The Princeton Guide to Ecology

Adaptive radiation is generally triggered by the appearance of available niche space, which could result from (1) intrinsic factors or key innovations that allow an organism to exploit a novel resource, and/or (2) extrinsic factors, in which physical ecological space is created as a result of climatic changes or the appearance de novo of islands. There are no general rules as to what taxa are more likely to undergo adaptive radiation, although some lineages may have certain attributes that facilitate adaptive radiation in the appropriate setting. The process of adaptive radiation is described below, as well as some prime examples of the phenomenon. Adaptive radiation is generally initiated by expansion of ecological amplitude of a taxon into newly available ecological space, followed by specialization, the process possibly facilitated through adaptive plasticity. Speciation associated with adaptive radiation may involve one or more of the following: founder events, divergent natural selection, sexual selection, and hybridization. Competition is generally implicated in divergent natural selection and in dictating the communities of species formed during the course of adaptive radiation. Current research is focused on (1) examining the molecular underpinnings of apparently complex morphological and behavioral changes that occur during the course of adaptive radiation, and (2) experimental manipulation of bacteria to assess the conditions under which adaptive radiation occurs.

adaptive radiation. Rapid diversification of an ancestral species into several ecologically different species, associated with adaptive morphological, physiological, and/or behavioral divergence

attenuation. Decline in number of species represented on islands with distance from a source of colonists

divergent natural selection. Selection arising from environmental forces acting differentially on phenotypic traits (morphology, physiology, or behavior) resulting in divergent phenotypes; reproductive isolation may occur as a side effect, either in sympatry or allopatry

ecological character displacement. Divergence in ecological traits (which may lead to reproductive isolation as a by-product) caused by competition for shared resources

ecological release. Expansion of habitat or use of resources by populations into areas of lower species diversity with reduced interspecific competition

ecological speciation. Process by which barriers to gene flow evolve between populations as a result of ecologically based divergent natural selection

ecomorph. A group of populations, species, etc., whose appearance is determined by the environment

escalation/diversification. Diversification of a herbivore/ parasite in concert with its host in which the adaptations of the host to counter exploitation by the herbivore or parasite build one on each other, and vice versa

escape and radiation. Diversification of a herbivore/ parasite in concert with its host in which the host is generally considered to radiate before exploitation and subsequent radiation by the herbivore or parasite, and vice versa

founder event. Establishment of a new population with few individuals that contain a small, and hence unrepresentative, portion of the genetic diversity

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