Determinants of habitat use and community structure of rodents in northern shortgrass steppe

1996 Spring.Includes bibliographical references.Patterns of distribution and abundance of small mammals reflect the responses of individuals to the spatial and temporal availability of resources and abiotic conditions, as well as interactions with conspecifics and other species. I examined habitat selection of two rodents, the deer mouse (Peromyscus maniculatus) and the northern grasshopper mouse (Onychomys leucogaster), on shortgrass steppe in north-central Colorado. Both species consume arthropods when these resources are plentiful, but grasshopper mice prey on other rodents and thus may have both competitive and predatory effects on deer mice. To examine these interactions, I conducted a removal experiment to determine the effect of grasshopper mice on microhabitat use, diet, and abundance of deer mice, and an odor-response experiment to determine whether olfactory cues mediate interactions between these species. Deer mice preferred shrubs at both individual and population levels, presumably to reduce predation risk. Mice oriented movements toward shrubs and traveled under shrubs more often than expected based on the density of shrubs on study plots. Population density also increased with increasing shrub density and aggregation. The response of mice to shrub cover was non-linear. Thresholds in the selective use of shrubs, movement patterns, and abundance occurred over a narrow range of shrub cover where shrubs were most aggregated, underscoring the importance of both shrub density and dispersion. Mice tended to accumulate in areas where their movements were most tortuous, suggesting that it is possible to generate testable predictions about patterns of abundance from individual movements. In contrast, grasshopper mice showed no affinity for shrub microhabitats, and instead oriented movements towards rodent burrows and disturbances created by pocket gophers (Thomomys talpoides). Results from pitfall trapping in different microhabitat types suggested that grasshopper mice used gopher mounds and burrows because of the concentration of insect prey in these microhabitats. The abundance of these microhabitats also was a better predictor of grasshopper-mouse abundance than were broad-scale, qualitative descriptors of macrohabitat type. The significance of these microhabitats across scales demonstrates the importance of spatial and temporal availability of prey to grasshopper mice. Even though grasshopper mice and deer mice show different habitat affinities, grasshopper mice may affect the surface activity and abundance of deer mice in areas where they co-occur. Deer mice decreased in number throughout the removal experiment on both control and removal sites, but the decline was greatest on controls, where grasshopper-mouse numbers increased. No shifts in microhabitat use were detected on removal sites, but deer mice increased their use of shrubs on control sites when grasshopper mice were most abundant. Because diets of deer mice did not differ between control and removal sites during the experiment, grasshopper mice apparently influenced the behavior and populations of deer mice through predation or interference rather than resource competition. Increases in the abundance of granivorous rodents on removal sites support this conclusion, and suggest that grasshopper mice, when abundant, can impact the composition of local assemblages on shortgrass steppe. However, if deer mice actively avoid contact with grasshopper mice, it is unlikely that this interaction is mediated by olfactory cues. When presented with odors of grasshopper mice, harvest mice, and clean cotton, deer mice showed no avoidance of grasshopper-mouse odors, regardless of season, sex or reproductive condition of respondents, or history of contact with grasshopper mice

Diet of Free-Roaming Cats Across a Gradient of Urbanization in Southern California (Abstract)

