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Browsing by Author "Wilson, Kenneth R., committee member"

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    Density, demography, and seasonal movement of snowshoe hares in central Colorado
    (Colorado State University. Libraries, 2011) Ivan, Jacob Scott, author; White, Gary C., advisor; Shenk, Tanya M., committee member; Wilson, Kenneth R., committee member; Doherty, Paul F., committee member; Romme, William H., committee member
    To view the abstract, please see the full text of the document.
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    Ecological consequences of warming climes for cold-adapted species – evidence from mountain goats
    (Colorado State University. Libraries, 2023) Hayes, Forest Parker, author; Berger, Joel, advisor; Bailey, Larissa L., committee member; Wilson, Kenneth R., committee member; McGrath, Daniel, committee member
    Global climate change from human activity is changing ecological communities at unprecedented rates. Coupled with recent and extraordinary loss of biodiversity, assessing the consequences for vulnerable species – and effecting proactive conservation – will be fundamental to stymieing these losses. Among the areas most strongly impacted by these changes are montane regions, which are warming at rates 2–5x the global average. Within those, cold-adapted organisms are among the most strongly impacted as they may experience thermal stress at moderate temperatures. Past species- and taxa-level responses to warming environs includes numerous concentrated extirpations at the southern peripheries of distributional ranges during the late Pleistocene. Less clear are localized capacities of cold-adapted species to mitigate thermal challenges against warming temperatures, especially through proximate behavioral and physiological adjustments. In this dissertation, I address three key tendrils of the ecological consequences of warming climes for cold-adapted species. First, I evaluate the role of snow patches in mediating the physiological impacts of warming temperatures. Despite strong associations between many taxa and cold environs, great uncertainty remains about the biological benefits, if any, of using persistent snow during summer months. Contrary to the prevalent hypothesis that persistent snow provides thermal relief for cold-adapted species, I demonstrate that use of snow patches facilitates insect avoidance and not thermoregulatory gains. While the duration and spatial extent of snow declines globally as the climate warms, its diminishing availability is likely to have substantive impacts to populations given a general pattern of associations between insects and temperatures at high elevations and latitudes. Next, I evaluate changes in spatial use relative to high temperatures and the influence of snow on resource selection. While thermal challenges to persistence are well evidenced through historical extirpations, attention to near-term shifts in resource use and snow as a driver of summer resource selection remains under-investigated. I found strong shifts in resource selection during periods of high temperature, with increased selection for cooler habitats, little effect from snow, and evidence of ecological tradeoffs in avoidance of heat. These results point to possible demographic consequences of changing behavior and illustrate the importance of proactive consideration of changing patterns of use in management policies. Finally, I evaluate the importance of climate refugia and human translocation for the applied conservation of biodiversity. Despite a long history of relocating wildlife, translocations outside native ranges have rarely been conducted for conservation and populations introduced beyond their native ranges have seldom contributed to in situ species conservation within native ranges. Herein, I identify three cases of introductions to climate refugia and highlight the untapped conservation value of existing populations outside of native ranges. I report species in these refugia offer not only a reservoir for reintroductions but also a buffer against temperature-driven distributional change and may prove invaluable in stymieing current and future loss of biodiversity under continued climate challenges. In concert, this dissertation addresses physiological and geographical consequences of warming climes for cold-adapted species, identifies the need for proactive conservation, and highlights one avenue through which meaningful conservation benefits may be achieved.
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    Improving ungulate habitat in a region undergoing rapid energy development: consequences for songbirds and small mammals
    (Colorado State University. Libraries, 2014) Bombaci, Sara Petrita, author; Pejchar, Liba, advisor; Wilson, Kenneth R., committee member; Paschke, Mark, committee member
    Habitat manipulation intended to mitigate the impact of energy development on game animals is well underway in the western U.S. Yet, the consequences of these actions for other species are not well understood. A habitat manipulation experiment was established in the Piceance Basin, a region of Colorado undergoing rapid energy development, to evaluate alternative methods (i.e. chaining, hydro-axe, and roller-chop treatments) for reducing pinyon-juniper woodlands to promote mule deer habitat. I use this experimental design to additionally test the initial effects of these treatments on birds and small mammals, and to evaluate selection of habitat components in treatments by birds and small mammals. I found lower bird species occupancy in all treatment plots compared to control plots; however the strength of this response varied by bird guild. I found a positive relationship between bird species occupancy and percent tree cover and a negative relationship between bird species occupancy and percent grass and forb cover. I found no evidence of differences in small mammal species occupancy or density between controls and treatments. I found a positive relationship between small mammal species occupancy and percent grass and forb cover. Species richness did not significantly differ between control and treatment plots for birds or small mammals. My approach and research findings can be used to inform habitat management and multiple-species conservation objectives in pinyon-juniper and sage-steppe ecosystems undergoing energy development. Specifically, I have identified that recently developed roller-chop and hydro-axe treatments have similar impacts to woodland bird guilds as traditional chaining treatments. I have also identified species that are sensitive to habitat mitigation treatments, and thus should be monitored if woodland reduction continues to be used as a habitat mitigation strategy. Since all bird guilds were positively associated with tree cover, woodland reduction strategies that promote landscape heterogeneity by leaving standing trees to provide structure for birds may have fewer impacts than those that clear large contiguous patches of woodland. This approach has the potential to increase the conservation value of habitat mitigation treatments for pinyon-juniper obligates as well as shrubland and grassland species.
