At the edges of developed areas, where natural habitats meet human habitats, animals are forced to undergo significant changes to survive and adapt. A closer look at what happens to these "animals on the edge" gives us sobering insights into the quality of our remaining wild lands.
The health of any natural area depends significantly on two factors: its overall size and what happens at its edges. When human development cuts into a forest, the newly-exposed edges are subject to a series of microclimatic changes: increased sunlight, temperature, relative humidity, and exposure to wind. Plants are the first to respond to these changes with increased leaf-fall, elevated tree mortality, and an influx of secondary-successional species.
The combined changes in plant life and microclimate create new habitats for animals. The more-reclusive of bird species move to the interior of the remaining forest while birds better adapted to edge environments develop strongholds on the periphery. Mammal populations, frequently requiring large areas of undisturbed forest to support their numbers, often decrease in size. If established territories have been destroyed, mammals must adjust their social structure to accommodate the closer quarters of the remaining forest.
Researchers have found that fragmented forests resemble islands. The human development that surrounds a forest "island" acts as a barrier to animal migration, dispersal, and interbreeding. In these island-like communities, species diversity is governed largely by the size of the remaining intact forest.
The changes in animal distribution and population that result from fragmentation illustrate a dynamic environment. It would be ideal if--when the bulldozers have disappeared--the environmental damages were to subside. Unfortunately this is rarely the case. The animals and wildlife left behind begin a complex process of adaptation and a long search for a new balance.
References:
- Ricklefs, R.E. Ecology. W.H. Freeman and Company. New York, NY. 104 (1990).
