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Experimental evidence that reserves benefit yield : a test in a natural microcosm Venter, Katsky 2006

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E X P E R I M E N T A L EVIDENCE THAT RESERVES BENEFIT YIELD: A TEST IN A N A T U R A L M I C R O C O S M by K A T S K Y VENTER B.Sc. Hon., The University of British Columbia, 2003 A THESIS SUBMITTED LN PARTIAL F U L F I L L M E N T OF THE REQUIREMENTS FOR THE D E G R E E OF MASTER OF SCIENCE In THE F A C U L T Y OF G R A D U A T E STUDIES (Zoology) THE UNIVERSITY OF BRITISH C O L U M B I A September 2006 © Katsky Venter, 2006 Abstract No-take reserves, in addition to protecting biodiversity, may ensure the maintenance of harvested species. It has been proposed that reserves can both directly limit harvesting (by decreasing the area available for extraction), and increase yield through dispersal into harvestable areas. Although theory and observational evidence generally support such claims, experimental evidence indicating that reserves can provide yield to surrounding areas remains scarce primarily because large scale experiments are prohibitive. We employed a moss-based microarthropod community to experimentally compare the effects of reserve presence, size, and number on yield. We found that no-take reserves increased the density, biovolume, and species richness of microarthropods in non-reserve areas, regardless of the spatial arrangement of reserves. Treatments with reserves had equal or greater total harvests (abundance or biovolume) than treatments without reserves, despite the loss in harvestable area due to reserve establishment. Partitioning the harvested microarthropods into broad taxonomic groups indicated that all taxa exhibited the same ranked effects of treatments even though taxa exhibited different trends in abundances through time. No differences between having a single large reserve or three small reserves (whose combine area was equivalent the single large reserve) were detected. The absence of an effect of reserve number may be a product of high dispersal or differences in densities between small and large reserves. These results provide strong evidence that reserves are capable of functioning as sustainable management tool, and that reserve size, but not number is important for increasing yield. ii Table of contents Abstract ii Table of contents iii List of tables iv List of figures v Acknowledgements vi Dedication vii Chapter 1: Introduction 1 1.1 General introduction 1 1.1.1 Reserves and harvest yields ...» 1 1.1.2 Reserves and species diversity 3 1.1.3 Microcosms in ecology 4 1.2 References 6 Chapter 2: Experimental evidence that reserves benefit yield: A test in a natural microcosm 9 2.1 Introduction 9 2.2 Methods 12 2.2.1 Experimental setup 12 2.2.2 Determination of harvest and treatment effect 16 2.2.3 Analyses 17 2.3 Results 18 2.4 Discussion 23 2.5 Acknowledgements 28 2.6 References 29 Chapter 3: Conclusion 33 3.1 References 37 iii Table of contents Abstract Table of contents List of tables List of figures Acknowledgements Dedication Chapter 1: Introduction 1.1 General introduction 1 1.1.1 Reserves and harvest yields 1 1.1.2 Reserves and species diversity 3 1.1.3 Microcosms in ecology '•' 4 1.2 References 6 Chapter 2: Experimental evidence that reserves benefit yield: A test in a natural microcosm 2.1 Introduction 9 2.2 Methods 12 2.2.1 Experimental setup 12 2.2.2 Determination of harvest and treatment effect 16 2.2.3 Analyses 17 2.3 Results 18 2.4 Discussion 23 2.5 Acknowledgements 28 2.6 References 29 Chapter 3: Conclusion 3.1 References 37 iii List of Tables Table 2.1. Comparison of treatments iv List of Figures Fig. 2.1. Microarthropod (a) density (individuals/18lcm2) and (b) total yield through time by treatment 19 Fig. 2.2. Microarthropod density through time by taxon 20 Fig. 2.3. Microarthropod (a) density, (b) total yield, (c) biovolume/160cm2, (d) total biovolume, (e) Local rarefied species richness, and (f) Species richness rarefied to 54 individuals in NRAs at week 40 22 v I would like to thank my supervisor, Diane Srivastava, for her input, guidance, support, and most of all for allowing me to develop and pursue my ideas. I would also like to thank Brian Starzomski and Jackie Ngai for numerous discussions, coffee breaks, and much needed manuscript edits, along with many other UBC faculty, students and staff who provided encouragement and inspiration. This thesis based on many hours of microarthropod sorting; thank you Derek Tan, Marius Aurelian, and Mike Jansen for help with this. I would also like to thank Daryl Suen who offered me continuous moral support throughout this thesis. vi This tfutsis is dedicated, zuitk alt my love, to my parents, loho are aCzoays therefor me. Thankjjou for everything. vii Chapter 1. Introduction 1.1 General Introduction The use of reserves as a management tool in harvested ecosystems has recently gained much attention, particularly in the marine realm. Reserves may allow the export of biomass to surrounding harvested areas, and benefit multiple species simultaneously. Traditional single-species management requires monitoring of catch, determination of stock abundance, recruitment, levels of sustainable harvest, and enforcing quotas. By contrast, reserves may be easier to implement and enforce as violations are more obvious, and spatial closures ensure the protection of a set proportion of the community (Allison et al. 1998). Additionally, reserves offer the benefits of protecting diversity within their borders, and buffer against overharvesting or stochastic environmental impacts (Agardy 1994; Allison et al. 1998; Grafton et al. 2005). Although reserves have been widely embraced as a management tool in marine systems, ultimately their success will be gauged by their ability to provide "spillover" (emigration of harvestable species) to the surrounding areas. 1.1.1 Reserves and harvest yields The majority of evidence in favor of reserves as a management option comes from theoretical models or observational studies. Theoretical studies generally support the claim that reserves are capable of maintaining or increasing yield (e.g. Guenette & Pitcher 1999; Hastings & Botsford 1999; Nowlis & Roberts 1999; Neubert 2003; Halpern et al. 2004; Rodwell & Roberts 2004; Gaylord et al. 2005; Grafton et al. 2005). Increases in yield are most likely to occur when the region is being heavily exploited (see 1 Guenette et al. 1998; Gerber et al. 2003 for review), although this is not always necessary (Grafton et al. 2005). Observational evidence generally supports theoretical claims that reserves can provide export to surrounding regions as a product of biomass accumulation within their borders. Increases in abundances and species richness within reserves have been noted after reserve establishment (Russ & Alcala 1996; Alcala et al. 2005), or when comparing reserves to other sites (Russ & Alcala 1996; Gell & Roberts 2003; Russ et al. 2004; Abesamis & Russ 2005; Alcala et al. 2005). Such increases have been linked to increase catch per unit effort/area (CPUE/A) (see Gell & Roberts 2003 for review). Occasionally these increases in CPUE have translated into increases in total catch for a region (Roberts et al. 2001), although this is rarely explicitly examined. Reserve placement, size and number may all affect the ability of a reserve to provide export to surrounding regions. For example, it has been argued than reserves placed in source areas (areas which are a net exporter of individuals) may provide more benefits than those placed in sink areas (Crowder et al. 2000). Similarly as reserve size increases the amount of export required from the reserve must increase in a direct manner for total catch to remain the same in the absence of effort redistribution. At some point, increasing reserve size will necessarily translate into decreases in total catch as the amount of exploitable area approaches zero. Additionally, for any given reserve size, it has been theorized that a number of small reserves will produce greater yields than a single large reserve (Hastings & Botsford 2003). 