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Aim We analysed the distributional patterns of six terrestrial vertebrate taxa from the Oaxacan Highlands (Sierra Mazateca, Nudo de Zempoaltepetl and Sierra de Juarez) through a cladistic biogeographical approach, in order to test their naturalness as a biotic unit. Location The Oaxacan Highlands, Mexico. Methods The cladistic biogeographical analysis was based on the area cladograms of the Pseudoeurycea bellii species group (Amphibia: Plethodontidae), the genus Chlorospingus (Aves: Thraupidae), the genera Microtus, Reithrodontomys and Habromys, and the Peromyscus aztecus species group (Mammalia: Rodentia). We obtained paralogy-free subtrees, from which the components were coded in a data matrix for parsimony analysis. The data matrix was analysed with Nona through

1. Roads may affect wildlife populations through habitat loss and disturbances, as they create an abrupt linear edge, increasing the proportion of edge exposed to a different habitat. Three types of edge effects have been recognized: abiotic, direct biotic, and indirect biotic. 2. We explored the direct biotic edge effects of 3- to 4-m wide roads, and also a previously unrecognized type of edge effect: social. We live-trapped two threatened endemic rodents from Cozumel Island (Oryzomys couesi cozumelae and Reithrodontomys spectabilis) in 16 plots delimited by roads on two sides, to compare edge effects between two adjacent edges (corners), single-edge and interior forest, on life history and social variables. 3. No significant edge effects were observed on the life-history variables, with the exception of differences in body condition between males and females of O. c. cozumelae near edges. Both species showed significant and contrasting effects on their social variables. 4. O. c. cozumelae was distributed according to its age and sex: the proportion of adults and males was higher in interior than near edges, while juveniles and females were more abundant near edges. More nonreproductive females were present in corners than in single-edge and interior, while the opposite distribution was observed for nonreproductive males. 5. The distribution of R. spectabilis was related to its age and reproductive condition, but not to its sex. The proportion of adults was significantly higher in corners, while juveniles were only caught in single-edge and interior quadrants. The proportion of reproductive individuals was higher in edge than interior quadrants, while reproductive females were only present in edge quadrants. 6. We found significant differences between the quadrants with the greatest edge exposure in comparison with other quadrants. The social edge effects we identified complement the typology of edge effects recognized in ecological literature. Our study provides insight into the effects that sharp road edges have on biological and social characteristics of small mammal populations, highlighting how such effects vary among species. Our findings have important conservation implications for these threatened species, but are also applicable in a broader context wherever there are abrupt edges caused by linear landscape features.

Environmental stochasticity in vital rates influences the dynamics of structured populations. Stochastic models of population dynamics often assume that vital rates vary independently, an assumption that may be violated in many populations. We estimated the survival of three species of grassland rodents – deer mouse Peromyscus maniculatus, white-footed mouse Peromyscus leucopus and western harvest mouse Reithrodontomys megalotis– using a long-term dataset. We used these data to assess the level of cross correlation and autocorrelation in stage-specific survival rates and the correlation between survival and selected environmental variables. We found little evidence of correlation among survival estimates in any species or correlation between survival and environmental variables. In contrast to other species in the region, our analyses suggest that survival rates in deer mice, white-footed mice and western harvest mice vary independently throughout the year.

We applied a rigorous, quantitative methodology to the analysis of local-scale spatial clustering of multiple murid mice (brush mice, Peromyscus boylii; deer mice, P. maniculatus; pinon mice, P. truei; western harvest mice, Reithrodontomys megalotis) infected or uninfected with hantaviruses. Rodents were sampled longitudinally from 1994 to 2001 on 23 trapping webs at 10 locations in the southwestern United States. This study provided an opportunity to apply meta-analysis techniques to an important ecological question. There were sufficient captures by species on 199 occasions (three consecutive nights) to compare general use of space using multi-response permutation procedures (MRPP). The MRPP results were then used in meta-analyses by species to determine if overall effects of spatial clustering of hantavirus-infected mice as well as categorical effects (elevation, season, site, and state) were present. Based on MRPP analyses, overall spatial clustering of hantavirus-infected mice was most pronounced for brush mice, followed by the deer mouse. Meta-analyses indicated significant overall effects of spatial clustering and varying categorical effects (elevation, season, site, state) of infected mice for each species compared. The overlapping space use by rodents might be an important factor affecting the local transmission of several hantaviruses.

