Dispersal Ability Determines the Role of Environmental, Spatial and Temporal Drivers of Metacommunity Structure (original) (raw)
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1. Metacommunity ecology addresses the situation where sets of local communities are connected by the dispersal of a number of potentially interacting species. Aquatic systems (e.g. lentic versus lotic versus marine) differ from each other in connectivity and environmental heterogeneity, suggesting that metacommunity organisation also differs between major aquatic systems. Here, we review findings from observational field studies on metacommunity organisation in aquatic systems. 2. Species sorting (i.e. species are 'filtered' by environmental factors and occur only at environmentally suitable sites) prevails in aquatic systems, particularly in streams and lakes, but the degree to which dispersal limitation interacts with such environmental control varies among different systems and spatial scales. For example, mainstem rivers and marine coastal systems may be strongly affected by 'mass effects' (i.e. where high dispersal rates homogenise communities to some degree at neighbouring localities, irrespective of their abiotic and biotic environmental conditions), whereas isolated lakes and ponds may be structured by dispersal limitation (i.e. some species do not occur at otherwise-suitable localities simply because sites with potential colonists are too far away). Flow directionality in running waters also differs from water movements in other systems, and this difference may also have effects on the role of dispersal in different aquatic systems. 3. Dispersal limitation typically increases with increasing spatial distance between sites, mass effects potentially increase in importance with decreasing distance between sites, and the dispersal ability of organisms may determine the spatial extents at which species sorting and dispersal processes are most important. 4. A better understanding of the relative roles of species sorting, mass effects and dispersal limitation in affecting aquatic metacommunities requires the following: (i) characterising dispersal rates more directly or adopting better proxies than have been used previously; (ii) considering the nature of aquatic networks; (iii) combining correlative and experimental approaches; (iv) exploring temporal aspects of metacommunity organisation and (v) applying past approaches and statistical methods innovatively for increasing our understanding of metacommunity organisation.
Oecologia, 2016
We examined variation in the composition of six freshwater organismal groups across various drainage basins in Finland. We first modelled spatial structures within each drainage basin using Moran eigenvector maps. Second, we partitioned variation in community structure among three groups of predictors using constrained ordination: (1) local environmental variables, (2) spatial variables, and (3) dummy variable drainage basin identity. Third, we examined turnover and nestedness components of multiple-site beta diversity, and tested the best fit patterns of our datasets using the "elements of metacommunity structure" analysis. Our results showed that basin identity and local environmental variables were significant predictors of community structure, whereas withinbasin spatial effects were typically negligible. In half of the organismal groups (diatoms, bryophytes, zooplankton), basin identity was a slightly better predictor of community structure than local environmental variables, whereas the opposite was true for the remaining three organismal groups (insects, macrophytes, fish). Both pure basin and local environmental fractions were, however, significant after accounting for the effects of the other predictor variable sets. All organismal groups exhibited high levels of beta diversity, which was mostly attributable to the turnover component. Our results showed consistent Clementsian type metacommunity structures, suggesting that subgroups of species responded similarly to environmental factors or drainage basin limits. We conclude that aquatic communities across large scales are mostly determined by environmental and basin effects, which leads to high beta diversity and prevalence of Clementsian community types.
Metacommunity size influences aquatic community composition in a natural mesocosm landscape
Oikos, 2014
Ecosystems are often arranged in naturally patchy landscapes with habitat patches linked by dispersal of species in a metacommunity. Th e size of a metacommunity, or number of patches, is predicted to infl uence community dynamics and therefore the structure and function of local communities. However, such predictions have yet to be experimentally tested using full food webs in natural metacommunities. We used the natural mesocosm system of aquatic macroinvertebrates in bromeliad phytotelmata to test the eff ect of the number of patches in a metacommunity on species richness, abundance, and community composition. We created metacommunities of varying size using fi ne mesh cages to enclose a gradient from a single bromeliad up to the full forest. We found that species richness, abundance, and biomass increased from enclosed metacommunities to the full forest size and that diversity and evenness also increased in larger enclosures. Community composition was aff ected by metacommunity size across the full gradient, with a more even detritivore community in larger metacommunities, and taxonomic groups such as mosquitoes going locally extinct in smaller metacommunities. We were able to divide the eff ects of metacommunity size into aquatic and terrestrial habitat components and found that the importance of each varied by species; those with simple life cycles were only aff ected by local aquatic habitat whereas insects with complex life cycles were also aff ected by the amount of terrestrial matrix. Th is diff erential survival of obligate and non-obligate dispersers allowed us to partition the beta-diversity between metacommunities among functional groups. Our study is one of the fi rst tests of metacommunity size in a natural metacommunity landscape and shows that both diversity and community composition are signifi cantly aff ected by metacommunity size.
