Showing papers by "Jonathan B. Losos published in 1998"

Contingency and Determinism in Replicated Adaptive Radiations of Island Lizards

Abstract: The vagaries of history lead to the prediction that repeated instances of evolutionary diversification will lead to disparate outcomes even if starting conditions are similar. We tested this proposition by examining the evolutionary radiation of Anolis lizards on the four islands of the Greater Antilles. Morphometric analyses indicate that the same set of habitat specialists, termed ecomorphs, occurs on all four islands. Although these similar assemblages could result from a single evolutionary origin of each ecomorph, followed by dispersal or vicariance, phylogenetic analysis indicates that the ecomorphs originated independently on each island. Thus, adaptive radiation in similar environments can overcome historical contingencies to produce strikingly similar evolutionary outcomes.

A comparative analysis of the ecological significance of maximal locomotor performance in caribbean anolis lizards.

Abstract: We examined the sprinting and jumping capabilities of eight West Indian Anolis species during three natural activities (escape from a predator, feeding, and undisturbed activity). We then compared these field data with maximal performance under optimal laboratory conditions to answer three questions: (1) Has maximal (i.e., laboratory) sprinting and jumping performance coevolved with field performance among species? (2) What proportion of their maximum capabilities do anoles sprint and jump in different ecological contexts? (3) Does a relationship exist between maximal sprinting and jumping ability and the proportion of maximal performance used in these contexts? Among species, maximal speed is tightly positively correlated with sprinting performance during both feeding and escape in the field. Sprinting speed during escape closely matches maximal sprinting ability (i.e., about 90% of maximum performance). By contrast, sprinting performance during undisturbed activity is markedly lower (about 32% of maximum) than maximal sprinting performance. Sprinting ability during feeding is intermediate (about 71% of maximum) between field escape and field undisturbed activity. In contrast to sprinting ability, jumping ability is always substantially less than maximum (about 40% of maximum during feeding and undisturbed activity). A negative relationship exists among species between maximal speed and the proportion to which species sprint to their maximal abilities during field escape.

Impact of a catastrophic hurricane on Island populations

Abstract: Lizard and spider populations were censused immediately before and after Hurricane Lili on islands differentially affected by the storm surge. The results support three general propositions. First, the larger organisms, lizards, are more resistant to the immediate impact of moderate disturbance, whereas the more prolific spiders recover faster. Second, extinction risk is related to population size when disturbance is moderate but not when it is catastrophic. Third, after catastrophic disturbance, the recovery rate among different types of organisms is related to dispersal ability. The absence of the poorer dispersers, lizards, from many suitable islands is probably the result of long-lasting effects of catastrophes.

Examination of factors potentially affecting dewlap size in caribbean anoles

Abstract: The dewlaps of anoles vary greatly in size, including some species that have no dewlap at all. The dewlap serves many purposes-including courtship, territorial interactions, species recognition, and predator deterrence-and must be an effective communicatory signal in different light environments. We measured dewlap size in 52 species of Caribbean anoles to test a variety of hypotheses concerning the evolution of dewlap size. Species with conspicuous body coloration or patterning tend to have relatively smaller dewlaps than do other species. In addition, the data suggest the possibility that species in poorly lit habitats may have relatively larger dewlaps than species in brighter habitats. By contrast, no relationship exists between relative dewlap size and structural habitat, display rate, or sexual size dimorphism. Further, comparisons of the dewlaps of sympatric species do not support the hypothesis that differences in dewlap size aid in species recognition.

A second Anolis lizard in Dominican amber and the systematics and ecological morphology of Dominican amber anoles. American Museum novitates ; no. 3249

Abstract: A fossil Anolis lizard in the collections of the American Museum of Natural History is the second anole preserved in amber from the Dominican Republic (Miocene epoch) to be studied. The fossil exhibits skeletal characters indicating that it is a juvenile member of a large clade of anoles that includes many extant Hispaniolan species and is characterized by close association between the clavicles and the lateral processes of the interclavicle. Standard external characters that can be scored in the fossil are identical to those of two of the four extant species in the A. chlorocyanus species group; however, because relatively few characters can be scored in the fossil, and because the polarities of the relevant characters are currently unknown, the fossil can be only tentatively referred to that group. The skeletal and external characters of the new fossil are also nearly identical to those of A. dominicanus, another Dominican amber anole; however, the latter fossil is relatively poorly preserved, and its currently known characters are identical to those of several extant species, including two species of the A. chlorocyanus species group. Body proportions and lamella counts of both amber fossils indicate that these Uzards are trunk-crown anoles, that is, members of an ecologically and morphologically denned class of anoles specialized for life high on the trunks and in the crowns of trees. This finding is consistent with referral of the fossil anoles to the A. chlorocyanus species group, all extant members of which are trunk-crown anoles. ' Associate Curator, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560. ^ Undergraduate Honor Student, Department of Biology, Washington University, St. Louis, MO 63130. ^ Associate Professor, Department of Biology, Washington University, St. Louis, MO 63130. Copyright © American Museum of Natural History 1998 ISSN 0003-0082 / Price $2.50 AMERICAN MUSEUM NOVITATES NO. 3249

An experimental study of interspecific interactions between two Puerto Rican Anolis lizards

Abstract: We analyzed the impact of interspecific interactions between two ecologically and morphologically distinct Puerto Rican lizards, Anolis gundlachi and A. evermanni, in an experimental design consisting of six 20 × 20 m plots divided into three blocks, each consisting of a pair of experimental and control plots. We removed A. gundlachi from experimental plots and monitored the response of A. evermanni. The reduction in the number of A. gundlachi resulted in a significant increase in the abundance of both adult and juvenile A. evermanni. We found no evidence for a shift in structural habitat use in A. evermanni in experimental plots. Two possible mechanisms, interspecific competition and intraguild predation, could explain the increase in abundance of A. evermanni after the removal of A. gundlachi. These results make clear that interactions still occur between A. gundlachi and A. evermanni even given their morphological and ecological differences.

Examination of Factors Potentially Affecting Dewlap Size in

Abstract: The dewlaps of anoles vary greatly in size, including some species that have no dewlap at all. The dewlap serves many purposes-including courtship, territorial interactions, species recognition, and predator deterrence-and must be an effective communicatory signal in different light environments. We measured dewlap size in 52 species of Caribbean anoles to test a variety of hypotheses concerning the evolution of dewlap size. Species with conspicuous body coloration or patterning tend to have relatively smaller dewlaps than do other species. In addition, the data suggest the possibility that species in poorly lit habitats may have relatively larger dewlaps than species in brighter habitats. By contrast, no relationship exists between relative dewlap size and structural habitat, display rate, or sexual size dimorphism. Further, comparisons of the dewlaps of sympatric species do not support the hypothesis that differences in dewlap size aid in species recognition.