A predator removal experiment was conducted in semi-arid grassland and woodland to find the boundary between regulation and non-regulation by predators. Predators were culled (112cats and 288 foxes) from an experimental area of 70km2 and compared with another block with little predator removal. Following the cull, predators were allowed to reinvade the experimental blocks. Rabbit numbers were monitored over a five month period by counting active burrow entrances.
In the treated area (predators removed), rabbits increased to higher densities than in the untreated area. When predators were allowed back into the treated areas, rabbit populations continued to increase and did not decline to the density in the untreated area.
1. High rabbit densities (rabbits escape predator regulation)
2. Low rabbit densities regulated by predators
The control of predators allowed the density of prey to increase beyond the upper limit for predator regulation of about 15 rabbits km-1. Following predator removal, prey densities increased and stayed at > 15 rabbits km-1 for the term of the experiment, even once the predators were allowed back into the area. High rabbit numbers (State 1), with no predator regulation could occur if rabbits experienced exceptionally good breeding conditions or if predators are controlled below the predator regulation point. Low rabbit numbers (State 2) with predator regulation could occur if drought or myxomatosis caused rabbit numbers to fall below the predator regulation point.
Contact
Jacqui Meyers
Email
jacqui.meyers@csiro.au
CSIRO Sustainable Ecosystems,
PO Box 284,
Canberra ACT 2601
Keywords
empirical data, predator-prey, foxes, Australia, semi-arid, rabbits, feral cats, population models, population density, density-dependent, experiment, drought, empirical data
