Environmental Engineering Reference
In-Depth Information
of food resources and thus determine the carrying capacity in any single
year. Furthermore, the stochastic nature of weather causes the carrying ca-
pacity of the environment to fluctuate or oscillate up and down from one
year to the next.
As a consequence populations will be forced to “track” these changes
over time. Individuals experiencing “good” years will have high reproduc-
tion and low mortality leading to high net population growth rates. But, if
the following year is a poor year, the population will have exceeded the car-
rying capacity set by environmental conditions the previous year (a lag ef-
fect) and so crash to a lower level.The fluctuation between good and bad
years could also lead to oscillatory population dynamics. But, unlike a de-
terministic system, the dynamics of a stochastic system fluctuate in an irreg-
ular or random way.There is no single attractor for stochastic systems.
The potential for stochastic events to influence dynamics of populations
creates a difficult empirical dilemma for managers. Populations whose dy-
namics are governed by deterministic processes are comparatively easy to
manage.The nature and strength of cause-effect relationships are easily dis-
cerned and predicted. So managers can manipulate deterministic factors to
achieve desired ends. Stochastic factors throw a proverbial monkey wrench
into management by increasing uncertainty.
Carrying Capacity and Population Overabundance
We have all probably experienced, read about, or seen on television cases
where a state wildlife management agency is called in to thin a deer herd
because it is said to be overpopulating a local area.The act of thinning the
herd by hunting evokes many different feelings in society.These feelings
often boil over into highly newsworthy protest events or injunction hear-
ings in court because defenders of animal rights often pit their interests
against the interests of defenders of the hunting fraternity and those sub-
urbanites who are tired of deer eating up their expensive ornamental plants.
From a management standpoint, it is a political problem that needs to be
dealt with quickly, usually by rapidly thinning the herd.
This action provides only a proximate solution to the environmental prob-
lem. It may result in a temporary fix that will require managers to thin the
herd once the population again reaches high numbers.To solve the problem,
we need to look deeper into the reasons for the problem in the first place.
Let's consider a hypothetical case in which a state environmental
management agency is charged with managing a public forest preserve.
