The ecology of a system of natural mesocosms: Rock pools in the Atlantic Forest

Abstract

Abstract The methodological trade‐off between the realism of natural systems and the tractability of artificial systems has led ecologists to praise the qualities of natural micro‐ and mesocosms as an ideal means for investigating the processes that organise biological communities. Among the different types of naturally occurring micro‐ and mesocosms, clusters of rock pools combine a global distribution with the simplicity, replicability, tractability and structural homogeneity that are desirable in model experimental systems. However, critical geographical data gaps in the study of rock pools must be filled if ecologists are to use these as global model systems in community ecology. In a year‐long study of a cluster of 181 rock pools in the Atlantic Forest of eastern Brazil, we conducted the first study on the ecology of freshwater rock pool communities in the entire Neotropical region, to the best of our knowledge. Building on published descriptions of the factors that drive community assembly within rock pools, we tested the hypotheses (1) that the effects of environmental factors prevail over those of spatial factors and (2) that pool volume and secondarily species interactions between consumers (anuran larvae), resources (leaf litter) and predators (dragonfly larvae) have a dominant role in driving species patterns of occurrence and abundance. Our hypotheses were generally supported as community structure was clearly influenced by the environmental characteristics of individual pools, and not to the spatial relations among them. Pool volume had a consistent, positive influence on the probability of occurrence of dragonflies and tadpoles of three anuran species, possibly through the influence of volume on hydroperiod. However, the species most strongly associated with larger pools were not those with longer times until metamorphosis, but those with larger egg clutches. In addition, species occurrences were positively associated with resource availability as measured by leaf litter mass (significantly so for Rhinella and dragonflies). These observations suggest that within these severely confined freshwater systems, indicators of environmental stability and reduced intraspecific competition could be important ultimate criteria for oviposition site selection. The ease of sampling and manipulating the rock pools at our Atlantic Forest site combined with the observation that these pools are governed by some of the same factors influencing community organisation in other rock pool systems around the world reinforces the merit of the system as a means to conduct global comparative studies of the ecology of communities and metacommunities.