In the ecosystem, a critical species is referred to as a keystone species. If a keystone species is removed, a catastrophic cascade can result. The gray wolf is a notable example.

When the gray wolf was eliminated in the 1920s from Yellowstone National Park, elk began to overgraze because there were fewer threats. Aspen, willow and cottonwood couldn't recover from increased feeding. This reduced beaver dams that, in turn, affected erosion and the aquatic ecosystem. Gray wolves were reintroduced in the mid-1990s. Since then, elk stay on the move and graze less, and willow, aspen and cottonwood have rebounded.

Another example occurs on Kiawah Island, where bobcats effectively control populations of rabbits, rodents and even deer.

Jeremy Webber, Trident Technical College graduate and technical service representative for Koppert Biological Systems, specializes in introducing predatory insects to control pests. While ladybugs are among the most famous insect predators, Webber customizes his releases based on the pest. He's had great success with parasitic wasps and predatory spider mites. By reducing pesticide applications, he's reduced the risk of resistant genes developing in insects that can render a pesticide ineffective.

One of Webber's clients is a strawberry grower that has problems with two-spotted spider mites. Webber couldn't release the predatory spider mite until the two-spotted spider mites appeared or they quickly would die without something to eat. Instead, they released a limited number of two-spotted mites to boost the predatory spider mite population before the natural outbreak occurred. When the two-spotted mites arrived, the predatory mites were waiting in huge numbers.

Low biodiversity can result in a lack of natural predation of insect pests. Examples would be artificially controlled environments such as greenhouses or monocultures such as a large field of corn. In these cases, there are fewer predators present, and pests can cause significant damage. To increase predators in your yard, here are some suggestions:

Increase diversity. Plant a variety of trees, shrubs, groundcover, flowers and vegetables. A higher diversity of plants supports a higher diversity of insects, including beneficial ones.

Allow insect presence. There's a limit to this, but insect pests that cause little harm to plants can support beneficial insects. For instance, aphids are consumed by ladybugs, lacewings, parasitic wasps and others. Where acceptable, such as the backyard, let the pests hang around, and the beneficials will, too.

Use native plants. While native plants have aesthetic appeal, I think one of their best contributions is the number of insects they support. Since native plants have been present for 500 years or more, they have evolved with insects feeding on them. In turn, this supports beneficial insects as well as birds, anoles and others.

Reduce pesticides. Avoid the “spray first, ask questions later” approach. First, find out what the problem is. Take a sample of the plant and, if possible, the insect to a garden center, Master Gardener or horticulturist to identify. They can tell you what it is and if it has to be controlled. When possible, use safe insecticide products such as soaps and oils. These products have minimal impact on beneficial insects. Synthetic insecticides will kill an insect pest but can wipe out beneficials, too. When the insect pest returns, there are fewer beneficials, which may result in a higher return of insect pests.

Evaluate thresholds. Most people like a tidy front yard, but the backyard often can be left a bit more natural. Consider areas that are “left to the birds” to support biodiversity.

Tony Bertauski is a horticulture instructor at Trident Technical College. Got a gardening question? Email gardening@postandcourier.com.