Fifty years of biological conservation
Robin J. PakemanAmanda E. BatesRichard T. CorlettGraeme S. CummingDavid G. JohnsLian Pin KohRafael LoyolaBea MaasLiba PejcharRichard B. PrimackTracey J. ReganRobin RothLaurent GodetDanielle DescoteauxVincent Devictor
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Metacommunity
Metacommunity
Ectotherm
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Although there has been growing interest in the effect of dispersal on species diversity, much remains unknown about how dispersal occurring at multiple scales influences diversity. We used an experimental microbial landscape to determine whether dispersal occurring at two different scales - among local communities and among metacommunities - affects diversity differently. At the local scale, dispersal initially had a positive effect and subsequently a neutral effect on diversity, whereas at the metacommunity and landscape scales, dispersal showed a consistently negative effect. The timing in which dispersal affected beta diversity also differed sharply between local communities and metacommunities. These patterns were explained by scale- and time-dependent effects of dispersal in allowing spread of species and in removing spatial refuges from predators. Our results suggest that the relative contribution of opposing mechanisms by which dispersal affects diversity changes considerably over time and space in hierarchical landscapes in which dispersal occurs at multiple scales.
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A recent challenge in community ecology is to understand under what conditions local and regional processes may be more important in shaping community structure. We investigated the role of dispersal mode and generation time for communities of macroinvertebrates in two sets of connected ponds during three consecutive years. We found no evidence that generation time affected metacommunity structure, possibly because statistical power was limited because the range of generation times present was small. In contrast, we found that the spatial structure of the macroinvertebrate metacommunities differed with dispersal mode in one of two sets of ponds. Passive dispersers showed positive distance-dissimilarity correlations, suggesting mass effects via the pond connections. These correlations did not stretch beyond the first pond downstream suggesting that, in this chain of connected ponds, intervening ponds effectively buffered dispersal. Active dispersers did not show any consistent spatial pattern, possibly because intensive over-land dispersal homogenized the metacommunity. Thus, although pond connections probably equally promoted dispersal of actively and passively dispersing macroinvertebrates, the implications for the structure of their metacommunities may depend on their dispersal mode. We conclude that dispersal mode has the potential to affect the mechanisms that are integral to metacommunity structure.
Metacommunity
Community
Distance decay
Mode (computer interface)
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Abstract Although metacommunity models generally formulate dispersal as a random, passive process, mounting evidence suggests that dispersal can be an active process depending on species fitness over the landscape, particularly in multitrophic communities. How different dispersal modes (i.e. from random to increasingly fitness‐dependent dispersal) modulate the effect of dispersal on biodiversity remains unclear. Here, we used a metacommunity model of food webs to investigate the effects of dispersal and habitat heterogeneity on biodiversity and how these effects may be dependent on dispersal mode. Our results showed that compared to isolated systems, random dispersal increased local food web diversity ( diversity) but decreased across‐community dissimilarity ( diversity) and regional food web diversity ( diversity), consistent with findings from competitive metacommunity models. However, fitness‐dependency could alter the effects of dispersal on biodiversity. Both and diversity increased with the strength of fitness‐dependency of dispersal, while diversity peaked at intermediate fitness‐dependency. Notably, strong fitness‐dependent dispersal maintained levels of and diversity similar to those observed in isolated systems. Thus, random dispersal and isolation (i.e. no dispersal) can be considered as two extremes along the continuum of fitness‐dependent dispersal, in terms of their effects on biodiversity. Moreover, both biodiversity‐habitat heterogeneity and biodiversity‐habitat connectivity relationships depended on the dispersal mode. Strikingly, under random dispersal, diversity decreased with habitat heterogeneity and connectivity, but under strong fitness‐dependent dispersal, it increased with habitat heterogeneity and remained unchanged as habitat connectivity increased. Our study highlights the context dependence of dispersal effects on biodiversity in heterogeneous landscapes. Our findings have useful implications for biodiversity conservation and landscape management, where management strategies should account for different modes of dispersal across taxa, thus different responses of biodiversity to habitat heterogeneity and connectivity.
