This Special Feature honors Robert M. (Bob) Timm, who was recognized by the American Society of Mammalogists in 2017 with the Joseph Grinnell Award for his contributions to education in mammalogy. Bob has made great educational contributions through formal classroom and field instruction, interactions with researchers, public outreach, and mentorship of graduate students. Bob also has promoted equity and human diversity in mammalogy and joyfully assisted international colleagues (especially Latin Americans). In this Festschrift, many of his Ph.D. students offer the results of their recent mammalian research on topics as diverse as taxonomy and species identification, functional morphology, and biogeography and conservation on an environmentally dynamic planet.

We describe a new species of Crocidura (Soricidae) from Sulawesi Island, Indonesia, documenting its novelty with both genetic and morphological characters. The new species is widespread on the island, with vouchered records from nine general localities distributed among five of the island's areas of endemism. Morphologically, the new species is readily distinguished from all other described Sulawesi Crocidura by its intermediate body size, gray pelage, and long, hairy tail. The new species was mainly captured in pitfalls placed in the ground, but we also obtained evidence that it readily climbs trees and may be scansorial in its locomotor habits. Populations of the new species sampled from across the island are closely related, separated by < 0.02 uncorrected mitochondrial p-distances. The new species is one member of an endemic radiation of shrews on Sulawesi now known to contain six valid species and several undescribed species, all within the genus Crocidura. Resolution of species limits and phylogenetic relationships in this radiation is hindered by habitat loss at type localities, historical designation of new species using very small sample sizes, and a lack of genetic data from type specimens.

Kami mendeskripsikan spesies baru Crocidura (Soricidae) dari Pulau Sulawesi, Indonesia, sekaligus mendokumentasikan keunikan karakter secara genetik maupun morfologi dari spesies tersebut. Spesies baru ini tersebar luas di Pulau Sulawesi, diketahui berdasarkan spesimen yang berasal dari sembilan lokasi umum yang tersebar di lima kawasan endemik di pulau tersebut. Secara morfologi, spesies baru ini dapat dibedakan dari spesies Crocidura lainnya dari Sulawesi berdasarkan ukuran tubuh yang sedang, rambut tubuh berwarna abu-abu, dan ekor yang panjang dan berambut. Spesies baru ini sebagian besar diperoleh dari perangkap sumuran yang ditanam didalam tanah, selain itu kami juga mendapatkan bukti bahwa spesies ini mampu memanjat pohon dan kemungkinan memiliki perilaku sebagai pemanjat. Beberapa populasi spesies yang dikoleksi dari Sulawesi ini mempunyai kekerabatan yang dekat, hanya dipisahkan oleh jarak proporsi DNA mitokondria (tidak terkoreksi) sebesar < 0.02. Spesies baru ini merupakan salah satu anggota dari suatu kelompok radiasi endemik cecurut di Sulawesi yang sampai saat ini diketahui terdiri atas enam spesies yang valid, dan beberapa spesies yang belum dideskripsikan, semuanya termasuk didalam genus Crocidura. Kepastian dalam menetapkan batasan jarak antar spesies dan hubungan kekerabatan genetik dari radiasi kelompok cecurut di Sulawesi terkendala oleh kerusakan habitat pada lokasi spesimen tipe, sejarah penamaan spesies yang hanya berdasarkan sampel yang sedikit, dan keterbatasan data molekuler dari spesimen tipe.

With more than 1,400 species of bats described worldwide, the order Chiroptera is second only to rodents in ecological and taxonomic diversity. Bats play critically important roles in natural systems as seed and pollen dispersers, predators of invertebrates and vertebrates, and sanguinivores. The Central American countries of Costa Rica and Nicaragua have at least 123 species of bats (in nine families and 66 genera), or nearly 10% of the world's known species. Because of the importance of proper species identification for ecological and systematic studies and conservation efforts, we present a dichotomous key to the bats of this region. Our goal is the positive, in-hand identification of living bats that may be released unharmed after identification. Identifying Neotropical bats and understanding the taxonomic changes that affect the names used for the various species over time can be a challenge. This key includes the 123 species known to occur in Costa Rica and Nicaragua as well as three that are expected to occur in these countries but which have not yet been recorded. We provide illustrations of key characters useful for differentiating bats to species and updated taxonomic notes to assist the reader in assessing the literature.

