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UBC Theses and Dissertations

Daily and seasonal interactions between salmonberry (Rubus spectabilis) and bumblebees (Bombus sitkensis).. 1980

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D A I L Y A N D S E A S O N A L I N T E R A C T I O N S B E T W E E N S A L M O N B E R R Y ( R U B U S S F E C T A B I L I S ) A N D B U M B L E B E E S ( B O M B U S S I T K E N S I S ) - I N S O U T H W E S T E R N B R I T I S H C O L U M B I A . b y G O R D O N S T E I N H O F F B . S . , B . A . , U t a h S t a t e U n i v e r s i t y , 1 9 7 6 , 1 9 7 7 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E i n T H E F A C U L T Y O F G R A D U A T E S T U D I E S D e p a r t m e n t o f Z o o l o g y We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E 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 J u l y 1 9 8 0 (e) G o r d o n S t e i n h o f f , 1 9 8 0 In presenting th i s thes i s in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i l ab le for reference and study. I further agree that permission for extensive copying of th is thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my written permission. Department of " Z . o a I o The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T.1W5 i i A b s t r a c t My study was designed to answer two main q u e s t i o n s : 1. ) Do the bees, through t h e i r f o r a g i n g behavior, a l t e r the r a t e s of salmonberry nectar p r o d u c t i v i t y ? 2 . ) Do the p l a n t s , through t h e i r r a t e s of nectar s e c r e t i o n , a l t e r the f o r a g i n g behavior of the bees? Since there are well-documented examples of m o r p h o l o g i c a l c o a d a p t a t i o n s between p l a n t s and t h e i r p o l l i n a t o r s , i t was r e a s o n a b l e to suppose t h a t p h y s i o l o g i c a l / b e h a v i o r a l c o a d a p t a t i o n s e x i s t as w e l l . Thus I hypothesized t h a t the above q u e s t i o n s would be answered i n the a f f i r m a t i v e . Though the two q u e s t i o n s have been i n d i v i d u a l l y s t u d i e d by s e v e r a l b i o l o g i s t s , I f e l t i t important to examine the p o s s i b l e r e c i p r o c a l responses of p l a n t s and p o l l i n a t o r s as they occur i n a n a t u r a l community c o n t e x t . Nectar p r o d u c t i v i t y of salmonberry f l o w e r s iBn bus s p e c t a b i l i s , Pursh) was i n v e s t i g a t e d u sing f l o w e r s i s o l a t e d f o r v a r i o u s l e n g t h s of time from i n s e c t v i s i t o r s . Nectar volumes were e x t r a c t e d using m i c r o p i p e t t e s and sugar c o n c e n t r a t i o n s w e r e determined with a hand r e f r a c t o m e t e r . Volumes and sugar c o n c e n t r a t i o n s were then used to c a l c u l a t e c a l o r i e s / h o u r . Nectar s t a n d i n g crop ( c a l o r i e s / f l o w e r ) was s i m i l a r l y d e r i v e d using untagged f l o w e r s . During the study I monitored temperature, sunshine l e v e l s , r e l a t i v e humidity, date of sampling, time of sampling, and the androecium diameters of a l l flowers sampled. I t was found t h a t an i n c r e a s e i n experimental e x t r a c t i o n r a t e brought about a corresponding decrease i n p r o d u c t i v i t y . i i i T h i s r e s u l t i s o p p o s i t e to t h a t r e p o r t e d by other a u t h o r s , yet i t was found that t h i s r e s u l t was not due to flower damage or to a r t i f i c i a l f e r t i l i z a t i o n of f l o w e r s . T h i s flower response t o simulated v i s i t a t i o n frequency may be of c o m p e t i t i v e advantage to f l o w e r s not being used by p o l l i n a t o r s present i n the area, P r o d u c t i v i t y and n e c t a r s t a n d i n g crop decreased as the salmonberry f l o w e r i n g season progressed, and decreased throughout the course of each day as r e l a t i v e humidity f e l l and a i r temperatures i n c reased. T h i s d e c l i n e i n p r o d u c t i v i t y r e f l e c t e d decreases i n volumes of nectar s e c r e t e d , though sugar c o n c e n t r a t i o n s i n c r e a s e d with i n c r e a s i n g sunshine l e v e l s . Younger f l o w e r s a p p a r e n t l y s e c r e t e d c a l o r i e s / h o u r a t higher r a t e s than o l d e r f l o w e r s , t h i s again r e f l e c t i n g t r e n d s i n volumes of n e c t a r s e c r e t e d . In each sample of ten f l o w e r s , t h e r e were f o u r which s e c r e t e d at r a t e s s i g n i f i c a n t l y higher than the remaining s i x . F u r t h e r , the f o u r most productive f l o w e r s s e c r e t e d at more p r e d i c t a b l e r a t e s i n terras of the environmental v a r i a b l e s monitored d u r i n g the study. Throughout the season t h e r e was a dramatic i n c r e a s e o f .bumblebees (Bombus s i t k e n s i s , Nylander) observed a t patches of salmonberry f l o w e r s . Throughout each day, the bees i n c r e a s e d i n d e n s i t y as sunshine l e v e l s and temperatures i n c r e a s e d and r e l a t i v e humidity f e l l . The bees foraged from the more p r o d u c t i v e younger f l o w e r s more f r e q u e n t l y than o l d e r f l o w e r s , and i n c r e a s i n g l y foraged from o l d e r f l o w e r s as n e c t a r abundance i n a l l f l o w e r s d e c l i n e d through the day and season. In a d d i t i o n , they may a l s o have been avoiding i n c r e a s i n g numbers of f l o w e r s i v they approached, though t h i s c o n c l u s i o n must remain t e n t a t i v e . Bumblebee behavior was more p r e d i c t a b l e d u r i n g the e a r l y morning hours of each day as opposed to hours i n the a f t e r n o o n . I t i s p o s t u l a t e d that, t h i s was because bumblebees experience more uniform energy c o n d i t i o n s i n the morning. Based on the d i s t r i b u t i o n curves of n e c t a r r e s o u r c e s and bee d e n s i t y , i t i s p o s t u l a t e d t h a t p l a n t s compete f o r p o l l i n a t o r s e a r l y i n the day and e a r l y i n the season, while bees compete f o r nectar l a t e r i n the day and l a t e r i n the season. T h i s h y p o t h e s i s i s f u r t h e r supported by o b s e r v a t i o n s on the s h i f t s i n bee f o r a g i n g behaviors. V T a b l e o f C o n t e n t s p a g e A b s t r a c t , i i T a b l e o f C o n t e n t s . . . . v L i s t o f T a b l e s . . . . v i L i s t o f F i g u r e s • v i i A c k n o w l e d g e m e n t s i x I . G e n e r a l I n t r o d u c t i o n . . . . . < > . . . . . . . . . . . 1 I I . F l o w e r P r o d u c t i v i t y „ 9 a . ) I n t r o d u c t i o n 9 b . ) M e t h o d s 1 0 c . ) R e s u l t s 1 9 d . ) D i s c u s s i o n . . . . . . . . . . . . . . . . . 5>1 I I I . F o r a g i n g B e h a v i o r . . . . . . . . . . . . . . . . . . . . . . . 6 8 a . ) I n t r o d u c t i o n • 6 8 b . ) M e t h o d s 7 0 c . ) R e s u l t s 7 2 d . ) D i s c u s s i o n 1 0 3 I V . C o n c l u s i o n s • • • • • • • 1 1 3 V . L i t e r a t u r e C i t e d 1 1 7 v i L i s t o f T a b l e s p a g e I s B a s i c s t a t i s t i c s f o r t h e n e c t a r p r o d u c t i o n o f a l l s a l m o n b e r r y f l o w e r s s a m p l e d 2l± I I : B a s i c s t a t i s t i c s f o r t h e n e c t a r p r o d u c t i o n o f t h e f o u r m o s t p r o d u c t i v e s a l m o n b e r r y f l o w e r s s a m p l e d a t e a c h e p i s o d e 2i\. I l l : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n c a l o r i e s / h o u r , f o r a l l s a l m o n b e r r y f l o w e r s . . . . . 2 9 I V : T e s t o f t h e d i f f e r e n c e b e t w e e n t h e m e a n s o f t w o f l o w e r p o p u l a t i o n s : a l l f l o w e r s s a m p l e d a n d t h e f o u r m o r e p r o d u c t i v e f l o w e r s s a m p l e d a t e a c h e p i s o d e 3 1 V : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , . I n c a l o r i e s / h o u r , f o r t h e f o u r m o s t p r o d u c t i v e s a l m o n b e r r y f l o w e r s s a m p l e d a t e a c h e p i s o d e 3 5 V I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n n u m b e r o f b e e s / 1 0 m i n x f l o w e r 7 8 V I I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n n u m b e r o f f l o w e r s u s e d / n u m b e r o f f l o w e r s i n v e s t i g a t e d 9 0 V I I I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n a v e r a g e a n d r o e c i u m d i a m e t e r u s e d / a v e r a g e a n d r o e c i u m d i a m e t e r p r e s e n t . 9 9 v i i L j s t o f F i g u r e s page 1 : Salmonberry f l o w e r s and bumblebee f o r a g e r s .......... 7 2 : Map o f the U n i v e r s i t y o f B r i t i s h Columbia Research F o r e s t , showing study s i t e s at Marion and Eunice Lakes 1 1 3 : Using a c a l i p e r s to determine the androecium diameter of a salmonberry f l o w e r .................... 1 7 i | : R e l a t i o n s h i p between date and the mean number of salmonberry flowers counted per meter i n 1 9 7 9 . . . . . . . 2 0 3>: Regression of androecium diameter and age o f salmonberry f l o w e r s 2 2 6: Histograms showing frequency d i s t r i b u t i o n s of p r o d u c t i v i t y values 26 7 : S c a t t e r p l o t o f date and salmonberry f l o w e r p r o d u c t i v i t y 3 7 8: E f f e c t o f the time e l a p s e d between samples on salmonberry n e c t a r p r o d u c t i v i t y 3 9 9 i E f f e c t o f the time e l a p s e d between samples on p r o d u c t i v i t y i n the f o u r most p r o d u c t i v e salmonberry flowers sampled at each episode, independent of seasonal e f f e c t s . i l l 1 0 : S c a t t e r p l o t of r e l a t i v e humidity and p r o d u c t i v i t y i n the f o u r most p r o d u c t i v e f l o w e r s sampled at each episode ........................................ kh 1 1 : E f f e c t o f the time e l a p s e d between samples on % sugar s e c r e t e d by salmonberry f l o w e r s , independent of seasonal e f f e c t s I4.7 1 2 : E f f e c t of the time elapsed between samples on In u l n e c t a r / h r s e c r e t e d by the f o u r most p r o d u c t i v e flowers sampled at each episode, independent. of seasonal e f f e c t s M-9 1 3 : S c a t t e r p l o t of r e l a t i v e humidity and In u l n e c t a r per hour s e c r e t e d by salmonberry, independent of season a l e f f e c t s £ 2 v i i i l l i : E f f e c t o f sunshine l e v e l s on In % sugar s e c r e t e d by salmonberry f l o w e r s , independent o f seasonal e f f e c t s 1 5 : S c a t t e r p l o t o f p r o d u c t i v i t y and date, independent of androecium diameter e f f e c t s ...... 6 1 1 6 : S c a t t e r p l o t of n e c t a r s t a n d i n g crop i n salmonberry flowers and date 7 3 175 S c a t t e r p l o t o f n e c t a r s t a n d i n g crop and p r o d u c t i v i t y i n nearby salmonberry f l o w e r s , independent of seasonal e f f e c t s 7 6 18: S c a t t e r p l o t o f number of b e e s / 1 0 min x f l o w e r and date 8 0 19: S c a t t e r p l o t o f number of b e e s / 1 0 min x flo w e r and date, i n c l u d i n g data gathered throughout the e n t i r e salmonberry season 82 2 0 : E f f e c t o f sunshine l e v e l s on number o f b e e s / 1 0 min x f l o w e r 8I4. 2 1 : S c a t t e r p l o t o f n e c t a r standing crop and number o f b e e s / 1 0 min x fl o w e r , independent of seasonal e f f e c t s . Includes data gathered before noon, 88 2 2 : S c a t t e r p l o t o f number o f flowers used per number of flowers i n v e s t i g a t e d and date 9 2 2 3 : S c a t t e r p l o t o f temperature and the number of flowers used/number of fl o w e r s i n v e s t i g a t e d , independent of seasonal e f f e c t s 9ij- 2 l i : S c a t t e r p l o t o f number of fl o w e r s used/bee and date « 9 7 23>: S c a t t e r p l o t o f average androecium diameter used/average androecium diameter present and date • 1 0 1 2 6 : S c a t t e r p l o t o f n e c t a r s t a n d i n g crop and androecium diameter used/androecium diameter present, independent of seasonal e f f e c t s 101+ I w o u l d l i k e t o e x p r e s s m y g r a t i t u d e t o m y s u p e r v i s o r , D r . W i l l i a m N e i l l , f o r h i s p a t i e n t e n c o u r a g e m e n t t h r o u g h o u t t h e s t u d y , a n d f o r h i s h e l p f u l c o m m e n t s o n t h e m a n u s c r i p t . T h a n k s a r e a l s o d u e t o J o h n M o r g a n f o r h i s i n v a l u a b l e h e l p w i t h t h e f i e l d w o r k , a n d t o N a d e n e S t e i n h o f f f o r h e r h e l p w i t h t y p i n g t h e m a n u s c r i p t . D u r i n g m y w o r k I h a v e b e e n s u p p o r t e d t h r o u g h a U B G F e l l o w s h i p , a M c L e a n F r a s e r M e m o r i a l F e l l o w s h i p a n d a d e p a r t m e n t o f Z o o l o g y t e a c h i n g a s s i s t a n t s h i p . 1 I . General I n t r o d u c t i o n Many f l o w e r i n g p l a n t s and the animals which p o l l i n a t e them a r e mutually dependent. Flowering p l a n t s of many genera u t i l i z e animals t o t r a n s p o r t p o l l e n between flowers, e v o l v i n g methods t o b e t t e r a t t r a c t p o l l i n a t o r s while at the same time l o s i n g the c a p a c i t y to u t i l i z e a l t e r n a t i v e modes of p o l l i n a t i o n such as water and wind ( P e r c i v a l , 1965; F a e g r i and van der P i j l , 1978). From the p l a n t ' s viewpoint, these animals can thus be c o n s i d e r e d a resource which may be present i n s u r p l u s amounts or may be a l i m i t i n g f a c t o r i n plant r e p r o d u c t i o n (Levin and Anderson, 1970; Lack, 1976).,Hany p o l l i n a t o r s p e c i e s , on the other hand, have evolved v a r i o u s c h a r a c t e r i s t i c s a l l o w i n g them t o be very e f f i c i e n t at u t i l i z i n g the food and sometimes s h e l t e r t h a t the p l a n t s provide as "rewards" f o r p o l l i n a t i o n s e r v i c e s ( H e i n r i c h and Raven, 1972), while a t the same time l o s i n g t h e i r a b i l i t y t o l i v e independent of the p l a n t s . The number of flowers a v a i l a b l e and the food and perhaps s h e l t e r they provide can thus be c o n s i d e r e d as reso u r c e s from an animal's viewpoint, and can again be s c a r c e or present i n s u r p l u s amounts (Mosguin, 1971; Poja r , 1974; H e i n r i c h , 1976a). T h i s " c o e v o l u t i o n " to the p o i n t where mutual dependence i s achieved a f f e c t s morphological, p h y s i o l o g i c a l and b e h a v i o r a l c h a r a c t e r i s t i c s of both components of the p l a n t - p o l l i n a t o r r e l a t i o n s h i p . S t u d i e s of morphological " f i t " between p l a n t s and t h e i r p o l l i n a t o r s are quite common. " 3 i r d f l o w e r s " a re g e n e r a l l y c h a r a c t e r i z e d by v i v i d l y c o l o r e d p e t a l s , long c o r o l l a s and 2 e l o n g a t e d s e x u a l p a r t s . B i r d p o l l i n a t o r s , on the other hand, show a s e n s i t i v i t y f o r red and have long b i l l s and tongues. B i r d f l o w e r s are a l s o o d o r l e s s , while b i r d p o l l i n a t o r s have s c a r c e l y any sense of s m e l l (Baker, 1961; Grant, 1266; Ca r p e n t e r , 1976; S t i l e s , 1 9 7 8 ; F a e g r i and van der P i j l , 1978). Examples o f mo r p h o l o g i c a l c o a d a p t a t i o n s between bees and bee f l o w e r s are a l s o numerous. Bee fl o w e r s are mech a n i c a l l y s t r o n g , o f t e n with f l o r a l " l i p s " which provide a s u r f a c e upon which bees can land and maintain a f o o t h o l d . The p e t a l s of these f l o w e r s are b r i g h t l y c o l o r e d , g e n e r a l l y yellow or blue, and the f l o w e r s are f r e q u e n t l y f r a g r a n t . Bees are known to have a keen sense o f odor, and are p h y s i c a l l y very strong i n s e c t s , a l l o w i n g them to g a i n entrance i n t o the semi-closed bee f l o w e r s (Free and B u t l e r , 1959; Baker, 1963; B e a t t i e , 1971; A l f o r d , 1975; F a e g r i and van der P i j l , 1978). S i m i l a r c o a d a p t a t i o n s e x i s t f o r other groups of animals (e.g., bats, f l i e s , b u t t e r f l i e s , b e e t l e s ) and the f l o w e r s they t y p i c a l l y p o l l i n a t e (Baker, 196 1; Gregory, 1963; P e r c i v a l , 1965; Thien, 1974; Howell, 1977; F a e g r i and van der P i j l , 1978). Many s t u d i e s s t r e s s the " r e c i p r o c a l p a t t e r n i n which f l o w e r s e x p l o i t the b e h a v i o r a l r e p e r t o i r e of i n s e c t s , and the i n s e c t s e x p l o i t the g e n e t i c parameters of the e x p r e s s i o n of f l o r a l form" (Macior, 1974, p. 760). I t i s of adapt i v e value f o r both the animals and the plants i f the p o l l i n a t o r s are able t o r e a d i l y r e a c t to p o s s i b l e changes i n food abundance, weather v a r i a b l e s and numbers of other p l a n t and animal s p e c i e s present i n the h a b i t a t . The i n t e r a c t i o n between p l a n t s and 11 b e h a v i o c a l l y p l a s t i c " p o l l i n a t o r s has r e c e i v e d much a t t e n t i o n i n recent 3 years. H e i n r i c h (1979a) has d e s c r i b e d the phenomenon he c a l l s "majoring" and "minoring" i n bumblebees, by which the bees forage on the f l o w e r s p e c i e s of g r e a t e s t n s c t a r abundance and yet p e r i o d i c a l l y sample f l o w e r s of other s p e c i e s , thereby monitoring resource abundance i n a l l s p e c i e s . Much r e c e n t work has been done cn the d i r e c t i o n a l i t y of bee movement i n r e l a t i o n t o l o c a l n e c t a r abundance. Pyke (1978a) and H e i n r i c h (1979b) have found that bees f o r a g i n g i n a rewarding f l o w e r patch tend to change d i r e c t i o n s on s u c c e s s i v e f l i g h t s between f l o w e r s , while those i n a n e c t a r d e p l e t e d patch tend to f l y i n only one d i r e c t i o n , more q u i c k l y talcing them out of the patch p r e s e n t l y b e i n g foraged. Pyke (1978a) has a l s o determined t h a t t h e r e i s a st r o n g negative r e l a t i o n s h i p between the d i s t a n c e of d e p a r t i n g f l i g h t and the presumed rewards the bees had o b t a i n e d . , That honeybees s h i f t f o r a g i n g behavior i n response to changes i n food resources i s widely known. S e v e r a l a u t h o r s have s t u d i e d the "dance language" of honeybee f o r a g e r s r e t u r n i n g t o the h i v e from the f i e l d (von F r i s c h , 1971; L i n d a u e r , 1971; Hichener, 1974). Through t h i s dance the f o r a g e r s are thought t o communicate to other workers the d i s t a n c e , d i r e c t i o n i r o n the h i v e and q u a l i t y o f c u r r e n t l y a t t r a c t i v e n e c t a r f l o w s . Honeybees are known to p r e f e r h i g h l y c o n c e n t r a t e d n e c t a r , and w i l l switch from a ne c t a r source of low c o n c e n t r a t i o n to one of a higher c o n c e n t r a t i o n ( V a n s e l l et a l . , 1942; B u t l e r , 1945). Honeybees are r e l a t i v e l y flower "constant" i n t h a t , d u r i n g each f o r a g i n g t r i p from the h i v e , they t e n d to v i s i t f l o w e r s of only one s p e c i e s - They are b e l i e v e d t o be more co n s t a n t than bumblebees (Michener, 1974; Grant, 1950), yet, whan n e c t a r r e s o u r c e l e v e l s 4 reach low l e v e l s t h i s high s e l e c t i v i t y i s g r e a t l y reduced ( F i l m e r , 1941; Grant, 1949). The f o r a g i n g behavior of hummingbirds and s u n b i r d s has a l s o been s t u d i e d i n some d e t a i l . I t has been found t h a t , i n g e n e r a l , the time spent f o r a g i n g by these b i r d s i s roughly p r o p o r t i o n a l to the energy obtained from the f l o w e r s being foraged (Wolf, 1975), Though Baket (1961) and Grant (1 949) r e p o r t t h a t hummingbirds d i s p l a y very low flow e r f i d e l i t y , s e v e r a l authors have found i n d i v i d u a l hummingbirds to "major" on p a r t i c u l a r f l o w e r s p e c i e s (Wolf and Hainsworth, 1971; F e i n s i n g e r , 1976; S t i l e s , 1978). I t i s accepted, however, that the f o r a g i n g behavior of n e c t a r i v o r o u s b i r d s i s more adaptable and o p p o r t u n i s t i c than chat of many i n s e c t p o l l i n a t o r s ( S t i l e s , 1978). Hummingbirds p r e f e r high nectar c o n c e n t r a t i o n s t o lower c o n c e n t r a t i o n s (Hainsworth and Wolf, 1976) , and fo r a g e from i n f l o r e s c e n c e s with many f l o w e r s ; f o r example, they avoid Ipomopsis aggregata i n f l o r e s c e n c e s with l e s s than seven f l o w e r s even though these i n f l o r e s c e n c e s occur with a frequency o f approximately 25% (Pyke, 1978b). A study by G i l l and Wolf (1975) shewed t h a t l a r g e r s u n b i r d s i n a community o f seven s u n b i r d s p e c i e s p r e f e r e n t i a l l y forage from c l o s e d m i s t l e t o e f l o w e r s . As the p r o p o r t i o n of c l o s e d f l o w e r s d e c l i n e s through the day the b i r d s i n c r e a s i n g l y add p r e v i o u s l y avoided open f l o w e r s t o t h e i r d i e t . S t u d i e s i n t o the " b e h a v i o r a l p l a s t i c i t y " of the p l a n t s i n the p l a n t - p o l l i n a t o r r e l a t i o n s h i p are not common. Sev e r a l authors b e l i e v e that i n t e r s p e c i f i c c o m p e t i t i o n f o r p o l l i n a t o r s has r e s u l t e d i n asynchronous blooming of p l a n t s p e c i e s occuring 5 i n the same h a b i t a t (Mosquin, 1971; P o j a r , 1974; Heithaus, 1974; S t i l e s , 1975; F r a n k i e , 1975; H e i n r i c h , 1975D, 1976b; fcaser , 1978). Yet s h i f t s i n a p l a n t s p e c i e s ' blooming time o c c u r s on an e v c l u t i c n a r y time s c a l e and does not allow p l a n t s to r e a c t to d a i l y or even h o u r l y changes i n p o l l i n a t o r abundance and b e h a v i o r . Flowers do show d a i l y c y c l e s o f nectar p r o d u c t i v i t y (Park, 1929; V a n s e i l et a l . , 1942; B u t l e r , 1945; Baker, 1961; F e i n s i n g e r , 1978; Corbet, 1978), but t h i s has not been shown to be a p l a n t response to p o l l i n a t o r s . S e v e r a l authors have observed that as sampling frequency i n c r e a s e s , the p r o d u c t i o n of nectar i n c r e a s e s as w e l l (Baw, 1953; Mel'nichenko, 1963; Kurina, 1974; F e i n s i n g e r , 1978). T h i s r e s u l t i n d i c a t e s that n a t u r a l p o l l i n a t o r s , through the use of f l o r a l n e c t a r r e s o u r c e s , may themselves i n c r e a s e the r a t e o f n e c t a r production i n f l o w e r s , I f t h i s i s t r u e , i t means t h a t p l a n t s change t h e i r r a t e of p r o d u c t i o n i n response to p o l l i n a t o r use, and perhaps, t h e r e f o r e , to c u r r e n t p o l l i n a t o r d e n s i t y i n the h a b i t a t . T h i s would i n d i c a t e a b e h a v i o r a l p l a s t i c i t y on a time s c a l e p r e v i o u s l y unsuspected i n p l a n t s . Hoaever, much more work needs to be done on the exact nature and extent of t h i s p r o d u c t i v i t y response i n the p l a n t kingdom. I t i s a l s o necessary to study t h i s response as i t o ccurs i n a community cont e x t , where the p l a n t s l i v e with and respond to d a i l y and seasonal changes i n p o l l i n a t o r abundance and behavior, weather v a r i a b l e s , s o i l moisture content and the presence of competing p l a n t s p e c i e s . Such s t u d i e s may allow i n c r e a s e d i n s i g h t i n t o the e v o l u t i o n a r y s i g n i f i c a n c e of nectar p r o d u c t i v i t y . 6 Salmonberry (Rubus s p e c t a b i l i s , Pursh) f l o w e r s s e c r e t e nectar and through t h i s a t t r a c t p o l l i n a t o r s ( F i g . 1). The f o l l o w i n g study i n v e s t i g a t e d p o s s i b l e changes i n salmonberry n e c t a r s e c r e t i o n as a response to s h i f t s i n p o l l i n a t o r v i s i t a t i o n freguency. At the same time, s h i f t s i n bee f o r a g i n g b e h a v i o r were i n v e s t i g a t e d as a p o s s i b l e response to v a r i a t i o n s i n f l o r a l nectar resources. The u l t i m a t e g o a l of t h i s study has been to f i t the responses of both components together to allow i n c r e a s e d understanding of the p l a n t - p o l l i n a t o r r e l a t i o n s h i p . The p l a n t - p o l l i n a t o r system s e l e c t e d f o r t h i s study was chosen p r i m a r i l y f o r ease of study. Throughout much of t h e i r f l o w e r i n g season, salmonberry p l a n t s produce l a r g e numbers of f l o w e r s . I t i s p o s s i b l e to sample the f l o w e r s f o r a v a i l a b l e n e c t a r using simple m i c r o p i p e t t e t e c h n i q u e s , and the p l a n t s can be found along f o r e s t roads, a l l o w i n g easy access. Though p o l l e n i s a l s o produced by the f l o w e r s and i s u t i l i z e d by bumblebees ( A l f o r d , 1975), s e v e r a l authors b e l i e v e t h a t p o l l e n i s " c o l l e c t e d c o i n c i d e n t a l l y with n e c t a r " (Inouye, 1977, p. 253) , t h a t p o l l e n i s c o n t i n u o u s l y p l e n t i f u l enough to meet colony needs and t h a t nectar i s tJie r e s ource which may l i m i t bumblebee colony growth ( H e i n r i c h , 1975a). The same assumption has been made, sometimes i m p l i c i t l y , throughout t h i s study, though whether i t i s an assumption which has a f a c t u a l b a s i s deserves f u r t h e r study. Bumblebees are d e s i r a b l e study animals s i n c e one can s a f e l y assume t h a t colony workers f l y f o r no o t h e r reason than to forage f o r food, and they forage r e l a t i v e l y unhindered by the presence of observers (Pyke, 1978a). 7 8 9 I I . FLOWER PRODUCTIVITY a.) In t r o d u c t i o n The purpose of t h i s study was p r i m a r i l y to i n v e s t i g a t e the e f f e c t s of bumblebee f o r a g i n g f r e q u e n c i e s upon salmonberry n e c t a r p r o d u c t i v i t y , measured as c a l o r i e s / h o u r . To be able to account f o r the v a r i a b i l i t y i n p r o d u c t i v i t y due t o sampling r a t e alone, s e v e r a l other v a r i a b l e s were s i m u l t a n e o u s l y monitored; these i n c l u d e d f l o w e r age, l e v e l of i n s o l a t i o n , r e l a t i v e humidity, time of day and date of sampling. The e f f e c t of these i n d i v i d u a l v a r i a b l e s upon n e c t a r p r o d u c t i v i t y were a l s o analyzed. S e v e r a l authors have noted that as sampling frequency i n c r e a s e s the p r o d u c t i o n of n e c t a r a l s o i n c r e a s e s (Raw, 1953; Mel'nichenko, 1963; Kurina, 1974; F e i n s i n g e r , 1978). T h i s response i s c o n s i d e r e d to be a d a p t i v e f o r the p l a n t s s i n c e they need not shunt energy i n t o n e c t a r p r o d u c t i o n when p o l l i n a t o r s are not present, and as p o l l i n a t o r demand i n c r e a s e s , cau then o f f e r resources i n p r o p o r t i o n to demand. I t i s necessary to o f f e r the r i g h t amount of reward to the p o l l i n a t o r s to keep thea moving from f l o w e r to flower w i t h i n the same p l a n t s p e c i e s i n an e f f o r t t o c o l l e c t needed food resources; too much reward and p o l l i n a t o r s simply gorge themselves and cease to t r a v e l amongst the f l o w e r s (hence cease to be e f f e c t i v e p o l l i n a t o r s ) , too l i t t l e and they become discouraged with the s p e c i e s upon which they are c u r r e n t l y f o r a g i n g and switch to another ( H e i n r i c h , 1975a), By being able to t r a c k p o l l i n a t o r demand p l a n t s p e c i e s can then c o n t i n u o u s l y o f f e r the a p p r o p r i a t e amount. 1 0 A seemingly reasonable method of determining the amounts o f nectar harvested by f o r a g i n g i n s e c t s i n v o l v e s comparing standing crop l e v e l s i n f l o w e r s open to f o r a g e r use with l e v e l s i n i s c l a t e d f l owers (see e.g., H e i n r i c h , 1976a). Yet i f f o r a g e r s are a c t i n g to i n c r e a s e the r a t e s of n e c t a r p r o d u c t i o n , t h i s method would c o n s i s t e n t l y underestimate true g u a n t i t i e s o f nectar harvested by p o l l i n a t o r s more a c t i v e than the ceseacher. I t seemed l i k e l y that the f i n d i n g s of other authors should h o l d f o r salmonberry, t h a t as sampling frequency i n c r e a s e s the c a l o r i e s / h c u r o f f e r e d by the f l o w e r s should a l s o i n c r e a s e . B. ) Methods Study s i t e : The study was conducted a t the UBC flesearch F o r e s t l o c a t e d near Haney, B.C. The 5157 hectare f o r e s t i s dominated by stands of Douglas f i r , western hemlock and western redce d a r . The a c t u a l study s i t e s were l o c a t e d along K30, the road j u s t n o r t h of Marion Lake, and along H20, the Eunice Lake road (see map, F i g . 2). E l e v a t i o n s of the s i t e s were, r e s p e c t i v e l y , 330 a e t e r s and 480 meters. The two s i t e s were very s i m i l a r i n terms of s p e c i e s p r e s e n t . The s i d e s of the roads were dominated by long rows o f salmonberry i n t e r m i x e d with stands of thimbleberry (feu bus p a r v i f l o r u s ) . Other f l o w e r i n g s p e c i e s were present i n the area (e.g., v i o l e t s , d a n d e l i o n s ) , many o f yhich have been d e s c r i b e d as h i g h l y a t t r a c t i v e to bees i n other areas (Mosquin, 197 1). Yet, i n my study areas salmonberry was the s p e c i e s of bee 11 F i g . 2: M a p o f t h e 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 R e a s e a r c h F o r e s t , s h o w i n g s t u d y s i t e s a t M a r i o n a n d E u n i c e L a k e s * 1 2 T H E UNIVERSITY OF BRITISH C O L U M B I A RESEARCH FOREST M A P L E R I D G E , B . C . Director: Professor J . Wallers. R.P.F. Address: U.B.C. Research Forest R.R.2 Maple Ridge. B.C. V2X 7E7 Phone: 463-8148 WELCOME TO THE RESEARCH FOREST This experimental forest Is dedicated to re- search, education,and demonstration in the forest sciences. You are invited to walk around the Forest — no vehicles, horses, or bicycles are permit- ted. We ask that you respect the prime func- ' tion of the Forest and do not tamper with research installations. — No fishing or hunting is allowed because of research projects concerning stream . ecology and wildlife — Dogs are not permuted as they hinder research into bhcktait deer — We do not allow camping or fires, our neighbour to the east, the Golden Ears Provincial Park, provides these facilities — The Forest Camp at the south end of Loon Lake is closed to the public. Please stay out of this area. P L E A S E T A K E Y O U R U T T E R H O M E WITH Y O U Legend . main road branch road building trail ( (_© contours at 100' intervals §E$I restricted a r e a ( n o public access) — i — powerline 1 3 p r e f e r e n c e , with s p e c i e s such as v i o l e t s and d a n d e l i o n s r e c e i v i n g no observed v i s i t s from bumblebees. Only near the end of the salmonberry f l o w e r i n g season d i d a t t r a c t i v e s p e c i e s such as t h i m b l e b e r r y begin t c flower. Bumblebees were by f a r the most frequent salmonberry flower v i s i t o r s a t the study s i t e s , these being predominantly Bombus s i t k e n s i s , Nylander, though o c c a s i o n a l l y i n d i v i d u a l s o f 3 . rcelanopygous and mi xtus were seen. "Flower f l i e s " (C r i o r h i n a luna) were common, but were f a r l e s s numerous than B. s i t k e n s i s and each f l y v i s i t e d f a r fewer f l o w e r s than d i d each B. s i t k e n s i s i n d i v i d u a l per u n i t time. A few hummingbirds were present i n the areas, but i t was r a r e to see them f o r a g i n g at salmonberry f l o w e r s . Present i n great abundance were s m a l l rove b e e t l e s of the genus Eusphalerum, which, though they flew i n f r e g u e n t l y , d i d c a r r y p o l l e n on t h e i r bodies (Barber, 1976), and may thus have been e f f e c t i v e p o l l i n a t o r s . The f o l l o w i n g study took p l a c e between May 3 and June 28, 1979. S e v e r a l authors have used nectar c o l l e c t e d from the honeystomachs of bees to analyse flower nectar c o n c e n t r a t i o n (e.g., S u t l e r , 1945) , yet t h i s method would have been f a r too cumbersome f c r the present study. P i p e t t i n g nectar from f l o w e r s was used i n s t e a d , the assumption being made that p i p e t t i n g techniques adeguately s i m u l a t e d the p o s s i b l e e f f e c t s of bumblebee f o r a g i n g upon n e c t a r p r o d u c t i o n . Samples of 10 flowers were used due to the need to c o l l e c t nectar samples as q u i c k l y as p o s s i b l e ; I found that e x t r a c t i n g n e c t a r from 10 f l o w e r s and measuring i t s volume and c o n c e n t r a t i o n r e g u i r e d 40 min t o 60 min to complete. Each flower was a r b i t r a r i l y chosen except f o r the 14 requirement t h a t i t be at l e a s t 2 " p l a n t s " d i s t a n t (approx. 3 meters) from other f l o w e r s i n the same oc other sampling groups. Salmonberry p l a n t s reproduce v e g e t a t i v e l y by means of rhizomes under the s o i l , thus i t i s d i f f i c u l t t o t e l l i f an above ground " p l a n t " i s t r u l y separate from a neighboring p l a n t . Barber (1976, p.60) s t a t e s t h a t "the a b i l i t y of salmonberry t o reproduce v e g e t a t i v e l y i s r e s p o n s i b l e f o r the l o c a l p e r p e t u a t i o n of c o l o n i e s " . Yet he a l s o s t a t e s t h a t , " s e e d l i n g s are sometimes found growing on peat, r o t t e n l o g s and stumps, mineral s o i l and alcn g r o a d s i d e s " (Barber, 1976, p.60). I t seems l i k e l y t h a t salmonberry p l a n t s growing along the r o a d s i d e s of the study s i t e s o r i g i n a t e d from many s e e d l i n g s which germinated f o l l o w i n g l o c a l d i s t u r b a n c e . T.