Grassland Rodents Research Articles

Rodent populations on the northern Great Plains respond to weather variation at a landscape scale

Abstract Extreme weather variation on the northern Great Plains of North America can potentially influence the abundance of grassland rodents across vast areas. We used the remains of 33,697 small mammals collected from owl pellets in central and western Canada over 15 years to determine the influence of weather on the annual abundance of deer mice (Peromyscus maniculatus), sagebrush voles (Lemmiscus curtatus), and meadow voles (Microtus pennsylvanicus). Weather variation affected the annual abundances of all 3 species; however, influence on deer mouse and sagebrush vole annual abundances was relatively small compared to that on meadow voles. This finding may indicate that factors other than weather (i.e., habitat availability) are more important for the abundance of deer mice and sagebrush voles at the landscape scale. In contrast, meadow voles were positively associated with the duration of snow cover above the hiemal threshold (20 cm), exhibiting up to 5-fold increases (i.e., irruptions) in abundance f...

The effects of natural capital protection on pastoralist’s livelihood and management implication in the source region of the Yellow River, China

The interaction among different livelihood capitals is a key to generate a deeper understanding of the livelihood sustainability. In this paper, we use net income per capita (economic capital), meat and milk production per capita (physical capital), and areas of fenced pasture, livestock shelter, grassland rodent control and planted grassland (physical capital) as proxy indicators of livelihood promotion, livelihood provision, and livelihood protection respectively. By developing a correlation model between pastoralists' livelihood protection and improvement, we found that (1) there is a statistically significant correlation between the pastoralists' livelihood protection and promotion; (2) based on the maximum effect of pastoralists' livelihood promotion and provision, there is a benchmark in the effect of the intervention intensity of livelihood capital (grassland resource protection) on livelihood improvement; (3) on basis of two indicators, i.e. net income per capita and meat production per capita, the reasonable scales of fenced pasture, livestock shelter and planted grassland are less than 843, 860 and 46 thousand hectares (hm(2)) per year respectively. With the marginal effect of livelihood protection, moderately decreased areas of fenced pasture and planted grassland, and increased area of livestock shelter is a critical to ensure pastoralist's livelihood sustainability.

Response of rodent assemblages to change in habitat heterogeneity in fruit-oriented nopal orchards in the Central High Plateau of Mexico

In the Central High Plateau of Mexico, perennial nopal (Opuntia spp.) orchards are used by several native rodent species. The effect of orchard aging on habitat heterogeneity and rodent assemblages are not known. I surveyed rodent community abundance, species richness, diversity and composition, and habitat heterogeneity (hab-H) in 3 nopal orchards—6 months (O1), 2 years (O2), and 12 years (O3) old—and 1 natural nopalera (NN). Hab-H increased with orchard age, and a unique rodent assemblage was associated with each nopal orchard. Grassland rodents dominated O1 and O2. The shrubby habitat of O3 supported a complex suite of rodents that included grassland and shrubland species, and the NN supported a rodent assemblage that was dominated by shrubland species. In O3, aging of the orchard had led to a hab-H and establishment of a rodent assemblage resembling that of NN. Similar ecological relationships are expected in other nopal orchards of the region. In view of my data, regional conservation efforts should take advantage of the mosaic of differently-aged nopal orchards, because they offer suitable conditions for different species of native rodents, particularly given that some of these species occupy natural habitats that are currently highly fragmented.

