Total Rodent Abundance Research Articles

Rodents' responses to manipulated plant litter and seed densities: implications for restoration.

Rodent populations in arid grasslands do not always track seed production, possibly due to high levels of plant litter. When natural disturbances are suppressed, litter accumulates becoming physically complex, causing rodents to harvest fewer seeds per equivalent time foraging. It also alters security from predation. Restoring natural disturbances may be an important element in conserving rodent communities. The aim of this study was to assess the influence of two levels of plant litter cover and seed densities on nocturnal rodent population characteristics in a semiarid grassland. Specifically, I hypothesized that kangaroo rats, pocket mice, grasshopper mice, and total rodents would be higher in the sparse plant litter treatment than dense litter, whereas deer mice would be lower in sparse plots. I further hypothesized that kangaroo rats and deer mice would be higher in the seed augmented treatment compared to the unseeded treatment. A prescribed fire removed litter in four of eight plots prior to sowing native seeds 1 year postfire into two burned and two unburned plots. Rodents were live-trapped during spring and fall 1 year. Sparse litter treatment had higher total rodent abundance, biomass, and frequency of offspring compared to dense plots indicating use of stored seeds. Banner-tailed kangaroo rats had higher abundance, implying reduced predation risk. Pocket mice body mass was greater in dense plots. After winter, seeded plots had higher kangaroo rat body mass and grasshopper mice abundance than unseeded, reflecting the use of stored seeds. These short term results demonstrate litter’s physical complexity may be equivalent to seed pulses on the responses of nocturnal rodents. Managers might positively influence grassland rodents by providing a mosaic of varying levels of plant litter.

Rodent assemblage structure reflects socioecological mosaics of counter-urbanization across post-Hurricane Katrina New Orleans

Often overshadowed by global trends in urbanization, counter-urbanization is also on the rise worldwide. Left unaddressed, counter-urbanization can result in conditions that imperil human well-being. For example, counter-urbanization is hypothesized to increase the prevalence of ecological hazards like synanthropic pest and pathogen host species by shifting habitat and resource availability. In this study, we addressed this hypothesis by examining whether the abundance or diversity of rodent hosts varies according to the prevalence of abandoned, unmaintained properties across a mosaic of counter-urbanization in post-Hurricane Katrina New Orleans (Louisiana, USA). We also sought to determine whether management of vacant lots can influence the abundance or diversity of rodents across counter-urbanizing landscapes. Analysis of capture data from multi-year trapping efforts across the greater New Orleans area showed that total rodent abundance was highest in residential areas with high levels of vacancy and unmaintained vegetation as well as low household income and low residency. Greater rodent abundance and richness also occurred in areas with features related to infrastructure loss, such as trash and debris, especially in winter. While these results highlight that property abandonment can augment populations of pest and pathogen host species, our findings also indicate that management of abandoned areas can potentially mitigate public health concerns in counter-urbanizing landscapes.

Landscape predictors of rodent dynamics in fragmented rainforests

Land-use change threatens a large number of tropical species (so-called ‘loser’ species), but a small subset of disturbance-adapted species may proliferate in human-modified landscapes (‘winner’ species). Identifying such loser and winner species is critically needed to improve conservation plans, but this task requires longitudinal studies that are extremely rare. We assessed this topic with small rodent assemblages in the Lacandona rainforest, a relatively new and highly dynamic agricultural frontier from southeastern Mexico. In particular, we measured the abundance of four rodent species in 12 forest sites during a 6 year period. We related changes in abundance to differences across time in landscape structure (i.e., percentage of forest cover, matrix contrast, number of forest patches, and forest edge density) surrounding each site. Total rodent abundance was almost two times higher in 2016 than in 2011, although abundances were generally low in all years. The abundance of Heteromys desmarestianus increased through time, mainly in forest sites with increasing matrix contrast. Oryzomys sp. also tended to increase in abundance, especially in sites with decreasing edge density. Sigmodon toltecus remained stable through time, but Peromyscus mexicanus tended to decrease in abundance, particularly in sites with decreasing edge density and increasing matrix contrast across time. Therefore, spatial variations in landscape structure lead to species-specific responses. If current deforestation rates persist, we predict a population decline of forest-specialist species (P. mexicanus), and an increase in generalist species (S. toltecus and Oryzomys sp.). Improving matrix quality is crucial for preventing the extinction of forest-specialist rodent species.

Long-term community change through multiple rapid transitions in a desert rodent community.

