Beavers as a Keystone Species_01

Have you ever played the game Jenga? In Jenga, players take turns removing one block at a time from a tower constructed of 54 blocks. Each block removed is then placed on top of the tower. The pattern of removal and reconstruction creates a progressively more unstable structure. With every turn, players need to decide which piece can be safely removed without bringing down the entire tower.

While Jenga is just a game reliant on the center of mass of the stacked objects, in nature, a similar but much more important challenge exists.

In nature, all living organisms must compete for basic needs. Animals compete for water, food, shelter, and air. Plants compete for sunlight, space, water, and air. Within a healthy ecosystem, living organisms may come and go, depending on the availability of resources. This fight for survival is an ongoing process with winners and losers, but are all organisms in the environment equally important? What if many organisms were reliant on the survival of one key organism? These special organisms are called keystone species. A keystone species is a species that other species within an ecosystem are extremely dependent on for their own survival. Scientists have placed keystone species into three categories: predators, mutualists, and ecosystem engineers.

You may know the shark as a predator, but they are more than that. Their presence keeps the marine environment healthy. For example, the shark prevents other organisms from over-populating an area and thus decimating food sources. An example of such a situation exists with tiger sharks that patrol the shallows off the coast of Australia. They keep smaller animals from overgrazing the grass beds, thereby keeping the ecosystem in balance. Not all keystone species are predators like the shark.

Bees too hold the position of a keystone species. Unlike the shark (a predator), bees have a mutualistic relationship with the ecosystem. Mutualism is when the actions of two organisms are beneficial to one another. For example, as bees take the nectar from flowers, they collect pollen and spread it from one flower to the next. This action enhances the odds of fertilization and greater flower growth. Nectar and pollen are also the primary food sources for the bees themselves.

There is perhaps no better example of an ecosystem engineer than the beaver. A beaver is a large semiaquatic rodent that was almost hunted to extinction in the 1800s because of the value of its pelt. Fortunately, since the 1900s, the beaver population has rebounded with protections being placed on them.