Studies on the effects of anthropogenic contamination on wildlife have largely been focused at the individual level. Biomarkers have been used to monitor changes in the health of individuals exposed to contaminants; however, little attention has been given to the effects of chronic exposure at the population or community levels. We studied rodent assemblages from uncontaminated (reference) sites (n = 5) and abandoned petrochemical landfarms (n = 5) in Oklahoma to investigate potential alterations in community structure and composition. Rodent assemblages inhabiting landfarms had lower species diversity, lower richness, and a more even distribution of individuals across species. Reference sites showed typical rodent assemblage structure dominated by hispid cotton rats (Sigmodon hispidus) and fulvous harvest mice (Reithrodontomys fulvescens). Assemblages inhabiting landfarms also were dominated by cotton rats; however, harvest mice were replaced by deer mice (Peromyscus maniculatus) on two landfarms. Contam...

Small mammal populations were characterized nine times during six sampling periods on six plots in five different fields of tall fescue (Festuca arundinacea Schreb.) to determine differences in their abundance and species composition associated with the presence or absence of the endophytic fungus Acremonium coenophialum Morgan-Jones & Gams. No differences were found in species richness (n=4 for both types) between endophyte-free (E - ) plots and endophyte-infested (E + ) plots. Capture success, number of individuals, total captures, and recapture rates were more for E - plots than for E + plots. All four species [eastern harvest mice (Reithrodontomys humulis Giglioli), short-tailed shrews (Blarina brevicauda Gray), pine voles (Microtus pinetorum McMurtrie), and cotton rats (Sigmodon hispidus Say & Ord)] were captured more often in E - than in E + plots. The diminished population densities of small mammals demonstrate the potential of E + tall fescue as a permanent ground cover for waste disposal sites, orchards, tree farms, irrigation ditch banks, golf courses, and other residential, commercial, and industrial situations where burrowing activities of mammals may create human hazards or financial burdens

An in situ investigation of structural chromosomal damage in wild rodents from a site contaminated with Aroclor 1254 was undertaken to compare effects observed in nature to those documented in previous laboratory studies. Laboratory assays indicate that Aroclor 1254 does not cause structural damage to chromosomes. However, the many variables at work in actual waste-site environments and receptor populations led us to question whether exposures under natural conditions could potentially lead to different results using the same assay systems. Individuals of three rodent species, Peromyscus leucopus, Sigmodon hispidus, and Reithrodontomys fulvescens, were collected from the contaminated site and three matched, pristine reference sites. Standard somatic metaphase chromosome preparations from bone marrow were examined for chromosomes lesions. Comparisons were made between conspecifics from the Aroclor-contaminated site and the reference sites. Significant increases in chromosome damage were not observed in animals from the Aroclor-contaminated site, indicating agreement between laboratory assays and an in situ application of this assay system.

Small herbivorous mammals living in successional patchy environments may be affected by both patch size variations and successional changes. If patch size affects densities of residents then larger patches should have higher densities compared to smaller patches because larger patches often have greater habitat diversity and lesser chances of stochastic events destroying the population. If patch size affects length of time animals spend on patches (persistence rates) then smaller patches should have lower persistence rates compared to larger patches because smaller patches contain fewer resources. Larger animals may be constrained by body size, as well as population size, to reside only on the larger patches because smaller patches do not contain enough resources. If successional changes affect resident animals that are host specific on colonizing plant species, then the effects may be noticeable immediately following field abandonment because plant species replacement rates are most rapid then. Four small mammal species were included: Sigmodon hispidus, Reithrodontomys mega- lotis, Microtus ochrogaster, and Peromyscus maniculatus. The field was divided into patches that varied in area by two orders of magnitude with patches of each size treatment placed in each section of the field. Patch size effects on densities and persistence rates of the four mammal species were tested with analyses of variance. Plant species were grouped according to seven life history traits so as to include relative percent cover of most plant species. Multiple linear regression analyses were used to identify which variables (patch size, field sections, and percent relative cover) significantly explained variations in small mammal densities. Effects of patch size on animal densities and persistence rates varied among animal species. The largest species, Sigmodon hispidus, was never found on the smallest patches, but densities of Reithrodontomys megalotis, Microtus ochrogaster, and Peromyscus manicu- latus were often highest on the smallest patches. Animal density variations were often significantly explained by patch size using multiple regression analyses (P ? .001). However, lack of consistent trends with respect to the other independent variables included in the equations and variable R2 values suggested that other, unmeasured, variables may have influenced the results. Persistence rates of the three species were often highest on the largest patches. Results suggested that animals visited small patches more often than large patches without staying, and used large patches to create territories. Small and medium patches may have been used as archipelagos of preferred habitat interspersed with less desirable habitat. The first stage of old-field succession was completed by the end of the 3rd yr: perennials replaced annuals as the dominant plant species. Neither patch size nor field sections sig- nificantly affected percent cover.