The clade comprising the soricid tribes Blarinellini (Blarinella) and Blarinini (Blarina and Cryptotis) is notable within the Soricidae (Eulipotyphla) for the large proportion of reportedly semifossorial species. To better define locomotor modes among species in these two tribes, we quantified purported locomotor adaptations by calculating 23 functional indices from postcranial measurements obtained from museum specimens of Blarina and Blarinella and published measurements for 16 species of Cryptotis. We then analyzed relative ambulatory–fossorial function of each species using principal component analyses and mean percentile rank (MPR) analysis of the indices. Species within the Blarinellini–Blarinini clade exhibit a graded series of morphologies with four primary functional groupings that we classified as “ambulatory,” “intermediate,” “semifossorial,” and “fossorial.” To obtain a preliminary overview of evolution of locomotor modes in this group, we mapped MPRs on a composite phylogeny and examined the resulting patterns. That analysis revealed that the most recent common ancestor of the Blarinellini–Blarinini clade most likely had an intermediate or semifossorial locomotor morphology. Individual subclades subsequently evolved either more ambulatory or more fossorial morphologies. Hence, evolution of locomotor traits within this clade is complex. Multiple shifts in locomotor mode likely occurred, and no single directional tendency is apparent either among the major modes or in levels of complexity.

Movement by mammals generally increases with body size, described by a positive exponent scaling with either home range area or day range distances. Below ca. 100 g, however, interspecific comparisons suggest a negative scaling, increasing movement with decreasing body size. Such a pattern is expected from the rising costs of thermoregulation below ca. 100 g, implying that it should also be observed in intraspecific comparisons. We tested this hypothesis by investigating the scaling exponent of daily home range with body mass for a small (< 100 g) marsupial, the gray slender mouse opossum, Marmosops incanus. We tracked 85 opossums (56 M, 29 F) with a spool-and-line device between August 1998 and October 2005 in the Serra dos órgãos National Park, a region of Atlantic Forest in the State of Rio de Janeiro, Brazil. Individual paths were mapped and daily home ranges quantified by the minimum convex polygon encompassing each path. We formulated linear models and compared them using Akaike information criteria. The best-supported model for females had only climatic season as a main determinant of daily home range, whereas the best model for males had body mass and reproductive season as the main effects. As predicted, the scaling exponent of daily home range with body mass of males was negative, in contrast with positive intraspecific exponents for opossums > 100 g estimated in a previous study. The inversion in scaling relationships around 100 g in opossums supports the rising costs of thermoregulation as the main cause of this general pattern in mammals. Effects of body mass are generally weak in intraspecific comparisons, but might still be detected after standardizing other effects, opening new possibilities for testing macroecological models at smaller scales.

Island biogeography theory (IBT) explains and estimates large-scale ecological patterns among islands and isolated habitat patches. Specifically, IBT predicts that the number of species per habitat patch differs as a function of area and isolation as a result of local colonization and extinction. Accurate estimates of species richness are essential for testing predictions of IBT, but differences in detectability of species can lead to bias in empirical data. Hierarchical community models correct for imperfect detection by leveraging information from across the community to estimate species-specific occupancy and detection probabilities. Using the fragmented Ozark glades as our model system, we constructed a hierarchical community model to 1) estimate site-level and regional species richness of small mammals while correcting for detection error, and 2) determine environmental covariates driving occupancy. We sampled 16 glades in southwestern Missouri in summer 2016–2017 and quantified mammal community structure within the glade network. The detected species pool included eight species, and the model yielded a regional species estimate of 8.6 species, with a mean of 3.47 species per glade. Species richness increased with patch area but not isolation, and effects of patch shape varied between species in the community.

