Author: Jonathan Losos Page 97 of 130

In an epic undertaking, Powell and Henderson have edited a monograph compiling the species occurrence of reptiles and amphibians on more than 700 Caribbean islands. In addition to the species lists, information on island size and location is provided, and introduced and extinct species are noted.

This work, an update on several previous such lists, will be enormously useful for biogeographers, ecologists, evolutionary biologists, and conservationists, among others, and the editors and authors are to be heartily thanked and congratulated for their efforts.

Now, an anole bone to pick.

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Anolis concolor from mangroves on San Andres island. Photo by Lee Fitzgerald

Almost all Caribbean anoles are descendants from a single colonizing species, whose descendants now occupy all of the Greater Antilles, the Lesser Antilles south through Dominica, and many other islands. Almost all of the remaining species are members of the roquet clade, occupying the southern Lesser Antilles and descended from a South American colonist. As we all know, these species have been extensively studied.

But colonization of Caribbean islands has occurred more than just these two times. Some other islands have been colonized by different colonists. None of these invasions has led to much in the way of evolutionary radiation and these species–in each case the only anole on the islands they occupy–have been little studied. We’ve previously discussed one such colonization, A. lineatus on Aruba and Curaçao. In addition, islands in the Pacific (yes, the Pacific!) have twice been colonized, leading to A. agassizi on little known Malpelo and A. townsendi on Cocos Island (incidentally, the island said to have beeen the inspiration for Isla Nublar in Jurassic Park).

And, finally, there are the presumed sister taxa, A. pinchoti and A. concolor, on the Colombian islands of Providencia and San Andrés. A smidgeon of research has been conducted previously on their ecology, and now a new paper in the South American Journal of Herpetology has examined their morphology. Calderón-Espinosa and Barragán Forero measured museum specimens of these species and compared them to published data on a variety of other Caribbean anoles. They found that neither species is a good match for any of the Greater Antillean ecomorphs, but that they are most similar to trunk-ground or trunk-crown anoles. By comparison, anoles of the Lesser Antilles are also most similar to these two ecomorphs. Anolis concolor attains an intermediate body size, similar to Lesser Antillean species that occupy islands on which they are no other anole species. By contrast, A. pinchoti is smaller and more similar to the smaller Lesser Antillean species on two-species islands.

Anoles are renowned for their convergent evolution. Further comparison of the many cases in which anoles have colonized relatively small islands should prove interesting.

M. L. Calderón-Espinosa and A. Barragán Forero (2011). Morphological Diversification in Solitary Endemic Anoles: Anolis concolor and Anolis pinchoti from San Andrés and Providence Islands, Colombia South American Journal of Herpetology

Anolis cristatellus from mesic habitats. Photo by Manuel Leal.

For obvious reasons, there is great concern about how species will cope with climate change–as the world gets hotter, will species be able to survive? Many studies have taken a macroscopic view, examining the geographic distribution of a species to divine what its temperature tolerances are and then projecting where it will be able to occur in the future. Although such approaches are useful as a first pass, direct study of the physiology of species is a much more informative way of determining how a species will be affected. An excellent example of just this approach was published recently by Gunderson and Leal in Functional Ecology (pdf here).

Mesic and xeric habitats. Photos courtesy Alex Gunderson (left) and Manuel Leal (right)

The authors studied the Puerto Rican crested anole, A. cristatellus, which occurs throughout Puerto Rico and the Virgin Islands. They focused on comparing populations living in cooler, wetter (mesic) habitats versus those living in hotter, drier (xeric) places. They found that in the field, mesic populations had an average body temperature of  about 29 C, whereas xeric populations averaged 32.5 C. However, using copper models as described in previous posts, the authors determined that a lizard randomly placed in a mesic habitat would have a temperature of about 29 C, whereas the random xeric lizard would be 33.5. In other words, the lizards are not thermoregulating in the mesic forest (lizards and randomly placed copper models have the same temperature), but they are actively altering their habitat use in the xeric areas to use cooler spots and thus keep their temperature lower than if they were sitting in random spots. In support of this conclusion, the mesic lizards were in the sun about as much as expected, but the xeric lizards were in the sun less often than predicted.

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