Abstract
Understanding the influences of dispersal limitation and environmental filtering on the structure of ecological communities is a major challenge in ecology. Insight may be gained by combining phylogenetic, functional and taxonomic data to characterize spatial turnover in community structure (β-diversity). We develop a framework that allows rigorous inference of the strengths of dispersal limitation and environmental filtering by combining these three types of β-diversity. Our framework provides model-generated expectations for patterns of taxonomic, phylogenetic and functional β-diversity across biologically relevant combinations of dispersal limitation and environmental filtering. After developing the framework we compared the model-generated expectations to the commonly used “intuitive” expectation that the variance explained by the environment or by space will, respectively, increase monotonically with the strength of environmental filtering or dispersal limitation. The model-generated expectations strongly departed from these intuitive expectations: the variance explained by the environment or by space was often a unimodal function of the strength of environmental filtering or dispersal limitation, respectively. Therefore, although it is commonly done in the literature, one cannot assume that the strength of an underlying process is a monotonic function of explained variance. To infer the strength of underlying processes, one must instead compare explained variances to model-generated expectations. Our framework provides these expectations. We show that by combining the three types of β-diversity with model-generated expectations our framework is able to provide rigorous inferences of the relative and absolute strengths of dispersal limitation and environmental filtering. Phylogenetic, functional and taxonomic β-diversity can therefore be used simultaneously to infer processes by comparing their empirical patterns to the expectations generated by frameworks similar to the one developed here.
Highlights
Understanding the processes that govern the assembly of local communities from regional species pools is a fundamental goal of ecological research, and both stochastic and deterministic factors are commonly thought to be important
It is clear that both stochastic and deterministic processes are at work simultaneously in most communities [5,6,7,8], and recent work has focused on evaluating the relative importance of these two sets of processes and on elucidating the factors that may shift that relative importance [9,10,11,12,13,14,15]
Expectations It is commonly assumed that stronger dispersal limitation leads to greater variance partitioned to space and to steeper slopes (‘spatial slopes’) for the regression of b-diversity against the spatial distance between communities
Summary
Understanding the processes that govern the assembly of local communities from regional species pools is a fundamental goal of ecological research, and both stochastic and deterministic factors are commonly thought to be important. One approach for inferring the relative influences of stochastic and deterministic processes is to examine spatial turnover in community structure by relating the amount of turnover (bdiversity) to variation in spatial distance and the abiotic environment [16,17,18,19]. This approach has been widely employed in studies of taxonomic b-diversity by characterizing communities in terms of lists of species names with or without information on relative abundances (reviewed in [20,21]). Several authors have recently proposed extending this species-based approach by including functional and phylogenetic information which should permit inferences that are more directly tied to ecological and evolutionary processes [22,23]
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