Free-roaming cats (Felis catus) are considered one of the most damaging invasive vertebrate pests in natural areas globally and are a major source of mortality for small animals in suburban and urban environments. Domestic cats are also considered to be a nuisance and a source of disease transmission to pet cats and to wildlife. Historically, the most common method of managing free-roaming cats has been euthanasia, but non-lethal approaches, such as trap-neuter-return (TNR), are increasing in popularity with the public. TNR-sterilized cats, subsidized by regular human feeding, remain in the environment and continue to prey upon wildlife and to be a source of disease and nuisance. However, the extent to which these cats depend on wild-caught prey vs. provisioned pet food is not clear. Moreover, if TNR colonies are located in areas of intensive human development, predation by these cats may be focused on commensal or widespread prey species rather than native species of conservation concern. Management of free-roaming cats aimed at protecting wildlife at the urban-wildland interface requires knowledge of the diet of cats across a gradient of land-use, from rural and natural open space to intensively developed suburban and urban areas. Our aim is to use stable isotope analysis to determine the diet of free-roaming cats in southern California, using ear tissue collected during TNR sterilization procedures. We will compare stable carbon and nitrogen isotope values of free-roaming cats, collected across a gradient of anthropogenic land use, to isotope values of potential prey and anthropogenic foods to determine whether they consume native or commensal prey, or rely on human-provisioned food. To date we have collected more than 300 cat ear tissue samples from veterinary clinics that perform spay and neuter procedures to support TNR programs in the greater Los Angeles metropolitan area. We have also coordinated with vector control agencies and wildlife rehabilitators in the region to collect samples of local commensal and non-commensal bird species, as well as collected samples of commercial pet food. Samples will be dried and homog­enized and sent to UC Davis Stable Isotope Facility for analysis using mass spectrometry. When results are received, we will use stable isotope mixing models to estimate the contributions of different food types to cat diets. Additionally, we will plot the capture locations of each cat in a geographic information system (GIS) and character­ize the landscape surrounding each cat using data layers depicting the type and amount of land use and degree of urbanization. We predict that free-roaming cats living in more urbanized areas will consume primarily pet food and commensal vertebrates such as rats and mice, pigeons, and house sparrows, whereas those living in less urbanized areas and closer to natural open spaces will consume more wild and native prey species. Preliminary data analyzed to date suggest that many trapped cats rely on anthropogenic foods, including pet food, rather than consuming wild-caught prey, and that consumption of these food resources increases with the degree of urbanization around cat capture locations. We hope that our results can help inform management decisions about how and where to permit the implementation of TNR, especially in areas likely to support native species of conservation concern

Space and Habitat Use of Coyotes (Canis latrans) in Suburban Southern California (Abstract)

The ability of coyotes (Canis latrans) to exploit resources in human-dominated environments has led them to increasingly come into conflict with people, for example by killing domestic animals or attacking children. Additionally, coyotes in these environments increase their exposure to anthropogenic threats, such as harassment, vehicle mortality, and rodenticides. Effective management of human-coyote conflicts requires a better understanding of how coyotes navigate the developed landscape. As part of a broader study of how the use of urban and suburban areas affects coyotes’ exposure to rodenticides, we examined movements and space use of coyotes across gradients of urbanization in Los Angeles and Orange County, California. We affixed GPS radio-collars to 12 coyotes (nine males, three females) and tracked them between August 2022 and December 2023. Radio-collars recorded location information approximately every 15 min, but we restricted our analyses to hourly locations. We used a 95% minimum-convex polygon (MCP) and 95%-kernel density estimate (KDE) to calculate the area used by each animal. Within each utilization area, we calculated the amount of impervious cover and the relative amount of open space and development, using publicly-available GIS data layers (National Land-Cover Database; U.S. Geological Survey 2021). Additionally, for each coyote, we calculated a measure of movement tortuosity (straightness index, SI; Batschelet 1981) to describe its tendency to take directed, straight-line movements or wander less linearly in the habitat. We calculated SI for nine coyotes for which we had hourly location data during the first 28 days after radio-collar deployment. SI values were calculated separately for diurnal and nocturnal movements of each coyote, and then for movements when it was traveling in areas with low (≤19%) vs. high amounts of impervious cover (Wurth et al. 2020), and in areas classified as open space vs. areas with human development. We used paired t-tests to compare mean SI values because movements and habitat use of individual coyotes were not independent. Utilization areas of coyotes (Table 1) ranged from 0.4 - 136.1 km2 (95% MCP) and 0.4 - 148.2 km2 (95% KDE). Excluding three coyotes that displayed wide-ranging, transient movements and considering only five animals that were tracked intensively (151-313 days) during the breeding and dispersal seasons, mean utilization area (95% MCP) was 2.16 km2 (SD = 1.79), which is our best estimate of home-range size. This estimate is about half the size of that typically reported for urban coyotes elsewhere (approximately 5 km2; Gehrt 2007, Gehrt et al. 2009, Franckowiak et al. 2019), including in the Santa Monica Mountains of southern California (Riley et al. 2003). However, it is similar to the estimate (2.1 km2) of Tigas et al. (2002) for coyotes living in fragmented coastal sage scrub and chaparral habitats in Los Angeles and Ventura County, where the urban landscape resembles our study area. Considering only the five non-transient coyotes that we tracked most intensively, on average, 67.2% of their home range was categorized as open space, whereas 32.8% had some level of human development (low-high intensity categories). On average, 68.3% of their home ranges were in areas with little impervious cover (<19%). In contrast, coyotes that displayed transient movements or that were tracked primarily during the dispersal season used areas with more human development (¯x = 55.5%) and more impervious cover (¯x = 50.8%). Coyotes in our study differed from those tracked by Riley et al. (2003), whose home ranges had only 15.6% developed area. In our study, coyotes still managed to use significant amounts of developed and semi-natural open space, despite the extensive degree of development in the region, although many limited their movements primarily to one or a few fragments of natural or modified open space. Diurnal movements were significantly more linear (higher SI) than nocturnal ones (t = 3.67, d.f. = 8, P = 0.006; Figure 1), suggesting that coyotes wander more at night, perhaps while foraging and engaged in conspecific interactions, and move in a more directed fashion during periods when people are active. However, for both diurnal and nocturnal movements, SI values did not differ significantly between movements in areas with low vs. high impervious cover, or in areas with large amounts of open space vs. human development. Both Tigas et al. (2002) and Riley et al. (2003) reported greater use of developed areas at night. Inclusion of data from longer time periods or using more refined categories of land use may increase our ability to detect differences in movements

