We describe the first new rodent species from Solomon Islands in more than 80 years. This new giant rat is known from a single specimen captured in a commercially felled Dillenia salomonensis tree on Vangunu Island. Morphologically, it closely resembles a fascinating secondary radiation of 3 species of Uromys (Cyromys) that are endemic to Guadalcanal Island. The cranium can be readily distinguished from those of other species of Uromys by its shorter maxillary tooth row, and shorter incisive foramina. The existence of this species has been suspected for over 2 decades. It is rare and cryptic, and conservation status is Critically Endangered due to its small distributional range, apparent low population densities, and rapid progress of commercial logging on Vangunu Island. Further surveys to locate additional animals and support for community led conservation initiatives on Vangunu are urgently needed to safeguard the species.

Apex predators directly and indirectly influence prey and predators at lower trophic positions (mesopredators). The lethal effect of apex predators on mesopredators is well documented, but they also could affect mesopredators in non-lethal ways. We investigated foraging decisions and perceived risk in the bat-eared fox (Otocyon megalotis), a small canid that is often killed by larger terrestrial carnivores and birds of prey. We used giving-updensity (GUD) experiments and observations of vigilance behavior to assess the influence of temporal, spatial, and anthropogenic factors on perceived risk in a population of bat-eared foxes at the Kuruman River Reserve, Northern Cape, South Africa. GUDs were higher during periods around the new moon and lower in the presence of researchers, suggesting that foxes are warier in darker conditions, but perceive an increase in relative safety in the presence of humans. Vigilance, however, did not vary with these same factors. Observational data revealed foraging success outside the experimental context did not differ with lunar period, implying that higher GUDs associated with new moons were not due to higher missed opportunity costs associated with foraging at patches. These results suggest that GUDs may be capable of detecting more subtle differences in perceived risk when compared to vigilance rates. We highlight the important considerations of using GUDs to examine perceived risk for a predatory species and emphasize that future studies using GUDs should quantify predators' risk-related decisions by documenting missed opportunity costs to determine the implications behind patch-use behavior.

Of 41 adult wolf-killed gray wolves (Canis lupus) and 10 probably or possibly killed by wolves from 1968 through 2014 in the Superior National Forest (SNF) in northeastern Minnesota, most were killed in months leading up to and immediately following the breeding season, which was primarily February. This finding is similar to a published sample from Denali National Park, and the seasonality of intraspecific mortality generally parallels the known seasonality of testosterone levels, scent-marking, howling frequency, and general interpack aggression. Males and females were killed in the same proportion as in the population of radiocollared wolves. The annual rate of wolf-killed wolves was not related to the annual wolf density. Our findings tend to support intraspecific mortality of adult wolves as a means to reduce breeding competition and to maintain territories.

Camera trapping is a powerful tool for studying mammal populations over large spatial scales. Density estimation using camera-trap data is a commonly desired outcome, but most approaches only work for species that can be individually recognized, and researchers studying most mammals are typically constrained to measures of site occupancy or detection rate. These 2 metrics are often used as measures of relative abundance and presumed to be related directly to animal density. To test this relationship, we estimated density, occupancy, and detection rate of male white-tailed deer (Odocoileus virginianus) using camera-trap data collected from 1,199 cameras across 20 study sites. Detection rate and density exhibited stronger positive linear correlation (r² = 0.80) than occupancy and density (r² = 0.27). When hunted and unhunted paired areas were compared, detection rate and density showed the same trend between paired sites 62.5% of the time compared to 87.5% for occupancy and density. In particular, agreement between estimates was lowest for pairs of sites that had the largest differences in surrounding housing density. Although it is clear occupancy and detection rate contain some information about density, models suggested different ecological relationships associated with the metrics. Using occupancy or detection rate as proxies for density may be particularly problematic when comparing between areas where animals might to move or behave differently, such as urban–wild interfaces. In such cases, alternate methods of density approximation are recommended.

