Test Your Knowledge on Keystone Species and Trophic Cascades

The Role of Keystone Species in Ecosystems

• The Earth is home to many habitats, each with a community of plants and animals, and each species is present in different numbers.

• The green world hypothesis proposed that predators keep herbivores in check, which regulates ecosystems.

• Robert Paine's experiment with removing starfish from a rocky Pacific shore showed that one predator could regulate the composition of an entire community.

• Paine coined the term "keystone species" to describe the power a single species can exert on an ecosystem.

• Keystone species have a huge impact, which extends well beyond the species they primarily prey on.

• Most species do not have large impacts, and it takes experiments to tease out the difference.

• Paine's experiment with removing urchins from tide pools showed that they were keeping kelp from growing, violating the green world hypothesis.

• James Estes continued Paine's work by studying the role of sea otters in the organization of nature.

• Estes discovered that sea otters, a predator, were controlling the urchins that fed on kelp, and removing them caused the kelp forests to disappear.

• Sea otters are another keystone species that regulate the structure of coastal marine communities.

• Estes later noticed that otter populations seemed to be declining, and discovered that killer whales were now eating otters due to the depletion of whales.

• The depletion of keystone species can have cascading effects on entire ecosystems.The Discovery of Trophic Cascades and Keystone Species

• Trophic cascades are the effects that predators have on the abundance and behavior of their prey and other species within an ecosystem.

• In the 1960s, ecologist Robert Paine discovered the concept of keystone species, which are species that have a disproportionate effect on the ecosystem relative to their abundance.

• Paine's experiment involved removing the starfish, a keystone predator, from a rocky shore ecosystem and observing the subsequent changes in the abundance of other species.

• Paine's experiment demonstrated that keystone species can have a profound effect on the ecosystem and that the removal of a keystone species can lead to the decline of other species within that ecosystem.

• Paine's work inspired ecologist James Estes, who conducted a similar experiment in the Aleutian Islands, where he found that the removal of sea otters, another keystone predator, led to the decline of kelp forests.

• Estes' work led to the discovery of trophic cascades, which are the effects that predators have on the abundance and behavior of their prey and other species within an ecosystem.

• The discovery of trophic cascades challenged the prevailing view of ecology, which focused on bottom-up effects, or the effects of abiotic factors like temperature and rainfall on ecosystems.

• The discovery of trophic cascades highlighted the importance of top-down effects, or the effects of predators on ecosystems.

• In the Aleutian Islands, the removal of sea otters led to an increase in sea urchin populations, which in turn led to the decline of kelp forests.

• In the North Pacific, the removal of whales led to an increase in killer whale populations, which in turn led to the decline of sea otter populations and the subsequent decline of kelp forests.

• The discovery of trophic cascades and keystone species has changed the way ecologists and conservationists view ecosystems and has given them new tools for managing and protecting these systems.

• Ignoring the role of apex predators and top-down effects in ecosystems can lead to mistakes and risks to the health and stability of these systems.