BIOL 303

• extrinsic heterogeneity: heterogeneity is a feature of the environment 
• intrinsic heterogeneity: heterogeneity is caused by the coupled action of environment and community 

• high- few species with the appropriate fundamental niche, reduced diversity 
• intermediate- promote higher diversity
• low- high competition, reduced diversity 

• can keep species below carrying capacity 
• competition exclusion unlikely 
• therefore number of species high 

populations that are spatially structured into assemblages of locally breeding populations with dispersal among them 

communities that are connected through dispersal of some individuals 

• patch-dynamics- allows co-existence in region 
• species sorting- dispersal allows shift in competition with environmental change 
• mass effects- species maintained in unfavourable habitats 
• neutral- occupancy is random, dependent on chance

an association of interacting species inhabiting some defined area 

a group of organisms that all make their living in a similar way

species accumulation curve

A measure of how evenly individuals are distributed among species independent of species number 

• number of species 
• species evenness