Body size and dispersal mode as key traits determining metacommunity structure of aquatic organisms
Ecology Letters, 2012
Relationships between traits of organisms and the structure of their metacommunities have so far mainly been explored with meta-analyses. We compared metacommunities of a wide variety of aquatic organism groups (12 groups, ranging from bacteria to fish) in the same set of 99 ponds to minimise biases inherent to meta-analyses. In the category of passive dispersers, large-bodied groups showed stronger spatial patterning than small-bodied groups suggesting an increasing impact of dispersal limitation with increasing body size. Metacommunities of organisms with the ability to fly (i.e. insect groups) showed a weaker imprint of dispersal limitation than passive dispersers with similar body size. In contrast, dispersal movements of vertebrate groups (fish and amphibians) seemed to be mainly confined to local connectivity patterns. Our results reveal that body size and dispersal mode are important drivers of metacommunity structure and these traits should therefore be considered when developing a predictive framework for metacommunity dynamics.
Ecology Letters, 2012
Dispersal is a major organising force in metacommunities, which may facilitate compositional responses of local communities to environmental change and affect ecosystem function. Organism groups differ widely in their dispersal abilities and their communities are therefore expected to have different adaptive abilities. In mesocosms, we studied the simultaneous compositional response of three plankton communities (zoo-, phytoand bacterioplankton) to a primary productivity gradient and evaluated how this response was mediated by dispersal intensity. Dispersal enhanced responses in all three planktonic groups, which also affected ecosystem functioning. Yet, variation partitioning analyses indicated that responses in phytoplankton and bacterial communities were not only controlled by dispersal directly but also indirectly through complex trophic interactions. Our results indicate that metacommunity patterns emerging from dispersal can cascade through the food web and generate patterns of apparent dispersal limitation in organisms at other trophic levels.
Metacommunity patterns across three Neotropical catchments with varying environmental harshness
Freshwater Biology, 2016
Summary Most metacommunity studies indicate that dispersal processes play a minor role compared with species sorting in explaining metacommunity organisation, in particular, in stream systems. However, the role of dispersal could vary with environmental harshness, as a result of frequent resetting of community succession by disturbances and the selection of generalist species from regional species pools. The importance of dispersal may also be mitigated by species dispersal ability. In this study, we explored how species sorting and dispersal shaped invertebrate and fish metacommunities across streams in three tropical headwater catchments in Bolivia with contrasting environmental harshness, including flow regime, altitude and climate conditions. We addressed the hypothesis that the relative roles of dispersal and species sorting vary with environmental harshness: we predicted that the role of species sorting would predominate in benign conditions, whereas that of dispersal would pr...
The Species Sorting concept, one of the models developed to explain patterns in metacommunity structure, suggests that relationships between biological communities and environmental conditions is the basic means of the species selection processes. A second concept is neutral theory, and the idea of neutral dynamics underpinning metacommunity structure, cannot be overlooked. The third mechanism is the Mass Effect concept, that focuses on the interaction between environmental condition and neutral effects. In the present study, we partitioned fish communities in streams between niche and neutral theory concepts, identifying the best representation of metacommunity structure, and assessed if linear and hydrographic distance were equivalent in the representation of neutral processes. The result points to the importance of species sorting mechanisms in structuring fish communities with neutral processes best represented by the linear distances. On the other hand, the best representation of species' niches was achieved with average values and variance of the local conditions.
