Question

To help aid in the control of the pest populations, we released over ten and a half million beneficial insects last year. . . . Ladybug beetles and lacewing larvae are examples of predators that help control aphids . . . and other soft-bodied insects. —Dennis Higbie, Director of Horticulture for Walt Disney World How might removing pest populations change a local ecosystem?

Answer 1

Pest needs to be clarified. Pest to whom? Humans may think mice are pests because they destroy crops, but to a hawk a mouse is dinner, and to a fish the mouse may be insignificant entirely.

Many of the animals humans think of as pests provide critical ecosystem services. Most typically they are nature's garbage disposals and convert larger organic matter into humus and soil. They can be food for other animals. Others are predators that provide ecosystem service by controlling populations of other animals (or plants). Remove any one part of the food system and the whole system can become imbalanced.

There's some excellent examples, particularly from Australia, where one animal was brought in to control pest populations. The problem is that the original pest population disappeared (and hence could not provide their own ecosystem service) and the introduced predatory animal population boomed. Now you have a bunch of hungry predators that become pests themselves.

The method of removal also matters. For example, poisons will enter the ecosystem with rather obvious effects. @DauntingIllusions