During summer and early autumn, reindeer and caribou (Rangifer tarandus) must exceed daily maintenance requirements for protein and energy to replenish body reserves for winter survival and reproduction. We estimated the maintenance requirements and the incremental costs of mass gain of captive female Siberian reindeer (R. t. tarandus) during summer and autumn by a mass balance approach. Intake (88 versus 56 g kg^−0.75 day⁻¹) and digestibility (89% versus 81%) of dry matter were greater in summer than in autumn on the same diet. Body mass increased over the summer and remained stable into autumn. At zero mass gain, reindeer required 911 kJ kg^−0.75 day⁻¹ digestible energy and 1.12 g kg^−0.75 day⁻¹ digestible nitrogen (N). Requirements of N were affected by endogenous losses of N in the feces that were 72–82% of total fecal N. During summer, reindeer would need to consume forage containing more than 9.5 ± 0.4 (SE) kJ g⁻¹ digestible energy and 1.17 ± 0.4 (SE) % digestible N to gain body mass at intakes of 98 g kg^−0.75 day⁻¹. Reindeer could use a mix of graminoids and browse to meet energy demands and gain fat (6–18 kJ g⁻¹) but may not be able to maintain or gain body protein in late summer as forages senesce and N contents decline below 1% of dry matter.

Olfactory cues are especially important for nocturnal mammals such as bats and can communicate an individual's condition and facilitate mate choice. Here, we introduce a novel odorous substance found on the forearm of reproductive male fringe-lipped bats (Trachops cirrhosus), which we term “forearm crust.” We continuously captured bats over a 3-year period to determine the prevalence and possible seasonal distribution of this forearm crust. We evaluated males to elucidate whether forearm crust was associated with specific morphological characteristics. Males with forearm crust were captured throughout the year, but we found an increase in captures of males with a forearm crust from September to December, prior to peak female pregnancy in March. All males with a forearm crust had enlarged chest glands and testes. Males with a forearm crust had significantly higher body condition indices than males without a forearm crust. We observed males in their natural roosts and in captivity, and describe a novel stereotyped behavior in which males scratch the body dorsally and ventrally, insert a claw into their mouth, and then lick their forearm repeatedly. Males with a forearm crust licked their forearm significantly more than males without a forearm crust. Together, these data suggest that this novel odorous forearm crust is a male reproductive trait. Further investigation is needed to understand its role in reproduction.

Drinking water is a critical resource for hibernating bats and its importance may be further increased when disease affects water balance. White-nose syndrome (WNS), a fungal disease that causes dehydration and electrolyte imbalance in bats, is associated with high mortality rates of several hibernating bat species in North America. Aside from restoring water balance, hibernaculum water sources may also provide minerals to bats, which could contribute to restoring electrolyte balance and reducing the impacts of WNS. However, hibernacula water sources may also be a source of toxic elements, such as heavy metals. We collected water samples from 12 hibernacula in New Brunswick, Canada, and determined the concentrations of 18 elements in each water sample (n = 103 samples). Aluminum, barium, calcium, chloride, magnesium, manganese, potassium, and sodium were the most common elements detected, with concentrations of aluminum, lead, and manganese above drinking water recommendations (developed for human consumption) in some samples. The concentrations of electrolytes in cave water were orders of magnitude below therapeutic concentrations. Sampling period (early hibernation, late hibernation) did not affect results, but water profiles differed among sites and sample types within a site (running water, standing water, ceiling drip, and ice). The water profiles we recorded in our study suggest little potential for secondary consequences of drinking water, whether positive (i.e., electrolyte or mineral supplementation) or negative (i.e., heavy metal contamination).

Understanding the distributions and environmental associations of rare species is a critical 1st step in their conservation and management. Federally endangered Florida bonneted bats (Eumops floridanus) are endemic to southern Florida and are believed to have one of the most limited geographic distributions of any bat in the United States. We conducted a large-scale acoustic survey of 330 points spread across approximately 38,000 km² over a 2-year period and used a hierarchical Bayesian approach accounting for imperfect detection to model the distribution and environmental associations of the Florida bonneted bat. Bat occupancy was negatively correlated with the amount of developed land within 5 km of the sampling point and positively correlated with the amount of crop-based agriculture within 5 km of the sampling point. Bat occupancy probabilities increased with the 30-year mean for minimum spring temperature and levels of annual precipitation, and decreased with the 30-year mean for levels of spring precipitation. Bat detection was positively influenced by Julian date and minimum temperature of the survey night. This study offers new insight into the habitat use of this endangered species. Results confirm that predicted changes in land cover and climate will be threats to the Florida bonneted bat.

