Amphibia-Reptilia 34 (2013): 437-449 Growth rates of black caiman (Melanosuchus niger) and spectacled caiman (Caiman crocodilus) from two different Amazonian flooded habitats Ronis Da Silveira 1,∗ , Zilca Campos 2 , John Thorbjarnarson 3,∗∗ , William E. Magnusson 4 Abstract. 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. Keywords: Alligatoridae, Crocodylia, demography, mark-recapture. Introduction Effective wildlife management requires infor- mation on the demography of the species in- volved, including an understanding of indi- vidual parameters, such as somatic growth (Rees and Crawley, 1989; Abercrombie, 1992; Wilkinson and Rhodes, 1997). Growth rates of crocodilians are complex, and can vary within a species according to age, size, sex, genetics, incubation conditions, season, habitat, location (Gorzula, 1978; Magnusson and Taylor, 1981; Webb et al., 1983; Hutton, 1987a; Jacobsen and Kushlan, 1989; Webb and Cooper-Preston, 1989; Booth, 2006) and could be density- 1 - Laboratório de Zoologia Aplicada à Conservação, De- partamento de Biologia, Instituto de Ciências Biológi- cas, Universidade Federal do Amazonas, Av. Gen. Ro- drigo Otávio 3000, CEP 69077000, Manaus, Amazonas, Brazil 2 - EMBRAPA Pantanal, CP 109, CEP 79320-900, Co- rumbá, Mato Grosso do Sul, Brazil 3 - Wildlife Conservation Society, PO Box 357520, Gai- nesville, Florida, USA 4 - Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia, CP 478, CEP 69011970, Man- aus, Amazonas, Brazil ∗ Corresponding author; e-mail: ronis@ufam.edu.br ∗∗ Deceased. dependent. Information on growth is important for determining age at sexual maturity, and un- derstanding relationships between age and fe- cundity of females (Wilkinson, 1983; Thorb- jarnarson, 1996; Campos et al., 2008). Body size also likely plays an important role in de- termining the reproductive success of males (Lang, 1987; Webb, Whitehead and Manolis, 1987). Most studies of crocodilian growth patterns have been based on mark-recapture studies and the relationship between growth rate and the size of individuals (Magnusson and Sanaiotti, 1995; Dalrymple, 1996; Saalfeld et al., 2008). This information is generally analyzed using sigmoidal growth models to describe the re- lationship between size and age of individu- als (Andrews, 1982). Use of these models for crocodilians has been criticized because growth rates of individuals within the same habitat can vary greatly and this can lead to errors in pre- dictions relating size and age (Webb, Buck- worth and Manolis, 1983; Magnusson et al., 1997) and mark-recapture studies of crocodil- ians frequently lack data on the growth of adults (Abercrombie, 1992). Ideally, growth models would be validated with information on the size © Koninklijke Brill NV, Leiden, 2013. DOI:10.1163/15685381-00002896