Environmental Gradients Linked to Human Impacts, Not Species Richness, Drive Regional Variation in Community Stability in Coral Reef Fishes

The stabilising effect of biodiversity on aggregate community properties is well-established experimentally, but its importance in naturally assembled communities at larger scales requires considering its covariation with other biotic and abiotic factors. Here, we examine the diversity-stability relationship in a 27-year coral reef fish time series at 39 reefs spanning 10° latitude on Australia's Great Barrier Reef. We find that an apparent relationship between species richness and synchrony of population fluctuations is driven by these two variables' covariation with proximity to coastal influences. Additionally, coral cover volatility destabilises fish assemblages by increasing average population variability but not synchrony, an effect mediated by changes in the intensity of density regulation in the fish community. Our findings indicate that these two environmental factors, both of which are strongly influenced by anthropogenic activity, impact community stability more than diversity does, but by distinct pathways reflecting different underlying community-dynamic processes.