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UNIVERSITY OF NEVADA, RENO (2006)

Lizards as a model system for investigating environmental change

Tull, John C.

Titre : Lizards as a model system for investigating environmental change

Auteur : Tull, John C.,

Grade : Doctor of Philosophy (PhD) 2006

Université de soutenance : UNIVERSITY OF NEVADA, RENO

Résumé
With human activities reducing the quantity and quality of space available for native wildlife, there is a need for tools to effectively assess the impacts of ecological stress on wildlife. I explored the use of fluctuating asymmetry (FA) as a means for evaluating population responses to stress in the environment. I found that the western fence lizard, Sceloporus occidentals, exhibits differences in FA between populations that inhabit public lands designated for off highway vehicle activities relative to public lands without heavy recreational uses. This study provides a benchmark for the use of FA in a conservation context where the goal is to assess the impacts of human activities on native wildlife populations. I also combined the use of FA with the exploration of species distributional shifts over a 45-year period to reveal lizard population responses to broader environmental changes. I examined weather data and found that the Mojave-Great Basin transitional zone in Saline Valley is rapidly warming. Based upon the prediction that lizard species distributions would be under greater environmental pressure to shift up along an elevational gradient, I further predicted that lizards would exhibit heightened FA in current versus past populations. I found significantly greater FA in the current population of the desert spiny lizard, S. magister, but not in the western fence lizard. Five of eight lizard species had upper distributional limits that were ≥100 m higher in elevation than 45 years ago. This evidence along with warming temperatures provides a plausible example of vertebrate species responses to global warming. Finally, I experimentally tested the effect of increased corticosterone (CORT) on developing embryos of western fence lizards. I found a marginal increase in FA for the CORT group, but no differences in sex, mortality, size and mass at birth, change in egg mass from days 11 to 33, or days to hatch. This finding supports the expectation that CORT levels might influence FA in developing S. occidentalis , but further exploration is warranted. Overall, FA is a useful, fairly simple, and efficient tool to apply to lizards in the genus Sceloporus for monitoring ecological change in wildlife populations.

Mots clés : BIOLOGY, ECOLOGY ; BIOLOGY, ZOOLOGY ; AGRICULTURE, FORESTRY AND WILDLIFE ; ENVIRONMENTAL SCIENCES

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