As wild species face anthropogenic stressors, they will either adapt, shift their geographic range, or decline, perhaps towards extinction. The relative scope of these responses has not been well studied, especially for climate change where geographic range shifts and population declines have been widely discussed but the potential for adaptation mostly ignored. Adaptation to anthropogenic stressors can occur through phenotypic plasticity and/or evolution. My thesis first establishes, based on field studies of wild snowshoe hares, a novel and high-profile stressor directly linked to climate change. The stressor arises from a decrease in snow duration due to climate change, which causes seasonal coat color molt of individual hares to become mismatched with their background. The immediate adaptive solution to this form of camouflage mismatch is phenotypic plasticity, either in phenology of seasonal color molts or in behaviors that reduce mismatch or its consequences. Based on nearly 200 snowshoe hares across a wide range of snow conditions and two study sites in Montana, USA that differed in elevation and climate, I found minimal plasticity in response to mismatch between coat color and background. I found that molt phenology varied between study sites, likely due to differences in photoperiod and climate, but was largely fixed within study sites where seasonal changes in phenology were limited across years of very different snow duration. Hares exhibited some plasticity in the rate of the spring molt in response to immediate snow conditions but temperature or snow cover were not strong modifiers of the white-to-brown molt phenology. I also found no evidence that individual hares modify their behavior in response to color mismatch. Hiding and fleeing behaviors and immediate microsite preference of hares were more affected by variables related to season, site, and concealment, than by color mismatch. Although hares do not appear to be responding to camouflage mismatch with behavioral plasticity, adaptation could also occur through evolutionary changes facilitated by natural selection. We found that the raw material for natural selection to act on does exist in our populations in the form of individual variation in coat color phenology and consequently in color mismatch. We also found high fitness costs of coat color mismatch, with hares suffering 3 to 7% lower weekly survival rates when mismatched against their background. Coupling these fitness costs to local estimates of increased seasonal color mismatch as snow duration decreases in the future, we predict that annual hare survival will decline up to 12% by mid- and 24% by late century. Such changes in survival are sufficient to cause increasing hare populations to decline strongly towards extinction, with annual population geometric growth rate decreasing by 11% (24%) by mid (late) century. We conclude that plasticity in molt phenology and behaviors in snowshoe hares is insufficient for adaptation to camouflage mismatch, and that potential adaptive responses to future climate change will have to be facilitated by natural selection. These results form the basis for future work to evaluate whether evolution by natural selection can operate fast enough to prevent decline of this species.
| Identifer | oai:union.ndltd.org:MONTANA/oai:etd.lib.umt.edu:etd-01162014-144459 |
| Date | 07 February 2014 |
| Creators | Zimova, Marketa |
| Contributors | Dr. Michael Mitchell, Dr. Doug Emlen, Dr. L. Scott Mills |
| Publisher | The University of Montana |
| Source Sets | University of Montana Missoula |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.umt.edu/theses/available/etd-01162014-144459/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Montana or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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