Robert Powell

Robert Powell
Avila University · Department of Biology

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145
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Introduction
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Publications

Publications (145)
Article
Invasive species are a major threat and primary driver of vertebrate extinctions on islands, including native and endemic lizards such as the West Indian Groundlizard (Genus Pholidoscelis). The genus comprises 19 extant species that range collectively from the Bahamas through the Greater Antilles south to Dominica in the Lesser Antilles. Few studie...
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Cryptogenic species are those whose native and introduced ranges are unknown. The extent and long history of human migration rendered numerous species cryptogenic. Incomplete knowledge regarding the origin and native habitat of a species poses problems for conservation management and may confound ecological and evolutionary studies. The Lesser Anti...
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Remarkably little is known about the demography of snakes in the family Boidae. This lack of information may be attributed in part to low population densities on the neotropical mainland, rendering capture-recapture methods impractical for many species. Conversely, islands support fewer species but snake densities can be much higher. Corallus grena...
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Large urban centers occur throughout the West Indies. Some native species of amphibians (e.g., Osteopilus spp.) and reptiles (e.g., many anoles, Anolis) readily exploit urban habitats, and other native species may survive in green habitat enclaves within cities. Some introduced species use both urban and relatively natural habitats. However, a few...
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To facilitate biological study we define “Caribbean Islands” as a biogeographic region that includes the Antilles, the Bahamas, and islands bordering Central and South America separated from mainland areas by at least 20 meters of water depth. The advantages of this definition are that it captures nearly all islands with endemic species and with at...
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Guana is a 297-ha island in the British Virgin Islands, a private wildlife sanctuary where human activity is largely restricted to small areas associated with an upscale resort hotel. Guana is free of mongooses and sustains a population of racers (Borikenophis portoricensis; Dipsadidae). Between 2001 and 2012 we marked B. portoricensis with Trovan...
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Citation: Rodríguez Gómez CA, Díaz-Lameiro AM, Berg CS, Henderson RW, Powell R. 2017. Relative abundance and habitat use by the frogs Pristimantis shrevei (Strabomantidae) and Eleutherodactylus johnstonei (Eleutherodactylidae) on St. Vincent. Caribbean Herpetology 58:1–12. Abstract St. Vincent, one of the Windward Islands of the Lesser Antilles, is...
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The thermal environment of ectotherms affects every aspect of their life history and many ectotherms must keep their body near an optimal temperature range through some form of thermoregulation. Because of the small size of geckos in the genus Sphaerodactylus, they are highly susceptible to overheating and desiccation. Also, because of their small...
Article
Animal communication among competitors often relies on honest signaling such that displays of aggression accurately reflect an individual's performance abilities. Moreover, the maintenance of honest signaling should be enhanced by the existence of consistent individual differences in behavior and performance, and individual-level correlations betwe...
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Abstract Both environmental factors and social factors affect an animal's choice of microhabitat. We explored the effects of humidity and the presence of conspecifics and predators on microhabitat selection by Brown-Speckled Sphaeros (Sphaerodactylus notatus; Squamata: Sphaerodactylidae). To test the effect of environmental moisture, we provided ge...
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The Brown Anole (Anolis sagrei) is a polymorphic species, with females often exhibiting one of three distinct pattern morphs. Efforts to correlate female-limited pattern polymorphism in anoles to ecological or physiological factors have largely been unsuccessful, with such correlations being either inconsistent among species or among populations of...
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In June 2012 on Eleuthera, Commonwealth of the Bahamas, we examined water-loss rates of Hemidactylus mabouia and Sphaerodactylus notatus to test the prediction that the larger, nocturnally active H. mabouia will experience comparatively lower mass-specific water-loss rates and percentage mass lost than the diminutive, diurnally active S. notatus. D...
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Effective and targeted conservation action requires detailed information about species, their distribution, systematics and ecology as well as the distribution of threat processes which affect them. Knowledge of reptilian diversity remains surprisingly disparate, and innovative means of gaining rapid insight into the status of reptiles are needed i...
