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

Abstract

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.

Non-deterministic reef fish community assembly in an upwelling-influenced transitional subprovince of the southwestern Atlantic

“…At the core of the HMSC model there are six data matrices: species abundances, environmental data, species traits, phylogenetic data, the spatio-temporal structure (study design) and spatial coordinates (detailed below). The pre-processing of abundance data from the UVC involved the trimming of the 153 species recorded to retain only those that: (1) were detected in all years, (2) were present in at least 5 censuses for at least 50% of the total years, or (3) reached an average abundance greater than 0.2 individuals per square meter per year (sensu Garcia, 2021;Gomes et al, 2023). This resulted in 72 species that were retained, of which six species are exclusive to the exposed area, 20 species are exclusive to the sheltered area, and the remaining 46 species occur in both areas.…”

“…Sampling sites were randomly grouped into four folds and abundance predictions were computed for each separately, avoiding the use of data from the focal fold to be used for fitting and prediction (Ovaskainen and Abrego, 2020). A short description of model functionalities has been reported by Gomes et al (2023) that applied a similar setup to communities of reef fishes from remote oceanic islands of the southwestern Atlantic.…”

“…A flexible diet and enhanced dispersal capability would have made it easier for a relatively large number of species to move around and explore transient environmental states provided by coastal upwelling. In fact, thermal affinity alone may not accurately explain changes in abundance in transitional regions with water stratification, range extension and depth distribution of species also being important (Gomes et al, 2023;Silva et al, 2023). The schematic representation shown in Figure 12 summarizes the assembly process discussed above.…”