Data from: Mesopredator release among invasive predators: controlling red foxes can increase feral cat density and alter their behaviour

The mesopredator release theory predicts that the density of subordinate
predators will increase as dominant predators decline. Persistent debate
around mesopredator release in part reflects the lack of robust,
replicated experiments to test this theory, and the use of population
indices which confound changes in mesopredator density and detectability.
This uncertainty has immediate impacts for conservationists who are faced
with managing sympatric invasive predators. We used replicated
experimental designs and spatially-explicit models to examine whether
mesopredator release of the feral cat Felis catus occurs in response to
targeted control of the introduced red fox Vulpes vulpes. We surveyed
three Control-Impact paired landscapes in a region with long-term fox
control (1080 poison baiting), and conducted a Before-After Control-Impact
Paired-Series experiment in another region. We used fox occurrence as a
simple metric of fox populations and estimated feral cat density with
spatial mark-resight models. Lethal fox control had varying effects on fox
occurrence, consistent with variation in the duration and intensity of
poison baiting. Correspondingly, responses in feral cat density ranged
from negligible to a 3.7-fold higher density in fox-baited landscapes. At
a fine spatial scale (200 m2), feral cat density was negatively associated
with fox occurrence probability across both regions. These results were
consistent with mesopredator release, although uncertainty was high in the
region where fox control had only recently commenced. Feral cat
detectability also varied across the (artificially-manipulated) gradients
of fox occurrence probability. In one region, nonlinear models indicated
that feral cats had lower detection and increased movement rates when
foxes were uncommon, giving way to density suppression at high fox
occurrence probabilities. Synthesis and applications. Our study provides
replicated, experimental evidence that dominant predator suppression can
be associated with a higher mesopredator density. Mesopredator release can
manifest as changes in both behaviour and density, distorting inference if
these processes are not distinguished. Our results may help explain why
fox control does not consistently improve native prey persistence,
suggesting integrated pest management may be necessary to improve
conservation outcomes.