The role of environmental filtering in the functional structure of fish communities in tropical wetlands

Abstract

AbstractUnderstanding the mechanisms that structure communities has been a major challenge in ecological theory. In wetlands with a clear seasonal hydroperiod (wet and dry seasons), such as Sian Ka'an Biosphere Reserve (SKBR), Mexico, fish communities experience successive habitat contraction/expansion, with a high mortality rate during the dry season. In this study, we tested the role of environmental filtering in structuring fish communities along an environmental gradient in permanent pools, during three consecutive stages of the dry season. We analysed fish communities using a functional dispersion index weighted by the relative abundance compared against a null model. While the concentration of dissolved oxygen remained low throughout the season, depth and temperature showed a gradient as the season progressed. Independently of their starting composition, at the end of the dry season the communities were dominated by a combination of the same three species. For the key function of locomotion, the functional dispersion was significantly lower at the end of the season in three of the five pools. For food acquisition, no significant differences were found. When the overall functional variation was considered, at the beginning of the dry season no single community differed significantly compared to the random models. However, as the season progressed, significant differences were recorded in four of the five pools. Our study supports the hypothesis that environmental filters have a major role in community structure in severe environmental conditions. Furthermore, our results show that the role of environmental filters gain importance as the dry season progresses.