“Species pool functional diversity plays a hidden role in generating β-diversity”

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Christopher J. Patrick and Bryan L. Brown (May 2018)

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Functional diversity of the species pool contributes to spatial variation in community composition

Link between functional and β-diversity explored, findings advance ecological theory

With global extinction rates continuing to accelerate, understanding the factors that generate and maintain biological diversity is imperative for conservation and ecosystem management. Chris Patrick at Texas A&M University–Corpus Christi and Bryan Brown at Virginia Tech University recently found evidence that the size of the functional differences among species in the species pool may be a vital missing piece of the larger biodiversity puzzle. β-diversity, the variation in the identities of species among different habitats, is an important part of biological diversity that bridges the biological diversity within local habitats and the number of species in regional species pools. While the size of species pool and habitat heterogeneity are considered important predictors of β-diversity, individual studies often produce conflicting results about the relative importance of these drivers.

Using invertebrate communities found in the Mid-Atlantic streams of the United States as a study system, Patrick and Brown found that after accounting for environmental heterogeneity and species pool size, watersheds with species pools with high functional diversity tend to have higher β-diversity. This transformative finding supports the existence of a link between functional diversity and β-diversity. Understanding this link will enhance our theoretical understanding of processes that generate biological diversity at landscape scales and provide avenues for methodological advances in metacommunity analysis. The result will help reconcile prior research on drivers of β-diversity and has applications across ecosystems and is important for both advancing ecological theory and providing new avenues of research for landscape scale conservation management.

Demonstration of the hypothesized relationship between functional diversity of the invertebrate species pool and β-diversity among communities within a watershed. The color in each stream segment on the right represents the composition of the community, with similar colors indicating similar communities. In the top panel the species pool has higher functional diversity and this results in larger differences in composition among local communities, e.g. β-diversity. This greater diversity of local communities is depicted as a greater variety of colors in watershed. (Credit: Christopher J. Patrick)

Abstract

Functional trait diversity is used as a way to infer mechanistic processes that drive community assembly. While functional diversity within communities is often viewed as a response variable, here we present and test a framework for how functional diversity among taxa in the regional species pool drive the assembly of communities among habitats. We predicted that species pool functional diversity should work with environmental heterogeneity to drive β-diversity. We tested these predictions by modeling empirical patterns in invertebrate communities from 570 streams in 52 watersheds. Our analysis of the field data provided strong support for the inclusion of both functional diversity and environmental heterogeneity in the models, and our predictions were supported when the community was analyzed all together. However, analyses within individual functional feeding guilds revealed strong context dependency in the relative importance of functional diversity, γ-richness, and environmental heterogeneity on β-diversity. We interpret the results to mean that functional diversity can play an important role in driving β-diversity; however, within guilds the nature of interspecific interactions and species pool size complicate the relationship. Future research should test this conceptual model across different ecosystems and in experimental settings using metacommunity mecocosms to enhance our understanding the role that functional variation plays in generating spatial biodiversity patterns.