(1) Rate of increase was measured for feral donkey
populations in parts of northern Australia as the average
exponential rate of increase, r, in a population subjected
to substantial reduction.
(2) The annual rate of increase was estimated to be r =
0.21. This estimate was compared with the exponential rate
of increase in another recovering donkey population and
found to be in close agreement.
(3) Ultimate and proximate factors regulating the
abundance of feral donkey populations were examined by
monitoring and sampling two populations; one at or close to
equilibrium density, the other below equilibrium density and
recovering from reduction.
(4) The size of the population at equilibrium density
remained stable over the 12 months of monitoring while the
size of the recovering population increased by 20 percent
(r = 0.18/yr).
(5) Growth and body condition were significantly
depressed in the population at equilibrium density
suggesting that donkey populations are limited by the food
resources available to them.
(6) Breeding occured over a discrete season, with
births occurring between September and February.
11
(7) Fecundity was high, with more than 75 percent of
mature females breeding in each year, and was independent of
population density.
(8) Adult and juvenile mortality were density
dependent, with mortality over the first six months of life
the most important demographic factor influencing rate of
increase in donkey populations, and hence population
abundance.
(9) Implications of the estimated rate of population
increase for the cost of long-term control of feral donkey
populations were examined by constructing numerical models
predicting the relative cost of ongoing control.
(10) These models were constructed using functions to
describe density dependent variation in population
productivity and the cost per donkey removed.
(11) The cost of removing donkeys at various population
densities was estimated using predator-prey theory. The
cost, measured in hours of helicopter time per removal, was
found theoretically and empirically to take the form of an
inverted functional response curve, with cost saturated at
high donkey densities.
(12) The utility of models predicting the cost of
continuing pest control is illustrated by comparing the
relative costs of two potential strategies for feral donkey
control.
| Identifer | oai:union.ndltd.org:ADTP/219532 |
| Date | January 1988 |
| Creators | Choquenot, David, n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright David Choquenot |
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