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I.1.4 Adaptive radiation

Adaptive radiation, evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life.

Adaptive radiations are best exemplified in closely related groups that have evolved in a relatively short time.

Characteristics

Four features can be used to identify an adaptive radiation:

  1. A common ancestry of component species: specifically a recent ancestry. Note that this is not the same as a monophyly in which all descendants of a common ancestor are included.
  2. A phenotype-environment correlation: a significant association between environments and the morphological and physiological traits used to exploit those environments.
  3. Trait utility: the performance or fitness advantages of trait values in their corresponding environments.
  4. Rapid speciation: presence of one or more bursts in the emergence of new species around the time that ecological and phenotypic divergence is underway.

Conditions

Adaptive radiation tends to take place under the following conditions:

  1. A new habitat has opened up: a volcano, for example, can create new ground in the middle of the ocean. An extinction event could effectively achieve this same result, opening up niches that were previously occupied by species that no longer exist.
  2. This new habitat is relatively isolated. When a volcano erupts on the mainland and destroys an adjacent forest, it is likely that the terrestrial plant and animal species that used to live in the destroyed region will recolonize without evolving greatly. However, if a newly formed habitat is isolated, the species that colonize it will likely be somewhat random and uncommon arrivals.
  3. The new habitat has a wide availability of niche space. The rare colonist can only adaptively radiate into as many forms as there are niches.

example- in the Paleogene Period (beginning 66 million years ago), of basal mammalian stock into forms adapted to running, leaping, climbing, swimming, and flying. Various modern types of mammals have evolved by the modification of limbs and other structures adapted to a wide variety of habitats.

  1. Running (in deer, cheetah, etc.),
  2. burrowing (in moles, rodents and rabbits),
  3. tree-climbing (in squirrel and sloth),
  4. flying (in bats and flying squirrel) and
  5. swimming (in seals, whales, etc.).

Example- Primates ( narrate with example)

Significance:

Adaptive radiations help in macro-evolution which divides a group into many new groups. This helps in survival in different habitat.

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