Restoration of the longleaf pine (Pinus palustris; LLP) ecosystem and its associated fauna is a principal goal of many land-management agencies in the southeastern United States. Prescribed fire and herbicide application are 2 common methods of LLP restoration. We employed a multi-scale approach to investigate how occurrence of fox squirrels (Sciurus niger) was influenced by fire frequency and herbicide application in LLP communities of northern Florida. We sampled 9-point, 4-ha grids of camera traps with 106 grids in fire treatments, 23 herbicide treatment grids, and 27 control grids. We evaluated a priori models for occurrence of fox squirrels at point, 4-ha patch, and home-range scales, and the influence of fire and herbicides on vegetation structure. Fox squirrel occurrence was positively associated with densities of turkey oak (Quercus laevis) at the patch scale, which were significantly less abundant in herbicide-treated areas. Fox squirrel occurrence was negatively correlated with fire interval and positively correlated with oak densities at a localized point scale. Additionally, fox squirrel point occurrences declined over time since the last fire. Fire produced habitat more favorable for fox squirrels than did herbicide treatments.

Our study builds on recent research on the role of drought refuges in facilitating the persistence of arid-dwelling rodents during extended dry periods by characterizing the spatial ecology and shelter use of the plains mouse, Pseudomys australis, a threatened Australian desert rodent that uses refuges. We radiotracked 18 P. australis in the western Simpson Desert, Australia, during November 2014 and May 2015, when individuals were expected to be confined to cracking clay refuge habitat. We also measured the dimensions (length, width, and perceived vertical depth) of shelter sites used by tracked individuals. A sufficient number of fixes (range = 17–64) for home range calculation by kernel density estimation was obtained for 11 of the 18 tracked individuals. Total ranges were calculated at the 90% isopleth and core areas at the 50% isopleth. The tracked animals occupied small home ranges (1.35 ± 0.56 ha) within cracking clay refuge habitat for the duration of the study. Individuals occupied distinct core areas, which were just 22.57 ± 1.54% the area of the total home ranges and centered on 1–2 frequently used burrows. Overlaps in total ranges and some burrow sharing were observed between neighboring individuals; however, core areas overlapped between only 1 pair of animals, suggesting that some group structuring may occur in P. australis refuge populations. Cracks used by tracked individuals were wider and deeper than burrows. Our study found that the short-term home ranges of the radiotracked P. australis during a dry period were situated entirely within cracking clay refuge habitat, and that shelter resources, and potentially social structuring, influence the use of space by this species.

We studied a rodent community in the San Joaquin Desert of California, United States, from 1993 to 2016. Using biannual trapping on a 144-trap plot, we found that mice of various species were rarely caught in appreciable numbers in contrast to many other studies of rodent communities in arid North America. Most captures were made of 3 species of kangaroo rats: giant kangaroo rat (Dipodomys ingens), Heermann's kangaroo rat (D. heermanni), and San Joaquin kangaroo rat (D. nitratoides). The site was dominated by D. ingens, which, in many years, was the only kangaroo rat captured. Precipitation varied extremely across the study period with 2 periods of high rainfall and 2 periods of well-below-average rainfall. The rodent community seems to have been responding to both bottom-up control and the competitive dominance of D. ingens. In particular, our trapping showed 2 complete cycles of abundance of D. ingens, from very high numbers to crashes with either no or only 2 individuals caught during a session. In both cases, the species recovered after these crashes in abundance. Although we found some D. ingens living to 4–5 years, and D. heermanni and D. nitratoides living up to 3 years, annual survivorship estimates were low compared with other studies of kangaroo rats. Other studies, however, were of much shorter duration and therefore may have missed eventual downturns in population abundances. Dipodomys ingens is a protected species, and from a conservation standpoint, our data indicate that populations can be highly resilient even in the face of high environmental variability.

