No support for purported effects of salt-tolerant stream invertebrates on the salinity responses of salt-sensitive stream invertebrates

Increases in salinity can severely affect freshwater ecosystems, and research on the salt tolerances of freshwater species, and factors that modify tolerance, can improve our understanding and prediction of the effects of salinity. In order to test the hypothesis that salt-tolerant freshwater invertebrates can alter the salinity responses of salt-sensitive freshwater invertebrates, publicly available data from a recent study of artificial mesocosms that claimed to confirm this hypothesis were analysed in the present study. No supporting evidence was found for the hypothesis, with apparent salinity responses of salt-sensitive invertebrates varying no more with greater or lesser exposure to salt-tolerant invertebrates than expected merely by chance. The original findings were apparently misguided through unrecognised confounding of the experimental design, inadequate statistical hypothesis testing and accepting ostensible effects without considering their biological and ecological plausibility.