Daniel Oliveira Mesquita

Ecology of a Cerrado Lizard Assemblage in the Jalapao Region of Brazil

Abstract We examined the relative roles of contemporary (species interactions) and historical factors (phylogeny) in structuring a lizard assemblage (14 species) from one of the last remaining large expanses of undisturbed Cerrado in Brazil. Niche breadth for microhabitat was low for all species in the assemblage, and microhabitat niche overlaps varied from none to almost complete and appeared associated with phylogenetic similarity. Mean microhabitat and diet overlaps among lizard species did not differ statistically from random, based on a pseudocommunity analysis, indicating a negligible role of contemporary factors in assemblage structure. Prey overlaps were highest within Gymnophthalmidae and Teiidae. A cluster analysis of principal component scores of morphometric variables revealed groups corresponding to lizard families, suggesting a strong association between morphology and phylogeny. Similarities among closely related species in microhabitat use, diel activity, and diet breadth, based on cladogram inspection, suggested that phylogeny might affect assemblage structure. However, a Canonical Phylogenetic Ordination (CPO) analysis revealed no significant phylogenetic effects on lizard microhabitat use or diet composition. We suggest that under-representation of species in major clades (low taxon sampling) renders it difficult to detect potential historical and ecological effects on assemblage structure.

The Ecology of Cnemidophorus ocellifer (Squamata, Teiidae) in a Neotropical Savanna

Abstract We studied the ecology of the lizard Cnemidophorus ocellifer Spix 1825 in the central Brazilian Cerrado. Cnemidophorus ocellifer was active on open ground, in sandy soils and rocky fields, during the hottest hours of the day. Mean body temperatures (37.5°C) were high, relative to sympatric lizard species, and more associated with substrate temperatures than with air temperatures. The thermal ecology of C. ocellifer seems to be tightly associated with an active mode of foraging. Termites were the most important prey, and there was no significant association between head dimensions and prey dimensions. Cnemidophorus ocellifer showed strong sexual dimorphism in body size and shape, with males having larger bodies and head dimensions, and females having longer and thicker bodies. Clutch size averaged 2.1 and was positively correlated with female SVL. Females were reproductively active during the dry season (May to September) and recruitment occurred from July to November. Males were reproductively active throughout the year, peaking from March to August, coinciding with the period of female reproduction. The reproductive cycle in C. ocellifer may be determined by the greater availability of direct sunlight and its physiological effects upon breeding activities, such as courtship and mating, during the dry season.

Geographical Variation in the Ecology of Populations of Some Brazilian Species of Cnemidophorus (Squamata, Teiidae)

Abstract We investigated geographical variation in ecological parameters among populations of Cnemidophorus cryptus, Cnemidophorus gramivagus, Cnemidophorus lemniscatus, Cnemidophorus ocellifer, and Cnemidophorus parecis, from three Brazilian biomes (Cerrado, Caatinga, and Amazonian Savannas). Lizards used mainly the open ground, with a high similarity in microhabitat use among populations. Differences in microhabitat use probably resulted from the availability of microhabitats and not from microhabitat preferences. Body temperatures were high and little influenced by environmental temperatures, there being no differences among populations. There were significant differences in diet among populations, with C. ocellifer from Caatinga and Cerrado consuming large quantities of termites, whereas Amazonian Savanna species used primarily ants and insect larvae. The data on reproductive seasonality indicated cyclical reproduction in seasonal biomes and continuous reproduction in unpredictable climate regions. We found significant differences in mean clutch size among populations, independent of body size, with C. lemniscatus having the smallest clutch size (1.50) and C. ocellifer from Cerrado the largest (2.10). There were fewer differences in clutch size among species from Amazonian Savannas, than between populations of C. ocellifer from Caatinga and Cerrado. Apparently, populations under seasonal climates concentrate their reproductive effort during the short reproductive season, producing larger clutches, whereas those under more stable or unpredictable climates reproduce continuously, yielding smaller clutches, corroborating the hypothesis that environmental conditions exert an important influence upon life-history parameters. There were significant differences in body shape among populations, but most of the variation was related to sex. We also observed significant differences in body size among populations, seemingly unrelated to differences in community structure, but the highly conservative morphology of Cnemidophorus species suggests the presence of historical constraints.

