Prolonged prey suppression by carnivores- predator-removal experiments

The hypothesis that carnivores can significantly
suppress prey populations after they collapse during
drought was tested by predator-removal experiments. Low
populations of rabbits (Oryctolagus cuniculus) responded
with significantly accelerated growth where foxes (Vulpes
vulpes) and feral cats (Felis catus) were continually shot.
Experiments in years of good pasture and poor were confirmatory.
After only 14 months, the rabbits were well on
their way to another eruption whereas untreated populations
had remained low for 2.5 yrs until a second drought.
These studies confirm the impact of carnivores found for
low populations of cyclical prey but there was no measurable
effect of predator-removal on the population declines
in our studies. They were due to aridity and poor pastures.
The concept of Environmentally Modulated Predation is
presented. Only after the intervention of a widespread environmental event is such limiting predation possible.
Drought is also the cause in arid Australia for dingoes (Canis
familiar& dingo) preying sequentially on rodents, rabbits
and red kangaroos, while wildfire was the cause in temperate
forests. Such environmental intervention may be more
widespread than usually considered, triggering some appa/-
ent predator-prey cycles. The major factors limiting rabbits
in inland Australia are: adequacy of green herbage during
breeding, food scarcity during average summers, critical
shortages of food and its low quality (including moisture
content) during 'crashes' in drought, followed by limiting
predation. Contrasting life-histories are one cause for the
ultimate escape of rabbit populations from limiting predation
as rabbits can breed continuously but carnivores seasonally
only.