Quaternary climatic oscillations affected species distributions worldwide, creating cycles of connectivity and isolation that impacted population demography and promoted lineage divergence. These effects have been well studied in temperate regions. Taxa inhabiting mesic montane habitats in tropical ecosystems show high levels of endemism and diversification in the distinct mountain ranges they inhabit; such a pattern has commonly been ascribed to past climatic oscillations, but few phylogeographic studies have tested this hypothesis. Here, we combine ecological niche models of species distributions with molecular data to study phylogeographic patterns in two rodents endemic to the highlands of Costa Rica and western Panama (Reithrodontomys creper and Nephelomys devius). In so doing, we apply a novel approach that incorporates a basic ecological principle: the expected positive relationship between environmental suitability and population abundance. Specifically, we use niche models to predict potential patterns of population connectivity and stability of different suitability levels during climatic extremes of the last glacial–interglacial cycle; we then test these predictions with population genetic analyses of a mitochondrial and a nuclear marker. The detailed predictions arising from the different levels of suitability were moderately to highly congruent with the molecular data depending on the species. Overall, results suggest that in these tropical montane ecosystems, cycles of population connectivity and isolation followed a pattern opposite to that typically described for temperate or lowland tropical ecosystems: namely, higher connectivity during the colder glacials, with isolation in montane refugia during the interglacials, including today. Nevertheless, the individualistic patterns for each species indicate a potentially wide gamut of phylogeographic histories reflecting particularities of their niches. Taken together, this study illustrates how phylogeographic inferences may benefit from niche model outputs that provide more detailed predictions of connectivity and finer characterizations of potential refugia through time.

A set of 182 populations of 76 mammal species in the United States and Canada, examined in natural conditions with minimized disturbances or management effects, shows that responses to climate change include negative responses, such as elevational range contractions, upward shifts and decreases in abundance, positive responses, such as range expansions, and no detectable responses. Responses vary among and within mammal species but many are correlated with species traits, particularly the responses linked to high extinction risks (= climate change risk: decreases in population sizes, range contractions, local extirpations). The traits showing the strongest links to differential responses to climate change are 1) body size—large mammals respond more often and most negatively to climate change, 2) activity times—few mammals with flexible active times respond to climate change, and 3) spatial distribution—high-latitude and high-elevation mammals responded more often to climate change. Using these traits and two approaches to trait weighting, I modeled the relative climate change risk for all 328 terrestrial, nonvolant mammal species in the United States and Canada across 10 levels of risk (low = 1–2, moderate = 3–4, moderate-high = 5–6, high = 7–8, very high = 9–10). The models predicted that 15% of these mammalian species are in the high- and very high-risk categories, including species from most orders. Many mammal populations and species listed as of conservation concern due to other human impacts by national or international agencies are also predicted by my models to be in the higher categories of climate change risk. My intention for these models is to clarify for managers and researchers which, where, and how mammals are responding to climate change relatively independent of other anthropogenic stressors (e.g., large-scale habitat change, overhunting) and to provide a preliminary assessment of species most in need of careful monitoring for climate change impacts.

The rise of the Panamanian Isthmus 3–4 million years ago enabled the first dispersal of mammals between North and South America in what is known as the Great American Biotic Interchange. Modern deforestation threatens the historic forest connectivity and creates new habitat for open-country species, as documented by recent expansions of North American coyotes (Canis latrans) and South American crab-eating foxes (Cerdocyon thous) into Central America. We used camera traps to map the expansions of these species into eastern Panama and found that, by 2015, coyote populations had colonized most agricultural area west of Lago Bayano. Most of our camera arrays east of this point documented crab-eating foxes, and evidence from roadkills showed some foxes had advanced farther west, but we never documented both species at the same camera-trap array, suggesting the possibility of fine-scale spatial avoidance. We used a data fusion approach to build species distribution models combining our camera surveys with records from the literature and roadkill. While the auxiliary data improved the predictive accuracy for both species, few clear habitat patterns emerged, which might reflect the generalist tendencies of these canids, or the fact that both are in the early stages of colonizing the region. Camera-trap photos showed that both species were nocturnal and revealed some dog-like morphology in coyotes, which could indicate their recent hybridization with dogs (Canis familiaris). Our continued monitoring of the Darién documented single coyotes moving through the western edge of the area in 2016 and 2018. This leaves only the great Darién forests between coyotes and South America. If deforestation continues in the region, these two invasive canids could represent the first of a new, Not-So-Great American Biotic Interchange, where generalist species adapted to human disturbance cross continents and threaten native biota.