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We examined the contributions of alterations in daily activity and behavioral selection of microhabitat to thermoregulation in a population of the lizard, Ameiva exsul (Teiidae), by combining data on lizard activity with data on the availability of sun-shade patches and operative temperatures (Te). By comparing Te distributions predicted by “no the...
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We examined maximal and ecological performance in Ameiva ameiva on Union Island, St. Vincent and the Grenadines. Maximal sprint speed was correlated positively with lizard body size but not with hind-limb or relative hind-limb length. Lizards in the field used over 85% of maximal capacity when escaping a putative predator, and the proportion of max...
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UNIVERSITY OF FLORIDA GAINESVILLE The FLORIDA MUSEUM OF NATURAL HISTORY is Florida's state museum of natural history, dedicated to understanding, preserving, and interpreting biological diversity and cultural heritage. The BULLETIN OF THE FLORIDA MUSEUM OF NATURAL HISTORY is a peer-reviewed journal that publishes results of original research in zoo...
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Typhlops tasymicris was known previously from only two specimens, both immature females collected on Grenada in 1968. In June 2010, we rediscovered the species on Union Island, St. Vincent and the Grenadines, where we encountered five individuals (and captured four) on the forested slopes above Chatham Bay. The new specimens agree closely with the...
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Union Island, St. Vincent and the Grenadines (8.4 km2) has an unusually diverse reptilian fauna for such a small area, but lacks native or well-established introduced amphibians. In June 2010, we conducted a rapid assessment of 10 sites (coastal or with some variation of dry forest habitats) chosen on the basis of vegetative complexity, height and...
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The slopes above Chatham Bay on Union Island, St. Vincent and the Grenadines, support one of the last mature secondary forests in the Grenadines. The characteristics of the forest allow it to support a unique herpetofauna that includes four small crevice- and litter-dwelling reptilian species (Gonatodes daudini, Bachia heteropa, Sphaerodactylus kir...
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In June 2010, on Union Island, St. Vincent and the Grenadines, we staged intraspecific and intergeneric interactions between Sphaerodactylus kirbyi and Gonatodes daudini (Sphaerodactylidae), which occur in sympatry and occasional syntopy on the slopes above Chatham Bay. Frequencies of most behaviours and frequencies of aggressive, submissive, and n...
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Non-native species are a growing worldwide conservation problem, often second only to habitat destruction and alteration as a cause of extirpations and extinctions. Introduced taxa affect native faunas through competition, predation, hybridization, transmission of diseases, and even by confounding conservation efforts focused on superficially simil...
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Gymnophthalmus pleii and G. underwoodi (Gymnophthalmidae) occupy xeric woodlands along the western coast of Dominica, whereas Sphaerodactylus fantasticus fuga (Sphaerodactylidae) is a dwarf gecko found in more mesic microhabitats in the same general area. We studied population densities and desiccation rates of all three species in order to determi...
Article
Ecologically versatile Anolis schwartzi from St. Eustatius (Lesser Antilles) occurs in various habitats, usually in shaded situations and often in higher densities when associated with rock piles, rock slides, and stone walls. In order to evaluate the mating systems of A. schwartzi in different habitats, we examined populations in rocky and adjacen...
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KURZFASSUNG Die Autoren beschreiben das Beuteverhalten des Teiiden Ameiva erythrocephala DAUDIN, 1802 in zwei Le-bensräumen. Gezielte Beobachtungen über insgesamt 6,7 Stunden zeigten, daß die Tiere bei der Nahrungssuche eine Kombination aus häufigen Ortswechseln und Grabphasen anwendeten. Futtersuchende A. erythrocephala be-wegten sich im Durchschn...
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In June 2008, we studied the natural history of Ameiva fuscata and interactions with sympatric Anolis oculatus in five adjacent habitats on the western (leeward) coast of Dominica, Lesser Antilles. Ameiva activity was positively correlated with mean temperature, peak activity corresponded to peak daily temperatures and we observed greatly reduced o...