Habitat utilization by Sigmodon hispidus, Reithrodontomys fulvescens, and Oryzomys palustris was compared to habitat availability, by determining if capture locations were random samples of the trapping grid with respect to mean cover of 10 plant species. A methodology, designed for this purpose and detailed in a companion paper (Kincaid and Bryant 1983), was used in which the Euclidean distance between mean vectors representing habitat utilization and availability was compared to that for random draws from the available resource spectrum. This distance (the habitat differential) was partitioned into separate components representing differential composition and dif- ferential productivity in the occupied habitats. Interspecies differences in habitat utilization were also considered relative to habitat availability. Each species utilized a habitat subset that differed significantly from the average available habitat. Sigmodon and Reithrodontomys were the most similar species, differing only in the pattern of their associations with grasses and cover. Oryzomys usually occurred in habitats dominated by dicots. Deviations for all species were usually attributable to differential composition, except for Sigmodon and Reithrodlontomvs in winter, when both exhibited significant productivity components. Habitats occupied by these rodents were significantly less heterogeneous than random subsets, but only Ory- zomys habitat always had reduced dimensionality of variation relative to that of the available habitat. Differential responsiveness to patterns of statistical variation in a patchy environment can be sufficient to produce habitat separation and is offered as a neutral model for the examination of higher-order processes.

We investigated the relative densities of granivorous, nocturnal desert rodents in small plots within two arid regions of Arizona to study how sympatric species avoid competitive extinction. The most common rodents were kangaroo rats, Dipodomys spp., and pocket mice, Perognathus spp. We attempted correlating the density of each species with several environmental measurements, derived from the soil's i) depth; ii) texture or iii) resistance to sheer stress; or from the plant's i) species diversity; ii) growth forms or iii) foliage density. Successful variables were derived from plant growth form and foliage density. The soil's resistance to sheer stress also seemed important for a few species. In general, kangaroo rats were associated with sparseness of vegetation; pocket mice with denseness. One group of mice, which we term bush mice, seemed to require bushes and included two Perognathus spp., three Peromyscus spp., and probably a harvest mouse (Reithrodontomys fulvescens). Two other Perognathus spp. were taken in grassy habitats. Some suitable habitats tended to be complementary to others, suggesting that species associated with them are competitors. Comparisons of the density and distribution of D. merriami, present in both regions but under different biotic circumstances, reinforces the opinion that competition is responsible for the complementariness of habitats. In some cases the evidence suggests that competitive coexistence is accounted for by the fact that different specializations are needed to escape predation in different environments. We use variables which correlate with the relative density of various species to construct a model of habitat complexity. The rodent species diversities obtained in our plots can be approximately accounted for by this model. The model is based on the premises that the rodents collectively discriminate four qualities of soil surface, and three heights and two densities of vegetation. In general, specializations based on biotic variables appear most important.

Three abundant rodents, the cotton rat (Sigmodon hispidus), the harvest mouse (Reithrodontomys fulvescens), and the rice rat (Oryzomys palustris) are sympatric in southeast Texas. From January 1970 to May 1970, six presumably homogeneous areas, three control, were live—trapped. Mark—release—recapture and selective removal techniques were used to monitor species composition within the areas. Estimates of the number of individuals per species, body weights, and sex ratios were obtained at 2—week intervals. When cotton rats were experimentally removed, no change in the mean weights of harvest mice or rice rats were revealed by linear regression analysis. When harvest mice and rice rats were removed, cotton rat females exhibited a significant increase in mean weight. A significant change in sex ratio of cotton rats, from a greater proportion of males to a greater proportion of females, was recorded in the areas where harvest mice and rice rats were removed. Although the number of captures per species declined...