We related presence and burden of stomach nematodes to body mass and reproductive allocation in hispid cotton rats (Sigmodon hispidus) from two long-running field studies in Virginia (1983–1984, n = 286; and 1988–1990, n = 425) and one from Georgia 1987–1989 (n = 459). Eighty percent of rats from the earlier Virginia sample were infected, with mean nematode mass of 1,311 mg. In the later samples, 23% (Virginia) and 33% (Georgia) were infected with mean nematode mass of 493 and 769 mg, respectively. Presence of nematodes was positively correlated with host body length for each sex in each sample. We used analysis of covariance to examine length-adjusted residuals for presence of nematodes and mass of nematodes for association with somatic and reproductive response variables. Both body and reproductive masses were either positively associated or not related to nematode presence in the two low-prevalence samples, and either negatively associated or not related to nematode presence in the high-prevalence sample. No relationships were detected between host mass and nematode mass per host in either sex in any sample. There was no effect of nematode presence on litter size of pregnant females, but there was a positive effect of nematode mass on litter size in Georgia. Recent theory provides several possible explanations for such neutral-to-positive effects of stomach nematodes on host fitness, including the evolution of host tolerance to the parasites, fecundity compensation by the hosts, and positive effects on host health via immune modulation.

The long-tailed shrew, Sorex dispar Batchelder, 1911, and Gaspe shrew, S. gaspensisAnthony and Goodwin, 1924, from the Appalachian Mountains of North America have been characterized as genetically highly similar, and that one is morphologically a clinal variate of the other, i.e., there is a single species. I measured 24 characters of the skull on 196 shrews from throughout the range of the species. Geographic variation in skull shape and size was not gradual or continuous, but abrupt. These abrupt changes in morphology are associated with major water barriers, primarily the Connecticut River, middle Saint John River, and the Strait of Canso, which separates mainland Nova Scotia from Cape Breton Island. The morphological analyses presented here and previous genetic studies indicate that S. dispar and S. gaspensis are likely conspecific. Shrews with the largest skull occur from North Carolina north to Vermont and are referable to S. d. dispar with S. d. blitchi as a synonym. Shrews from New Hampshire northeast to southern New Brunswick and mainland Nova Scotia have a medium-sized skull and are referable to a new subspecies. Those from northern New Brunswick, Gaspe Peninsula of Quebec, and Cape Breton Island have a small skull and are referable to S. d. gaspensis. The skull morphology of S. d. gaspensis and the new subspecies are more similar to each other than to S. d. dispar. Results of this study differ from those of previous morphological studies because measurement error and within-group variation were reduced, which allowed for visibility of otherwise “hidden” between-group differences, or geographic variation.

Chaetodipus nelsoni occurs on rocky substrates across the Mexican Altiplano. We investigated phylogeographic diversity within the species using morphologic, karyotypic, and molecular data. Data from nuclear (AFLP) and mitochondrial DNA support three distinct genetic groups with minimal substructuring coincident with biogeographic barriers previously identified in the Chihuahuan Desert and drainage basins of the Altiplano. We examined the morphological and karyotypic data in light of the molecular data. The results support recognition of three species within the currently accepted widespread C. nelsoni: 1) C. nelsoni restricted to a distribution centered on the El Salado River Basin; 2) elevation of C. n. collis to species, with two subspecies: one centered on Trans-Pecos Texas, the other on the Mapimí Basin (new subspecies); and 3) recognition of a new species, C. durangae, centered on the Nazas Basin and upper Río Mezquital drainage.

Miniopterus schreibersii is a cave-dwelling bat species with a wide distribution in the western Palearctic spanning southern and central Europe, North Africa, Anatolia, the Middle East, and the Caucasus. We investigated the social structure and its effects on the genetic makeup of this species, using 10 nuclear microsatellite markers and a partial fragment of the mitochondrial cytochrome b gene. Samples were examined from the species' entire circum-Mediterranean range. Local structuring that was previously detected among populations of M. schreibersii using mitochondrial markers was not observed for microsatellite markers, indicating male-biased dispersal for the species. Some support was found for postglacial expansions in Europe, with Anatolia potentially acting as the primary refugium during the Last Glacial Maximum (LGM). However, support for this hypothesis is not as strong as that previously detected using mitochondrial DNA markers. This is likely due to the diminishing effect of male-mediated dispersal, replenishing the nuclear diversity faster than the mitochondrial diversity in regions that are relatively far from the glacial refugia.

