Literaturdatenbank
Literaturdatenbank |
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Inman, R. D. (2008). How elusive behavior and climate influence the precision of density estimates of desert tortoise populations. Unpublished thesis M.S. University of Nevada, Reno.
Added by: Admin (21 Nov 2009 11:53:14 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: Inman2008 View all bibliographic details  |
Categories: General Keywords: Gopherus, Gopherus agassizii, Habitat = habitat, Nordamerika = North America, Schildkröten = turtles + tortoises, Testudinidae Creators: Inman Publisher: University of Nevada (Reno) |
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| Abstract |
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Testudinidae In our world of continued urban growth, the encroachment of human activities on biological communities and ecosystems has increased the need for conservation measures aimed at preserving our world's unique biodiversity. This especially true for threatened or endangered species, where conservation measures are aimed at recovering a species or increasing the probability of species persistence. To be effective, these measures require knowledge of population-level attributes and processes such as population growth, density, and distribution. Knowledge of these population characteristics often can be difficult to attain, and requires study of how individuals in a population interact with each other and their environment. This research is aimed at furthering our knowledge of how desert tortoises ( Gopherus agassizii ) interact with their thermal environment, and is intended to improve our understanding of the assumptions and pitfalls of estimating the population density of desert tortoises. I use climate space and operative temperature ( T e ) models to investigate interactions between desert tortoises and their environments as a means to quantify activity patterns of tortoises throughout the season of activity (spring-early summer). I show that the activity patterns of desert tortoises were variable among individuals (each individual was different from 50% of all other individuals) and only repeatable from day-to-day 50% of the time. This variance in the behavior of individuals causes estimates of population density to be imprecise when using distance-based methods for estimating population density. Distance methods require an estimate of the behavior of individual tortoises in order to estimate the proportion of the population that is available to be sampled. Current methods to estimate this are inadequate for assessing the variance in the behavior of individuals. I show a more accurate estimate of the variance in availability, which is substantially larger than current methods suggest. I incorporate more accurate estimates of availability to be sampled into calculated estimates of population density, and I show that lack of precision in density estimates may forfend detecting changes in population density over time (It is generally thought that population growth rates would rarely exceed 1% per year). An inability to assess trends in population growth may thwart assessing the effectiveness of recovery actions for this federally threatened species.
Added by: Admin |