[2] Certain common characteristics apply to various taxa within the animal kingdom, which traits are often sorted among amphibians, reptiles, mammals, avafauna, arthropods and lower life forms.
For many amphibians, an annual breeding cycle applies, typically regulated by ambient temperature, precipitation, availability of surface water and food supply.
Annual breeding cycles sometimes apply to mammals, with regulating environmental effects including seasonal temperature variation and food availability.
The polar bear is an example of a mammal who uses a maternity den, whose locations are influenced by migration movements of this species to the seasonal Arctic pack ices.
Evidence from mammalian and bird populations indicated that inbreeding depression often significantly adversely affects birth weight, reproduction and survival, as well as resistance to environmental stress, disease and predation.