While studies increasingly document long-term change in community composition, whether long-term change occurs gradually or via rapid reorganization events remains unclear. We used Latent Dirichlet Allocation (LDA) and a change-point model to examine the long-term dynamics of a desert rodent community undergoing compositional change over a 38-yr span. Our approach detected three rapid reorganization events, where changes in the relative abundances of dominant and rare species occurred, and a separate period of increased variance in the structure of the community. These events coincided with time periods, possibly related to climate events, where the total abundance of rodents was extremely low. There are a variety of processes that could link low abundance events with a higher probability of rapid ecological transitions, including higher importance of stochastic processes (i.e., competitive interactions or priority effects) and the removal of structuring effects of competitive dominants or incumbent species. Continued study of the dynamics of community change will provide important information not only on the processes structuring communities, but will also provide guidance for forecasting how communities will undergo change in the future.

The influence of wildlife water developments and vegetation on rodent abundance in the Great Basin Desert

AbstractRodent communities have multiple functions including comprising a majority of the mammalian diversity within an ecosystem, providing a significant portion of the available biomass consumed by predators, and contributing to ecosystem services. Despite the importance of rodent communities, few investigations have explored the effects of increasing anthropogenic modifications to the landscape on rodents. Throughout the western United States, the construction of artificial water developments to benefit game species is commonplace. While benefits for certain species have been documented, several researchers recently hypothesized that these developments may cause unintentional negative effects to desert-adapted species and communities. To test this idea, we sampled rodents near to and distant from wildlife water developments over 4 consecutive summers. We employed an asymmetrical before-after-control-impact (BACI) design with sampling over 4 summers to determine if water developments influenced total rodent abundance. We performed an additional exploratory analysis to determine if factors other than free water influenced rodent abundance. We found no evidence that water developments impacted rodent abundance. Rodent abundance was primarily driven by vegetation type and year of sampling. Our findings suggested that water developments on our study area do not represent a significant disturbance to rodent abundance and that rodent abundance was influenced by the vegetative community and temporal factors linked to precipitation and primary plant production. Our findings represent one of the 1st efforts to determine the effects of an anthropogenic activity on the rodent community utilizing a manipulation design.

Postcatastrophic successions of a rodent population

Successions of a rodent population have been investigated in the forest biocenoses of the Visim Nature Biosphere Reserve (Sverdlovsk oblast, Middle Ural) after a catastrophic windfall and two fires. Differences in the values of the total abundance of rodents and their ratio in the community before natural catastrophes and at different postcatastrophic demutational succession stages are revealed. Structural alterations in a rodent population are associated with different responses of the species to the anemogenic and pyrogenic transformation of their microhabitat environment and can be considered compensatory mechanisms maintaining the sustainability of small mammal communities under the impact of natural catastrophic factors.

Long‐term variations in rodent abundance in a rural landscape of the Pampas, Argentina

AbstractThe goal of this study was to analyze the variations in abundance of rodent communities over the last 24 years in a rural area, and their relation to possible changes in climatic variables and land use. The principal change in the area observed along the study period was an increase in the area covered by soybean. The habitats studied were crop fields and borders. The total abundance of rodents did not show a significant trend of variation over time in crop fields while in borders the abundance in autumn–winter (A–W) showed a significant trend to decrease over time. The different rodent species showed a differential response over time. While Calomys laucha and C. musculinus showed a decrease between the period before and after the soybean expansion, Akodon azarae did not change its abundance over time. The mean minimum temperature increased over time while the number of days with frost decreased. Total rodent abundance in A–W was positively associated with the cumulated precipitation of the previous spring–summer period and negatively with the cumulated precipitation of the same period. We conclude that rodent abundance variations in crop fields and borders of the study area are influenced by precipitation, but the observed trends of variation over time are better explained by changes in agricultural practices than by meteorological variables.

Movement patterns of a specialist predator, the weaselMustela nivalis exploiting asynchronous cyclic field voleMicrotus agrestis populations

We investigated habitat selection and movement characteristics of male weaselsMustela nivalis Linnaeus, 1766 during the breeding season through radio-telemetry in Kielder Forest (KF) in order to assess how weasel movement is influenced by prey dynamics, mate searching and predation risk, and whether the scale of weasel movement corresponds to the spatial scale of the asynchronous, multi-annual vole population cycles observed in KF. Weasels used habitats with a high proportion of grass cover to a much larger extend than habitats with less grass cover and moved through the latter habitats faster and / or straighter. Habitats with high amounts of grass cover also had the highest field vole abundance, although total rodent abundance did not differ between habitats. The selection of this habitat by weasels might reflect weasels preferring field voles as prey or avoiding habitats with little grass cover and high intraguild predation risk. Five out of 8 male weasels radio-tracked had low day-to-day site fidelity and moved between different clear cuts. Three other males were resident in a single clear cut. This variation may reflect mate searching by male weasels. The observation that most weasels (5 out of 8) roamed over large areas and the scale of their dispersal potential suggests, that if they regulated vole populations, they should have a greater synchronising effect on the spatial scale of vole population dynamics than what is observed in vole populations in KF.

