  Humans are the ultimate ecosystem engineers who have profoundly transformed
the world's landscapes in order to enhance their survival. Somewhat
paradoxically, however, sometimes the unforeseen effect of this ecosystem
engineering is the very collapse of the population it intended to protect. Here
we use a spatial version of a standard population dynamics model of ecosystem
engineers to study the colonization of unexplored virgin territories by a small
settlement of engineers. We find that during the expansion phase the population
density reaches values much higher than those the environment can support in
the equilibrium situation. When the colonization front reaches the boundary of
the available space, the population density plunges sharply and attains its
equilibrium value. The collapse takes place without warning and happens just
after the population reaches its peak number. We conclude that overpopulation
and the consequent collapse of an expanding population of ecosystem engineers
is a natural consequence of the nonlinear feedback between the population and
environment variables.
