Patterns of community variability depend on habitat variability and habitat generalists in natural aquatic microcosms

Habitat variability is largely an external mechanism influencing community variability by affecting abundances and precipitating other community changes but the nature of this influence is poorly understood. The absence of systematic quantitative studies appears to be a major reason for this deficiency. To address the problem, we have evaluated community and population variability in invertebrate communities collected from 49 coastal Jamaican rock pools with contrasting levels of habitat variability.We calculated a multivariate index of habitat variability based on temporal changes in physicochemical variables. Variability in diversity indices (Simpson’s and Shannon-Wiener), evenness (2 measures), and species richness represented community variability while species rank correlations and community constancy represented changes in community structure. Additionally, we analyzed the impact of three habitat generalists (harpacticoid copepod (Nitocra spinipes Boeck), cyclopoid copepod (Orthocyclops modestus Herrick), and the ostracod (Potamocypris sp.)) on overall community variability. As habitat variability increased, both community and population variability increased. Community structure (ranked abundances) was more variable in variable habitats compared to non-variable habitats but communities in these variable habitats retained greater constancy of composition suggesting that highly variable habitats are dominated by a few species with good dispersal abilities. Rare species may come and go, but the dominant species persist in these habitats.Habitat generalists influenced temporal community variability differently, especially evenness (based on the Shannon-Wiener index). Positive relationships were found between the variability in evenness and population variability of the ostracod and cyclopoid copepod. A negative relationship was found between the variability in evenness and the variability of harpacticoid copepods.Our study suggests that individual communities or assemblages respond independently and asynchronously to environmental factors, a view originally proposed by Gleason (1917). We conclude that the form of community structure in variable habitats remains constant. The species composition and relative abundances can change over time but the relative abundance of the dominant species stays high and the remaining species, regardless of their numbers, make relatively small contributions to the overall community variability pattern.