Turtles and tortoises (chelonians) have been integral components of global ecosystems for about 220 million years and have played important roles in human culture for at least 400,000 years. The chelonian shell is a remarkable evolutionary adaptation, facilitating success in terrestrial, freshwater and marine ecosystems. Today, more than half of the 360 living species and 482 total taxa (species and subspecies combined) are threatened with extinction. This places chelonians among the groups with the highest extinction risk of any sizeable vertebrate group. Turtle populations are declining rapidly due to habitat loss, consumption by humans for food and traditional medicines and collection for the international pet trade. Many taxa could become extinct in this century. Here, we examine survival threats to turtles and tortoises and discuss the interventions that will be needed to prevent widespread extinction in this group in coming decades.
Replicate adaptive radiations are dichotomous morphological patterns related to resource use and repeated in a series of isolated habitats. Biologists have long noted a dichotomy in relative head width and alveolar width among species of map turtles ( G a p h j s ) , particularly with regard to adult females, which are much larger than adult males in all 12 species. I measured plastron length (PL), head width (HW), and alveolar width (AW) of nearly 2300 specimens representing the 12 recognized species, and used allometric regressions to investigate this genus as an example of both sexual dimorphism in trophic morphology and replicate adaptive radiation. Sexual dimorphism was noted in HW after correction for PL, with females having wider heads than males of simiiar body sizes, but AW as corrected for HW was not dimorphic, thus absolute differences in AW are the simple result of differences in HW. Sexual differences in HW probably relate to the dimorphic niches of G@hys, as females of three species have been reported to occupy deeper water further from shore than conspecific males. Based on predicted HW at maximum PL in adult females, species were categorized as mega-, meso-, or microcephalic. Differences in relative head width are related to differences in degree of molluscivory, with little molluscivory in microcephalic females, moderate to high molluscivory in mesocephalic females, and high molluscivory iri megacephalic females. Distributions of Gr@temys species in sympatry and dopatry reveal patterns consistent with structuring of distributions via competitive interactions. Superimposing data on relative HW on a phylogeny of the genus suggests there may have been one or two episodes of character displacement, with subsequent character assortment, in Gr@-@ys evolution. This conclusion is similar to the current model for the evolution of body size during the radation of Anolis lizards in the northern Lesser Antilles.
2000The h e a n sofiety of London ADDITIONAL KEY WORDS-trophic morphologysexual dimorphismcharacter displacementcharacter assortmentmolluscivory.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.