Environmental correlates of species richness for native freshwater fish in Oregon, U.S.A.

Abstract

Summary Aim To better understand how environmental factors affect fish species richness across the state of Oregon. Location Oregon, U.S.A. Methods A database showing collection locations of 4911 fish specimens in the Oregon State University museum was modified by the Oregon Natural Heritage Program to include probable occurrences, and mapped within a grid of 375 hexagons that cover the state. The individual species maps of freshwater fish in Oregon were reviewed and revised by thirty regional fish biologists and then synthesized into a single map of native species richness. We used regression tree analysis (RTA) and multiple linear regression (MLR) to assess patterns of fish species richness with twenty environmental, three anthropogenic, and two historical variables. Results RTA explained 66% of the variation in native species richness, associating richness with annual air temperature range, minimum January temperature, introduced species richness, and stream density. MLR explained 68% of native species richness variation and associated richness with maximum July temperature, air temperature range, standard deviation of monthly temperature, stream density, introduced species richness, and basin connectivity. Main conclusions We conclude that for these data and at this scale, native fish species richness in Oregon is associated with annual climatic extremes, spatial variability of climate, stream density, basin connectivity, and introduced fishes.