Life in the trees: the ecology and life history of Kentropyx striatus (Teiidae) in the lavrado area of Roraima, Brazil, with comments on the life histories of tropical teiid lizards

The ecology and life history of the tropical teiid lizard Kentropyx striatus were studied in a grassland of northern Brazil, the lavrado area. The area, located nearly at the equator, experiences a prolonged dry season with a wet season extending from May to September. Total annual rainfall averages 1750 mm. Lizards were nonrandomly distributed among habitat patches and microhabitats. Most individuals were in trees and shrubs surrounding temporary and permanent water. Most individuals were observed active during late morning, the time period during which feeding and social interactions were observed. Lizards bask to achieve active body temperatures averaging 35.7 ± 0.23 °C. Body temperature is correlated with both substrate and air temperatures; foraging lizards maintained higher temperatures than basking lizards regardless of whether they were in sun, and lizards sampled when there was cloud cover had lower body temperatures than those sampled when sun was available. Females reach sexual maturity at 74 mm snout–vent length (SVL), produce 3–9 eggs per clutch, reproduce more than once per season, and commence reproduction during the wet season. Lizards hatch from eggs at 31 mm SVL. Maturity appears to be reached in 1 year or less. Overall, female reproductive characteristics are similar to those of other tropical teiid lizards that have been studied, with body size explaining much of the variance in reproductive characteristics across species. There is pronounced sexual dimorphism, with males larger in body size as well as certain other characteristics independent of body size. Sexual dimorphism appears to be a consequence of sexual selection. The diet is varied, but is dominated volumetrically by frogs, eruciform larvae, and spiders. Lizard body size accounted for only 5.5% of the variance in prey size and there was no difference in prey size due to sex. The occurrence of frogs and lizards in K. striatus stomachs suggests that teiid lizards may influence the structure of lizard and frog assemblages. The similarity of K. striatus to other studied tropical teiids in reproductive characteristics, morphology, activity period, activity temperatures, and diet underscore the conservative nature of the ecology of teiid lizards, presumably a consequence of their mode of prey acquisition.

Ecology and life history of the wide-foraging lizard Kentropyx calcarata (Teiidae) in Amazonian Brazil

Kentropyx calcarata is a widely foraging terrestrial lizard that is most common in edge situations (riparian, tree falls) in tropical lowland rain forest of South America. Various microhabitats are used, and lizards often forage in vegetation off the ground in a leaf-gleaning fashion. Body temperatures during activity average 37.6 °C in sun and 35.7 °C in shade, body temperature always being higher than that of the substrate or air. Daily activity appears to be associated with availability of direct sunlight. Differences in lizard body size (reflecting age), activity times, prey composition, and prey size are apparent between Rondônia (dry season) and Pará (wet season) populations. Sexual dimorphism is evident in head size, males having longer and wider heads than females, presumably due to sexual selection. Clutch size varies from 4 to 10, and the reproductive season appears to be prolonged. Natural nests occurred in sandy areas exposed to full sun along stream banks. Overall, K. calcarata in the Amazon region is more similar in ecology to other teiid lizards studied in drastically different environments than to sympatric lizards in other families.

Influence of detectability and ability to escape on natural selection of conspicuous autotomous defenses

Antipredatory adaptations in which a predator's attack is diverted to body parts that may be sacrificed or are less vulnerable sometimes depend upon the conspicuousness of the body part attacked. The predator's attention is drawn to the emphasized part, which serves as a decoy. Such defenses appear paradoxical in that they increase the probability of detection. However, they simultaneously increase the probability of postdetectional escape enough to decrease the overall probability of being killed. Based on probabilities of detection and of escape following detection, a simple model predicts the conditions in which autotomy and related defenses are favored. For a conspicuous decoy, equilibrium values of the increases in probabilities of detection and of escape following detection are given. Data on the conditional probability of escape after detection are discussed for the scincid lizards Eumeces fasciatus and E. laticeps, which have brightly colored autotomous tails. Versions of the model that split the predator–prey encounter into several successive stages are outlined briefly and illustrated by the data for the two lizard species. Strategies for measuring the probabilities and testing the model's predictions are considered.

