Ronis Da Silveira

Niche partitioning and morphology of two syntopic Tropidurus (Sauria : Tropiduridae) in Mato Grosso, Brazil

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Conservation implications of commercial hunting of black and spectacled caiman in the Mamirauá Sustainable Development Reserve, Brazil

Abstract During the annual dry season, illegal hunting of black and spectacled caiman in the Mamiraua Sustainable Development Reserve in western Brazilian Amazon is widespread Peres and Carkeek, 1993 . Hunting occurs throughout the reserve, but is particularly intense in the northern Panaua region, where it provides the primary source of income for local residents during the dry season. While hunting prior to 1970 was principally to obtain caiman skins for sale, hunting today is entirely for the sale of caiman meat. People in the region do not eat the meat themselves, but after salting sell it to buyers who mix it with fish and in turn sell it in Para state, Brazil, and in Colombia. Preliminary information suggests that the annual harvest is approximately 115 metric tons of fresh caiman meat, which would represent a harvest of 5230 black caiman and 2865 spectacled caiman. Despite this illegal hunting, the population of black caiman has one of the highest reported densities for Amazonia. The impact of hunting on wild populations may be reduced because the hunters take mostly adult and subadult males, from relatively accessible parts of the reserve. Hunting in the Mamiraua reserve illustrates that a sustained harvest of caiman populations may be possible under the right conditions.

Monitoring the Distribution, Abundance and Breeding Areas of Caiman crocodilus crocodilus and Melanosuchus niger in the Anavilhanas Archipelago, Central Amazonia, Brazil

Caiman crocodilus crocodilus and Melanosuchus niger occur throughout most of the Anavil- hanas Archipelago, located in the lower Rio Negro, Central Amazonia. The observed densities of these species vary from 0 to 58 per km of shoreline and 0 to 8 per km of shoreline, respectively. Multiple regression analysis indicated that the temperature difference between the water and the air, and water depth affected the observed density of C. crocodilus during spotlight surveys in the Archipelago. Percentage illumination by the moon, cloud cover, frequency of occurrence of grass, and food availability did not significantly affect the observed density of C. crocodilus. Nine hatchling groups of M. niger that hatched in 1992 were found on islands near the north bank of the Rio Negro, and 15 of 20 hatchlings groups of C. crocodilus were found closer to the south bank, indicating a tendency for separation of nesting areas. Discriminant function analysis indicated that water depth and presence of grass were correlated with the occurrence of hatchling groups. Melanosuchus niger hatchling groups occurred in areas with deeper water and more grass than those of C. crocodilus. This study showed that surveying hatchling groups in the Anavilhanas Archipelago is more efficient than surveying for subadults and adults, which, by itself, can give false impressions about the suitability of areas for conservation of breeding populations of these species.

Depredation by Jaguars on Caimans and Importance of Reptiles in the Diet of Jaguar

Abstract The jaguar (Panthera onca) is the largest Neotropical felid and in many parts of its range reptiles form a significant but relatively minor component of its diet. However, in the seasonally flooded varzea forests of the Amazon, terrestrial mammals, which form an important component of jaguar diet in other habitats, are largely absent and jaguars switch to alternative prey, including arboreal mammals and reptiles. In the Mamirauá Sustainable Development Reserve in the western Brazilian Amazon, we document predation by jaguars on two species of caiman (Caiman crocodilus and Melanosuchus niger), which are abundant in this varzea habitat. The smaller C. crocodilus seems to be particularly vulnerable because of its size and tendency to spend more time on land than the larger M. niger. Jaguars not only kill and eat caiman but are also a significant predator on eggs of both species. We place our findings into the context of jaguar predation on reptiles by reviewing studies of jaguar diet in a variety of biomes.

Diets of Spectacled and Black Caiman in the Anavilhanas Archipelago, Central Amazonia, Brazil

Stomach contents were collected from 213 Caiman crocodilus with snout-vent lengths (SVL) between 15 cm and 115 cm, and 25 Melanosuchus niger with SVLs from 15 cm to 95 cm, in the Anavilhanas Archipelago, Rio Negro, Central Amazonia. The prey types consumed by the two species were generally similar. However, fish were common in the diet of C. crocodilus but absent from the M. niger. Snails (Po- macea) occurred in 24% of stomachs of M. niger, but in only 2% of C. crocodilus. The mean mass of food and the mean proportion of fish consumed increased, while the mean proportion of terrestrial invertebrates decreased significantly with the size class of C. crocodilus. The mean proportion of molluscs consumed increased significantly with the size class of M. niger, but there was no relationship between the mean mass of food or the mean proportion of other prey categories and size class in this species. However, the sample included only subadults. The mean size of all prey consumed, and of fish, increased significantly with size of C. crocodilus. However, there was no relationship between the mean size of prey in the categories ter- restrial invertebrates, shrimps, or crabs, and the size of C. crocodilus. The mean size of all prey consumed was positively related to the size of M. niger. The mean mass of food consumed by C. crocodilus varied with the water body type (lake or canal), but there was no effect of season as indexed by the water level of the Rio Negro. Seasonal variation in the proportion of fish, terrestrial invertebrates, and shrimps consumed by C. crocodilus differed among water body types. Empty stomachs occurred in 24% of the C. crocodilus and 20% of the M. niger. Individuals with food in the stomach had eaten small volumes, suggesting that

