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in species composition and body size diversity between communities under Gyrinus and Notonecta predation ..... body size class using anova in statistica v6.1 (StatSoft Inc., Tulsa, ...... R Foundation for Statistical Computing, Vienna, Austria.
Journal of Animal Ecology 2010, 79, 1000–1011

doi: 10.1111/j.1365-2656.2010.01715.x

Prey dispersal rate affects prey species composition and trait diversity in response to multiple predators in metacommunities Jennifer G. Howeth*† and Mathew A. Leibold Section of Integrative Biology, University of Texas at Austin, 1 University Station C0930, Austin, TX 78712, USA

Summary 1. Recent studies indicate that large-scale spatial processes can alter local community structuring mechanisms to determine local and regional assemblages of predators and their prey. In metacommunities, this may occur when the functional diversity represented in the regional predator species pool interacts with the rate of prey dispersal among local communities to affect prey species diversity and trait composition at multiple scales. 2. Here, we test for effects of prey dispersal rate and spatially and temporally heterogeneous predation from functionally dissimilar predators on prey structure in pond mesocosm metacommunities. An experimental metacommunity consisted of three pond mesocosm communities supporting two differentially size-selective invertebrate predators and their zooplankton prey. In each metacommunity, two communities maintained constant predation and supported either Gyrinus sp. (Coleoptera) or Notonecta ungulata (Hemiptera) predators generating a spatial prey refuge while the third community supported alternating predation from Gyrinus sp. and N. ungulata generating a temporal prey refuge. Mesocosm metacommunities were connected at either low (0Æ7% day)1) or high (10% day)1) planktonic prey dispersal. The diversity, composition and body size of zooplankton prey were measured at local and regional (metacommunity) scales. 3. Metacommunities experiencing the low prey dispersal rate supported the greatest regional prey species diversity (H’) and evenness (J’). Neither dispersal rate nor predation regime affected local prey diversity or evenness. The spatial prey refuge at low dispersal maintained the largest difference in species composition and body size diversity between communities under Gyrinus and Notonecta predation, suggesting that species sorting was operating at the low dispersal rate. There was no effect of dispersal rate on species diversity or body size distribution in the temporal prey refuge. 4. The frequency distribution, but not the range, of prey body sizes within communities depended upon prey dispersal rate and predator identity. Taken together, these results demonstrate that prey dispersal rate can moderate the strength of predation to influence prey species diversity and the local frequency distribution of prey traits in metacommunities supporting ecologically different predators. Key-words: body size, connectivity, invertebrate predator, metacommunity, metapopulation, size-selective predation, spatial refuge, temporal refuge, zooplankton Introduction Large-scale spatial processes may interact with niche-based community structuring mechanisms to determine local and regional assemblages of predators and their prey (Holt 1993). Across regional spatial scales, biogeographical history (Schluter & Ricklefs 1993), predator and prey dispersal distances (Cronin et al. 2000; Hammond, Luttbeg & Sih 2007) and the *Correspondence author. E-mail: [email protected] †Present address: Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520, USA.

strength of environmental gradients (Werner & McPeek 1994; Chase 2003) interactively determine predator-prey spatial co-occurrence patterns. The taxonomic and functional diversity of predators represented in the landscape can further affect both prey assemblages and the spatial distribution of prey traits (Chalcraft & Resetarits 2003a; DeWitt & Langerhans 2003). At the local community scale, selective predators may exclude prey species (Sih et al. 1985; Spiller & Schoener 1998), facilitate prey coexistence through suppression of dominant competitors (Paine 1966; Leibold 1996; Shurin & Allen 2001), or alter prey densities via apparent competition (Holt 1977; Bonsall & Hassell 1997). Recent

