South American Living Metatherians: Physiological Ecology and Constraints

Abstract

South American living metatherians are relatively inconspicuous and comprise ca. 10 % of the region's mammal species richness. Most of them are small-sized (<150 g), with long tails and grasping hands and feet, and resemble one another in their general appearance. Individuals are solitary, nocturnal or crepuscular, and most of them are arboreal or scansorial. Two orders are exclusive of South America (Microbiotheria and Paucituberculata), while a third (Didelphimorphia) ranges from Patagonia (Argentina) to the border between USA and Canada. The ecology, physiology, and reproductive traits of living South American marsupials have been poorly studied. This chapter describes several aspects of their natural history and how they influence their recent distribution, as they probably did so throughout the Cenozoic. Physiological constraints include variable energetic costs for regulating metabolic processes, due to low rates of metabolism, the possibility to enter torpor/hibernation, and the storage of different types of fat tissues available for those varied processes. Reproduction, which can be characterized by a short gestation period and long, energy-demanding, breeding period, shows specific differences in strategies (e.g., semelparity, partial semelparity, iteroparity) and their main traits (e.g., litters per year and litter size, teat number). South American marsupials make a complete use of the habitat available to them and have a broad, generally opportunistic and omnivorous diet. These adaptations, combined with a general small size, small energy expenditure on foraging and other daily activities, limit their distribution. Despite these constraints, South American marsupials seem to thrive in environments where competition with other animals might be strong (e.g., tropical and subtropical climates), or where a few small mammals can survive (e.g., temperate and temperate-cold climates) due to several environmental limitations.