Phylogeny and Ecology Determine Morphological Structure in a Snake Assemblage in the Central Brazilian Cerrado

Abstract To investigate the role of ecological and historical factors in the organization of communities, we describe the ecomorphological structure of an assemblage of snakes (61 species in six families) in the Cerrado (a savanna-like grassland) of Distrito Federal, Brazil. These snakes vary in habits, with some being fossorial, cryptozoic, terrestrial, semi-aquatic, or arboreal. Periods of activity also vary. A multivariate analysis identified distinct morphological groups associated with patterns of resource use. We report higher niche diversification compared to snakes in the Caatinga (a semi-arid region in northeastern Brazil), with fossorial and cryptozoic species occupying morphological space that is not occupied in the Caatinga. Monte Carlo permutations from canonical phylogenetic ordination revealed a significant phylogenetic effect on morphology for Colubridae, Colubrinae, Viperidae, Elapidae, and Boidae indicating that morphological divergence occurred in the distant past. We conclude that phylogeny is the most important factor determining structure of this Neotropical assemblage. Nevertheless, our results also suggest a strong ecological component characterizes a peculiar snake fauna.

Ecology of the Gecko Gymnodactylus geckoides amarali in a Neotropical Savanna

Abstract We describe the ecology of the gecko Gymnodactylus geckoides amarali in the Cerrado of central Brazil and using published data, compare it with the conspecific Gymnodactylus geckoides geckoides from the Caatinga of northeastern Brazil. Gymnodactylus geckoides amarali is rupicolous, living primarily in rock crevices in “campos rupestres” (rocky fields), which are highly patchy in Cerrado. Field body temperatures were low and associated with environmental temperatures, suggesting thermoconformity. Termites were the most important food item, and consumption was greatest during the dry season. We suggest that access to termites is facilitated by the shallow soils used by G. g. amarali and by its well-developed chemosensory apparatus. Reproduction was concentrated in the dry season, a pattern known for very few Cerrado squamates, possibly because of the higher availability of termites during that period. Clutch size was significantly correlated with female size, a pattern unknown in any other gecko, and there was no association between egg size and female size. Gymnodactylus geckoides amarali produced larger clutches of smaller eggs relative to G. g. geckoides, presumably because of the high climatic unpredictability of the Caatinga. We detected a significant sexual dimorphism in both body size and shape: females were larger and had smaller heads than males. We suggest that large female size is likely a plesiomorphic character of gekkonids and that large head size in males results from sexual selection theory.

Niche expansion and the niche variation hypothesis: does the degree of individual variation increase in depauperate assemblages?

The niche expansion and niche variation hypotheses predict that release from interspecific competition will promote niche expansion in depauperate assemblages. Niche expansion can occur by different mechanisms, including an increase in within‐individual, among‐individual, or bimodal variation (sexual dimorphism). Here we explore whether populations with larger niche breadth have a higher degree of diet variation. We also test whether populations from depauperate lizard assemblages differ in dietary resource use with respect to variation within and/or among individuals and sexual dimorphism. We found support for the niche expansion and niche variation hypotheses. Populations in assemblages with low phylogenetic diversity had a higher degree of individual variation, suggesting a tendency for niche expansion. We also found evidence suggesting that the mechanism causing niche expansion is an increase in variation among individuals rather than an increase in within‐individual variation or an increase in bimodal variation due to sexual dimorphism.

A CRITICALLY ENDANGERED NEW SPECIES OF CNEMIDOPHORUS (SQUAMATA, TEIIDAE) FROM A CERRADO ENCLAVE IN SOUTHWESTERN AMAZONIA, BRAZIL

We describe a new species of Cnemidophorus from a Cerrado enclave in southwestern Amazonia, Rondônia state, Brazil. This species is apparently endemic to Cerrado enclaves in the vicinity of the city of Vilhena, a region under intensive anthropic pressure due to the expansion of soybean plantations. A discriminant analysis indicated that femoral pores and scales around the tail are the best discriminators among Brazilian species of Cnemidophorus. A naïve Bayesian network constructed with categorical (mostly coloration) variables indicated that the new species had high conditional probabilities of dorsolateral fields absent, vertebral field spotted, and paravertebral lines absent. The analyses revealed clear distinctions between species of Cnemidophorus that range north and south of the the Amazon River. The new species may have evolved as a result of vicariance, following the isolation of peripheral enclaves of Cerrado in southwestern Amazonia after the late Pleniglacial. The restricted range in small areas, under extreme human pressure around Vilhena, makes this species one of the most critically endangered elements of the Brazilian herpetofauna.