 2010 The Authors. Journal compilation  2010 British Ecological Society

Multiple predators in prey metacommunities 1001 advances in metacommunity theory suggest that predator and prey dispersal rates among local communities can modify these effects on local and regional predator-prey assemblages (Holt 1993; Shurin & Allen 2001; Amarasekare 2006). However, empirical work in multi-trophic metacommunities has largely focused on the impacts of a single predator in constant prey environments (e.g. Holyoak & Lawler 1996; Kneitel & Miller 2003; Cadotte, Fortner & Fukami 2006 but see Warren 1996; Holyoak 2000; Cadotte & Fukami 2005) and has yet to adequately address how predator and prey dispersal may affect prey composition in response to predator functional diversity represented in the region. In predator-prey metacommunities, local communities may support functionally dissimilar predators in both space and time (Cadotte & Fukami 2005; McCann, Rasmussen & Umbanhowar 2005; Amarasekare 2007; Hammond et al. 2007). Spatial heterogeneity in selective predator incidence can generate spatial prey refuges (Sih 1987; Sih & Wooster 1994) and thus promote regional predator-prey coexistence (Cadotte & Fukami 2005). Likewise, temporally variable predator occurrence from movement behaviour or colonization-extinction dynamics can yield temporal prey refuges (Sih 1987; Howeth & Leibold 2008). Prey dispersal rates in metacommunities may interact with this spatial and temporal variation in predator incidence to facilitate prey tracking of local predation (‘species sorting’; Leibold & Norberg 2004) or generate source-sink dynamics in prey (‘mass effects’; Holyoak & Lawler 1996). Recent empirical evidence suggests that the spatial frequency of prey species and prey traits maintained in metacommunities will depend in part upon prey dispersal rates among local communities (Warren 1996; Cadotte & Fukami 2005; Cadotte et al. 2006). For example, prey immigration may mediate the negative impact of local predator selectivity by delivering migrant prey representative of the range of species maintained in the regional pool, and may thereby reduce local prey extinction risk (Sih & Wooster 1994; Holyoak & Lawler 1996; Shurin 2001). Additionally, ecologically important prey traits directly selected by predation, including body size and avoidance behaviour, may only persist in a local community through prey immigration (Leibold & Norberg 2004; Urban et al. 2008). Although prey dispersal rate may be important in shaping prey species and trait composition at multiple scales, the relative effects of dispersal may depend on the breadth of functional diversity represented in the regional predator species pool. In this study, we tested for interactive effects of prey dispersal rate and spatially and temporally heterogeneous predation from different predators on prey structure in experimental pond metacommunities. Pond metacommunity assemblages were modelled after two naturally co-occurring and differentially size-selective invertebrate predators, backswimmers Notonecta and whirligig beetles Gyrinus, and their zooplankton prey. Experimental metacommunities consisted of three pond mesocosm communities, where two of the three communities maintained a spatial prey refuge through constant predation from Gyrinus sp. or N. ungulata

Say while the third community maintained a temporal prey refuge by alternating Gyrinus sp. and N. ungulata incidence in simulated colonization and extinction. Mesocosm metacommunities were connected at either low or high planktonic prey dispersal which reflected dispersal rates likely to alter zooplankton diversity based upon metacommunity models (Mouquet & Loreau 2002, 2003) and field studies (Michels et al. 2001; Cohen & Shurin 2003). Low dispersal approximated 7% of the demographic turnover rate of zooplankton in this experiment (0Æ10 day)1; estimated from Gillooly 2000), while high dispersal approximated 100% of the turnover rate. In accord with metacommunity theory, we hypothesized that local communities at low prey dispersal would be more diverse than communities at high dispersal (Mouquet & Loreau 2002, 2003), while high dispersal metacommunities would support a smaller, and less equitably distributed, regional prey species pool from regional homogenization (Mouquet & Loreau 2003). Due to differences in foraging of Gyrinus and Notonecta, we expected these predators to produce local prey assemblages with contrasting size distributions (following Chalcraft & Resetarits 2003b). Yet, we predicted that differences in prey size structure among the three local communities would be reduced at high dispersal as a consequence of regional homogenization.