Buffering and plasticity in vital rates of oldfield rodents

1. Under the hypothesis of environmental buffering, populations are expected to minimize the variance of the most influential vital rates; however, this may not be a universal principle. Species with a life span <1 year may be less likely to exhibit buffering because of temporal or seasonal variability in vital rate sensitivities. Further, plasticity in vital rates may be adaptive for species in a variable environment with reliable cues. 2. We tested for environmental buffering and plasticity in vital rates using stage-structured matrix models from long-term data sets in four species of grassland rodents. We used periodic matrices to estimate stochastic elasticity for each vital rate and then tested for correlations with a standardized coefficient of variation for each rate. 3. We calculated stochastic elasticities for individual months to test for an association between increased reproduction and the influence of reproduction, relative to survival, on the population growth rate. 4. All species showed some evidence of buffering. The elasticity of vital rates of Peromyscus leucopus (Rafinesque, 1818), Sigmodon hispidus Say & Ord, 1825 and Microtus ochrogaster (Wagner, 1842) was negatively related to vital rate CV. Elasticity and vital rate CV were negatively related in Peromyscus maniculatus (Wagner, 1845), but the relationship was not statistically significant. Peromyscus leucopus and M. ochrogaster showed plasticity in vital rates; reproduction was higher following months where elasticity for reproduction exceeded that of survival. 5. Our results suggest that buffering is common in species with fast life histories; however, some populations that exhibit buffering are capable of responding to short-term variability in environmental conditions through reproductive plasticity.

The ecology ofBartonellaspp. infections in two rodent communities in the Mazury Lake District region of Poland

Prevalence and abundance of Bartonella spp. infections were studied over a 3-year period in woodland and grassland rodents in North-Eastern Poland. Prevalence of bacterial infections was similar in the two rodent communities, with one leading host species in each habitat (46.3% in Apodemus flavicollis versus 29.1% in Myodes glareolus in forest, or 36.9% in Microtus arvalis versus 13.7% in Mi. oeconomus in grassland). Prevalence/abundance of infections varied markedly across the 3 years with 2006 being the year of highest prevalence and abundance. Infections were more common during autumn months in My. glareolus and A. flavicollis, and in juvenile and young adult (age classes 1 and 2) My. glareolus and Mi. oeconomus than in adults (age class 3). Higher prevalence and abundance of Bartonella infections were found in male A. flavicollis in comparison to females. These data are discussed in relation to the parasite genotypes identified in this region and with respect to the role of various ecological factors influencing Bartonella spp. infections in naturally infected host populations.

Ecological and biological factors involved in the transmission ofEchinococcus multilocularisin the French Ardennes

In order to identify the respective importance of the ecological and biological factors involved in the transmission of Echinococcus multilocularis, we estimated grassland vole intermediate host (Microtus sp. and Arvicola terrestris) population densities, in relation to the diet of the definitive host (red fox, Vulpes vulpes) and with the prevalence of E. multilocularis in the fox population. The study was conducted in the Ardennes, north-eastern France, which is an area with a high incidence of alveolar echinococcosis. Surface index methods showed that Microtus was the most abundant intermediate host in the area. Furthermore, Microtus was present in one-third of the 144 faeces and 98 stomach content samples examined and represented more than two-thirds of the rodent occurrences. Red fox predation on Microtus was significantly correlated with Microtus relative abundance. In contrast, the relative abundance of A. terrestris was very low. This species, as well as Clethrionomys glareolus and Apodemus sp., was little consumed. E. multilocularis prevalence in foxes was determined from carcasses and reached 53% (95% confidence interval 45-61%). Intensity of infection varied from 2 to 73,380 worms per fox, with 72% of the sampled worm burden harboured by 8% of the sampled foxes. The selected explanatory variables (sex, year, age class, health and nutritional condition, and season) failed to predict prevalence rate and worm burden. The high prevalence rate in foxes indicates the possibility of intense E. multilocularis transmission, apart from periods, or in landscapes, favourable to large population outbreaks of grassland rodents.

