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We used radio-telemetry to record how Caiman yacare (Cy) and Melanosuchus niger (Mn) responded to the intrusion of the Maniqui river into Cedral Lagoon in the Bolivian Amazon. Nine M. niger and 3 C. yacare were followed between December 2015 and May 2016. Both species showed a gradual reduction in mean monthly range from December (19.96 ha Mn and 1.74 ha Cy) to May 2016 (0.08 ha Mn and 0.24 ha Cy). Habitat use was fairly constant throughout the months for both species, Melanosuchus niger used mainly open swampy forests and Cyperaceae Marshes, while C. yacare used more islands and flooded grasslands. This study shows that both species of caimans responded to changes in depth and vegetation types, as their habitat as a whole was changed by river intrusion. [ABSTRACT FROM AUTHOR]

We conducted a study of black caiman (Melanosuchus niger) growth rates using data from a long-term markrecapture study carried out in the Rupununi region of Guyana between 2005 and 2015. In contrast to previous studies, growth rates of black caiman declined with increasing size and this decline occurred more rapidly for females. Size-at-age models predicted that males and females reach asymptotic sizes of 178.2-189.0 cm SVL and 140.1-143.4 cm SVL, respectively. Our results suggest that growth rates of black caiman in the Rupununi region follow the same general patterns as for other crocodilians, and that disparities with previous black caiman studies may be largely related to density-dependent factors, among other possibilities. However, future studies that include large black caiman of known ages are needed to validate our findings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]