Revista Chilena de Historia Natural 78 (2): 183-198, 2005
RESEARCH ARTICLE
Uniformity in the basal metabolic rate of marsupials: its causes and
consequences
Most of the variation (98.8 %) in basal rate of metabolism (BMR) in 70 species of
marsupials is correlated with body mass, although lowland species have higher basal rates than highland species and burrowers have
lower basal rates than non-burrowers. These factors collectively account for 99.2 % of the variation in marsupial BMR. Marsupials differ
in BMR from eutherians by having no species with a high basal rate by general mammalian standards, even when consuming
vertebrates or grass, food habits that are associated with very high basal rates in eutherians. The absence of high basal rates in
marsupials reflects the absence of a correlation of rate of reproduction with basal rate, a correlation present in eutherians.
These differences have two consequences: (1) marsupials are less tolerant of cold environments than eutherians, and (2) marsupials
coexist with eutherians only when both have food habits associated with low basal rates and therefore when eutherians have reduced
rates of reproduction. In Australia and South America marsupial carnivores diversified in the absence of eutherian equivalents. The
importation to mainland Australia of dingos by humans appears to have been the immediate cause for the extinction of thylacines,
Tasmanian devils, and eastern quolls. Carnivorous marsupials in South America were replaced by eutherians with the completion of
the Panamanian land bridge. Macropods, which have lower basal rates than eutherian grazers, survive in central Australia probably
because of their adjustment to xeric environments, whereas introduced domestic stock require the provision of water by
humans.
Key words:
coexistence,
competitive exclusion, eutherians, marsupials, reproduction
