Adaptive radiation is the rapid diversification of a group of organisms from a single ancestral species into many new forms, typically set off when environmental change opens up new resources or ecological opportunities. Darwin's finches are a classic case: around fifteen species descended from a single ancestor that reached the Galapagos roughly three million years ago, each evolving a beak suited to a different food source, from cracking tough seeds to probing for insects to feeding on cactus nectar. The cichlid fishes of Africa's Great Lakes, with roughly 2,000 species across Lakes Tanganyika, Malawi, and Victoria, are the most species-rich modern example, filling ecological roles that elsewhere are divided among several fish families, and Hawaii's honeycreepers, silverswords, and lobelioids each underwent their own separate radiations on the islands. Adaptive radiation is generally triggered by the loss of competitors or predators, the evolution of a key innovation, dispersal into an isolated environment full of unfilled niches, or a mass extinction that clears ecological space, any of which can reduce competition enough for a population to diversify into it.
Facts
PeriodicityNot a recurring or periodic event: a burst of diversification triggered once an ecological opportunity opens, rather than a process on a fixed timetable. 1 ScaleRanges from a single island archipelago, as with Darwin's finches on the Galapagos, to whole new lake basins such as the Rift Valley Lakes formed by tectonic movement of the East African Rift. 1 First DescribedBest known and most widely documented through Darwin's finches on the Galapagos Islands, the case study that gives the process its prototypical example. 1 Identification
Distinguishing AppearanceIdentified by four features occurring together: a recent common ancestry among the diversified species, a correlation between their traits and their environments, a genuine performance advantage from those traits, and a burst of rapid speciation around the same time. 1 Connections
Associated With
Source Adaptive radiation (Wikipedia)
Demonstrated By
The cichlid fish of the African Great Lakes are among the most widely cited examples of explosive adaptive radiation.
Source Encyclopaedia Britannica
Source Encyclopaedia Britannica
Source Encyclopaedia Britannica
Sources
1. Adaptive radiation (Wikipedia)
Wikimedia FoundationLead section, first sentence
adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new environmental niches.
Conditions section, on new habitats and lake basins
the tectonic movement that formed the East African Rift, ultimately leading to the creation of the Rift Valley Lakes, is an example of this.
Lead section, second sentence
The prototypical example of adaptive radiation is finch speciation on the Galapagos ("Darwin's finches"), but examples are known from around the world.
Characteristics section, second listed feature
A phenotype-environment correlation: a significant association between environments and the morphological and physiological traits used to exploit those environments.
Associated With: Allopatric speciation, Examples section, Darwin's finches, on the mechanism of initial diversification
One proposition is that the finches were able to have a non-adaptive, allopatric speciation event on separate islands in the archipelago, such that when they reconverged on some islands, they were able to maintain reproductive isolation.
View the Source Encyclopaedia Britannica
Encyclopaedia Britannica, Inc.- Demonstrated By: Lake Baikal
- Demonstrated By: African Great Lakes
- Demonstrated By: Lake Tanganyika
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