Materials and methods STUDY SYSTEM

Ponds serve as a model system in which to address the influence of predator functional diversity on prey structure at local and regional spatial scales in metacommunities. Pond communities are nested within a landscape of terrestrial matrix where species diversity is jointly determined by regional species dispersal rates and the local environment (Shurin 2001; Cottenie et al. 2003; Howeth & Leibold 2010). Local pond communities are spatio-temporally connected in part by actively dispersed predators and passively dispersed prey (Caceres & Soluk 2002; Chase 2003; Chase & Ryberg 2004). Two functionally dissimilar invertebrate predators, the whirligig beetle Gyrinus (Coleoptera: Gyrinidae) and the backswimmer Notonecta (Hemiptera: Notonectidae), coexist locally in natural ponds (Clark 1928) and are patchily distributed among ponds in a metapopulation structure (Svensson 1985; Briers & Warren 2000). Adult Notonecta are relatively large (body length 11–12 mm; Rice 1954) and less gapelimited than Gyrinus (4–5 mm; Oygur & Wolfe 1991). Notonecta swims vertically through the water column while preying upon largebodied zooplankton (Scott & Murdoch 1983; Arner et al. 1998); whereas Gyrinus remains on the water surface and opportunistically preys upon small-bodied zooplankton (Svensson 1985; Oygur & Wolfe 1991). Here, we constructed pond mesocosm metacommunities to resemble these natural predator-prey assemblages. We consider the triad of mesocosm communities connected by dispersal to be the ‘regional’ spatial scale or the ‘metacommunity,’ and each mesocosm community to be the ‘local’ spatial scale.

EXPERIMENTAL DESIGN

The pond mesocosm experiment was conducted at Michigan State University’s Kellogg Biological Station (Hickory Corners, Michigan,

 2010 The Authors. Journal compilation  2010 British Ecological Society, Journal of Animal Ecology, 79, 1000–1011

1002 J. G. Howeth & M. A. Leibold USA) from 23 May–21 August 2003. On 23 May, twenty-four 322 L polyethylene stock tank mesocosms were acid washed and filled with 20 L of silica sand for substrate and 300 L of well water. Well water was measured for ambient levels of total nitrogen (N) and phosphorus (P) using spectrophotometric methods. N (NaHNO3) and P (NaH2PO4) were subsequently added to each tank to achieve target nutrient levels of 2100 lg L)1 N and 150 lg L)1 P which reflect the upper range of N and P found in natural ponds of the region (Hall et al. 2007). Weekly additions of N (0Æ173 g tank)1) and P (0Æ009 g tank)1) maintained target levels and offset 5% day)1 loss of nutrients to the bottom substrate. On 29 May, mesocosms received 200 mL of a pond water inoculum containing a diverse regional assemblage of zooplankton, algal and bacterial communities representative of biota from 16 south-central (Barry and Kalamazoo Counties) Michigan ponds. After inoculation, communities were allowed to reach near-equilibrium for c. 1 month. All mesocosms were covered with 1 mm screen mesh lids to prevent exchange of organisms with the outside environment. On 26 June, six adult individuals each of Gyrinus or Notonecta were added to one of the two mesocosms supporting constant food webs in each metacommunity. Half (n = 2) of the cyclical predation communities received Gyrinus while the remaining half received Notonecta. The predator species in the cyclical predation communities were switched every 14 days, where the two predators never coexisted in time within the same local community. Six adult individuals of the appropriate species were added at the start of each new cycle. Of the two predators, only Notonecta reproduced during the experiment. Juvenile notonectids were removed from both cyclical and constant predation communities during the predator switching events in order to maintain standardized predation pressure. Low and high prey dispersal treatments were initiated in mesocosm metacommunities on 4 July. To simulate prey dispersal within a metacommunity of the low dispersal treatment, water was manually moved among the three communities once per week with an integrated depth polyvinyl chloride (PVC) sampler (5% tank water volume per week, roughly equivalent to 0Æ71% day)1; 8 L week)1 transferred from each of the two constant communities to the community supporting cyclical predation and 8 L subsequently transferred back to each constant community; Fig. S1a, Supporting information). This low dispersal rate approximates natural levels of zooplankton dispersal found among hydrologically isolated ponds in south-central Michigan (Cohen & Shurin 2003). To achieve high dispersal within a metacommunity (31Æ1 L day)1, 10% tank water volume per day, roughly equivalent to 70% per week) water was transferred among the three communities with a centrifugal water pump through 19 mm PVC pipe (Fig. S1b, Supporting information). Water was pumped from the constant environment tanks to the variable tank first and then allowed to flow back to equilibrate water levels, in a scheme similar to the manualtransfer used in the low dispersal treatment. Based upon data presented in Michels et al. (2001), this rate approximates high zooplankton dispersal among natural ponds that are hydrologically connected. Each community in the low dispersal treatment supported a pump and PVC loop to control for possible pumpinduced disruption of predator-prey interactions and any negative effects on plankton mortality sustained in the high dispersal treatment (Fig. S1a, Supporting information). Predator exclusion screens, consisting of overlapping 6 mm mesh hardware cloth sheets, covered the ends of the PVC pipes to prevent inter-community exchange of invertebrate predators. All water pumps were activated for 1 min daily during the evening (19.30–19.31 h), when

