28.10
Keystone Species
Measures of species biodiversity, such as richness (i.e., the number of species present) and evenness (i.e., their relative abundance), describe an ec…
In architecture, a keystone is the central stone in an arch that holds the other stones in place. If the keystone is removed, the structure collapses.
A keystone species plays a key role in the structure of an ecological community by influencing the number and variety of species through ecological interactions, including predation, competition, and habitat modification.
Relative to its abundance in the community, a keystone species has a disproportionately large effect on community structure.
If the keystone species is removed, the community structure can change dramatically, often leading to major shifts in species composition.
For example, in kelp forest ecosystems along the Pacific coast, sea otters are a keystone species.
These otters consume large quantities of sea urchins, which mainly graze on kelp. Without predation by sea otters, the sea urchin population increases dramatically and can destroy the kelp forests.
Species such as fish, crabs, and clams that depend on kelp forests decline significantly, resulting in the formation of urchin barrens.
Biodiversity describes the variety of life in a community and is often discussed in terms of species richness, which is the number of species present, and evenness, which is their relative abundance.
Sea otters promote biodiversity by reducing the sea urchin population. They are the primary predator in the kelp forest and help regulate this population.
So, many species that live in kelp forests rely on sea otters to protect their habitat.
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Q1: What makes a keystone species different from other species in an ecosystem?
A keystone species has a disproportionately large effect on community structure relative to its abundance. Through predation, competition, and habitat modification, keystone species influence the number and variety of other species. Their removal causes dramatic changes in community structure and species composition, unlike most other organisms whose absence produces minimal ecosystem effects.
Q2: How do sea otters maintain kelp forest biodiversity?
Sea otters are keystone predators that consume large quantities of sea urchins, which graze on kelp. By regulating sea urchin populations through predation, sea otters prevent urchin barrens and protect the kelp forests that support fish, crabs, clams, and other species. This predator-prey interaction promotes biodiversity by maintaining habitat structure and species richness.
Q3: What happens to an ecosystem when a keystone species is removed?
Removing a keystone species triggers dramatic shifts in community structure and species composition. In kelp forests, sea otter removal allows sea urchin populations to explode, destroying kelp and creating urchin barrens where dependent species decline. Similarly, wolf removal from Yellowstone caused elk populations to soar, leading to overgrazing that destroyed habitats and altered abiotic factors like stream stability.
Q4: How does biodiversity relate to species richness and evenness?
Biodiversity describes the variety of life in a community and is measured by species richness, the number of species present, and evenness, their relative abundance. Keystone species like sea otters promote biodiversity by reducing dominant species populations, allowing more species to coexist. This increases both richness and evenness within the community.
Q5: Why is recognizing keystone species important for conservation?
Identifying keystone species is essential for ecosystem maintenance and restoration. Gray wolves reintroduced to Yellowstone restored ecosystem balance by controlling elk populations, which recovered habitats and nutrient cycling. Understanding keystone roles allows ecologists to implement more effective conservation strategies and predict how ecosystem changes will cascade through communities.
Q6: How do keystone species differ from foundation species and dominant species?
Keystone species exert disproportionate influence through predation and competition despite low abundance. Foundation species like kelp are habitat-forming organisms that physically support ecosystems. Dominant species like mussels are simply the most abundant organisms. Each plays distinct ecological roles in shaping community structure and biodiversity.
Q7: What ecological interactions allow keystone species to control community structure?
Keystone species exert top-down control over lower trophic level organisms through predation, competition, and habitat modification. Sea otters use predation to regulate sea urchins, while gray wolves control elk populations. These interactions reduce resource exploitation by dominant species, allowing greater species coexistence and maintaining ecosystem balance.