Phylogeny and co-occurrence of mammal species on Southeast Asian islands

Abstract

Aim: Islands have often been used as model systems in community ecology. The incorporation of information on phylogenetic relatedness of species in studies of island assemblage structure is still uncommon, but could provide valuable insights into the processes of island community assembly. We propose six models of island community assembly that make different predictions about the associations between co-occurrences of species pairs on islands, phylogenetic relatedness and ecological similarity. We then test these models using data on mammals of Southeast Asian islands. Location: Two hundred and forty islands of the Sundaland region of Southeast Asia. Methods: We quantified the co-occurrence of species pairs on islands, and identified pairs that co-occur more frequently (positive co-occurrence) or less frequently (negative co-occurrence) than expected under null models. We then examined the distributions of these significantly deviating pairs with respect to phylogenetic relatedness and ecological differentiation, and compared these patterns with those predicted by the six community assembly models. We used permutation regression to test whether co-occurrence patterns are predicted by relatedness, body size difference or difference in diet quality. Separate co-occurrence matrices were analysed in this way for seven mammal families and four smaller subsets of the islands of Sundaland. Results: In many matrices, average numbers of negative co-occurrences were higher than expected under null models. This is consistent with assemblage structuring by competition, but may also result from low geographic overlap of species pairs, which contributes to negative co-occurrences at the archipelago-wide level. Distributions of species pairs within plots of phylogenetic distance × ecological differentiation were consistent with competition, habitat filtering or within-island speciation models, depending on the taxon. Regressions indicated that co-occurrence was more likely among closely related species pairs within the Viverridae and Sciuridae, but in most matrices phylogenetic distance was unrelated to co-occurrence. Main conclusions: Simple deterministic models linking co-occurrence with phylogeny and ecology are a useful framework for interpreting distributions and assemblage structure of island species. However, island assemblages in Sundaland have probably been shaped by a complex idiosyncratic set of interacting ecological and evolutionary processes, limiting the predictive power of such models.