Complex phylogenetic origin and geographic isolation drive reef fishes response to environmental variability in oceanic islands of the southwestern Atlantic

Abiotic and biotic factors are known drivers that modulate community assembly from a regional species pool. Recent evidence has highlighted the intrinsic role of phylogenetic history on communities' response to the environment. Understanding its exact role poses a challenge because community assembly is embedded in a spatio-temporal context where dispersal capabilities and biotic interactions may also determine species niches, especially in isolated oceanic islands. We unravelled how reef fish abundances from four oceanic islands in the southwestern Atlantic responded to environmental variability through seven years considering their phylogenetic history, functional traits and species co-occurrence patterns. Species response to environmental variation was assessed through a multivariate hierarchical generalized linear mixed model that allows the inclusion of spatio-temporal random effects, fitted with Bayesian inference. We found a strong phylogenetic signal (0.98) and a relatively low variance in abundance explained by functional traits, from around 30% in spring to 33% in summer, based on a posterior probability > 0.9. The most important environmental factor was surface chlorophyll-a concentration, a proxy for primary productivity, explaining up to 23% of abundance variance. The global spatial and temporal effects on abundance were also low, with a maximum of 18% for sampling sites in spring. Our study offers a synthesis of the influence of complex phylogenetic history and geographical isolation on reef fish species niches in isolated oceanic islands, gaining new insights into how assembly processes have shaped these isolated communities.

Automated summary

Recent evidence has highlighted the important role of phylogenetic history in shaping communities' response to the environment. In our study, we investigated the response of reef fish abundances to environmental variability on four oceanic islands in the southwestern Atlantic, considering phylogenetic history, functional traits, and species co-occurrence patterns. We found a strong phylogenetic signal and surface chlorophyll-a concentration to be the most important environmental factor.