Demographic Response of a Grassland Rodent to Environmental Variability

We used stage-structured matrix population models, derived from 3 years with disparate levels of precipitation, to assess the potential effects of climate change on annual population growth (k) of deer mice (Peromyscus maniculatus). Populations of deer mice increased during a year of normal precipitation (k ¼ 1.69 6 0.02 SE) and a wet year (k ¼ 1.03 6 0.02), but declined in a dry year (k ¼ 0.34 6 0.02). Life-table response experiment analyses indicated that reduced survival of adults in the dry year, and reduced survival of pups and juveniles in the wet year, exerted the greatest influence on variation in population growth. Stochastic models that projected populations of deer mice for a 50-year period predicted that populations would not be able to persist if mean annual precipitation was reduced � 11% by increasing the frequency of dry years. Furthermore, the stochastic population growth rate declined more quickly when the probability of a normal year was reduced, simulating increased variability in rainfall, relative to other scenarios examined. Our stochastic models indicate that a relatively small reduction in mean precipitation could result in substantial population declines of P. maniculatus in the mixed-grass prairie of central North America.

Demography and environmental stochasticity: empirical estimates of survival in three grassland rodents

AbstractEnvironmental 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.

The roles of landscape context, niche breadth, and range boundaries in predicting species responses to habitat alteration

ABSTRACTExtant species in human‐dominated landscapes differ in their sensitivity to habitat loss and fragmentation, although extinctions induced by environmental alteration reduce variation and result in a surviving subset of species with some degree of ‘resistance’. Here, we test the degree to which variable responses to habitat alteration are (1) essentially an inherent property of a taxon subject to constraints imposed by its geographical range, as suggested by Swihart et al. (2003), (2) a function of the landscape in which a species occurs, or (3) a function of spatial trends occurring on large scales. We used data collected on 33 vertebrate species during 2001–04 across the upper Wabash River basin, Indiana, in 35 square ‘landscapes’, each 23 km2 in size. Six species of forest rodent, six species of grassland rodents, seven species of bats, eight species of aquatic turtles, and six species of amphibians were sampled at 504, 212, 590, 228, and 625 patches, respectively. The fraction of patches of primary habitat (e.g. forests for tree squirrels, wetlands for aquatic turtles) occupied by a target species was used as a response variable. On a basin‐wide scale, 47% of variation in proportional occupancy among species could be explained by taxon‐specific variables; occupancy rates were related positively to niche breadth and negatively to the proximity of a geographical range boundary. After controlling for species effects, landscape‐level occupancy rates varied significantly for 16 of 33 species, with variation partitioned among landscape variables alone (mean = 11% of variation), spatial trend variables alone (26%), and both variable sets jointly (8%). Among landscape variables, percentage forest cover positively affected occupancy rates of three bat species and a tree squirrel. Variation in occupancy rates among landscapes was consistent with large‐scale spatial trends for 13 species. Our findings demonstrate the general importance of niche breadth as a predictor of species responses to habitat alteration and highlight the importance of viewing the effects of habitat loss and fragmentation at multiple spatial scales.

Rodent Communities in an Exurbanizing Southwestern Landscape (U.S.A.)

Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little-studied impacts on biological diversity. We captured rodents on 48 traplines in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in exurban housing developments, grazed and embedded in development, or neither grazed nor embedded in development. Independent of habitat or development, rodent species richness, mean rank abundance, and capture rates of all rodents combined were negatively related to presence of livestock grazing or to its effects on vegetative ground cover Exurban development had no obvious effects on rodent variety or abundance. Results suggest southwester.n exurban developments can sustain a rich assemblage of grassland and savanna rodents if housing densities are low and houses are embedded in a matrix of natural vegetation with little grazing.

Factors Driving Small Rodents Assemblages from Field Boundaries in Agricultural Landscapes of Western France

In this study, we investigated the factors driving diversity and abundance of small rodent species inhabiting permanent linear habitat patches within high-intensified agricultural landscapes of western France. Multivariate (co-inertia) analysis was used to analyse relationships of habitat and landscape descriptive variables with rodent records. Two main ecological gradients were recognized according to statistical analysis. Relationships of species occurrence with environmental factors were interpreted according to their main life traits. The first ecological gradient clearly differentiated communities from hedges to those of grass-dominated linear banks. This first gradient was associated with the prevalence of forest versus grassland rodent species. This partitioning seems to reflect rather ecological requirements of species than competitive interactions. Small rodents diversity and abundance were inversely evolving along this gradient. The second factor influencing species assemblages was associated to landscape heterogeneity surrounding the permanent habitats. According to this second gradient, species seemed to be selected in relation to their ability to disperse and to use cultivated fields. Maximum diversity was generally observed in heterogeneous permanent habitats with mixed vegetation structure but hedges are important to produce biomass for predators.

