One of the three largest systems of black-tailed prairie dog (BTPD) colonies is located in northwestern Chihuahua, Mexico. During the last two decades, the area occupied by these colonies has been highly reduced and fragmented. Previous studies suggested that agriculture, poisoning, cattle overgrazing and shrub encroachment could be the factors responsible for such declines. However, the severe drought occurring in the region between 1994 and 2004 has not been considered in this equation. Because these populations occur in arid regions at the southern edge of the species range, they could be especially sensitive to changes in plant productivity. Furthermore, fragmentation of colonies may accelerate population declines due to size and isolation effects. In this study, I analyzed species-habitat relationships at different spatial and temporal scales to understand the causes of recent declines of BTPDs in northwestern Chihuahua. The most severe loss of colony area and most local extinctions occurred between 1988 and 2000, but most likely before 1997. Extinction of colonies before 2000 mostly occurred at small and isolated colonies in low-productivity areas. The coincidence of greatest area decline with the occurrence of most intense drought suggests a prominent role of drought in the population collapse. Overall, patterns of BTPD occurrence and abundance in Chihuahua are greatly influenced by spatial and temporal variation in forage cover. Although BTPDs were more likely to occur in open areas with short vegetation, increased forage cover positively predicted occurrence. High levels of forage cover during the dry season were positively related with BTPD density, juvenile production and population rate of change, but forage cover during the preceding rainy season was a negative predictor of demographic indices. High plant productivity during humid periods seems to have negative impacts on BTPD populations, presumably because the rapid plant growth reduces visibility and predator detection by BTPDs. The most influential landscape variable was the effective isolation of colonies. Although increased isolation may reduce the probability of occurrence at a given site, highly isolated locations may support high population densities. Contrary to my original predictions, I did not detect significant impacts of human-related factors on BTPD distribution and abundance. / Ecology

Thesis (Ph. D.)--University of North Texas, May, 2007. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 282-295).

Master of Science / Biology / David A. Haukos / The lesser prairie-chicken (Tympanuchus pallidicinctus) has experienced range-wide population declines and range contraction since European settlement. Due to ongoing declines, lesser prairie-chickens were listed as threatened under the Endangered Species Act in 2014; however, uncertainty regarding the legal status of the species has developed following a judicial decision to vacate the listing in September 2015. Regardless, new research is required for conservation planning, especially for understudied portions and temporal periods of the occupied range. I evaluated nonbreeding lesser prairie-chicken survival using known-fate models, and tested for the influence of environmental, landscape and predator effects on weekly survival. I estimated nonbreeding home-range size using fixed kernel density estimators and Brownian Bridge movement models for VHF and Satellite tagged lesser prairie-chickens, and measured habitat use during the 6-month nonbreeding period (16 September – 14 March). I also determined the influence of lek location on space use intensity within home ranges using resource utilization functions. Female survival was high (0.75, SE = 0.05) and consistent across nonbreeding seasons, but not explainable by selected variables. Mean home range size for birds with GPS transmitters (955 ha, SE = 128.5) was 215% larger than for individuals with VHF transmitters (303 ha, SE = 24.1) and 136% greater during the 2014-2015 nonbreeding season than the 2013-2014 season. Males and females were tied to leks throughout the nonbreeding season, and this relationship was not variable across the months of the nonbreeding season. Proportions of habitat used differed among study sites, but temporal trends were not evident. Lesser prairie-chickens exhibited consistency among ecoregions for home-range, space use, and survival; however, with differing habitat use among regions, management should be on the regional scale. Agriculture and energy development have caused fragmentation of the landscape where lesser prairie-chickens evolved. I used known fate survival models to test if landscape composition or configuration within sites caused survival to differ by site, as well as within home ranges to determine if functional relationships exist between weekly survival and landscape configuration or composition. I used Andersen-Gill models to test whether distance to anthropogenic features affected hazard rates. Differences in survival rates between sites, with survival rates 50% greater in Clark County, Kansas compared to Northwestern, Kansas, corresponded to differences in the amount of grassland habitat on the landscape, but study-site configuration was not measurably different. Increasing the number of patch types within home ranges increased survival, indicating positive effects of heterogeneity. In addition, as distance to fences decreased, lesser prairie-chickens experienced greater risk. Overall, further breakup of grassland landscapes that lesser prairie-chickens occupy should be avoided, to avoid habitat loss and fragmentation thresholds that could further affect survival rates. Additionally, fences should be removed or avoided around active leks.

Doctor of Philosophy / Department of Agronomy / Clenton E. Owensby / Most rangelands are harvested at some point during the year and removal of plant leaf area and biomass alters a host of ecosystem processes including gas exchange. An experiment was conducted in 2005 and 2006 to study the effects of clipping tallgrass prairie at different dates on water vapor and CO2 fluxes. A portable, non-steady-state chamber was designed to measure CO2 and water vapor fluxes from small plots in less than 40 s. A combination of sunlit and shaded readings allowed measurements of net carbon exchange (NCE) and ecosystem respiration (RE); by summing NCE and RE, gross canopy photosynthesis (GCP) was calculated. Throughout the two-year study, the chamber had a minimal effect on microclimate, i.e., average chamber temperature increased 2.9° C, while chamber pressure increased only 0.3 Pa during measurements, and photosynthetically active radiation attenuation was 10%. The immediate effect of all clipping treatments was a loss of leaf area that led to reductions in GCP, NCE, and RE and in most cases decreased water vapor flux. Further patterns of carbon flux were governed by the amount of water stress during canopy development, while water vapor flux rates varied with water availability. Canopies that developed during periods of low water stress quickly increased carbon flux rates following precipitation after a mid-season drought. However, flux rates of canopies, which developed during the mid-season drought, responded considerably slower to subsequent water availability. A separate experiment was conducted from June-October of 2006 to estimate GCP, leaf area index (LAI), and total aboveground biomass with a hyperspectral radiometer. Indices such as the Normalized Difference Vegetation Index and the Simple Ratio were used to estimate LAI and biomass had poor correlations with measured values. However, GCP was significantly correlated to all six indices derived in this study. While GCP measured from June-October was significantly correlated with all indices, removal of the senesced canopy scans recorded during October greatly increased the relationship.

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