«<is# I f e l t t h a t the above requirement would helF assure t h a t f l o w e r s sampled would be on separate p l a n t s . Small bags c o n s t r u c t e d of Nitex n e t t i n g (mesh opening, 0.2 mm) were used t o exclude a l l animals from f l o w e r s under study, i n c l u d i n g b e e t l e s of the genus Eusphalerum. Nectar was removed from the f l o w e r s using Drummond "microcaps", d i s p o s a b l e micro- p i p e t t e s . Each flower was d r a i n e d f i r s t with a 25 u l tube f o l l o w e d by a 10 u l tube. Tubes were c a r e f u l l y manipulated to gather a l l nectar p o s s i b l e without causing e x t e n s i v e damage to f l c r a l n e c t a r i e s . Sampling f r e q u e n c i e s were s e l e c t e d a f t e r o bserving f r e q u e n c i e s of bumblebee v i s i t s to patches o f salmonberry f l o w e r s e a r l y i n the season. During three o b s e r v a t i o n s e s s i o n s , each f l o w e r i n a patch was v i s i t e d by a bee an average o f every 0.67 he, 1.3 hr and 1.2 hr. Samplings with p i p e t t e s Here thus set at 2 hours, 4 hours, 6 hours and 8 hours, i n s t e a d of 12 hours, 24 hours and 36 hours as used by Baw 15 (1953). Due to the need to c o l l e c t approximately 10 f l o w e r s i n each sample, sampling c o u l d not be much more f r e q u e n t , yet I f e l t t h a t the s e l e c t e d f r e g u e n c i e s r e f l e c t b i o l o g i c a l r e a l i t y m o r e c l o s e l y than dc previous s t u d i e s . For ease of r e c o r d i n g and r e p o r t i n g , sampling frequency data are expressed i n terms of the time e l a p s e d between group samplings. T h i s value i s the denominator of the frequency e x p r e s s i o n , 1 sample/x hours, thus the time elapsed between samples i s i n v e r s e l y p r o p o r t i o n a l to the sampling frequency. A l s o recorded were the volume of nectar obtained from each f l o w e r and the % sugars present i n the n e c t a r , measured using a F i s h e r Instruments hand r e f T a c t o m e t e r . Depending upon the sampling r a t e s a s s i g n e d each group, f l o w e r s c o u l d be sampled up to 3 or 4 times a day. Fresh groups of f l o w e r s were chosen each morning due to the p o s s i b i l i t y of flower damage r e s u l t i n g from s a u p l i n g t echniques. Nectar volume and % sugars were converted to c a l o r i e s / h o u r a s f o l l o w s {.Hob-urt Montgomerie, personal communication) . I t was assumed here that nectar i s composed p r i m a r i l y of the d i s a c c h a r i d e sucrose and i t s components, glucose a n d f r u c t o s e , though ether substances are known to be present i n very low c o n c e n t r a t i o n s (Baker and Baker, 1975). Ihe mg s u c r o s e / u l s o l u t i o n corresponding to each r e f r a c t o m e t e r r e a d i n g was o b t a i n e d from weast (1976). M u l t i p l y i n g t h i s value by the measured u l of sample, then f u r t h e r m u l t i p l y i n g by the c o n s t a n t 3»7 c a l o r i e s / m g of sucrose ( H e i n r i c h and Raven, 1972), y i e l d s t h 2 number of c a l o r i e s a v a i l a b l e from each f l o w e r . D i v i d i n g t h i s by the time e l a p s e d between samplings then y i e l d s 16 the c a l o r i e s / h c u r f o r each f l o w e r . To determine flower age, a s t r u c t u r a l f e a t u r e of the flower was needed as an a c c u r a t e i n d i c a t o r . From previous o b s e r v a t i o n s , I f e l t that the diameter of the androecium (anther r i n g ) would make a s u i t a b l e i n d i c a t o r due to i t s ease of measurement as w e l l as the apparent i n c r e a s i n g o f the diameter with age. On A p r i l 25, 20 unopened flo w e r buds were tagged along approximately 1/2 mile of the r a r e l y used f o r e s t road, G10. For 4 days t h e r e a f t e r measurements of each androecium diameter were made using a s m a l l c a l i p e r s ( F i g . 3). F o r those cases i n which the anther r i n g was a c i r c u l a r , the measurement was made along the dimension judged to be the average. The androecium diameter was recorded f o r each, flower measured f o r p r o d u c t i v i t y . . I n s o l a t i o n was c o n t i n u o u s l y monitored each day using an a c t i n o g r a p h manufactured by Heather Measure C o r p o r a t i o n of Sacramento, C a l i f - I n s o l a t i o n data c o l l e c t e d d u r i n g p r o d u c t i v i t y s t u d i e s i s expressed as average " l e v e l s " per hour of nectar p r o d u c t i o n . These f i g u r e s , when m u l t i p i e d by the instrument c o n s t a n t (k=0. 405), y i e l d the more standard u n i t s , cal/cm 2/min, though raw l e v e l s were used f o r the a n a l y s i s i n t h i s study. R e l a t i v e humidity was measured 2 or 3 times d a i l y using a s t a n d a r d s l i n g psychrometer s u p p l i e d by T a y l o r Instrument Company of Rochester, N.Y. Time o f day was recorded f o r each sample; data were then transformed i n t o "hours a f t e r s u n r i s e " , a more b i o l o g i c a l l y meaningful measurement. A census of f l o w e r s was taken each week, which c o n s i s t e d of simply walking three 9 c t s l a i d out upon the road, each t r a n s e c t separated by 3 meters, and counting a l l f l o w e r s seen along one s i d e of the 1 7 F i g . 3 : Using a c a l i p e r s to determine the androecium diameter of a salmonberry f l o w e r ( p e t a l s not shown). 18 19 road. C.) S e s u l t s A peak, i n numbers of f l o w e r s a t the study s i t e o c c u r r e d on Hay 15 ( F i g . 4), with a d r a s t i c d e c l i n e o c c u r r i n g on May 28. The r i s e cn June 5 r e p r e s e n t s a s h i f t i n study areas to Eunice Lake. Flower numbers here slowly d e c l i n e d i n l a t e June, and salrconberry flowers c o u l d no longer be found i n the f o r e s t area at t h i s time.. Androecium diameter data were ad j u s t e d to r e f l e c t the a c t u a l age of the f l o w e r s , not merely the number of days s i n c e t a g g i n g . When choosing a bud, i t i s i m p o s s i b l e t o know i t s t r u e age p r i o r t o opening. Thus, buds in c l u d e d i n the sample were probably not a l l i d e n t i c a l ages. For the graph i n F i g . 5, a bud, on the day i t f i r s t opens, i s c o n s i d e r e d as 1 day o l d , p r i o r t o that i t i s considered as 0 days o l d . Androecium diameter i s h i g h l y c o r r e l a t e d with flower age (r=.8389, p<.001). T a b l e I l i s t s b a s i c s t a t i s t i c s f o r the v a r i a b l e s , c a l / h r , % sugars and ul n e c t a r / h r , while a frequency histogram f o r the v a r i a b l e , c a l / h r , i s shown i n F i g . 6. The average flower s e c r e t e d 0.81 u l n e c t a r / h r which was composed of 23% sugar, thus making a v a i l a b l e 0.67 c a l / h r . These values are somewhat misleading s i n c e they are based on data c o l l e c t e d u s i n g s e v e r a l s a c p l i n g r a t e s , which may have i n f l u e n c e d n e c t a r p r o d u c t i v i t y . A p o o l i n g of data was necessary here s i n c e l i t t l e i n f o r m a t i o n i s a v a i l a b l e f o r any one sampling r a t e used d u r i n g the study. A model using a stepwise r e g r e s s i o n procedure, adding 20 F i g . }i: R e l a t i o n s h i p between date and the mean number of salmonberry flowers counted per meter i n 1 9 7 9 . Bars i n d i c a t e one ± standard d e v i a t i o n o f each sample mean. 2 1 <D O w U O H 2 0 16 1 2 8 h i o 1 I I f 1 M a r l o n L a k e S i t e I I J. T T i E u n i c e L a k e S i t e T i t 7 I * i 1 T f M a y 1 M a y 1 3 M a y 2 5 J u n e 6 J u n e 18 J u n e 3 0 Date 2 2 F i g . Regression o f androecium diameter and age o f salmonberry f l o w e r s . 2 3 2k Table I : B a s i c s t a t i s t i c s f o r the n e c t a r p r o d u c t i o n of a l l salmonberry flowers sampled. Table I I : B a s i c s t a t i s t i c s f o r the n e c t a r p r o d u c t i o n o f the f o u r most p r o d u c t i v e salmonberry flowers sampled at each episode. 2 5 T a b l e I N M i n f 0 M a x M e a n S t d D e v 9 5 ^ c i c a l / h r 7 7 9 1 3 . 3 1 0 . 6 7 0 . 9 8 0 . 6 0 0 . 7 I + % s u g a r s 5 5 7 2 . 7 8I4 .O 2 3 . 5 10. Ii 2 2 . 6 2k.k' u l n e c t a r / h r 786 0 1 5 . 0 0 0 . 8 1 1 . 2 3 0.73 0 . 9 0 T a b l e I I N M i n M a x M e a n S t d D e v 9 5 ^ CI c a l / h r 3 3 U 0 1 3 . 3 1 1 . 0 8 1 .26 O.9I4- 1 . 2 2 % s u g a r s 2 5 8 1 0 . 0 i j . 9 . 0 2 3 . 6 9 . 0 2 2 . 5 2 1 + . 7 u l n e c t a r / h r 3314- 0 1 5 . 0 1.26 1 . 5 7 1.09 1.14-3 26 P i g . 6: Histograms showing frequency d i s t r i b u t i o n s of p r o d u c t i v i t y v a l u e s . a) F o r a l l salmonberry f l o w e r s sampled, each X = 9 o b s e r v a t i o n s . b) For more p r o d u c t i v e flowers sampled at each episode, each X s 3 o b s e r v a t i o n s . Frequency of Observations (each X=9) 0. 359 ••xxyxxxxxxxxx^xxxxxxxxxxxxxxxxxxxxxxxxxx* . 50000 166 f X X X X X X X X X / X X X X X X V X X 1 .0000 + X X X X X X X X X X X •xxxxxxxx la ' 1 .5000 71 2.0000 44 f X X X X X 2.5000 ?.?. + X X X 3.0000 9 +x 3.5000 3 +x 4.0000 2 +x 4.5000 2 + x 5.0000 1 • X 5.5000 0 6.0000 0 + 6.5000 1 +x 7.0000 0 •f 7.5000 0 8.0000 1 +x 8.5000 0 + 9.0000 0 9.5000 0 + 10.000 0 + 10.500 0 11.000 0 + 11.500 0 12.000 0 12.500 0 + 13.000 0 + 13.500 1 + x 14.000 0 Frequency of Observations (each X=3) 0. 35 +xxxxxxxxxxxxxxxxxxxxxxxxxxxxx .50000 84 •xxxxxxxxxxxxxxxxxxxxxxxxxxxx 1.0000 50 + X X X X X X X X X X X X X X X X X 1.5000 44 + X X X X X X X X X X X X X X X 2.0000 30 + X X X X X X X X X X 2.5000 21 + X X X X X X X 3.0000 9 • X X X 3.5000 3 + X 4.0000 2 • X 4.5000 2 +x 5.0000 I • X 5.5000 0 6.0000 0 + 6.5000 I • X 7.0000 0 • 7.5000 0 •f- 8.0000 1 • X 8.5000 0 + 9.0000 0 9.5000 0 10.000 0 • 10.500 0 11.000 0 * 11.500 o 12.000 0 + 12.500 0 13.000 0 13.500 1 + X l ' i .000 0 (b ) 28 v a r i a b l e s i n t o the model as long as they accounted f o r v a r i a b i l i t y remaining from p r e v i o u s l y i n t r o d u c e d v a r i a b l e s , was c o n s t r u c t e d f o r p r o d u c t i v i t y (cal/hr) and i s presented i n T a b l e I I I . The data used f o r the model and f o r a l l subsequent analyses (unless otherwise noted) were transformed by t a k i n g the n a t u r a l l o g a r i t h m (In) of the data. For many analyses performed, i n c l u d i n g the m u l t i p l e r e g r e s s i o n model, t h i s t r a n s f o r m a t i o n r e s u l t e d i n higher c o r r e l a t i o n c o e f f i c i e n t s than d i d the o r i g i n a l values or a l t e r n a t i v e t r a n s f o r m a t i o n s . A v a r i a b l e was i n c l u d e d i n the model i f the " t " s t a t i s t i c a s s o c i a t e d with i t i s s i g n i f i c a n t a t p<.05. . V a r i a b l e s s e l e c t e d i n the p r o d u c t i v i t y model i n c l u d e the time e l a p s e d between samples as w e l l as date, androecium diameter, number of flowers/meter, r e l a t i v e humidity and the hours a f t e r s u n r i s e at which each sampling was done. The model accounts f o r 37% of p r o d u c t i v i t y v a r i a b i l i t y , i n c l u d i n g each fl o w e r i n each group of 10 sampled, f o r a l l sampling f r e q u e n c i e s . To i n v e s t i g a t e the p o s s i b i l i t y t h a t these r e s u l t s were o f f s e t by " d e f e c t i v e " f l o w e r s , (those which s e c r e t e d n e c t a r w e l l belcw the mean due to c h a r a c t e r i s t i c s not determined i a t h i s s t u d y ) , the data were reanalyzed using only the 4 most h i g h l y p r o d u c t i v e f l o w e r s i n each sample group. Some b a s i c s t a t i s t i c s and a histogram f o r these f l o w e r s are provided i n Table I I and F i g . 6. Mean p r o d u c t i v i t y f o r these f l o w e r s was 1.08 c a l / h r . A t e s t to determine the s i g n i f i c a n c e of the d i f f e r e n c e between the mean of these " p r o d u c t i v e " f l o w e r s and that of a l l f l o w e r s sampled (Table IV) shows that the two groups d i d s e c r e t e s i g n i f i c a n t l y d i f f e r e n t amounts of n e c t a r , (at a s i g n i f i c a n c e 29 T a b l e I I I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n c a l o r i e s / h o u r , f o r a l l s a l m o n b e r r y f l o w e r s . a.) V a r i a b l e s s e l e c t e d f o r t h e m o d e l . b ) V a r i a b l e s n o t s e l e c t e d . c ) S t e p s i n m o d e l c o n s t r u c t i o n . ANALYSIS AT STEP 9 FOR 19.V19 N= 708 OUT OF 1182 SOURCE REGRESSION ERROP TOTAL CF SUV OF SQRS MEAN SQUARE 9 6 98 707 46 .903 7C.976 125.88 5.2115 .11315 •MULTIPLE R= .61042 R-SQR= .37261 SE= .33637 F-STAT 46.06C SIGN IF .0000 a) VARIABLE CONSTANT 1.V1 5. V5 1C.V10 ll . V U 14. V14 15. V15 16. V16 18.V18 23.V23 PART IAL COEFFICIENT STO ERROR T-STAT SIGNIF 22.276 3.6327 6. 132C .0000 .09630 .16797 -1 .65374 -2 2. 5694 .0104 10378 -.14828 .53788 -1 -2. 7567 .006 0 .23096 .82819 -1 . 13212 -1 6. 2687 .0000 . 20 602 .29574 -2 .53169 -3 5. 5623 .0000 -. 14 221 -.83959 .22120 -3. 7956 .0002 -.11968 -.23381 .73412 -1 -3. 1849 .0015 . 33 5 73 .41066 .43612 -1 9. 4163 .0000 .08002 .23379 .11023 2. 1209 .0343 -.21194 -6.0474 1.0555 -5. 7295 .CCOO date diameter r e l . humidity # flowers/meter In date In hours a f t e r sunrise In time elapsed between samples In diameter In r e l . humidity REMAINING b ) 2. V2 3. V3 4. V4 17.V17 24.V24 PARTIAL SIGNIF .01580 -.03386 .02718 . C1 8 50 •C6152 .6767 .3714 .4731 .6253 . 1041 hours a f t e r sunrise time elapsed between samples sunshine In sunshine In # flowers/meter REGRESSION OF 19.V19 USING FORWARD SELECTIGN EP P.-SQR STO ERROR * VAR VARIABLE PARTIAL SI ON I F 1 . 18816 .38046 1 14.V14 IN -.43377 .0000 2 .26806 .36151 2 16.V16 IN .31372 .000 0 3 .31379 .35028 3 lO.VlO IN .24^97 .0000 4 .32519 . 3476 1 4 15.V15 IN -. 128S6 .0006 5 .33315 . 34.5 80 5 23.V23 T »* -.10862 .0039 6 .35501 .34033 6 11 .VI1 IN .18105 .0000 7 .36338 .338 3 5 7 5. V5 IN -.113*3 . 0025 8 .36856 .33721 8 1 .VI IN .09025 .0168 9 .37261 .33637 9 16..V18 IN .0 8002 .0343 o 3 1 Table IV: Test o f the d i f f e r e n c e between the means of two fl o w e r p o p u l a t i o n s : a l l f l o w e r s sampled and the f o u r more p r o d u c t i v e flowers sampled at each e p i s o d e . ' 3 2 F o r p r o d u c t i v i t y data, the sample means are p r o p o r t i o n a l to the v a r i a n c e s . T h e r e f o r e , a square r o o t t r a n s f o r m a t i o n has been performed on a l l data used f o r the f o l l o w i n g t e s t s , as recommended by O s t l e and Me rising. ( 1 9 6 5 ) . P a r t 1 : Test o f equal v a r i a n c e s of the two p o p u l a t i o n s o~i = o~£ , an assumption o f the t e s t i n p a r t 2 . Using . 0 5 s i g n i f i c a n c e l e v e l . u s i n g s%F ( n r,w n j r l} s,= 0 . 5 6 sNo.31 s4= 0 . 5 1 i s * = 0 . 2 9 sf.0 . 3 1 = 1 . 0 7 s* 0 . 2 9 F{3lH-\\(ir?-i)-- F(3S3,*?.rtf>AS-") s 0 . 8 8 0 . 8 8 ^ 1 . 0 7 ^ 1 . 1 3 so must accept t h a t CJ*=<5\[» 3 3 P a r t 2 : D i f f e r e n c e b e t w e e n t h e means o f two f l o w e r p o p u l a t i o n s . u s i n g ( u , - u j = ( x , - x a ) - t s ^ - x ^ where x,= s a m p l e mean o f p o p u l a t i o n 1 = 0 . 8 7 xA= s a m p l e mean o f p o p u l a t i o n 2 = 0 . 6 1 s ( * , - 5 ^ " s ^ p / n ^ s * p / n u sS - (n,-l)s, •<• (n;,-l)st = ( 3 3 3 > ( 0 . 3 1 ) * ( 7 7 8 1 ( 0 . 2 9 ) ~ " ( n , - l ) +• (nl-l) ; 3 3 3 "+ 7 7 8 = 0 . 3 0 s c V ? 0 " 0.30 /331++ 0 . 3 0 / 7 7 9 = 0 . 0 0 1 2 8 F o r 9 5 % ' c o n f i d e n c e l i m i t s , ' t ( > y ? r , , , , ^ = 1 , 9 6 2 so ( u , - u j - ( 0 . 8 7 - 0 . 6 1 ) t ( 1 . 9 6 2 ) (O.Olx) = 0 . 2 6 1 - 0 . 0 8 o r 0 . 3 I + and 0 . 1 8 34 l e v e l of .05 f o r d e t e r m i n a t i o n of the " t " s t a t i s t i c ) . , A r e g r e s s i o n model c o n s t r u c t e d f o r these more p r o d u c t i v e f l o w e r s i s presented i n T a b l s V. fiany of the same v a r i a b l e s are i n c l u d e d here as i n the f i r s t model, yet here the model accounts f o r 54% of p r o d u c t i v i t y v a r i a b i l i t y . Hence, f o r each sample of 10 f l o w e r s there was a subset of f l o w e r s which produced n e c t a r a t r a t e s s i g n i f i c a n t l y higher than the other f l o w e r s , and whose p r o d u c t i v i t y i s more p r e d i c t a b l e using the v a r i a b l e s measured i n t h i s study. A s t r i k i n g s e a s o n a l e f f e c t can be seen i n p r o d u c t i v i t y data, and i t i s p a r t i c u l a r l y f o r t h i s reason t h a t d i s c u s s i o n of a "mean" p r o d u c t i v i t y value i s m i s l e a d i n g . As F i g . 7 shows, c a l o r i e s o f f e r e d g r a d u a l l y decreased as the suamer progressed; a s e a s o n a l mean does not r e f l e c t d i f f e r e n c e s between what was o f f e r e d d u r i n g d i f f e r e n t days and weeks. A h i g h c o r r e l a t i o n e x i s t s between c a l / h r of a l l f l o w e r s sampled and date (r-=-.4280, p<.001), and date was the f i r s t v a r i a b l e s e l e c t e d as being of s i g n i f i c a n t e x p l a n a t o r y value i n the s e a s o n a l r e g r e s s i o n model (Table I I I ) . C a l / h r s e c r e t e d by the f o u r most p r o d u c t i v e f l o w e r s of a group i s even more h i g h l y c o r r e l a t e d with date (r=-.5667, p<„001). To gauge the e f f e c t s of the time elapsed between samples ("TEBS") upon n e c t a r p r o d u c t i v i t y ( c a l / h r ) , a s c a t t e r g r a m of the data i s provided i n F i g . 8. As TEBS i n c r e a s e d , c a l / h r i n c r e a s e d as w e l l , though a g r e a t deal of v a r i a b i l i t y can be observed (r=. 1012, p<.01 f o r a l l f l o w e r s , and r=. 1362, p<.02 f o r more p r o d u c t i v e f l o w e r s ) . To view t h i s r e l a t i o n s h i p independent o f the strong seasonal e f f e c t s , F i g . 9 i l l u s t r a t e s the r e s i d u a l s of 3 5 Table V: Stepwise r e g r e s s i o n model b u i l t f o r the v a r i a b l e , In c a l o r i e s / h o u r , f o r the f o u r most p r o d u c t i v e salmonberry flowers sampled at each episode. a) V a r i a b l e s s e l e c t e d f o r the model. b) V a r i a b l e s not s e l e c t e d . c) Steps i n model c o n s t r u c t i o n . A N A L Y S I S AT S T E P 6 F C P U . V 1 9 N= 3 0 0 OUT OF 334 SOURCE REGRESS I CN ERROR T O T A L DF 6 293 299 SUM OF SORS NEAN SCLARE 3 4 . 7 3 2 2 8 . 8 7 5 6 3 . 6 0 7 5 . 7 8 8 7 . 9 8 5 4 9 F - S T A T 5 8 . 7 4 0 S IGNIF . 0 0 0 0 M U L T I P L E R= . 7 3 8 9 5 R-S0R= . 5 4 6 0 4 SE= . 3 1 3 9 2 a) b) V A R I A B L E P A R T I A L C O E F F I C I E N T STO ERROR T - S T A T S I G N I F C O N S T A N T 1 7 . 4 2 5 4 . 6 6 6 8 3 . 7 3 3 8 . 0 0 0 2 1.V1 - . 3 5 4 6 0 - . 1 1 1 7 8 -1 . 1 7 2 2 0 - 2 - 6 . 4 9 15 . 0 0 0 0 1 0 . V I O .2 42 76 . 7 5 4 3 6 - 1 . 1 7 6 1 0 -I 4 . 2 8 3 6 . 0 0 0 0 11 .VI I . 2 2 5 3 7 . 2 6 2 7 8 - 2 . 6 6 3 6 3 - 3 3 . 9 5 9 7 . 