Justin D. Hoffman

BIOGEOGRAPHIC RELATIONSHIPS OF POCKET GOPHERS IN SOUTHEASTERN COLORADO

Biogeographic relationships of Pappogeomys castanops, Thomomys bottae, and Geomys bursarius were studied at the margins of their ranges in southeastern Colorado. The dis- tributions of P. (astanops and T. bottae overlap by nearly 5 km on Mesa de Maya but are allopat- ric below the mesa. In the zone of sympatry, where these two species occupy adjacent burrows in the same soils and vegetation, the average depths of their feeding burrows differ significantly. This relationship apparently represents an intermediate stage in competitive exclusion, which influen- ces the biogeography of P. castanops and T. bottae in southeastern Colorado. The distributions of P. castanops and G. bursarius overlap by nearly 65 km below Mesa de Maya, but this overlap represents parapatry rather than sympatry. The biogeographic relationship of P. castanops and G. bursarius in southeastern Colorado is the result of ecological specialization, agricultural activities, and the Dust Bowl of the 1930s.

Factors influencing long-term population dynamics of pronghorn (Antilocapra americana): evidence of an Allee effect

Abstract Populations of pronghorn (Antilocapra americana) are subjected to multiple forms of density-dependent and density-independent regulation. Little is known about the combined effects of these variables across multiple populations throughout the landscape. The objectives of this study were to examine long-term trends in density and recruitment in pronghorn and to assess how different forms of regulation influence these trends. We used multiple density-dependent and density-independent explanatory variables in a model selection process to explain variation in pronghorn density and July fawn ∶ doe ratios from 1955 to 1993 in 4 pronghorn management units in Nebraska. We also investigated levels of density-dependent feedback in each management unit. Examination of long-term population trends suggested that pronghorn populations in Nebraska exhibited an Allee effect (inverse density dependence), in which population growth decreases as density decreases. We suggest that variation in rangeland condition and presence of adequate forage could explain the presence of the Allee effect. Both density-dependent and density-independent variables affected pronghorn populations, with density of cattle, spring precipitation, abundance of winter wheat, and hunting harvest most important for explaining fluctuations in pronghorn densities. Snow depth and density of cattle best explained yearly July fawn ∶ doe ratios. The importance of each factor was variable across the different management units. Management objectives aimed at improving access to and abundance of food resources during times when rangeland condition is poor could prevent drastic declines in pronghorn populations.

Observations of reproduction in mountain lions from Nebraska

ABSTRACT. Occurrences of mountain lions (Puma concolor) in Nebraska have been steadily increasing; however, reproductive activity in mountain lions has not been documented in the state. We present the first evidence of mountain lion reproduction in Nebraska since mountain lions recolonized the state in the early 1990s, On 28 February 2007, a spotted kitten was hit by a vehicle in northwestern Nebraska; and based on body length and weight, we estimate its age at 3.9 months. On 20 December 2008, a female mountain lion and spotted kitten were photographed in the northwestern part of the state, On 9 May 2009, a female mountain lion with a juvenile was also photographed. All records were from the Pine Ridge region of Dawes County, Nebraska, Our records suggest that mountain lions are establishing a permanent population in at least one region of Nebraska.

EFFECTS OF LAND USE AND SOIL TEXTURE ON DISTRIBUTIONS OF POCKET GOPHERS IN KANSAS

Abstract Research on the distributions of 2 species of pocket gopher in Kansas, the plains pocket gopher (Geomys bursarius) and the yellow-faced pocket gopher (Cratogeomys castanops), revealed large tracts of land within their distributions that neither species occupies. We hypothesized that habitat and land-use practices in these tracts exclude pocket gophers. To test this hypothesis, we compared the relative frequencies of soil-texture and land-cover types within unoccupied tracts with those in surrounding tracts where pocket gophers occur. Our results indicated that the unoccupied tracts consisted largely of areas with fine-textured soils that are planted to crops. The crops, mainly corn, wheat, and grain sorghum, were harvested and disked annually, and even the roadside ditches adjacent to the cropland were plowed and planted. We concluded that pocket gophers are unable to inhabit these areas because land-use practices have destabilized the habitats, eliminating both refugia and dispersal corridors.

Characterization of a Contact Zone between Two Subspecies of the Big Brown Bat (Eptesicus fuscus) in Nebraska

Abstract Two subspecies of the big brown bat (Eptesicus fuscus) are reported to occur in Nebraska. The eastern race, E. f. fuscus, is reportedly bigger and darker than its western counterpart E. f. pallidus. Where these 2 subspecies come in contact is the subject of debate. We used external, cranial, and colorimetric data to investigate geographic variation among populations of E. fuscus in Nebraska to determine the location of the zone of contact between E. f. fuscus and E. f. pallidus. We discovered significant variation in external, cranial, and colorimetric data, suggesting that E. fuscus is represented by 2 subspecies in Nebraska. Our results showed that E. f. pallidus is smaller, possesses lighter pelage, and is restricted to the northern and western parts of Nebraska, whereas E. f. fuscus is larger, possesses darker pelage, and occurs in southern and southeastern parts of the state. Populations located between these regions represent intergrades of the 2 subspecies. We suggest that the subspecific boundary represents a broad zone of integration running in a northeast to southwest direction and may reflect the position of temperature and precipitation clines.

