Gene flow in a heterogeneous matrix with human disturbance
Our analysis using multiple genetic distances and statistical techniques
identified topography as the most significant landscape barrier
affecting gene flow in Taiwanese leopard cats. Contrary to our
expectations, resistance to movement increased with elevation, even
though natural forests dominate mountainous regions. This outcome may be
explained by their preference for forest edges, which provides easy
access to both refuge in forests and prey in agricultural landscapes
(Rajaratnam et al., 2007). Tracking studies conducted in Taiwan suggest
the leopard cats there prefer densely vegetated natural habitats and
avoid areas with human activities (van der Meer et al., 2023). An
alternative explanation is derived from the concept of the energy
landscape, whereby landscape complexity influences animals to adopt the
most energetically efficient movement patterns (Shepard et al., 2013;
Wilson, Quintana, & Hobson, 2012). We observed a positive correlation
between resistance and roughness (a proxy of topological complexity),
but resistance only increased significantly at high roughness levels and
at higher elevations (>1,000 m). Thus, landscape complexity
alone does not fully explain why elevation hampers connectivity at lower
elevations. We propose a third potential explanation based on the
typical physiological intolerances to large temperature variation of
tropical organisms (Janzen, 1967). We found that the distribution of
leopard cats in Taiwan is negatively correlated with minimum temperature
(Fig. S9), indicating that low temperatures may limit their expansion
and movement. Unlike their relatives in temperate areas, tropical and
subtropical leopard cats are typically restricted to lowlands
(Rajaratnam et al., 2007; Ross et al., 2015). Moreover, elevation as a
significant barrier has been reported for a diversity of taxa in
tropical regions (Monteiro et al., 2019).
Linear features such as paved roads and highways are artificial
structures known to have a significant impact on gene flow in many
species (Clark et al., 2010; Kuehn et al., 2007; Robinson et al., 2012),
and highways have been identified as physical barriers that impede
movement and lead to a decline in genetic diversity (Epps et al., 2005).
Huge artificial linear features may also act as behavioral barriers
(Kimmig et al., 2020; Laundré, Hernández, & Altendorf, 2001). For
leopard cats in Taiwan, the avoidance of highways may be driven by a
perceived risk associated with high-speed traffic and strong
illumination. In contrast, we found that unfenced roads presented low
resistance, serving as corridors that facilitate movement. Such roads
are often located in areas of lower human activity and traffic volume
compared to highways. In mountainous regions, roads are typically
situated in valleys at lower elevations and are surrounded by natural
forests, making them suitable for leopard cat movement (Chen et al.,
2016; Pei, 2008). Although vehicle collisions pose a significant
mortality risk for leopard cats in Taiwan (at least 50 road-kills
recorded between 2012 and 2017; Chen et al., 2019), they may still
utilize roads as corridors to avoid areas of other human activity.
Similar patterns have been observed for foxes, which prefer sites of low
human density and activity rather than completely avoiding human
constructions (Adkins & Stott, 1998). These findings highlight how
different linear landscape features influence connectivity and can
contribute to our understanding of dispersal processes in vagile
carnivores.