Padrões de movimentação e área de uso de jacarés (Paleosuchus trigonatus e Caiman crocodilus) em um fragmento florestal no perímetro urbano amazônico

Abstract

The spatial ecology of crocodilians has been widely studied over time, highlighting the influence of biological factors (e.g. body size and sex), environmental factors (e.g. habitat availability and seasonality), and behavioural factors (e.g. territoriality and reproduction) on their spatial dynamics. The dwarf caiman (Paleosuchus trigonatus) and spectacled caiman (Caiman crocodilus) exhibit complex habitat-use behaviour. Both species occur throughout the Amazon, with C. crocodilus also extending into northeastern Brazil. This study aimed to assess movement patterns, home range, and core activity areas of caimans in relation to rainfall, body size, sex, and individual variation in an urban forest fragment in Manaus, Amazonas, Brazil. All individuals were measured (snout–cloaca length - SCL; total length - TL) and sexed. Body size was measured using a metal tape (cm), and sex was determined by the presence or absence of a penis, detected through visual inspection of the cloaca with a metal probe or by manual cloacal palpation. We used Generalised Linear Mixed Models (GLMMs) to analyse average monthly movement in relation to SCL, sex, and monthly precipitation, and to evaluate home range and core activity areas in relation to SCL and sex. Over eight years, 30 caimans were tracked in the UFAM fragment and surrounding areas: 12 males (11 P. trigonatus, 1 C. crocodilus) and 18 females (15 P. trigonatus, 3 C. crocodilus). Due to similar space-use patterns, we analysed the two species together. Movement was not influenced by any of the evaluated variables. Home range and core activity areas were affected by sex when all individuals were included. However, excluding one outlier (P. trigonatus PT09), body size showed a positive influence. Individual characteristics had the strongest effect in all models. The overall mean home range (KDE 95%) was 0.466 ± 1.235 km² (range: 0.004 - 6.904 km²), and the mean core activity area (KDE 50%) was 0.095 ± 0.270 km² (range: 0.001 - 1.526 km²). For home range, sex had a significant effect (p = 0.003), as it did for core areas (p = 0.006), both driven in part by the outlier PT09. Our findings contribute to identifying patterns of adaptation and vulnerability of these species in fragmented habitats essential for effective conservation strategies. They also provide insights relevant to sustainable urban planning, promoting coexistence between these predators and altered environments. This study advances our understanding of caiman spatial ecology in urban settings. Future research on crocodilians in Brazilian urban forest fragments should consider additional variables such as artificial structures, water pollution, vegetation structure, and waterbody availability to better assess their spatial ecology in these environments.