Ecology and life history of the scansorial arboreal lizard Plica plica (Iguanidae) in Amazonian Brazil

A field study on two populations of the tropical iguanid lizard Plica plica in the Brazilian Amazon revealed that this lowland forest species is diurnal, occurs on vertical smooth-barked trunks of the largest trees in the forest, and feeds mostly on ants. Comparisons between rainy season samples from Pará and dry season samples from Rondonia show that even though lizards ate, on average, the same number of prey, prey were larger in Rondonia and prey diversity was greater in Pará. Lizards sleep on tree trunks or similar surfaces when available, apparently leaving the trees only to deposit eggs. Clutches are deposited in palm litter and inside rotted palm trunks. Clutch size averages 2.9 ± 0.1 eggs and is significantly correlated with female snout–vent length. The reproductive season appears to be extended in that females produce at least two clutches. Relative clutch mass of females is low compared with that of other sit-and-wait foraging lizard species, and this, coupled with the flattened morphology, presumably reflects adaptations for maintaining the center of gravity near vertical smooth tree trunks.

Life on the edge: the ecology and life history of the tropidurine iguanid lizard Uranoscodon superciliosum

An Amazonian population of the iguanid lizard Uranoscodon superciliosum was studied in lowland tropical wet forest in central Pará, Brazil. These nonheliothermic lizards are restricted to densely vegetated habitats near (often over) water, particularly riverbanks and small forest streams, where they utilize small-diameter perches and feed on a wide variety of invertebrates, apparently at the water's edge. They mature at moderate to large size at an age of about 1.5 years. Production of moderate-sized clutches of eggs is seasonal, and reproduction and fat storage both cycle in association with rainfall and flooding. Although they occur in fairly high densities, social interaction is uncommon and sexual dimorphism is not pronounced. The ecology and life history of this lizard seem to be strongly influenced by the unusual habitat specialization.

Induction of sexual receptivity in the female broad-headed skink, Eumeces laticeps, by estradiol-17 beta

Sexual receptivity in the female scincid lizard Eumeces laticeps occurs naturally only during the spring breeding season, which is also when maximal follicular development occurs. The presumption that high estrogen levels are coincidentally present and the need for a reliable method of inducing sexual receptivity for behavioral studies prompted tests of the hypothesis that estrogen induces sexual behavior. A series of experiments established that estradiol-17 beta induces sexual behavior. A series of experiments established that estradiol-17 beta induces sexual receptivity within 4 days when injected every other day at 2.0 micrograms in 20 microliters peanut oil in intact or ovariectomized females. In behavioral tests conducted during August, all control females (intact or ovariectomized injected with vehicle only) rejected courtship whereas all females receiving estrogen copulated. Estrogen injections also induced a statistically significant change from rejection to receptivity within individuals. Initial attempts to implant estradiol-17 beta in Silastic tubes killed all females so treated.

WE. Tail loss, tail color, and predator escape in Eumeces (Lacertilia: Scincidae): age-specific differences in costs and benefits

The tail loss adaptation in Eumeces of the southeastern United States is complex. Juveniles possess tails that are colored differently from those of adults and apparently distract the attention of potential predators from the body to the tail. Adult tails are cryptically colored. Frequency of tail loss is high across size groups. Experiments on growth of tailed and tailless juveniles suggest no effect of tail loss on growth and, thus, there may be little cost of tail loss to juveniles other than the temporary loss of the autotomy adaptation. Lipids in adult tails constitute nearly 50% of total standing lipids and are reduced during reproduction similar to other lipid reserves. This suggests that tail loss in adults is expensive, particularly prior to or during the breeding season. We suggest that the high costs of tail loss in Eumeces are offset by the increased probability of predator escape via tail loss. Tail loss data are minimal estimates of escape via distraction of a predator's attack to the tail as indicated by predation experiments. The presence, coloration, and behaviors of the tail may result in a high proportion of predation attempts being redirected to the tail followed by total misses.