Myotis lavali was described from the M. nigricans complex based on museum specimens from the Caatinga of northeastern Brazil. Current records of the species from about 10 localities suggest that M. lavali seems to occur throughout the South American dry corridor, with peripheral records in the Atlantic Forest. Based on new distribution records, we assess if M. lavali is endemic to the South American dry diagonal corridor through species distribution modeling using an ensemble approach. We obtained 35 occurrences for the species and built a consensus scenario based on 12 algorithms to model its distribution. Even using different thresholds to assign presence and absence of M. lavali, 95–99% of its predicted distribution is within the dry corridor, with few areas in the boundary of the Atlantic Forest, especially in deciduous forests. Therefore, our results support that M. lavali is indeed very likely restricted to the dry diagonal and, although it occupies forested areas, the core of its distribution lies in the Caatinga and in the Cerrado regions of Brazil.

The extrinsic factors that most influence animal activity are weather and light conditions, which can be assessed at hourly, monthly, and even lunar-cycle timescales. We evaluated the responses of tropical aerial-insectivorous bats to temperature, rainfall, and moonlight intensity within and among nights. Temperature positively affected the activity of two species (Cormura brevirostris and Saccopteryx bilineata). Moonlight reduced Myotis riparius activity and increased the activity of Pteronotus rubiginosus and S. leptura. Rainfall can promote an irregular activity peak during the night compared to nights without rainfall, but the bats in our study were not active for a longer time after a rainfall event. Our findings indicate that moonlight and temperature are the variables with the highest impact on the activity of tropical insectivorous bat species and that some species are sensitive to small variations in rainfall among and within nights.

The ecology, and particularly the diet, of treeshrews (order Scandentia) is poorly understood compared to that of their close relatives, the primates. This stems partially from treeshrews having fast food transit times through the gut, meaning fecal and stomach samples only represent a small portion of the foodstuffs consumed in a given day. Moreover, treeshrews are difficult to observe in the wild, leading to a lack of observational data in the literature. Although treeshrews are mixed feeders, consuming both insects and fruit, it is currently unknown how the relative importance of these food types varies across Scandentia. Previous study of functional dental morphology has provided an alternative means for understanding the diet of living euarchontans. We used dental topographic metrics to quantify aspects of functional dental morphology in a large sample of treeshrews (n = 58). We measured relief index, Dirichlet normal energy, and three-dimensional orientation patch count rotated, which quantify crown relief, occlusal curvature, and complexity, respectively. Our results suggest that treeshrews exhibit dental morphology consistent with high levels of insectivory relative to other euarchontans. They also suggest that taxa such as Dendrogale melanura and Tupaia belangeri appear to be best suited to insectivory, whereas taxa such as T. palawanensis and T. gracilis appear to be best adapted to frugivory. Our results suggest that Ptilocercus lowii is characterized by a dentition better adapted to insectivory than the early primate Purgatorius. If P. lowii represents a good modern analogue for primitive euarchontans, this contrast would support models of primate origins that include a shift to greater frugivory.

Spatial relationships among conspecifics can provide insights into numerous aspects of social behavior. Spatial data may be particularly important for characterizing the behavior of difficult-to-study species such as subterranean rodents, direct observations of which are challenging. To characterize the social organization of the cururo (Spalacopus cyanus), a subterranean species in the rodent family Octodontidae, we used radiotelemetry to quantify spatial relationships within populations of this species located in Parque Nacional Bosque Fray Jorge and Santuario de la Naturaleza Yerba Loca, Chile. Specifically, we sought to determine if adults in this diurnal species share burrows and subterranean nests, the two criteria typically used to identify subterranean rodents as social. Analyses of radio fixes collected during February–March 2003 revealed that cururos at both Fray Jorge and Yerba Loca shared nighttime nest sites; cluster analyses of these data identified multiple spatially distinct subsets of adults in each population. Overlap of minimum convex polygons constructed from radio fixes collected during daylight hours suggested burrow sharing by animals in both populations. Cluster analyses of overlap values revealed the same spatially distinct groups of individuals identified from analyses of nest sharing; in addition, these analyses revealed one cluster of animals in each population that was not evident from analyses of nighttime data. Collectively, these results confirm that cururos are social, with adults in both study populations sharing burrow systems and communal nests. Our findings add to the growing understanding of social organization in octodontid rodents and reveal a new system for comparative studies of the ecology and evolution of behavioral variation in burrow-dwelling mammals.

