The Cascade Effect

Updated: Mar 27, 2018

By Professor Elizabeth Jordan, Science Writer

An ecosystem is a living and connected organism and all living things within it have unique and diverse roles, contributing to the ecosystem in various ways. While some roles overlap, each can be essential to a system and it’s only by relying on one another that an ecosystem can grow and thrive. All organisms affect their environment in different ways and intensities.

Some species have an unusually high impact on the biodiversity of their food webs. These keystone species are usually indicative of a high level of biodiversity in which there are many kinds of organisms within a system. Their absence is usually marked with the opposite, an ecosystem with far less variety.

These keystone species can be herbivores or carnivores, but they are all united by the huge role they play within their environment. Their presence or absence directly impacts a wide variety of other species, occasionally altering the entire makeup of an ecosystem.

Some of these effects are obvious at a glance. For example, wolves are considered to be a keystone species. When wolf populations decline, due to poaching, deforestation, and other changes, deer populations grow as a result. With fewer predators, more deer survive into adulthood and go on to have even more fawns.

Because deer consume a great amount of vegetation, their population growth negatively impacts insects, birds, other herbivores, and countless other species that rely on the vegetation for shelter and food. Once thrown out of balance, the entire ecosystem must readjust to this deer abundance, often resulting in a huge loss in biodiversity.

Top predators are not the only keystone species. Mega-herbivores like elephants can also act as maintainers of the ecosystem. Elephants help ensure the health of the African Savannah by overturning trees and shrubs, exposing new, damp soil and upturning vegetation. This creates new homes for lizards, small herbivores, and other animals and also helps spread vegetation by dispersing the seeds of local plants and trees.

The presence of elephants also significantly reduces the amount of savannah that burns in wild fires as their paths and movements keep vegetation growth in check. Preventing these fires and limiting their intensity allows animal and plant life to growth and thrive in their environment, continuing the ecosystems cycle.

Whether it be wolves or elephants, the presence of keystone species has a positive impact that spreads across the ecosystem in what’s known as a trophic cascade. In a trophic cascade, the success or failure of one organism doesn’t affect just its own species; it effects all those within the ecosystem.

Because of this interconnectedness, poaching can have negative impacts that go on to affect not only elephant populations. The decrease in the African elephant population is tragic for elephants and the ecosystem. The resulting loss of biodiversity on the African savannah will have detrimental consequences for years to come, be it wild fires or the tourist industry. Ensuring their protection helps guarantee their survival and the rest of the savannah’s. 


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