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.

African Elephant (Loxodonta africana)

1. Location: African savannah grasslands
2. Ecological Role: Ecosystem engineer keystone species
3. Primary Function: Shapes vegetation structure by feeding on shrubs and trees.
4. Impact on Ecosystem:
   1. Prevents shrub encroachment, maintaining open grassland habitats.
   2. Facilitates grass growth that supports herbivores such as zebras, wildebeest, and gazelles.
   3. Creates microhabitats for birds, insects, and small mammals through tree-felling and dung deposition.
   4. Enhances soil fertility by redistributing organic matter and nutrients.
5. Outcome of Removal:
   1. Savannahs become overgrown with woody plants.
   2. Grasses decline → herbivore populations fall → predators lose food sources.
   3. The entire ecosystem shifts toward a woodland state, reducing biodiversity.

Importance of Keystone Species in Sustainability

1. Keystone species maintain equilibrium by regulating populations, ensuring balanced resource use, and preventing domination by a few species.
2. They support species diversity, resilience, and nutrient cycling, which are essential for ecosystem sustainability.
3. Their roles make ecosystems self-regulating, allowing long-term persistence and recovery after disturbances.

Consequences of Keystone Species Loss

1. Cascading trophic effects: Disruption of predator-prey dynamics can destabilize entire food webs.
2. Loss of biodiversity: Competitive exclusion may eliminate weaker species.
3. Habitat degradation: Reduced structural diversity leads to fewer ecological niches.
4. Ecosystem collapse: When balance is lost, systems may shift to a new, less productive equilibrium.