Extinction of large Malagasy primate species altered their community assemblage trait structure

Background/Question/Methods

Previous research showed that the phylogenetic structure of Malagasy primate communities consist of species more distantly related than expected by chance, while African, Asian and Neotropical primate assemblages are random. This overdispersion pattern in Madagascar might be a result of strong interspecific competition because of trait similarities in closely related taxa. This very different community assembly pattern in Malagasy primate communities might also be due to the extinctions of many species on the island after human colonization which altered community phylogenetic structures. The goal of our study was to understand the role of evolutionary relatedness and species traits in structuring the composition of Holocene and extant Malagasy primate communities by examining the associations between phylogenetic assemblages and trait similarities within lemur communities in different areas across Madagascar. We test the hypothesis that recent extinctions of large bodied lemurs during the Holocene resulted in the current overdispersed pattern of phylogenetic and trait structure of current communities. Species composition was gathered for 44 Extant and 18 Holocene communities. A phylogenetic tree was constructed for this study including the 68 known extant species and 16 extinct species. Holocene communities were recreated from archeological findings in different subfossil sites. Two phylogenetic metrics were calculated for each community to measure the relative phylogenetic distance between species. We also quantified the community trait structure by measuring trait distance between sister taxa, and evenness and richness of the trait in each community.  

Results/Conclusions

The majority of both extant and Holocene communities were found to be phylogenetically overdispersed assemblages with species more distantly related than expected by chance. The extinction of large species thus does not seem to be responsible for the difference in phylogenetic structure of the Malagasy assemblages. Trait structures of the communities, however, were affected by extinctions. Species in the Holocene communities showed greater divergence in body mass than expected by chance, while the extant were random. This difference may be due to a selective hunting of large species by early Malagasy settlers that resulted in their extinction. Interestingly, the diet assemblage in the Holocene communities was random which differs from the divergent diet composition of the extant communities. Perhaps the larger body size of the extinct species allowed frugivores and folivores to exploit different niches within their guild reducing competition. Extant lemur species are within a narrow body size range, making competition possibly more important in determining dietary assemblages.