The importance of biogeographical history and extant environmental conditions as drivers of freshwater decapod distribution in southern South America

Abstract

A topical issue in macroecology is whether the distribution of organisms is related to biogeographical history or current environmental conditions. Distributions of freshwater decapods in southern South America have been mainly attributed to historical factors, such as geoclimatic events, marine ingressions, tectonic uplifts and glaciations. Here, we test the hypothesis that current distributions are strongly influenced by local environmental conditions. Generalised linear models were used to quantify the importance of altitude, stability of the waterbody, annual temperature range (ATR), pH and conductivity on the distribution of five freshwater decapod families in Argentina (Sergestidae, Palaemonidae, Parastacidae, Aeglidae and Trichodactylidae), while accounting for effects of latitude and longitude. Decapod occurrence was strongly associated with interacting spatial and environmental factors. Latitudinal and/or longitudinal gradients were important predictors for the occurrence of Acetes paraguayensis (Sergestidae), Palaemonidae, Aeglidae and Trichodactylidae. However, the longitudinal pattern for Palaemonidae was reversed, increasing from east to west, when environmental variables were included in the analyses, whereas for Trichodactylidae, the longitudinal pattern was sufficiently explained by inclusion of local environmental variables. Altitude, water stability and ATR were important predictors of all families, while Palaemonidae, Parastacidae and Trichodactylidae were significantly associated with pH and Palaemonidae and Aeglidae with conductivity. Interactions terms were often significant, especially with latitude. Our results show that the macrodistribution of freshwater decapods is not solely a result of historical processes, a finding that disagrees with current understandings. Significant relationships between decapod occurrence and environmental variables indicates limited plasticity and strong adaptation to local habitats, highlighting the importance of including environmental factors in studies of crustacean biogeography and macroecology.