Mechanisms of maintenance of species diversity

Organises coexistence mechanisms into those that stabilise — making each species recover when rare, because it limits itself more than it limits others — and those that merely equalise, reducing fitness differences without producing that self-limitation.

Sample size

theoretical synthesis across coexistence mechanisms

Stable coexistence requires that intraspecific competition exceed interspecific competition. Mechanisms achieving this include resource partitioning, environmental fluctuation combined with differing responses, and spatial variation with limited dispersal.

• Theoretical synthesis; applying it to a particular field system requires measurements that are often unavailable.
• Distinguishing stabilising from equalising mechanisms empirically remains difficult.

• Competitive exclusion

  Two species limited by exactly the same thing, in an unchanging environment, cannot coexist indefinitely. Nature rarely offers an unchanging environment — which is why so many similar species do coexist.

• Competitive exclusion

  Species coexist stably when each is held back more by its own kind than by the other. Being different is not enough on its own — what matters is whether a species recovers when it becomes rare.

• Ecology

  Disturbed systems sometimes return to something like what they were, sometimes settle into a different arrangement and stay there, and sometimes keep changing. Which one happens is a question, not a property of nature.