Ecosystems are complex and diverse, with many levels and intricate relationships between organisms. Removing any level from an ecosystem disrupts a delicate balance that may have evolved over millions of years. These systems are comprised of a series of checks and balances between predator and prey, that tend to balance the whole. The removal of the top predators in an ecosystem has several impacts, some of which are expected, and others surprising.
The most obvious result of the removal of the top predators in an ecosystem is a population explosion in the prey species. Predators keep herbivore populations in check. The reverse is also true, of course — predator populations are limited by the availability of prey. When prey is abundant, predator populations increase because more young are able to survive. More predators kill more prey, which, along with food scarcity, decreases the population. When prey becomes more scarce, the predator population declines until prey is again more abundant. Therefore, the two balance each other. When the predators are removed, prey populations explode.
Without any predators to limit population growth, herbivorous prey species reproduce without check, and all of them are hungry. More herbivores eat more plants, and without anything to control them, they can quickly degrade their habitat. This puts pressure on the plants that they depend on for food, sometimes to the point of impeding plant reproduction and defoliating the habitat. This is known as a trophic cascade, and in extreme cases, can lead to the complete destruction of the ecosystem.
One of the more surprising effects of the removal of the top predators from ecosystems is the resulting behavioral changes in the prey species. This was played out in Yellowstone National Park in Wyoming. As the forest became more degraded, authorities began culling the deer and elk herds in an attempt to control the population, but it had no effect on habitat degradation. Then they reintroduced wolves, the top predator, back into the ecosystem, and the habitat began to recover. Studies have shown that the reason for the change was because the deer and elk had changed their eating habits. With no predators, they stayed in one place and ate down to the roots. With wolves to watch out for, they browsed lightly, and moved on.
Population Sickness and Migration
With no predators to control the population and alter feeding behavior, the prey species quickly degrade and over-run its habitat. As food becomes scarce, the population becomes sick and malnourished, and will either move or crash. Many will seek new habitats, and may end up in people’s backyards, eating their gardens and becoming nuisance animals. In the case of the “islands” created by the flooding of Lake Guri in Venezuela after the dam was built, plants got more toxic, and the howler monkeys trapped by the water went mad after their population explosion.
Written by Maria Dolph