Climate Change As a Driver of the Homogenization of New York's Stream Fish Fauna

Homogenization of fish faunas across landscapes has been attributed to widespread species introductions coupled with extirpation of endemic species.  From 1927-1940, New York State conducted intensive watershed surveys of the State’s fish fauna, which included 4058 stream sites.  Stream surveys were conducted on a similar scale over the last two decades, and included 3057 sites.   Frequency of occurrence data indicate significant changes in the distributional patterns of fishes between the two survey periods, and results of multivariate analyses are indicative of homogenization of the stream fish fauna across the state.  Bray-Curtis values show that similarity of individual watersheds to all other watersheds has increased in all cases.  Climate change appears to be a significant driver of changes in large scale patterns of distribution leading to homogenization.   Species that have exhibited the greatest range expansions are those that prefer the warmest water temperatures and those species with the most marked contractions of range are those that are least tolerant of high water temperatures.  The southern extent of a species’ range was a significant predictor of whether a species would exhibit an increase or decrease in distribution over the study period and explained 40% of the variability of species range changes.