11.4. CooperationIntra-specific cooperation results in increased reproduction and/or survival of organisms in groups as compared to isolated organisms. This is called group effect which was first analyzed Allee (1931) and is often called "Allee effect".
Group effect results in the increase of population growth rate with increasing population density when density is low. There is more danger of extinction in populations with group effect because there is a minimum population density below which population declines until it is gone.
Cooperation between different species is relatively rare in nature and we will not study its models. Usually it has a form of symbiosis.