María Ana Dacar

Geographic and seasonal variability in feeding behaviour of a small herbivorous rodent

Foraging strategies have traditionally been modelled as a result of food selection in response to one factor, as for instance resource availability, deterrent compounds or nutrients. Thus, a trade-off is assumed between plasticity (generalist strategy) and efficiency (specialist strategy). Nevertheless, several studies have demonstrated that animals cope behaviourally with food supply variation. For instance, desert-dwelling rodents partially compensate for nutritional bottlenecks through diet selection. The aim of our study was to test how foraging behaviour matches spatial and temporal variations in the trophic environment and how modelling hypotheses help us to understand the resultant foraging strategy. Our animal study model was the small cavy Microcavia australis, a widely distributed herbivorous rodent. Fieldwork was carried out in four places, in wet and dry seasons. We found significant differences in plant cover, plant diversity and niche breadth, and diet selection revealed a complex foraging strategy. M. australis shows a behavioural repertoire that exceeds single-criterion categories; therefore, we appeal to theoretical models that consider ecological and physiological perspectives. We classified the small cavy as a facultative specialist displaying a thoroughly opportunistic strategy based on the plasticity of the behavioural phenotype. We finally discuss the evolutionary relevance of our results and propose further investigation avenues.

New eco-morphological-behavioural approach of the chinchilla rats in the pre-Andean foothills of the Monte Desert (Argentina)

This study characterizes the ecology, behaviour and morphology of populations of Abrocoma schistacea and A. uspallata in north-western Argentina. We carried out live-trapping, tagging and recapture during 2006–2008. Burrow structure and vegetation were described. Diet composition and the activity of chinchilla rats were defined. Both species inhabit rock crevices in the pre-Andean foothills of the Monte Desert. Some of their morphological specializations for saxicolous life, such as foot pads for better traction on rocky surfaces and reduced nails, are convergent with those of other saxicolous species. Both species appear to be diurnal, with activity peaking in the early morning. Dietary analyses suggest trophic specialization by both species. Density of A. schistacea was of 0.15 ± 0.06 individuals ha−1; with individuals living in groups of 3–4 animals. Given their low abundance, restricted distribution and high level of habitat and food specialization, we urge that populations of this species be protected through effective management.

Unvarying diet of a Neotropical desert marsupial inhabiting a variable environment: the case of Thylamys pallidior

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.

Feeding strategies of a small mammal (Phyllotis xanthopygus, Rodentia Cricetidae) at diverse altitudes in the Central Andes, Argentina

Knowledge of feeding habits not only contributes information related to the resources that individuals need to survive and breed, but also leads to insights about the interactions between a species and its environment. The optimal foraging theory explains diet selection by several attributes of the trophic scenario such as availability, diversity, quality and predictability of food. Other models propose that digestive tract mass increases under high metabolic demands by cold, affecting food choice and intake. Thus, diet selection emerges as a behavioural trait shaped by intrinsic and extrinsic factors. The goal of our study was to determine variation in the trophic scenario among sites at different elevations, as well as variation in phenotypic traits relevant to the nutritional and energy balance in Phyllotis xanthopygus. This small rodent is widely distributed along the Andes Mountains. We assessed diet selection and digestive tract size in individuals collected at three elevations across its distribution range. Results on dietary proportion of specific trophic categories (green parts, fruits and arthropods) showed that P. xanthopygus alternates between omnivory and granivory/frugivory. Richness, diversity and quality of the available resources evidenced a relatively low-quality trophic scenario at high altitude. Nevertheless, the diets built in by animals from diverse altitudes lacked differentiation in quality or diversity. P. xanthopygus seems to behaviourally compensate environmental variation to cope with nutritional requirements, by changing diet composition and proportion of items included. The resultant uniform diet quality is consistent with the absence of variation in the gastrointestinal tract size. Considering the spatial variability and seasonality of the region, a behavioural response is probably the most convenient strategy to overcome short-term environmental heterogeneity. In a plastic species such as P. xanthopygus, behaviour is a fundamental aspect to take into account by predictive models in the forecasts of climate change effects on biological diversity.

Abrocoma schistacea (Rodentia: Abrocomidae)

Abstract: Abrocoma schistacea Thomas, 1921 is an abrocomid rodent commonly known as the Sierra del Tontal chinchilla rat. This medium-sized chinchilla rat is a rock specialist that inhabits the pre-Andean foothills of southern San Juan Province (Argentina) within an elevation range of 1,100–2,900 m. Its saxicolous specializations include padded feet with leathery tubercles on the pads. Incisors are large and orthodont; molariform teeth appear broad. A. schistacea is a creosotebush dietary specialist that can be distinguished from other chinchilla rats by living in groups of 3–4 individuals. This species is categorized as of low conservation concern in Argentina but is currently listed as “Data Deficient” by the International Union for Conservation of Nature and Natural Resources.