Commentary: A Darwinian approach to community ecology

Abstract

news and update ISSN 1948-6596 commentary A Darwinian approach to community ecology In A Darwinian approach to plant ecology the late John Harper argued that evolution should be the conceptual basis for all plant ecology (Harper 1967). Quoting extensively from the Origin of Spe- cies, and taking examples from ecological restora- tion, interspecific competition and life-histories, his thesis was that evolution is central to under- standing the diversity of adaptations and interac- tions in plants. Forty-odd years later this vision is playing out with the availability of information on the evolutionary history of species allowing ecolo- gists to explore the links between evolution and ecology in ever more imaginative and detailed ways. In a new synthesis of our current under- standing of the links between evolutionary theory and community ecology, Cavender-Bares and col- leagues present a compelling case that community ecology has been revolutionised in the past 10 years through advances in phylogenetics and the application of evolutionary ideas. They argue that evolution is central to understanding interactions between species, the diversity of life histories and in deciding between competing hypotheses for species diversity. Evolution and community assembly Communities are vague entities at best (Ricklefs 2008) and the processes driving community com- position are varied. On the one hand communities may be assembled primarily through migration, for example when habitat is cleared and a com- munity is formed through immigration. On the other, if a community is allowed to develop and essentially left undisturbed for a long period, spe- cies will evolve in situ. This division is as old as ecology itself, reflecting the difference between Clements’ and Gleason’s theories on communities. The ‘modern synthesis’ for community ecology (e.g. for recent reviews see Ricklefs 2008, 2009, Vellend 2010) is that the species present within an area are determined by the relative balance of four processes: speciation, extinction, dispersal and ecological sorting. Traditional community ecology has put a great deal of emphasis on eco- logical sorting in a narrow sense, particularly fo- cussing on the details of processes and interac- tions at the micro scale. However as Ricklefs (2009) succinctly puts it, “The presence of shrub X might exclude herb Y from a 1-m 2 study plot, but much is left unexplained, including why X and Y are there is the first place”. Historical factors must play a huge role in determining the composition of a community, through biogeography, speciation and adaptation. The imprint of these historical processes can be untangled if we know the phy- logeny of the species present. What can phylogeny tell us? Phylogeny can tell us about the degree to which various historical factors shape the distribution of traits and diversity. It is straightforward to statisti- cally test whether differences in species traits (specifically those which relate to niches) scale with phylogenetic distance or not. The expecta- tion is that nearer to the tips of a phylogeny, spe- cies would be more divergent if niche processes are important, particularly character displace- ment. On the other hand, at larger scales phyloge- netic niche conservatism should mean that larger clades are reasonably distinct. Phylogeny will also be informative about the species that we might expect to co-occur. For example, competition at small scales will deter- mine which species co-occur. Such processes may occur on scales of even a few metres. On the other hand at intermediate spatial scales we would expect to see phylogenetic clustering: as a consequence of its biogeographic history a group will be restricted to a given area. Of course these predictions are only the expectation under one scenario: in practice other factors could operate. For instance, if species are highly mobile they would be expected to show less of an imprint of evolutionary history on their traits and phylogeography as they will show less spatial clustering and be adapted across a wider range of habitats. Modern phylogenetic compara- tive approaches allow a suite of patterns of diver- sity of traits and diversity to be modelled and tested. When we look at small scales the composi- tion of species within a community will reflect the interplay between the effects occurring at all of these scales as well as the outcome of ecological sorting. Biogeography and history determine the pool of species that can form a community. Then © 2009 the authors; journal compilation © 2009 The International Biogeography Society — frontiers of biogeography 1.2, 2009