We conducted systematic trials of four herpetofauna survey methods to assess their effectiveness in the Chihuahuan desert. Drift fences with pitfall and funnel traps, pitfall traps without fences, artificial habitats (with and without water added), and line transects were paired in arroyos and adjacent uplands. Times taken to set up, maintain, and remove survey materials were recorded. Twenty-seven captures or detections of six species were recorded. While the unwatered artificial habitats were most efficient in capture rate for all species pooled, the distribution of the species captured indicated that to give representative results, surveys should incorporate a combination of techniques. More extensive trials would be useful in confirming these results and assessing seasonal effects.

Maternal nutrition during pregnancy and postnatal offspring nutrition may influence offspring traits. We investigated the effects of maternal and postweaning offspring dietary nitrogen on immune function and hematology in two species of rodent: the hispid cotton rat (Sigmodon hispidus), a primarily herbivorous rodent, and the fulvous harvest mouse (Reithrodontomys fulvescens), an omnivore. These two species responded differently to the same levels of treatment, with cotton rats primarily influenced by maternal diet and harvest mice by postweaning offspring diet. Cotton rats born to mothers on high-nitrogen diets had lower values of mean corpuscle volume and hemoglobin and greater concentrations of serum immunoglobulins. Spleen size, cell-mediated immune response, and the number of splenocytes and thymic platelets were lower in cotton rats born to mothers on low- and high-nitrogen diets. High-nitrogen offspring diet increased kidney and liver mass in cotton rats. Harvest mice had increased kidney mass on high-nitrogen maternal diets; however, changes in offspring diet after weaning reduced hematological parameters in individuals fed low-nitrogen diets. Body length was also affected, with harvest mice born to mothers fed low- and high-nitrogen diets having shorter lengths. Splenocyte cellular activity was greater in offspring born to mothers on high-nitrogen diets in both species.

The contribution of small mammals to nitrogen cycling could have repercussions for the producer community in the maintaining or perhaps magnifying of nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of small mammals in an old-field ecosystem and estimate the amount of fecal and urinary nitrogen deposited annually. To address this objective, we used models from laboratory studies and combined these with data from field studies to estimate dietary nitrogen and monthly and annual nitrogen outputs from fecal and urine deposition of five rodent species. The models accounted for monthly fluctuations in density and biomass of small-mammal populations. We estimated that the minimal amount of nitrogen deposited by rodents was 1.0 (0.9-1.1) and 2.7 (2.6-2.9) kg Nha(-1) year(-1) from feces and urine, respectively, for a total contribution of 3.7 (3.5-4.0) kg Nha(-1) year(-1). Hispid cotton rats (Sigmodon hispidus) accounted for >75% of the total nitrogen output by small mammals. Our estimates of annual fecal and urinary nitrogen deposited by rodents were comparable to nitrogen deposits by larger herbivores and other nitrogen fluxes in grassland ecosystems and should be considered when assessing the potential effects of herbivory on terrestrial nitrogen cycles.

ii Notice The U.S. Environmental Protection Agency through its Office of Research and Development funded, and managed the research described herein. It has been subjected to the Agency's peer and administrative review and has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. All research projects making conclusions or recommendations based on environmentally related measurements and funded by the U.S. Environmental Protection Agency are required to participate in the Protection Agency Quality Assurance Program. This project was conducted under an approved Quality Assurance Project Plan. The procedures specified in this plan were used without exception. Information on the plan and documentation of the quality assurance activities and results are available from the Principal Investigator. iii Foreword The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation's land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life. To meet this mandate, EPA's research program is providing data and technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the future. The National Risk Management Research Laboratory is the Agency's center for investigation of technological and management approaches for preventing and reducing risks from pollution that threatens human health and the environment. The focus of the Laboratory's research program is on methods and their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that reduce the cost of compliance and to anticipate emerging problems. NRMRL's research provides solutions to environmental problems by: developing and promoting technologies that protect and improve the environment; advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical support and information transfer to ensure implementation of environmental regulations and strategies at the national, state, and community levels. This publication has been produced as part of the Laboratory's strategic long-term research …

