Population Ecology of Mesembriomys-Gouldii (Rodentia, Muridae) in the Wet-Dry Tropics of the Northern-Territory

A population of the black-footed tree-rat Mesembriomys gouldii was studied between September 1980 and January 1983 in tropical open-forest in the Northern Territory. Twenty-four males and 32 females were captured over 2900 wire-cage trap-nights. Abundance peaked in May-June and October-November of each year, reflecting increased trappability of adults and/or influxes of immature animals following breeding pulses in an otherwise non-seasonal reproductive pattern. There was a marked increase in population during 1981, followed by a general decline to very low numbers during 1982. Females outnumbered males throughout most of the study, and particularly between March and July each year when more young females than males entered the trappable population. Marked seasonal differences in composition, transiency and trappability were apparent between the male and female populations, suggesting a relatively non-social behavioural pattern. The preference shown by M. gouldii for relatively stable, structurally diverse open-forest areas, which are characterised by shrubs and trees with conspicuous and/or fleshy fruits, accords with the limited data on diet. It is further suggested that a geographically but not temporally restricted food resource may explain the patchy distribution and non-seasonal breeding pattern recorded for this species. Climatic variability (particularly rainfall), through its influence on plant phenology and food availability, may strongly influence demographic changes, however, and was deemed responsible for both the population increase in 1981 and the subsequent marked decline during 1982. Long-term studies are needed in the wet-dry tropics to clarify the relationship between many such mammal species and their environment.