Journal of the North American Benthological Society, 2011
Explaining the mechanisms underlying patterns of species diversity and composition in riverine networks is challenging. Historically, community ecologists have conceived of communities as largely isolated entities and have focused on local environmental factors and interspecific interactions as the major forces determining species composition. However, stream ecologists have long embraced a multiscale approach to studying riverine ecosystems and have studied both local factors and larger-scale regional factors, such as dispersal and disturbance. River networks exhibit a dendritic spatial structure that can constrain aquatic organisms when their dispersal is influenced by or confined to the river network. We contend that the principles of metacommunity theory would help stream ecologists to understand how the complex spatial structure of river networks mediates the relative influences of local and regional control on species composition. From a basic ecological perspective, the concept is attractive because new evidence suggests that the importance of regional processes (dispersal) depends on spatial structure of habitat and on connection to the regional species pool. The role of local factors relative to regional factors will vary with spatial position in a river network. From an applied perspective, the long-standing view in ecology that local community composition is an indicator of habitat quality may not be uniformly applicable across a river network, but the strength of such bioassessment approaches probably will depend on spatial position in the network. The principles of metacommunity theory are broadly applicable across taxa and systems but seem of particular consequence to stream ecology given the unique spatial structure of riverine systems. By explicitly embracing processes at multiple spatial scales, metacommunity theory provides a foundation on which to build a richer understanding of stream communities.
A comparative analysis of metacommunity types in the freshwater realm
Ecology and Evolution, 2015
Most metacommunity studies have taken a direct mechanistic approach, aiming to model the effects of local and regional processes on local communities within a metacommunity. An alternative approach is to focus on emergent patterns at the metacommunity level through applying the elements of metacommunity structure (EMS; Oikos, 97, 2002, 237) analysis. The EMS approach has very rarely been applied in the context of a comparative analysis of metacommunity types of main microbial, plant, and animal groups. Furthermore, to our knowledge, no study has associated metacommunity types with their potential ecological correlates in the freshwater realm. We assembled data for 45 freshwater metacommunities, incorporating biologically highly disparate organismal groups (i.e., bacteria, algae, macrophytes, invertebrates, and fish). We first examined ecological correlates (e.g., matrix properties, beta diversity, and average characteristics of a metacommunity, including body size, trophic group, ecosystem type, life form, and dispersal mode) of the three elements of metacommunity structure (i.e., coherence, turnover, and boundary clumping). Second, based on those three elements, we determined which metacommunity types prevailed in freshwater systems and which ecological correlates best discriminated among the observed metacommunity types. We found that the three elements of metacommunity structure were not strongly related to the ecological correlates, except that turnover was positively related to beta diversity. We observed six metacommunity types. The most common were Clementsian and quasi-nested metacommunity types, whereas Random, quasi-Clementsian, Gleasonian, and quasi-Gleasonian types were less common. These six metacommunity types were best discriminated by beta diversity and the first axis of metacommunity ecological traits, ranging from metacommunities of producer organisms occurring in streams to those of large predatory organisms occurring in lakes. Our results showed that focusing on the emergent properties of multiple metacommunities provides information additional to that obtained in studies examining variation in local community structure within a metacommunity.
Elements of metacommunity structure and community-environment relationships in stream organisms
1. Most metacommunity studies aim to explain variation in community structure using environmental and spatial variables. An alternative is to examine patterns emerging at the level of an entire metacommunity, whereby six models of metacommunity structure (i.e. random, chequerboards, nestedness, evenly spaced, Gleasonian gradients and Clementsian gradients) can be examined. 2. We aimed to test the fit of six competing models of metacommunity structure to extensive survey data on diatoms, bacteria, bryophytes and invertebrates from three drainage basins in Finland, along a latitudinal gradient from 66°N to 70°N. 3. Species were mainly distributed independently of one another (following the Gleasonian model) in the southernmost drainage basin (66°N), whereas there were discrete community types, with sets of species responding similarly along environmental gradients (following the Clementsian model), in the northernmost drainage basin (70°N). The patterns found were not directly related to an expected relationships between environmental heterogeneity and metacommunity structures, but rather to the geographical location of the drainage basin. 4. There is evidently among-region variation in the best-fit models of metacommunity structure of stream organisms. These metacommunity patterns may show some similarities among biologically disparate organismal groups sampled at the set of the same sites, although the underlying environmental drivers of those patterns may vary between the groups.