Are caiman nests microhabitats? Assessing their ecological role across different levels of anthropogenic disturbance.

Wild vertebrates face increasing threats from human activities, particularly land-use changes, which disrupt ecological interactions and ecosystem structure. Animal-built structures, such as nests, can provide resources for diverse species, especially under conditions of environmental stress. Here, we evaluate whether broad-snouted caiman nests function as microhabitats for other vertebrates across varying levels of anthropogenic disturbance in Santa Fe, Argentina. Over four nesting seasons we monitored 64 nests in forests, savannahs and floating vegetation using camera traps, examining vertebrate species richness, interactions and visitation frequency. A total of 100 species were recorded, including 74 birds, 23 mammals and 3 reptiles. Amphibians and some reptiles could not be identified, as most photographs were nocturnal or because of their small size. Species richness was highest in the driest nesting season and in forest nests, but unrelated to anthropization. Of the species observed, 62% interacted with the nests through commensalism, predation or indirectly. The Interaction Strength Index (ISI) proved to be a reliable indicator of use of caiman nests. Caiman nests are structurally and ecologically relevant elements, as they provide resources for a wide variety of species. Including such structures in conservation strategies could contribute to more comprehensive approaches that go beyond a species-level focus.