As humans continue to alter natural habitats, many wild animals are facing novel suites of environmental stimuli. These changes, including increased human–wildlife interactions, may exert sublethal impacts on wildlife such as alterations in stress physiology and behavior. California ground squirrels (Otospermophilus beecheyi) occur in human-modified as well as more pristine environments, where they face a variety of anthropogenic and naturally occurring threats. This makes this species a valuable model for examining the effects of diverse challenges on the physiology and behavior of free-living mammals. To explore potential sublethal effects of habitat modification on O. beecheyi, we compared body masses, behaviors, and fecal glucocorticoid metabolite (FGM) levels for free-living squirrels in human-disturbed versus undisturbed habitats. Prior to these analyses, we validated the use of FGMs in this species by exposing captive O. beecheyi to pharmacological and handling challenges; both challenges produced significant increases in FGMs in the study animals. While FGM responses were repeatable within captive individuals, responses by free-living animals were more variable, perhaps reflecting a greater range of life-history traits and environmental conditions within natural populations of squirrels. Animals from our human-disturbed study site had significantly higher FGMs, significantly lower body masses, and were significantly less behaviorally reactive to humans than those from our more pristine study site. Thus, despite frequent exposure of California ground squirrels to human impacts, anthropogenic stressors appear to influence stress physiology and other phenotypic traits in this species. These findings suggest that even human-tolerant mammalian species may experience important sublethal consequences due to human modifications of natural habitats.

Populations of large carnivores are declining in many parts of the world due to anthropogenic activity. Some species of large carnivores, however, are able to coexist with people by altering their behavior. Altered behaviors may be challenging to identify in large carnivores because these animals are typically cryptic, nocturnal, live at low densities, and because changes in their behavior may be subtle or emerge slowly over many years. We studied the effects of livestock presence on the movements of one large carnivore, the spotted hyena (Crocuta crocuta). We fit 22 adult female spotted hyenas with GPS collars to quantify their movements in areas with and without livestock or herders present, in and around a protected area in southwestern Kenya. We investigated anthropogenic, social, and ecological effects on the speed of movement, distances traveled, long-distance movements, and extraterritorial excursions by spotted hyenas. Hyenas living primarily within the protected area, but in the presence of livestock and herders, moved faster, traveled over longer distances, and were more likely to be within their territories than did conspecifics living in areas without livestock and herders. Hyenas of low social rank were more likely than hyenas of high social rank to engage in long-distance travel events, and these were more likely to occur when prey were scarce. The movement patterns of this large African carnivore indicate a flexibility that may allow them to persist in landscapes that are becoming increasingly defined by people.

Identifying landscape features and processes that facilitate the persistence of populations is particularly important for invasive mammal species, because it can focus management interventions on relatively small areas. We used camera traps to test predictions concerning the relative abundance of invading chital deer (Axis axis) on seven cattle ranches in northern Australia: that abundance of chital deer would be highest near permanent water and near homesteads, and that dingoes (Canis dingo) reduce abundance of chital deer. Distance from the nearest homestead determined deer abundance (as indexed by images per camera-day), with negligible abundance > 4 km from homesteads. In contrast, distance from homestead did not predict abundance of feral pigs (Sus scrofa), macropods, or dingoes. Abundance of chital deer also declined with increasing distance from water, as did feral pig abundance. There was no relationship between either macropod or dingo abundance and distance to water. The abundance of chital deer was unaffected by dingo abundance, but 75–100% of dingo scats collected within 1 km of homesteads contained chital deer. The high abundances of chital deer near homesteads are likely due to increased food quality or quantity, or protection from dingoes, but these hypotheses require further testing. We conclude that homesteads and permanent water are important determinants of the distribution and abundance of invasive chital deer in northern Australia (i.e., they are “invasion hubs” for this species). Our results suggest that, during the dry season, managers should survey for and attempt to control chital deer within 4 km of homesteads and within 3 km of water.

