Environmental Engineering Reference
In-Depth Information
Management must balance the interests of a wide range of constituents.
Some constituents use it for sports activities or recreation such as swimming.
Some use it for observing wildflowers, songbirds, and deer. Suppose that the
reserve was managed in such a way that it attracted deer to that location.
The deer residing there would obviously consume some of the vegetation.
Resource consumption, in turn, leads to births and the population begins
to grow, putting increased pressure on the vegetation. The management
agency becomes concerned because there is documented scientific evidence
(e.g., McShea et al. 1997; Cote et al. 2004) that dense deer populations can
prevent forest regeneration by eating tree seedlings. Deer can also alter the
vegetation such that songbirds no longer reside in an area.Thus, important
services of the nature preserve (e.g., forests, wildflowers, and songbirds)
sought by the public stand to be jeopardized by a growing deer herd.
To head off this potential problem, managers look to other geographic
locations that contain deer populations and try to come up with a repre-
sentative number of deer that could be sustained locally in the preserve. Sup-
pose the broad consensus was that the preserve should support no more than
thirty deer. Based on this, management asserts that the carrying capacity of
the preserve is thirty deer and then formulates all future management pol-
icy around that number.
However, it often happens that the deer population within a preserve is
larger than this number or grows far beyond this number. Suppose that in
our case that number was 120 individuals. By management's reckoning, we
have a crisis because the deer population is exceeding its carrying capacity
of thirty. Suppose that management went ahead and resolved this overabun-
dance problem by culling the population back down to thirty animals and
then left things alone. Often, we find that when this is done the popula-
tion rebounds to its previous size of a hundred or more individuals within
as short a time span as five years.This outcome then precipitates the next
round of crisis management.
The problem is that this management crisis is probably more an artifact
of policy based on superficial thinking than on the biology underlying pop-
ulation growth and carrying capacity.To understand what I am driving at,
let's apply some of the principles laid out above.
The herd culling represents a perturbation intended to bring the popu-
lation down to its predetermined carrying capacity for the preserve. In prin-
ciple then, if the deer population was restored to its carrying capacity by
management, we should see births in the population balance deaths (figure
