Who Will Be the Apex Predator When Climate Change Effects Local Streams?

Air temperatures are expected to rise approximately 4° C over the next 50 years as a result of global climate change. As temperatures rise, the range of habitats will shift along the latitudinal gradients, potentially causing local species decline. This is especially true for less mobile species that are limited in their ability to disperse and colonize new habitats, for example specific fish species. Studying the response of aquatic populations to stream temperature rise will enable more accurate predictions of abundance, which will lead to more appropriate conservation efforts. Warmer temperatures will increasingly favor species with a higher thermal tolerance, including many nonnative species. As these species colonize new habitats, they are predicted to increase in population size and distribution, which could impact native species. Brook Trout (Salvelinus fontinalis) populations are native to headwater streams in the Appalachians of North America. This species is of high conservation need, with threats including stream temperature rise and competition with nonnative species, particularly Brown trout (Salmo trutta). Because Brown Trout have a have a higher thermal tolerance than Brook Trout, future competition is expected to decrease Brook Trout population sizes. Using an experimental stream system and video we evaluated the effects of brown trout on brook trout behavior and habitat use in experimental streams across three temperatures at the upper, lower, and intermediate thresholds for brook trout. In addition, we also measured short-term growth rate at these three different temperature thresholds over the course of several weeks. We hypothesize that competitive advantage and preferential habitat positions will shift from brook trout to brown trout with increasing temperatures. We also hypothesize that there will be decreased brook trout growth in the presence of brown trout as temperatures increase. Brook trout are a recreationally and culturally important species, which indicate high water quality, and it is important to preserve this native trout to maintain biodiversity