Modelling the spatial distribution of Echinococcus multilocularis infection in foxes

Alveolar echinococcosis is a rare but fatal disease in humans and is caused by the fox tapeworm Echinococcus multilocularis. The densities of fox and grassland rodent populations and the interactions between them influence E. multilocularis transmission rates in Europe. Successful rabies control has caused fox populations and E. multilocularis prevalence rates to increase in many European countries. The potential increase of the infection pressure on the human population motivates the monitoring of the infection status of foxes over space and time. Detection of E. multilocularis antigen levels in fox faecal samples collected in the field might provide a pragmatic methodology for epidemiological surveillance of the infection status in wildlife hosts across large areas, as well as providing an indication of the spatial distribution of infected faeces contaminating the environment. In this paper, a spatial analysis of antigen levels detected in faeces collected in the Franche-Comté region of eastern France is presented. In Franche-Comté, rodent outbreaks have been observed to originate in areas rich in grassland. Spatial trends in fox infection levels were modelled here as a function of the composition ratio of grassland in the landscape derived from the CORINE land-cover map. Kriging models incorporating the grassland trend term were compared to a variety of models in which five alternative trend expressions were used: the alternative trend expressions included linear and quadratic polynomials on the x and y coordinates with and without a grassland term, and a constant mean model. Leave-one-out cross-validation indicated that the estimation errors of kriging with a trend models were significantly lower when the trend expression contained the grassland index term only. The relationship between observed and predicted antigen levels was strongest when the estimated range of autocorrelation was within the home range size of a single fox. The over-dispersion of E. multilocularis in foxes may therefore account for the majority of spatial autocorrelation locally, while regional trends can be successfully modelled as a function of habitat availability for intermediate hosts.

THREE METHODS FOR ASSESSING RICHNESS AND COMPOSITION OF SMALL MAMMAL COMMUNITIES

Analysis of pellets of Tyto alba and scats of Genetta genetta and Shennan livetrapping were compared to assess richness and composition of small mammal communities in a Mediterranean area (NE Spain). Owl pellets provided 17 small mammal species (17,232 individuals), genet scats 14 species (2,145 individuals), and livetrapping 9 species (1,488 individuals). Owl pellets oversampled insectivores and grassland rodents and undersampled tree-dwelling and woodland rodents. Genet scats and livetrapping overs amp led woodland rodents and undersampled insectivores and grassland rodents. After controlling for sample size and elevation differences between methods by means of analysis of covariance (ANCOV A) and rarefaction, owl pellets contained higher richness for small samples(<50 individuals), and scats contained higher richness for large samples (> 100 individuals), both having higher richness than livetrapping regardless of sample size. We concluded that both indirect methods provided complementary infonnation of small mammal communities, detecting the 19 small mammal species known to be present in the study area.

Is the matrix really inhospitable? Vole runway distribution in an experimentally fragmented landscape

Habitat fragmentation is a common feature of modern landscapes, with significant impacts on the population densities of and space use by animals. A frequent model system for studying these effects is that of voles (Microtus spp.) and other rodents in experimentally fragmented grasslands. Design of these study sites is motivated by landscape theory, and often assumes that the matrix between discrete experimental habitat patches is inhospitable to focal species. Our census of M. ochrogaster runways in an experimentally fragmented landscape in eastern Kansas indicates that voles make substantial use of the mowed matrix, and that such use increases with degree of habitat fragmentation. Census season (winter, summer) was also an important predictor of observed runway distributions. Our results suggest that voles may have home ranges that include multiple small fragments and also the intervening matrix, leading to overestimates of population density. While the assumption that the matrix is inhospitable in experimentally fragmented habitats may be justified in many cases, studies using the model system of Microtus spp. or ecologically similar rodents in grasslands should incorporate methods that account for use of the matrix.