zooplankton were distributed throughout the water column during diel vertical migration.

SAMPLING

Mesocosm metacommunities were sampled for zooplankton (i) on 25 June prior to imposition of predation and dispersal treatments; (ii) on 3 July with the predation treatment imposed but prior to the dispersal treatment; (iii) and subsequently every 7 days through 22 August with both predation and dispersal treatments imposed. Tanks were sampled with a 1 L depth-integrated PVC sampler to remove 10Æ5 L of water from each tank. Ten liters of the sample were filtered through 80 lm mesh to isolate zooplankton. Zooplankton samples were cleaned manually to rid of debris and were preserved in 5% acid-sucrose iodine solution for later microscopic enumeration in the laboratory. Following Smith (2001), cladoceran zooplankton were identified to species for Alona affinis, Bosmina longirostris, Ceridodaphnia reticulata, Chydorus sphaericus, Daphnia pulex, Scapholeberis mucronata and Simocephalus serrulatus (species hereafter referred to by genus) and copepods were identified to the orders Calanoida and Cyclopoida. Further, adult and juvenile stages of Ceriodaphnia, Daphnia, Scapholeberis and copepods (copepodite stage) were assessed independently. Body lengths of c. 25 individuals of each species and stage were measured to obtain a mean species and stage-specific body length.

REGIONAL AND LOCAL PREY DIVERSITY

Three different prey diversity measures: (i) species diversity (Shannon index, H’, in Magurran 2004 using log10); (ii) species richness (S); and (iii) species evenness (Shannon index, J’, in Magurran 2004 using log10) were calculated at local and regional spatial scales for each predator-prey metacommunity (Fig. S1c, Supporting information). Regional diversity measures represented the sum of unique species or taxonomic groups (for S) or individuals (for H’ and J’) sampled in the three communities of the metacommunity on a sample date. Local species richness did not differ among mesocosm metacommunities at the start of the experiment prior to imposition of prey dispersal and predation treatments (one-way anova; F 7,16 = 0Æ94, P = 0Æ51). Therefore, to evaluate predation and dispersal treatment effects on prey diversity, local and regional diversity measures were each averaged over weeks 3–6 (to align with density analyses below) and the final two sample dates of the experiment, weeks 5–6. Mean values were assessed for normality with a Shapiro– Wilks test prior to analysis with one-tailed Welch’s t-tests (regional) and split-plot anovas (local) in the R statistical environment (R Development Core Team 1996) and SAS v9Æ1 (SAS Institute, Cary, North Carolina, USA), respectively. One-tailed t-tests were employed because of an a priori hypothesis based upon metacommunity theory. In order to evaluate the effect of prey dispersal rate and predation regime on prey composition in the three communities of each metacommunity, a permutational multivariate analysis of variance was performed in permanova v6 (Anderson 2001, 2005). A split-plot design was not possible in permanova, and thus a two-way analysis was employed. Juvenile and adult counts were combined for each prey species, except for the copepodites which were excluded because they were not assigned to order. The permanova was conducted on Bray–Curtis dissimilarity measures calculated from log10 (x + 1) transformed species density data generated from a mean of sampling weeks 3–6. In the Bray–Curtis distance measure, abundant and rare species contribute equally to the dissimilarity

