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The European rabbit Oryctolagus cuniculusis an exotic herbivorous mammal undergoing an active phase of geographical expansion in the arid ecosystems of Argentina. The Adaptive Flexibility Hypothesis states that populations at the range edge (new populations) will exhibit greater flexibility in the use of resources compared with populations located in the range core (older populations). The objective of this work was to compare the rabbit’s use of spatial and trophic resources in relation to the establishment time of their populations. The sampling was carried out for 2 years (2017 and 2018) in sites with different establishment times for rabbit populations. Random sampling stratified by type of habitat was applied using 115 fixed strip transects of 1,000 m2laid out across the study areas. Fresh rabbit signs were recorded in each transect, and environmental and anthropic variables were measured. Our results show that the individuals from the range edge are more selective in the use of habitat than those from the range core. At the microhabitat level, we observed a pattern in the particular components of habitat use by rabbits mainly linked to food availability and proximity to water. From a trophic perspective, rabbits could show flexible adjustment to novel conditions and environments in the range edge. The variability in resource use by the European rabbit confirms its ecological flexibility, pivotal for their advance toward new environments in Argentina.

The Andes are known to be one of the most species-rich regions on Earth, with their origination promoting formation of new habitats and acting as climatic barriers. This orogenic event was structured latitudinally with 3 major segments having different formation times and with different environmental and historical conditions. The Andean region has been historically important in the evolutionary history of small mammals and is considered the region of Earth with the highest values of rodent species richness and turnover. Therefore, the region provides an excellent opportunity to evaluate mechanisms involved in structuring rodent assemblages and beta diversity patterns. Here, we assessed spatial patterns of rodent beta diversity along the Andes Mountains, with specific goals of examining patterns of turnover and nestedness as 2 recognized processes that drive species composition. We explored the role of spatial, climate, and historical factors on beta diversity patterns using geographic range maps for 432 rodent species to construct a species presence–absence matrix. We used piecewise regressions to identify latitudinal breakpoints in turnover and nestedness, and conducted multiple regressions and variation-partitioning approaches to assess the contribution of each set of postulated drivers in shaping beta diversity patterns. Beta diversity decreases from north to south. The highest turnover was located at the Northern Andes (5°N and 10°S) and western-central Andes (20°S and 35°S). Nestedness was higher below 40°S and in some areas of the western-central Andes between 15° and 20°S. Turnover and nestedness registered breakpoints coincident with the Central and Southern Andes limit. Turnover explained most of the beta diversity for all segments, although within the Southern Andes there was also some contribution of nestedness. In all segments, beta diversity was mainly explained by spatial factors with minor contributions from spatially structured climate (Northern Andes), interaction of all factors (Central Andes), and the interaction between current climate and history (Southern Andes).Beta diversity of Andean rodents decreases latitudinally, with turnover as the dominant process and nestedness with higher contribution in the Southern Andes. Beta diversity break points partially support Andean orogenic history reflected among latitudinal segments. Figure 3 of this manuscript is recommended for promoting this research.

The coexistence of ecologically similar species is facilitated by differential use of resources along habitat, diet, and/or temporal niche axes. We used feces of non-native rabbit (Oryctolagus cuniculus), hare (Lepus europaeus), goat (Capra hircus), and the native plains viscacha (Lagostomus maximus) to compare the utilization of spatial and trophic resources in an arid ecosystem of Argentina. We expected herbivores to present differential responses in the use of at least one of the niche axes (habitat and/or trophic) associated with seasonal changes in resource availability and according to the origin of the species (native, non-native). We evaluated habitat use and selection through Chi-squared goodness-of-fit tests and Bonferroni confidence intervals, and factors shaping habitat selection (particular components of the habitat type) using generalized linear mixed-effects models. We analyzed the seasonal compositions of diets, breadth of trophic niches, and dietary overlaps. The assemblage of herbivores did not segregate markedly in spatial resource use, showing that hares and goats were more generalist than rabbits and plains viscacha in the utilization of different habitat types. Native and non-native herbivores overlapped markedly in the trophic niche dimension but segregated to some degree in the use of space during wet and dry seasons. The four herbivores shared a similar diet composition. Among dietary items, grasses contributed high percentages during the wet season. Under conditions of resource limitation (dry season), the native plains viscacha differed in feeding strategy from the non-native herbivores. These results deepen our understanding of likely underlying mechanisms that allow coexistence of native and non-native herbivores in an arid ecosystem.