Patterns of Rodent Abundance on Open‐Space Grasslands in Relation to Suburban Edges

Abstract: Relatively little is known about the response of grassland rodent populations to urban and suburban edges. We live‐trapped rodents for three summers on 65 3.1‐ha grassland plots on open space of the city of Boulder, Colorado, and compared capture rates among species according to habitat type, percentage of the 40 ha surrounding each plot that was suburbanized, and proximity to a suburban edge. Deer mice ( Peromyscus maniculatus) and hispid pocket mice ( Chaetodipus hispidus) were more abundant on interior than on edge plots in mixed grasslands, whereas prairie voles ( Microtus ochrogaster) were captured more often on interior than on edge plots in tallgrass/hayfields. House mouse ( Mus musculus) abundance did not differ between edge and interior plots. Native rodents as a group were captured more often on interior than on edge plots in both habitat types. For each native species, plots with the highest capture rates were in landscapes &lt;10% suburbanized. We conclude that proximity to suburban landscapes had a strongly negative effect on the abundance of native rodents in open‐space grasslands.

DIVERSITY OF A GRASSLAND RODENT COMMUNITY AT VARYING TEMPORAL SCALES: THE ROLE OF ECOLOGICALLY DOMINANT SPECIES

Using a long-term data set (1989–1999), we examined how changes in abundance of 2 ecologically dominant species, prairie voles (Microtus ochrogaster) and hispid cotton rats (Sigmodon hispidus), affected the local diversity of a grassland rodent community at varying temporal scales. Species richness was associated positively with long-term fluctuations in the abundance of prairie voles and cotton rats over the 10-year period. Although increased vole densities consistently had a significantly negative effect on total community evenness, evenness of other community members was unaffected by fluctuating vole densities. Presence of cotton rats negatively affected both the relative abundance of other community members and the species richness during the years of high density (1991–1995), but did not exhibit longer-term influences. Thus, despite their numerical dominance, changes in prairie vole abundance had little ecological effect on the rest of the community, whereas the influence of cotton rats was density- and temporally dependent.

Water vole (Arvicola terrestris scherman) density as risk factor for human alveolar echinococcosis.

Concern is growing in Europe about alveolar echinococcosis (AE) with the increase in grassland rodent and red fox populations, intermediate and definitive hosts for Echinococcus multilocularis, respectively. The objective of this study was to assess the influence of rodent densities on human AE distribution. Spatial Poisson regression analyses were performed with geomorphologic features, landscape composition, climatic characteristics, and water vole density as independent variables. The outcome consisted of AE cases diagnosed over the period 1980-1992. High vole density yielded a 10-fold risk (relative risk [RR] = 10.34, 95% confidence interval [CI] = 2.78-38.39), and the first plateau (400-700 m altitude) compared with the plain (200-400 m) was associated with a large increase in risk (RR = 7.10, 95% CI = 1.30-38.63). These results confirm that human AE is strongly influenced by the densities of arvicolid species. Foxes feeding almost exclusively on grassland rodents when the latter expand could mediate this relation.

