Hydrologic and thermal conditions occupied by a species within a single watershed predict the geographic extent of occurrence of freshwater fishes

Abstract

Hydrologic regimes and water temperatures are primary predictors of freshwater species occurrence. Although these variables have been demonstrated to be important in regulating species diversity at particular locations, whether species occurrences across lotic habitats within a single, relatively small watershed can predict the full geographic extent of a species is unclear. We use river reach estimates of streamflow and water temperature derived from a watershed-scale hydrologic model, coupled with body size measures, to investigate whether the type and variability of thermal and hydrologic habitat used by fish species within the Mobile River Basin (MRB) can predict the overall geographic extent of occurrence (GEO) for these taxa. Locality data for 108 species of fishes within MRB, one of the most ecologically diverse watersheds in the United States, were intersected with streamflow and water temperature estimates to characterize minimum and maximum streamflow and water temperature conditions and thermal breadth (range of thermal conditions) occupied by each species. Among all species, variation in GEO was associated with variation in thermal breadth and body size. Thermal variables were also important predictors of variation in GEO among Cyprinidae. Flow variables were important predictors of variation in GEO for Centrarchidae, Ictaluridae, and Percidae and within Etheostoma and Percina. Results generally indicate that species with large body size, relatively broad thermal tolerances, or preference for relatively high discharge environments tend to exhibit broader distributions across North America, yet these relationships vary among taxonomic groups.

Climate disequilibrium of fishes along elevation and latitudinal gradients: Implications for climate tracking

“…Most evidence against the climate equilibrium hypothesis comes from invasion biology, whereby many non‐native species exhibit climatic niche expansions into colder or warmer climates in their introduced range (Early & Sax, 2014; reviewed in Guisan et al, 2014). Fewer assessments have tested the climate equilibrium hypothesis across thermal gradients in species' native ranges, especially for elevation gradients, likely due to the need for temperature and distribution data at fine spatial resolutions (Kambach et al, 2019; VanCompernolle et al, 2019). However, such studies reached similar conclusions on a lack of support for the climate equilibrium hypothesis.…”

“…Migratory species are more likely to overfill their cold‐edge boundaries because (1) they are big‐bodied species with strong swimming abilities and (2) migrations allow them to occupy seasonal habitats that are outside their non‐migratory, thermal range (Comte & Olden, 2018). Hence, because migratory species have such high vagility, they are likely to track climatic changes better than small‐bodied species with low vagility (Radinger et al, 2017; Sunday et al, 2015; VanCompernolle et al, 2019).…”