In parts of the world such as the Pacific Islands, Australia, and New
Zealand,introduced vertebrate predators have caused the demise of indi
genous mammal and bird species. A number of releases for reestablishme
nt of these mammal species in mainland Australia have failed because p
redators extirpated the new populations. The nature of the decline of
both extant populations and reintroduced colonies provides information
on the dynamics of predation. Predator-prey theory suggests that the
effects of predation are usually inversely dependent on density (depen
satory) when the prey are not the primary food supply of exotic predat
ors. Thus, such predators can cause extinction of endemic prey species
. Three types of evidence can be deduced from the predator-prey intera
ctions that allow predictions for conservation: (1) whether per capita
l rates of change for prey increase or decrease with declining prey de
nsities, (2) whether predation is depensatory or density-dependent, an
d (3) the overall magnitude of predation. If this magnitude is too hig
h for coexistence, then the degree of predator removal required can be
predicted. If the magnitude of predation is sufficiently low, then th
e threshold density of prey that management must achieve to allow pred
ator and prey to coexist can also be predicted. We analyzed published
reports of both declining populations and reintroduced colonies of end
angered marsupial populations in Australia. The observed predation cur
ves conformed to the predictions of predator-prey theory. Some, such a
s the black-footed rock-wallaby (Petrogale lateralis), were classic al
ternate prey and were vulnerable below a threshold population size. Ot
hers, such as the brush-tailed bettong (Bettongia penicillata), have a
refuge at low numbers and thus offer the best chance for reintroducti
on. Our predictions suggest a protocol for an experimental management
program for the conservation of sensitive prey species: (1) determinat
ion of net rates of change of prey with declining population, (2) impr
ovement of survivorship through habitat manipulation, (3) improvement
of survivorship through predator removal, (4) determination of the thr
eshold density above which reintroductions can succeed, and (5) manipu
lations to change interactions form Type II to Type III. The task in t
he future is to determine how to change the vulnerability of the prey
so that they can have a refuge at low numbers.