Category: Ecomorphs
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Ecomorphs (or "ecological morphotypes") represent classic and particularly straightforward examples of convergent evolution. As there is a close relationship between morphological and ecological variation, similar environmental conditions may lead to the repeated evolution of the same morphology. This is reflected in the term ecomorph, which refers to ecological equivalents or convergent adaptive types. When studying ecomorph diversity in freshwater fish, Kirk Winemiller remarked: "The concept of ecological convergence and independent evolution of equivalent ecomorphotypes deserves special attention because of its implications for general ecological and evolutionary theory" (Winemiller 1991, Ecological Monographs, vol. 61, p. 361).
Ecomorphs can be found in many animal groups, but one of the most famous examples is the Anolis lizards of the Caribbean. There are striking similarities between various species on different islands, representing specific anolid ecomorphs that reflect the type of habitat, such as "twig ecomorphs" with short limbs and "trunk ecomorphs" with long limbs. Among the lizards, there are also sand-dwelling ecomorphs that inhabit arid regions of Africa, the Americas and Australia. Members of six distantly related lizard families have independently adapted to this extreme environmental setting and converged on many shared aspects of morphology and behaviour, from sand-diving to collecting early morning dew on specialised skin surfaces.
The amphibians provide striking cases of ecomorphological convergence, too. Particularly remarkable are the frogs of Madagascar and those of Asia that show compelling, but independent, similarities between burrowing, arboreal, rock-dwelling and torrential ecomorphs. So too the Madagascan mantellid frogs are strikingly convergent with the neotropical poison-arrow frogs (the dendrobatids).
One of the classic mammalian ecomorph examples concerns different cat-like species that evolved a sabre-tooth morphology. Two distinct ecomorphs are recognised ("dirk-tooth" with elongate sabres and "scimitar-tooth" with somewhat shorter canines), which evidently represent different hunting strategies, and both evolved repeatedly in different felid groups, as well as showing parallels in the thylacosmilid marsupials of South America.
Further striking cases have been documented amongst the fish (notably the tuna/lamnid shark ecomorphs that show convergence in terms of locomotion and thermoregulation) and also birds are useful in the general documentation of ecomorphs, with ecomorphological convergence observed in vultures and other raptors (where different diets and hunting strategies are reflected in beak and hindlimb morphology).
