Researcher Disturbance Has Minimal Impact on Natural Predation of Caiman Nests in Central Amazonia
Predation is one of the major causes of crocodilian egg mortality. Many studies have suggested that opening nests, handling eggs, and capturing attending females may increase predation rates, but the influence of such activities on nest predation has not been quantified. For that reason, we studied the impacts of different research activities on nests of wild Spectacled Caimans (Caiman crocodilus crocodilus) from a flooded forest (várzea) in the Piagaçu-Purus Sustainable Development Reserve, Central Amazonia. During the 2010 nesting season, predation on eggs in disturbed nests was generally higher than in nests without research activities found in the same area. However, natural predation rates in similar habitat were not significantly different, suggesting that predation rates on disturbed nests, though elevated, remain within the broad range found in undisturbed nests. We conclude that the benefits in knowledge gained from research activities will generally out-weigh the small increase in nest predation that could result from research activities. A predação constitui uma das principais causas de mortalidade dos ovos em crocodilianos. Vários autores sugerem que o abrir os ninhos, manusear os ovos e capturar as respetivas fêmeas, poderá aumentar as taxas de predação. No entanto, o impacto destas atividades ainda não foi quantificado. Por esse motivo, nós estudamos diferentes níveis de impacto de pesquisa nos ninhos e respetivas fêmeas de jacaretinga (Caiman crocodilus crocodilus) na floresta de várzea da Reserva de Desenvolvimento Sustentável Piagaçu-Purus, Amazónia Central. Durante a época de nidificação de 2010, a predação dos ovos em ninhos perturbados por actividades de pesquisa foi, de maneira geral, superior ao observado em ninhos não perturbados, encontrados no mesmo local. No entanto, as taxas de predação naturais em habitat semelhante não demonstraram ser significativamente diferentes, o que sugere que as taxas de predação em ninhos perturbados, mesmo apesar de elevadas, permanecem dentro do intervalo observado em ninhos não perturbados. Desta forma, concluímos que todo o conhecimento obtido durante actividades de pesquisa irá compensar a possibilidade de um pequeno aumento na predação dos ninhos, que poderá surgir em consequência de abrir os ninhos e manusear os ovos ou as fêmeas.Abstract
Resumo
Proportion of depredated nests in the nine combinations of levels of impact (treatments) applied during this study. The numbers represent the treatment combinations applied (see Table 1). The lines connect combinations of treatment levels with the same impact applied to nests.
Probability of a nest being depredated after research activities in relation to the absence, presence, or capture of the attending females. These values were estimated using a binomial logistic regression analysis. The numbers represent the different combinations of levels of impact applied in this study (see Table 1). The lines connect combinations of levels with the same level of impact applied to the nest (see Materials and Methods for more information on nest treatments). The letters represent the subgroups created by Tukey's post hoc test at P < 0.05.
Mean predation rate on Caiman crocodilus crocodilus nests in our experiment in comparison with natural predation observed in the 2009 nesting season in the same area of PP-SDR and in the 2009 and 2010 nesting seasons around Piranha Lake. Each point in the graph represents a water body. Lines connect predation rates from the same water body in different years. Because we were not able to revisit nests at the end of the nesting season, predation rate estimates from PP-SDR 2009, Piranha 2009, and Piranha 2010 were based on first visit to nests and represent minimum values.
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