Distribution and Status of the Yellow-faced Pocket Gopher in Kansas

Abstract Previous research suggests that the yellow-faced pocket gopher (Cratogeomys castanops) occupies a restricted range in western Kansas that is surrounded by the range of the plains pocket gopher (Geomys bursarius), which is regarded as a superior competitor. To determine whether the plains pocket gopher has encroached on the range of the yellow-faced pocket gopher in the past 35 years and to better understand the geographic relationships of these species, we trapped pocket gophers in western Kansas and collected soil texture and land cover data. We used ArcView 3.2 to map the distributions of these species in the study area, as well as the kinds of soil and land cover found in their potential home ranges. Although the distributions of the 2 species overlap, they are strictly parapatric. The apparent cause of this parapatric relationship is differential tolerance of soil textures. The distribution of the yellow-faced pocket gopher in Kansas is limited to just 7 counties divided into 2 populations, both surrounded by the distribution of the plains pocket gopher. We found no evidence that the range of the plains pocket gopher has expanded at the expense of the yellow-faced pocket gopher in the past 35 years. Thus, although the yellow-faced pocket gopher remains a “species of greatest conservation need” in Kansas because of agricultural threats, it evidently is not imperiled at this time.

Statistical Confusion Among Graduate Students: Sickness or Symptom?

Abstract Statistics is one of the most important yet difficult subjects for many ecology and wildlife graduate students to learn. Insufficient knowledge about how to conduct quality science and the ongoing debate about the relative value of competing statistical ideologies contribute to uncertainties among graduate students regarding which statistical tests are most appropriate. Herein, we argue that increased education of the available statistical tests alone is unlikely to ameliorate the problem. Instead, we suggest that statistical uncertainties among graduate students are a secondary symptom of a larger problem. We believe the root cause lies in the lack of education on how to conduct science as an integrated process from hypothesis creation through statistical analysis. We argue that if students are taught to think about how each step of the process will affect all other steps, many statistical uncertainties will be avoided.

First Record of Pseudorabies in Feral Swine in Nebraska

In 2007, two new populations of feral swine were discovered in Nance and Valley counties, Nebraska, USA. Necropsies and serologic testing was done on two individuals from the Nance County herd. Results indicated that a lactating sow had positive antibodies for pseudorabies virus (PRV). Investigations conducted by Nebraska Game and Parks Commission Law Enforcement division confirmed that the infected individual was transported illegally to Nebraska, USA, from Texas, USA. All domestic swine herds located within an 8 km radius of the infected individual tested negative for antibodies to PRV. Our results provide a clear example of how diseases can spread because of anthropogenic activities and highlight the need for disease surveillance and monitoring in the import of invasive species.

Examination of Annual Variation in the Adult Sex Ratio of Pronghorn (Antilocapra americana)

Abstract The adult sex ratio (ASR) is an important component of a populations demographics and can be used as an indicator of a populations status. However, the causes of annual variation in ASRs are unknown for many species. Fluctuations in ASR can arise through demographic stochasticity and intense selective harvesting. In this study we investigate the long-term patterns of variation in the ASRs (bucks: 100 does) for four populations of pronghorn (Antilocapra americana) in western Nebraska. We used multiple variables in a model selection process to predict annual fluctuation of pronghorn ASRs. We found that the number of bucks: 100 does significantly varied over the four populations. The best predictors of annual variation in pronghorn ASRs were variable across all populations. The number of pronghorn bucks harvested in the previous years hunting season and the previous years density of pronghorn were the most common predictors of ASR fluctuation. Buck harvest was an important predictor variable in only two of the four populations. Variation of harvest strategies within the populations could account for the lack of importance of buck harvest in half of the populations. The relationship between density and ASR is novel but difficult to interpret due to lack of data on birth sex ratios and fawn survival. More data on pronghorn demographics are needed in order to better explain the connection between density and ASR.

Recent occurrence of an American black bear in Nebraska

Abstract We report on a young male, cinnamon-phase American black bear (Ursus americanus) that was collected in northwestern Nebraska on 12 May 2008. This specimen represents the first black bear taken in Nebraska since 1907. Cranial characteristics and mass of the individual indicated a 15–16 month old bear. This bear may have dispersed from the Laramie Mountains in southeastern Wyoming along the North Platte River into western Nebraska. This record adds to the growing number of cases where large carnivores are reinvading previously occupied territory in the Great Plains. These reinvasions potentially have broad ecological implications to local prey populations and overall biodiversity.