2 1.1.2 Reserves and species diversity There is a large amount of literature concerning whether biodiversity can best be conserved by a single large reserve or several small reserves (SLOSS) in terrestrial ecology. Having multiple smaller reserves may decrease the likelihood of a chance event (such as a fire or disease epidemic) destroying the entire reserve system (Simberloff & Abele 1975). On the other hand, single large reserves may be better able to maintain the original community (Diamond 1976), as area sensitive species (e.g. higher tropic level species and or those that require large ranges) are repeatedly lost after habitat fragmentation, and edge habitats may not be suitable for 'interior' species . No clear consensus has been reached in the SLOSS debate (for review see Ovaskainen 2002), in part because scale is such a large factor in this debate. Region size will affect the amount of habitat heterogeneity it possesses as a simple product of sampling. Therefore, at large spatial scales biodiversity may be best represented within several smaller reserves which are able to capture different habitats and ecosystems, and thus species. Throughout the SLOSS debate attention has been focused on diversity within reserves, with the surrounding matrix incapable of supporting species; this is generally not the case. How this theory extends to contributions reserves can make to non-reserve areas is uncertain. As the line between conservation and management blurs, integrating knowledge from both streams will allow rapid advancement of community-based management strategies such as reserves. This thesis simultaneously considers the effect of reserves on both yield and diversity in harvested areas. 3 1.1.3 Microcosms in ecology The empirical evidence in favor of reserves as a management tool remains largely observational (Willis et al. 2003). The scarcity of experimental evidence is likely a product of the scale at which the 'target systems' (be they terrestrial or aquatic) operate. Conducting replicated, randomized experiments at scales large enough to capture community-level effects is logistically prohibitive. Microcosms may allow the experimental assessment of such questions in natural communities. These systems posses more realism and complexity than can be incorporated into theoretical models, while being small, and short-lived in comparison to the target systems (Srivastava et al. 2004). Microcosms allow us to assess various hypotheses and generate new avenues of research, but there are limitations, however, in direct extrapolation of results obtained from such systems to other systems of interest (Carpenter 1996; Schindler 1998). Regardless of such limitations, insights obtained from model systems, be they at the level of the organism (e.g. Drosophila), population (e.g. yeast), or community (e.g. beaker microcosms), have long guided biological research, providing many valuable contributions to our current understanding of natural systems. We use the moss microarthropod community to determine the effects of reserve number and area on harvest. The moss microarthropod community is composed primarily of mites (Acari), springtails (Collembola), nematodes, small insects, spiders, centipedes and millipedes. This faunal food web is based on detritus, algae, fungi, and moss, although the moss provides mainly structural habitat. The fauna in this community vary in their trophic positions, generation times (which range from a few days to several months), dispersal abilities and other life history traits. This community has been used in 4 the past to assess the effects of fragmentation and habitat corridors on species richness ((Gilbert et al. 1998; Gonzalez et al. 1998; Hoyle & Gilbert 2004), how species area relationships vary with trophic level (Hoyle 2004, Venter & Srivastava, in prep.) and how region size and connectivity affect the ability of a system to respond to disturbances (Starzomski et al. in prep.). Using the moss microarthropod community we experimentally determine how reserves size (25% and 50% of the region) and number (one or three reserves) affect harvest amount, biovolume and diversity in comparison to harvests obtained from regions without reserves. 5 1.2 References Abesamis R.A. & Russ G.R. (2005) Density-dependent spillover from a marine reserve: Long-term evidence. Ecological Applications, 15, 1798-1812 Agardy M.T. (1994) Advances in Marine Conservation - the Role of Marine Protected Areas. Trends in Ecology & Evolution, 9, 267-270 Alcala A.C. , Russ G.R., Maypa A.P. & Calumpong H.P. (2005) A long-term, spatially replicated experimental test of the effect of marine reserves on local fish yields. Canadian Journal of Fisheries and Aquatic Sciences, 62, 98-108 Allison G.W., Lubchenco J. & Carr M.H. (1998) Marine reserves are necessary but not sufficient for marine conservation. Ecological Applications, 8, S79-S92 Carpenter S.R. (1996) Microcosm experiments have limited relevance for community and ecosystem ecology. Ecology, 11, 677-680 Crowder L.B. , Lyman S.J., Figueira W.F. & Priddy J. (2000) Source-sink population dynamics and the problem of siting marine reserves. Bulletin of Marine Science, 66, 799-820 Diamond J.M. (1976) Island Biogeography and Conservation - Strategy and Limitations. Science, 193, 1027-1029 Gaylord B., Gaines S.D., Siegel D.A. & Carr M.H. (2005) Marine reserves exploit population structure and life history in potentially improving fisheries yields. Ecological Applications, 15, 2180-2191 Gell F.R. & Roberts C M . (2003) Benefits beyond boundaries: the fishery effects of marine reserves. Trends in Ecology & Evolution, 18, 448-455 Gerber L.R., Botsford L.W., Hastings A., Possingham H.P., Gaines S.D., Palumbi S.R. & Andelman S. (2003) Population models for marine reserve design: A retrospective and prospective synthesis. Ecological Applications, 13, S47-S64 Gilbert F., Gonzalez A. & Evans-Freke I. (1998) Corridors maintain species richness in the fragmented landscapes of a microecosystem. Proceedings of the Royal Society of London Series B-Biological Sciences, 265, 577-582 Gonzalez A., Lawton J.H., Gilbert F.S., Blackburn T.M. & Evans-Freke I. (1998) Metapopulation dynamics, abundance, and distribution in a microecosystem. Science, 281, 2045-2047 Grafton R.Q., Kompas T. & Lindenmayer D. (2005) Marine reserves with ecological uncertainty. Bulletin of Mathematical Biology, 67, 957-971 6 Guenette S., Lauck T. & Clark C. (1998) Marine reserves: from Beverton and Holt to the present. Reviews in Fish Biology and Fisheries, 8, 251-272 Guenette S. & Pitcher T.J. (1999) An age-structured model showing the benefits of marine reserves in controlling overexploitation. Fisheries Research, 39, 295-303 Halpern B.S., Gaines S.D. & Warner R.R. (2004) Confounding effects of the export of production and the displacement of fishing effort from marine reserves. Ecological Applications, 14, 1248-1256 Hastings A. & Botsford L.W. (1999) Equivalence in yield from marine