Browsing by Author "Detling, James K., advisor"
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Item Open Access Cattle use of prairie dog towns on the Shortgrass Steppe of Colorado(Colorado State University. Libraries, 2000) Guenther, Debra A., author; Detling, James K., advisor; Rittenhouse, L. R. (Larry Ronald), 1940-, committee member; Steingraeber, David Allen, 1953-, committee memberStudies on the mixed-grass prairie have found that native large herbivores preferentially graze on prairie dog towns. I investigated the use of prairie dog towns by cattle (Bos taurus) in northeast Colorado by conducting surveys of cattle and vegetation on the Shortgrass Steppe Long Term Ecological Research Site from June-August, 1999. Twelve pastures containing 15 black-tailed prairie dog (Cynomys ludovicianus) towns were surveyed three times a week, and the number of cattle on the towns and their behavior were recorded. A subset of three pastures was intensively surveyed twice weekly wherein the habitat and activity of a randomly chosen focal animal was recorded every six minutes for 3.5 hours. Bite and step counts of other individuals were recorded for five-minute intervals. Vegetation height and cover data were collected monthly on each of the six habitat types. Resource selection functions for driving survey data indicated no significant difference between prairie dog town use and availability. Regression analysis showed no correlation between rain events and prairie dog town use by cattle. The intensively surveyed pastures yielded similar results: i.e., cattle did not significantly prefer or avoid the prairie dog towns. Cattle spent 60% of their time grazing, 13% resting, and 15% traveling when present on prairie dog towns. These percentages were not significantly different from most other habitat types. There were no significant differences in the number of bites per step taken by cattle on towns compared to off town swales, Atriplex canescens terraces, and crested wheatgrass (Agropyron cristatum) strips. Five plant species palatable to cattle occurred in relatively high frequencies (36-65%) on prairie dog towns. In general, bare ground, litter, and vegetation cover on prairie dog towns did not significantly differ from most other habitat types. Vegetation on prairie dog towns was however significantly shorter on (mean= 6.7cm) than that off (mean= 11.9cm) prairie dog towns. This research indicates that cattle on the shortgrass steppe use prairie dog towns randomly and do not avoid them despite the shorter vegetation on prairie dog towns. However, cattle do not prefer to graze on prairie dog towns as bison (Bison bison) do on the mixed-grass prairie.Item Open Access Fine-scale habitat use by black-footed ferrets (Mustela nigripes) released on black-tailed prairie dog (Cynomys ludovicianus) colonies in New Mexico(Colorado State University. Libraries, 2010) Chipault, Jennifer G., author; Detling, James K., advisor; Biggins, Dean E., advisor; Reich, Robin M., committee memberBlack-footed ferrets (Mustela nigripes) are among the most endangered animals in North America. The dependency of ferrets on diminishing prairie dog {Cynomys spp.) colonies for prey and shelter has been detrimental to their persistence in the wild. Reintroductions of captive-born ferrets into remaining prairie dog complexes have become crucial to the conservation of the species. Gaps in knowledge of ferret behavior hinder the success of these reintroductions. In this study, fine-scale prairie dog burrow density use by captive-born ferret kits was analyzed to inform future management. In September 2007, captive-born ferrets were released on a black-tailed prairie dog (C. ludovicianus) colony on the Vermejo Park Ranch in northern New Mexico. Locations {n = 46) from 16 ferret kits experimentally released in areas of comparatively low and high prairie dog burrow densities were obtained via spotlight surveys. Ten kits were subsequently translocated to low and high burrow density areas on other Vermejo colonies and located thereafter (« = 53). For two months, habitat use was quantified by mapping all burrow openings within a 30 m radius of where ferrets were located. Spatial autoregressive models and spatially-explicit t-tests were used to account for autocorrelation in the used burrow densities. It was hypothesized that ferrets released in, or translocated to, areas of low burrow densities would move so as to increase their localized burrow densities as they spent more nights in the wild. It was also hypothesized that ferrets released in, or translocated to, high burrow density areas would maintain high used burrow densities. There was an inverse relationship between used prairie dog burrow densities and nights in the wild for ferrets released in high burrow density areas. For ferrets translocated to high burrow density areas, a pattern was not detected in burrow densities over time, which does not contradict the hypothesis for these ferrets. However, burrow densities used by ferrets released in, and translocated to, low burrow density areas did not increase over time as expected. With the number of nights in the wild converted to release or translocation burrow densities versus ferret-used burrow densities, average used burrow densities increased for ferrets placed in low burrow density areas, and average used densities decreased for ferrets placed in high burrow density areas. Used burrow densities on most inhabited colonies were similar to available densities, except for one colony, where used densities were lower than available densities. Because newly-released ferrets in this study used burrow densities similar to densities available at the colony level, releasing ferrets on colonies offering overall high burrow densities might increase reintroduction success rates. Furthermore, burrow densities directly correlated with prey densities in this study. Ferrets used higher burrow densities before midnight; future research on ferret habitat use should consider within night variation. Other studies on ferret habitat use after release are necessary; kits monitored for more than two months, or with experience in the wild at a younger age, might select high burrow density areas within colonies as predicted.Item Open Access Nonlinear responses to food availability shape effects of habitat fragmentation on consumers(Colorado State University. Libraries, 2009) Blackburn, Heather B., author; Detling, James K., advisor; Hobbs, N. Thompson, advisorFragmentation of landscapes is a pervasive source of environmental change. Although understanding the effects of fragmentation has occupied ecologists for decades, there remain important gaps in our understanding of the way that fragmentation influences populations of mobile organisms. In particular, there is little tested theory explaining the way that fragmentation shapes interactions between consumers and resources. I propose a simple model that explains why fragmentation may harm consumers even when the total amount of resources on the landscape remains unchanged. In the model, I show that nonlinearity in the relationship between resource availability and benefit acquired from resources can cause a decrease in benefits to consumers when landscapes are subdivided into isolated parts. This decrease is the result of simple mathematical properties of the form of the relationship between resource availability and benefit, and is more severe with greater nonlinearity, with increasing fragmentation, or with greater unevenness of resource availability between fragments. I tested the predictions of the model using a laboratory system of cabbage looper (Trichoplusia ni) larvae on artificial landscapes. Consistent with the model's predictions, survivorship of larvae decreased with a combination of fragmentation and heterogeneity in resource availability. However, average mass of surviving larvae did not change in response to fragmentation alone. With basic knowledge of consumer resource use patterns and landscape structure, these observations can aid in making both generalized and quantitative predictions about the resource-mediated effects of fragmentation on consumers.