0 0 0 1 I S .V 15 - . 2 0 5 2 2 - . 3 7 2 4 2 . 1 0 3 7 6 - 3 . 5 8 9 3 . 0 0 0 4 1 6 . V 1 6 . 4 4 2 7 1 . 52 0 4 9 . 6 1 5 8 6 -I 8 . 4 5 1 4 . 0 0 0 0 2 3 . V 2 3 - . 2 1 2 0 5 - 5 . 1 6 0 2 1 . 3 8 9 3 , - 3 . 7 1 4 2 . 0 0 0 2 R E M A I N I N G P A R T I A L S I G N I F 2 . V2 . 03321 . 5 7 0 6 hours a f t e r sunrise. 3 . V 3 - . C J 4 3 9 . 5 5 7 0 time elapsed between samples 4 . V4 - . 04691 . 4 2 2 9 sunshine 5. V5 . 0 3 3 3 5 . 5 6 8 9 diameter 1 4 . V L4 - . C t 2 3 8 . 2 8 6 4 In date 1 7 . V I 7 - . 0 5 5 0 1 . 3 4 7 2 In sunshine 1 8 . V I 8 . C 4 7 1 0 . 4 2 1 1 : In di ameter 2 4 . V 2 4 . C 5 6 5 7 . 3 3 3 8 In # flowers/meter date r e l . humidity # flowers/meter In hours a f t e r sunrise In time elapsed between samples In r e l . humidity R E G R E S S I O N OF 1 9 . V 1 9 LS ING FORWARD S E L E C T I C N c) S T E P R-SOR STD ERROR '# VAR V A R I A E L E P A R T I A L S IGN IF 1 . 3 2 9 3 3 . 3 7 8 3 5 1 I . V I I N - . 5 7 3 8 7 . OCOO 2 . 4 3 1 4 4 . 3 4 8 9 5 2 1 6 . V 1 6 IK . 3 9 0 2 0 .0000" 3 . 4872 7 . 3 3 192 3 1 C. VI C I N . 3 1 3 3 5 . 0 0 0 0 4 . 5 1 5 2 8 . 3 2 3 2 9 4 1 5 . V 1 5 IN - . 2 3 3 7 4 . COOO 5 . 5 2 4 6 7 . 3 2 0 6 E 5 l l . V l l IN . 1 3 9 1 9 . 0 1 6 6 6 . 5 4 6 0 4 . 3 1 3 9 2 6 2 3 . V 2 3 IN - . 2 1 2 0 5 . 0 0 0 2 3 7 F i g , 7 : S c a t t e r p l o t of date and salmonberry f l o w e r p r o d u c t i v i t y ( i n c a l o r i e s / h o u r ) . 38 I n (c a l o r i e s / h o u r + 1.0) 3 . 0 0 T 2.50 2.00 1.50 1.00 0.50 0.00 *• X X 5?X | x K x xSxx x P xM^x X x X « x x * X x 8 *** - * X - H - K - X " XX XX XX x « x ^ x x X * x v * X xX XX X x x X x s XX X X X X X XX XX v X X £ x x x X x x x K x -x-x (- X X X' X X X v X « * X x ^ X vXX x x x -X^X> r=-.J.L280 p<.001 n=779 X x X x x * If K x i * -*-X-X—- x K x X* X x ^ x May 3 May 15 May 27 June 8 June 20 J u l y 2 Date F i g . 8: E f f e c t o f the time e l a p s e d between samples on salmonberry f l o w e r p r o d u c t i v i t y ( i n c a l o r i e s / h r ) . l n ( c a l o r i e s / h o u r + 1 . 0 ) 3 . 0 0 T r = . 1 0 1 2 p < . 0 1 n - 7 7 9 1 . 0 0 i 0 . 5 0 j 0 . 0 0 x x X -X- X X i X 1 X y A tt * X X x X x X X X X X X -*- X X X X X X X X n X X X X X X Time Elapsed Between Samples (hours) P i g . 9! E f f e c t of the time e l a p s e d between samples on p r o d u c t i v i t y ( i n c a l o r i e s / h o u r ) i n the f o u r most p r o d u c t i v e salmonberry f l o w e r s sampled at each episode, independent of seasonal e f f e c t s . h2 R e s i d u a l s o f r e g r e s s i o n o f I n ( c a l o r i e s / h o u r -(-1.0) o n d a t e 2 . 1 0 T x X X X X X X X X X X X X H X X X X X X X X X X X I X X X X X X X X X X X X X rs.i4.091 p<.001 n=33i+ 1 1 T i m e E l a p s e d B e t w e e n S a m p l e s ( h o u r s ) 43 the r e g r e s s i o n cf c a l / h r on date p l o t t e d a g a i n s t TEDS f o r the more p r o d u c t i v e f l o w e r s . The s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n (r=.4091, p<.001) c l e a r l y shows that as TEB3 i n c r e a s e d , n e c t a r p r o d u c t i v i t y a l s o i n c r e a s e d . Of course, the f a c t t h a t TEBS i s i n c l u d e d i n the m u l t i p l e r e g r e s s i o n model demonstrates t h a t sampling frequency e x p l a i n s a s i g n i f i c a n t amount of p r o d u c t i v i t y v a r i a b i l i t y independent of a l l other v a r i a b l e s i n c l u d e d i n the model. The s e a s o n a l model f o r a l l flowers sampled i n c l u d e s androecium diameter as being s i g n i f i c a n t l y r e l a t e d t o nectar p r o d u c t i o n . Independent of s e a s o n a l e f f e c t s , s m a l l e r diameter f l o w e r s showed a s l i g h t tendency to s e c r e t e c a l o r i e s of nectar at higher r a t e s than d i d l a r g e r diameter f l o w e r s (r=-.Q750, p<„05)» I t i s i n t e r e s t i n g to note that androecium diameter i s not i n c l u d e d i n the r e g r e s s i o n model f o r the more p r o d u c t i v e f l o w e r data. As r e l a t i v e humidity decreased throughout the season there was a s i g n i f i c a n t decrease i n p r o d u c t i v i t y (r=« 3599, p<.00 1), and the r e l a t i o n s h i p i s s t r o n g e r i f one c o n s i d e r s data f o r only the p r o d u c t i v e f l o w e r s (r=.4024, p<.0Q1, F i g . 10). B e l a t i v e humidity i s i n c l u d e d i n the r e g r e s s i o n models f o r p r o d u c t i v i t y (Tables I I I and V), and, of c o u r s e , s i g n i f i c a n t l y c o r r e l a t e s with p r o d u c t i v i t y independently of date (r=.2152, p<.001 f o r a l l f l o w e r s , and r=.2046, p<.001 f o r p r o d u c t i v e f l o w e r s ) . The r e l a t i o n s h i p between sunshine and c a l / h r throughout the season was s i g n i f i c a n t l y negative (r=-.2482, p<.001 f o r p r o d u c t i v e f l c w e r s ) . Yet, independent of seasonal e f f e c t s , no r e l a t i o n s h i p e x i s t e d between c a l o r i e s produced and sunshine. kh P i g . 10: S c a t t e r p l o t o f r e l a t i v e humidity and p r o d u c t i v i t y ( i n c a l o r i e s / h r ) i n the f o u r most p r o d u c t i v e f l o w e r s sampled at each episode. l n ( c a l o r i e s / h o u r +. 1 . 0 ) 3 . 0 0 T p < . 0 0 1 n = 3 2 6 x x X X X X X X g X X X —1 x-x- X X X X X X ii t -X hXX- X X x X x x X X X X -X- X X X x x* X X X * X X X X - X%X X * ; *x : X X * — 5 0 . 0 6 0 . 0 7 0 . 0 8 0 . 0 R e l a t i v e Humidity 46 The time at which the samples were taken, expressed as hours a f t e r s u n r i s e (HAS), i s i n c l u d e d i n both r e g r e s s i o n models. The c o r r e l a t i o n between HAS and p r o d u c t i v i t y (cal/hr) i s s i g n i f i c a n t (r=-.1155, p<.05), however, with date e f f e c t s removed the c o r r e l a t i o n i s no l o n g e r s t a t i s t i c a l l y s i g n i f i c a n t . R e l a t i o n s h i p s between the v a r i a b l e s , c a l / h r , u l n e c t a r / h r , and % sugars are of i n t e r e s t . The sampling date c o r r e l a t e s i n v e r s e l y with u l n e c t a r / h r , and p o s i t i v e l y with % sugars, ( r e s p e c t i v e l y , r=-.6189, p<.001, and r=.2197, p<,001 f o r p r o d u c t i v e f l o w e r s ) . Thus, as the season progressed, salmonberry f l o w e r s produced lower volumes of a more h i g h l y c o n c e n t r a t e d n e c t a r . S e a s o n a l l y , as TEBS i n c r e a s e d the % sugar w i t h i n the n e c t a r i n c r e a s e d (r=.2495, p<.00 1 f o r a l l flowers and r=.4348, p<.001 f o r p r o d u c t i v e f l o w e r s ) . The r e l a t i o n s h i p i s s t r o n g e r when date e f f e c t s are removed, ( f o r a l l f l o w e r s , r=.3436 , p<.001, F i g . 11). Throughout the season, u l n e c t a r / h r i s not s i g n i f i c a n t l y c o r r e l a t e d with TEBS, yet when sea s o n a l e f f e c t s are removed there i s a s i g n i f i c a n t p o s i t i v e r e l a t i o n s h i p (r=»2317, p<.001. F i g . 12, f o r p r o d u c t i v e f l o w e r s ) , i n d i c a t i n g t h a t i n c r e a s e s both i n volume and sugar c o n c e n t r a t i o n were r e s p o n s i b l e f o r the i n c r e a s i n g of c a l / h r with i n c r e a s e d TEBS. On the other hand, with an i n c r e a s e i n flower androecium diameter t h e r e was an i n c r e a s e i n % sugars but a decrease i n ul n e c t a r / h r ( f o r a l l f l o w e r s , r e s p e c t i v e l y , r=.3293, p<.001 and r=-.2469, p<.001), and the same p a t t e r n s can be observed independent of date, (r=. 1736, p<.001 and r=-. 1083, p<.01). Here, as w e l l as f o r c a l / h r , data f r o a the more p r o d u c t i v e kl F i g . 1 1 : E f f e c t o f the time elapsed between samples on % sugar s e c r e t e d by salmonberry f l o w e r s , independent o f seasonal e f f e c t s . R e s i d u a l s o f r e g r e s s i o n o f ln{% s u g a r s + 1 . 0 ) on date 1 , 2 0 j 0 . 6 0 0 . 0 0 - 0 . 6 0 j - 1 . 2 0 4 - 1 , 8 0 x X X X x X X X X X X X X X X X X a X x X X X X X a X X X * X n I x X X X X K X x x X X X x X X X r = . 3 i i 3 6 p < . 0 0 1 n - 5 5 7 3 5 7 9 Time E l a p s e d Between Samples (hours) 1 1 k9 Fig» 12: E f f e c t o f the time elapsed between samples on I n u l nectar/hour s e c r e t e d by the f o u r most pro d u c t i v e flowers sampled at each episode, independent o f seasonal e f f e c t s . 5 0 R e s i d u a l s of r e g r e s s i o n of l n ( u l n e c t a r / h o u r * 1 . 0 ) on date 2 . 1 0 T 1 . 5 0 0 . 9 0 0 . 3 0 f - 0 . 3 0 4 • 0 . 9 0 + 1 x X X X X X X X X X X X I X X X X X X X M 5 X X X X X X X X X X X r - . 2 3 1 7 p < . 0 0 1 n = 3 3 3 1 H ••— i— 5 . 7 9 Time Elapsed Between Samples (hours) 1 1 5 1 flowers shov weaker c o r r e l a t i o n s , p a r t i c u l a r l y f o r u l nectac/houc. Nectar volumes decreased as r e l a t i v e humidity decreased throughout the season, (r=.4865, p<.001 f o r more p r o d u c t i v e f l o w e r s ) , yet % sugar i n c r e a s e d with sunshine l e v e l s (r=.5671, p<.001). Without the e f f e c t s of date the same p a t t e r n s ace e v i d e n t ( f o r a l l f l o w e r s , r e s p e c t i v e l y , r=„3637, p<-001 and r=. 5491, p<.001, F i g s . 13 and 14). D.) D i s c u s s i o n Though no p r e v i o u s i n f o r m a t i o n i s a v a i l a b l e f o r salmonberry, Szklanowska (1972) found t h a t r a s p b e r r i e s (Bubus idaeus) produce 27 mg sugar/day, while b l a c k b e r r i e s (Bubus f r u t i c o s u s ) produce 15 mg sugar/day, o r , r e s p e c t i v e l y , 7.68 c a l / h r and 4.27 c a l / h r , assuming a "day" to c o n s i s t of 13 hours. His measurements were made under optimum c o n d i t i o n s f o r nectar s e c r e t i o n , which Szklanowska r e p o r t s as being sunny, moderately humid days f o l l o w i n g c o o l n i g h t s . Whitney (1978) recorded a r a s p b e r r y p r o d u c t i o n value of 4 mg sugar/day, or 1.14 c a l / h r , which may r e p r e s e n t an average value over an e n t i r e season o r simply a s i n g l e measurement made under sub-optimal c o n d i t i o n s . Measurements made i n t h i s study p l a c e the mean of salmonberry n e c t a r s e c r e t i o n a t 1.08 c a l / h r f o r the more p r o d u c t i v e f l o w e r s . T h i s r e f l e c t s many days i n the f l o w e r i n g season o f salmonberry, not a l l r e p r e s e n t i n g optimum c o n d i t i o n s . May 18 was the day of h i g h e s t p r o d u c t i o n , the average f o r the most productive f l o w e r s on that day being 3.24 c a l / h r , with .95 c o n f i d e n c e l i m i t s being F i g . 1 3 i S c a t t e r plot, o f r e l a t i v e humidity and I n u l nectar/hour s e c r e t e d by salmonberry, independent of seasonal e f f e c t s . 53 Residuals o f r e g r e s s i o n of l n ( u l n e c t a r / h r + 1 . 0 ) on datd 2 . 2 0 1 . 6 0 1 . 0 0 1 O.iiO - - 0 . 2 0 + - 0 . 8 0 5o X x. x x x X X r z . 3 6 3 7 p < t . 0 0 1 n = 7 6 6 x' x X X X 6 0 . 0 X X X X X X x xx x£ X X 7 0 . 0 xx xx X . X X X 'x X x>x x^x x x x; x : x X NX X X X x ***x x X x x X : x v xx x $ 'I; x x *x 8 0 . 0 X X * X X X x£ x x X X X xx: \ X X X X X X 8 X* X xx X X X X X X X X X X X X X X —( 9 0 . 0 1 0 0 . 0 R e l a t i v e Humidity Sk F i g . l l i : E f f e c t of sunshine l e v e l s on In % sugar s e c r e t e d by salmonberry f l o w e r s , independent of seasonal e f f e c t s . 55 R e s i d u a l s o f r e g r e s s i o n o f ln{% sugars +• 1 ,0) on date 1.30 0 . 7 0 o.io \ - 0 . 5 0 - l . i o t •1.70 5 . 0 X X X X x x $*$** > < ^ > i x * x Sxx * x x * x X. x x x x X x X XX x x r = . 5*1.91 p < . 0 0 1 n=523 x x 2 5 . 0 14.5.0 65.0 8 5 . 0 1 0 5 . 0 Sunshine L e v e l s / h r of P r o d u c t i o n 125.0 56 s e t at 0-6.71 c a l / h r . Apparently, salisonberry produces a t approximately the same l e v e l s as do other s p e c i e s of Rubus. The extreme v a r i a t i o n i n salmonberry nectar p r o d u c t i v i t y on s e a s o n a l and d a i l y time s c a l e s i s s t r i k i n g , and may have d r a s t i c consequences on i n s e c t f o r a g e r s . Production s t r o n g l y decreases as the season progresses, s h i f t i n g from d a i l y averages of 2-07 c a l / h r , 2.45 c a l / h r and 3.24 c a l / h r (May 16,17,18), down to d a i l y averages l a t e r i n the season of .31 c a l / h r , .32 c a l / h r and ,08 c a l / h r (June 2 1,22,27). T h i s decrease i n c a l / h r c l o s e l y r e f l e c t s a corres p o n d i n g decrease i n nectar volumes s e c r e t e d throughout the salmonberry f l o w e r i n g season. The c o n c e n t r a t i o n of sugars i n the n e c t a r i n c r e a s e s at the same time, yet the i n c r e a s e i s net enough to o f f s e t the d e c l i n e i n c a l o r i e s o f f e r e d r e s u l t i n g from d e c l i n e s i n volumes s e c r e t e d . P r o d u c t i o n w i t h i n s i n g l e days, (that i s , independent of d a t e ) , i s a l s o h i g h l y v a r i a b l e , with a trend f o r i n c r e a s e d c a l o r i c p r o d u c t i o n e a r l y i n the day, when r e l a t i v e humidity l e v e l s are h i g h e s t , t h a t drops o f f s t e a d i l y as sunshine l e v e l s i n c r e a s e . T h i s again r e f l e c t s trends i n volumes of nectar s e c r e t e d ; as the day passes the p l a n t s produce s m a l l e r amounts of nectar while the c o n c e n t r a t i o n of the nectar i n c r e a s e s . T h i s c o u l d mean t h a t the nectar i s a c t u a l l y s e c r e t e d a t higher c o n c e n t r a t i o n s , or t h a t i t i s s e c r e t e d at c o n c e n t r a t i o n s s i m i l a r to those e a r l y i n the day and r a p i d l y evaporated to higher l e v e l s . T h i s p a t t e r n has been observed by s e v e r a l authors working on v a r i o u s p l a n t s p e c i e s ( B u t l e r , 1945; P e r c i v a l , 1965; f e i n s i n g e r , 1978; Corbet, 1978), and helps t o account f o r s e v e r a l of the c o r r e l a t i o n s noted p r e v i o u s l y , f o r example, t h a t 57 p r o d u c t i o n (cal/hr) c o r r e l a t e s p o s i t i v e l y with r e l a t i v e humidity. S e a s o n a l l y , the c o o l , r a i n y days t y p i c a l of s p r i n g i n the f o r e s t give way g r a d u a l l y to the warm, sunny days of summer. Thus, r e l a t i v e humidity and sunshine l e v e l s are h i g h l y c o r r e l a t e d with p r o d u c t i v i t y s e a s o n a l l y . Corbet (1978) d i s c u s s e s p o s s i b l e a d a p t i v e v a l u e s o f such a p a t t e r n of d a i l y nectar s e c r e t i o n : Let us i n s t e a d regard f l o w e r s as s o p h i s t i c a t e d gadgets f o r d i s p e n s i n g n e c t a r at the r i g h t c o n c e n t r a t i o n a t the r i g h t time. I f there i s a degree of c o n c e n t r a t i o n s p e c i f i c i t y among p o l l i n a t o r s , there w i l l be a s e l e c t i v e advantage f o r f l o w e r s whose morphology and s e c r e t o r y p e r i o d i c i t i e s i n t e r a c t with the l o c a l c l i m a t e i n such a way as to i n c r e a s e the l i k e l i h o o d t h a t the nectar w i l l be at an a p p r o p r i a t e c o n c e n t r a t i o n at a time of day when a s u i t a b l e p o l l i n a t o r i s a c t i v e (Corbet, 1978, p-27) . , Yet why must the fl o w e r s s e c r e t e l a r g e amounts of d i l u t e nectar e a r l y i n the morning to allow e v a p o r a t i o n to b r i n g i t t o "appropriate' 1 c o n c e n t r a t i o n s r a t h e r than simply s e c r e t e nectar a t the proper c o n c e n t r a t i o n a t the time the p o l l i n a t o r s are a c t i v e ? I t seems l i k e l y that a i r and p o s s i b l y s o i l moisture l e v e l s are r e s p o n s i b l e f o r t i m i n g of n e c t a r s e c r e t i o n , s e c r e t i o n being highest when p l a n t s have high l e v e l s of s u r p l u s moisture a v a i l a b l e . Huber (1956) has found t h a t f o r s e v e r a l p l a n t s p e c i e s , the n e c t a r has the same composition as the phloem sap, and t h a t f o r p l a n t s which have n e c t a r i e s s u p p l i e d by a l a r g e amount of xyiem, production i s reduced by d e f i c i e n t s o i l 58 moisture and i s i n c r e a s e d with an i n c r e a s e of moisture- He has found, f u r t h e r , t h a t the amount of sugar s e c r e t e d i s s e n s i t i v e to changes i n t r a n s p i r a t i o n r a t e . To view s e c r e t i o n a p a r t from p o s s i b l e environmental c o n s t r a i n t s upon the p l a n t s seems u n r e a l i s t i c . According t o Shuel (1955) , i n c r e a s e d i n s o l a t i o n r e s u l t s i n i n c r e a s e d n e c t a r s e c r e t i o n (mg s u g a r / u n i t time) i n white c l o v e r . P e r c i v a l (1965, p.97) w r i t e s t h a t , s p e c i e s d i f f e r i n t h e i r response t o i n s o l a t i o n . In Cuba the f i n e s t nectar p l a n t , the white 'Campanula 1 (Ipomoea s i d a e f o l i a ) s e c r e t e s best d u r i n g hot days with b r i g h t sunshine, but i n another Cuban p l a n t , the C o r a l Vine (Antigonon l e p t o p u s ) , strouo i n s o l a t i o n d i m i n i s h e s the flow as the day wears on, and flow i s continuous on cloudy days, Fahn (1949) d i s c o v e r e d t h a t i n one l o c a t i o n i n P a l e s t i n e , Teccmaria c a p e n s i s shews a c l e a r r i s e i n dry weight of nectar a v a i l a b l e with a drop i n temperature. In t h i s study I found t h a t salmonberry produces more t o t a l mg sugar i n g e n e r a l l y c o o l e r c o n d i t i o n s ; as i n s o l a t i o n i n c r e a s e s only percentage sugar i n c r e a s e s while volume secreted g r e a t l y d i m i n i s h e s . Shuel (1955) s p e c u l a t e d that the i n c r e a s e he observed i n p r o d u c t i v i t y with i n c r e a s