Diets of Commensal Roof Rats (Rattus rattus) in California (Abstract)

Roof rats (Rattus rattus) are a successful invasive species worldwide because of their ability to exploit their commensal relationship with humans. They are opportunistic feeders that use a wide range of natural and anthropogenic food sources. Because some rodent control methods, such as traps and rodenticides, threaten non-target wildlife species, understanding the diets of roof rats can help develop targeted approaches to better control these pests. Our aim is to use stable isotope analysis and stomach contents analysis to determine the diets of roof rats collected in agricultural, urban, and suburban areas in California. We hypothesized that diets of roof rats trapped in agricultural areas would contain crop plants and food resources associated with the agricultural environ­ment (arthropods, mollusks), whereas those from urban and suburban areas, e.g., schools, residential zones, would consume a broader range of food sources, including anthropogenic foods such as pet food, trash, and produce from gardens and fruit trees. To date, we have obtained roof rat carcasses from control efforts across the state, including our own trapping in southern California. Rats were frozen until they could be dissected in the lab. From each rat, we removed the gastrointestinal tract and took a small sample of ear tissue for stable isotope analysis; all tissues were stored in 95% ethanol. Ear tissue samples were dried, cut into small pieces, and weighed before sending them to the UC Davis Stable Isotope Facility for stable carbon (C) and nitrogen (N) isotope analysis. Stomachs were dissected under a dissecting microscope and food items were identified using reference keys. Preliminary analyses of stomach contents revealed significant amounts of what appears to be plant material, seeds, arthropod parts, and rodenticide bait, as well as many roundworms. Isotopic analysis of ear tissue of 64 rats from four Central Valley counties and urban/suburban rats from three southern California counties (n = 65) and Yolo County (n = 14) showed that δ13C values of rats from urban settings were significantly enriched compared to rural rats (Figure 1; F = 4.52, d.f. = 1, 141, P = 0.053), which is consistent with an urban diet containing more anthropogenic foods. δ13C values of urban roof rats were also much more variable (coefficient-of-variation, CV = 8.7%) than that of rats from agricultural areas (CV = 3.6%), which showed remarkably little variation within a site, indicative of feeding on a concentrated, shared resource. δ15N of rats differed significantly between agricultural counties (F = 195.9, d.f. = 3, 60, P <0.0001), as well as between urban rats from Yolo County and southern California (F = 10.87, d.f. = 1, 77, P = 0.0015). Mean δ15N of rats from Kings and Yolo counties was 6.1‰ lower than that in Kern and Tulare counties (Figure 1), suggesting that Kings and Yolo County rats consume a mostly plant-based diet, whereas those from Kern and Tulare either consume more animal-based material or, possibly, feed on a food source that is enriched in heavy-nitrogen, e.g., fertilizer. We do not yet have sufficient samples of potential prey to identify what these rats might be eating or to estimate contributions of different food types to diet using a stable isotope mixing model, which is our ultimate aim

