KEY CONCEPT Ecological succession is a process of change in the species that make up a community.

Species richness is the number of species in a community Species evenness is the relative abundance of each species In both of the examples, species richness is identical (same number of species), but the example to the right has greater species evenness than the example to the left.

Latitude and Species Richness In general, species richness is greatest near the equator, and larger areas support more species. Species interactions such as predation can promote species richness.

Community Stability and Species Richness Disturbances can alter a community by eliminating or removing organisms or altering resource availability. Species richness may improve a community’s stability Areas of low species richness may be less stable in the event of an ecological disturbance.

Succession occurs following a disturbance in an ecosystem. a sequence of biotic changes damaged communities are regenerated new communities arise in previously uninhabited areas

There are two types of succession. Primary succession — started by pioneer species Occurs in areas that have been recently exposed to the elements and lack soil (bare rock)

Example of primary succession Lichen - any complex organism of the group Lichenes, composed of a fungus insymbiotic union with analga and having a greenish, gray, yellow,brown, or blackish thallus that grows in leaflike, crustlike, orbranching forms on rocks, trees, etc.

Secondary succession — started by remaining species Occurs in areas where the original ecosystem has been cleared by a disturbance.

Example of Secondary Succession

Summary of Succession