Differences in renal and alimentary water conservation account for differences in the distribution of tammar and parma wallabies on Kawau Island, New Zealand

Abstract

Surveys of two wallaby species on Kawau Island, New Zealand, indicated that their distribution was stable so as to permit niche partitioning. Multivariate analysis of environmental factors associated with the relative distribution of tammar and parma wallabies suggested that their distribution may be influenced by the availability of fresh water. Tammar wallabies have greater renal size, mass and relative medullary area than parma wallabies and thus may have greater renal water-conserving capabilities. The tammar colon is significantly longer than that of the parma wallaby and the water content of distal digesta is lower in tammar than in parma wallabies, indicating that the former species may also have greater colonic water-resorption capabilities. A laboratory comparison of the water consumption of tammar and parma wallabies showed that the former drink significantly less than the latter.

The superior ability of tammar wallabies to colonise drier areas may have contributed to their survival in the presence of the closely related parma wallaby.