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

Abstract

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