Environmental Engineering Reference
In-Depth Information
This is effectively the management scenario that I have been discussing all
along.This is the target deer density that management needs to maintain
to protect high levels of the other services of the forest preserve that soci-
ety values.Thus, management must cull the herd on a regular basis to avoid
the recurring boom-bust cycles arising from periodic culling. Management
(an extrinsic factor) must lower the herd below its carrying capacity to
achieve desired ends.
The utility of presenting information in this way is that it forces individ-
uals with conflicting interests to make their values explicit. Management
options can then be explored in ways that match ecological principles to
value-oriented objectives.
This line of reasoning also allows us to address another very muddled
concept that has been popularized by society.We hear that deer herds are
now highly abundant because we have exterminated many of their natural
predators such as wolves, coyotes, and bears. As a consequence, hunting is
required as a substitute for missing predators in order to restore ecosystems
back to their natural balance.The problem once again is that human values
undergird the reasoning applied to the definition of “natural balance.” Ac-
cording to the ecological principles laid out above, carrying capacity does
not include mortality from predation because it is an extrinsic factor, not
an intrinsic one. Predators limit prey populations below the prey popula-
tion's carrying capacity.The extent to which this occurs depends upon the
predator's hunting efficiency as depicted by the open squares PL1 and PL2.
What this means is that loss of predators allows prey populations to increase
from a former balance or equilibrium toward a new one: carrying capac-
ity.What is implicit in society's wish to “restore the natural balance” is that
society wants deer populations to stabilize at levels observed when preda-
tors were historically present, which is much below another balance—their
biological carrying capacity.This suggests that we should abandon describ-
ing systems in terms of their “natural balance” and instead use the explicit
terms we have learned such as carrying capacity and predator limitation.
This example illustrates how easily ecological science can become en-
tangled with environmental advocacy.The reserve managers in my case ex-
ample applied some ecological principles, but applied them only enough to
advocate a certain set of values. As I pointed out in chapter 2, to remain
objective and credible, ecological science must be presented in ways that
honestly and clearly reveal the suite of management options to those in-
terested in mediating environmental problems. Ecological science can do
