Population synchrony (synchrony), the simultaneous increase or decrease in the abundances of two or more populations contribute to species extinctions when populations reach low densities at many sites at the same time. Because more specialized species tend to be less abundant, they suffer when environment and species they interact with vary over time. This disadvantage should be compounded when a) habitat generalists and specialists fluctuated asynchronously but less so if they synchronize and b) other species fluctuated synchronously but less so if they were asynchronous or antisynchronous. Strong disadvantage translates into species loss. Therefore, synchrony and species richness should relate differently depending on habitat traits of species that synchronize, remain asynchronous (portfolio effect) or vary antisynchronously.
We analyzed synchrony among aquatic invertebrate species using community and population data obtained in 15 annual censuses from 49 natural microcosms (rockpools) located on Jamaican coastal fossil reef. Species were categorized into habitat specialists and generalists based on their environmental tolerances and distribution. We also considered effects of species richness, habitat variability, abundance distribution, and species turnover as possible confounding factors.
Results/Conclusions
Synchrony among species generally elevated aggregate community variation at low richness but did so less in rich communities, where anti-synchrony appeared to supplant synchrony. Further, although mean synchrony was similar among generalists-generalist and generalist-specialist pairs, synchrony and species richness related differently in these two species combinations. Richness related positively to synchrony within generalist-specialist pairs but not in other species combinations where the relationship was either negative or absent. We conclude that a mix of habitat generalists and specialists is a significant yet veiled condition for maintenance of elevated richness.