Reading Practice 86

Keystone species play a disproportionately large role in maintaining the structure, diversity, and functioning of ecosystems. While all species contribute to their environments, the loss of a keystone species can trigger cascading effects that disrupt entire ecosystems. Keystone species can exist at various trophic levels, from predators to ecosystem engineers, and their influence often outweighs their numerical abundance.

One of the best-known examples of a keystone species is the sea otter. Found in coastal ecosystems of the northern Pacific Ocean, sea otters feed on sea urchins, which, in turn, graze on kelp forests. When sea otters are removed from these ecosystems, sea urchin populations explode, leading to the overgrazing of kelp forests and a significant loss of biodiversity. Kelp forests provide habitat and food for a wide array of marine organisms; thus, their decline disrupts the entire ecosystem.

Similarly, apex predators such as wolves also play a critical keystone role. The reintroduction of wolves into Yellowstone National Park in the 1990s had profound ecological consequences. By preying on deer and elk, wolves reduced overgrazing and allowed vegetation such as willows and aspens to recover. This recovery benefitted other species, including beavers, which used the restored vegetation to build dams that created aquatic habitats for numerous organisms.

In addition to predators, ecosystem engineers like beavers are keystone species in their own right. By constructing dams, beavers transform streams into ponds and wetlands, thereby creating new habitats that support a high diversity of life. These wetlands act as natural water filters, improve water quality, and mitigate flooding. The absence of beavers in such ecosystems often leads to a sharp decline in habitat diversity and ecosystem services.

Despite the critical roles keystone species play, many are threatened by human activities, such as habitat destruction, pollution, and climate change. Efforts to conserve these species are essential not only for their survival but also for the preservation of the ecosystems they sustain.