e d i n s o l a t i o n i s due to an i n c r e a s e i i i p h o t o s y n t h e s i s . Barber (1976) found t h a t salmonberry does d i s p l a y an i n c r e a s e i n p h o t o s y n t h e s i s with i n c r e a s e d i n s o l a t i o n , yet he d i d not i n v e s t i g a t e p a t t e r n s of n e c t a r p r o d u c t i v i t y i n h i s study. I t may be that the i n c r e a s e i n nectar c o n c e n t r a t i o n observed i n t h i s study i s due not only to high r a t e s of 59 e v a p o r a t i o n but a l s o to an a c t u a l i n c r e a s e i n c o n c e n t r a t i o n of the l i q u i d s e c r e t e d due to higher r a t e s o f p h o t o s y n t h e s i s , along with i n c r e a s i n g l y unfavorable moisture c o n d i t i o n s f o r nectar s e c r e t i o n . The p l a n t s may s e c r e t e more c a l o r i e s d u r i n g the s p r i n g and e a r l y morning hours due to a f a v o r a b l e moisture balance, yet these times are a l s o c o o l and t h e r e f o r e a c t i v e p o l l i n a t o r s are o p e r a t i n g at heavy c a l o r i c c o s t . Increased c a l o r i c output by the p l a n t s may be necessary t o allow the i n s e c t s a c t i v e d u r i n g these t i n e s to forage with even a small net energy g a i n ( H e i n r i c h , 1975a; Reader, 1977). , The negative c o r r e l a t i o n between androecium diameter and n e c t a r p r o d u c t i v i t y ( c a l / h r ) i s q u i t e weak yet s i g n i f i c a n t . S i n c e androecium diameter c o r r e l a t e s so s t r o n g l y with flower age, t e n t a t i v e c o n c l u s i o n s can be made concerning f l o r a l age and f l o r a l p r o d u c t i v i t y . G.W. Wood has explored t h i s q u e s t i o n and w r i t e s : In some p l a n t s , the o l d fl o w e r s s e c r e t e more nectac than the young ones, i n o t h e r s , the r e v e r s e r e l a t i o n s h i p e x i s t s ; son>e p l a n t s may have a high n e c t a r y i e l d i n the old flowers but have a s i m i l a r q u a n t i t y of sugar to the young f l o w e r s . In b l u e b e r r y , both nectar volume and nectar sugar content per c l o n e i n c r e a s e through much of the bloom p e r i o d . T h e r e f o r e , i f we assume a d i r e c t r e l a t i o n s h i p between y i e l d of nectar or nectar sugar and bee v i s i t a t i o n , present evidence would show that the blueberry i s more a t t r a c t i v e to nectac g a t h e r i n g i n s e c t s towacds the 60 l a t t e r p a r t of the bloom p e r i o d (Wood, 1961, p. 1039)... For salmonberry, the younyer f l o w e r s seem t o be the most p r o d u c t i v e , i n terms of c a l / h r , s i n c e they put out the g r e a t e s t amounts of h i g h l y c o n c e n t r a t e d n e c t a r . Older f l o w e r s put out l e s s n e c t a r but at an a p p a r e n t l y higher c o n c e n t r a t i o n , thus weakening the r e l a t i o n s h i p between c a l / h r and age. T h i s does not n e c e s s a r i l y mean that o l d e r f l o w e r s a c t u a l l y s e c r e t e higher c o n c e n t r a t i o n s cf n e c t a r , but simply t h a t they s e c r e t e s m a l l amounts which may undergo more r a p i d e v a p o r a t i o n due to the i n c r e a s e d s u r f a c e area/volume of the s m a l l e r drops. The i n c r e a s e d androecium diameter of o l d e r flowers as opposed to younger f l o w e r s d o u b t l e s s a i d s i n the more r a p i d e v a p o r a t i o n of the s m a l l amounts present. P e r c i v a l (1965) d i s c u s s e s the i n c r e a s e of % sugar s e c r e t e d as blossoms of orange t r e e s age, c l a i m i n g t h a t " i t s a t t r a c t i o n f o r i n s e c t s does not d i m i n i s h " (p.S2). I t seemed p o s s i b l e t h a t the s t r o n g , negative c o r r e l a t i o n between p r o d u c t i v i t y and date was due t o the f a c t t h a t as the season progresses the average age of f l o w e r s a v a i l a b l e i n c r e a s e s (r= 33257, p<.00 1). Yet, the r e g r e s s i o n models d i s c u s s e d p r e v i o u s l y i n c l u d e both flower diameter and date as s i g n i f i c a n t v a r i a b l e s , and the r e s i d u a l s of the r e g r e s s i o n of c a l / h r on diameter are s i g n i g i c a n t l y c o r r e l a t e d with date ( F i g . 15, r=- -3861, p<.001). These f a c t s l e a d to the c o n c l u s i o n t h a t f l o w e r s of a l l ages produce at lower r a t e s with the passing o f summer, perhaps due to decreased s o i l moisture, or perhaps due to the shunting c f energy to f r u i t production as i n c r e a s i n g numbers o f f l c w e r s on each p l a n t are f e r t i l i z e d . Some authors might even 6 1 F i g . 1 ^ : S c a t t e r p l o t o f p r o d u c t i v i t y ( i n c a l o r i e s / h r ) and date, independent o f androecium diameter e f f e c t s . 6 2 Residuals of r e g r e s s i o n o f l n ( c a l o r l e s / h r + 1 . 0 ) on diameter 2 . 3 0 T 1 . 9 0 4 1.50 I 1 . 1 0 * * x 0 . 7 0 0 . 3 0 : ; X . , x •0.10 -JJ" »x \> j ; X •0.50 t - X X X * X X l x X x* x „Xx Ix*S iii* xxxx x ~ X X X * X X X x X * x x>< X x» xX X *x XX X X ) X X x* M X x* x~ X X x x x X X x x xx X X i K x 8 x x xx X x Xxxx I** X X r * - . 3 8 6 l p < . 0 0 1 n ^ 7 7 9 x x x x x x Ox xx x x x x xxx | x i x X XX. x^x*. * x x X Xx xx8* ^ f i f i x cx x x x X x X * x x X X *** *x — x x x x May 3 May 15 May 2 7 June 8 June 2 0 J u l y 2 Date 6 3 maintain t h a t p l a n t s are g r a d u a l l y c u t t i n g back production to guarantee c o n s i s t e n t , e f f i c i e n t , p o l l i n a t o r a c t i v i t y i n higher a i r temperatures. The f a c t that the most p r o d u c t i v e f l o w e r s show no c o r r e l a t i o n between flower diameter and p r o d u c t i v i t y may be due to s e v e r a l f a c t o r s . I t may be that a very l a r g e sample s i z e i s necessary f o r the r a t h e r weak r e l a t i o n s h i p to become apparent, or i t may mean t h a t the p r o d u c t i v i t y of these f l o w e r s i s u n i f o r m l y h i g h , r e g a r d l e s s of diameter. F e i n s i n g e r (1978) has d i s c o v e r e d the e x i s t e n c e of "bonanza" flo w e r s on i n d i v i d u a l s of s e v e r a l t r o p i c a l p l a n t s p e c i e s . The present study has shown t h a t r a t h e r h i g h l y p r o d u c t i v e f l o w e r s may e x i s t i n salmonberry as w e l l ; at l e a s t , at each sampling some f l o w e r s are producing a t l e v e l s w e l l above lower producing f l o w e r s . Many authors have noted the high h e t e r o g e n e i t y which c h a r a c t e r i z e s n e c t a r production i n p l a n t s ( H e i n r i c h , 1975a; F e i n s i n g e r , 1978), arguing t h a t i t encourages e f f i c i e n t p o l l i n a t i o n . Once unproductive salmonberry f l o w e r s are removed frcm c o n s i d e r a t i o n , r e l a t i o n s h i p s between p r o d u c t i v i t y and date, sampling freguency, as well as c l i m a t i c v a r i a b l e s are s t r o n g e r , i n d i c a t i n g t h at many flowers are unproductive due to v a r i a b l e s not measured i n t h i s study (e.g., flower height, d i s t a n c e from f l o w e r to main stem, m i c r o c l i m a t i c e f f e c t s at i n d i v i d u a l flower s i t e s , and p o s s i b l y p r o p e r t i e s i n h e r e n t w i t h i n each fl o w e r i n a d d i t i o n to f l o w e r age). The present study shows that sampling frequency has a s i g n i f i c a n t impact upon p r o d u c t i v i t y , yet s u r p r i s i n g l y , cue e f f e c t i s j u s t the opposite of previous f i n d i n g s . Here, as 64 sampling frequency decreases n e c t a r v o l t e s and n e c t a r sugar c o n c e n t r a t i o n i n c r e a s e , thus i n c r e a s i n g c a l / h r o f f e r e d . The i n c r e a s e i n % sugar i s not s u r p r i s i n g , s i n c e f l o w e r s sampled i n f r e q u e n t l y have n e c t a r exposed longer to e v a p o r a t i o n . Yet even with e v a p o r a t i o n e f f e c t s the volume/hour i n c r e a s e s . T h i s r e s u l t i s e s p e c i a l l y i n t r i g u i n g when one i s reminded that Raw (1953) obt a i n e d the o p p o s i t e r e s u l t with two s p e c i e s of fiubus (R.« idaeus and R. f r u t i c o s u s ) . One e x p l a n a t i o n of the adaptive value of the flower response found here i s i n terms of p l a n t c o m p e t i t i o n f o r p o l l i n a t o r s . Given the f a c t that bumblebees have the a b i l i t y to s e l e c t between fl o w e r s ( d i s c u s s e d i n Chapter I I I ) , i t i s reasonable to assume t h a t they d i s c r i m i n a t e on the b a s i s of nectar standing crop. P l a n t s having f l o w e r s being u t i l i z e d by very few p o l l i n a t o r s might be expected to i n c r e a s e t h e i r n e c t a r production r a t e s i n an e f f o r t by each p l a n t to a t t r a c t t h e few p o l l i n a t o r s i n the area, whereas p l a n t s with f l o w e r s which are being used at a very high r a t e would i n d i v i d u a l l y b e n e f i t by keeping p r o d u c t i o n r a t e s low. Many p o l l i n a t o r s i n the area, competing amongst themselves f o r f l o r a l n e c t a r , v i r t u a l l y guarantee t h a t every f l o w e r w i l l be v i s i t e d . T h i s argument c o u l d a l s o e x p l a i n why the model b u i l t f o r nectar p r o d u c t i v i t y i n c l u d e d the v a r i a b l e , number of flowers/meter, as having e x p l a n a t o r y value independent of date. I n c r e a s e d numbers of f l o w e r s i n the r e s e a r c h area would presumably r e s u l t i n i n c r e a s e d p l a n t c o m p e t i t i o n f o r the a v a i l a b l e p o l l i n a t o r s . . P o l l i n a t i o n b i o l o g i s t s f r e q u e n t l y c a l l upon c o m p e t i t i o n to h e l p e x p l a i n c e r t a i n observed t r a i t s i n both p l a n t s and t h e i r p o l l i n a t o r s . The b r i g h t c o l o r s o f showy a l p i n e f l o w e r s have been 65 e x p l a i n e d by i n v o k i n g p l a n t c o m p e t i t i o n f o r the few p o l l i n a t o r s which are a c t i v e i n a l p i n e c o n d i t i o n s (Pojar, 1974), and such p l a n t c o m p e t i t i o n has been used to e x p l a i n o b s e r v a t i o n s o f asynchronous blooming periods of f l o w e r i n g p l a n t s i n the same g e o g r a p h i c a l area (Mosquin, 197 1; Heithaus, 1974; H e i n r i c h , 1976b). On the other hand, c o m p e t i t i o n among p o l l i n a t o r s f o r f o r a g i n g s i t e s has been used t o e x p l a i n v a r i a t i o n i n tongue le n g t h s of bumblebees ( H e i n r i c h , 1976a; Inouye, 1977) , d i f f e r i n g s i z e s of bumblebees (Horse, 1978) , and temporal d i f f e r e n c e s i n a c t i v i t y between p o l l i n a t o r s p e c i e s ( L i n s l e y e t a l . , 1973). The r e s u l t s presented here i n d i c a t e t h a t p l a n t c o m p e t i t i o n f o r p o l l i n a t o r s may be o c c u r r i n g only during c e r t a i n p e r i o d s i n the day and durin g c e r t a i n days or weeks of a blooming season. During ether p e r i o d s i t may be the case t h a t the p o l l i n a t o r s are f o r c e d i n t o a c o m p e t i t i v e s i t u a t i o n f o r f l o r a l r e s o u r c e s . T h i s apparent s h i f t i n co m p e t i t i o n has a l s o been d i s c u s s e d by Mosquin (1971). An a l t e r n a t i v e e x p l a n a t i o n f o r the o b s e r v a t i o n t h a t c a l / h r decreases with sampling frequency i n v o l v e s the f i n d i n g t h a t , as f e r t i l i z a t i o n o c c u r s , n e c t a r p r o d u c t i v i t y decreases d r a m a t i c a l l y (Shuel, 1978). The present study i n v o l v e d the removal of nectar from f l o w e r s up to f c u r times a day. Though the g l a s s m i c r o p i p e t t e s used c o u l d not have t r a n s f e r r e d much p o l l e n , the many e n t r i e s i n t o the flowers c o u l d i n some way have simulated normal p o l l i n a t i o n , perhaps even the removal of nectar s i g n a l l i n g the flower that p o l l i n a t i o n had indeed o c c u r r e d . Thus, c o m p e t i t i o n between fl o w e r s may not need t o be invoked as an e x p l a n a t i o n f o r the d i f f e r e n c e i n pro d u c t i o n between f l o w e r s 6 6 sampled i n f r e q u e n t l y and those sampled o f t e n . I t i s worth noting that under the com p e t i t i o n e x p l a n a t i o n , flowers which are not beinq used r a i s e p r o d u c t i o n l e v e l s , while under the second i t i s f l o w e r s which are being f r e q u e n t l y u t i l i z e d which then decrease p r o d u c t i v i t y . I do not b e l i e v e t h a t the p i p e t t i n g techniques used here damaged the f l o w e r s . E a r l y i n the season s e v e r a l f l o w e r s were sairpled 3 or 4 times throughout a 2 or 3 day p e r i o d . Although the volumes s e c r e t e d decreased as the day progressed, the next morning there were present l e v e l s of ne c t a r lower than l e v e l s measured the previous morning, yet not low enough to i n d i c a t e t h a t damage had occurred to the n e c t a r i e s . Bather, I b e l i e v e the lower l e v e l s were due to advancing flower age, a f u l l day being a s i g n i f i c a n t time u n i t i n the l i f e of a f l o w e r which l a s t s only 5-7 days. To f u r t h e r i n v e s t i g a t e the p o s s i b i l i t y of f e r t i l i z a t i o n and/or f l o r a l damage confounding the r e s u l t s , s e v e r a l of the ana l y s e s p r e v i o u s l y d i s c u s s e d were performed on data gathered from f l o w e r s sampled only once. T h i s means t h a t f l o w e r s i n c l u d e d i n the analyses were a l l entered twice, once f o r i n i t i a l n e c tar removal and again f o r f i n a l n e c t a r sampling. With the e f f e c t s of date removed, the time elapsed between samples i s s i g n i f i c a n t l y c o r r e l a t e d with p r o d u c t i v i t y (r=. 1410, p<. 002, n=510). Hith the e f f e c t s of sunshine, r e l a t i v e humidity and date removed there i s s t i l l a s i g n i f i c a n t , p o s i t i v e c o r r e l a t i o n (r=. 1176, p<.02, n=450), Thus, the decrease i n p r o d u c t i v i t y with i n c r e a s e d sampling frequency was not dus to flower damage or t o i n c r e a s e d f e r t i l i z a t i o n . 67 I t s hould be emphasized that the present study was conducted i n the f i e l d , where p r o d u c t i v i t y i s under the i n f l u e n c e of many f a c t o r s which vary independently ( P e r c i v a l , 1965). Many of these were not measured i n t h i s study, such as flower h e i g h t , p l a n t h e i g h t , number of flowers per p l a n t , e t c . The v a r i a b l e s which were measured may not have a c c u r a t e l y r e f l e c t e d c o n d i t i o n s r e a l i z e d by each flower on each salmonberry plant*. Sunshine l e v e l s were measured with an a c t i n o g r a p h placed on a l o g g i n g road, yet many p l a n t s and flowers experienced very d i f f e r e n t sunshine c o n d i t i o n s i f shaded sometime during the day. R e l a t i v e humidity was s i m i l a r l y measured i n the middle o f a road, yet the r e l a t i v e humidity value of importance t o the p l a n t s should be that of the a i r surrounding the p l a n t , and the r e l a t i v e humidity value of importance to values of n e c t a r volume and c o n c e n t r a t i o n should be that of the a i r i n s i d e each flower. Even though these sources of e r r o r s u r e l y i n c r e a s e d the v a r i a t i o n i n n e c t a r p r o d u c t i v i t y measured during t h i s study, i t i s encouraging t h a t the r e g r e s s i o n models presented e a r l i e r can account f o r 545? of production v a r i a b i l i t y . To s u b s t a n t i a t e the c l a i m made here, t h a t high sampling frequency has a negative impact upcn p r o d u c t i v i t y , salmonberry p l a n t s should be r a i s e d under otherwise c o n s t a n t l a b o r a t o r y c o n d i t i o n s while the r e l a t i o n s h i p i s again e x p l o r e d . The s t r o n g e s t c o n c l u s i o n one can make here i s t h a t a negative r e l a t i o n s h i p i s d e f i n i t e l y i n d i c a t e d . 