Diet overlap and relative abundance of sympatric dasyurid carnivores: a hypothesis of competition

Authors


Abstract

1.  Diet overlap among age and sex classes of sympatric dasyurid carnivores (Marsupialia: Dasyuridae) at Cradle Mountain National Park in Tasmania, Australia, was determined to assess the likelihood of current interspecific competition, which could influence and explain the disparate population densities of the three species.

2.  The carnivore guild divided into two groups based on body size and prey size, within which diet overlapped: Tasmanian devils (Sarcophilus laniarius) and male spotted-tailed quolls (Dasyurus maculatus), which consumed larger prey species, and female spotted-tailed quolls and eastern quolls (D. viverrinus), which consumed smaller prey species. Male spotted-tailed quolls overlapped in diet with adult devils in winter, but not in summer. However, in summer the small number of male spotted-tailed quolls overlapped in both body weight and diet with a large cohort of young devils. Too few data were obtained to repeat these analyses with female and young spotted-tailed quolls and eastern quolls, but results indicated that a similar pattern of overlap may occur.

3.  Spotted-tailed quolls would experience the highest degree of dietary overlap with another species of carnivore, with all age and sex classes experiencing overlap for much of the year. Adult devils and young eastern quolls would both be free of overlap for more than half the year.

4.  No indications of seasonal food limitation, when competition is most likely to occur, were found during this study, but this may occur over a longer time scale.

5  If the high degree of diet overlap experienced by spotted-tailed quolls means higher competitive pressure, this may explain the low density of this species at Cradle Mountain.

6.  These results, high levels of interference experienced by spotted-tailed quolls, and the behavioural and numerical dominance of devils, the largest species in the guild, support Brown & Maurer’s (1986) and Cotgreave’s (1993) ideas that competitive dominance may be more important than energetic equivalence in determining relationships between body size and abundance in local assemblages of animals.

Ancillary