Human-induced changes of landscapes are a major threat to biodiversity and global Earth systems. Habitat loss and degradation reduce population sizes and restrict animal movement, gene flow, and landscape connectivity, thereby undermining the long-term viability of wildlife populations. These impacts are particularly pronounced for apex species, which typically require large home ranges, occur at low population densities, and have historically been heavily persecuted by humans.
The Asian black bear (Ursus thibetanus) is a wide-ranging large mammal distributed across Asia. While its distribution has expanded over the past 40 years on Honshu, Japan’s main island, the species has experienced a severe decline on Shikoku Island. The current Shikoku population is restricted to a small area in the eastern part of the island and consists of approximately 30 individuals, forming a critically small and isolated population facing a high risk of inbreeding. This decline is thought to be driven by persecution arising from human–bear conflict and the large-scale transition of natural forests into plantation forests; however, the extent to which landscape structure constrains habitat use and movement has not been quantitatively evaluated.
In this study, we applied a multi-scale modeling framework to assess how human-modified landscapes influence the space use and movement of Asian black bears on Shikoku Island. We first estimated the spatial distribution of high-quality habitat at the landscape scale using Resource Selection Function (RSF) modeling. RSFs were constructed separately by sex and season (mating season and hyperphagia), resulting in four models. We evaluated fine-scale relationships between movement and landscape features using integrated Step Selection Function (iSSF) modeling. Then, based on parameters from the iSSF models, we conducted simulations to evaluate potential movement from the current population range to other suitable habitats.
Across all season–sex combinations, RSF analyses consistently identified three high-quality habitat areas (western, central, and eastern areas) on Shikoku Island. Movement simulations based on iSSF models revealed no movements from the current habitat to the nearby high-quality habitat area in any season–sex combination.
Our results show that the current population of the Shikoku Asian black bear is constrained in its space use and movement by landscape-level barriers that severely limit functional connectivity, resulting in isolation within a single suitable habitat. These findings underscore that human-induced landscape modifications disrupt functional connectivity, thereby threatening the persistence of this critically endangered population and highlighting the urgent need for connectivity-focused conservation strategies.