68 I I I . FOBAGING BEHAVIOB a.) I n t r o d u c t i o n A growing number of s t u d i e s c l e a r l y demonstrate that as food r e s o u r c e s become s c a r c e , animals cease to f o r a g e i n a s p e c i a l i z e d manner and i n c r e a s i n g l y accept a broader range o f food items a v a i l a b l e . Werner and H a l l (1974) found t h a t b l u e g i l l s u n f i s h w i l l feed upon only l a r g e r s i z e s of Daphnia as long as food abundance remains high. With l i m i t e d abundance the f i s h u t i l i z e a wider range of prey s i z e s . S i m i l a r l y , Krebs et a l . (1977) found that great t i t s were n o n - s e l e c t i v e at low prey encounter r a t e s while at h i g h e r r a t e s the b i r d s s e l e c t e d only l a r g e r s i z e d prey. Smith et a l . (1978) o b t a i n e d the a p p a r e n t l y o p p o s i t e r e s u l t , t h a t as food became s c a r c e on the Galapagos I s l a n d s , each s p e c i e s of Darwin*s f i n c h s e l e c t e d a narrower range of food items. However, as the authors admit, the f a c t t h a t food r e s o u r c e s changed q u a l i t a t i v e l y d u r i n g t h e i r study makes d i f f i c u l t a comparison with the s t u d i e s p r e v i o u s l y mentioned. The purpose of t h i s study was t o assess changes i n bumblebee f o r a g i n g behavior accompanying s h i f t s i n the f l o r a l n e c t a r rewards o f f e r e d , various environmental f a c t o r s , and date. Bee f o r a g i n g behavior examined i n t h i s study i n c l u d e d the number of f o r a g e r s encountered a t v a r i o u s flower patches per u n i t time, the percentage of f l o w e r s a c t u a l l y used a f t e r being approached by the bees, and the average androecium diameter of f l o w e r s used by the tees. In c o o l , r a i n y c o n d i t i o n s bumblebees, being exothermic, 69 would not be expected to f l y f r e q u e n t l y , s i n c e f l i g h t i n c o o l e r c o n d i t i o n s i s e n e r g e t i c a l l y very c o s t l y ( H e i n r i c h , 1975a). However, i f a c c l o n y were s h o r t of s t o r e d n e c t a r , bumblebees should f l y more f r e q u e n t l y i n inclement c o n d i t i o n s than i f an abundance were present ( A l f o r d , 1975); indeed, bumblebees have been observed f o r a g i n g i n even n e a r - f r e e z i n g temperatures ( H e i n r i c h and Baven, 1972). S e v e r a l authors b e l i e v e t h a t , i n the presence of an abundance of s t o r e d n e c t a r , bumblebee workers do not f l y under even the best weather c o n d i t i o n s ( H e i n r i c h , 1979a; A l f o r d , 1975). I suspected t h a t s t r o n g c o r r e l a t i o n s would be found between numbers cf bees f o r a g i n g and sunshine l e v e l s , temperature and r e l a t i v e humidity. Yet, i t was a l s o hypothesized t h a t , assuming that bumblebees seek t o maximize t h e i r net energy g a i n (Pyke, 1978), a s t r o n g , p o s i t i v e c o r r e l a t i o n s h o u l d e x i s t between number of bees f o r a g i n g and n e c t a r s t a n d i n g c r o p . Bumblebees do not u t i l i z e a l l f l o w e r s upon which they l a n d , and they do net land upon a l l flowers they approach. Upon approach, they uay "decide" to forage from a flower or to avoid i t a l t o g e t h e r . F a e g r i and van der P i j l (1978) write t h a t bees have a very keen sense of odor. K a u f f e l d and Sorensen (1971) thought t h a t honeybees i n i t i a l l y s e l e c t f l o w e r s by e o l e r , but t h a t a t c l o s e r d i s t a n c e s honeybees are guided by aroma. In a s e r i e s of experiments, von F r i s c h (1971) t r a i n e d honeybees to feed on sugar s o l u t i o n placed i n s i d e a s m a l l cardboard box. The box a l s o contained a f r a g r a n t f l o w e r or a few drops of scented o i l . The bees were then o f f e r e d an array of c l e a n boxes, ncne of which co n t a i n e d sugar s o l u t i o n , t u t one contained the s c e n t used f o r t r a i n i n g . The bees would a l i g h t and e n t e r only the scented 70 box- When o f f e r e d an a r r a y of boxes, one of which was scented and another b r i g h t l y c o l o r e d , the bees flew towards the c o l o r e d box. Yet they h e s i t a t e d about an i n c h from the box entrance and began to f l y about the entrances of the other boxes. They entered only the scented box. I t seems reasonable to assume t h a t , through an a b i l i t y to d i f f e r e n t i a t e aroma i n t e n s i t i e s , bumblebees should choose f l o w e r s which y i e l d the g r e a t e s t amounts of. n e c t a r s t a n d i n g crop. Yet the bees can a f f o r d to be so choosy only when th^re i s a s u r p l u s of nectar a v a i l a b l e i n r e l a t i o n to colony demands. Once nectar becomes a scarce resource bees should u t i l i z e v i r t u a l l y a l l f l o w e r s they approach, s i n c e even s l i g h t amounts of n e c t a r present would be worth h a r v e s t i n g . In g e n e r a l , as r e s o u r c e s become l i m i t i n g bees should g r a d u a l l y choose to forage from a g r e a t e r f r a c t i o n of the f l o w e r s they i n v e s t i g a t e . T h i s s i t u a t i o n i s roughly analogous to t h a t i n which pr e d a t o r s choose s m a l l e r prey items as the t o t a l numter of prey d e c l i n e s . Assuming that a c e r t a i n range of f l o w e r ages i s most pr o d u c t i v e (Wood, 196 1), I f u r t h e r hypothesized t h a t while n e c t a r was p l e n t i f u l the bees would be observed t o p r e f e r f l c w e r s of a c e r t a i n age, and t h e r e f o r e , of a c e r t a i n androecium diameter (Chapter I I ) . As nectar reward c o n d i t i o n s d e c l i n e through the salmonberry season bees would u t i l i z e a wider range of f l o w e r s . B,) Methods The study was conducted between May 3 and June 28, 1979. 7 1 Buirilebees were observed at v a r i o u s times o f day throughout the season f o r a g i n g on patches of salmonberry f l o w e r s , each o b s e r v a t i o n s e s s i o n l a s t i n g 10 minutes, as i n Free (1955) and K a u f f e l d and Sorensen (1971). other authors have used 15 minute s e s s i o n s ( P a r r i s h and Bazzaz, 1978), yet I f e l t t h a t 15 minute s e s s i o n s would r e s u l t i n high v a r i a b i l i t y due to weather changes during the s e s s i o n . The patches observed were l o c a t e d along the margins of o l d l o g g i n g roads (K30 and H20, DBC Research F o r e s t ) . Since i t was r a r e to f i n d c l e a r l y d i s t i n c t patches of f l o w e r s , patches o f t e n had t o be chosen by simply marking o f f an e a s i l y observable area of a l a r g e number cf f l o w e r s . T y p i c a l l y , a f r e s h o b s e r v a t i o n patch was chosen once a week. Each morning, before o b s e r v a t i o n s were made, each f l c w e r i n a patch r e c e i v e d a numbered t a g , i t s androecium diameter was measured and a record of i t s general c o n d i t i o n was made. Since bumblebees are very p e r c e p t i v e of new o b j e c t s i n t h e i r environment, simple tags were c o n s t r u c t e d out of masking tape i n an e f f o r t to avoid c o l o r e d ribbons which may have been o v e r l y a t t r a c t i v e to bees, a fey o b s e r v a t i o n s made on untagged patches confirmed the b e l i e f t h a t the tags themselves were not a t t r a c t i n g bees i n t o tagged patches. During 10 minute s e s s i o n s the number of bees e n t e r i n g a patch was noted, and f o r each bee i t was recorded which f l o w e r s were i n v e s t i g a t e d and which f l c w e r s were a c t u a l l y u t i l i z e d . A bee "foraged" i f i t a c t u a l l y landed upon a f l o w e r . Any d e v i a t i o n i n f l i g h t towards a flower which was not then landed upon was de f i n e d as " i n v e s t i g a t e d " . The r a t i o used i n the f o l l o w i n g a n a l y s e s was c a l c u l a t e d by d i v i d i n g the t o t a l number of f l o w e r s 72 used by a l l the bses e n t e r i n g the patch d u r i n g a s e s s i o n by the t o t a l number of f l o w e r s i n v e s t i g a t e d . The o b s e r v a t i o n of a simple change i n diameters used by the bees would not be c o n v i n c i n g , s i n c e t h i s c ould be due to a change i n androecium diameters of flowers present. For t h i s reason, the r a t i o , average androecium diameter used/average androecium diameter present, was i n v e s t i g a t e d . As was done i n p r o d u c t i v i t y s t u d i e s , sunshine l e v e l s d u r i n g the days of t h i s study were c o n t i n u o u s l y monitored, and r e l a t i v e humidity was measured 2-4 times a day. Temperature was a l s o recorded once an hour while o b s e r v a t i o n s were being conducted. L e v e l s of nectar standing crop a v a i l a b l e were measured a t v a r i o u s times of day throughout the season. 10 f l o w e r s were i n c l u d e d i n each s t a n d i n g c r o p sample, each flower being drained of n e c t a r present using f i r s t a 25 u l m i c r o p i p e t t e f o l l o w e d by a 10 u l m i c r o p i p e t t e . Each volume was analyzed f o r % sugar with a hand r e f r a c t o m e t e r . C a l o r i e s of n e c t a r present c o u l d then be c a l c u l a t e d using values of volume and % sugar, as d e s c r i b e d i n the p r e v i o u s c h a p t e r . Cm) R e s u l t s There was a s i g n i f i c a n t p o s i t i v e r e l a t i o n s h i p between p r o d u c t i v i t y and nectar s t a n d i n g crop over the season (r=.4481, p<.00 1). As the season progressed, the standing c r o p f e l l d r a m a t i c a l l y ( F i g . 16, r=-.4477, p<.001), and s e a s o n a l l y , s t a n d i n g crop decreased as r e l a t i v e humidity decreased and decreased with i n c r e a s e d sunshine l e v e l s (r=.2024, p<.001 and F i g . 1 6 : S c a t t e r p l o t of n e c t a r s t a n d i n g crop ( c a l o r i e s / f l o w e r ) i n salmonberry f l o w e r s and date. 7k C a l o r i e s / F l o w e r 1 5 0 . 0 0 T 1 2 0 . 0 0 + 9 0 . 0 0 f *x 6 0 . 0 0 |x x , x 3 0 . 0 0 0 . 0 0 May 8 x x X X cX X xx x v$ *** Xx Xx X X X X X v x x x K x x*„ -t- May 20 X X X x x X |X X 2 xHx X X X xx x xx*; x^X y S X X Xv X 8 r = - . i | l i 7 7 p < . 0 0 1 n = 9 0 2 Jifi ftxxx nipt U*x*— ax- June 1 June 1 3 D a t e June 2 5 J u l y 7 75 r=-. 1525, p<« 001)- F i g . 17 presents the r e s i d u a l s of the r e g r e s s i o n c f standing crop on date p l o t t e d a g a i n s t p r o d u c t i v i t y . - Independent of date, as flower nectar p r o d u c t i v i t y i n c r e a s e d t h e r e was a corresponding i n c r e a s e i n n e c t a r standing crop (r=„2955, p<.001). A stepwise r e g r e s s i o n model of numbers of bee f o r a g e r s per 10 minutes per flower ("bee d e n s i t y " ) throughout the season i n c l u d e s the f o l l o w i n g v a r i a b l e s as b e i n y s i g n i f i c a n t : date, sunshine l e v e l s and the s t a n d i n g crop of nectar i n nearby f l o w e r s (Table V I ) , the s t a n d i n g crop v a l u e s r e p r e s e n t i n g the averages of each group of 10 f l o w e r s sampled. These v a r i a b l e s t o g e t h e r accounted f o r approximately 54% of the v a r i a t i o n i n bee d e n s i t y . Date alone accounts f o r by f a r the majority of v a r i a t i o n (45%), and a scattergram of bee d e n s i t y vs. date i s provided i n F i g . 18 (r=.6585, p<.001). "Throughout the season" i s d e f i n e d here as i n c l u d i n g the dates May 3 to June 8. C o r r e l a t i o n s made which i n c l u d e dates a f t e r June 8 are not so s t r o n g as when these dates are excluded, t h i s being due, I'm convinced, to the blooming at t h i s time of other p l a n t s p e c i e s with f l e v e r s which' are a t t r a c t i v e to the bees. A c l o s e examination of the graph o£ bee d e n s i t y and dates through June 28 ( F i g . 19) show a p o i n t , June 8, a f t e r which the bees decreased i n number. T h i s was the date when patches of blueberry (Vaccinium spp.) and t h i m b l e b e r r y (Bubus p a r y i f l o r u s ) were beginning to blcom i n the r e s e a r c h area, s p e c i e s h i g h l y a t t r a c t i v e to bumblebees. From F i g . 20 one could conclude that as sunshine l e v e l s i n c r e a s e d through the season, bee d e n s i t y i n c r e a s e d as w e l l P i g . 17! S c a t t e r p l o t o f n e c t a r s t a n d i n g crop ( c a l o r i e s / f l o w e r ) and p r o d u c t i v i t y ( c a l o r i e s / h o u r ) i n nearby salmonberry f l o w e r s , independent o f seasonal e f f e c t s . Residuals of r e g r e s s i o n of c a l o r i e s / f l o w e r on date 125.00 j 95.00 | r= . 2 9 5 5 p<.001 n= 8 3 l t 65.00 x x 35.00 { X X X x x - 2 5 . 0 0 X M x x 8 x X 8 X X X X X X X; *• x; x' 8« * x X X x. XX kx x % * X* X X X X X 0 . 0 0 0 . 5 0 1.00 1.50 C a l o r i e s / H o u r 7 8 T a b l e V I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e . I n n u m b e r o f b e e s / 1 0 m i n x f l o w e r ( " b e e d e n s i t y " ; . a ) V a r i a b l e s s e l e c t e d f o r t h e m o d e l . b ) V a r i a b l e s n o t s e l e c t e d . c ) S t e p s i n m o d e l c o n s t r u c t i o n . ANALYSIS AT STEP 4 FOR 53.V53 N= 404 OUT OF 561 SOURCE REGP ESSION ERROR TOTAL DF 4 399 403 SUM OF SORS MEAN SQUARE 1.51C2 1.2675 2.7777 .37754 .31768 F- STAT 118.64 SIGNIF .OOJO MULTIPLE R= .73734 R-SQR= .54367 SE= .56363 -1 VARIABLE PARTIAL COEFFICIENT STO ERROR T-STAT SIGNIF CON STANT 1 .VI 4. V4 24.V24 31.V31 .26270 . 18903 .21944 . 17084 .99C94 . 162 69 .11496 -.42333 -.11077 -1 -2 -1 .22835 .29914 -2 .29898 -3 .94223 -1 .31981 -2 4.3396 5.4384 3.8452 -4.4929 -3.4635 .OOJO .0000 • OCJ 1 .OCOO .0006 date sunshine In date In standing crop REMAINING PARTIAL SIGNIF 3. V3 -.02705 .5896 hours a f t e r sunrise 5. V5 , .08557 .0874 temperature 6.V6 .00754 .3805 r e l . humidity 8. V8 .09267 .0641 standing crop 26.V26 -.02606 . 6033 In hours after sunrls,e 27.V27 .02483 .6206 In sunshine 28.V23 .06034 .1086 In temperature 2 9.V29 .00718 .8862 In r e l . humidity REGRESSION OF 53.V53 USING FORWARO SELECTION STEP R-SOR STO ERROR # VAR VARIABLE 1 .45441 .61399 -1 1 1.V1 2 .51367 .58041 -1 2 24.V24 3 .52995 .57132 -1 3 4.V4 4 .54367 .56363 -1 4 31.V31 IN IN IN IN PARTIAL SIGNIF .6 7410 -.32956 .18299 -. 17084 .0000 .0000 .0002 .0 006 S c a t t e r p l o t o f number o f b e e s / 1 0 min x f l w (bee d e n s i t y ) and date. 8 1 l n ( 1 . 0 + • # b e e s / l O m i n x f l o w e r ) 0 . 5 0 O.I4.O r - - . 6 5 8 5 p < . 0 0 1 n - - 5 6 l X X 0 . 3 0 X X X X x x x x 0 . 2 0 J x x x x X X X X 0 . 1 0 i 0 . 0 0 x x x x x y x X * x x X X X X X X' X ff- " X X X X X X X x x x x X X X X X X X X X x x X X X-X K ' t - ' X X X-K X 1- X X May 2 May 1 0 May 1 8 May 26 June 3 June D a t e 82 F i g . 1 9 ! S c a t t e r p l o t o f number of bees/10 min x f l w (bee d e n s i t y ) and date, i n c l u d i n g data gathered throughout the e n t i r e salmonberry season. 8 3 l n ( l , 0 +• #bees/lO min x flo w e r ) 0 . 5 0 T o.ko { 0 . 3 0 f 0 . 2 0 0 . 1 0 f r = . l i 3 6 7 p ^ . 0 0 1 n - - 8 0 7 x * x XX 5 x xxx $$x 0 . 0 0 k* WH<^ ~x X xxxx X xxx xxxx xxxx x x x X X X XX X X XX x x x x x x x x X x X XX XX XX X X XX XX XX XX XX XX feXXX' X X X X — I XXXXX——*-*-<—••—xxxx x-̂ x-x xxx- May 3 May l£ May 2 7 June 8 June 2 0 J u l y 2 Date F i g . 20: E f f e c t o f sunshine l e v e l s on number o f bees/10 min x f l w (bee d e n s i t y ) . 85 ln(1.0+#bees/lO min x flower) O.ILOT o .35t 0.30 0.25 0.20 0.15 0.10 0 .05 + 0.00 X X X X r = . i i l i . 9 3 p-c.001 n= i i 9 1 x x X x x X X X X X X x x x x X X X $ X X X X x x X X x x x x . X X X x X X X x x x X X x x x ~ X X X X X X X X X X X X X X x x x x x x x x X X X X X X X 5 x x x X X X X X X x x x X X X X X X x x x x x g X X XX X ' " X X £ x X x x x x S x x x X X 5 X x X"X X X X X X i X X X-X XI x- X X X X X x a X X x x x +- 0 16 2li 32 LLO Sunshine Lev e l s 8 6 (r=„4493, p<«001) i There i s , however, a g r e a t d e a l o f v a r i a b i l i t y i n the data, a c t i v i t y values were o f t e n q u i t e low a t even the higher ranges of sunshine l e v e l s . Although the l e v e l of sunshine i s i n c l u d e d i n the stepwise r e g r e s s i o n model as p r o v i d i n g s i g n i f i c a n t e x p l a n a t o r y value independent cf date e f f e c t s , i t s c o n t r i b u t i o n i s not very g r e a t . S e a s o n a l l y , bee d e n s i t y i n c r e a s e d as r e l a t i v e humidity d e c l i n e d (r=-. 1174, p<»0 1). To view t h i s r e l a t i o n s h i p independently of date, the c o r r e l a t i o n between the r e s i d u a l s of a r e g r e s s i o n of bee d e n s i t y on date and r e l a t i v e humidity values was examined. The c o r r e l a t i o n (r=-. 1266) i s s i g n i f i c a n t with p<. 01. Temperature c o r r e l a t e s p o s i t i v e l y with bee d e n s i t y throughout the season (r=.2990, p<. 00 1), but i s not c o r r e l a t e d s i g n i f i c a n t l y once date e f f e c t s are removed (r=.0545, p>.05). I would conclude from these r e s u l t s t h a t as sunshine and temperature l e v e l s i n c r e a s e d and r e l a t i v e humidity decreased d u r i n g the course of the season, t h e r e was a strong i n c r e a s e i n bee d e n s i t y , yet with the s e a s o n a l e f f e c t removed there was only a very weak tendency f o r an i n c r e a s e i n f o r a g e r numbers with these environmental f a c t o r s . As bee d e n s i t y i n c r e a s e d throughout the season nectar s t a n d i n g crop d e c l i n e d (r=-.5731 , p<.001). Nectar s t a n d i n g c r o p (average c a l o r i e s / f l o w e r per sample of 10 flowers) i s included i n the r e g r e s s i o n model as e x p l a i n i n g a s i g n i f i c a n t percentage of the v a r i a t i o n i n bee d e n s i t y independently of date (Table V I ) . As i s the case f o r sunshine l e v e l s , however, the percentage i t does e x p l a i n i s very low, the c o r r e l a t i o n c o e f f i c i e n t between the r e s i d u a l s of r e g r e s s i o n of bee numbers on date and s t a n d i n g crop being -.0973 (p<.05). A n a l y s i s on data 87 gathered only before noon shows s t a n d i n g crop to be more h i g h l y c o r r e l a t e d with bee numbers, again , independent of date ( F i g . 21, r=-.2185, p<«001).. I t i s i n t e r e s t i n g t o note t h a t f l o w e r d e n s i t y had a very s t r o n g r e l a t i o n s h i p with bee d e n s i t y throughout the season (r= ~.HH97, p<.001), yet when the e f f e c t of date was removed there was not a s i g n i f i c a n t c o r r e l a t i o n between bee d e n s i t y and flower d e n s i t y (r=-.0053). I t i s a l s o i n t e r e s t i n g to n o t i c e that on May 28 there was a l a r g e surge i n bee d e n s i t y , j u s t as t h e r e was a d r a s t i c decrease i n nectar s t a n d i n g crop a v a i l a b l e per flower ( F i g s . 