Animals that live in the alpine zone survive on the razor's edge of environmental tolerances, often making them more sensitive to changes in climate than in lower elevation ecosystems. Research at NWT indicates that in the alpine zone, the growth and survival of animals, like pikas and marmots, and the phenology of insects, like flower pollination by bumble bees, can provide important early warning signs of global climate change.
The American pika (Ochotona princeps) is considered a sentinel species for detecting ecological effects of climate change. This hamster-sized lagomorph, or "rock rabbit," is an icon of rocky landscapes that survives harsh alpine winters by living under an insulating blanket of snow. Pikas don't hibernate, so they need a store of food to last them through the winter. In alpine areas, they use the short summer months to collect and store a haypile of grasses and forbs. Building a haypile can be hot work during the summer for these round, furry animals that are built to retain heat, so pikas take refuge in the cool spaces under boulderfields, especially rocky features that harbor sub-surface permafrost and seasonal ice (Millar and Westfall 2010). In the winter pikas rely on the insulation of snow to keep them warm by protecting them from exposure to extremely cold temperatures. In a warming climate, pikas are expected to have more trouble gathering the resources they need to survive a harsh winter. NWT researchers are studying the insulating properties of snow cover and the combined effects of summer and winter temperatures, snow cover, and the presence of subsurface ice on the survival of pikas.
This research is aimed not only at understanding how climate affects the pika, but how the pika might be used as biological indicator of sub-surface ice and other water features key to the productivity of western watersheds. The disappearance of pikas may indicate a reduction in snow cover and sub-surface water resources, which are difficult to measure directly.
More immediately, elevated levels of stress in pikas may provide early warning of a reduction in these water resources. NWT researchers are attempting to relate stress hormones and other metrics of stress to the climate experienced by individual pikas, with the hope that this research will lead to a simple biological indicator of watershed health.
Growth rate and survival analyses of Yellow-bellied marmot populations on Niwot Ridge and in adjacent Green Lakes Valley indicate strong differences between locations that might be related to climate, and that these effects may contribute to the breakdown of social structure typical of marmot populations.
Field sampling indicates that juveniles have not been found to persist beyond their first year on Niwot Ridge. Juveniles have been found to often survive their first year in GLV. Our working hypothesis is that differences between the two locations are due to the lower insulation layer of snow over the hibernacula on the ridge areas. Current work is relating yearly snowpack to survival and growth rates. These differences in survival may also translate to changes in social structure. Ridge marmots do not have cohesive social colonies, indicating a breakdown of social structure. In contrast, marmot populations in the Green Lakes Valley have typical social colonies with female matrilines and one dominant male.
Indirect effects of climate change can also occur through changes in mutualisms that evolve through the matching of functional traits between partners, such as tongue length of pollinators and flower tube depth of plants. Using a long-term dataset, we found that in two alpine bumble bee species, decreases in tongue length have evolved over 40 years (Miller-Struttmann et al. 2015). Long-tongued pollinators specialize on flowers with deep corolla tubes, whereas shorter-tongued pollinators generalize across tube lengths. Co-occurring flowers have not become shallower, nor are small-flowered plants more prolific. Declining floral resources because of warmer summers appear to favor generalist foraging, leading to a mismatch between shorter-tongued bees and the longer-tubed plants they once pollinated.
Miller-Struttmann NE, Geib JC, Franklin JD, Kevan PG, Holdo RM, Ebert-May D, Lynn AM, Kettenbach JA, Hedrick E and Galen C (2015) Functional mismatch in a bumble bee pollination mutualism under climate change. Science 349:1541-1544
This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-1637686. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necesarily reflect the views of the National Science Foundation.
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