reserves and traditional fisheries management. Science, 284, 1537-1538 Hastings A. & Botsford L.W. (2003) Comparing designs of marine reserves for fisheries and for biodiversity. Ecological Applications, 13, S65-S70 Hoyle M . (2004) Causes of the species-area relationship by trophic level in a field-based microecosystem. Proceedings of the Royal Society of London Series B-Biological Sciences, 271, 1159-1164 Hoyle M . & Gilbert F. (2004) Species richness of moss landscapes unaffected by short-term fragmentation. Oikos, 105, 359-367 Neubert M.G. (2003) Marine reserves and optimal harvesting. Ecology Letters, 6, 843-849 Nowlis J.S. & Roberts C M . (1999) Fisheries benefits and optimal design of marine reserves. Fishery Bulletin, 97, 604-616 Ovaskainen O. (2002) Long-term persistence of species and the SLOSS problem. Journal of Theoretical Biology, 218, 419-433 Roberts C M . , Bohnsack J.A., Gell F., Hawkins J.P. & Goodridge R. (2001) Effects of marine reserves on adjacent fisheries. Science, 294, 1920-1923 Rodwell L.D. & Roberts C M . (2004) Fishing and the impact of marine reserves in a variable environment. Canadian Journal of Fisheries and Aquatic Sciences, 61, 2053-2068 Russ G.R. & Alcala A.C. (1996) Marine reserves: Rates and patterns of recovery and decline of large predatory fish. Ecological Applications, 6, 947-961 Russ G.R., Alcala A . C , Maypa A.P., Calumpong H.P. & White A.T. (2004) Marine reserve benefits local fisheries. Ecological Applications, 14, 597-606 7 Schindler D.W. (1998) Replication versus realism: The need for ecosystem-scale experiments. Ecosystems, 1, 323-334 Simberloff D.S. & Abele L .G. (1975) Island Biogeography Theory and Conservation Practice. Science, 191, 285-286 Srivastava D.S., Kolasa J., Bengtsson J., Gonzalez A., Lawler S.P., Miller T.E. , Munguia P., Romanuk T., Schneider D.C. & Trzcinski M.K. (2004) Are natural microcosms useful model systems for ecology? Trends in Ecology & Evolution, 19, 379-384 Willis T.J., Millar R.B., Babcock R.C. & Tolimieri N. (2003) Burdens of evidence and the benefits of marine reserves: putting Descartes before des horse? Environmental Conservation, 30, 97-103 8 Chapter 2. Experimental evidence that reserves benefit yield: A test in a natural microcosm 2.1 Introduction Humans are having devastating impacts on the Earth's fauna. One critical impact is the overharvesting of wild animals for food. For example, bushmeat harvesting (i.e. the hunting of wildlife for meat), currently removes 1-4.9 million metric tons yr"1 of faunal biomass from Central Africa (Wilkie & Carpenter 1999; Fa et al. 2002) approximately six times the sustainable amount (Bennett 2002). At the same time, fisheries have lead to wide spread crashes in fish populations, with global large predatory fish biomass reduced to an alarming 10% of pre-industrial levels (Myers & Worm 2003). In Africa, the link between marine and terrestrial harvests is further hastening the collapse of wildlife populations in both realms (Brashares et al. 2004). Furthermore, such indiscriminate and unregulated harvesting is only expected to increase with human population growth. Management strategies which can both meet sustainable exploitation needs and protect biodiversity are needed. Reserves - areas from which extraction is prohibited - were originally used simply to preserve natural communities. More recently, reserves have also been used to sustain exploitable biomass; the rationale is that biomass will accumulate in the reserves and eventually 'spill over' into the surrounding harvestable areas via density-dependant 1 A version of this chapter will be submitted for publication. Venter, K. & Srivastava, D.S. Experimental evidence that reserves can benefit yield: a test in a natural microcosm 9 process or diffusion (Willis et al. 20G3). Moreover, reserves may not only increase the amount of yield but may also be effective tools for preserving diversity of both exploited and non-target species. Such increases in diversity may offer insurance against fluctuations in the abundance of particular stocks (Hilborn et al. 2003). Furthermore, reserves may provide colonists to non-reserve areas (NRAs), increasing regional diversity and buffering communities against catastrophic events (Loreau et al. 2003). Although the use of reserves as management tools is primarily restricted to marine systems, terrestrial reserves may be capable of functioning in a similar manner if constructed as a combination of fully protected and hunted areas (Joshi & Gadgil 1991; McCullough 1996; Novaro etal. 2000; Milner-Gulland & Bennett 2003) In spite of these proposed benefits, the ability of reserves to serve as source populations and boost yield is still uncertain. To date, evidence of a spillover effect is largely limited to mathematical models or observational studies. Theory predicts that reserves have the ability to maintain or increase total yield (e.g. Guenette & Pitcher 1999; Hastings & Botsford 1999; Nowlis & Roberts 1999; Neubert 2003; Halpern et al. 2004; Rodwell & Roberts 2004; Gaylord et al. 2005; Grafton et al. 2005) particularly when harvest intensity is high (also see Guenette et al. 1998; Gerber et al. 2003 for review). However, not all reserve configurations will have positive effects on yield. Observational studies have also shown increases in catch per unit effort (CPUE) or area (CPUA) after reserve construction (Russ & Alcala 1996; Alcala et al. 2005), or in comparison to non-reserve areas (Russ & Alcala 1996; Gell & Roberts 2003; Russ et al. 2004; Abesamis & Russ 2005; Alcala et al. 2005), although evidence is ambiguous (Willis et al. 2003). 10 Although promising, observational evidence is often confounded by the non-random placement of reserves or lack of temporal or spatial replication (Willis et al. 2003). Similarly, mathematical models are limited by their simplifications and failure to include species interactions. Experimental evidence for the efficacy of reserves is sorely needed. The potential for a reserve to provide spillover is, in part, determined by its design. Considerable theoretical and empirical research on reserve design has focused on comparing the effects of a single large versus several small reserves of the same total area. The spatial partitioning of reserve area may have consequences for the amount of spillover. In particular, the perimeter to area ratio will be higher for several small reserves than for a single large reserve, likely increasing the potential for emigration from multiple smaller reserves (Hastings & Botsford 2003), while larger reserves may have higher population densities and greater species diversity(Connor et al. 2000). In addition, optimal designs for biodiversity conservation may conflict with those that provide the most benefits for resource exploitation. Even if reserves serve as source populations, they still may not provide a net benefit in terms of yield, as they decrease the area available for harvesting. Consequently, the success of reserves as a management tool will be determined by the balance between the loss of exploitable areas versus the increase in harvestable biomass through spillover. Currently, total reserve area recommendations for maximizing yield and/or biodiversity range from 20-50% of management regions (Halpern & Warner 2003). How such differences in total reserve area affect the net impact of a reserve on yield is uncertain. 