Published since 1946
Spatial Response to Climate by Predators and Prey in the Intermountain West, "Chasing the Green Wave"
The U.S. Geological Survey's Utah Cooperative Fish and Wildlife Research Unit is working with a consortium of other cooperative research units and universities to examine relationships of climate to trophic linkages between forage productivity, native ungulates and a top predator across landscapes in the western United States. The project is funded through NASA's Biodiversity and Ecological Forecasting Program and led by Thomas Edwards of the Utah Unit and the Department of Wildland Resources at Utah State University.
The first step in the analysis was to generate data sets of forage productivity. Under the lead of Joe Sexton from the University of Maryland's Global Land Cover Facility, a set of "stacks" of a satellite-based (MODIS) metric called the Normalized Difference Vegetation Index (NDVI) was developed. NDVI has been successfully used to assess plant nutritional quality and to model ungulate-forage relationships. The "stacks" were computed on a daily basis between 2000 and 2013. The more than 5,000 NDVI layers serve as the basis for how ungulates move across landscapes in response to daily changes in forage quality and quantity as measured by NDVI.
Researchers next created a database comprised of time-referenced geospatial locations for cougars (Puma concolor), mule deer (Odocoileus heminous), elk (Cervus elaphus) and bighorn sheep (Ovis canadensis) telemetered and tracked on or near the Colorado Plateau. The combination of animal GPS data and agency-derived demographic data is the basis for models of spatial patterns of ungulates on a daily interval. Animated videos that track the vegetation and snow cover and overlay them with animal use patterns are available online.
One of the first tasks was to determine the extent to which the sometimes behaviorally cryptic study animals engaged in activities that masked satellite-based GPS collars, making detection difficult. Kirsten Ironside, a Ph.D. candidate at Northern Arizona University and SCEP (Student Career Experience Program) student with the USGS Southwest Biological Science Center, modelled the extent to which skyview ? the visibility of the radio collar ? affected location fixes on the study animals. Her results are helping provide adjustments to detection rates and locations of the telemetered study animals.
Several of the research modules have been completed thus far. One of these examines relationships in mule deer productivity and so-called peak-of-season (POS) NDVI values, a measure of plant phenology. This research, led by David Stoner, a post-doctoral research fellow at Utah State University, has clearly demonstrated linkages between deer productivity and NDVI. As precipitation shifts latitudinally from winter-based snowfalls to summer-based monsoonal precipitation, variability in demographic metrics of mule deer exhibit increased inter-annual variability on a spatial gradient ranging from central Arizona to northern Utah. Given climate projections of a northward shift in monsoon and decreased winter-based snowfall, it is likely that management agencies will see increased inter-annual variability on deer reproduction in more northerly ranges of the mule deer.
One of the first forage-ungulate-predator analyses focused on forage-predation risk trade-offs. Here, Kathleen Longshore and colleagues at the USGS Western Ecological Research Center modeled use of escape terrain by female bighorn sheep with young in relation to the NDVI forage metric. Analyses indicate female bighorn sheep with lambs remain in escape terrain, thereby reducing predation risk from cougar but requiring they remain in areas with lower forage quality and quantity during the energy demanding neonatal growth period ? the trade-off. More intriguing is an observed daily pattern, where females are leaving escape terrain midday to forage in non-escape terrain having higher forage quality as indicated by NDVI. This daily behavioral pattern reduces risk of encounter with cougars during their active hunting periods. Once young are weaned, female's movements across the landscape more closely track the higher NDVI forage values.
These and other research models are being used to predict movement patterns and densities of ungulates across the study area, which will then be used as a predictor for modeling cougar movement using a decade of records collected from more than 80 intensely monitored individuals across the study region. Once fit to data, the cougar movement models can be used to predict the habitat use and traversibility over the study area for cougars. Resulting movement surfaces will be modified by spatially-explicit estimates of survival from known fates of more than 200 cougars to derive analogs of density. With the habitat use and occupancy surfaces from this analysis, researchers will then analyze the habitat and movement of cougars to assess the sustainability of the regional cougar metapopulation.
The research is not only providing models of how ungulates are moving across large spatial extents in the Intermountain west, but how these movement patterns are dictated by annual precipitation cycles. When coupled with climate change projections, we can examine potential implications for managing wildlife populations in the face of climate change.
Each month, the ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This month's article was written by Dr. Thomas Edwards, research ecologist with the Utah Cooperative Fish and Wildlife Research Unit and the Department of Wildland Resources at Utah State University.