Use of time, space, and food by the gymnophthalmid lizardPrionodactylus eigenmanni from the western Amazon of Brazil

The gymnophthalmid lizard Prionodactylus eigenmanni lives in leaf litter of terra firme forest in the western Amazon. Lizards are active during sunny and cloudy periods and body temperatures are 27.2 ± 0.19°C (mean ± SE). Body temperatures did not correlate with substrate or air temperatures: P. eigenmanni apparently gain heat by seeking temporary patches of relatively warm microhabitat. Two populations (Rio Ituxí in Amazonas and central Rondônia) were compared with respect to diet and morphology. The diet consists of a wide variety of invertebrates, but spiders, homopterans, orthopterans, and roaches constitute the majority of food items. Prey types and sizes in the two localities were similar. Females are larger than males and there is no apparent sexual dimorphism in head size as is found in many other lizards. Even though the two populations were studied in different seasons, there was no indication that wet versus dry season affected the ecology of these lizards.

Geographical ecology of the gymnophthalmid lizard Neusticurus ecpleopus in the Amazon rain forest

Lizards in four distantly separated populations of the gymnophthalmid lizard Neusticurus ecpleopus in the Amazon region of South America were strikingly specific in habitat and microhabitat use, being restricted to streams and swamps and living between the water line and the bank-forest interface. They were as likely to be active during cloudy periods as during sunny periods, but most individuals were not exposed to direct insolation while active. Activity occurred through much of the day, with most activity at two sites during between 11:00 and 14:30. Body temperatures were 27.0 ± 0.02°C and were correlated with substrate temperatures. Body temperatures were higher than substrate temperatures, indicating behavioral or possibly physiological thermoregulation. These lizards ate a variety of prey, but eight prey categories accounted for a major proportion of the total diet at all sites. There were differences among sites in prey type, prey size, relative prey size, and total stomach fullness. Even though there was some size variation among sites, variation in other morphological characters was more striking. Even withstanding the differences among populations in ecological and morphological characteristics, it appears that much of the ecology of N. ecpleopus is constrained by fidelity to specific habitat patches (stream banks) distributed linearly through lowland tropical forest.

Ecology of the arboreal tropidurid lizard Tropidurus (=Plica) umbra in the Amazon region

The tropidurid lizard Tropidurus umbra lives on medium-sized trees in lowland tropical forest of the Amazon region. Individuals may be active on tree trunks in sun or shade, with most activity occurring from 11:00 to 13:00. Body temperatures average 29.1 °C. The diet consists nearly exclusively of ants and there is no relationship between prey size and lizard size. Females reach sexual maturity at 79 mm snout–vent length (SVL) and males at 78 mm SVL. Although there appears to be no sexual dimorphism in SVL, males have relatively larger heads than females. Clutch size is usually two eggs and females appear to produce more than one clutch per season. Comparisons with other studied tropidurid lizards suggest that dietary specialization on ants, reduced sexual dimorphism, and reduced clutch size are derived characters.

The role of habitat shift in the evolution of lizard morphology: evidence from tropical Tropidurus

We compared morphology of two geographically close populations of the tropical lizard Tropidurus hispidus to test the hypothesis that habitat structure influences the evolution of morphology and ecology at the population level. T. hispidus isolated on a rock outcrop surrounded by tropical forest use rock crevices for refuge and appear dorsoventrally compressed compared with those in open savanna. A principal components analysis revealed that the populations were differentially distributed along an axis representing primarily three components of shape: body width, body height, and hind-leg length. Morphological divergence was supported by a principal components analysis of size-free morphological variables. Mitochondrial DNA sequences of ATPase 6 indicate that these populations are closely related relative to other T. hispidus, the rock outcrop morphology and ecology are derived within T. hispidus, and morphological and ecological divergence has occurred more rapidly than genetic divergence. This suggests that natural selection can rapidly adjust morphology and ecology in response to a recent history of exposure to habitats differing in structure, a result heretofore implied from comparative studies among lizard species.

Maximizing male reproductive success in the broad-headed skink (Eumeces laticeps): preliminary evidence for mate guarding, size-assortative pairing, and opportunistic extra-pair mating

