Landscape determinants of fish reproductive guilds

Abstract

Species dependent on freshwaters are declining globally. Understanding natural and anthropogenic environmental drivers affecting community structure and species occurrence is crucial for planning management and conservation actions. The aim of this study was to determine which landscape characteristics constrain reproductive guilds in wadeable streams and to explore the influence of reproductive strategy on fish occurrence. We expected reproductive guilds to differ in their associations with landscape determinants (i.e., the landscape characteristics found to constrain our reproductive guilds). This study was conducted in the Delaware River Basin in North America. We compiled existing stream survey and geospatial data from multiple government agencies and scientific organizations for 552 sites. We used ordination and regression techniques to identify important landscape determinants and their associations with reproductive guilds. We identified 12 variables that explained 20.6% of the total variation in reproductive guild composition. Slope, land cover and disturbance variables drove the position of reproductive guilds in ordination space. All reproductive guilds differed in the set of landscape-scale determinants that were selected during modelling. Best subsets of variables selected in regression models indicate that reproductive guild occurrence is significantly explained by catchment characteristics. These characteristics include measures of slope, land use and land cover, disturbance, and climate. Differences in determinants and relationships with reproductive guilds found in regression models, and gradients identified, indicate the importance of different landscape-scale determinants for specific reproductive guilds. Furthermore, our findings suggest a link between the environmental requirements of reproductive guilds and landscape-scale characteristics.