Age structure is the number of individuals of each age within the population.
Biological diversity is the variety of life from the genetic make-up of species to populations, habitats, and ecosystems. Conservation is the management of a natural resource so that it can be sustained over the long-term. Conservation biology is a multidisciplinary science that has developed to deal with the crisis of declining biological diversity. Critical habitat , a term used in the Endangered Species Act, includes areas in which are found the physical and biological features essential to the conservation of a species. Cross-fostering is a captive propagation technique in which the young or eggs of one species are raised by another species.