Habitats, stress, and evolutionary rates

Habitats of organisms are expressed as an interaction between stress intensity, magnitude of environmental fluctuations, and energy availability from resources. Under this model organisms should evolve broad biological properties defined by such physical characteristics. When energy is severely restricted under the continuing constant stress of adversity‐selection, or in widely fluctuating and highly stressful environments, little evolutionary change is expected; relict species and ‘living fossils’ are the respective expectations. In rather stable abiotic environments where resources are limited habitat preferences may develop leading to specialization and ultimately adaptive radiations. On the other hand major new innovations are more likely in highly disturbed resource‐rich habitats. Evidence from the living and fossil biota is presented which is consistent with these conclusions.