Environmental Engineering Reference
In-Depth Information
paratively thick beaks.Those individuals take in more energy than the thin-
ner-beaked members of their population. Individuals with thicker beaks
thus survive and reproduce better than individuals with thin beaks. Over
time, the majority of individuals in the population will be thick beaked,
which is reflected as an increase in the mean value of the measured beak
depths among birds that remain alive in the population during and imme-
diately after drought. Natural selection favors increasing beak depth. If the
drought conditions persisted, or El Niño drought events become more fre-
quent and longer lasting, we could eventually see the thin-beaked pheno-
type become rarer and rarer and even disappear altogether.
The tendency to favor thick beak depth can be reversed when there is a
period of rainy conditions and disproportionately higher production of thin
seeds, because thick beaks are not sufficiently nimble to pick up these seeds.
This results in a population containing individuals with comparatively thin-
ner beak depths on average. So environmental conditions that fluctuate back
and forth cause mean beak depths in a population to fluctuate back and
forth accordingly.Traits that are favorable to individuals in one kind of en-
vironment may not be as favorable in other environmental conditions. As
the environmental conditions of the game—the playing field—change, so
do successful strategies.
It is conceivable, then, that any human action that alters the environment,
from local changes in land use patterns to serious insults such as habitat frag-
mentation, pollution, and climate change on regional and global scales, has
the potential to change the course of
evolution. Human alteration of the
environment imposes brand new nat-
ural selection pressures on existing
strategies within the world's biota.
This can then kick off a string of
changes in coping strategies.The im-
plication here is that changes in indi-
vidual strategies ultimately change
the nature of the playing field and the
game in a continuous feedback cycle.
This is what ecologists call a complex adaptive system (Levin 1999).The
perpetual feedback cycles that lead to adaptive change coupled with the
myriad, simultaneous impacts that humans have even on a single location
creates a high degree of uncertainty about the root cause of change in
Traits that are favorable to individu-
als in one kind of environment may
not be as favorable in other environ-
mental conditions. As the environ-
mental conditions of the game—
the playing field—change, so do
successful strategies.
