The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage is called or known as adaptive radiation. It starts with a recent single ancestor. This process results in the speciation and phenotypic adaptation of species. These species exhibiting different morphological and physiological traits. Thus, they can exploit a range of divergent environments. Adaptive radiation can be graphically illustrated as a bush, or clade, of coexisting species on the tree of life.
Identification of Adaptive Radiation
Four features can be used to identify an adaptive radiation:
- A common ancestry of component species: Specifically, a recent ancestry.
- A phenotype-environment correlation: A significant association between environments and the morphological and physiological traits used to exploit those environments.
- Trait Utility: The performance or fitness advantages of trait values in their corresponding environments.
- Rapid Speciation: Presence of one or more bursts in the emergence of new species at the time of ecological and phenotypic divergence.
Causes of Adaptive Radiation
- The evolution of a novel feature. It may permit a clade to diversify by making new areas of morpho-space accessible. A classic example is the evolution of a fourth cusp in the mammalian tooth. This trait permits a vast increase in the range of foodstuffs which can be fed on.
- Evolution of this character has thus increased the number of ecological niches available to mammals. The trait arose a number of times in different groups during the Cenozoic, and in each instance, was immediately followed by an adaptive radiation.
- Birds find other ways to provide for each other, i.e. the evolution of flight opened new avenues for evolution to explore, initiating an adaptive radiation opportunity.
- Adaptive radiations often occur as a result of an organism arising in an environment with unoccupied niches, such as a newly formed lake or isolated island chain. The colonizing population may diversify rapidly to take advantage of all possible niches. In Lake Victoria, an isolated lake which formed recently in the African rift valley, over 300 species of cichlid fish adaptively radiated from one parent species in just 15,000 years.
- Adaptive radiations commonly follow mass extinctions: following extinction, many niches are left vacant. A classic example of this is the replacement of the non-avian dinosaurs and the end of the Cretaceous, with mammals at of brachiopods by bivalves at the Permo-Triassic boundary.