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    Invasive predator-prey dynamics and monitoring in Guam forests
    (Colorado State University. Libraries, 2021) Hanslowe, Emma B., author; Bailey, Larissa L., advisor; Boone, Randall B., committee member; Wilson, Kenneth R., committee member; Yackel Adams, Amy A., committee member
    Managing invasive predators on islands is a global conservation priority because they are causally linked to the extinction and endangerment of hundreds of insular species. Sympatric invasive prey species further threaten native biota and complicate invasive predator management; top-down and bottom-up trophic forces following invasive predator management can negate costly control efforts and worsen invasive predator impacts. The growing possibility of landscape-scale suppression of the invasive brown treesnake (Boiga irregularis) on the island of Guam created the needs for 1) a cost-effective tool for monitoring brown treesnakes' invasive endothermic prey, and 2) improved understanding of the trophic dynamics between brown treesnakes and invasive small mammals. To address the first need, we tested the accuracy of chew-cards as a rat density index. Chew-card counts were correlated with rat capture-mark-recapture density estimates across a range of rat densities found in the region, and we thus consider chew-cards a suitable tool for indexing invasive rat density in these tropical island forests. To address the second need, we conducted systematic visual surveys targeting brown treesnakes and small mammals for up to three years during and after predator (snake) control treatments. There was strong support for site-specific treatment effects of predator control, but consistent top-down and bottom-up trophic effects on average small mammal and snake counts, respectively. This work adds to our growing understanding of invasive predator-prey dynamics on islands and has direct management implications for predator control and ecological restoration on Guam. Specifically, small mammal monitoring and control are likely critical components of a management strategy for long-term snake suppression to allow reintroduction of native vertebrates on Guam.
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    Survey estimators of domain means under shape restrictions
    (Colorado State University. Libraries, 2018) Oliva Avilés, Cristian M., author; Meyer, Mary C., advisor; Opsomer, Jean D., advisor; Breidt, F. Jay, committee member; Wang, Haonan, committee member; Wilson, Kenneth R., committee member
    Novel methodologies that introduce shape-restricted regression techniques into survey domain estimation and inference are presented in this dissertation. Although population domain means are frequently expected to respect shape constraints that arise naturally on the survey data, their most common direct estimators often violate such restrictions, especially when the variability of these estimators is high. Recently, a monotone estimator that is obtained from adaptively pooling neighboring domains was proposed. When the monotonicity assumption on population domain means is reasonable, the monotone estimator leads to asymptotically valid estimation and inference, and can lead to substantial improvements in efficiency, in comparison with unconstrained estimators. Motivated from these convenient properties adherent to the monotone estimator, the two main questions addressed in this dissertation arise: first, since invalid monotone restrictions may lead to biased estimators, how to create a data-driven decision for whether a restriction violation on the sample occurs due to an actual violation on the population, or simply because of chance; and secondly, how the monotone estimator can be extended to a more general constrained estimator that allows for many other types of shape restrictions beyond monotonicity. In this dissertation, the Cone Information Criterion for Survey Data (CICs) is proposed to detect monotonicity departures on population domain means. The CICs is shown to lead to a consistent methodology that makes an asymptotically correct decision when choosing between unconstrained and constrained domain mean estimators. In addition, a design-based estimator of domain means that respect inequality constraints represented through irreducible matrices is presented. This constrained estimator is shown to be consistent and asymptotically normally distributed under mild conditions, given that the assumed restrictions are reasonable for the population. Further, simulation experiments demonstrate that both estimation and variability of domain means are improved by constrained estimates, in comparison with unconstrained estimates, mainly on domains with small sample sizes. These proposed methodologies are applied to analyze data from the 2011-2012 U.S. National Health and Nutrition Examination Survey and the 2015 U.S. National Survey of College Graduates. In terms of software development and outside of the survey context, the package bcgam is developed in R to fit constrained generalised additive models using a Bayesian approach. The main routines of bcgam allow users to easily specify their model of interest, and to produce numerical and graphical output. The package bcgam is now available from the Comprehensive R Archive Network.