Rodent Communities in Active and Inactive Colonies of Black-Tailed Prairie Dogs in Shortgrass Steppe

Black-tailed prairie dogs (Cynomys ludovicianus) alter shortgrass-steppe landscapes in ways that are expected to affect other mammals. I sampled rodent populations at 31 sites on the Pawnee National Grasslands, Colorado, including 18 active colonies, 6 colonies that had been unoccupied for .6 years (inactive), and 7 grassland sites without prairie dogs (controls). Rodents were livetrapped for 4 consecutive nights at each site between May and August 2004 to estimate relative abundance. I also measured vegetation and habitat characteristics. Northern grasshopper mice (Onychomys leucogaster) and 13-lined ground squirrels (Spermophilus tridecemlineatus) were captured on most (� 87%) of the sites and comprised 40% and 34% of individuals captured, respectively. Species richness ranged from 1 to 6 species, but most sites had only these 2 species. Grasshopper mice tended to be more abundant on colony sites than on controls, although differences were not statistically significant. Ground squirrels were least abundant on active colonies, and most abundant on inactive colonies, followed by controls. Habitat types did not differ in their abundance of any other species or in total rodent abundance; however, active colony area influenced total rodent abundance, with small colonies supporting fewer individuals. Controls supported the most rodent species, in part because these sites consistently had taller grass, which presumably provided habitat and food for less common species (Chaetodipus hispidus, Perognathus flavus, and Reithrodontomys megalotis). In shortgrass steppe, active colonies provided habitat for grasshopper mice, which may be involved in maintenance and spread of plague, but did not support consistently higher rodent species richness than the surrounding grasslands.

Rodent seed predation and GUDs: effect of burning and topography

We examined the relationships between seed predation and the habitat into which a seed falls, abundance of rodents within that habitat, and foraging pattern of rodents within that habitat. Using seed plots, we assessed seed predation in burned and unburned tallgrass prairies at biweekly intervals between May and September in 2001 and 2002. Significantly more seed was removed from plots in burned than unburned prairies. Rodent abundance did not differ between burned prairie and unburned prairie, although the abundance of omnivorous–granivorous rodents (herbivores excluded) was greater in burned than unburned prairie. Proportion of seed removed in burned and unburned prairies was independent of both total rodent abundance and abundance of omnivorous–granivorous rodents. We also measured giving-up density (GUD) of rodents in burned and unburned prairies during the spring and summer of 2002. GUDs did not differ significantly in burned and unburned prairies. However, rodents had a higher GUD in uplands than in limestone breaks or lowland habitats. Our results suggest that rodent foraging in tallgrass prairie is affected by microhabitat and that rodent abundance is not sufficient to predict seed predation.

Effects of residential density on sonoran desert nocturnal rodents

We compared nocturnal rodent distributions among residential developments and in adjacent undeveloped native habitat remnants in Tucson, Arizona during October 1994. We trapped rodents in 2 low density (0.5 houses/ha) developments, 2 medium density (7.5 houses/ha) developments, and in 4 adjacent blocks of undeveloped native habitat using trap lines of 50 snap traps spaced at 2 traps every 10 meters. We compared species abundance, species richness, and total abundance among the 4 site types in a contingency table using a 2-tailed Fisher's exact test, and used post-hoc tests where the null hypothesis of no difference among sites was rejected. We encountered 144 individuals representing 5 species of nocturnal rodents in 1200 trap nights. Of 4 native rodent species, none were captured in medium housing density sites. House mice (Mus musculus) were captured only in medium housing density sites. Total rodent abundance was lower in both the medium density residential and the adjacent undeveloped sites than in either low density or adjacent undeveloped sites. Low density housing must be included in the developing matrix if the full complement of native nocturnal rodents is to be retained in Tucson.

Experimental confirmation of interspecific competition between native and introduced mice

AbstractThis paper tests the hypothesis that Pseudomys novaehollandiae shows competitive superiority over Mus musculus. Experimental removals of P. novaehollandiae on four I ha treatment plots and additions on a further four I ha plots show significant effects of interspecific competition when compared to two I ha unmanipulated control plots. Significant effects of P. novachollandiae populations on the abundance of M. musculus populations were observed for number of captures/day, abundance/trapping session and for the recruitment of new individuals over the post‐removal period, thus allowing rejection of the null hypothesis in each case. There was an apparent ceiling on the total rodent abundance which is indicative of a resource limitation. The resource in short supply appears to be space, but it is not clear if the competition is for food or shelter resources contained within such space or for the space per se, but the latter seems less likely.The confirmation of this interspecific competition supports the inferences drawn from a considerable amount of indirect evidence, largely descriptive, obtained from previous studies in the Myall Lakes National Park. This study also shows that competition is one of the mechanisms controlling the replacement of species in the succession following disturbance and lends support to the habitat accommodation model proposed for such succession. These points support previous statements on the importance of interspecific competition as a determinant of the structure of these small‐mammal communities.