Abstract

Several lines of evidence suggest that male Eumeces laticeps may increase reproductive success by 1) mating with larger females to increase clutch size, 2) mate guarding to be present during the female's receptive period and/or prevent sperm competition, and 3) engaging in extra-pair copulations. Clutch size increases with female body size, establishing a potential advantage of male preference for large female mates. Mate association lasts up to 8 days and possibly longer, with a mean of nearly 5 days. Males may remain with females during a major portion of the mating season, which preliminary data suggest lasts about two weeks, suggesting that mate-guarding may reduce the level of polygyny. Tethered introductions of intruder males to consort pairs showed that consort males use aggressive behavior to exclude other males from the vicinity of females. Eumeces laticeps exhibits strong positive size-assortative pairing, suggesting the possible importance of male choice of large mates. Female preference for large males could account for this relationship, but only if large females prefer the largest possible males within the acceptable size range and aggressively exclude other females from preferred males. Females are sometimes aggressive to each other, especially near nest sites, but aggression is suppressed by males, as shown by tethered introduction of females to consort pairs. Size-assortative pairing may be based in part on male preference if males can prevent larger females from aggressively excluding smaller ones. In addition to preferentially guarding large females, males not currently guarding mate with any females not large enough to deter them aggressively. A field observation of an extra-pair copulation, responses by consort males to introduced females, and the lack of size preference in the absence of consorts suggest that males may engage opportunistically in extra-pair copulations to increase reproductive success and are not then choosy about female size.

Organization of a taxonomically diverse lizard assemblage in Amazonian Ecuador

Of 22 lizard species studied in eastern Ecuador, 21 were diurnal. Ten were active foragers and 12 were sit-and-wait foragers. Considerable variation existed in habitat and microhabitat distribution and body temperatures among species. Body size varied over an order of magnitude (20–270 mm snout–vent length). Most morphological (size-free) variation among species (77%) was accounted for by two principal component axes and appears tied to phylogeny. Prey size was correlated with lizard size and species were separated by prey size. Low overlaps in microhabitat, habitat, and prey type also separated species. Pseudocommunity analysis indicated structure in the consumer–resource matrix. In some comparisons, prey overlaps among species were greater within than between higher taxa, and closely related species tended to be found in similar habitat patches and microhabitats, suggesting that resource-use patterns are determined to some extent by phylogeny. Ecology, morphology, and phylogeny appear tied together in a complex manner, with resource partitioning contributing to maintenance of structure. Historical interactions among closely related species may have been important in determining which species within particular clades invaded and persisted within local assemblages in lowland forest.

Ecology of the lizard Norops oxylophus (Polychrotidae) in lowland forest of southeastern Nicaragua

The lizard Norops oxylophus used a variety of microhabitats distributed linearly along streams in southeastern Nicaragua. Body temperatures averaged 27.8 °C and lizards typically were in shade. Lizards spent 98.16% of their time stationary and 1.84% moving. The rate of movement was low (0.001 m∙s−1) even when corrected for time not moving (0.071 m∙s−1). Caterpillars, spiders, ants, and various orthopterans composed most of the diet. Prey size was only weakly correlated with lizard snout–vent length (SVL) and there was no sexual difference in prey size independent of SVL. Lizards averaged 0.01 prey attacks/min and most lizards spent less than 0.15% of their time feeding. Males were larger than females, but females had a relatively larger body and greater mass. Females reach sexual maturity at 49 mm SVL and produce clutches of a single egg in rapid succession. Males reach sexual maturity at 53 mm SVL. Many ecological characteristics of N. oxylophus reflect a set of characteristics evolving early in the N. fuscoauratus series of the anoline lineage that has contributed to their ecological success in stream habitats of Caribbean lowland forest.

Ecology of the lizard Kentropyx pelviceps (Sauria: Teiidae) in lowland rain forest of Ecuador

Kentropyx pelviceps was studied in lowland tropical forest of eastern Ecuador. Most individuals were first observed in leaf litter of treefall gaps or forest, approximately 30% being first observed above ground on trunks or branches of fallen trees. Activity occurred from 10:00 to 16:00 in microhabitats receiving maximum insolation. Body temperatures of active lizards averaged 34.1 ± 0.4 °C. Lizards active when sun was available had higher body temperatures than lizards active when sun was not available. When sun was available, lizards spent more time moving and moved farther than when sun was not available. When sun was hidden behind clouds, lizards typically ceased foraging, pressed their bodies against the substrate, and basked, receiving direct exposure. Most time active was allocated to basking, presumably as a result of limited availability of sunlight. Prey consisted primarily of roaches, orthopterans, and spiders, and prey size was determined to a large extent (69.6% of variation) by lizard body size. Males and females reached sexual maturity at 80 mm snout–vent length. Males reached a larger maximum size than females, and sexual dimorphism was apparent in nearly all morphological characteristics of adults when the effect of size was removed. Clutch size averaged 6.5 ± 0.3 eggs, and there was no relationship between clutch size and female size. Evidence suggests that the breeding season is extended. Comparisons with other studied species of Kentropyx suggest that many aspects of the ecology of K. pelviceps in eastern Ecuador are affected by the reduced time available for activity resulting from reduced sun availability.