11 We experimentally examine how reserves impact harvest using a model community composed of moss-inhabiting microarthropods. This is, to our knowledge, the first experimental test of how reserve design, both in terms of reserve number and size relative to non-reserve areas (NRAs), affects harvest. The use of a model community allows us to conduct replicated experiments which are normally impossible in exploited systems. The moss-microarthropod community is a complete, naturally assembled, multitrophic community whose small scale and short generation times allows for rapid and highly-replicated experiments. This community is extremely diverse, with taxa (mites, springtails and other small insects, and spiders) that differ widely in life history traits such as fecundity, life span and motility. Harvest intensity and reserve structure can be easily manipulated in this miniature landscape. Using this system, we determine how reserve number and total area affect the harvestable abundance, biomass, and species richness in NRAs. We manipulated reserve size and spatial arrangement and measured their effects on biovolume, density, and species richness of moss microarthropods. 2.2 Methods 2.2.1 Experimental setup In this study we created miniature moss 'regions' to which we applied various reserve designs and monitored the effects of harvesting. Moss (Racomitrium canescens), containing microarthropod communities, was collected from a moss-covered rocky outcrop in Squamish, British Columbia, Canada in July 2004. The collected moss was cut into 50 circular 'regions', each 45 cm in diameter. Each region was then placed into a 12 mesh-bottomed circular ring (45cm in diameter) with rims 2 cm in height, and relocated to a covered outdoor location on the University of British Columbia. The mesh bottom of the rings allowed us to simulate harvest on the treatments without removing the NRA moss from the ring (see below). Each region was randomly allocated to one of 5 treatments (n=10 per treatment); no reserve (NR), single small reserve (1SR), three small reserves (3SR), single large reserve (1LR), or three large reserves (3LR) (Table 1). The total reserve area of both the 3SR and 1SR treatments represented 25% of each region, while the total reserve area of the 3LR and the 1LR treatments represented 50% of each region. For each treatment, the reserves were created by cutting out a circular patch of moss from the region (Table 1). A circle of mesh was then placed under each of the newly-cut reserves. To facilitate future removal of the reserve, thin wires were attached to the mesh such that when the reserve was replaced into the region the wires would project above the height of the moss. The reserve was then replaced in the same location and orientation as before removal and the same procedure was followed in all subsequent removals. Once reserves were replaced there was no detectable border between reserve and non-reserve area. 13 Table 1. Comparison of treatments; no reserve (NR), single small reserve (1SR), three small reserves (3SR), single large reserve (1LR), or three large reserves (3LR). Percent of region allocated to reserve Number of reserves Total reserve area Size of each reserve N R Ocm' 1SR 25% 398 cm' 398 cm2 3SR 25% 398 cm' 133 cm' 1LR 50% 795 cm' 795 cm' 3LR 50% 795 cm' 265 cm' Microarthropods were harvested from the NRA of each region every eight weeks, skipping January (low temperatures meant that most species would be in resting stages and incapable of responding to extraction at that time). As the generations times of the harvested species vary from a few days to several months (Walter & Proctor 1999) an eight week harvest interval represented a broad range of impact for individual species; from minimal to severe. To harvest a region, reserves were removed and replaced with plastic foam disks of equal size. The remaining NRA was then brought to the lab and placed in a Tullgren funnel. In the funnel, a heat gradient caused the microarthropods to migrate down through the moss and soil until they eventually fell through the underlying mesh into a 7:2:1 mixture of ethanol:glycerol:water to be preserved for later analysis. Harvesting 14 always occurred two days after watering. Microarthropod individuals progressively extract over time, therefore an extraction that is stopped before completion only removes a portion of the fauna. Based on initial calibrations, we determined that 4.6 days of extraction were needed to harvest 50-80% of the total microarthropods within the NRA at room temperature. We therefore applied this extraction period to all NRAs. After harvesting, the regions were returned to the outdoor facility and reserves replaced until the next harvest. Microarthropod extraction rates depend on soil moisture. Seasonal variation in rainfall would have introduced large temporal variation in harvest efficiencies, confounding any real change in harvestable biomass. We therefore excluded rain with transparent roofs placed 2m over moss regions. Each moss region was watered by hand with an average of 1.6L water week"1 (total yearly rainfall in Vancouver / 52 weeks). Watering usually consisted of 1.6L water each week although occasionally, to allow seasonal drying between watering, patches were watered 3.2L every other week. Drying occurs frequently in coastal British Columbia, and fungal growth can occur when it is prevented. Watering was always reverted to 1.6L week"1 two weeks before harvesting. The full experiment lasted 40 weeks, starting in July 2004 and ending in May 2005. Each region was subjected to a total of five harvests over the duration of the experiment. 15 2.2.2 Determination of harvest and treatment effect Effects of harvesting were tracked through time by counting microarthropods extracted during the first, third (week 16) and final (week 40) harvests. To determine microarthropod yield from the NRA of each region we counted a subsample of individuals extracted during the first, third and final harvests. Subsampling was conducted by pouring each sample into a transparent 10cm diameter dish then counting % of the total area of the dish in four randomly-selected subsections. All individuals were counted under a Leica MZ16 dissecting scope (60-120x magnification) and allocated to one of five broad groupings; Mesostigmatid mites, Prostigmatid mites, Oribatid mites, Collembola (springtails), and other microarthropods (spiders, centipedes, millipedes, and insects). These taxonomic groupings loosely correspond to life history differences such as trophic position, life span and dispersal ability. This procedure resulted in an equal proportion of each sample being counted, and these abundances were then scaled to calculate the density and total number of individuals extracted per region. In total, more than 130,000 individuals were counted. Larger microarthropods, including spiders, centipedes, and non-Collembola insects, were too rare to be considered for analyses. To determine the effects of reserve design on species richness and biomass, five replicates from the final harvest of each treatment were randomly selected for a more in-depth examination. Subsampling in this case was done by spreading each entire sample evenly into a wax-bottomed Petri dish. A 20% portion of this dish (consisting of eight randomly selected aliquots) was sorted under a dissecting scope. Morphological distinctiveness was used to divide individuals into morphospecies (hereafter species) as 16 only a fraction of mite species (the dominant taxa) have been taxonomically described. Our separation methods have been verified by acarologists for a subset of taxa (see Acknowledgements). Voucher specimens of each morphospecies are available at the Department of Zoology, University of British Columbia; digital photographs and line illustrations of most species are also available online at www.zoology.ubc.ca/~srivast/mites. Measurements were taken from each species in order to calculate biovolume. The length, width and height of each species was measured to the nearest micrometer under the dissecting scope. Each species was also described as being either ellipsoid or cylindrical in shape and the appropriate geometrical formulas for each shape was used to calculate biovolume. A total of 8306 individuals and 119 species were identified. 