Drivers of interspecific synchrony and diversity-stability relationships in floodplain fish communities

Diversity and interspecific synchrony are among the main drivers behind the temporal stability of community abundance. Diversity can increase stability through the portfolio effect, while higher synchrony generally decreases stability. In turn, species interactions and similar responses to environmental variation are considered the main factors underlying the strength of interspecific synchrony, despite the challenges in determining their relative roles. The analysis of the relationship between interspecific synchrony and the trait (or phylogenetic) distance between species can increase the robustness of inferences about these factors. Here, we used pairwise interspecific and community-wide analyses to investigate, respectively, the drivers of interspecific synchrony and the influence of trait and phylogenetic diversity on the stability of fish communities. For that, we used 18 years of fish abundance data from the Upper Paraná River floodplain. At the interspecific level, we used quantile regressions to test within-guild relationships between interspecific synchrony and trait and phylogenetic distance between species. At the community level, we tested the relationships between community-wide synchrony, stability, and (trait and phylogenetic) diversity. We found that interspecific synchrony decreased with trait and phylogenetic distances. In the community-level analysis, we found that more synchronous fish communities were less stable, but the relationship between diversity and stability was in general weak. At the interspecific level, our study highlights the role of similar responses to environmental variation in driving species' temporal dynamics. At the community level, the strength of the relationships between trait or phylogenetic diversity and community stability depended on the feeding guild. On the other hand, we found strong relationships between synchrony and stability. These results suggest that increased synchrony levels in response to regional environmental changes could decrease the stability of fish communities in this floodplain.