2.1J Keystone species Notes

1. A keystone species is one that exerts a disproportionately large impact on the structure, diversity, and stability of an ecosystem relative to its abundance.
2. Keystone species are not always the largest or most numerous, but their roles are irreplaceable.
3. Even though keystone species may be few in number, their ecological roles are critical for maintaining balance and sustainability within the community.
4. They often:
   1. Control Populations: Prevent any one species from dominating.
   2. Maintain Diversity: Support a variety of species by creating or preserving habitats.
   3. Stabilize Ecosystems: Ensure the ecosystem remains balanced and functional.

Key Characteristics of Keystone Species

1. Disproportionate ecological influence: Their impact exceeds what would be expected based on population size or biomass.
2. Regulation of population dynamics: They control other species’ populations (often competitors, prey, or plants).
3. Maintenance of biodiversity: Prevent domination by a single species, sustaining species richness.
4. Promotion of habitat complexity: Their behavior or feeding creates diverse niches.
5. Stabilization of ecosystems: Contribute to resilience against disturbances.

Purple Sea Star (Pisaster ochraceus)

1. Location: North Pacific coast (rocky intertidal zones)
2. Ecological Role: Predator keystone species
3. Primary Function: Regulates mussel (Mytilus californianus) populations, preventing them from monopolizing rocky surfaces.
4. Impact on Biodiversity:
   1. Controls the overabundant mussel population.
   2. Creates open space for other organisms like barnacles, limpets, algae, and anemones to thrive.
   3. Enhances species diversity and community structure.
5. Outcome of Removal:
   1. Without sea stars, mussels proliferate and outcompete other species.
   2. The ecosystem shifts to a low-diversity community dominated by mussels.
   3. Demonstrated by Robert Paine’s classic 1966 ecological experiment.