Genetic diversity and population structure of Amazonian crocodilians

We used the mitochondrial cytochrome b gene to study the population genetic structure of Melanosuchus niger (Brazil: Negro and Purus Rivers, Lake Janauaca; French Guiana: Kaw River swamps), and Caiman crocodilus (Brazil: Purus River, Lake Janauaca; French Guiana: Kaw River swamps). We found 10 haplotypes in M. niger and 9 haplotypes in C. crocodilus . Nested clade analysis indicated that isolation-by-distance was an important population dynamic in M. niger , but was unable to differentiate between isolation-by-distance, historical fragmentation or range expansion in C. crocodilus . Fus Fs statistic supported the hypothesis of a demographic expansion in one out of four and two out of three sampled localities of M. niger and C. crocodilus , respectively. Populations of M. niger in central Amazonia also appeared to show differentiation that was correlated with water type. These results are compatible with the life-style of these two crocodilians; C. crocodilus is a habitat generalist and appears to disperse rapidly to newly available habitats, while M. niger is a more sedentary habitat specialist. Both species appear to be recovering from unregulated over-harvesting, however, their responses are life-history and, potentially, ecologically-dependent.

Population genetic analysis of Caiman crocodilus (Linnaeus, 1758) from South America

The genetic structure of Caiman crocodilus was investigated using a 1085 bp mtDNA fragment of the cytochrome b gene. Inferences were based on 125 individuals from nine localities in Peru, Brazil and French Guiana. With the exception of Mamiraua Lake, Anavilhanas Archipelago and the Tapara Community which show a signal of demographic expansion, the sampled localities are in a mutation-drift genetic equilibrium. Divergence between the Amazon basin and extra-Amazon basin localities is significant; however, inference from Nested Clade Analysis cannot distinguish between continuous range expansion, long distance colonization or past fragmentation; however, past fragmentation is unlikely due to low number of mutational steps separating these two regions. The divergence is probably maintained by the reduced ability of C. crocodilus to cross salt water barriers. Within the Amazon basin, continuous range expansion without isolation-by-distance is the most likely process causing genetic structuring. The observed genetic patterns are compatible with the ecology of C. crocodilus, and history of human exploitation. As commercial hunting depleted more valuable species, C. crocodilus expanded its range and ecological niche, prompting hunters to harvest it. Following a period of intense hunting, C. crocodilus is now experiencing recovery and a second population expansion especially in protected areas.

Growth rates of black caiman (Melanosuchus niger) and spectacled caiman (Caiman crocodilus) from two different Amazonian flooded habitats

Rates of growth and survival in wild populations are affected by the physical environment, biotic interactions, and density-dependent processes, such as growth and fecundity. However, the relative importance of these factors in long- lived reptiles is poorly understood. We analyzed growth rates of Melanosuchus niger and Caiman crocodilus coexisting in two areas of the Brazilian Amazon with very different environmental characteristics. Growth rates of Caiman crocodilus at the two sites were similar, but M. niger grew more slowly in the area with higher productivity and higher density of caimans. Growth rates of the same species from other sites and of the temperate-zone Alligator mississippiensis indicate large differences among sites, but little evidence that these differences are primarily due to differences in productivity or temperature. Demographic models used to estimate sustained yields from caiman harvests should take into account the likely importance of density-dependent growth.

Feeding Behavior of Two Sympatric Caiman Species, Melanosuchus niger and Caiman crocodilus, in the Brazilian Amazon

Abstract We studied the feeding behaviors of two sympatric species of caimans (Melanosuchus niger and Caiman crocodilus) during the dry season in the Mamirauá Sustainable Development Reserve, Amazonas State, Brazil. Observations were made in 50 × 13 m plots located along the land-water interface. We investigated the influence of interspecific density and the effects of temperature and water depth on the feeding behaviors of both species. We identified three principal categories of feeding behavior: trapping (with the body perpendicular to the shore, the caiman captures prey swimming close to the shore), active search (with the head under the water, the caiman searches for benthic prey), and jumping (leaping partially out of the water and capturing fish or other under water invertebrates prey). Using multiple linear regression, we found that water temperature had a negative effect on trapping by M. niger; and water depth did not affect feeding behaviors in either species. Density of M. niger did not affect either the density or the frequency of feeding by C. crocodilus. Results suggest that environmental factors have little influence on the feeding behaviors of the caimans we studied, and there is probably little interspecific competition for food during the dry season.

Factors Affecting the Number of Caimans Seen during Spotlight Surveys in the Mamirauá Reserve, Brazilian Amazonia

Abstract Between 1995 and 1998 we studied the effects of water level, moon phase, and site on the number of caimans observed in spotlight surveys in the Mamirauá Sustainable Development Reserve, Brazilian Amazonia. Multiple linear regression analyses including water level of the Amazon River and the moon phase explained 91 and 73% of the variance in number of Melanosuchus niger seen in spotlight surveys in Lago Mamirauá and Cano Mamirauá, respectively, and 60 and 76%, respectively, of the variance in the number of Caiman crocodilus seen. Water level had a statistically significant and negative effect on the number of M. niger and C. crocodilus seen. Moon phase had no significant effect on the number of C. crocodilus seen, but more M. niger were detected in Lago Mamirauá on nights with more moon light. The regression equations derived for Lago Mamirauá and Cano Mamirauá did not adequately predict the variation in numbers seen in 18 other water bodies in the Mamirauá Reserve. Analysis of covariance showed an interaction between water level and site on the numbers of M. niger and C. crocodilus observed in the spotlight surveys in these water bodies, indicating that the effect of water level depends on the site. In these analyses, moon phase did not have a significant effect on either species, and there was no interaction between moon phase and site. To monitor natural tendencies, or impacts (e.g., controlled commercial hunting), on caiman populations of Mamirauá Reserve, it will be necessary to undertake regular spotlight surveys in many water bodies of all types at a narrow range of water level to have confidence in the results.