2.2.3 Analyses Times series data (density and total yield) were log-transformed and each time period analyzed with ANOVA. We did not conduct repeated-measures analyses as the time x treatment interaction was of minor interest compared to the differences between treatments at particular harvests (first, middle and final). Comparisons of species richness were conducted using rarefied data. Each subsample was rarefied to both the number of individuals within 160 cm 2 section of NRA moss (which varied by replicate) and the number of individuals found in the smallest subsample (54 individuals). As biomass and species richness data did not always conform to the assumptions of regression even when 17 transformed, non-parametric regression on ranked values was conducted when needed. All data was analyzed in JMP 5.1. 2.3 Results Microarthropod densities in NRAs were similar between all treatments at the start of the experiment ( F ^ = 1.136, P = 0.352), but rapidly diverged by week 16 ( F ^ s = 11.618, P = 0.0001), remaining so until the end of the experiment (1*4,45 = 8.5 88, P = 0.0001) (Fig. 1 a.). Densities were highest in the 50% reserve treatments (1LR and 3LR), followed by the 25% reserve treatments (1SR and 3SR), and lowest in the regions lacking reserves (NR). The NR treatment showed a steady decline in microarthropod densities throughout the experiment. The number of reserves (one or three) within each category of total reserve area had no effect on NRA density in either week 16 or week 40 (Fij37 = 0.13, P = 0.72, and F ^ 7 = 0.48, P = 0.49, respectively). Total yield depends not only on the harvest per unit area, but also on the area harvested. In this system, the increase in harvest density with reserves was counterbalanced by the decrease in area available for harvest; there were no differences between treatments in total yield at either week 16 or week 40 (F^s = 1.25, P = 0.30 and F4;45= 1.70, P = 0.17, respectively) (Fig. 1 b.). A N O V A , however, is generally less powerful than regression in detecting trends (Cottingham et al. 2005). Using regression analyses, there was a slight but significant increase in total yield with the proportion of region allocated to reserve (final harvest, R 2 = 0.08, P =0.045). We conclude therefore 18 that reserves have either neutral or positive effects on total yield. Note that this was the case even though the area from which microarthropods could be extracted in the NR treatment was twice that available for harvest in the 50% reserve treatments. — • — N R — A - 1 S R A 3 S R _ Q _ 1 L R • 3 L R Fig. 1. Microarthropod (a) density (individuals/18lcm2) and (b) total yield through time by treatment; no reserve (NR), single small reserve (1SR), three small reserves (3SR), single large reserve (1LR), or three large reserves (3LR). Error bars are ± 1 S.E. * Significant difference between treatments, one-way ANOVAs, P < 0.05. These patterns in density combine effects on multiple taxonomic groups. However, taxa differed in response to the experimental conditions. For example Collembola increased in abundance over the experiment while Mesostigmata decreased (Fig. 2 b and c). Despite these temporal differences, the rank order of treatment effects was similar within each taxonomic group (Fig. 2). 19 Fig. 2. Microarthropod density through time by taxon (a) Oribatid (b) Collembola (c) Mesotigmatid, and (d) Prostigmatid. All densities are the natural logarithms of individuals/18 lcm 2 . * one-way ANOVAs, P < 0.001. Reserve area but not spatial arrangement affected biovolume, density and species richness. The more in-depth data showed no effect of reserve number (after controlling for proportion of region allocated to reserve) on numbers of individuals (V\,n = 0.0022, P 20 = 0.964), biomass (Fi,i 7= 0.084, P = 0.776) or species richness ( F i > n = 3.123, P - 0.095 and Fij7= 0.0015, P = 0.970 for species rarefied to 160cm2 and 54 individuals respectively). Rather, all metrics seemed to be closely related to the total area allocated to reserve. As no effect of reserve number was observed, all further analyses are conducted as regressions against the proportion of the region being allocated to reserve. Densities in NRAs at the end of the experiment increased significantly with increasing reserve size (Fig. 3 a), corroborating the time series data presented in Fig 1 a, as expected. This difference in densities between treatments was so large that it translated into a positive relationship between total yield and proportion of region allocated to reserve (Fig 3 b). Converting numbers of individuals to biovolume we see that these relationships persist (Fig 3 c, d). Local species richness (species 160cm"2) in the NRAs increased with increasing area allocated to reserve (Fig 3 e). This response in species richness is due to the greater density of individuals in reserve treatments. Correcting for differences in local density by rarefying all samples to 54 individuals produced a non-significant relationship between the number of species per individual and percent reserve (Fig 3 f). 21 2000 0 25 50 percent of region allocated to reserve 10000 "D C 0) o CD Q. W 20 18 16 J 14 i 12 10 * 8 6 4 2 0 25 50 percent of region allocated to reserve Fig. 3. Microarthropod (a) density, (b) total yield, (c) biovolume/160cm2, (d) total biovolume, (e) Local rarefied species richness, and (f) Species richness rarefied to 54 individuals, in NRAs at week 40. Data is present untransformed, log transformations were used for regression analyses. Lines indicate significant relationships, a= 0.05. 22 2.4 Discussion We found that no-take reserves increased the density, biovolume, and species richness of microarthropods in non-reserve areas, regardless of the spatial arrangement of reserves. Treatments with reserves had equal or greater total harvests (abundance or biovolume) than treatments without reserves, despite the loss in harvestable area due to reserve establishment. In other heavily exploited systems similar increases in catch per unit effort (CPUE) after reserve establishment have been observed (see Gell & Roberts 2003 for review), or predicted (see Gerber et al. 2003 for review), though rarely if ever has this been shown experimentally. These studies attribute the positive effects of reserves on CPUE to spillover, which may also explain our experimental results. The increase in CPUE for regions with reserves established quickly (being apparent by week 16), and was maintained for the duration of the experiment (40 weeks). This rapid response may be due, in part, to the fact that we established reserves before harvesting began, as tends to be the case in terrestrial systems. In contrast, marine reserves are generally established in already exploited systems, which may result in a greater delay between establishment and the resultant promotion of yield, as biomass must first recover within the reserves before spillover effects can occur. However, this time delay may be minimal, as Halpern and Warner (2002) have shown that biomass, abundance, and diversity can recover within 3 years in marine communities. 