report, HQ96288-RE. Nussbaum, R . A . & G . W . Clothier. 1973. Population structure, growth and size of larval Dicamptodon ensatus (Escholtz). Northwest Science 47: 218-227. Nussbaum, R . A . , E . D . Brodie Jr. & R . M . Storm. 1983. Amphibians and Reptiles of the Pacific  Northwest. University Press of Idaho, Idaho. Orchard, S. 1984. Amphibians and Reptiles of British Columbia: A n ecological review. Ministry of Forests Publication, Research Branch. W H R - 1 5 . Victoria, B . C . Parker, M . S . 1993. Size-selective predation on benthic macroinvertebrates by stream-dwelling salamander larvae. Archiv fur Hydrobiologie 128: 385-400. Parker M . S. 1994. Feeding ecology of stream-dwelling Pacific Giant Salamander larvae (Dicamptodon  tenebrosus). Copeia 1994: 705-718.  128  Peterson J.T. & P.B. Bayley. 1993. Colonization rates of fishes in experimentally defaunated warmwater streams. Transactions of the American Fisheries Society 122: 199-207. Petranka, J.W. 1984. Sources of interpopulational variation in growth responses of larval salamanders. Ecology 65: 1857-1865. Petranka, J.W. & A.Sih. 1986. Environmental instability, competition and density-dependent growth and survivorship of a stream-dwelling salamander. Ecology 67: 729-736. Petranka, J.W., M.E. Eldridge & K.E. Haley. 1993. Effects of timber harvesting on Southern Appalachian Salamanders. Conservation Biology 7: 363-370. Petranka, J.W. 1994. Response to impact of timber harvesting on salamanders. Conservation Biology 8: 302-304 Pollock K.H., J.D. Nichols, C. Brownie & J.E. Hines. 1990. Statistical Inference for capturerecapture experiments. Wildlife Monographs 107: 1-97. Primack, R.B. 1993. Essentials of conservation biology. Sinauer Association Inc., Massauchussetts. Ralph, S.C, G.C Poole, L.L. Conquest & R.J. Naiman. 1994. Stream channel morphology and woody debris in logged and unlogged basins of Western Washington. Canadian Journal of Fisheries and Aquatic Sciences 51: 37-51. Randall, M.G.M. 1982= The dynamics of an bisection population throughout it's altitudinal distribution: Coleophora alticollela (Lepidoptera) in Northern England. Journal of Animal Ecology. 51: 993-1016. Reeves, G.H., F.H. Everest & J.R. Sedell. 1993. Diversity of juvenile anadromous salmonid assemblages in coastal Oregon basins with different levels of timber harvest. Transactions of the American Fisheries Society 122: 309-317. Resetarits, W.J.Jr. 1991. Ecological interactions among predators in experimental stream communities. Ecology 72: 1782-1793. Richardson, J. 1994. Pacific Giant Salamander Species Account. Unpubl. Draft account prepared for the Ministry of Environment, Lands and Parks, Wildlife Branch. Richardson, J.S. & W.E. Neill. 1995. Distribution patterns of two montane stream amphibians and the effects of forest harvest: the Pacific Giant Salamander and Tailed Frog in southwestern British Columbia. Unpubl. Report to the British Columbia Ministry of Environment, Lands and Parks. Rogers, D.J. & S.E. Randolph. 1986. Distribution and abundance of tsetse flies (Glossina species). Journal of Animal Ecology 55: 1007-125.  129  R u s s e l l , A . P . , G . L . P o w e l l & D . R . H a l l . 1996. G r o w t h and age o f the A l b e r t a long-toed salamander (Ambystoma macrodactylum krausei): a c o m p a r i s o n o f t w o methods o f e s t i m a t i o n . C a n a d i a n J o u r n a l o f Z o o l o g y 74: 397-412. R u x t o n , G . D . & M . D o e b e l i . 1996. Spatial self-organization and persistence o f transients i n a metapopulation m o d e l . Proceedings o f the R o y a l S o c i e t y o f L o n d o n 2 6 3 : 1153-1158. S h o o p , C R . 1974. Y e a r l y variation i n l a r v a l s u r v i v a l o f Ambystoma maculatum. E c o l o g y 5 5 : 440-444. S k e l l y , D . K . & E . M e i r . 