Environmental and human-mediated factors influence vertebrate occupancy
in two tropical ecosystems
Abstract
A species presence within its geographic range can be influenced by
environmental variables and disturbance history, resulting in particular
occupancy patterns. Understanding the factors affecting occupancy is
essential to evaluate the impact of human activities on species and
design conservation or restoration measures. For tropical vertebrates,
there is little understanding of how multiple factors influence
occupancy and interactions with other species under different conditions
and disturbance levels. In this study, we evaluated how natural and
human-mediated factors determine the presence of mammals and terrestrial
birds in two tropical landscapes that share some species but differ in
the type of ecosystems and the degree of human disturbance. We adjusted
single-season occupancy models for each species to assess the key
variables (human-influenced and natural) determining its presence in
each landscape, and co-occurrence models to evaluate potential
inter-specific relationships. Although species richness was similar
between landscapes, small, generalist species had a higher occupancy in
the more disturbed landscape (ψ 0.58 Vs 0.40), while larger species had
a higher occupancy in the less disturbed one (ψ 0.79 Vs 0.21). Species
in the more fragmented and altered landscape were mainly affected by
human-mediated variables, although the effect was not always negative,
with smaller species being favored by such conditions. In contrast, in
the less altered landscape, environmental variables were more
determinant of vertebrate occupancy. Additionally, the number,
magnitude, and direction of species interactions usually changed from
one landscape to another. Results from this study contribute to the
broader understanding of the mechanisms that determine vertebrate
occupancy in tropical ecosystems. They confirm how human disturbance can
have a direct effect on occupancy of larger species of mammals, and
demonstrate how in more altered ecosystems factors associated with human
presence may become more limiting or more beneficial than natural ones
becoming the primary determinants of occupancy.