23 It has been argued that several smaller reserves would better serve the goal of maximizing yield than a single large reserve (e.g. Guenette & Pitcher 1999; Hastings & Botsford 2003). Partitioning a reserve into multiple areas substantially increases the perimeter, and therefore the emigration rate. We did not find differences due to reserve number, even though large reserves had perimeters that were 40% less than the three smaller reserves combined. There are two possible explanations for the absence of an effect of reserve number on catch number and biovolume. First, at the scale examined, movement rates may be rapid enough to minimize differences due to reserve number. High dispersal can effectively erase the 'spatial' component of the reserves, making them more analogous to traditional management where harvest is simply reduced. This motility effect is likely not just specific to moss microarthropods; many marine reserves are frequently small relative to the dispersal abilities of species. For example, in a review of reserve effects, 26% of reserves included in the study were 1km2 or less in size (Halpern 2003), while many marine species disperse more than 20km (Shanks et al. 2003). Alternatively, even if subdividing reserves increases spillover rate, this effect might be counterbalanced by lower densities within smaller reserves. Since we do not have information on reserve densities, we are not able to discount this explanation. However we note that observational evidence indicates reserve population densities are independent of reserve size in marine systems (Halpern 2003). Reserve number had no effect on abundances, biovolume, or species number, over a doubling of total reserve area. The absence of a reserve-number effect may indicate that the argument over optimal reserve number is not as important as previously thought, and 24 is certainly less important than the proportion of a region dedicated to reserves which strongly affected yield. That is not to say that differences could not arise at other scales or for other systems; we have chosen to examine regions placed randomly in a single uniform habitat. Further study directed towards determining the effects of varying scale, habitat heterogeneity, and reserve placement as well as harvest intensity is required to evaluate the generality of these results. Although no specific reserve design is optimal for all species (Norse et al. 2003), we found that the presence of any reserve was sufficient to promote densities of all taxa in NRAs. Furthermore, all taxa exhibited the same ranked effects of treatments through time (Fig. 2). Taxa responded similarly despite differences in generation times (from days to months), fecundity (one to > 100 eggs), trophic level (from fungivores to secondary predators), size (<200 pm to >1000 pm), and dispersal capabilities. Each of these life history traits could theoretically alter the response of a species to a reserve design, affecting its ability to recover numerically after a harvest (a product of a taxons generation time and fecundity), its probability of leaving the reserve (a function of size and motility), or the effect of the harvest on its prey (which varies with trophic level). In a review of 86 studies of marine reserves by Halpern (2003), reserves had similar effects on all functional groups with the exception of invertebrates, for which results were unclear. It must be noted, however, that the review by Halpern (2003) was limited to a narrow range of taxa and variable datasets (Roberts et al. 2003). Additionally, most modeling and empirical studies (including this study), do not evaluate effects on species with direct seasonal migration, where it has been proposed that reserves benefits will be 25 proportional to the length of time these individuals spend in reserves (Bohnsack 1994). Our results indicate that reserves may benefit a wide range of non-migratory species even if the reserve was not designed specifically for that purpose. So far we have considered the effect of reserves on harvest yields. A second major goal of reserve construction is the protection of biodiversity. However, the optimal reserve design for promoting high yields may conflict with arrangements for optimizing biodiversity. As mentioned before, Hastings and Botsford (2003) concluded that the requirements of maximum sustainable yield were best met by many small reserves which maximized export from reserves, in contrast, conservation was best served by a few large reserves which decreased the likelihood of a species leaving the reserve. A similar argument concerning the ability of a single large reserve versus several small reserves (SLOSS) to conserve biodiversity has been long debated in terrestrial ecology (see Ovaskainen 2002 for review). These effects of reserve number all concern local species diversity within reserves. However regional diversity also includes diversity in harvested areas, and the impact of reserves on NRA diversity has rarely been examined. We demonstrate that NRA diversity increases with total reserve area, largely as a product of increased densities, but is unaffected by subdivision of this total area into smaller reserves. Our results suggest that management aimed at promoting yield and conserving biodiversity may not be in conflict. Rather, the two community features responded positively to reserve size but were unaffected by subdivision. 26 By maintaining higher densities of individuals in NRAs, and exhibiting the capacity to serve as a source of immigrants, reserves may be able to provide 'insurance' against stochastic events or management uncertainties (McCullough 1996; Loreau et al. 2003). Although such benefits are hard to quantify, the dramatic decline in densities in regions lacking reserves that was observed over the 40 weeks of this study in regions lacking reserves, and the demonstrated ability of reserves to provide recruits to the surrounding areas, speak to the ability of reserves to enhance regional resistance and/or resilience. The promotion of harvest diversity may also have economic importance, buffering against changes in environmental (Hilborn et al. 2003) or market conditions. One caveat is that, although insights can be gleaned from model communities, results cannot be directly scaled to other systems. Our experimental design mimicked as closely as possible realistic harvesting impacts (intensity and frequency) and reserve sizes, scaled to the size and generation times of the constituent species. However, how the dispersal abilities of moss microarthropod species differ from other terrestrial and aquatic systems is uncertain. It is also uncertain how our indiscriminate harvesting will translate to situations in which harvest is highly targeted at a few species. Such limitations are necessary concessions to using model systems, much in the same way as simplifying assumptions are inevitable in mathematical models. Rather than draw direct analogies between the moss-microarthropod system and any particular harvested system, we use it as a "natural microcosm" (Srivastava et al. 2004) to test the generality of theory before applying it to other situations. 