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New insights into responses of Yellowstone wolves to environmental changes

Methods developed in study of Yellowstone wolves may ultimately help improve predictions of wildlife responses to environmental changes in various ecosystems

A study of the wolves of Yellowstone National Park has improved predictions of how these animals will respond to environmental changes. The study, which was partially funded by the National Science Foundation, appears in the December 2, 2011 issue of Science.

The study, which is part of the Yellowstone Wolf Project, involved tracking changes in various characteristics of the wolves of Yellowstone National Park ever since these animals were reintroduced to the park in 1995. Some tracked characteristics–such as population size–are related to population ecology. Other tracked characteristics–such as coat color–are genetically determined through evolution.

The project also involved using a new model to compare the collected data on Yellowstone wolf characteristics to environmental conditions through the years covered by the study.

Conditions in the park during each year were defined along a continuum from “good years” to “bad years”–with good years more favorable to wolf survival than bad years.

Tim Coulson of Imperial College London, the lead author of the study, explains, “The novelty of the new model is that it looks at how the frequencies of changes in environmental conditions along the ‘good to bad’ year continuum simultaneously impact many wolf characteristics.”

Results indicate that:

  • Environmental changes will inevitably generate simultaneous ecological and evolutionary responses in the Yellowstone wolves.
  • Changes in mean environment conditions will impact the size of the Yellowstone wolf population more than will changes in the variability of environmental conditions.
  • A single environmental change may impact various wolf characteristics differently, depending on which particular aspects of wolf biology it impacts.
  • For example, suppose environmental conditions in a “good year” helped increase the population size of Yellowstone wolves by increasing their survival rates. Also, suppose that a grey coat color would confer a survival advantage to wolves. Then, under those particular “good” conditions, an increase in the size of the wolf population would be expected to produce an increase in the prevalence of grey coats among the wolves.

    By contrast, suppose that certain environmental conditions in a “good year” helped increase the population size of Yellowstone wolves by increasing the availability of their prey. Because the availability of prey and coat color are not related to one another, under those particular “good” conditions, an increase in the size of the wolf population would not be expected to produce an increase in the prevalence of grey coats among the wolves.

    Coulson says that increasing the specificity of the model’s predictions requires collecting more data on the ecological and evolutionary responses of Yellowstone’s wolves to various environmental conditions and on the relationships of these responses to one another.

    As part of this effort, the Yellowstone Wolf Project research team is currently studying the differential impacts of various environmental changes on ecological and evolutionary characteristics of Yellowstone wolves during various stages of their life cycles. The team is also working to identify the types of environmental conditions–such as the sizes of various populations of prey species and the amount and residence time of snow on the ground–that define good, bad and intermediary years for wolves.

    The researchers hope that the once the methods developed through this study are refined, they may be applicable to other types of species, such as insects or crop pests, that live in other types of ecosystems.

    What’s more, Coulson suggests that these methods may ultimately help answer questions about human populations. As just one example, the methods developed through this study might ultimately be used to help predict the impacts of the ongoing obesity epidemic on survival and fertility rates and the resulting influence of those variables on the growth rate of selected human populations.

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