Triggering adaptive radiation
An adaptive radiation generally means an event in which a lineage rapidly diversifies, with the newly formed lineages evolving different adaptations. Different factors may trigger adaptive radiations, but each is a response to an opportunity.
Release from competition/vacated niches
Specialization may subdivide a single niche into many new niches. For example, cichlid fishes have diversified in East African lakes into more than 600 species. This diversification may have been possible because different fish lineages evolved to take advantage of different foods (including insects, algae, mollusks, small fish, large fish, other fishes' scales, and even other fishes' eyes!).
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Beetle photo © Windsor Aguirre; Cichlid photos courtesy of Michael K. Oliver, Ph.D.
Understanding Evolution © 2015 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California