Members of Haplomylomys, a subgenus of Peromyscus, are widely distributed in northwestern Mexico and the southwestern United States; due to its taxonomic complexity, the systematics and biogeography of this group have been widely studied. However, the evolutionary relationships between island taxa within the eremicus group remain poorly understood. Our goals were to assess the evolutionary history of Haplomylomys, and to identify geological and climatic events that might have affected its evolutionary history. Phylogenetic relationships were analyzed using 3 mitochondrial gene fragments (Cytb, COI, and COIII) from 61 individuals collected throughout the geographic range of Haplomylomys. Maximum likelihood and Bayesian phylogenetic analyses identified 2 main clades. The 1st includes P. californicus; the 2nd, all the species within the eremicus group divided into 4 clades. Taken together, our phylogenetic analysis and genetic divergence values suggest several taxonomic changes are needed among insular members of the eremicus group. Molecular dating analysis indicates that the phylogeny of Haplomylomys is possibly correlated with the formation of the Colorado River, the latest embayment of the Gulf of California during the Neogene, the trans-peninsular seaway in the central Vizcaino region, and the Last Glacial Maximum; these events may have had an effect at the species and subspecies level for Haplomylomys taxa.

Using 26 cranial measurements, we conducted a morphometric study on 113 adult skulls of the currently recognized rabbits Sylvilagus brasiliensis and S. sanctaemartae from Colombia, Ecuador, and Peru. Five morphological groups are identified of which 4 warrant species-level recognition. North and west of the Andes, S. gabbi occupies the lowlands of northern Colombia and northwestern Ecuador. Sylvilagus sanctaemartae is morphologically indistinguishable from S. gabbi and is a synonym of it. Two species live in the Andes of Colombia: S. fulvescens in the Western and Central Andes and S. apollinaris in the Eastern Andes. East of the Andes, Sylvilagus brasiliensis defilippi is found in the tropical Orinoco and Amazon basins of Colombia, Ecuador, and Peru, and S. brasiliensis andinus occurs in the Andes of Ecuador. These 2 subspecies intergrade in the Amotape-Huancabamba Zone of extreme southern Ecuador and adjacent west-central Peru. The eastern distributional limit of S. b. defilippi outside the study area in South America is unknown. An additional 50 skulls of S. gabbi and 14 of S. dicei were examined from Costa Rica and Panama to compare with the rabbits from South America. The data show that S. gabbi exhibits no noticeable geographic variation from Central America to northern Colombia and northwestern Ecuador. Sylvilagus dicei from the Cordillera de Talamanca of Costa Rica and Panama is morphologically most similar to S. fulvescens from the Western and Central Andes of Colombia and they are likely closely related. Methods are presented to identify all taxa and the distribution of each taxon is provided. This taxonomic arrangement is based on few specimens. Accordingly, species boundaries and phylogenetic relationships should be tested by focusing future collecting and morphological and molecular research in high-priority areas such as: 1) along the Colombian–Ecuadorian border from the Pacific Coast, across the Andes into the Amazon Basin; 2) Amotape-Huancabamba Zone of Ecuador and Peru; and 3) Eastern Andes of Colombia.