Environmental heterogeneity shapes the traits of natural populations, including space use and burrowing behavior. We studied the red viscacha rat (Tympanoctomys barrerae), a semifossorial rodent with patchy distribution in drylands of west‐central Argentina, to provide ecological data on habitat and burrow features of this specialist species. We collected data on 165 burrows and 55 individuals from 2017–2018 and observed correlations between different vegetation types, vegetation diversity, and physical attributes (e.g., soil hardness). A high number of individual red viscacha rats was negatively associated with herbs. The number of burrow entrances was positively associated with harder soils and negatively associated with vegetation cover. Our results suggest that the species' patchy distribution is strongly associated with environmental heterogeneity of these arid environments, and consequently provide an essential step towards conserving their populations across their geographic range. A greater number of red viscacha rats was associated with a low proportion of herbs in west‐central Argentina during 2017–2018. Burrow entrances were positively associated with soil hardness and negatively associated with vegetation cover in each site. Environmental heterogeneity could modulate abundances and burrowing of this highly specialized desert rodent.

Male-only obligate semelparity is a well-studied reproductive strategy in some Australian marsupials. This strategy has not been documented in South American species, although semelparity in both sexes occurs in some Neotropical didelphids. The fat-tailed mouse opossum, Thylamys bruchi, is an endemic species of the temperate Monte Desert, in Argentina. Seasonality and predictability of resources are two of the attributes associated with habitats where marsupial semelparity has evolved, and both are characteristic of the Monte Desert. We aimed to characterize the life-history strategy of T. bruchito explore if it can be considered a semelparous species. We studied a fat-tailed mouse opossum population for 7 years with two different capture techniques (Sherman traps and nest boxes). Thylamys bruchishowed strong seasonality in abundance, with the highest captures during summer and autumn. Reproduction and weaning coincided with the most favorable period of the year with respect to climate and resource availability. Every year we observed a single cohort with little overlap until weaning of young. After breeding, all adults disappeared from the population; however, unlike any other didelphids, males showed delayed mortality and died, along with females, after weaning. We found no evidence of survival to a second breeding season for either sex. We therefore propose T. bruchias a desert-dwelling marsupial with a semelparous reproductive strategy. Because the severity of winters may be acting as an important constraint on the energetic balance of adults in this population, we propose that challenging climatic conditions, coupled with the seasonality and high predictability of food resources, may have contributed to the evolution of the extreme reproductive strategy in this didelphid marsupial.

Viscacha rats (genus TympanoctomysYepes, 1942) are ecologically, physiologically, and behaviorally unusual octodontid rodents endemic to the Monte and Patagonian desert biomes of Argentina. The geographic ranges of the different species of Tympanoctomyshave been described in general terms but have not been associated with spatial and climate data. Within species, populations are patchily distributed and genetically distinct. We investigated the predicted distribution of Tympanoctomysand the influence of climate fluctuations on their geographic range in historical, current, and future, scenarios. Our objectives were to characterize the environmental niche of the genus, propose a paleoclimatic context for the oldest fossils, characterize the environmental niches for T. barreraeand T. kirchnerorum, and forecast potential future distributions for these taxa. Ecological niche models were constructed using occurrence records from 1941 to the present wherein we identified several precipitation and temperature variables as important predictors of the geographic distributions of the genus, and the species T. barreraeand T. kirchnerorum. Based on our models’ results, we hypothesize that the distribution of Tympanoctomyshas contracted from historical to modern times. At the species level, T. kirchnerorumlikely experienced the most dramatic change, suffering a large contraction of its historical distribution resulting in its limited present distribution. Given these findings, projected future climate fluctuations and global warming are expected to affect the distributions and persistence of these species.

Habitat partitioning is considered one of the main mechanisms of coexistence among small mammals. This is especially evident in arid environments where resources are particularly scarce. Habitat characteristics such as vegetation heterogeneity and complexity are expected to increase species coexistence, increasing the number of microhabitats that can be occupied by species with different requirements. The Andean foothills can be considered as an ecotone between the Monte and Altoandina phytogeographic provinces as they harbor species from both. Consequently more species are thought to coexist in this area. The objectives of this study were to assess the macro- and microhabitat selection of the small mammal assemblage inhabiting the Andean foothills during wet and dry season and to determine how animals segregate environmental resources to ensure their coexistence. We found that habitat selection occurs at both scales in the Andean foothills. Two species, Eligmodontia moreniand Phyllotis xanthophygus, were capable of distinguishing among macrohabitat types, whereas all species showed habitat selection at the microhabitat scale. We registered selection during both seasons, with some overlap of resource selection during the wet season and the greatest segregation of microhabitat resources during the dry season. Therefore, this work evidence that the assembly of small mammals is sensitive to habitat structure especially in dry seasons where resources are constraints due to arid conditions of Andean foothills.

