Adaptive Radiation, Ecological Opportunity, and Evolutionary Determinism

Abstract

Adaptive radiation refers to diversification from an ancestral species that produces descendants adapted to use a great variety of distinct ecological niches. In this review, I examine two aspects of adaptive radiation: first, that it results from ecological opportunity and, second, that it is deterministic in terms of its outcome and evolutionary trajectory. Ecological opportunity is usually a prerequisite for adaptive radiation, although in some cases, radiation can occur in the absence of preexisting opportunity. Nonetheless, many clades fail to radiate although seemingly in the presence of ecological opportunity; until methods are developed to identify and quantify ecological opportunity, the concept will have little predictive utility in understanding a priori when a clade might be expected to radiate. Although predicted by theory, replicated adaptive radiations occur only rarely, usually in closely related and poorly dispersing taxa found in the same region on islands or in lakes. Contingencies of a variety of types may usually preclude close similarity in the outcome of evolutionary diversification in other situations. Whether radiations usually unfold in the same general sequence is unclear because of the unreliability of methods requiring phylogenetic reconstruction of ancestral events. The synthesis of ecological, phylogenetic, experimental, and genomic advances promises to make the coming years a golden age for the study of adaptive radiation; natural history data, however, will always be crucial to understanding the forces shaping adaptation and evolutionary diversification.

Founder niche constrains evolutionary adaptive radiation

“…This is supported by a large body of work on extant adaptive radiations (3,8,9,11,15,18,19). In addition, evolutionary experiments with bacteria have provided direct evidence that links environmental components of ecological opportunity to patterns of adaptive radiation (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30).…”

“…niche evolution | ecological opportunity | biodiversity R apid diversification of a single lineage into organisms with different niches-adaptive radiation-underpins the evolution of biodiversity (1)(2)(3)(4). Here, we define a niche as the complex of reciprocal ecological interactions between an organism and its environment that governs organismal fitness (following refs.…”

“…Although the dynamics of adaptive radiation are determined by the interplay of many factors, two universal prerequisites are sufficiency of founder evolvability and availability of ecological opportunity (1)(2)(3)(4)(8)(9)(10)(11)(12). Founder evolvability concerns the maximal range of derived organisms with different niches that can be accessed from the founding ancestor by mutation and recombination over an interval of evolutionary time (3,8,(13)(14)(15)(16). Ecological opportunity for adaptive radiation emerges when the environment allows the possibility of invasion and persistence of multiple derived organisms with different niches (17).…”

“…Since Simpson (2) formulated the requirements for adaptive radiation in the 1950s, the environment has been established as a major determinant of ecological opportunity (3). This is supported by a large body of work on extant adaptive radiations (3,8,9,11,15,18,19).…”

Evidence for determinism in species diversification and contingency in phenotypic evolution during adaptive radiation

“…The theory of AR driven by EO suggests that this deterministic early-burst process governs both speciation and ecomorphological diversification, where ecological limits ultimately guide declines in rates as niches are filled [7,17]. However, an intriguing possibility is that species diversification is deterministic, while ecomorphological differences are intrinsic to the particular clade [3,[18][19][20]. Thus, AR via EO may result in contingent morphological evolution, while processes associated with rates of diversification may be heavily deterministic.…”