Comparing patterns of taxonomic, functional and phylogenetic diversity in reef coral communities

Abstract

Biodiversity defines the variety of living organisms on this planet and is often quantified by the total number of species. However, species richness is insufficient in accounting for the differences in evolutionary history and the functions species contribute to the ecosystem. To address this shortcoming, phylogenetic diversity and functional diversity are increasingly being quantified and studied to inform ecological theory and conservation prioritisation. For scleractinian reef corals, congruence, mismatch and complementarity among different biodiversity components remain unknown, but recently available trait and phylogenetic data provide a robust test of these relationships. Here, we examine the taxonomic, functional and phylogenetic diversity of corals across a gradient of diversity in Singapore. Relationships among the biodiversity components at 25 reef sites are compared to identify patterns of mismatch or congruence for testing the precision of using one as a proxy for another. Furthermore, we examine community assembly of corals using null models derived from randomised community data. Our results show that correlations among biodiversity components are generally positive but weak, with species-dependent (non-abundance-weighted) metrics more strongly correlated with one another than species-independent (abundance-weighted) measures. No single biodiversity component could predict another precisely to be used as a reliable proxy for coral communities. Therefore, if trait diversity and evolutionary history were to be set as conservation targets, it is essential to maximise functional diversity and phylogenetic diversity explicitly when identifying areas or assemblages for management. Null models reveal the presence of more-than-expected similarities in trait combinations and evolutionary relationships among species in most reef communities. These findings suggest that environmental filtering under high levels of coastal development and sedimentation may be associated with coral community composition on Singapore’s reefs. Our approach provides new insights into the relationships between different components of coral diversity and has important applications for marine conservation planning.