Euneomysis a genus of sigmodontine rodent endemic to South America, distributed along the Andes of Argentina and Chile and in adjoining Patagonian steppe. Here, we studied specimens of Euneomysfrom different localities in the Central Andes, Mendoza Province, Argentina. Karyotypic analyses confirm the presence of a new karyomorph of Euneomys chinchilloides, the form 2n= 34, FN = 62–64. This new karyomorph differs from the form E. chinchilloideswith 2n= 36, FN = 64–66. The chromosome complement with 2n= 36 has an extra pair of small acro-telocentric chromosomes that is not present in individuals with 2n= 34. We also found small differences in molecular analyses with the mitochondrial COI gene. We recovered two monophyletic clades, one with specimens with 2n= 34 and the other one with specimens with 2n= 36, which are separated by a range of 0.7 to 1.2 % sequence divergence. Individuals from the two clades also show some morphological differences. Significant difference in the length of ear was found between the specimens with 2n= 34 and 36, and qualitative differences in the shape of the incisive foramen, the palate, and the palatine fossa were observed. The modification on fundamental and diploid number that we found between the two karyomorphs of E. chinchilloidescan be the result of tandem chromosome fusion; such rearrangements are strongly negatively heterotic and lead to reproductive isolation between differentiated populations. Thus, the integrated cytogenetic, molecular, and morphologic analyses show concordant differentiation between the two karyomorph types of the uncommon E. chinchilloidesfrom the Southern Central Andes of Argentina. The evidence presented here might reflect a recent and/or incipient allopatric speciation event. Further investigations are needed to elucidate the taxonomic and distributional status of species of Euneomys.

The wild boar, Sus scrofa, was first introduced for hunting purposes in Argentina in 1906 and presently occupies a wide range of habitats. Understanding the food habits of invasive species is important for predicting the effects of animal food consumption on the environment and on human activities, such as farming. The wild boar is an omnivorous, opportunistic species whose diet is determined by the relative abundance of different types of foods. In general, the wild boar’s diet has been widely studied in the world, both as a native and invasive species, but little is known regarding food resource selection in the Monte Desert biome. Our study assessed the seasonal variation in the diet of wild boars, as well as the nutritional quality of consumed items. Further, we determined the diet selection of this species. Diet analyses were based on faecal samples collected over two seasons (wet and dry) in 1 year. Herbs were the most frequently consumed food item, with wild boars showing a selection for them in both seasons. The wild boar uses food resources according to seasonal availability (larger trophic niche breadth under higher plant diversity, as in the wet season). In turn, within each season, it selects items of high forage quality and high carbohydrate contents. In conclusion, this foraging strategy enables wild boar to maximize energy budget through food selection in order to survive in a semi-arid environment such as the Monte Desert.The wild boar, Sus scrofa, was first introduced for hunting purposes in Argentina in 1906 and presently occupies a wide range of habitats. Understanding the food habits of invasive species is important for predicting the effects of animal food consumption on the environment and on human activities, such as farming. The wild boar is an omnivorous, opportunistic species whose diet is determined by the relative abundance of different types of foods. In general, the wild boar’s diet has been widely studied in the world, both as a native and invasive species, but little is known regarding food resource selection in the Monte Desert biome. Our study assessed the seasonal variation in the diet of wild boars, as well as the nutritional quality of consumed items. Further, we determined the diet selection of this species. Diet analyses were based on faecal samples collected over two seasons (wet and dry) in 1 year. Herbs were the most frequently consumed food item, with wild boars showing a selection for them in both seasons. The wild boar uses food resources according to seasonal availability (larger trophic niche breadth under higher plant diversity, as in the wet season). In turn, within each season, it selects items of high forage quality and high carbohydrate contents. In conclusion, this foraging strategy enables wild boar to maximize energy budget through food selection in order to survive in a semi-arid environment such as the Monte Desert.