27 At present much of the opposition to the establishment of reserves appears to come from harvesters (Suman et al. 1999) who fear that reserves will displace them and remove large portions of the available catch by making it' off-limits'. Evidence of neutral or positive effects of reserves on harvest is therefore important for justifying reserves to scientists and harvesters alike. To date much of the evidence in favor of reserves has been from model simulations. The few empirical studies are often limited by focusing on responses within, rather than outside, reserves, lack of data prior to reserve construction, or ambiguous results due to low statistical power (Willis et al. 2003). Although we are limited in the extrapolation of our results to other systems, we have provided here, to our knowledge, the first explicit experimental test of how reserve designs compare in their ability to sustain yield. Our results indicate unequivocally that reserves are capable of maintaining or increasing total catch, and suggest that they may provide benefits over other management options, through insurance against chance events or mismanagement, and the promotion of local biodiversity. 2.5 Acknowledgements J. Shurin, S. Guenette, J. Ngai and B. Starzomski provided useful comments on an early version of this manuscript. D. Tan, M. Aurelian, and M . Janssen aided in sorting of the mites and experimental setup. The following acarologists aided in verifying identifications: Valerie Behan-Pelletier, Hans Klompen, Heather Proctor, Cal Welbourn, and particularly David Walter. We thank the Ohio State University Acarology Summer Program for providing unpublished identification keys and taxonomic training. D.S. was supported by grants from the Natural Sciences and Engineering Council of Canada, and K.V. was supported by a University of British Columbia Graduate Fellowship and entrance scholarship. 28 2.6 References Abesamis R.A. & Russ G.R. (2005) Density-dependent spillover from a marine reserve: Long-term evidence. Ecological Applications, 15, 1798-1812 Alcala A . C , Russ G.R., Maypa A.P. & Calumpong H.P. (2005) A long-term, spatially replicated experimental test of the effect of marine reserves on local fish yields. Canadian Journal of Fisheries and Aquatic Sciences, 62, 98-108 Bennett E.L. (2002) Is there a link between wild meat and food security? Conservation Biology, 16, 590-592 Bohnsack J.A. (1994) How marine fishery reserves can improve reef fisheries. Proceedings of the Gulf and Caribbean Fisheries Institute, 43, 217-240 Brashares J.S., Arcese P., Sam M.K., Coppolillo P.B., Sinclair A.R.E. & Balmford A. (2004) Bushmeat hunting, wildlife declines, and fish supply in West Africa. Science, 306, 1180-1183 Connor E.F., Courtney A.C. & Yoder J.M. (2000) Individuals-area relationships: The relationship between animal population density and area. Ecology, 81, 734-748 Cottingham K.L. , Lennon J.T. & Brown B.L. (2005) Knowing when to draw the line: designing more informative ecological experiments. Frontiers in Ecology and the Environment, 3, 145-152 Fa J.E., Peres C A . & Meeuwig J. (2002) Bushmeat exploitation in tropical forests: an intercontinental comparison. Conservation Biology, 16, 232-237 Gaylord B., Gaines S.D., Siegel D.A. & Carr M.H. (2005) Marine reserves exploit population structure and life history in potentially improving fisheries yields. Ecological Applications, 15, 2180-2191 Gell F.R. & Roberts C M . (2003) Benefits beyond boundaries: the fishery effects of marine reserves. Trends in Ecology & Evolution, 18, 448-455 Gerber L.R., Botsford L.W., Hastings A., Possingham H.P., Gaines S.D., Palumbi S.R. & Andelman S. (2003) Population models for marine reserve design: A retrospective and prospective synthesis. Ecological Applications, 13, S47-S64 Grafton R.Q., Kompas T. & Lindenmayer D. (2005) Marine reserves with ecological uncertainty. Bulletin of Mathematical Biology, 67, 957-971 Guenette S., Lauck T. & Clark C. (1998) Marine reserves: from Beverton and Holt to the present. Reviews in Fish Biology and Fisheries, 8, 251-272 29 Guenette S. & Pitcher T.J. (1999) An age-structured model showing the benefits of marine reserves in controlling overexploitation. Fisheries Research, 39, 295-303 Halpern B.S. (2003) The impact of marine reserves: Do reserves work and does reserve size matter? Ecological Applications, 13, SI 17-S137 Halpern B.S., Gaines S.D. & Warner R.R. (2004) Confounding effects of the export of production and the displacement of fishing effort from marine reserves. Ecological Applications, 14, 1248-1256 Halpern B.S. & Warner R.R. (2002) Marine reserves have rapid and lasting effects. Ecology Letters, 5, 361-366 Halpern B.S. & Warner R.R. (2003) Matching marine reserve design to reserve objectives. Proceedings of the Royal Society of London Series B-Biological Sciences, 270, 1871-1878 Hastings A. & Botsford L.W. (1999) Equivalence in yield from marine reserves and traditional fisheries management. Science, 284, 1537-1538 Hastings A. & Botsford L.W. (2003) Comparing designs of marine reserves for fisheries and for biodiversity. Ecological Applications, 13, S65-S70 Hilborn R., Quinn T.P., Schindler D.E. & Rogers D.E. (2003) Biocomplexity and fisheries sustainability. Proceedings of the National Academy of Sciences of the United States of America, 100, 6564-6568 Joshi N.V. & Gadgil M . (1991) On the Role of Refugia in Promoting Prudent Use of Biological Resources. Theoretical Population Biology, 40, 211-229 Loreau M . , Mouquet N. & Gonzalez A. (2003) Biodiversity as spatial insurance in heterogeneous landscapes. Proceedings of the National Academy of Sciences of the United States of America, 100, 12765-12770 McCullough D.R. (1996) Spatially structured populations and harvest theory. Journal of Wildlife Management, 60, 1-9 Milner-Gulland E.J. & Bennett E.L. (2003) Wild meat: the bigger picture. Trends in Ecology & Evolution, 18, 351-357 Myers R.A. & Worm B. (2003) Rapid worldwide depletion of predatory fish communities. Nature, 423, 280-283 Neubert M.G. (2003) Marine reserves and optimal harvesting. Ecology Letters, 6, 843-849 30 Norse E.A., Grimes C.B., Ralston S., Hilborn R , Castilla J.C., Palumbi S.R., Fraser D. & Kareiva P. (2003) Marine reserves: the best option for our oceans? Frontiers in Ecology and the Environment, 1, 495-502 Novaro A.J., Redford K.H. & Bodmer R.E. (2000) Effect of hunting in source-sink systems in the neotropics. Conservation Biology, 14, 713-721 Nowlis J.S. & Roberts C M . (1999) Fisheries benefits and optimal design of marine reserves. Fishery Bulletin, 97, 604-616 Ovaskainen O. (2002) Long-term persistence of species and the SLOSS problem. Journal of Theoretical Biology, 218, 419-433 Roberts C M . , Andelman S., Branch G., Bustamante R.H., Castilla J . C , Dugan J., Halpern B.S., Lafferty K.D., Leslie H., Lubchenco J., McArdle D., Possingham H.P., Ruckelshaus M . & Warner R.R. (2003) Ecological criteria for evaluating candidate sites for marine reserves. Ecological Applications, 13, S199-S214 Rodwell L.D. & Roberts C M . (2004) Fishing and the impact of marine reserves in a variable environment. Canadian Journal of Fisheries and Aquatic Sciences, 61, 2053-2068 Russ G.R. & Alcala A.C. (1996) Marine reserves: Rates and patterns of recovery and decline of large predatory fish. Ecological Applications, 6, 947-961 Russ G.R., Alcala A . C , Maypa A.P., Calumpong H.P. & White A.T. (2004) Marine reserve benefits local fisheries. Ecological Applications, 14,597-606 Shanks A.L . , Grantham B.A. & Carr M.H. (2003) Propagule dispersal distance and the size and spacing of marine reserves. Ecological Applications, 13, S159-S169 Srivastava D.S., Kolasa J., Bengtsson J., Gonzalez A., Lawler S.P., Miller T.E. , Munguia P., Romanuk T., Schneider D . C & Trzcinski M.K. (2004) Are natural microcosms