In their article in the July 2005 issue of The American Naturalist, Yssa D. DeWoody, Zhilan Feng, and Robert K. Swihart (Purdue University) model species' occupancy within a patchy dynamic landscape. They derive deterministic persistence thresholds which depend jointly upon the spatial and temporal structure of the landscape, reinforcing the importance of spatio-temporal connectivity. This model has the potential to predict various consequences of different land-use strategies and thus serve as a practical conservation tool. Because the model permits patches to operate on different time scales, it allows the classic definition of a patch to be expanded, which could help to quantify the benefits of temporary refugia.
Two of the greatest threats to biodiversity worldwide are the loss and fragmentation of native habitat. A consequence of ongoing degradation is that more and more species are being challenged to survive as spatially structured populations within patchy landscapes. The fate of these species depends in part on their perceptions of the spatial and temporal structure of the landscape: a species' dispersal ability and the isolation of patches interact across varying temporal scales to determine colonization potential. For example, the suitability of a patch can be altered due to anomalous weather events or predictable drought cycles, forest fires or crop rotations in agricultural settings. These events, regardless of whether they are harmful or helpful, stochastic or deterministic, change the landscape and thus influence the species' survival.
Currently, DeWoody and colleagues are testing their hypotheses in experimental landscapes consisting of distinct flour patches inhabited by sawtooth grain beetles. This system will enable them to validate the model, refine methods for parameter estimation, and explore the limits of these persistence thresholds within a stochastic environment.
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