Abstract: Studies on the diet and other aspects of the natural history of Neotropical marsupials have focused mainly on a few species from tropical and forest habitats. Research on desert marsupials, on the other hand, is almost absent outside Australia. The desert mouse opossum, Thylamys pallidior, is a small marsupial which inhabits the arid lands of Argentina, Chile, Bolivia, and Peru. In Argentina, it occurs in the Monte desert, a highly seasonal system with a heterogeneous landscape which affords a good opportunity to perform comparisons among different environmental situations. We analyzed fecal samples from 123 individuals and compared their diet among different seasons, habitat types, sexes, and ages. The diet of T. pallidior was composed of 68.7% of arthropods and 31.3% of plant material, mainly leaves (24.6%). We found no significant differences in the proportions of any main food category consumed for any of the factors analyzed. Consumption of both plant and animal material seems to be important in the diet of T. pallidior which manages to keep their proportions constant despite the strong variability and seasonality of the habitat. Contrary to most didelphid species, but similarly to most mammals of this area, leaves seem to represent an important source of food possibly because of their abundance and stability in the Monte desert. This represents the first study to focus on the diet of a Thylamys species inhabiting an arid environment.

The coexistence of desert small mammals can be explained by differences in microhabitat use, morphology, body size, diet and foraging. The aim of this study was to quantify the structure of small mammal assemblages and the seasonal fluctuations in their abundance using mark – recapture techniques in habitats of different structural heterogeneity (mesquite forest, creosotebush community, and sand dunes) in the temperate Monte desert of Argentina. Habitat heterogeneity was characterised by 10 vegetation variables. The mesquite forest and the creosotebush community showed the highest diversity and habitat heterogeneity. The relative abundance of each species underwent remarkable variations between habitats. The sigmodontinae rodents Graomys griseoflavusand Eligmodontia typuswere the dominant species in the mesquite forest and sand dunes, respectively, whereas no dominant species was observed in the creosotebush habitat. Abundance varied throughout the year, reaching maximum density in autumn and spring.

Tympanoctomys barreraeis a monotypic octodontid. This species is endemic to the desert area of central-western Argentina where it is restricted to salt basins and sand dunes. T. barreraeshaves off the epidermis ofAtriplexleaves before consuming them. This reduces electrolyte intake. Like two other unrelated salt-flat dwelling rodents, Dipodomys micropsand Psammomys obesus, T. barreraeuses the lower incisors to scrape the hypersaline tissue away from Atriplexleaves, only it spends less time in the shaving process. This difference could be accounted for by a peculiar anatomical structure: two bundles of stiff hairs on either side of the mouth that may be functionally similar to a second set of lower incisors.

Two large groups of rodents inhabit South America: the hystricognaths and the murids. It has been postulated that while the former show a high degree of specialization to desert habitats, the murids are not well adapted to xeric conditions. We studied the renal structure and function of selected desert-dwelling murid and octodontid (hystricognath) rodents from Argentina to evaluate levels of adaptation to aridity. Our results show that the murids Salinomys, Andalgalomys, Calomysand Eligmodontiahave the highest renal indices and urine concentration among Argentine desert rodents. The octodontid Tympanoctomys barreraeshows higher renal indices and urine osmolarity than those of its close relativesOctomys mimaxand Octodontomys gliroides. We compare the renal traits of the Argentine desert murids with those of other world-desert rodents such as North American heteromyid rodents. The results show that these Argentine murid rodents posses renal adaptations to conditions which are as impressive as those of both octodontids and the classic desert-adapted heteromyids.

Octodontid rodents have a long evolutionary history in arid landscapes of South America. The red vizcacha rat, Tympanoctomys barrerae, is a monotypic, micro-endemic species that inhabits salt pan-sand dune habitats in west-central Argentina. Its natural history is almost unknown. We present an analysis of the ecology, morphology, behavior, and physiology of the red vizcacha rat and assess the overall degree of convergence of this species with rodents that inhabit similar habitats in different deserts. Our results show that Tympanoctomys barreraeis highly adapted to salt flat basin habitats. Its diet of halophytic vegetation with a high salt content, and physiological and anatomical traits related to salt consumption, are similar to those found in some members of the families Heteromyidae (Dipodomys microps) of North America, and Muridae (Psammomys obesusand Rhombomys opimus) of Africa and Asia. Similarities include feeding behavior, diet composition, kidney morphology, and urine concentration, among other traits. Tympanoctomys barreraeis more similar to these desert rodents than it is to confamilials that do not feed on halophytes.

Use of vegetation patches by small mammals in the arid Andean foothills of Argentina was studied. The species showed relatively high habitat specialization. Microhabitat use differed between the dominant species, the rodentsCalomys musculinusandGraomys griseoflavus. Patterns of habitat occupancy accord with their distribution at the plot or the geographical scales. Species affinities for vegetation variables suggest that habitat structure is an important factor in structuring the small mammal communities of the Andean foothills.

