Using richness of native and non-native aquatic species along a climatic gradient to test the intermediate disturbance hypothesis

The intermediate disturbance hypothesis (IDH) has been thoroughly investigated, but much controversy has been found for supporting its assumptions, which rely largely on the nature of the disturbance, spatial scale, and biological predictors tested. In this paper, richness of native and non-native species along a suite of Neotropical aquatic ecosystems across a broad latitudinal and geographical range was used to test the IDH predictions. An extensive literature survey was performed to compile native species richness and the occurrence of several taxonomic groups listed as non-native for twenty-four coastal rivers and bays evenly distributed into three climatic zones (tropical, transitional, and subtropical). The climatic gradient was confirmed by NMDS and PERMANOVA, but IDH predictions were only significantly supported for native and total species richness in the coastal bays. The distribution patterns of non-native marine species showed a linear instead unimodal pattern of increase with latitudinal climatic gradient, but the responses are complex and dependent of many non-exclusive factors, such as the sampling effort per ecosystem and the potential interference of other disturbance gradients that should be further addressed to unravel the role of IDH for non-native species distribution.