 2010 The Authors. Journal compilation  2010 British Ecological Society, Journal of Animal Ecology, 79, 1000–1011

Multiple predators in prey metacommunities 1003 between sites. Thus, Bray–Curtis is especially appropriate for normalized density data (Legendre & Legendre 1998). To test for differences in variance in species composition between dispersal and predation treatments, we calculated the Bray–Curtis distance of the replicates from their treatment centroids, and compared the mean distances between treatments using permutation anova in permdisp2 (Anderson 2004). permanova and permdisp2 tests were performed using 10 000 unrestricted permutations of Bray–Curtis distance measures. For effects shown to be statistically significant at a = 0Æ05, post hoc pairwise comparisons with the permanova t-statistic assessed treatment differences. To determine the response of individual prey taxa to dispersal rate and predation regime, an indicator species analysis, IndVal (Dufrene & Legendre 1997), was employed in PC-ORD v4 (McCune & Mefford 1999). In this method, an indicator value (I.V.) represents a percentage score corresponding to a species strength of treatment level specificity, as determined by species densities, where a score of 100 is a perfect predictor or ‘indicator’ of the treatment level. The cyclical and two constant predation communities were evaluated independently for dispersal and predation treatment level indicators. For prey communities under cyclical predation, one Gyrinus-Notonecta predation cycle was evaluated by averaging species density data for each of two 2-week predation periods, sampling weeks 3–4 and weeks 5–6. For prey communities under constant predation, species density data for weeks 3–6 were averaged for the analysis. Juvenile and adult counts were combined (copepodites excluded), and species density data were log10 (x + 1) transformed. Statistical significance of a species’ I.V. was evaluated by comparing the observed I.V. to a null distribution generated through 10 000 Monte Carlo permutations. The proportion of simulated I.V. greater than or equal to the observed I.V. determined significance for an a of 0Æ05.

SPATIAL AND TEMPORAL PREY REFUGES

A measure of beta diversity, Sorenson’s dissimilarity (Magurran 2004), was used to evaluate effects of dispersal rate and predator identity on species composition between the two communities in the spatial refuge (constant predation) and within the community in the temporal refuge (cyclical predation) (Fig. S1c, Supporting information). For the temporal refuge, beta diversity was calculated from mean density data taken from weeks 3–4 and weeks 5–6 to encompass alternating predation from Gyrinus and Notonecta. For the spatial refuge, beta diversity was calculated from mean density weeks 3–6 to align with the temporal analysis. To detect responses of individual species to predator identity in the spatial and temporal refuges within each dispersal treatment, this same density data was contrasted between Gyrinus and Notonecta regimes. Diversity and log10 density values were analysed with one-tailed Welch’s t-tests in the R statistical environment.

REGIONAL AND LOCAL PREY SIZE STRUCTURE

The role of prey dispersal rate on the distribution of prey body sizes within the predator-prey metacommunity was assessed by calculating the proportion of individuals within body size classes at the local and regional scale. Each species and stage was assigned to a body size class based upon mean body length (mm), where size classes were defined by log10 0Æ1 mm increments. Species and life-history stage densities (juvenile and adult, where applicable) were averaged over weeks 3–6 and weeks 5–6, and subsequently were converted to proportional representation for each body size class. Size class propor-

tions for each community and metacommunity were arcsine square root transformed and analysed for the effects of dispersal rate and body size class using anova in statistica v6.1 (StatSoft Inc., Tulsa, OK, USA).