16 and 18). The r e g r e s s i o n model c o n s t r u c t e d f o r the v a r i a o l e , number of flowers used/number of f l o w e r s i n v e s t i g a t e d , (•*# used/* inv") i s presented i n Table V I I . V a r i a b l e s chosen as s i g n i f i c a n t account f o r on l y 13X of v a r i a b i l i t y i n the data, however, many r e l a t i o n s h i p s e x i s t which ate of i n t e r e s t . # used/# inv i n c r e a s e d s i g n i f i c a n t l y as the season progressed (r=.1973, p<.001), yet t h i s s i g n i f i c a n c e i s most l i k e l y due to the great number of data p o i n t s i n v o l v e d (n=316, F i g . 22). With date e f f e c t s removed, there i s no r e i a t i o a s h i p between sunshine l e v e l s and # used/* i n v , nor between bee d e n s i t y and the l a t t e r v a r i a b l e . Independent of date, there i s a s i g n i f i c a n t negative c o r r e l a t i o n between # used/# inv and temperature ( F i g . 23, r= ".2327, p<.001), and a r a t h e r weak, p o s i t i v e c o r r e l a t i o n with r e l a t i v e humidity (r=.1279, p<.05). Apparently, t h e r e was a d e c l i n e i n # used/# inv as temperature i n c r e a s e d and the a i r became d r i e r d u r i n g the course of a day. Though # used/# i n v i n c r e a s e d with d e c l i n i n g s t a n d i n g crop over the season (r= 88 P i g . 21: S c a t t e r p l o t o f n e c t a r s t a n d i n g crop ( c a l o r i e s / f l o w e r ) and number o f bees/10 min x f l w (bee d e n s i t y ) , independent of seasonal e f f e c t s . Includes data gathered b e f o r e noon. 8 9 R e s i d u a l s of r e g r e s s i o n o f l n ( 1 . 0 + # b e e s / l 0 min x f l o w e r ) on date 0 . 3 0 T 0 . 2 0 + 0 . 1 0 0 . 0 0 - 0 . 1 0 & - 0 . 2 0 6C X fee X X X X 0 . 0 0 r = - . 2 l 8 5 p < . 0 1 n = l i i 5 - X X X X X XX 1 0 . 0 0 X X x x x x X X X X X X X 2 0 . 0 0 3 0 . 0 0 iiO.OO C a l o r i e s / f l o w e r 5 0 . 0 0 90 T a b l e V I I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n n u m b e r o f f l o w e r s u s e d / n u m b e r o f f l o x ^ e r s i n v e s t i g a t e d ( " # u s e d / # i n v " ) . a ) V a r i a b l e s s e l e c t e d f o r t h e m o d e l . b ) V a r i a b l e s n o t s e l e c t e d . c ) S t e p s i n m o d e l c o n s t r u c t i o n . ANALYSIS AT STEP 3 FOR 35.V35 N= 249 OUT OF 561 SOURCE REGRESS I ON ERROR TOTAL MULTIPLE R= DF 3 245 248 SUM OF SORS MEAN SQUARE 4.7181 32.534 37.252 1.57 27 . 13279 ,35589 R-S0R= .12665 SE= .36440 F-STAT 11.844 SIGN IF .0000 VARIABLE PARTIAL COEFFICIENT STO ERROR T-STAT SIGNIF CONSTANT -28.660 14.326 -2.0035 .04b5 5. V5 -.14673 -. 18727 .80657.-1 -2.3217 .0211 28.V28 .13497 9.9456 4.6646 2.1321 .0340 3 1.V31 -.26471 -.66069 -1 .15377 -1 -4.2966 : .0000 REMAINING PARTIAL SIGNIF .1. VI -.03033 .6359 date 3.V3 -. 10093 .1141 hours after sunrise 4 . V4 .01773 .78 20 sunshine 6. V6 -.03535 .5811 r e l . humidity 8. V8 -.02197 . 7317 standing crop 24.V24 -.C8967 ' .1609 In date 26.V26 -.0 70 60 . 2700 In hours after sunrise 27.V27 .0 54 74 .3927 In sunshine 29.V29 -.03057 .6333 In r e l . humidity 52.V52 -.09057 .1567 bee density 53.V53 -.09292 .1462 In bee density temperature In temperature In standing crop REGRESSION OF 35.V35 USING FORWARD SELECTION STEP R-SQR STD ERROR it VAR VARIABLE 1 .05920 2 .11045 3 .12665 .37668 .36702 .36440 31 .V31 5. V5 28.V28 IN IN I N PARTIAL SIGNIF -.24331 -.23340 .13497 .0001 .0002 .0340 92 F i g . 22: S c a t t e r p l o t o f number o f f l o w e r s used p e r number o f flowers i n v e s t i g a t e d (# used/# i n v ) and date. 93 l n ( # f l w s used/#flws i n v e s t i g a t e d + 1 . 0 ) 2 . 0 0 1.75 T 1.50 i 1.25 \ 1 . 0 0 o .75 o .5o 0.25 0 . 0 0 * X X X x x r = . 1 9 7 3 p < . 0 0 1 n = 3 l 6 X X X X X X X X X X X X X X X X X X X X X X X X X X X x x » X X x x X X X X ~ x x x x X x x x x X X X X X X X X X X X X X x x X X X X x 8 „ X X X X X x X x X * x X X X X S i x X X " I * X X X X x X X * x x x X * x x x X x X x x x X x X X X X X X X X X x x X x X X x x X X v X X * X x x x x " x x X X X x * & S x x X x x x May 3 May 1 1 May 1 9 May 2 7 Date June ]± June 1 2 9k P i g . 2 3 : S c a t t e r p l o t o f temperature and the number o f flowers used/number of flowers i n v e s t i g a t e d (# used/rT i n v ) , independent of seasonal e f f e c t s . 95 R e s i d u a l s o f r e g r e s s i o n o f ln( # f l w s used/#flws i n v e s t i g a t e d +• 1 . 0 ) on date 1 . 2 0 T 0 . 8 0 o.iio 4 0 . 0 0 -o.iio 4 - 0 . 8 0 X X x x x ~ x r = - . 2 3 2 7 p < . 0 0 1 n = 3 l 6 x X X x x XX x X X X XX * X X X X xxx x X X X X jX X u X X X x x * x x X X * * X X X x x He x x X x X XX X X X * x * . X X X X XX XX X X X X )C< x x x X X x x x x x x ^ x X X x x x x x x v x X * x x * X x x x x xx x xx X X X X * * B X x x x * X X * X X X X X X< X X x x x * x^ >x X X x xXx x x><x X  y XX \ x x x v x x x x x x x x X X XX X X X X x — 1 ^ 5 . 0 5o.o 55 . 0 6 0 . 0 65 . 0 7 0 . 0 Temperature (°F) 9 6 -2928, p<.001), there was not a s i g n i f i c a n t r e l a t i o n s h i p between the two v a r i a b l e s independent of seasonal e f f e c t s (r=-.1051, p>.05) . S e v e r a l of these r e l a t i o n s h i p s are s t r o n g e r d u r i n g the morning hours, yet, without seasonal e f f e c t s , the same patterns are e v i d e n t . Temperature and # used/# i n v are s t i l l n e g a t i v e l y c o r r e l a t e d {r--.2479, p<.05), while the l a t t e r v a r i a b l e i s n e g a t i v e l y c o r r e l a t e d with bee d e n s i t y (r=-. 1670), though the . r e l a t i o n s h i p i s not s i g n i f i c a n t (p>.05) . These c o r r e l a t i o n s seem to i n d i c a t e t h a t bee d e n s i t y and # used/# inv were a c t i n g i n o p p o s i t i o n , though t h i s c o n c l u s i o n must remain extremely t e n t a t i v e due t o the l a c k of c o n s i s t e n t r e l a t i o n s h i p s between the v a r i a b l e s j u s t examined. I t i s i n t e r e s t i n g to note that the v a r i a b l e , # f l o w e r s used/bee, d i d i n c r e a s e as the season progressed and the l e v e l s of s t a n d i n g crop f e l l ( F i g . 24, r=.5733, p<.001) . The r e g r e s s i o n model f o r average androecium diameter used/average androecium diameter present ("diam used/diam present") i s shewn i n Table V I I I , where sunshine, temperature and n e c t a r s t a n d i n g crop were chosen as s i g n i f i c a n t v a r i a b l e s , t o g e t h e r accounting f o r 39% of v a r i a b i l i t y i n a l l data, and 49% of v a r i a b i l i t y i n data gathered only before noon. For a l l data, diair used/diam present i n c r e a s e d as the season progressed ( F i g . 25, r=.2960, p<»001). Diam used/diam present i n c r e a s e d with i n c r e a s i n g bee d e n s i t y (r=- 2835, p<.001), and i n c r e a s e d with d e c l i n i n g s t a n d i n g crop l e v e l s (r=-.5338, p<.001). Independent of s e a s o n a l e f f e c t s , there was no r e l a t i o n s h i p between bee d e n s i t y and diam used/diam present (r=.0662, p>.05) , 97 F i g . 2li: S c a t t e r p l o t o f number of f l o w e r s used/bee and date. 98 l n ( 2 . 0 + #flowers used/bee) 2.30 2.00. 1.70 1.14-0 4 I . I O 4 0 . 8 0 0 . 5 0 * X May 3 r=.5733 p<r.001 n=555 x x x x x x x x x x x x x xxxx xxxx X X X X X X X X X X X X X X x x x x X *. X X X X X x x x X X X X * X X X X X X x x x x x £ x x x x x x X X B X X X * x x x x x X X X X X X X X x x x x x x x x x x x x x x x x X x X X x x x x x g I X X X X X X x x x x X X X X X x x X X X X X X May 11 May 19 May 27 Date June [j. June 12 99 T a b l e V I I I : S t e p w i s e r e g r e s s i o n m o d e l b u i l t f o r t h e v a r i a b l e , I n a v e r a g e a n d r o e c i u m d i a m e t e r u s e d / a v e r a g e a n d r o e c i u m d i a m e t e r p r e s e n t . a ) V a r i a b l e s s e l e c t e d f o r t h e m o d e l . b ) V a r i a b l e s n o t s e l e c t e d . c ) S t e p s i n m o d e l c o n s t r u c t i o n . ANALYSIS AT STEP 4 FOR 5C3.V50 N= 226 OUT OF 561 SOURCE REGRESS I ON ERROR TOTAL DF 4 221 225 SUM OF SQRS ' MEAN SQUARE 3.5465 5.4516 8.9981 .88662 .24668 F-STAT 35.942 S IGNIF .COCO MULTIPLE R= .62780 R-SQR= ,39414 SE= .15706 VAR IABLE PARTIAL COEFFICIENT STD ERROR T-STAT SIGNIF CONSTANT 4. V4 5. V5 23.V26 31.V31 . 13908 -. 19362 . 17714 -.56418 •15.922 .26208 -2 -.10544 5.5682 -.73562 -1 6. 3934 .12553 -2 .35939 -1 2.0811 .72417 -2 -2.4904 2.0878 -2.9338 2.6756 -10.158 .0135 .0380 .003 7 .0080 .OQuO sunshine temperature In temperature In standing crop REMAINING PARTIAL SIGNIF 1. VI -.06954 .3023 date 3.V3 -.06319 . 3487 hours a f t e r sunrise • 6.V6 -.109 41 .1040 r e l . humidity 8. V8 .08864 .1882 standing crop 24.V24 -.06561 .3305 In date 26.V26 -.05700 .3980 In hours after sunrise 2 7. V27 .01107 . 8697 In sunrise 29.V29 -.10781 . 1092 In r e l . humidity 52.V52 .01860 .7829 bee density 53.V53 .02581 .7022 In bee density 12.V12 .03896 . .5636 # used/# inv 35. V35 .07613 .2537 In # used/r" inv REGRESSION OF 50.V50 USING FORWARD SELECTION STEP R-SOR STD ERROR # VAR VAR IABLE PARTIAL SIGNIF 1 .31453 . 16594 1 31.V31 I N -.56083 .0000 2 .36126 .16054 2 5. V5 I N -.26111 .0001 3 .38219 .15824 3 28.V28 . IN . 18099 .0066 4 .39414 .15706 4 4. V4 IN ,1393b .C-380 1 0 1 F i g . 2 5 : S c a t t e r p l o t of average androecium diameters used/average diameters p r e s e n t and date. 1 0 2 l n ( d l a m used/diam present-I- 1.0 ) 1.20 1.00 I o.8o 4 0 . 6 0 4 O.ILO 0.20 May 3 r=,2960 p<r.001 n=278 x x x x x x x X X X X X a x X x x a X X X x M x * X X X £ * X X X » X .X x x M x X x x x X x x X X * X X * x x x X x X X May 11 May 19 May 2 7 June Ix. Date June 12 1 0 3 but the l a t t e r v a r i a b l e d i d show an i n c r e a s e with d e c l i n i n g s t a n d i n g crop l e v e l s ( F i g . 26, r=-.3190, p<. 00 1). Data c o l l e c t e d b efore noon s t i l l chos diam used/diam present to be n e g a t i v e l y c o r r e l a t e d with standing crop (r=-.2998, p<.0 1), and a weak, p o s i t i v e r e l a t i o n s h i p e x i s t s between the former v a r i a b l e and bee d e n s i t y (r=.2222, p<.052). Thus, as bee d e n s i t y i n c r e a s e d and n e c t a r s t a n d i n g crop l e v e l s decreased, the bees for a g e d from i n c r e a s i n g l y l a r g e r diameter f l o w e r s r e l a t i v e to the s i z e of f l c w e r s p r e s e n t . D « ) D i s c u s s i o n From the data j u s t presented i t seems c l e a r t h a t B. s i t k e n s i s do modify f o r a g i n g behavior to meet changing food resource c o n d i t i o n s throughout each day d u r i n g the salmonberry f l o w e r i n g season, t h i s behavior being the average androecium diameter of f l o w e r s used by the bees during a s e s s i o n . Ihe data f u r t h e r i n d i c a t e that the r a t i o of the average number of f l o w e r s foraged by the bumblebees during an o o s e r v a t i o n s e s s i o n to the average number of f l o w e r s i n v e s t i g a t e d may a l s o be changing as f o c d c o n d i t i o n s vary. When nectar r e s o u r c e s are at high l e v e l s r e l a t i v e l y few bumblebees forage per f l o w e r , t h i s s i t u a t i o n o c c u r r i n g during the e a r l y morning hours of a t y p i c a l day when p r o d u c t i v i t y i s h i g h e s t . Standing crop l e v e l s are a l s o high e a r l y i n the f l o w e r i n g season as opposed to l a t e r days, while number o f f o r a g e r s i s r a t h e r low e a r l y i n the season. During each day, as bee numbers b u i l d , the standing crop i n each flower decreases, J.Uii F i g . 2 6 : S c a t t e r plot, of n e c t a r s t a n d i n g crop ( c a l o r i e s / f l o w e r ) and androecium diameter used/androecium diameter p r e s e n t , independent of seasonal e f f e c t s . 1 0 5 R e s i d u a l s o f r e g r e s s i o n o f l n ( d i a m u s e d / d i a m p r e s e n t 4-1.0 ) o n d a t e 0.60 O . i j . 0 Jx 0 . 2 0 x x o.oo A - 0 . 2 0 I - O . l i O $ 0 . 0 0 x x X X 1 0 . 0 0 x* X x< X X X X X X X X X r = - . 3 1 9 Q p < . 0 0 1 n=269 2 0 . 0 0 3 0 c 0 0 C a l o r i e s / f l o w e r I L 0 8 0 0 5 0 . 0 0 106 presumably due to the removal of the n e c t a r by the i n s e c t s . P r e v i o u s a u t h o r s have found t h a t bee f o r a g e r numbers reach a peak about midmoming, or 10-11:00 (Free, 1955; A l f o r d , 1975), and Corbet (1978) d e s c r i b e s t h i s same n e g a t i v e r e l a t i o n s h i p between bee numbers and c a l o r i e s a v a i l a b l e , Nectar i s not r e p l a c e d s i n c e f l o w e r p r o d u c t i v i t y reaches a peak i n the e a r l y morning and s t e a d i l y decreases as the day proceeds (Chapter II) . S i m i l a r l y , f o r a g e r numbers s t e a d i l y b u i l d as the summer proceeds; t h i s , and the f a c t t h a t p r o d u c t i v i t y peaks i n e a r l y summer and then g r a d u a l l y d e c l i n e s (Chapter I I ) , keeps standing crop l e v e l s g u i t e low l a t e r i n the season. A f t e r May 27, the numbers of salmonberry f l o w e r s decreased d r a s t i c a l l y , a b r u p t l y i n c r e a s i n g the numbers of bee f o r a g e r s pec f l o w e r . The i n c r e a s e d number of f o r a g e r s seem to have suddenly c u t s t a n d i n g crop l e v e l s to a very s m a l l f r a c t i o n of p r e v i o u s l e v e l s , Corbet (1978) argues that i n s e c t s may f o r a g e f o r f l o r a l n e c t a r j u s t at the time of day when the i n c r e a s i n g vapor pressure d e f i c i t evaporates the l i q u i d to the c o n c e n t r a t i o n a p p r o p r i a t e f o r the i n s e c t ' s c a l o r i c demands. Standing crop data gathered d u r i n g t h i s study show that the minimum c o n c e n t r a t i o n v a l u e s f o r most days do not reach e x c e s s i v e l y low l e v e l s . The lowest c o n c e n t r a t i o n values recorded during each day e a r l y i n the season averaged approximately 18-2054, with d a i l y mean values being around 21-2755. Honeybees i n C a l i f o r n i a i g n o r e orange blcssom n e c t a r e a r l y i n the morning, when i t c o n t a i n s o n l y 16X sugar. They switch to orange nectar i n the afternoon when the n e c t a r c o n c e n t r a t e s to 30% sugar through e v a p o r a t i o n ( V a n s e l l , Watkins and Bishop, 1942). Jamieson and A u s t i n (1956) found t h a t 107 honeybees are abl e t o d i s t i n g u i s h between sucrose s o l u t i o n s of 40 and 50%. The d i f f e r e n c e s between salmonberry nectar c o n c e n t r a t i o n s i n the morning and midsscrning do not seem great enough to support Corbet's b e l i e f . The f a c t t h a t bumblebee f o r a g e r s are not so a c t i v e i n the e a r l y morning i n d i c a t e s , I b e l i e v e , t h a t f a c t o r s other than c a l o r i e s a v a i l a b l e are determining i n s e c t f o r a g i n g behavior, the obvious c a n d i d a t e s being weather v a r i a b l e s . The c a l o r i c c o s t o f f l i g h t i s decreased a t r e l a t i v e l y high temperatures { H e i n r i c h , 1975a). Thus I f e e l t h a t , i n t h i s study, butthlebee f o r a g e r s i n c r e a s e i n numbers as the day proceeds due t o i n c r e a s i n g a i r temperatures, and not due p r i m a r i l y t o any pr o p e r t y of the nectar rewards alone. According to t h i s e x p l a n a t i o n , bees must make f o r a g i n g d e c i s i o n s based on opposing demands placed upon them by weather c o n d i t i o n s and by flower p r o d u c t i v i t y p a t t e r n s . While Corbet's main p o i n t t h a t d a i l y p a t t e r n s of f l o r a l rewards must be i n v e s t i g a t e d before p o l l i n a t o r a c t i v i t y can be adequately understood i s c e r t a i n l y a p p r e c i a t e d , t r y i n g to e x p l a i n bumblebee forager numbers simply on the b a s i s of f l o r a l rewards may be misleading. I t i s reasonable to c l a i m that the decrease i n standing crop through the day i s due to i n c r e a s i n g numbers of ne c t a r f o r a g e r s and decreasing n e c t a r p r o d u c t i v i t y , yet i t i s d i f f i c u l t to know i f there i s any i n c r e a s e i n fo r a g e r numbers due, i n t u r n , to the low l e v e l s of s t a n d i n g crop. I t i s b e l i e v e d t h a t bumblebee c o l o n i e s send out g r e a t e r numbers of f o r a g e r s when food resources are sca r c e as opposed to p l e n t i f u l times ahen s u r p l u s n e c t a r i s s t o r e d i n the hive ( A l f o r d , 1975). Thus t h i s 1 0 8 e f f e c t c o u l d have i n f l u e n c e d the i n c r e a s e i n f o r a g e r numbers observed through the day i n t h i s study. As the season advances, p r o d u c t i v i t y i n salmonberry flowers d e c l i n e s (chapter I I ) , s t a n d i n g crop l e v e l s a l s o d e c l i n e , yet bumblebee f o r a g e r numbers c o n t i n u a l l y i n c r e a s e . Since bumblebee c o l o n i e s do i n c r e a s e i n numbers throughout the e a r l y summer, i t i s again d i f f i c u l t to know whether the seasonal i n c r e a s e i n f o r a g e r numbers observed i s a response to the d e c r e a s i n g l e v e l s of n ectar a v a i l a b l e , or due to the seasonal b u i l d u p i n colony numbers, or both. So t h i s q u e s t i o n c o u l d be e x p l o r e d i n more d e t a i l , an attempt was made t o e n t i c e emerging queens to use b u r i e d nest boxes- U n f o r t u n a t e l y , t h i s attempt met with no succe s s . I t does seem t h a t s e a s o n a l l y , as i s the case f o r each day, bumblebees do not forage d u r i n g the p e r i o d s when l e v e l s o f n e c t a r o f f e r e d are g r e a t e s t . T h i s i s , a g a i n , probably not due t o i n t r i n s i c p r o p e r t i e s of the n e c t a r , but i s due to the f a c t t h a t queens do not emerge from t h e i r winter t o r p o r to found c o l o n i e s u n t i l c l i m a t i c c o n d i t i o n s reach