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Theoretically, dispersers should target the habitat where prospects for fitness will be highest. Aiming for a habitat similar to the natal area (natal habitat-biased dispersal) has been hypothesized as a probable rule of thumb for dispersers, but has received very little empirical support to date. We investigated similarities between natal and post-dispersal settlement sites with radio-collared Siberian flying squirrels ( Pteromys volans L.). Juveniles born in small patches and raised in nests close to patch edge settled in small patches and used nests close to edges after dispersal. In addition, post-dispersal use of dreys (versus cavities) was similar to that observed in natal sites. However, the quality of settlement habitat was unrelated to the quality of the natal site, which suggests that natal experience on average-quality habitats may not lead to ecological traps for flying squirrels. This study provides evidence that habitat selection at the landscape scale is influenced by habitat of natal area.
Ecological trap
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Metacommunity
Density dependence
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Difference in dispersal ability is a key driver of species coexistence in metacommunities. However, the available frameworks for interpreting species diversity patterns in natura often overlook trade-offs and evolutionary constraints associated with dispersal. Here, we build a metacommunity model accounting for dispersal evolution and a competition–dispersal trade-off. Depending on the distribution of carrying capacities among communities, species dispersal values are distributed either around a single strategy (evolutionarily stable strategy, ESS), or around distinct strategies (evolutionary branching, EB). We show that limited dispersal generates spatial aggregation of dispersal traits in ESS and EB scenarios, and that the competition–dispersal trade-off strengthens the pattern in the EB scenario. Importantly, individuals in larger (respectively (resp.) smaller) communities tend to harbour lower (resp. higher) dispersal, especially under the EB scenario. We explore how dispersal evolution affects species diversity patterns by comparing those from our model to the predictions of a neutral metacommunity model. The most marked difference is detected under EB, with distinctive values of both α- and β-diversity (e.g. the dissimilarity in species composition between small and large communities was significantly larger than neutral predictions). We conclude that, from an empirical perspective, jointly assessing community carrying capacity with species dispersal strategies should improve our understanding of diversity patterns in metacommunities.
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Although it is well‐known that dispersal of organisms within a metacommunity will influence patterns of coexistence and richness, theoretical and experimental studies generally assume that dispersal rates are constant through time. However, dispersal is often a highly variable process that can vary seasonally and/or when stochastic events (e.g. wind storms, droughts, floods) occur. Using a well‐known source–sink metacommunity model, we present novel predictions for local and regional species richness when stochasticity in dispersal is expressly considered. We demonstrate that dispersal stochasticity alters some of the predictions obtained with constant dispersal; the peak of the predicted hump‐shaped relationship between dispersal and local species richness is diminished and shifted towards higher values of dispersal. Dispersal stochasticity increases extinction probabilities of inferior competitor species particularly in metacommunities subjected to severe isolation events (i.e. decreases of dispersal) or homogenization events (i.e. sudden increases of dispersal). Our results emphasize how incorporating dispersal stochasticity into theoretical predictions will broaden our understanding of metacommunities dynamics and their responses to natural and human‐related disturbances.
Metacommunity
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Climate change is increasingly affecting the structure and dynamics of ecological communities both at local and at regional scales, and this can be expected to have important consequences for their robustness and long-term persistence. The aim of the present work is to analyse how the spatial structure of the landscape and dispersal patterns of species (dispersal rate and average dispersal distance) affects metacommunity response to two disturbances: (i) increased mortality during dispersal and (ii) local species extinction. We analyse the disturbances both in isolation and in combination. Using a spatially and dynamically explicit metacommunity model, we find that the effect of dispersal on metacommunity persistence is two-sided: on the one hand, high dispersal significantly reduces the risk of bottom-up extinction cascades following the local removal of a species; on the other hand, when dispersal imposes a risk to the dispersing individuals, high dispersal increases extinction risks, especially when dispersal is global. Large-bodied species with long generation times at the highest trophic level are particularly vulnerable to extinction when dispersal involves a risk. This suggests that decreasing the mortality risk of dispersing individuals by improving the quality of the habitat matrix may greatly increase the robustness of metacommunities.
Metacommunity
Extinction (optical mineralogy)
Habitat Fragmentation
Metapopulation
Extinction debt
Local extinction
Persistence (discontinuity)
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