Contemporary examination of community structure requires analyzing multiple dimensions of biodiversity to provide a more holistic understanding of the ecological and historical factors involved in the formation and maintenance of local communities. We used empirical data on bat communities across Mexico to investigate patterns of taxonomic and phylogenetic diversities. More specifically, we 1) characterized phylogenetic structure using multiple measures of diversity and identified environmental factors that serve as potential drivers of the underlying structure, 2) determined whether any bat community showed evidence of phylogenetic overdispersion or underdispersion and characterized how taxonomic structure differed among overdispersed, randomly dispersed, and underdispersed sites, and 3) examined the relationship between phylogenetic diversity and size of the regional species pool. We used 3 indices of phylogenetic diversity (Faith's index [FI], mean nearest neighbor distance [MNND], and mean pairwise distance [MPD]) to quantify patterns of evolutionary relatedness in bat communities across Mexico. To determine whether a particular community was overdispersed, randomly dispersed, or underdispersed, we used randomization procedures with latitudinal and longitudinal constraints to define the regional species pool for each bat community. We used regression trees to investigate which climatic factors explained variation for each measure of phylogenetic diversity. Precipitation and longitude were correlated with FI, temperature was correlated with MNND, and temperature along with latitude and longitude were correlated with MPD. We found that just over one-half of the communities were underdispersed, just under one-half were randomly dispersed, and only 1 was overdispersed. Each measure of phylogenetic diversity was differently affected by the size of the regional species pool.

Biodiversity is being threatened by human activities worldwide. Inside protected areas, anthropogenic activities are mostly under control. However, outside protected areas, threatened or endangered species still need protection, and identification of a species' habitat requirements is essential for conservation planning. We gathered information on habitat characteristics of and anthropogenic threats to the Chinese pangolin (Manis pentadactyla), a critically endangered species for which such baseline data are scarce. We found closed-canopy forest nearest water sources at an altitude from 555 to 1,740 m to be suitable habitat for Chinese pangolins. Forest fires, livestock grazing, distance to nearest footpath, and distance to nearest household were negatively associated with presence of Chinese pangolins. To protect the Chinese pangolin outside of the reserve system, we recommend public awareness programs and campaigns to protect habitat in addition to directly protecting this species against hunting and trading.

Many mammals create food stores to enhance overwinter survival in seasonal environments. Strategic arrangement of food within caches may facilitate the physical integrity of the cache or improve access to high-quality food to ensure that cached resources meet future nutritional demands. We used the American pika (Ochotona princeps), a food-caching lagomorph, to evaluate variation in haypile (cache) structure (i.e., horizontal layering by plant functional group) in Wyoming, United States. Fifty-five percent of 62 haypiles contained at least 2 discrete layers of vegetation. Adults and juveniles layered haypiles in similar proportions. The probability of layering increased with haypile volume, but not haypile number per individual or nearby forage diversity. Vegetation cached in layered haypiles was also higher in nitrogen compared to vegetation in unlayered piles. We found that American pikas frequently structured their food caches, structured caches were larger, and the cached vegetation in structured piles was of higher nutritional quality. Improving access to stable, high-quality vegetation in haypiles, a critical overwinter food resource, may allow individuals to better persist amidst harsh conditions.

Some species of scatter-hoarding rodents direct seed dispersal by dispersing seeds into areas where the densities of conspecific trees are low. This behavior seems to be an immediate response to cache pilferage and is accomplished by multiple movements. We evaluated whether this directed dispersal also occurs when the scatterhoarding rodents Maxomys surifer disperse seeds away from parent trees when no pilferage has occurred. We simulated parent trees by releasing seeds at different sites in semi-natural enclosures, which prevent pilferage, in Xishuangbanna region, Southwest China. We found that M. surifer preferred to disperse seeds into areas with fewer conspecific seeds and that seeds cached in areas of low seed density were more likely to survive than those in areas of high density. Our results indicate that M. surifer could provide directed dispersal when they initially disperse seeds away from parent trees, without pilferage. This finding suggests that directed seed dispersal is not an immediate response after pilferage, but an instinctive behavior to reduce the potential for density-dependent cache pilferage. Further, our study indicates that directed seed dispersal is important to mast-seeding plants or species whose seeds are unlikely to be dispersed several times by scatter-hoarding animals.

