Showing papers by "Jonathan B. Losos published in 2001"

Predators increase the risk of catastrophic extinction of prey populations

Abstract: There has been considerable research on both top-down effects and on disturbances in ecological communities; however, the interaction between the two, when the disturbance is catastrophic, has rarely been examined. Predators may increase the probability of prey extinction resulting from a catastrophic disturbance both by reducing prey population size and by changing ecological traits of prey individuals such as habitat characteristics in a way that increases the vulnerability of prey species to extinction. We show that a major hurricane in the Bahamas led to the extinction of lizard populations on most islands onto which a predator had been experimentally introduced, whereas no populations became extinct on control islands. Before the hurricane, the predator had reduced prey populations to about half of those on control islands. Two months after the hurricane, we found only recently hatched individuals--apparently lizards survived the inundating storm surge only as eggs. On predator-introduction islands, those hatchling populations were a smaller fraction of pre-hurricane populations than on control islands. Egg survival allowed rapid recovery of prey populations to pre-hurricane levels on all control islands but on only a third of predator-introduction islands--the other two-thirds lost their prey populations. Thus climatic disturbance compounded by predation brought prey populations to extinction.

Natural restoration of the species-area relation for a lizard after a hurricane.

Abstract: We document the decimation and recovery of the commonest lizard species, Anolis sagrei, on 66 islands in the Bahamas that were directly hit by Hurricane Floyd in September 1999. Before the hurricane, an island's area was a better predictor of the occurrence of A. sagrei than was its altitude. Immediately after, altitude was a better predictor: Apparently all lizards on islands lower than about 3 meters maximum elevation perished in the storm surge. After about 1 year, area again became the better predictor. By 19 months after the hurricane, A. sagrei populations occurred on 88% of the islands they formerly occupied. Recovery occurred via overwater colonization and propagation from eggs that survived inundation, mechanisms that were enhanced by larger island area. Thus, natural processes first destroyed and then quickly restored a highly regular species-area distribution.

Experimental studies of adaptive differentiation in Bahamian Anolis lizards

Abstract: Populations of the lizards Anolis carolinensis and A. sagrei were experimentally introduced onto small islands in the Bahamas. Less than 15 years after introduction, we investigated whether the populations had diverged and, if so, whether differentiation was related to island vegetational characteristics or propagule size. No effect of founding population size was evident, but differentiation of A. sagrei appears to have been adaptive, a direct relationship existed between how vegetationally different an experimental island was from the source island and how much the experimental population on that island had diverged morphologically. Populations of A. carolinensis had also diverged, but were too few for quantitative comparisons. A parallel exists between the divergence of experimental populations of A. sagrei and the adaptive radiation of Anolis lizards in the Greater Antilles; in both cases, relative hindlimb length and perch diameter are strongly correlated. This differentiation could have resulted from genetic change or environmentally-driven phenotypic plasticity. Laboratory studies on A. sagrei from a population in Florida indicate that hindlimb length exhibits adaptive phenotypic plasticity. Further studies are required to determine if the observed differences among the experimental populations are the result of such plasticity. Regardless of whether the differences result from plasticity, genetic change, or both, the observation that anole populations differentiate rapidly and adaptively when exposed to novel environmental conditions has important implications for understanding the adaptive radiation of Caribbean anoles.