Habitat relations within lowland grassland rodent communities in Taiwan

Patterns of habitat use by murid rodents were examined in lowland grasslands in Taiwan. Fifteen grassland sites were live‐trapped in 1990, and 16 microhabitat variables were measured at each of 539 trap stations in the sampling sites. Mus caroli, Apodemus agrarius, Rattus losea, and Bandicota indica were captured regularly during the sampling. Rattus norvegicus and Nivivenrer coxingi were captured infrequently. The analysis focused on the four common species. Mus caroli, R. losea, and B. indica have been considered to be commensals of humans and to be largely dependent upon agricultural crops. However, these species were captured in natural habitats, often far from agricultural areas. M. caroli and R. Iosea were by far the most abundant species.Vertical stratification of the habitat did not increase the number of species or overall rodent abundance. Rather, sites with well‐developed grass cover and little vertical development of vegetation above the grass layer had the highest overall densities of rodents.Use of habitat was very similar among the four common species and was concentrated in areas with dense grass cover. Overlap in habitat use was particularly extensive in the core areas of greatest occupancy. Relative population abundances (number of individuals captured per trap station) of the four species were related weakly to the microhabitat variables. These variables were better predictors of capture probabilities of M. caroli and R. losea at individual trap stations, as revealed by multiple logistic regression. Abundances and capture probabilities did not appear to be affected by the presence or abundance of other species.It is suggested that body size differences may facilitate coexistence of these four species of ecologically similar murids. Beginning with the smallest species (M. caroli), body masses of each subsequent species in the series differ by at least a factor of two. These grassland communities may be somewhat resistant to invasion by more similar‐sized species of murids.

Failure to Detect Senescence in Persistence of Some Grassland Rodents

Several recent papers raise the question of how frequently senescence is detectable in survival estimates from natural populations of mammals. If animals do not age, the probability of disappearance is constant through time. This null hypothesis leads to the prediction that lengths of residence on a trapping grid, censused monthly, will follow a geometric distribution. After testing for survival differences between sexes and among seasons, I compared lengths of residence (persistence) from capture—recapture data for five species of small rodents in an old—field habitat near Lawrence, Kansas, USA to geometric distributions. Gender did not influence persistence on the grid for any species, but persistence of Microtus ochrogaster and Reithrodontomys megalotis varied significantly with season. All species showed a tendency for high rates of disappearance in the 1st mo after individuals were marked. When the analysis was limited to individuals residing on the area for at least 1 mo, neither Peromyscus maniculatus, P. leucopus, nor Sigmodon hispidus departed significantly from the geometric model. Seasonal analysis of Reithrodontomys megalotis was precluded by small samples, but data for all seasons combined seemed to indicate age— (or persistence—) specific rates of disappearance, as did M. ochrogaster, except those first captured in spring. To identify which patterns were consistent with senescence, I regressed rates of disappearance against persistence, testing for positive slope. Only those M. ochrogaster first captured in winter and autumn exhibited senescence by these criteria, despite disappearance rates of R. megalotis that increased sharply beyond persistence of 5 mo. The regression test for P. maniculatus indicated senescence even though the geometric test failed to indicate persistence specificity. The regression method alone is not a reliable test of senescence, because if does not incorporate variances of estimated probabilities of survival. Any approach derived from horizontal life tables potentially confounds seasonality with aging, making determination of senescence equivocal. In my data there is little convincing evidence that survival in the wild decreases with age in these rodents.

Ability of Prairie Rodents to Find Seeds in Plant Litter

-Differential abilities of white-footed mice (Peromyscus leucopus), deer mice (P. maniculatus) and fulvous harvest mice (Reithrodontomys fulvescens) to find seeds covered by 0 and 75 g of litter were assessed during laboratory foraging trials. All individuals collected significantly fewer seeds in aquaria with litter. Mean percent reduction in seed harvest between 0 and 75 g of litter was significantly greater for P. leucopus than either P. maniculatus or R. fulvescens, which did not differ significantly. Mean grams of seeds harvested significantly decreased with increased amounts of litter (0, 25, 50, 75, 100 and 125 g) for P. leucopus and R. fulvescens. Interspecific differences for mean percent reduction in seed harvest for sparse (25 g) and deep/dense (100 and 125 g) litter were nonsignificant; however, seed harvest was significantly lower for P. leucopus than R. fulvescens in moderate litter (50 and 75 g). Our results imply that differences in the ability of grassland rodents to collect seeds in plant litter may be partially responsible for species-specific patterns of microhabitat