Distributional congruence among aquatic plants, invertebrates and fishes within the Río Paraguay Basin, Paraguay

Abstract

Null hypotheses concerning random distributions of species with respect to subregions and macrohabitats within the Río Paraguay are tested with data from 131 species of macrocrustaceans and benthic invertebrates and 186 species of aquatic plants. The patterns are compared to the results for the distributions of fishes presented by Chernoff et al. (2004). The invertebrate data demonstrate the identical pattern among subregions as evident in the fish distributions. The results support the recognition of two zones: i) the Río Paraguay zone containing portions of Río Paraguay and Río Negro, and ii) the Río Apa zone containing Río Apa and Riacho La Paz. For all data sets, the Río Paraguay zone has higher species richness than the Río Apa zone. The boundary between the two zones is abrupt, which is also supported by the plant data. Only 11 of 186 species of plants were found in both zones. There is no congruence of pattern among macrohabitats. The invertebrate and plant similarity matrices contain many values that are not different from mean random similarities among macrohabitats. The plant data set demonstrates a relationship among shore and sand habitats that experience greater currents than do other macrohabitats. The plants found in backwater habitats had little similarity to other macrohabitats. Based on these observations, we conclude that significant habitat within each of the zones must be preserved to maintain a large portion of the biodiversity.