Plague outbreaks in prairie-dog colonies associated with El Niño climatic events

The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.Plague (Yersinia pestis) was introduced to the western U.S. in the mid-20th century and is a significant threat to the persistence of black-tailed prairie dog (Cynomys ludovicianus) populations. The social, colonial habits of prairie dogs make them particularly susceptible to plague, and many flea species, including known carriers of plague, are associated with prairie dogs or their extensive burrow systems. Mortality during plague epizootics, or outbreaks, is nearly 100% (Cully and Williams 2001; J. Mammal. 82:894), resulting in the extinction of entire colonies. In northern Colorado, prairie dogs exist in metapopulations (Roach et al. 2001, J. Mammal. 82:946), in which colonies naturally isolated by topography, soils and vegetation are connected by dispersal. Dispersal of either infected prairie dogs or plague-resistant reservoir species is hypothesized to spread plague among colonies. Plague outbreaks therefore may disrupt the dynamics of prairie-dog metapopulations and affect regional persistence. In the context of a century of past eradication efforts that have drastically reduced prairie-dog numbers, and increasing agricultural and urban development, plague represents a relatively new and unique threat to prairie dogs and the species that are closely associated with them. Poster presented at the 6th SGS Symposium held on 1/10/03

Do Scent Lures Increase Visitation of Bait Stations by Urban Roof Rats?

Roof rats (Rattus rattus) are invasive commensal rodents that pose a significant threat to both natural and manmade environments. Like other commensal rodents, roof rats are often controlled with rodenticides placed within bait stations, but rats can be slow to visit stations or avoid them altogether. We tested whether the addition of a scent lure (Airzonix; VM Products) would increase visitation and use of bait stations in 36 residential yards in Orange County, California. We placed two EZ-Secured (VM Products) stations, one containing a scent lure and non-toxic bait (treatment) and one containing bait only (control), in each yard, and monitored them continuously with digital game cameras for three weeks. We compared time to discovery and entry, bait consumption, and nightly roof rat activity between scent lure and control stations. The addition of a scent lure did not reduce time to discovery or entry significantly, nor did it increase bait consumption or rat activity, although rat behavior differed around scent lure and control bait stations. Overall, although roof rats discovered bait stations fairly quickly (median time to discovery 124-195 h), they entered and consumed bait in only a fraction (50-60%) of the stations, and were slow to enter stations (median time to entry 318-387 h), underscoring that additional techniques are still needed to improve the attractiveness and efficacy of bait stations

Do Trap-Neuter-Return (TNR) Practices Contribute to Human–Coyote Conflicts in Southern California?

