From Small Forest Streams to Large Amazonian Rivers: How Four Sympatric and Sometimes Syntopic Crocodilians Divide Space

Syntopic species share the same habitat in time and space. Thus, although some species might have completely coincident spatial distributions on a relatively broad scale, most are syntopic only in certain locations. Four species of caimans (Crocodylia: Alligatoridae) occur throughout the Amazon basin, but they are rarely found living in syntopy. In locations where all four caiman species coexist, their distributions and occurrences have not been studied simultaneously to determine to what degree they partition space. We carried out extensive spotlight night-surveys from 2013 to 2017 to better understand how the four caiman species coexist in sympatry and quantify the degree to which they differ in habitat use and space occupancy. The strictly Amazonian species of caimans —Melanosuchus niger and Paleosuchus trigonatus—were less likely to occur close to each other than other species pairs, suggesting that these species occupy different sections within waterbodies in the same microbasin. Caiman crocodilus had the highest encounter rates and was mainly associated with varzea floodplains and exhibited a high degree of spatial overlap with Melanosuchus niger. Paleosuchus trigonatus was the only species showing encounter rates increasing with the proportion of nonflooded forest around waterbodies but that relationship was not statistically significant. Based on spatial distributions, Paleosuchus palpebrosus seem to be the species that most often shares space with other Amazonian caiman species, because it was the only regularly syntopic species. The fact that each species represented its own most frequent neighbor indicates a clustered distribution of caimans, likely a result of habitat segregation among species. Although the phylogenetically related species tended to occupy the same ecosystem, habitat partitioning may enable the coexistence of four crocodilian predators in one catchment.