Results REGIONAL AND LOCAL PREY DIVERSITY

Prey dispersal rate altered prey species diversity at regional spatial scales in predator-prey metacommunities (Fig. 1a; Table 1). The high dispersal metacommunities were less diverse (H’) than low dispersal metacommunities. High dispersal significantly decreased regional species evenness (J’); yet there was only a marginal effect of dispersal rate on regional richness (S, Fig. 1c and e). These regional effects were strongest at the end of the experiment, averaged over weeks 5–6. At the local spatial scale, the influence of dispersal rate on diversity measures was less apparent (Table 1). Diversity was reduced in high dispersal communities relative to low dispersal communities, but this effect was only marginally significant for weeks 5–6 and NS for weeks 3–6 (Fig. 1b). There was no impact of dispersal rate or predation on local species richness or evenness for weeks 5–6 (Fig. 1d and f). However, there were marginal effects of dispersal, and a dispersal by predation interaction, on local prey species richness for weeks 3–6. Prey dispersal rate influenced local prey species composition in metacommunities (permanova; dispersal F1,18 = 2Æ12, P = 0Æ05; predation, F2,18 = 1Æ14, P = 0Æ35; dispersal · predation, F2,18 = 0Æ34, P = 0Æ98). There was no effect of predation regime, nor an interactive effect of predation and dispersal, on community composition. Dispersal rate did not alter the variance in community composition (permdisp2; dispersal F1,18 = 0Æ84, P = 0Æ37; predation, F2,18 = 3Æ77, P = 0Æ04; dispersal · predation, F2,18 = 1Æ41, P = 0Æ28). In contrast, predation affected community variance, with Gyrinus and Notonecta communities differing from one another and where Notonecta communities exhibited the greatest dispersion (mean Bray–Curtis within-treatment dissimilarities: G = 26Æ15, N = 35Æ28, G-N = 31Æ94; post hoc treatment contrasts; G · N, t = 2Æ68, P = 0Æ02, GN · G; t = 1Æ28, P = 0Æ22; G-N · N, t = 1Æ45, P = 0Æ17). There was no interactive effect of predation regime and dispersal rate on community variability. The indicator analysis identified key species responsible for dispersal-induced changes in community composition (Table 2). Two small-bodied zooplankters, Bosmina and Chydorus, were significant indicators of the low dispersal rate reflecting their greater densities in low dispersal metacommunities (Fig. 2a–f; Fig. S2, Supporting information). The remaining species in the experiment showed no trends in abundance by dispersal treatment (Fig. S3, Supporting information). Only one species, the large-bodied Daphnia, served as a significant indicator of predator identity. Daphnia was more abundant in Gyrinus communities than in Notonecta communities (Fig. 2g and h; Fig. S2, Supporting informa-

 2010 The Authors. Journal compilation  2010 British Ecological Society, Journal of Animal Ecology, 79, 1000–1011

1004 J. G. Howeth & M. A. Leibold (b) 1.0

0.8

*

0.6 0.4 0.2

Local diversity (H')

Regional diversity (H')

(a) 1.0

0.0

0.8

+ 0.6 0.4 0.2 0.0

Low

Low

High

Dispersal rate

+

8.0

Dispersal rate (d) 10.0

Local richness (S)

Regional richness (S)

(c) 10.0

6.0 4.0 2.0 0.0

8.0 6.0 4.0 2.0 0.0

Low

Low

High

Dispersal rate (e) 1.0

(f)

0.8

*

0.6 0.4 0.2 0.0

1.0 0.8 0.6 0.4 0.2 0.0

Low

High

Dispersal rate

Local evenness (J')

Regional evenness (J')

High

High

Dispersal rate

Low

High

Dispersal rate

tion). Daphnia additionally served as an indicator of the low dispersal rate for communities under cyclical predation (Fig. 2i).

SPATIAL AND TEMPORAL PREY REFUGES

Beta diversity values in both the spatial and temporal refuges were lower on average in the high dispersal metacommunities, indicating an increase in compositional similarity, but they did not significantly differ from the low dispersal metacommunities (spatial refuge, beta diversity mean ± SE; low dispersal, 0Æ61 ± 0Æ14, high dispersal, 0Æ56 ± 0Æ11; onetailed t-test, t = )0Æ32 d.f. = 5Æ82, P = 0Æ38; temporal refuge, low dispersal, 0Æ61 ± 0Æ10, high dispersal, 0Æ50 ± 0Æ16; t = )0Æ59, d.f. = 4Æ92, P = 0Æ29).

Fig. 1. Regional and local prey diversity in predator-prey metacommunities. (a) Regional prey species diversity (H’) as a function of low and high prey dispersal rate. (b) Local prey species diversity as a function of prey dispersal rate and predation from Gyrinus sp. (black bars), Gyrinus sp.-Notonecta ungulata (striped bars) and Notonecta ungulata (gray bars). (c) and (d) Regional and local prey species richness (S). (e) and (f) Regional and local prey species evenness (J’). Closed circles and dashed line represent the mean response for low and high dispersal treatments. Statistically significant dispersal effects: + P < 0Æ1; * P < 0Æ05. Statistical analysis reported in the results. Values are mean sampling weeks 5 and 6 + 1 SE, n = 4.