useful model systems for ecology? Trends in Ecology & Evolution, 19, 379-384 Suman D., Shivlani M . & Milon J.W. (1999) Perceptions and attitudes regarding marine reserves: a comparison of stakeholder groups in the Florida Keys National Marine Sanctuary. Ocean & Coastal Management, 42, 1019-1040 Walter D.E. & Proctor H . C (1999) Mites : ecology, evolution and behaviour. CABI Publishing, Sydney. Wilkie D.S. & Carpenter J.F. (1999) Bushmeat hunting in the Congo Basin: an assessment of impacts and options for mitigation. Biodiversity and Conservation, 8, 927-955 31 Willis T.J., Millar R.B., Babcock R.C. & Tolimieri N. (2003) Burdens of evidence and the benefits of marine reserves: putting Descartes before des horse? Environmental Conservation, 30, 97-103 32 Chapter 3. Conclusion Resistance to reserve implementation comes, in part, from concern that reserves will reduce yield by removing a portion of the exploitable area from the harvestable pool. Using a moss microarthropod community we experimentally show that reserves can maintain or increase total regional yield. Reserves not only had no negative effect, but regions with reserves produced higher yields than regions without reserves. In addition, reserves increased diversity in non-reserve areas (NRAs), primarily through increased densities. Such increases in diversity may help guard against fluctuation in abundance of particular stocks (Hilborn et al. 2003). Export from reserves always compensated for any decrease in harvestable area the reserves represented, regardless of reserves area (25% or 50% of the region) or number (one or three). It must be cautioned that extrapolation of results beyond the reserve sizes examined here is not recommended, particularly as there is necessarily a point at which further increases in reserve size will translate into decreases in harvest. Similarly, the absence of an effect of reserve number may be a product of the relative scale at which experimentation took place. It is possible that increasing region sizes used in this study may accentuate differences between several small reserves and a single larger reserve, particularly when region size increases to a point at which proportionally few individuals are able to recolonize NRAs between harvests due to limited dispersal abilities. Further study is needed to evaluate the generalizability of these results. Harvesting effort was not displaced by reserves (which can be simulated by increasing effort in NRAs) in this study. Instead, reserves equated to a spatially-explicit 33 elimination of harvesting effort, and therefore a decrease in total effort. Although, similarly, most models do not evaluate the effect of effort redistribution (Gerber et al. 2003), some have indicated that reserves are capable of offsetting this redistribution (Grafton et al. 2005). Further experimentation of how redistribution of effort affects the ability of reserves to maintain yield are needed. We will, however, point out here that redistribution may not be necessary if the ultimate goal is to obtain harvests equal to those extracted from unmanaged systems. Although effort was reduced by as much as half in regions with reserves (as a direct result of reserve establishment) total harvest did not decrease, but rather showed slight increases. Further study into how reserves function in direct comparison to traditional management strategies may also prove fruitful. Traditional single-species management methods rely on reducing effort, as do reserves, but by either creating temporal closures or decreasing effort across, an entire region. It may be that reserves and more traditional management options are similar in their ability to maintain yield in many situations, but consideration must also be given to how these strategies compare in their costs, ability to protect biodiversity, and guard against overharvesting. In situations where harvesting affects a wide range of fauna (e.g. bushmeat hunting, many coral fisheries, or any fishery with large proportional bycatch) community-based management (such as reserves) may be necessary. Aside from examining the consequences of effort redistribution, many other avenues of research related to reserve design and construction remain to be explored. In this study we initially intended to gather information on regional diversity after 56 weeks of experimental harvesting (which includes diversity within the reserves). This was unfortunately not possible due to raccoon tampering shortly before a final census could 34 be conducted. For this reason we have focused solely on effects of reserves on NRAs in this paper, but reserves are generally established with two main goals in mind; maintaining yield and preserving biodiversity (Hastings & Botsford 2003). However, it is unclear whether the optimal reserve designs for promoting both biodiversity and yield at a regional scale are compatible (Hastings & Botsford 2003). Additionally, as mentioned before, varying region size may provide insights into the generalizability of our results, particularly our findings of no effect of reserve number. Experimental examination of how reserve placement (whether in source or sink areas) affects yield or diversity will also prove invaluable in assessing the amount of information required before siting reserves. These examples of future research directions (by no means exhaustive) may be experimentally addressed in the moss microarthropod system used here, which has proven itself highly amenable to such questions, but ultimately successful management decisions will need to be based on experimental evidence obtained from the systems of interest (large scale marine and terrestrial communities). Such experimentation, although so far prohibitive, may become possible as reserves become more widely used. This study provides replicated experimental evidence that reserves are capable of increasing total catch in surrounding NRAs. Such evidence, although obtained from a model system, provides support for the generally-held, though weakly supported, belief that reserves provide sustainable export to harvested areas (Willis et al. 2003). We also show that reserve size - but not number - is important in increasing total yield, with large reserves (comprising 50% of the total region) producing the highest total yields. Combining these results with the more widely acknowledged ability of reserves to protect 35 biodiversity within their borders provides a strong argument in favor of reserve implementation, particularly in regions where harvesting is affecting a wide range of species. 36 3.1 References Gerber L.R., Botsford L.W., Hastings A., Possingham H.P., Gaines S.D., Palumbi S.R. & Andelman S. (2003) Population models for marine reserve design: A retrospective and prospective synthesis. Ecological Applications, 13, S47-S64 Grafton R.Q., Kompas T. & Lindenmayer D. (2005) Marine reserves with ecological uncertainty. Bulletin of Mathematical Biology, 67, 957-971 Hastings A. & Botsford L.W. (2003) Comparing designs of marine reserves for fisheries and for biodiversity. Ecological Applications, 13, S65-S70 Hilborn R., Quinn T.P., Schindler D.E. & Rogers D.E. (2003) Biocomplexity and fisheries sustainability. Proceedings of the National Academy of Sciences of the United States of America, 100, 6564-6568 Willis T.J., Millar R.B., Babcock R.C. & Tolimieri N. (2003) Burdens of evidence and the benefits of marine reserves: putting Descartes before des horse? Environmental Conservation, 30, 97-103 37 

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