Competitive Interactions Between Creek Chub (Semotilus atromaculatus) and Brook Trout (Salvelinus fontinalis) under the Influence of Rising Temperatures

The natural distribution of many freshwater fish species are limited by their thermal tolerances, both because a species cannot inhabit an area outside its tolerance range and because of increased stress when in environments approaching the limits of its tolerance range. Many species may mediate temperature change physiologically, behaviorally, or both but these changes often may change or compromise interspecific dynamics through the effects on feeding behavior, growth rate, immune responses, and social behavior. In the Appalachian Mountains, creek chub (Semotilus atromaculatus) are found in warm-water and cold-water streams, the latter of which are also inhabited by brook trout (Salvelinus fontinalis). Brook trout have a lower tolerance for warmer temperatures than creek chub, and require higher oxygen concentrations, which decrease in warmer waters. As the temperatures of cold-water streams continue to increase due to anthropogenic climate change and land use, brook trout are under more thermal stress, which negatively affects their ability to compete with creek chub. To examine the influences that temperature has on competitive interactions between these species, we observed feeding behavior, aggression, and space use differences at three different temperatures (18°C, 20°C, and 22°C) among dyad pairs for all combinations of species (brook trout/brook trout, brook trout/creek chub, creek chub/creek chub). Results show that an increase in temperature causes decreased appetite and aggression in brook trout and increased competition between the two focal species. This may have implications in the range restriction of brook trout, and the decreased dominance of a top predator may lead to diverse impacts on stream community dynamics