Geographical ecology of a Neotropical lizard: Ameiva ameiva (Teiidae) in Brazil

The large-bodied teiid lizard Ameiva ameiva was studied at eight different sites in four major South American habitats of Brazil: caatinga, cerrado, Amazonian rain forest, and Amazonian savanna. We found striking similarity in ecological attributes of this lizard among very different habitats. Activity is concentrated in late morning and early afternoon; active body temperatures average 37.9 ± 0.09 °C and vary little among sites or throughout the day; the diet consists of a variety of vertebrates and invertebrates but is dominated by grasshoppers, roaches, beetles, spiders, and insect larvae; and niche breadths for prey are similar among study sites but the actual composition of the diets varies. There is minimal morphological variation among sites (mostly size); the most striking morphological variation is between the sexes. Males reach larger body sizes and have relatively larger heads than females. Juveniles have relatively larger heads than would be predicted on the basis of body size alone. Sexual selection may explain the sexual differences in head size of adults, whereas the relatively large heads of juveniles may be associated with food competition with sympatric teiid lizards. Clutch size varies from 1 to 11 eggs, is related to female body size (snout–vent length), and varied among study sites. Similar variation among sites occurs in egg size but not in relative clutch mass. An interesting positive relationship was found between body size and relative clutch mass. In a population from the state of Rondônia egg dry mass was correlated with female size, indicating that individual offspring size is, to some extent, a consequence of female size. The reproductive season is extended for all populations and it appears that predictability of rainfall may regulate the season length. Reasons for the apparent success of A. ameiva in a diversity of habitats on a large geographic scale include its large body size, foraging mode, and preferred microhabitat (ecotones and disturbed areas).

Ecology of the whiptail lizard Cnemidophorus deppii on a tropical beach

The whiptail lizard Cnemidophorus deppii was studied during late dry season on a tropical beach on the Pacific coast of Nicaragua. Most aspects of the ecology of this species are similar to those of other active foraging lizard species studied. Individual C. deppii spend most of a typical daily activity period on sand moving from vegetation patch to vegetation patch, presumably in search of food. The amount of time spent in the sun is greatest in early morning and at its lowest level at midday. The average rate of movement was 0.048 ± 0.004 m/s. Body temperatures of active lizards averaged 40.0 ± 0.25 °C, and most activity occurred during morning and late afternoon. Body temperatures were significantly lower in whiptails active during the morning than later in the day. Forty-two types of prey were identified in stomachs, with termites, spiders, and various orthopterans accounting for most of the diet volumetrically. There was no correlation between lizard size and prey size. There was a significant negative relationship between prey width and the number of prey in stomachs. Snout–vent length (SVL) at sexual maturity was 60 mm for females and 58 mm for males. Mature females averaged 63.8 ± 0.7 mm SVL and produced clutches varying from 1 to 3 eggs ([Formula: see text]). Oviductal eggs averaged 13.6 ± 0.64 × 7.7 ± 0.21 mm in size. There was no significant relationship between female SVL and clutch size. Relative clutch mass was similar to that for other active foraging lizard species. Sexual dimorphism was apparent in coloration (males brightly colored), body size (males larger), and relative head size (male heads larger independent of body size differences). These differences presumably are due to sexual selection.

Ecology of isolated open-formation Tropidurus (Reptilia: Tropiduridae) in Amazonian lowland rain forest

Ecological, morphological, and life-history characteristics of three as yet undescribed populations of open-formation Tropidurus species in Rondônia and a population of Tropidurus oreadicus in Pará, Brazil, that are isolated on rock outcrops completely surrounded by lowland tropical forest were compared with similar characteristics of a eurytopic open-formation close relative, Tropidurus hispidus, and a crevice-adapted close relative, Tropidurus semitaeniatus, from an open-formation (caatinga) habitat in northeastern Brazil. Individuals of the isolated Amazonian populations do not enter the forest, but escape into narrow crevices on rock outcrops when disturbed. They are restricted to the only habitat patch in tropical forest similar to open-formation habitats, granitic rock outcrops. The outcrops maintain cerrado and caatinga vegetation and published paleoecological data indicate that the forested area surrounding the outcrops in Rondônia was cerrado in the recent past. Individuals in the isolated Tropidurus populations are morphologically flattened compared with T. hispidis, clutch size is reduced, and relative clutch mass is reduced, as is observed in other crevice-adapted species of lizards. Females deposit eggs under granitic cap rocks, like the flattened lizard T. semitaeniatus. The most parsimonious explanation for the set of characteristics shared by these four isolated lizard populations is that natural selection has led to an adjustment of behavior, morphology, and certain life-history characteristics in response to the high ecological risks associated with entering surrounding forest. It remains unclear whether this occurred once (which assumes a common ancestor), followed by canalizing selection, or the populations converged independently on similar morphology and ecology (which assumes different ancestors). The direction of divergence in behavior, morphology, clutch size, relative clutch mass, and nesting behavior in isolated populations of Tropidurus species remains unknown.