Given the phylogenetic proximity and similar morphology of opossums (Didelphis spp.), they are good models to study factors that facilitate or impede coexistence of syntopic species and to better understand how landscape changes affect species distributions and habitat use. For this purpose, we used single-species and two-species occupancy models using records of D. albiventris, considered the dominant species, and D. aurita from a camera-trap survey conducted in an agricultural and conservation landscape in the Atlantic Forest of Argentina. We evaluated which factors determined the probability of species occurrence: habitat preferences or interspecific relationships. We also estimated the overlap in daily activity patterns between species, and evaluated changes in D. aurita activity in response to the occupancy probability of D. albiventris. Didelphis aurita had higher occupancy probabilities in the continuous native forest, whereas D. albiventris had higher occupancy probabilities in fragmented forests with less complex and more open vegetation structure, and greater proximity to buildings. Both opossums were almost absent in pine plantations. Results of the co-occurrence models and the overlap in diel activity suggest that D. aurita is not avoiding D. albiventris. Occurrences of these two opossums most probably reflect different adaptations by each species to different habitats, and competitive interactions seem to play a minor role in shaping their current distributions. Didelphis albiventris may be replacing D. aurita mainly as a result of changing environmental conditions, which become unfavorable to the latter but promote the creation of new habitat for the former.

We generated potential distribution models for 14 sigmodontine rodent species that inhabit the Andean–Patagonian forest region and adjacent areas, and retrieved the main climatic variables responsible for these models. Our main objective was to compare these climatic variables and the distribution patterns generated for each species, and explore the effects of the physical environment in shaping the composition of rodent communities in the area. We retrieved a total of 1,215 records of species presence from 580 sites. Maxent was used to generate potential distribution models for the 14 rodent species studied. We used a total of 20 variables obtained from the WorldClim database, including elevation and 19 bioclimatic variables, in addition to normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI). Our results showed a clear discrimination between two groups of rodents, one concentrated in the western part of our study area, with more humid climate and a rugged mountainous and discontinuous habitat, and another inhabiting the eastern, drier part of our study area, which appears to be more uniform in habitat characteristics. These groups showed a mosaic of phylogenetically non-related species from different tribes, that probably arrived or expanded into Patagonia during the last millennia. The overlap of all models showed the forest-steppe ecotone east of Nahuel Huapi Lake and south to –43° latitude as the area with the highest species richness (8–11 species). All species showed a high correspondence with temperature and precipitation that define patterns at a landscape scale, with little to very little information contained in the typical vegetation variables that would define local conditions.

The long-tailed pygmy rice rat Oligoryzomys longicaudatus (Rodentia, Cricetidae) experiences marked population density fluctuations. This species is the major reservoir of the Andes orthohantavirus associated with the hantavirus pulmonary syndrome in southern Argentina, and information on dispersal patterns at different population densities, or differences in dispersal between the sexes during those periods, could contribute to understanding risk of viral transmission among individuals. We examined the spatial genetic structure of O. longicaudatus at a local scale to elucidate how variation in population density influences dispersal patterns. Effective dispersal levels were estimated through spatial genetic autocorrelation (SGA) analyses in periods of different density, and for females and males separately, within an area of 510 × 180 m, using seven microsatellite loci. In autumn (high-intermediate and intermediate densities), SGA was primarily determined by females, which show philopatric behavior in defense of their nests and newborns. In summer (low density), neither sex showed SGA, which could be due to spacing behavior combined with high recruitment rates among adjacent environments. At high-intermediate densities, females remained close to each other, contracting their home ranges. These established individuals would “fence” the area, preventing the immigration of individuals from proximate areas, until population density declines again. We detected differential patterns of effective dispersal for both sexes in different stages of the annual and inter-annual population phases of O. longicaudatus. Since high levels of gene flow were reported for both sexes in summer and for males in all analyzed seasons, the transmission risk of diseases such as hantavirus pulmonary syndrome would be high at a local scale.