A keystone species is a species that has a disproportionately large impact on the environment relative to its abundance

• It is analogous to a keystone in an arch – it fundamentally supports the whole structure and prevents it from collapsing
  

Keystone species may influence communities in a number of ways:

• Predators – they can exert pressure on lower trophic levels to prevent them from monopolising certain resources
  

• Mutualism – they can support the life cycle of a variety of species within a community (e.g. pollinators / seed dispersal)
  

• Engineers – they can refashion the environment in a manner that promotes the survival of other species
  

There are numerous examples of keystone species within different communities:

• Sea otters (predator) exert top-down pressure on sea urchins which graze on kelp, preventing urchin overpopulation and kelp destruction
  

• Honey bees (mutualist) pollinate a wide variety of plant species, ensuring the continuation of the plant life cycle 
  

• Beavers (engineer) build dams that transform the environment in a manner that allows certain other species to survive
  

Keystone Species