Different processes drive spatial variation in species richness and community composition. Standard measures of species richness and composition are important in conservation and ecology, but they may be less informative in terms of evolutionary history and functional diversity. Phylogenetic community ecology is increasingly used to test deterministic (e.g. niche differentiation and competitive exclusion) and stochastic hypotheses of community assembly. Integrating traits with phylogenetic relatedness across space is also used to provide additional information on the role of isolation and speciation in driving biodiversity patterns in different environments. In this study, 28 Diptera families covering a broad range of functional characteristics were analyzed in three classes of wetlands (bogs, swamps, marshes) in the Montreal Metropolitan area and surroundings. The objectives were to examine the taxonomic, phylogenetic and phenotypic structure of wetland Diptera communities and assess if rarity is deterministic or essentially stochastic. We also examined how beta- and phylobeta- diversity are related to local environmental conditions, patch area, and/or surrounding landscape.
Results/Conclusions
Phylogenetic community structure analyses revealed high value and complementarity to standard measures in explaining patterns of species variation. We found indications that the bog habitats support closely related species filtered by harsher environmental conditions. There was less species composition heterogeneity in bogs compared to the other two habitats as bog emerged from a slow peat accumulation process and the plant composition is characteristic and only locally abundant with only a few species that can survive in these acid and low nutrient conditions. Neutral processes are more important in marshes and swamps, as dispersal limitation explained species abundance dynamics of small and common species within habitat type. The assembly of marsh communities may be seen as recent processes with a balance between neutral processes and environmental filtering, while the assembly of swamp habitats can be seen as solely neutral processes. Clustering, thus environmental filtering, increased with environmental extremes. Rare species tended to be distantly related to common species as a phylogenetic signal was found. We found that rare species have unique habitat requirements and that the high diversity and abundance are maintained by temporal turnover of species with similar traits filtered by the environment.