Temperature-dependent performance as a driver of warm-water fish species replacement along the river continuum

Abstract

Replacement of fish species by their congeners along gradients of stream size is common in warm-water streams, but the causative environmental factors driving this turnover are not fully understood. We used laboratory experiments to test for differences in temperature-dependent egg hatch success and age-0 food ration size for three congeneric cyprinids that differ in abundance along temperature–stream size gradients. Headwater species (Pimephales promelas and Pimephales notatus) had lower thermal optima and narrower thermal breadths for hatch success compared with a river mainstem species (Pimephales vigilax). Temperature sensitivity of ration size was lowest for P. promelas, intermediate for P. notatus, and highest for P. vigilax. Using an empirical stream temperature model, we predicted water temperatures and projected hatch success and ration size for 7974 stream segments in Kansas, USA. Projected hatch success from May to July and ration size from July to September generally matched abundance–stream size patterns, suggesting that increasing temperature along the river continuum may drive replacements among Pimephales species. Our findings combined with evaluations of timing and duration of spawning seasons will improve mechanistic understanding of species replacements along the river continuum.