A history of timber harvest in West Virginia has reduced red spruce (Picea rubens) forests to < 10% of their historic range and resulted in considerable habitat fragmentation for wildlife species associated with these forests. The Virginia northern flying squirrel (Glaucomys sabrinus fuscus) has been described as a red spruce obligate subspecies that must traverse this fragmented landscape to disperse among remnant red spruce patches. Food availability in the forest matrix surrounding red spruce may be a limiting factor to successful dispersal of G. s. fuscus. We examined the diet of flying squirrels using stable isotope analysis and used vegetation surveys to determine the availability of diet items in the habitats encountered by G. s. fuscus in the matrix surrounding red spruce fragments. Stable isotope analysis suggested hypogeous fungi, epigeous fungi, and invertebrates contributed the most to the diet of G. s. fuscus, followed by lichen. Tree buds contributed the least in spring, and beechnuts contributed the least in fall. The vegetation surveys revealed that no habitat type had a greater availability of the diet items that contributed most to the assimilated diet of G. s. fuscus, suggesting that stand age and structure may be more important for diet-item availability than habitat type.

Carnivorous mammals < 25 kg typically prey on species < 50% of their body mass but can choose prey whose energy value varies from small proportions of their daily needs to exceeding them. We hypothesized that for carnivores < 25 kg specializing in vertebrate prey, prey sizes closest to meeting daily energy needs would be most frequently depredated. We tested this hypothesis by reconstructing the diet of Humboldt martens using 528 scats and calculating the proportion of metabolizable energy (PME) that each prey taxon contributed to the diet. Overall, mammals dominated the diet (PME = 72%), followed by birds (PME = 22%), with berries, insects, and reptiles contributing < 10% PME. Sciurids comprised the largest proportion of all prey, representing 42% of overall PME, ranging from 29% (spring) to 51% (summer). While > 37 prey taxa were identified in the annual diet, only 11 contributed > 5% PME in any single season and the 4 dominant prey taxa in any single season represented 59–64% of that season's PME. Medium-sized prey (85–225 g) composed 55–66% PME from summer through winter and 2.6 to 8.4 times PME compared to small (< 40 g) and large (> 250 g) prey during these 3 seasons, respectively. When PME for the most frequently consumed individual medium-sized prey (e.g., chipmunks) declined seasonally, martens switched to alternative medium-sized prey (2.8- and 2.5-fold increases in medium-sized birds and flying squirrels, respectively), increased use of large prey (> 8-fold increase), but changed use of small prey least. The annual importance of medium-sized prey, and seasonal shifts to similar-sized or larger prey during winter-spring seasons, both support our hypothesis that the most frequently depredated prey in the diet of Humboldt martens have body sizes closest to meeting daily energy needs.

A primary objective of community ecology is to understand the conditions that allow species to coexist by identifying how co-occurring species use and share space and resources. The European pine marten (Martes martes) and the stone marten (M. foina) are syntopic mustelids with similar morphology and ecology for which differential habitat use, especially differential use of resting sites, appears to be the main driver underlying their coexistence. Organisms commonly respond to their environment across a range of scales and habitat selection is a hierarchical process where each level reflects distinct behavioral processes. We performed an optimized multiple-level (i.e., selection of home range in the study area and selection of specific habitat components within the home range) and multiple-scale study of resting-site habitat selection. Each covariate was tested separately across a range of prespecified scales and then combined into a single multivariable, multiscale model. The 2 species differed significantly in their habitat selection at both levels. Stone martens selected buildings, whereas pine martens selected forest patches. However, both species avoided open areas and selected shrubs and hedges, confirming that syntopy was likely to occur with possible interactions between species. Differences in the spatial scale of resting-site selection, when both species selected the same landscape elements, might also contribute to this coexistence. Overall, stone martens showed higher interindividual variability in habitat selection than pine martens, and this variability was influenced by age and sex. Whether this variability was due to a greater behavioral and ecological plasticity of stone martens or to interactions with pine martens forcing stone martens to use suboptimal habitat remains unclear. In addition, stone martens generally avoided areas associated with high trapping pressure. However, a percentage of subadult males selected these areas, which could have serious consequences for the stone marten population.

