Keystone Species

Keystone species, by their natural behavior, determine the condition of other species in an ecosystem. If keystone species decline or go extinct, an entire ecosystem may not survive. Wilson has suggested with other ecologists that past extinctions were very likely due to the decline of certain keystone species that, in turn, caused ecosystem imbalance. Ecosystem imbalance occurs when one or more components disappear, putting stress on the remaining members of the ecosystem.

Sea otters and bees are but two examples of the many keystone species found in ecosystems. Sea otters’ main food is sea urchins. By holding sea urchin populations in check, otters keep them from devouring kelp forests and seaweeds that are home to hundreds of types of fish, perhaps thousands of species overall. Bees benefit ecosystems by pollinating plants and trees, which provide protective cover for other plants and habitat for insects. The insects then serve as a food source for many bird species, upon which foxes feed, upon which raptors feed.

Foundation species play a slightly different role from keystones. They change habitat in a way that enhances it for other species. African elephants play the role of foundation species through their feeding activities in which they crack and uproot trees, which helps open up areas of land and aerates soil. This condition promotes the growth of grasses for grazing animals, and eventually small bushes and woodlands follow the grasslands. The new vegetation favors tree grazers, insects, birds, and the predators that hunt them. Elephant feeding behavior therefore benefits not only ecosystems but an entire community.

In predation, one organism hunts, kills, and eats another organism(s) for its nutrition. Predators are carnivores or omnivores, and their prey are usually omnivores and herbivores. Predators play a keystone role by regulating populations of prey animals and thereby maintaining balance within food webs. Examples of predator keystone species are wolves, lions, alligators, white sharks, and owls.

Predators furthermore keep populations of prey in check in a nonrandom manner. In other words, they do not usually attack the first prey animal they find, but rather select their prey. Predators remove old, weak, and sick animals and, as a consequence, the remaining strong and healthy population passes on its genes to offspring. Healthy prey populations then support healthier and perhaps larger predator populations. For example, years marked by very large North American deer populations have resulted in above average mountain lion populations. The converse situation may also occur in which as a prey population declines, predators regulate their numbers to avoid starvation.

Another set of relationships in biological communities comes not necessarily from feeding habits, but from other aspects of animal lifestyle. These relationships are called symbiosis, and biological communities contain three main types: mutualism, commensalism, and parasitism. In mutualism, two or more species benefit from each others’ activities. For example, the bacteria living in the gut of termites receive a safe, nutrient-rich habitat, while they provide a benefit to the termite by digesting woody food. In commensalism, one species benefits and the other is neither helped not harmed. Redwood sorrel, a small herb that lives in the shade of redwood trees, has a commensal relationship with the redwoods. Shade from the tall trees gives the sorrel its preferred habitat but the redwood tree receives no known benefit. Finally, parasitism is a relationship in which one organism benefits and the other is harmed. As an example, Phytophthora fungus lives on oak and other trees as a parasite and the fungus eventually kills the tree.

Source of Information : Green Technology Biodiversity (2010)