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.