6. Patterns of Evolution
Divergent Evolution
Most evolutionary change appears to be DIVERGENT EVOLUTION, with ancestral species evolving into two or more species that become specialised to occupy different niches.
This may be due to the ancestral species spreading out to occupy new habitats with differing conditions. The populations then become genetically isolated.
When an ancestral species diverges into a large number of species occupying separate niches, the process is called ADAPTIVE RADIATION. this has occurred with many of the ancestral species that originally colonised New Zealand, and then spread out to occupy different habitats, in which they then diversified.
Adaptive radiation is a relatively rapid process that involves the FOUNDER EFFECT.
Convergent Evolution
CONVERGENT EVOLUTION is a pattern of evolution where different, non-(recently)-related groups develop similar adaptations. This is not due to a common ancestor, but is due to independent random mutations being selected for in different groups, as there is similarity in their SELECTION PRESSURES.
Therefore, convergent evolution is related to mutation and natural selection. Areas of the world with harsh environments could have non-related species that look the same through different or similar random mutations being selected for.
The two groups don't hybridise due to RIMs.
Coevolution
CO-EVOLUTION is defined as two species that act as selection pressures on the evolution of each other, so both species reinforce each others’ phenotype. Both species have exerted selection pressures on each other over time; adaptaitons in one species have led to reciprocal adaptations in the other. A co-evolutionary relationship develops, where over time, two species develop specific adaptations to enable their existence in the presence of the other organism.
An advantage of coevolution is that it results in the species having adaptations that can be helpful in surviving. Coevolution could allow a species to become more specialised to be the only species that survive in a particular niche - this means less competition for a particular resource.
The disadvantage of coevolution is that any change or loss of one species may cause loss of the other species. Also, coevolution results in lack of variation, which makes a species vulnerable to habitat change.
Convergent evolution and coevolution are similar because they are both the result of selection pressures acting on reproductively isolated populations.
Convergent and co-evolution are different because convergent evolution is more about all species having similar selection pressures and so develop similar structures. Whereas with coevolution, any change in one provides the selection pressure for changes in the other.