Phylogenetic structure of plant communities along environmental gradients: a macroecological and evolutionary approach

Theses(doctorate).

Series: Dissertationes biologicae Universitatis Tartuensis ; 383.  Summary in Estonian.

Evolution plays an important role in the way species are assembled into communities of different habitat types and along environmental gradients. However, the emerging diversity patterns remain poorly understood. In this thesis, patterns of plant community phylogenetic structure were investigated in response to current and historical environmental gradients. The main findings are that (1) forest communities consist of more closely related species at low latitudes, whereas in grassland communities, species are more closely related in the temperate zone. This pattern probably results from woody lineages being evolutionary older than herbs and grasses, emerging in the tropics and selectively dispersing to colder regions. (2) Species with different life-cycle strategies respond contrastingly to desertification. Annuals show phylogenetic clustering at medium-to-high aridity, perennials at low aridity. This indicates a strong effect of environmental filtering on annuals along the aridity gradient and the presence of closely related perennials with strong competitive abilities in mesic communities. (3 and 4) In wet and cold habitats of the Atlantic Forest Domain, tree communities are phylogenetically overdispersed when related to deep past evolutionary events but clustered when related to recent events. Co-existing species in habitats with water limitation and high soil salinity are closely related when related to past evolutionary events and show random phylogenetic structure when related to recent events. These differences probably arise from the coexistence of old Gondwanan and more recent Neotropical lineages. The results of this thesis add insights into the use of phylogenetic information to investigate the origin and maintenance of diversity . The results are also significant in the context of current climate change and habitat destruction because these events threaten the evolutionary history that species share in natural communities.