Climate Change and the Rocky Mountains - Impact of Global Changes on Mountains: Responses and Adaptation - page 444

relatively unknown, but recent empirical evidence suggests that salmonid
fi shes can rapidly adapt via natural selection to climate warming (Crozier
et al. 2011, Kovach et al. 2012).
Interspecifi c differences in life histories and thermal niches suggest
that the effects of changing climate patterns are unlikely to be consistent
across species, populations and ecosystems. For example, bull trout may
be more sensitive than cutthroat trout to the direct effects of climate
warming (Wenger et al. 2011a). Bull trout have optimal temperatures that
are substantially lower than those of other salmonids, so spawning and
rearing habitats are constrained to a patchwork of cold headwater habitats
across river networks (Selong et al. 2001). Additionally, bull trout are fall
spawners, which are particularly susceptible to frequent high winter fl ows
(Wenger et al. 2011a). Increasing temperatures and fl ood risks pose serious
threats to this declining species. In some cases, however, future stream
temperature warming may benefi t trout living in the coldest environments
of the Rockies. Al-Chokhachy et al. (2013) linked future stream temperatures
with fi sh growth models to investigate how changing thermal regimes
could infl uence the future distribution and persistence of Yellowstone
cutthroat trout in the Greater Yellowstone Ecosystem. For high-elevation
populations, there were signifi cant increases in fi sh growth attributable
both to warming of cold water temperatures and to extended growing
seasons. However, these benefi ts could be offset by the interspecifi c effects of
corresponding growth of sympatric, non-native fi shes currently occupying
lower elevation streams. Finally (Crozier and Zabel 2006), demonstrated that
Chinook salmon ( Oncorhynchus tshawytsha ) have widely variable responses
to temperature throughout the Salmon River basin in Idaho, resulting in
very different projections of population size and probability of persistence
across the basin.
In addition to the direct effects on habitat quality, climate warming
will indirectly affect native salmonids and aquatic biota by exacerbating
interactions with non-native, invasive species. Climate changes may
facilitate the expansion of invasive species or modify interactions among
native species through competition, predation, disease and introgressive
hybridization (Rahel et al. 2008). In many cases, stream temperature
increases are exacerbating biotic interactions by facilitating expansion
of non-native species into native fi sh habitats (Wenger et al. 2011a). For
example, many populations of native cutthroat trout have been displaced
from natal habitats through competitive interactions with introduced brook
trout, brown trout ( S. trutta ), and rainbow trout. Laboratory experiments
and natural studies show that non-native salmonids may have a competitive
growth advantage at warmer temperatures. In the Northern Rockies,