There were differences in prey species densities as a function of predator identity in spatial, but not temporal, prey refuges within low and high dispersal metacommunities (spatial, Table S1, Supporting information; temporal, one-tailed t-test; all species, P > 0Æ1; Table S2, Supporting information). In the spatial prey refuge of low dispersal metacommunities, Chydorus, Daphnia and Scapholeberis supported higher densities in the presence of Gyrinus, suggesting an effective refuge from direct or indirect effects of Notonecta predation (Fig. 3a–f, Table S1, Supporting information). There was no difference in the densities of these species between the two community types in the high dispersal metacommunities. Simocephalus was the only species that supported different densities in the two constant predation communities of high dispersal metacommunities, where

 2010 The Authors. Journal compilation  2010 British Ecological Society, Journal of Animal Ecology, 79, 1000–1011

Multiple predators in prey metacommunities 1005 Table 1. Regional and local prey species diversity (H’), richness (S) and evenness (J’) in predator-prey metacommunities. Diversity measures were contrasted across dispersal rate (low, high) and predation (Gyrinus sp., Notonecta ungulata, Gyrinus sp.-Notonecta ungulata) treatments. t, F Response variable Regional Diversity (H’) Richness (S) Evenness (J’) Local Diversity (H’)

Richness (S)

Evenness (J’)

t, F

Treatment

d.f.

weeks 3–6

P-value

weeks 5–6

P-value

Dispersal Dispersal Dispersal

5Æ38 3Æ74 5Æ98

)2Æ10 )1Æ85 )1Æ46

0Æ04** 0Æ07* 0Æ11

)2Æ72 )1Æ67 )3Æ11

0Æ02** 0Æ09* 0Æ01**

Dispersal Predation Dispersal · Predation Dispersal Predation Dispersal · Predation Dispersal Predation Dispersal · Predation

1, 6 2, 12 2, 12 1, 6 2, 12 2, 12 1, 6 2, 12 2, 12

0Æ29 1Æ74 2Æ45 5Æ16 0Æ29 3Æ19 0Æ36 1Æ79 1Æ08

0Æ61 0Æ22 0Æ13 0Æ06* 0Æ76 0Æ08* 0Æ57 0Æ21 0Æ37

4Æ46 1Æ00 1Æ54 2Æ88 1Æ14 0Æ78 2Æ55 0Æ88 2Æ49

0Æ08* 0Æ40 0Æ25 0Æ14 0Æ35 0Æ48 0Æ16 0Æ44 0Æ12

Results reported from one-tailed Welch’s t-tests (regional) and split-plot anovas (local) on mean diversity values from weeks 3 to 6 and weeks 5 to 6. Significance levels for probability values: *P < 0Æ1; **P < 0Æ05.

Table 2. Results of the indicator species analysis assessing the strength of prey taxa association with prey dispersal rate (D; L = low, H = high) and predator identity (P; G = Gyrinus sp., N = Notonecta ungulata) by predation regime (constant, cyclical) in predator-prey metacommunities. Constant dispersal

Cyclical dispersal

Constant predation

Cyclical predation

Species

D

I.V.

I.V.rand

P

D

I.V.

I.V.rand

P

P

I.V.

I.V.rand

P

P

I.V.

I.V.rand

P

Chydorus Alona Bosmina Scapholeberis Ceriodaphnia Cyclopoid Simocephalus Calanoid Daphnia

L L L L H H H L H

65Æ5 54Æ9 73Æ6 55Æ4 54Æ6 50Æ4 55Æ8 46Æ8 53Æ3

38Æ9 51Æ1 56Æ2 54Æ5 52Æ9 52Æ9 53Æ3 52Æ2 54Æ5

0Æ05** 0Æ28 0Æ02** 0Æ33 0Æ35 0Æ92 0Æ24 0Æ76 0Æ57

L L L L L L H L L

68Æ2 55Æ1 80Æ4 59Æ9 50Æ9 54Æ0 43Æ8 38Æ3 61Æ5

36Æ0 54Æ2 48Æ5 54Æ4 55Æ5 51Æ8 52Æ2 45Æ5 53Æ9

0Æ03** 0Æ39