INTRODUCTION
A species geographic range is the result of complex interactions between
its intrinsic characteristics and environmental factors (Brown et al.,
1996). At such broad spatial scales, climate and other biophysical
conditions play a major role (Lomolino et al., 2006). Additionally,
recent studies have shown that anthropic factors can have an effect on
species range size (Di Marco & Santini, 2015) and vulnerability to
extinction (Di Marco & Santini, 2015). Such vulnerability may vary
across biomes within the species range, reflecting the interaction
between anthropic effects and environmental factors.
For most species, geographic ranges are composed of multiple local
populations that interact with each other (Andrewartha & Birch, 1954)
and are distributed across areas with high environmental heterogeneity.
At the local scale (landscape, or local populations) the way in which
environmental conditions and species interactions influence distribution
(occupancy) is less known and continues to be debated (Araújo &
Rozenfeld, 2014; Blanchet et al., 2020; Cazelles et al., 2016),
especially with regards to the underlying processes that account for the
observed patterns. However, there is increasing empirical evidence
showing that at the local scale, species occupancy probabilities are
often influenced by both environmental factors and the presence or
absence of interacting species (Rota et al., 2016).
Some studies indicate that organisms can adapt differently to
heterogeneous conditions in different parts of their ranges, showing
plasticity (Sagarin et al., 2006), and in this sense the factors that
affect their occupancy could vary across sites. In a similar fashion,
the presence and magnitude of human impacts can modify positively or
negatively occupancy. Human activities such as agricultural and urban
expansion or hunting have been shown to affect negatively biodiversity
through degradation and fragmentation of habitats, even causing local
extinctions (Foley et al., 2005; Kinnaird et al., 2003; Tscharntke et
al., 2012). On the other hand, human activities (voluntarily or
involuntarily) can also provide food and refuge to some species,
specially to those that are opportunistic (Fedriani et al., 2001; Oro et
al., 2013), subsidizing their presence and abundance. These changes can,
in turn, affect species interactions (trophic and competitive).
Understanding how habitat characteristics, species interactions and
anthropic factors affect patterns of occupancy of species is crucial for
making management and conservation decisions (Guisan & Thuiller, 2005;
Williams et al., 2002). This can help to minimize the impact of human
activities on biodiversity, and inform restoration processes, by
focusing on factors that are more important for certain species.
Mammals and terrestrial birds play important roles in the maintenance of
ecosystem stability and biodiversity in tropical forests (Jansen et al.,
2010; Sekercioglu, 2006; Terborgh, 1988). Many of these species are
particularly vulnerable to local extirpations due to anthropic effects,
such as hunting and habitat degradation, while others can be favored by
anthropic subsidies (i.e. small and medium-sized mammals) (Fedriani et
al., 2001; Oro et al., 2013; Porras et al., 2016). For this reason, they
represent an ideal group for understanding the variation in factors that
determine their presence in different landscapes. Colombia has a high
diversity of mammals and terrestrial birds that occur in different
habitats subject to varying degrees of human disturbance. The Middle
Magdalena (MML) and Orinoquia landscape (OL), the two landscapes studied
here, present differences in their predominant ecosystems as well as
their level of human influence. The MML, while originally composed of
vast humid tropical forests and wetlands, is now dominated by
agricultural land uses, mainly cattle farming and palm oil, with high
levels of fragmentation. Forests remnants are usually of less than 100
hectares. The OL is composed of different ecosystems, mainly savannas
dissected by riparian forests, it has a much lower human density, and
the predominant activity of extensive cattle farming has not resulted in
drastic forest loss or degradation.
We use occupancy modeling to evaluate the factors that determine species
presence within these two landscapes and assess how the importance of
such factors (natural vs human-mediated) vary from one landscape to
another. We also evaluate the prevalence of inter-specific interactions
inferred though the effect of one species in the occupancy of another,
and how these vary across landscapes. Discerning how occupancy is
determined by environmental and anthropic factors in landscapes with
different levels of disturbance can help to understand how species are
affected by or are adjusting to human influence in tropical ecosystems.