Bioavailable nitrogen is a limiting nutrient throughout the Eastern United States. Research demonstrates that exposure to large doses of nitrogen leads to deleterious environmental impacts. However, effects of chronic exposure to lower doses of nitrogen are not well known. Since 1998, we conducted an integrated multidisciplinary study investigating ecosystem feedback associated with chronic exposure to low doses of nitrogen. In this nitrogen-limited ecosystem, the ability of the soil system to adapt to new nitrogen inputs was degraded by the first winter season when soil nitrate concentration (indicated by extract concentration) increased 590%. Increased concentrations of nitrate were especially evident on fertilized plots (P<0.0001) but also were measured on plots that were only fenced to manipulate herbivore abundance (P=0.0443). Changes to the plant, macro invertebrate, herbivore, and microbial communities each reduced ecosystem nitrogen use efficiency thereby producing a selfreinforcing positive feedback loop leading to conditions favoring greater concentrations of soil nitrate. Because all of these effects occur together, it is unclear whether the results seen in soil nitrogen Jorgensen, Holub, and Mayer are Ecologists and Gonsoulin is a Microbiologist, U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, P.O. Box 1198, Ada, OK 74820. E-mail: Jorgensen.Eric@EPA.GOV. Silva is a Soil Scientist and West is a Microbiologist, Oak Ridge Institute for Science and Education, Oak Ridge, TN 37831. Tunnell is a Range Scientist, Clark and Parsons are Wildlife Scientists, and Engle and Hellgren are Professors, Oklahoma State University, Stillwater, OK 74078. chemistry are from one or some combination of them working together. What is clear however is that changes to trophic feedbacks associated with chronic exposure to low levels of bioavailable nitrogen resulted in an annual mean nitrogen excess of 105.6%. Although it was not our goal to measure mass balance for all nitrogen loss pathways, we estimate that ecosystems similarly exposed to excess or new sources of nitrogen may be at risk and are capable of leaching essentially all new nitrogen additions during seasons of dormancy. These experiments demonstrate that even the relatively small amount of nitrogen deposited in precipitation has the capacity to change multiple aspects of ecosystem structure and function.

Increasingly, models of physical habitat variables (i.e. vegetation, soil) are utilized as indicators of small mammal habitat suitability or quality. Presumably, use of physical habitat models indicating habitat suitability or quality would be improved and enhanced by the extensive amount of research that has been conducted for these species. However, current knowledge of small mammal habitat associations is based mostly upon site specific empirical observation, not the quantitative data that are the foundation of habitat modeling. Small mammal data are affected by technique-related capture variability. Existing data do not demonstrate that fine spatial and temporal variability associated with technique substantially affects habitat models. Small mammal abundance also exhibits ecologically important high spatial and temporal variability. Microhabitat spatial variability is a poor predictor of trap use compared to larger spatial scale phenomena in mesic and xeric biomes. Habitat suitability has been modeled with accuracy ranging between 80 and 93% for 14 species. This accuracy is achieved by filtering out stochastic temporal variability that was not related to physical habitat indicators. Inclusion of stochastic temporal variability degrades model performance, especially in ecosystems where predictive vegetation and substrate variables are essentially constant. Development of indicator mathematical models can be facilitated when a species’ ecology is carefully considered and where mathematics and biology are equally incorporated when conceiving and developing indicators.

Seeds from 12 grass species were studied relative to mode of wetting and time of exposure to water to document interspecific differences in imbibition characteristics. Imbibition causes seeds to become wet, and wet seeds are more detectable to consumers than dry seeds. Thus, germination potential and ability to remain undetected by consumers may represent an important trade-off Seeds wetted for 0-192 h in vials imbibed water at rates equivalent to seeds wetted by contact with wet paper towels pressing against their seed coat, except for seeds of Avena sativa, which weighed more after wetting in 2-mL vials with free water (0.471 g vs. 0.432 g). Seeds from different species imbibed water at different rates. These data show that interspecific variation in imbibition for seeds is high and support an expectation that imbibition potential can interact with detectability to consumers in an evolutionary trade-off.

The examined effects of habitat boundary on small mammals at the White Sands dune complex in the Tularosa Basin of south-central New Mexico from 22 May to 15 July 1996. The dunes that distinguish White Sands are unique. Their leading edge forms an abrupt boundary where they encroach upon adjacent desert-basin saltbush flat. We live-trapped small mammals on the boundary between and within the White Sands dunes and adjacent saltbush habitats to examine effects of this boundary on distribution, diversity and movement of small mammals. Chaetodipus penicillatus was captured most frequently within the dunes. Dipodomys ordii tended to be captured less frequently 10 m within the saltbush habitat than elsewhere. Animal movements perpendicular to the dune boundary differed among dune and saltbush habitats for Perognathus flavus and D. ordii even though habitats were similar in vegetative structure and supported an equivalent number of individual small mammals. A behavioral barrier is apparent between habitats along the edge of the White Sands dune boundary. There was no evidence of an edge effect at the spatial scale of our sampling plots. Characteristics of diversity and abundance normally associated with edge effect may not be highly expressed in arid ecosystems.

From January to May, 1993 we collected 725 skulls from barn owl (Tyto alba) pellets at three active nests in foothills of the Sacramento Mountains, southern New Mexico. To estimate rodent abundance, we concurrently live-trapped 1,555 rodents, from 48 trapping grids distributed in six habitat types near the nests, and marked 1,236 of these with monel ear tags. Prey taken by owls was not concordant with any possible combination of availability. Barn owls demonstrated a considerable selectivity for Sigmodon and Perognathus, while failing to capture Chaetodipus and Peromyscus in numbers representative of their abundance. Sigmodon was abundant in only one uncommon habitat type that was not close to nests. Barn owl selection for Sigmodon indicates that they forage in favored habitat patches. Further, because Reithrodontomys and Peromyscus also occurred in this habitat but were not taken in great numbers, we also conclude that barn owls selected favored prey species within favored habitat patches.