One possible contributor to the unusually high number of conflicts between coyotes (Canis latrans) and people in urban southern California, USA, may be the abundance of free-roaming domestic cats (Felis catus; cats) subsidized by feeding and augmented by trap-neuter-return (TNR) programs. To determine if coyotes regularly prey on and consume cats, we combined visual and molecular-genetic approaches to identify prey items in stomachs of 311 coyotes from Los Angeles County and Orange County, provided to the South Coast Research and Extension Center, in Irvine, California, between June 2015 and December 2018. We detected cat remains in 35% of the stomachs of 245 coyotes with identifiable meals, making cats the most common mammalian prey item consumed and more common than reported previously. Using a geographic information systems approach, we then compared landscape characteristics associated with locations of coyotes that ate cats to public shelter records for TNR cat colonies. Cat-eating coyotes were associated with areas that were more intensively developed, had little natural or altered open space, and had higher building densities than coyotes that did not eat cats. Locations of TNR colonies had similar landscape characteristics. Coyotes associated with TNR colonies, and those that were euthanized (vs. road-killed), were also more likely to have consumed cats. The high frequency of cat remains in coyote diets and landscape characteristics associated with TNR colonies and cat-eating coyotes support the argument that high cat densities and associated supplemental feeding attracted coyotes. Effective mitigation of human–coyote conflicts may require prohibitions on outdoor feeding of free-roaming cats and wildlife and the elimination of TNR colonies

Quantum Robots and Environments

Quantum robots and their interactions with environments of quantum systems are described and their study justified. A quantum robot is a mobile quantum system that includes a quantum computer and needed ancillary systems on board. Quantum robots carry out tasks whose goals include specified changes in the state of the environment or carrying out measurements on the environment. Each task is a sequence of alternating computation and action phases. Computation phase activities include determination of the action to be carried out in the next phase and possible recording of information on neighborhood environmental system states. Action phase activities include motion of the quantum robot and changes of neighborhood environment system states. Models of quantum robots and their interactions with environments are described using discrete space and time. To each task is associated a unitary step operator T that gives the single time step dynamics. T = T_{a}+T_{c} is a sum of action phase and computation phase step operators. Conditions that T_{a} and T_{c} should satisfy are given along with a description of the evolution as a sum over paths of completed phase input and output states. A simple example of a task carrying out a measurement on a very simple environment is analyzed. A decision tree for the task is presented and discussed in terms of sums over phase paths. One sees that no definite times or durations are associated with the phase steps in the tree and that the tree describes the successive phase steps in each path in the sum.Comment: 30 Latex pages, 3 Postscript figures, Minor mathematical corrections, accepted for publication, Phys Rev

Long-term ecological research on Colorado Shortgrass Steppe

The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.Poster presented at the LTER All Scientists Meeting held in Estes Park, CO on September 10-13, 2012

The association between lithium use and neurocognitive performance in patients with bipolar disorder

Lithium remains the gold standard for the treatment of bipolar disorder (BD); however, its use has declined over the years mainly due to the side effects and the subjective experience of cognitive numbness reported by patients. In the present study, we aim to methodically test the effects of lithium on neurocognitive functioning in the largest single cohort (n = 262) of BD patients reported to date by harnessing the power of a multi-site, ongoing clinical trial of lithium monotherapy. At the cross-sectional level, multivariate analysis of covariance (MANCOVA) was conducted to examine potential group differences across neurocognitive tests [California Verbal Learning Test (CVLT trials 1–5,CVLT delayed recall), Wechsler Digit Symbol, Trail-making Test parts A and B (TMT-A; TMT-B), and a global cognition index]. At the longitudinal level, on a subset of patients (n = 88) who achieved mood stabilization with lithium monotherapy, we explored the effect of lithium treatment across time on neurocognitive functioning. There were no differences at baseline between BD patients that were taking lithium compared with those that were not. At follow-up a significant neurocognitive improvement in the global cognitive index score [F = 31.69; p < 0.001], CVLT trials 1–5 [F = 29.81; p < 0.001], CVLT delayed recall [F = 15.27; p < 0.001], and TMT-B [F = 6.64, p = 0.012] was detected. The cross-sectional and longitudinal (on a subset of 88 patients) investigations suggest that lithium may be beneficial to neurocognitive functioning in patients with BD and that at the very least it does not seem to significantly impair cognition when used therapeutically.acceptedVersio