A Species Tolerance Index for Maximum Water Temperature

Abstract

Abstract A weighted species association tolerance index with respect to water temperature (WSATI-WT) is based on the final temperature preferendum (FTP) of each of the fish species present in a locale of a stream ecosystem. The WSATI-WT is a measure of the distributional consequences of “behaviour” or habitat selection of an interactive set of species with respect to temperature and extends the indicator species concept to an entire association of fishes. Several relationships were exploited to estimate the FTP of several species for which direct estimates were not available: FTP inferred directly from behavioral responses are found to be related approximately by a 1:1 ratio with optimal temperatures for growth, upper lethal temperatures estimated using ultimate upper incipient lethal temperatures,or critical temperature maximum, are related to the FTP by a straight-line relationship across species (within a limited temperature range). When the WSATI-WT was tested in the field, we found positive relationships between it and maximal summer habitat temperatures. The WSATI-WT can be used with observed maximum summer stream water temperatures to forecast change in index scores from a known reference community structure due to warming.