Detecting Variation in Microhabitat Use in Low-Diversity Lizard Assemblages across Small-Scale Habitat Gradients

Abstract If community structure is influenced by habitat structure at a local level, then it should be possible to tie species occurrence to key habitat variables. We used a pitfall-trap system to determine the relationship of species composition, species diversity (relative abundance), and community structure to habitat structure along a transect through a habitat gradient in the Brazilian Cerrado. A total of 531 individuals of 12 lizard species were sampled. A species accumulation curve based on EstimateS and a curve-fitting protocol predicted 12 species at day 22 and all species by about day 40. We registered 12 species at day 11. Trapping success declined through time, likely because of a combination of removal along the transect and seasonal environmental change (wet to dry). The more open end of our transect experienced higher temperatures in all microhabitats sampled, suggesting thermal structure associated with vegetative structure. A Canonical Correspondence Analysis showed that lizard species composition and relative abundance respond to variation in vegetative and physical structure of the habitat at small scales. Consequently, maintenance of habitat gradients should be considered in programs aimed at maintaining local biodiversity.

Ecology of Anolis nitens brasiliensis in Cerrado Woodlands of Cantao

Abstract We studied the ecology of Anolis nitens brasiliensis during late-dry and early-wet season 2005 in a Cerrado habitat in Tocantins state, Brazil. Most lizards were found on tree trunks or leaf litter in non-flooded igapó forest. Most were found in shade or filtered sun on both cloudy and sunny days. Body temperatures (Tbs) averaged 30.6°C and did not vary among microhabitats. Microhabitats exposed to direct sun consistently reached extremely high temperatures whereas microhabitats in shade or filtered sun provided temperatures throughout the day allowing lizard activity. Nineteen prey categories were found in lizard stomachs, but the diet was dominated by spiders, crickets/grasshoppers, ants, and beetles. Although lizards that ate large prey ate fewer prey, no correlation existed between size or number of prey and lizard body size (SVL). Males were larger in SVL and mass than females, and males had relatively longer hind limbs than females. Females were variable but larger in body width. In general, the ecology of Anolis n. brasiliensis is similar to that of its Amazonian relatives, with the exception that it lives in a more thermally extreme environment and is active at slightly higher Tbs. Ecological traits of this lizard, particularly its reliance on relatively low Tb for activity, suggest that it might be particularly vulnerable to local extinction if its habitat is altered. The presence and apparent widespread distribution of A. n. brasiliensis in the Cerrado provides further evidence that the “vanishing refuge” theory cannot account for geographical patterns of distribution in the A. nitens complex.

Ecological release in lizard assemblages of neotropical savannas

We compare lizard assemblages of Cerrado and Amazonian savannas to test the ecological release hypothesis, which predicts that niche dimensions and abundance should be greater in species inhabiting isolated habitat patches with low species richness (Amazonian savannas and isolated Cerrado patches) when compared with nonisolated areas in central Cerrado with greater species richness. We calculated microhabitat and diet niche breadths with data from 14 isolated Cerrado patches and Amazon savanna areas and six central Cerrado populations. Morphological data were compared using average Euclidean distances, and lizard abundance was estimated using the number of lizards captured in pitfall traps over an extended time period. We found no evidence of ecological release with respect to microhabitat use, suggesting that historical factors are better microhabitat predictors than ecological factors. However, data from individual stomachs indicate that ecological release occurs in these areas for one species (Tropidurus) but not others (Ameiva ameiva, Anolis, Cnemidophorus, and Micrablepharus), suggesting that evolutionary lineages respond differently to environmental pressures, with tropidurids being more affected by ecological factors than polychrotids, teiids, and gymnophthalmids. We found no evidence that ecological release occurs in these areas using morphological data. Based on abundance data, our results indicate that the ecological release (density compensation) hypothesis is not supported: lizard species are not more abundant in isolated areas than in nonisolated areas. The ecology of species is highly conservative, varying little from assemblage to assemblage. Nevertheless, increases in niche breadth for some species indicate that ecological release occurs as well.