1997. Rule-based m o d e l s for evaluating m e c h a n i s m s o f distributional change. C o n s e r v a t i o n B i o l o g y 11: 5 3 1 - 5 3 8 . Slaney, P . A . & A . D . M a r t i n . 1997. T h e watershed restoration p r o g r a m o f B r i t i s h C o l u m b i a : accelerating natural recovery processes. W a t e r Q u a l i t y R e s e a r c h J o u r n a l o f C a n a d a 3 2 : 3 2 5 346. S o u l e , M . E . & K . A . K o h n . 1989. R e s e a r c h priorities for conservation b i o l o g y . Island Press, Washington. Southerland, M . T . 1986. T h e effects o f variation i n streamside habitats o n the c o m p o s i t i o n o f mountain salamander c o m m u n i t i e s . C o p e i a 1986: 7 3 1 - 7 4 1 . Spellerberg, I.F. 1992. E v a l u a t i o n and assessment for conservation: e c o l o g i c a l guidelines for determining priorities for nature conservation. C h a p m a n & H a l l , L o n d o n . Stenseth, N . C . & W . Z . L i d i c k e r . 1992. A n i m a l dispersal: s m a l l m a m m a l s as a m o d e l . C h a p m a n & Hall, London. Thrush, S.F., R . B . Whitlatch, R . D . Pridmore, J . E . Hewitt, V . J . C u m m i n g s & M . R . W i l k i n s o n . 1996. Scale-dependent recolonization: T h e role o f sediment stability i n a d y n a m i c sandflat habitat. E c o l o g y 77: 2472-2487. T h u r o w , G . R . 1997. E c o l o g i c a l lessons f r o m T w o - l i n e d salamander translocations.  Transactions  o f the I l l i n o i s State A c a d e m y o f Science 9 0 : 7 9 - 8 8 . T u m l i n s o n , R . G . R . C l i n e & P. Z w a n k . 1990. Surface habitat associations o f the O k l a h o m a salamander (Eurycea tyrenensis). H e r p e t o l o g i c a 4 6 : Tyler, J . A . & W . W . Hargrove. resource landscapes:  169-175.  1997. P r e d i c t i n g spatial distributions o f foragers o v e r large  a m o d e l i n g analysis o f the i d e a l free d i s t r i b u t i o n . O i k o s 7 8 :  376-386.  130  W a h b e , T . R 1996. T a i l e d F r o g s (Ascaphus truei, Stejneger) i n natural and m a n a g e d coastal temperature rainforests o f southwestern B r i t i s h C o l u m b i a , C a n a d a . M . S c . T h e s i s , D e p a r t m e n t o f Forest Sciences, U n i v e r s i t y o f B r i t i s h C o l u m b i a . W a l d m a n , B . & J . S . M c K i n n o n . 1993. Inbreeding and outbreeding i n fishes, a m p h i b i a n s , a n d reptiles. T h e natural history o f inbreeding and outbreeding: theoretical and e m p i r i c a l perspectives. N . W . T h o r n h i l l , ed. U n i v e r s i t y o f C h i c a g o Press, C h i c a g o . W e l s h J r . , H . H . 1991. R e l i c t u a l amphibians a n d o l d - g r o w t h forests. C o n s e r v a t i o n B i o l o g y 3: 3 0 9 319. W e l s h Jr. H . H . & A . J . L i n d . 1996. Habitat, correlates o f the Southern T o r r e n t S a l a m a n d e r Rhyacotriton  variegatus (Caudata: R h y a c o t r i t o n i d a e ) , i n N o r t h w e s t e r n C a l i f o r n i a . J o u r n a l o f  H e r p e t o l o g y 30: 3 8 5 - 3 9 8 . W i l t e n m u t h , E . B . 1997. A g o n i s t i c behavior and use o f c o v e r b y s t r e a m - d w e l l i n g l a r v a l salamanders (Eurycea wilderae). C o p e i a 1997: 4 3 9 - 4 4 3 . Z a r , J . H . 1984. Biostatistical A n a l y s i s , 2 n d E d i t i o n . Prentice H a l l , N e w Jersey.  131  Appendix 1: Chapman's Modification of the Lincoln-Peterson Method  N=(r+  l)(n + 1) -1 (m + 1)  l~ (r + 1) (n + 1) ( r - m) (n - m1/2 1 (m + l) (m + 2) J L 2  where N = estimated population size, r = number of animals caught, marked and released in the first sample, n = the total number of animals caught in the second sample, and m = the total number of marked animals caught in the second sample (Chapman 1951).  