Untangling the assembly of littoral macroinvertebrate communities through measures of functional and phylogenetic alpha diversity

Abstract

Abstract Recent studies have shown that species, functional and phylogenetic diversity are related to different environmental drivers, suggesting that different aspects of alpha diversity may be complementary and may provide different information about community assembly. Such multi‐facet community assembly studies are, however, rare in the freshwater realm. We examined the responses of species richness, functional alpha diversity and phylogenetic alpha diversity of littoral macroinvertebrates to environmental gradients in near‐pristine boreal lakes. We also examined community assembly mechanisms using null models of functional or phylogenetic clustering, overdispersion and randomness as indications of different assembly mechanisms. We found that the alpha diversity indices examined responded differently to the underlying environmental gradients. Also, phylogenetic and functional alpha diversity indices showed different levels of overdispersion, clustering and randomness, which also varied slightly between the analyses based on abundance and presence–absence data. These results suggested that different alpha diversity indices may provide different information about overdispersion (e.g. caused by biotic interactions) and clustering (e.g. caused by environmental filtering), and emphasised the fact that most individual lakes were inhabited by species that were merely random draws from the functional or phylogenetic species pools available in the study region. Our findings suggested that some individual lakes are assembled by deterministic mechanisms, including environmental filtering and biotic interactions, whereas most individual lake macroinvertebrate communities constitute random draws from the regional species pool or are affected by the antagonistic effects of different assembly processes. Our results may stem from site‐specific context dependency in the assembly mechanisms, which might also be a reason why statistical models in aquatic community studies typically explain only a small part of variation in community composition and local diversity.