Habitat fragmentation reduces biodiversity and affects ecological processes that are fundamental for maintaining ecosystem services. We investigated how landscape structure—percent forest cover, patch density, percent cover by edge, perimeter-area ratio, and spatial heterogeneity—affects the diversity of mammalian carnivores at multiple extents within 22 Atlantic Forest landscapes. We hypothesized that 1) species richness of carnivores is positively related to forest cover; and 2) the occurrence of species will vary according to its sensitivity to forest loss and its preference for forest or open areas. Species richness, composition, and occurrence of mammalian carnivores were correlated with several landscape structure metrics. Due to a high correlation among the metrics, we adopted forest cover as the principal predictor variable. We compared a forest cover model to a null model using Akaike Information Criterion (AICc), and evaluated other fragmentation metrics using a redundancy analysis. Carnivore species richness was positively related to forest cover and negatively associated with other fragmentation metrics. However, the responses to landscape structure differed among species, possibly due to their differences in habitat use. Landscape configuration is an important factor influencing carnivore species composition. Forest cover can explain some, but not all, carnivore species occurrence. Our results reinforce the protection of forests as fundamental to the conservation of carnivore species and the ecological processes in which they participate.

Activity patterns reflect adaptations to local biological and physical conditions. We estimated the activity patterns of 3 mesocarnivore species in a semiarid environment in northeastern Brazil: the ocelot (Leopardus pardalis), crab-eating fox (Cerdocyon thous), and oncilla (Leopardus tigrinus). We compared the overlap of daily activity among these species and to apex predators. We also estimated nighttime activity of these mesocarnivores during 2 years and compared activity peaks with those of apex predators and potential prey. All 3 mesocarnivores were nocturnal, with ocelots having only 1 record during daytime. Coefficients of overlap with larger predators were high (Δ₁ > 0.7) for all pairwise comparisons, since all species were very nocturnal. Nighttime-only activity comparisons (Kolmogorov–Smirnov tests) showed that activity of oncillas differed from that of both larger mesocarnivores and jaguar activity, suggesting temporal segregation. Contrary to our expectations, rodent activity was dissimilar from that of ocelots and crab-eating foxes, but activity of rodents and oncillas was relatively synchronous. Activity of both cat species seems limited to the cooler nighttime, and nocturnal behavior of oncillas more likely reflects activity of potential prey rather than regulation by intraguild predators. Future studies in arid regions should consider climatic factors when estimating activity patterns.

Cranial ontogenetic analyses improve our understanding of function from developmental, ecological, and evolutionary perspectives. Akodon montensis is an abundant, omnivorous forest species that occupies many habitat types. We used traditional and geometric morphometric approaches to describe ontogenetic variation in skulls of A. montensis. We tested for sexual dimorphism and described patterns of variation associated with both age and size based on 6 postweaning age classes. We found no evidence for sexual dimorphism. Growth patterns showed an initial narrowing of the braincase, and associated changes in the rostrum as specimens reached adulthood. Older animals had an elongated rostrum and palate. Geometric morphometric analysis revealed allometric variation associated with the basicranium for the entire age series, while traditional morphometric analyses showed allometric variation in the facial component. The patterns found for A. montensis are similar to those of other species of Akodon. We characterize ontogenetic patterns for Akodontines, the second most diverse Sigmodontine tribe, and a model group for studies of shape change in generalist rodents.

Coexistence between species with similar niche requirements is often facilitated by displacement of morphological, behavioral, or physiological characteristics. Experiments comparing treatments with and without the presence of potential competitors are ideal for testing hypotheses of interspecific competition. Here, we investigate a fundamental aspect in the natural history of a species: the home range. We determined whether co-occurrence can influence the home range size of 2 subterranean rodent species, Ctenomys flamarioni and C. minutus. We evaluated home range size in populations of both species in allopatry and sympatry along the coastal plain of southern Brazil. Animals were radiotracked, and the home range size of each individual was estimated using grid cells and minimum convex polygon methods. We found no significant differences in home range size between sites or species, and the interaction was nonsignificant. We also found no relationship between home range size and body mass or sex. Our results suggest that co-occurrence may not influence home range size in these species, perhaps due to environmental adaptations that facilitate coexistence (e.g., microhabitat segregation and dietary modifications). Further, the characteristics of the sandy dune habitat may act as environmental filters, favoring similar home range sizes for both species.