adequate l e v e l s , and, a f t e r colony i n i t i a t i o n , i t takes a c e r t a i n amount of time to b u i l d up colony numbers. Thus, n e i t h e r d a i l y nor s e a s o n a l l y are the bees a b l e t o take advantage of peaks i n nectar p r o d u c t i v i t y ( c a l / h r ) . As f o r a g e r numbers i n c r e a s e and standing crop l e v e l s decrease d a i l y and s e a s o n a l l y , bees approach and u t i l i z e f l o w e r s with a wider spectrum of androecium diameters, whereas when numbers are low they forage from f l o w e r s with s m a l l e r androecium diameters, (or, they use younger f l o w e r s ) . T h i s adds weight t o the c o n c l u s i o n d i s c u s s e d i n the pre v i o u s chapter t h a t nectar p r o d u c t i v i t y i s g r e a t e s t i n young f l o w e r s and g r a d u a l l y f a l l s as 109 the f l o w e r s age. The data i n d i c a t e t h a t , as f o r a g e r numbers i n c r e a s e , (and nectar l e v e l s d e c r e a s e ) , the bees may be a c t u a l l y u t i l i z i n g a s m a l l e r f r a c t i o n of the f l o w e r s that they approach. T h i s f i n d i n g i s e x a c t l y opposite t o that p r e v i o u s l y p r e d i c t e d . That the a c t u a l number of f o r a g e r s c o r r e l a t e s with the l a t t e r behaviors does not, I b e l i e v e , i n d i c a t e t h a t i n c r e a s e d bee t r a f f i c i n the patch d i r e c t l y causes the bees t o a l t e r these b e h a v i o r s . Even on busier a f t e r n o o n s , a maximum of only 9 bees appeared per 10 minutes, and i t was extremely r a r e f o r any d i r e c t i n t e r a c t i o n s to occur between them. I t i s a l s o h i g h l y u n l i k e l y t h a t weather f a c t o r s d i r e c t l y i n f l u e n c e changes i n these b e h a v i o r s , s i n c e c o r r e l a t i o n s between these v a r i a b l e s are o f t e n not i m p r e s s i v e i f they e x i s t at a l l . The answer as to what d i r e c t l y causes changes i n # used/# i n v and diam used/diam present most l i k e l y l i e s i n the nectar s t a n d i n g crop a v a i l a b l e to the f o r a g e r s . C a l o r i e s / f l o w e r c o r r e l a t e s well with average diam used/average diam present, and i s chosen i n r e g r e s s i o n models f o r i t and f o r # used/# i n v . According to t h i s e x p l a n a t i o n , as bee d e n s i t y i n c r e a s e s , the nectar s t a n d i n g crop d e c l i n e s i n p r e f e r r e d f l o w e r s , which consequently i n f l u e n c e s the bees to d i v e r s i f y the fl o w e r ages they accept. They a l s o , a p p a r e n t l y , forage from an ever s m a l l e r f r a c t i o n of the flo w e r s they approach, p o s s i b l y because many more f l o w e r s become empty of f l o r a l rewards s u f f i c i e n t t o s u s t a i n bee usage. The p r e d i c t i o n made e a r l i e r , t h a t the bees should u t i l i z e more of the f l o w e r s they approach as nectar rewards d e c l i n e s t i l l makes sense as long as there i s enough reward i n the 110 f l o w e r s used t o al l o w bees to make even a small net energy p r o f i t . There presumably does e x i s t a l e v e l of nectar at which the bees can no lo n g e r a f f o r d t o forage upon c e r t a i n f l o w e r s , and i t i s at t h i s p o i n t that bees begin to again a v o i d many f l c w e r s they approach, as they d i d when resources were q u i t e p l e n t i f u l . Even though s t a n d i n g crop l e v e l s were monitored throughout t h i s study, p i p e t t e t e c h n i q u e s were f a r too crude to i n v e s t i g a t e t h i s nectar l e v e l at which the bees began to avoid u n p r o f i t a b l e f l o w e r s . Often bees c o u l d be observed f o r a g i n g from f l c w e r s I had p r e v i o u s l y "emptied" using p i p e t t e s . Thus I b e l i e v e t h i s p o i n t o f u n p r o f i t a b i l i t y l a y beyond my measurement c a p a b i l i t y . The f a c t t h a t # f l c w e r s used/bee i n c r e a s e s as the season progresses i n d i c a t e s that each i n d i v i d u a l bee i s working harder as standing crop c o n d i t i o n s d e c l i n e . T h i s h e l p s to e x p l a i n the o b s e r v a t i o n t h a t bumblebees take the time t o c a r e f u l l y i n v e s t i g a t e new o b j e c t s i n t h e i r environment during the e a r l y weeks of s p r i n g , while paying l i t t l e a t t e n t i o n t o thera l a t e r i n the summer,. I t i s a l s o i n t e r e s t i n g t h a t many o f the r e l a t i o n s h i p s p r e v i o u s l y d i s c u s s e d are more h i g h l y c o r r e l a t e d when ob s e r v a t i o n s made during only the morning hours a r e c o n s i d e r e d . Since i t i s l i k e l y that the bees have d e p l e t e d any s t o r e d food resources d u r i n g the n i g h t ( A l f o r d , 1975), each bee would presumably be s t r o n g l y motivated to gather food once the a i r temperature allows c o s t e f f i c i e n t f l i g h t . Each bee would forage i n approximately the same manner s i n c e each faces s i m i l a r food and weather c o n d i t i o n s . As the hours pass, however, each bee 111 accumulates d i f f e r e n t amounts of food, { l e v e l s of nectac s t a n d i n g crop being g u i t e heterogeneous), and so can d e v i a t e to a g r e a t e r extent from the f o r a g i n g behavior of other bees. By e a r l y a f t e r n o o n , t h e r e f o r e , d i f f e r e n c e s i n f o r a g i n g h i s t o r i e s of each bee lead to a g r e a t d e a l of v a r i a b i l i t y i n f o r a g i n g behavior. I t may be the case as w e l l t h a t , i n the a f t e r n o o n , n e c t a r standing crop l e v e l s are so low t h a t many bumblebees can no l o n g e r forage e f f i c i e n t l y r e g a r d l e s s o f the number of f l o w e r s they u t i l i z e . Thus they may r e s t f o r s e v e r a l hours or f o r the r e s t of the day. A l t e r n a t i v e l y , the bees c o u l d be s h i f t i n g t h e i r a c t i v i t i e s t c another p a r t of the f o r e s t where the rewards are more a t t r a c t i v e through the a f t e r n o o n , bumblebees being o f t e n h i g h l y mobile (Adrian Belshaw, p e r s o n a l communication). These e x p l a n a t i o n s would perhaps account f o r the f a c t t h a t even though sunshine l e v e l s are high, there are o f t e n very few bees observed f o r a g i n g . The f i n d i n g s here correspond n i c e l y with s t u d i e s by H e i n r i c h (1979a) and Hhitham (1977) on bumblebee f o r a g i n g behavior as i t s h i f t s i n r e l a t i o n t o food r e s o u r c e s . H e i n r i c h found t h a t , as food resources become s c a r c e through h i g h bumblebee c o m p e t i t i o n , bumblebees extend t h e i r f o r a g i n g a c t i v i t i e s to p l a n t s p e c i e s r a r e l y used when r e s o u r c e s are a t h i g h e r l e v e l s . Whitham found t h a t , as resources become s c a r c e , the bees a c t u a l l y forage from C h i l o p s i s i n a d i f f e r e n t manner than when times are good, i n c r e a s i n g l y u s i n g "groove n e c t a r " as w e l l as the p r e f e r r e d "pool n e c t a r " . The present study shows t h a t as food l e v e l s d e c l i n e bumblebees expand the range of a c c e p t a b l e flower " i n d i v i d u a l s " , i n c r e a s i n g l y u s i n g o l d e r 112 f l o w e r s which produce l e s s n e c t a r thaa p r e v i o u s l y p r e f e r r e d younger f l o w e r s . As shown i n the previous bumblebee s t u d i e s , bumblebees i n c r e a s i n g l y become " g e n e r a l i s t s " i n t h e i r f o r a g i n g a c t i v i t i e s , a r e s u l t c o n s i s t e n t with c u r r e n t e c o l o g i c a l theory (Pyke e t a l . , 1977). U n l i k e other s t u d i e s , however, no r e l a t i o n s h i p could be found i n t h i s study between numbers of bee f o r a g e r s and flower d e n s i t y . Haddington (1976) found f l o w e r d e n s i t y to be an e x c e l l e n t p r e d i c t o r of h a l i c t i d bee d e n s i t y , and Thomson (197b) found a s i m i l a r i n c r e a s e i n f l o w e r v i s i t o r s with an i n c r e a s e i n f l c a e r d e n s i t y . However, these s t u d i e s were conducted i n meadows, whereas the present study was conducted on f l o w e r s which grew along a road. A f t e r f o r a g i n g one flower, a bee i n a meadow should have a l a r g e r arc from which to choose another f l c w e r or patch of f l o w e r s than should a bee f o r a g i n g along a road. T h i s i s t r u e not only because salmonberry p l a n t s along a road occur i n a narrow width and the f l o w e r s are l o c a t e d predominantly on the o u t e r edges of p l a n t s , but a l s o because bumblebees tend t c forage at a r a t h e r c o n s t a n t h e i g h t above the ground, Thus, bees along a road need to pass through l e s s dense areas t o a r r i v e a t a f l o w e r - r i c h area. 1 1 3 I V . C O N C L U S I O N S In t h i s study the f o l l o w i n g r e s u l t s were obtained: 1 . ) there e x i s t s a s t r o n g c o r r e l a t i o n between the androecium diameter of salmonberry f l o w e r s and flo w e r age. 2. ) there e x i s t s high h e t e r o g e n e i t y among f l o w e r s i n nectar p r o d u c t i v i t y . Four out of ten f l o w e r s sampled s e c r e t e d nectar a t s i g n i f i c a n t l y higher r a t e s than the remaining s i x . 3. ) nec t a r p r o d u c t i v i t y i n salmonberry f l o w e r s d e c l i n e d as the f l o w e r i n g season progressed. P r o d u c t i v i t y was high when r e l a t i v e humidity was high and decreased as l e v e l s of sunshine i n c r e a s e d through the day and through the season. P r o d u c t i v i t y was h i g h e s t i n young f l o w e r s and d e c l i n e d with i n c r e a s i n g flower age. 4. ) a d e c l i n e i n sampling frequency brought about a corresponding d e c l i n e i n n e c t a r p r o d u c t i v i t y . As the time elapsed between samples i n c r e a s e d , f l o r a l p r o d u c t i v i t y i n c r e a s e d as w e l l . 5 . ) bumblebee d e n s i t y c o r r e l a t e s b e t t e r with v a r i o u s weather v a r i o u s weather and p r o d u c t i v i t y v a r i a b l e s e a r l y i n the day, as opposed to durin g the a f t e r n o o n . T h i s i s presumably because i t was only i n the morning that the bees experienced uniform energy c o n d i t i o n s . 6. ) with an o v e r a l l d e c l i n e i n a v a i l a b l e n e c t a r , the bees i n c r e a s i n g l y s e l e c t e d o l d e r f l o w e r s from which to f o r a g e . They a l s o may have been a v o i d i n g i n c r e a s i n g l y g r e a t e r numbers o f fl o w e r s they approached. These flowers <iere presumably empty o f 114 nectar l e v e l s s u f f i c i e n t to maintain f o r a g i n g . 7 . ) there was no r e l a t i o n s h i p between bee d e n s i t y and flowe r d e n s i t y . Though p i p e t t e s were used t o study the e f f e c t s of sampling frequency, i t was assumed t h a t p i p e t t i n g techniques adequately s i m u l a t e the e f f e c t s of bee f o r a g i n g on the f l o w e r s . If t h i s assumption i s v a l i d , then bumblebees do have the c a p a c i t y to a l t e r the r a t e s of nectar p r o d u c t i v i t y while n e c t a r l e v e l s i n f l c w e r s s i m u l t a n e o u s l y i n f l u e n c e bumblebee f o r a g i n g behavior. During the course of a s i n g l e day, nectar p r o d u c t i v i t y i s h i g h e s t d u r i n g the c o o l , morning hours when bee f o r a g e r s are i n f r e q u e n t . P r o d u c t i v i t y a l s o peaks e a r l y i n the f l o w e r i n g season, when a bee colony s t i l l c o n s i s t s of only one queen and perhaps a few workers. I t may be the case that p r o d u c t i v i t y i s highest at these times due not o n l y t o moisture e f f e c t s but a l s o to the lack of f o r a g e r s at t h i s time, which i n f l u e n c e s the f l c w e r s to s e c r e t e nectar at higher r a t e s . Though I b e l i e v e t h a t moisture f a c t o r s are of primary importance, the p o s s i b l e impact of a c t u a l f o r a g e r use on p r o d u c t i v i t y at these times s h o u l d be f u r t h e r i n v e s t i g a t e d . The bees i n c r e a s e i n d e n s i t y as a i r temperature i n c r e a s e s , other authors f i n d i n g t h a t they reach maximum l e v e l s a t 1000- 1100 hr. That they peak during the midmorning hours, r a t h e r than i n the a f t e r n o o n , suggests t h a t p r o d u c t i v i t y does p a r t i a l l y determine the time a t which the bees forage. The opposing e f f e c t s of these f a c t o r s should be explored i n more d e t a i l , perhaps using s i m u l a t i o n models of energy flow between fl o w e r s and bees. As the bees i n c r e a s e i n d e n s i t y , both d a i l y and 115 s e a s o n a l l y , they i n c r e a s i n g l y s e l e c t o l d e r flowers and seen t o a v o i d f l o w e r s with i n s u f f i c i e n t n e c t a r rewards, thus perhaps s t i m u l a t i n g empty f l o w e r s to produce at a h i g h e r r a t e . T h i s c o n c l u s i o n concerning avoidance of c e r t a i n f l o w e r s approached i s based on i n c o n s i s t e n t evidence, and thus should be explored i n more d e t a i l i n a l a b o r a t o r y s e t t i n g where confounding f a c t o r s can be adequately c o n t r o l l e d . As mentioned i n Chapter I I , p l a n t s may be competing f o r p o l l i n a t o r s e a r l y i n the season and e a r l y i n the mornings. The i n c r e a s e i n p r o d u c t i v i t y with decreased sampling frequency may be a p h y s i o l o g i c a l a d a p t a t i o n t o enhance a p l a n t ' s c o m p e t i t i v e a b i l i t y . S t u d i e s should be done to d i s c o v e r i f salmonberry p l a n t s are a c t u a l l y engaged i n mutual c o m p e t i t i o n at t h i s time. Many f l o w e r s should be removed from the study s i t e s and the seed s e t examined i n the remaining f l o w e r s . Competition between p l a n t s would then be i n d i c a t e d i f the r e p r o d u c t i v e output a c t u a l l y d i d i n c r e a s e . The data i n d i c a t e t h a t , l a t e r i n the season, and l a t e r i n the day, the bees are competing f o r n e c t a r r e s o u r c e s , s i n c e i t i s d u r i n g these times t h a t measured n e c t a r l e v e l s are low and bees accept a wider d i v e r s i t y of flower ages. Bumblebees at my s i t e s r a r e l y i n t e r a c t e d d i r e c t l y , p o s s i b l e c o m p e t i t i o n o c c u r r i n g i n s t e a d through e x p l o i t a t i o n of nectar r e s o u r c e s . Future s t u d i e s should be done i n v o l v i n g the removal of s e v e r a l l o c a l bee c o l o n i e s t o observe the e f f e c t s on the r e p r o d u c t i v e output of the remaining c o l o n i e s . I t should be a simple matter to count the number of queens and drones produced per c o l o n y near the end of the summer, yet i t would be a huge task to even f i n d the n e s t 116 s i t e s a t my study a r e a s . flosguin (1971) i s the only study of which I am aware i n the p o l l i n a t i o n ecology l i t e r a t u r e which, through an examination of a c t u a l p l a n t - p o l l i n a t o r community c h a r a c t e r i s t i c s , d i s c u s s e s the p o s s i b i l i t y t h a t c o m p e t i t i o n may be s h i f t i n g from the animal component to the p l a n t component as the summer proceeds. Other s t u d i e s have i m p l i e d t h a t , i f resources become l i m i t i n g i n a h a b i t a t , i t i s cnly one component of the r e l a t i o n s h i p which s u f f e r s . In the a l p i n e , i t i s p l a n t s which compete f o r a few p o l l i n a t o r s (Pojar, 1974), while H e i n r i c h argues t h a t i n the bogs of Maine i t i s nectar r e s o u r c e s which are sometimes l i m i t i n g , p o s s i b l y l e a d i n g to "resource p a r t i t i o n i n g " i n bumblebees ( H e i n r i c h , 1976a). However, i f i t i s n a t u r a l s e l e c t i o n which b r i n g s about the high degree cf morphological and b e h a v i o r a l f i t observed between p l a n t s and t h e i r p o l l i n a t o r s , i t i s f a r more l i k e l y t h a t , i n any given h a b i t a t , competition f o r l i m i t e d r e s o u r c e s s h o u l d be o c c u r r i n g amongst the p l a n t s f o r p o l l i n a t o r s , a l t e r n a t i n g with p e r i o d s of c o m p e t i t i o n amongst the p o l l i n a t o r s f o r p l a n t s . I have documented here c i r c u m s t a n t i a l evidence that t h i s i s o c c u r r i n g at my study s i t e s . The s h i f t i n a p o l l i n a t o r s c a r c e community t o a nectar s c a r c e community may not be gradual, ft very sudden plunge i n nectar s t a n d i n g crop i s v i s i b l e i n F i g . 19, c o r r e s p o n d i n g to a drop i n number of f l c w e r s per meter i n the h a b i t a t ( F i g . 21). T h i s sudden l e s s of f l o w e r s may have r e s u l t e d i n a suddenly very d i f f e r e n t world from a bumblebee's p o i n t of view. 117 LITERATURE CITED A l f c r d , D. V. 1975. Bumblebees. Davis-Poynter L i m i t e d , London. Baker, H.G. 1961. The a d a p t a t i o n s of f l o w e r i n g p l a n t s to n o c t u r n a l and c r e p u s c u l a r p o l l i n a t o r s . Q u a r t e r l y Review of Biology 36:64-73. Baker, H.G. 1963. E v o l u t i o n a r y mechanisms i n p o l l i n a t i o n b i o l o g y . Science 139:377-883. Baker, H.G. and I. Baker, 1975. 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