Abstract

Environmental filtering and competitive exclusion can act simultaneously to shape the structure of communities, but disentangling them has proved difficult. Specifically, environmental filtering may restrict establishment at a site to a set of species sharing particular traits permitting local persistence. Mutual exclusion of ecologically similar or phylogenetically related species can also dictate community composition. Patterns of phylogenetic structure allow assessment of the relative influence of these processes. Using phylogenetic patterns of community structure, this study aims to assess the predominant processes structuring odonate communities along a broad-scale environmental gradient in Quebec. Phylogenetic analyses of forty lentic (i.e. lake) odonate communities revealed that co-occurring species in temperate regions were more related than expected by chance, suggesting a predominant role of environmental filtering. Site-to-site variation in phylogenetic structure was related to pH. That is, the most alkaline lakes, found in temperate regions, were the most phylogenetically clustered, suggesting that pH acts as a main environmental filter of odonate communities. However, environmental filtering may not be the only important process. One alternative explanation is that temperate communities are phylogenetically clustered because damselflies are disproportionally diverse relative to dragonflies in this region. Specifically, the recent radiation of damselflies in temperate regions could have increased the diversity of this group in the temperate species pool, which could then shape local communities in that region. Nevertheless, further analyses suggested that environmental filtering along a pH gradient, rather than the evolutionary history of the species pool, shapes odonate communities in Quebec.