Here, we characterize and compare rodent assemblages from crop fields and rangelands of the 4 Pampa districts included in Buenos Aires province, Argentina, to analyze the role of regional context, land use, and vegetation structure in determining the structure of rodent assemblages at the plot scale. Habitat generalist species (Calomys laucha and Mus musculus) tended to be more abundant in crop fields, whereas habitat specialists (Akodon azarae and Oxymycterus rufus) tended to be more abundant in rangelands. However, the degree of spatial segregation between habitat generalists and specialists and the associations between particular rodent species and land use differed among districts. The abundance of the dominant species (C. laucha and A. azarae) was positively associated with vegetation height. We also found a positive association between the abundance of the dominant species in a certain land use and the representation of that land use in the Pampa district, which suggests an effect of the regional context on local assemblages. Our results show that the structure of the rodent assemblage in a certain plot is the result of the interaction between the district the plot is in and the land use (and management) it is under. Future studies could shed light to the mechanisms behind the district effect observed in this study.

Drylands occupy almost 50% of the Earth's surface and are increasingly affected by extensive land uses such as grazing. These practices affect multiple biotic and abiotic interactions mainly through loss of habitat and resources available for native wildlife. We examined the effects of local vegetation conditions on resource selection by a small mammal species in drylands with different resource availability. The study was conducted in a semi-arid woodland that included an area protected from livestock grazing and human settlement for more than 50 years, the Man and the Biosphere Ñacunán Reserve, and an adjoining area that has experienced long-term cattle grazing. We tracked radio-collared individuals of Graomys griseoflavus, the most abundant small mammal in the Ñacunán region, and calculated resource selection functions (RSFs) to evaluate habitat selection. We modeled resource selection using a suite of habitat variables measured in both areas. We hypothesized that long-term changes in vegetation associated with livestock grazing would substantially influence habitat selection. G. griseoflavus selected vegetation patches with relatively greater cover of forage species (i.e., taxa commonly consumed) and avoided open spaces; they also selected sites with greater species richness and cover of grasses and trees. Although resource selection patterns were generally similar under both management conditions (i.e., under passive restoration and grazing), the strength of selection was greater in the grazed area. The final RSF model validated well with k-fold cross-validation (R2 = 0.61). Because of the importance of rodents in ecosystem function, management to meet their resource requirements could be an important tool for habitat restoration in degraded drylands.

Niche segregation has been proposed as the driving factor facilitating species coexistence by reducing interspecific competition. Nonetheless, although niche segregation has been widely studied, few studies have examined it in disturbed environments. Because of their dependence on mature forests, arboreal squirrels are model organisms for studying how sympatric species coexist in disturbed habitats. We examined niche segregation between Sciurus aureogaster and S. oculatus in an oak-pine forest of Pinal de Amoles, Querétaro, Mexico, disturbed by insect infestation and deforestation. We were interested in the degree of niche overlap in activity patterns, space and tree use, and feeding behavior. Because S. aureogaster has a greater geographic distribution and occurs in a wider range of habitats, we predicted that it would show wider niche values, and would be more tolerant to disturbance compared to S. oculatus. We also predicted that nests would be situated in areas with low deforestation pressure. We searched for squirrels, nests, and tree stumps while walking along dirt roads and trails, and through the dense part of the forest. Levin's measure of niche breadth and Pianka's measure of niche overlap were used to evaluate how both species segregate across resource dimensions. Number of stumps was used to evaluate deforestation pressure around nests and squirrels within 30-m-radius circles. S. aureogaster showed slightly narrower niche breath values in 5 out of 7 dimensions compared to S. oculatus. We found high niche overlap values in all dimensions examined. Both squirrel species strongly relied on pine (Pinus) trees for feeding, traveling, and nesting. S. aureogaster and S. oculatus were observed in areas with similar disturbance, and nests were situated in areas with medium deforestation pressure. Pine trees were mostly logged illegally and for forest sanitation, posing a serious threat to the persistence of arboreal squirrels within the study area.