Biology Reference
In-Depth Information
Figure 7.2. Numerical responses, i.e., changes in annual rates of population growth,
(Mitscherlich equations) of red kangaroo populations (1978-1984) to
summer-autumn rainfall in (a) the Western kangaroo management zone of South
Australia, and (b) the Central and Eastern kangaroo management zones of South
Australia. In both examples, annual rates of population growth increase with
rainfall, but at very high rainfalls the increase becomes more and more
asymptotic. From Cairns and Grigg (
1993
). Reprinted by permission of the
authors and Taylor & Francis.
Cairns, personal communication). Although some individuals move over
large distances (maximum recorded, over 300 km), most appear to remain
in a relatively small area of a few (
<
8) km
2
(Priddle
1987
, references
therein). Reproduction appears to be more or less continuous, the maxi-
mum number of young per adult female is about 1.5 per annum. The diet
of Macropus rufus consists of grasses, forbs, chenopod sub-shrubs, and some
shrubs (Barker
1987
). Potential competitors for food are sheep and
rabbits. Grazing efficiency of red kangaroos, sheep, and rabbits is about
the same, they all reduce biomass to about 20-50 kg/ha, depending on
the biomass of unpalatable plant species present. They also need about the
same amount of food per day, when expressed as metabolic weight
(60-80 g/kg
0.75
/day), and when food is not limited. At biomasses of
above 300 kg/ha, competition between these herbivores for food is minimal
(Short
1987
). Availability of food depends on rainfall; Figure
7.2
shows
examples of numerical responses (changes in annual rates of population
increase, r) of red kangaroo populations to variations in summer-autumn
rainfall in two regions in the South Australian pastoral zone, surveyed
