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Journal Publications
Gunn A., Miller F.L. and
Barry S.J. Conservation of erupting ungulate populations on islands – a
comment. Rangifer, 24 (2), 2003 (PDF = 173KB)
Abstract:
A generalised model for herbivores
experiencing abundant forage over time is that their numbers erupt and
then decline. This model has been applied to fluctuations in caribou
(Rangifer tarandus) populations especially those on islands. Since this
generalised model for erupting herbivores was first proposed, two
assumptions have slipped in (1) that an erupting population will crash; and
(2) that the crash will be density-dependent. The problem with the
assumptions is that, without testing, they can lead to inappropriate
management such as culls. The first assumption arises from uncritical use of
earlier accounts and the second assumption from not discriminating between
the effects of environmental
variation from the effects of the high herbivore numbers on forage
availability (density-dependence). Often typical density-dependent effects
such as lowered initial reproduction, early survival of calves, and
subsequent calf, yearling and juvenile survival are used to justify the
contention that there are too many herbivores. But such reasoning is flawed
unless cause/effect relationships are established and the role of
environmental variation is evaluated. We argue that it is overly simplistic
to believe that every population’s subsequent performance and fate will
follow a singular pattern with only one paramount factor driving and
ultimately dictating an inevitable outcome. The relative importance of
unpredictable abiotic factors in influencing and causing intricate variation
in the response of ungulate populations should be investigated, no matter
whether those factors are sporadic or periodic. |
