Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change

Abstract

Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km 2 ), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species' physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations.global change | hydrology | invasive species | niche model | distribution modeling N early all broad-scale analyses of climate effects on freshwater species have focused on temperature shifts, to the exclusion of other climate-driven drivers. Although temperature is a critical determinant of metabolic and physical processes (1), important ecosystem effects on streams and rivers may also be mediated by flow regime and biotic interactions. Flow regime has been described as a "master variable" (2) that controls or influences many aspects of the physical aquatic environment, as well as the timing of reproduction and migration of many organisms (3). Biotic interactions are increasingly recognized as important components of climate-species relationships (4, 5), but are rarely included in projections of species distributions under future climates, with some notable exceptions (6). Competitive interactions in particular are not commonly modeled (but see ref. 7), despite interest in invasive-native species interaction under climate change (8). It is likely that all three factors-temperature, flow regime, and biotic interactions-will play important roles in future aquatic species distributional shifts (8-11).Trout serve as excellent model organisms for examining how these mechanisms could alter population dynamics and species distributio...

Slow climate velocities of mountain streams portend their role as refugia for cold-water biodiversity

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Observed groundwater temperature response to recent climate change

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Environment shapes invertebrate assemblage structure differences between volcanic spring-fed and runoff rivers in northern California

“…Coldwater habitat in the western USA and elsewhere is projected to decline significantly with decreasing summer base flows and increasing stream temperatures (Stewart et al 2005, Bryant 2009, Wenger et al 2011. These 2 climate-induced effects may have a negative synergistic effect on coldwater biota as the time between elevated summer water temperature and autumn base flow declines (Arismendi et al 2013).…”