Assessing Spatial-Temporal Heterogeneity of Rangelands
Heterogeneous landscapes alter ecological interactions by modifying fluxes of organisms, material and energy. Most constituent ecological processes and patterns are regulated by dynamics occurring simultaneously at several spatial or temporal scales. However, it remains unclear how animals perceive and integrate these patterns. Consequently, a given landscape has functionally different geometries that depend in part on the scale of perception by animals. However, resource geometry is also rapidly modified in response to seasonality or through disturbance such as fire. It is unknown how these factors influence animal perception of resource distributions. The objectives of this study are to evaluate landscape level plant-animal interactions at multiple spatial scales and to develop a series of predictive spatial models that characterize specific plant and animal responses to landscape resource heterogeneity. Landscape heterogeneity will be evaluated using conditional spatial simulation of ground-truthed data in conjunction with digital imagery obtained from a tethered blimp remote-sensing platform developed for use on this project.
Suspended below the blimp from a tilt-swivel gimbal are two 35mm cameras which can be aimed and triggered remotely from the ground to capture paired color and infra-red imagery for analyzing fine-scale plant spatial distributions.
Color and near-infrared slides are scanned and georeferenced using GPS ground control points. Resulting images are color-separated and histogram-matched (calibrated) to a selected reference image, and then spectrally-classified. Classification and regression tree (CART) procedures are used to evaluate our ability to discern various community types. Plant species gradients are identified via indirect gradient analysis (multi-dimensional scaling, detrended correspondence analysis) of georeferenced ground-truthing data.
A second major component of this research involves the evaluation of ungulate responses to forage spatial heterogeneity. Because of differences in digestive morphology and feeding style, we predict that ungulate species will differ in how they perceive and respond to the abundance and spatial complexity of forage resources on the landscape. Animal responses to fine-scale resource heterogeneity are being evaluated by observing the feeding behavior of white-tailed deer and Angora goats free-ranging within 3 ha enclosures established in a variety of pastures and range conditions. Deer and goat spatial responses to forage distributions are continuously recorded during observation periods using a high-resolution video camera mounted on the blimp, and suspended over the enclosure. Simultaneous ground observations of animal foraging behavior provide details on animal diet selection patterns and foraging efficiency.
Although white-tailed deer and Angora goat are similar in body size, relatively subtle differences in digestive morphologies and feeding adaptations produce clear differences in their spatial responses to identical forage resources. The images below represent spatial responses of white-tailed deer (left) and Angora goats (right) recorded during approximately 10 hours of foraging within the same 1 ha enclosure.
Animal spatial responses will be compared to plant spatial distributions and used to evaluate hypotheses regarding the relative importance of resource heterogeneity, important forage species and plant spatial distributions on animal dispersion and feeding performance.
We anticipate that this research effort will enhance our understanding of the importance of spatial-temporal patterns of resource heterogeneity on animal foraging behavior and patterns of landscape use by ungulates. Additional investigations underway include evaluations of fine-scale vegetative composition and structure in oak woodland savanna communities and influence of plant and animal dispersion on tick survival and abundance.
This research project is a collaborative effort involving the following individuals: Blake Murden, Christine Doucet, and Ken Risenhoover, Dept. Wildlife & Fisheries Sciences, Texas A&M University; Markus Walsh, Dept. Rangeland Ecology, Texas A&M; Barbara Walsh, Dept. Veterinary Pathobiology, Texas A&M; and Charles Taylor, Texas Agricultural Experiment Station, Sonora Research Center.
Additional information regarding this and other wildlife research being conducted at the TAES Sonora Research Center can be obtained from Ken L. Risenhoover, Department of Wildlife & Fisheries Sciences, Texas A&M University, College Station, Texas 77843-2258. This page last updated 2-25-97.