Climate Change and the Rocky Mountains - Impact of Global Changes on Mountains: Responses and Adaptation - page 453

regimes in stream networks. Natal spawning and rearing habitats are often
fragmented and constrained to the coldest headwater streams (<13ºC; Jones
et al. 2013). As air and water temperatures continue to increase, the lower
portions of stream networks, which are used by bull trout for foraging,
migrating and overwintering habitat, may become thermally unsuitable and
headwater spawning and rearing streams may become isolated because of
increasing thermal fragmentation during summer (Isaak et al. 2010, Jones
et al. 2013; Fig. 20.5). Bull trout are also fall spawners, which may explain
why populations typically fare poorly in streams with frequent high
winter fl ows and suggests that the recent increases in winter fl ood risks
across portions of the Rocky Mountains are a cause for concern. Currently,
conservation efforts are focusing on maintaining natural connections and
a diversity of coldwater habitats over a large spatial scale to conserve the
full expression of life history traits and processes infl uencing the natural
dispersal among populations.
Freshwater algae invades with warming waters
Climate warming may also promote expansion of invasive plants in aquatic
ecosystems. Didymosphenia geminata ( didymo ) is a freshwater alga (Fig. 20.7)
native to North America that has recently spread to lower latitudes and
warmer waters, and increasingly forms large blooms that cover streambeds
Figure 20.7. Didymosphenia geminata (didymo) is a freshwater alga that may cause dramatic
changes in the diversity and abundance of aquatic insect species when algae blooms occur
in warming Rocky Mountain streams and rivers. Such losses would impact the entire food
web (Credit: Joe Giersch, USGS).
Color image of this figure appears in the color plate section at the end of the topic.