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One species of Leptodactylus and three species of Eleutherodactylus have been recorded from Dominica, a Lesser Antillean island of recent volcanic origin. The Mountain Chicken Frog (Leptodactylus fallax) is native and listed on the IUCN Red List as "critically endangered" due mainly to overhunting, habitat loss, and the effects of chytridiomycosis....
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Two dipsadid snakes occur on the island of Dominica, Lesser Antilles. In June 2008, we conducted visual encounter surveys to document activity periods of Alsophis sibonius and Liophis juliae at Cabrits National Park. Based on 165 observations of A. sibonius over the course of 71.25 search hours, we determined that daytime activity is bimodal and in...
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The hcrpetofauna of the Dominican Republic consists of 39 frogs (two of which are introduced), 110 squa-mates (olle possibly extinct and three or fOUf introduced), one crocodilian, three turtles (one introduced), plus fOUf species of sea turtles. Renccting the recent "Glohal Amphibian Assessment", 32 of 37 (86%) on· live species of amphibians are i...
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In June 2008, we conducted a survey of Dominican herpetofaunal communities in habitats variously disturbed by human activity. Our rapid assessment found the highest abundance and species richness in moderately to substantially modified areas. We found relatively few species and low numbers of individuals in relatively natural high-elevation sites,...
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We examined 152 Ameiva plei from four sites on Anguilla and from Scrub Island, a nearby satellite, and 12 A. corax from Little Scrub Island, another Anguillian satellite, generated indices of condition by dividing mass (g) by SVL (mm), and quantified degrees of eutrombiculid chigger mite infections by measuring the total areas (mm2) of each lizard...
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The lizard genus Anolis (Polychroti-dae) is essentially ubiquitous in the West Indies, with most species confined to one island bank. How-ever, human-mediated transport of materials, plants, and animals has introduced species across natural boundaries, sometimes with deleterious effects on native anoles. Among the most recent introductions is Anoli...
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In June 2006, we staged male/male (m/m), male/female (m/f), and female/female (f/f) (seven each) interactions between pairs of Sphaerodactylus vincenti vincenti (Sphaerodactylidae) from St. Vincent, West Indies, and evaluated 23 types of behaviours. Behavioural repertoires differed significantly between types of interactions. Six individual behavio...
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We examined population densities and structural microhabitat use by Anolis griseus and A. trinitatis at eight sites on the leeward (western) coast of St. Vincent, West Indies. Estimates of population density based on the Schnabel method varied according to habitat complexity and ranged to 5,208/ha for A. griseus (a higher estimate at one site was n...
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Like other Lesser Antillean islands, human-modified habitats are prevalent on much of St. Vincent, especially in coastal regions. Eighteen terrestrial species of reptiles and amphibians are known to occur on the island. Some species demonstrate considerable versatility, and are found in both altered and relatively natural habitats. Others, however,...
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The Lesser Antillean island of St. Vincent harbors 18 species of terrestrial amphibians and reptiles: four frogs (including the endemic Pristimantis shrevei), one turtle, ten lizards (including endemic Anolis griseus and A. trinitatis), and three snakes (including endemic Corallus cookii and Chironius vincenti). In addition, four species of marine...
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Although a highly visible component of the West Indian herpetofauna, few data address the biology of Curly-Tailed Lizards (Leiocephalus). We examined sexual dimorphism in size and head shape and reproductive life-history characteristics for five species of Leiocephalus from the Dominican Republic. Many hypotheses have been posited to explain head s...
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We documented population densities, microhabitat preferences, desiccation rates, and diets of Sphaerodactylus vincenti on St. Vincent, West Indies. We predicted and observed high densities (to 5,625/ha) in moist, shaded leaf-litter. Such microhabitats provide refuges, access to prey, and protection against water loss, because S. vincenti is vulnera...
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From 2001-2005, we collected and individually marked 219 Alsophis portoricensis anegadae from Guana Island, British Virgin Islands, during the months September-October to determine morphometric characters, evaluate incidence of scarring and tail damage, and assess habitat use and activity. Males were longer than females and significantly heavier an...