132  co  s o  O CD  rt o CO T3 rt X rt x : rt -o rt CO 3 X)  CO  CO  3  3  o  e ©  ,o  ro CU rt  a £  CU  a  o "•4—>  CO  3 co  CO  X) CO  3  I."3 CO  •o  £  p—1  o  3  "3  03  3  kH  CO  rt  rt •-H  s  rt rtO  C  i UH  £  ly ov  3 O  CO  IH  CO  X  c3 3 3  CO  CO X CO  o  X co  co  c  of  CO  <rt  3  ^ " O co  P  CO  to  rt  y •a -5 X!  £  CO  IX  x  co  CD  O  fc  rt  O co  •x  '55 CO g o OH  IH  PH  E  CO  3  rt  •*—*  -w  3 <s fi rtCO CD£  b •=  •PHH  2j» co CD rt cd  £ £ r-  H  O  »H  CO  .2  PH  * co  c i rt  •3 o o  u  3  CD  Xi  c3  '1 /—\  cs  p  ON ON  — " rt 3 co  CO  3 "3  P  25  rt rt co co <U - 1 _ rt 4 >-  rt _  CO  1  CD co  co  CO  s  O  x S3  DH CO  >  >> CO  CO  rt  ~ CD CD c  t3  rt  _3  co  -8' •<= g  £ £  x^  X)  'o  CD  x  3 * CO IH rt CO 3 "co " co CO o £ 3 co £ co X CO X > rt xx : 3rt 3^  i3  rt V-c  gro  CO  rt  X  CO  CO  § 5  3 co rt CO £ CO co X V-c rt W> CO co CO _3 X VH 3  C  7.  CO  "rt  PH  CD  X  CO  CD  l-l  .  O co .N X  rt _s  lH  < co  co co CO  X co <Vi rt co co -o .3  rt  1  CD  rt ,— R--.3  ci) CO in PH  C  3  X  co  us  c  3  co  ° £ sO  rt rt rt  1  rto  rt  val  CO  c  CO  to  3  £ fi 3 •£ fi rti "c3 rt rt co co CO "rt T3 O rt > O rt PH " o O rt T3 rt £ -o O CO co  sal  I  CO  disp  If rt  T3 CO  3  X  wh  rt  rt  of  T3 P  CO  rac  N  rt CO  S O  'co  C  CO CD - O T3 CO  3 1  £ o CD - O CD  5  co CO  4>  c §  CO  ^  '1  •s 1  rt > O  £ p  3 CO CU  I CO  "3 > o S  CD >  -3 rt  CO  CS  IS  "3 3  £ 3 rt ^3  3 O 'rt  CD  rt co C^H 0  3 O  PH  £  O  OH  co 3 O 00  2"  rt Ho  rt  rt  fi  ^ 3  .ti  CO CO CO  CO  fi  co  3  CD  Q  £ o U  co rt CO  '3  ri  u  '1  o  rt  CU  o CD  Q S  a a  o  133  Appendix 3 Estimating the Probability of one-time capture in the removal zone T h i s technique w a s used to estimate the p r o b a b i l i t y that a larvae caught o n l y o n c e i n the r e m o v a l zone remained resident but undetected u n t i l the end o f the experiment. A larvae w a s assumed to have c o l o n i s e d the r e m o v a l zone o n the first d a y it w a s captured i n this area. B e t w e e n this date and the end o f the experiment there were n possible s a m p l i n g occasions i n w h i c h it c o u l d be recaptured g i v e n it w a s a l i v e a n d w i t h i n the study area. T h e p r o g r a m C A P T U R E w a s then u s e d to estimate the m e a n p e r o c c a s i o n capture p r o b a b i l i t y o f larvae at each site ( B u r n h a m et a l . 1994). T h i s p r o b a b i l i t y w a s used to calculated an expected number o f recaptures g i v e n the a n i m a l r e m a i n e d alive and i n the r e m o v a l zone until the end o f the experiment. F o r e x a m p l e let us assume that a larvae w a s first caught i n the r e m o v a l zone i n the 10 th mark-recapture after m a n i p u l a t i o n but never again i n the r e m a i n i n g four s a m p l i n g intervals L e t us further assume that the mean capture p r o b a b i l i t y o f larvae over this time p e r i o d 0.15 p e r o c c a s i o n . T h e p r o b a b i l i t y o f the a n i m a l b e i n g present o n a l l subsequent s a m p l i n g days but not detected w a s calculated as f o l l o w s : P ( never detected i n 4 occasions I present) = ( 1 - 0 . 1 5 ) = 4  0.52  ( E q n . 1)  T h u s there is a 5 2 % probability this a n i m a l r e m a i n e d i n the zone after first capture but w a s not captured again. It was arbitrarily d e c i d e d that a n y larvae w i t h a greater than 5 0 % probability o f non-detection w o u l d be c o n s i d e r e d a c o l o n i s t under the Statistically probable m o d e l .  134  

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