Systematics of the Anolis roquet Series of the Southern Lesser Antilles

Abstract: -We report a phylogenetic analysis of approximately 1330 bases of mitochondrial DNA sequence for eight species of the Anolis roquet series (Anolis aeneus, Anolis bonairensis, Anolis extremus, Anolis griseus, Anolis luciae, Anolis richardi, Anolis roquet, Anolis trinitatus). These data contain 410 characters that are parsimony informative for the A. roquet series plus three outgroup species. A parsimony analysis of these data, combined with previously published allozymic data, reveals a single most parsimonious tree with strong support for seven internal branches. Anolis bonairensis and A. luciae are sister taxa and together form a sister taxon to a group containing the other species. Relationships among A. griseus, A. trinitatus, and a clade containing the remaining species are unresolved. Within the latter clade, A. richardi is the sister taxon to a group containing A. aeneus, A. extremus, and A. roquet, with the latter two species being sister taxa. Reanalysis of previously published allozymic data produces no conflicts with the mtDNA tree for wellsupported branches. Parsimony analysis of the combined allozymic and DNA data gives a tree identical in topology to the tree resulting from the DNA analysis alone. In contrast to earlier studies, our phylogenetic analyses indicate that neither the small-bodied (A. aeneus, A. trinitatus) nor the large-bodied (A. griseus, A. richardi) species form monophyletic groups. The Anolis roquet series occupies the southern Lesser Antilles from Martinique to Grenada, including Barbados to the east, as well as two islands in the Venezuelan and Netherlands Antilles to the west (see Fig. 1; Underwood, 1959; Gorman and Dessauer, 1966; Gorman and Atkins, 1967, 1969; Gorman, 1968). Monophyly of this group is supported by allozymic and behavioral data (Gorman and Atkins, 1969). The A. roquet series is phylogenetically distinct from the Anolis bimaculatus species group occupying the northern Lesser Antilles (from Dominica northward), to which it appears not to be closely related (Etheridge, 1960; Gorman and Dessauer, 1966; Gorman and Atkins, 1969; Gorman et al., 1980; Guyer and Savage, 1986, 1992; Jackman et al., 1999). The Grenada and St. Vincent island banks each contain a pair of sympatric species, one large-bodied and the other considerably smaller. The other banks as well as the two western islands each contain single species intermediate in body size (Lazell, 1972; Schoener and Gorman, 1968; Roughgarden, 1995). The natural history of this group has been described by Gorman (1968), Schoener and Gorman (1968), Lazell (1972), and Gorman and Stamm (1975). 2 Corresponding Author. E-mail: creer@biology. wustl.edu Phylogenetic hypotheses for the A. roquet series have been proposed previously by Gorman and Atkins (1969) and Yang et al. (1974), based on karyotypic and allozymic data, and by Lazell (1972), based on morphology. Some immunological data have also been reported (Wyles and Gorman, 1980; Schochat and Dessauer, 1981). Roughgarden (1995) included the A. roquet series in a phylogenetic tree of the entire genus, in which he showed those relationships that appear well supported by the above works. Since the 1970s, many new techniques have been developed for systematic analysis, including statistical methods for assessing confidence in the results, both in terms of whole trees and individual branches. It is now possible to compare trees derived from different datasets in terms of branch support and test a variety of specific phylogenetic hypotheses in a statistically rigorous fashion. Most recently, Giannasi et al. (2000) have published trees derived from analysis of cytochrome b mitochondrial DNA sequence. Jackman et al. (1999) used sequences from the ND2 gene of the mitochondrial genome and adjacent regions to identify large-scale relationships among Anolis lizards. Based on their study, this particular region also appears suitable for analyzing relationships within various Anolis subclades. Here, we present mtDNA sequences from this region for species in the A. This content downloaded from 207.46.13.128 on Wed, 07 Sep 2016 06:32:03 UTC All use subject to http://about.jstor.org/terms SYSTEMATICS OF THE ANOLIS ROQUET SERIES

Evolutionary Relationships of the Anolis bimaculatus Group from the Northern Lesser Antilles

Abstract: Lizards in the Anolis bimaculatus group from the northern Lesser Antilles have played an important role in theoretical and empirical developments in ecology, behavior, and evolution over the last four decades. Despite intense interest, the lack of a formal phylogenetic analysis for the bimaculatus group has limited comparative and historical evolutionary analyses. Here we present a phylogenetic analysis of species relationships within the bimaculatus group based on separate and combined analyses of mitochon- drial DNA and previously published allozyme data. These analyses indicate that (1) the wattsi group of small anoles is a basal, well-supported monophyletic group; (2) the large anoles A. bimaculatus and A. leachi are not sister species-rather, there is a well-supported sister relationship between A. bimaculatus and A. gingivinus; (3) the A. marmoratus complex from the Guadeloupean archipelago is deeply differentiated and paraphyletic, with A. sabanus, A. lividus, and possibly A. oculatus nested within it; (4) the phylogenetic position of A. leachi is not well resolved, but a combined analysis of mtDNA and allozyme data favor placing A. leachi as the sister taxon to the (A. marmoratus, A. lividus, A. sabanus, A. oculatus) group; and (5) the phylogenetic position of A. nubilus remains uncertain pending additional data. The proposed phylogeny elucidates the evolutionary history and biogeography of the bimaculatus group and allows a reassessment of the character displacement and taxon cycle/loop hypotheses.

Adaptive radiation versus intraspecific differentiation: morphological variation in Caribbean Anolis lizards

Abstract: Lizards in the genus Anolis have experienced adaptive radiation in the Greater Antilles, producing a suite of species morphologically adapted to use different parts of the environment. In the Lesser Antilles, adaptive radiation has not occurred, but on some islands, interpopulational variation is high and represents adaptation to different habitats. We compared the extent of morphological differentiation among Greater Antillean habitat specialists with that exhibited among populations of two species, Anolis marmoratus and A. oculatus, from the Lesser Antillean islands of Guadeloupe and Dominica. Although extensive, intraspecific divergence in the Lesser Antilles is substantially less in magnitude than the differences among habitat specialists in the Greater Antilles. All populations of A. marmoratus are most similar to Greater Antillean trunk-crown habitat specialists, but populations of A. oculatus differ in their affinities: some are similar to trunk-crown anoles, but others are more similar to trunk-ground habitat specialists.