Behavioural mechanisms of competition in small dasyurid marsupials

The competitive behaviour of three species of small dasyurid marsupial, Antechinus swainsonii, Antechinus stuartii and Sminthopsis murina, was assessed in specially designed enclosures and smaller encounter cages, by videotaping the activity of pairs of animals, both as conspecifics and members of different species (except for A. swainsoni versus S. murina). Spatio-temporal analyses revealed differences in activity patterns and interactions within and between the species. Interference competition occurred in all intraspecific and interspecific comparisons tested. Encounter competition was judged to be the mechanism operating as all animals entered into interactions with other individuals. Encounters were particularly prevalent within Antechinus, indicating that they were more social than the relatively solitary Sminthopsis. Avoidance behaviour occurred between the two Antechinus species and this may enable them to coexist, so that this mechanism may be considered to be avoidance competition. The smaller competitor, S. murina, showed avoidance of the larger A. stuartii. Intraspecific competition was judged to be stronger than interspecific competition, but the latter could have more severe consequences, with the death of the smaller species occurring in some situations. This highlighted the asymmetric nature of competition, with body size determining the outcome of interactions between species.