The ‘algarrobo’Prosopis flexuosais an important food resource in the Monte Desert of Argentina. Native, domestic, and exotic mammals consume the fruit of this legume and disperse the seed through faeces. In the present study we analyse the effect that different dispersal agents (cattle, horse, European wild boar, rodents, gray fox) have on seed damage, viability, and germination. Cattle increase germination at the expense of reduced viability, whereas horses maintain viability but do not contribute to a prompt germination response. Among native mammals, the gray fox maintains seed viability without increasing germination, whereas rodents affect seed viability but enhance germination rates. The European wild boar, however, damages all of the seeds it consumes.

Temperate and semi-arid regions of Argentina are undergoing rapid habitat conversion as a result of several human activities (i.e. grazing, logging, agriculture, etc.). These arid ecosystems contain many endemic species and have played an important role in the evolution of South American biota. The Man and Biosphere Reserve of Ñacuñán (12,800ha) is located in the central region of the lowland Monte Desert. The reserve is a stand within a highly disturbed matrix characterized by deforestation (i.e. mesquite,Prosopis)and overgrazing. Major vegetational and animal communities recovered after the reserve was fenced in 1972, and Ñacuñán thus provides critical data describing the recovery of biotic and abiotic components of the Monte Desert when anthropogenic assaults are minimized. Indeed, the Reserve of Ñacuñán protects many distinctive habitats of the Monte Desert, including mesquite forest, or algarrobal, and several representative animals of the South American biota (i.e. tinamous, rhea, marsupials, edentates and caviomorph rodents). Several research projects on community ecology, herbivory, disturbances, ecology and ecophysiology have been or are being developed in the reserve. Although the town of Ñacuñán lies within the reserve, the link between the research community and the local people has not been strong, persistent or effective. The reserve is the most important site in Argentina for monitoring the ecological health of the Monte Desert and for developing indicators of desertification. Its potential is great for long-term ecological research and for strengthening the infrastructure of science. Sustainable development in the next millennium requires integrating the activities of the research, local people, ranch landowners and governmental sectors so as to infuse science-based proposals into management and conservation initiatives.

Biodiversity patterns are the result of the interaction of numerous contemporary factors and historical opportunities for allopatric speciation. Several hypotheses regarding climatic features and topographic characteristics have been reported as determinants of species richness along elevation gradients. However, how these factors interact to shape small mammal species richness along the dry Andes ecosystem is not well understood. The objectives of this paper were to analyze patterns of species diversity along the central dry Andes, and to evaluate how climatic and topographic factors explain diversity patterns. Our results showed a positive and monotonie relationship between small mammal species richness and altitude, whereas abundance patterns showed a midelevation peak. Climate and topography were the most important predictor variables explaining small mammal species richness and abundance patterns in the Andes. This study underlines the role of the Andes in promoting and sustaining biodiversity, as well as the need to encourage conservation planning in mountain ecosystems.

Space use in deserts usually has been considered only along the horizontal dimension; however, vertical structure could be an important variable for habitat segregation among small mammal species. Our study assessed the use of vertical space by small mammals of the Monte Desert by live-trapping animals at different heights. We recorded 1,336 captures of 4 rodent and 1 marsupial species in 27,600 trap nights. All 5 species were captured on the ground and in tree layers, but only the gray leaf-eared mouse (Graomys griseoflavus) and the desert mouse opossum (Thylamys pallidior) used vertical space appreciably. G. griseoflavus used the arboreal space independently of habitat, plant species, or branch diameter, whereas T. pallidior showed a more selective behavior, being present at greater heights and on large-diameter branches of Prosopis trees. All rodent species used lower more than higher parts of arboreal strata. They used vertical space more or only during the dry season when resource availability is low. Our study suggests that vertical structure offers greater opportunities to acquire resources when these are scarce and plays a role in the coexistence of small desert mammals.

Much of South America consists of diverse arid and semiarid regions characterized by high mammal endemism as a result of a complex interplay between place and lineage histories. In this review we summarize and highlight several biogeographical and ecological features of the small mammals of South America drylands, with special focus on the Monte Desert biome. We provide information on population characteristics, community structure, food and habitat use, and responses to disturbances. Major findings at different scales include the distinctiveness and high species turnover across South American drylands and Monte Desert ecoregions; synchronous population fluctuations with high variability between years; herbivory and omnivory as dominant trophic strategies; community structure organized through habitat and food segregation; and the importance of a landscape mosaic of grazed and ungrazed areas for maintenance of small and medium-sized mammal diversity.