Taken together, non-determined legal status territories, areas with fragile and conflict-affected situations status, joint marine regimes, and transboundary river basins cover significant portions of the world's terrestrial and marine areas. Non-determined legal status territories cover approximately 4.6 million square kilometers, while areas with fragile and conflict-affected status extend over 37 million square kilometers. Figure 3 shows the geographic distribution of FCS countries across the world. International joint marine regimes cover over 400,000 square kilometers, and transboundary river basins encompass a vast area of nearly 62 million square kilometers. These regions, often characterized by geopolitical tensions and environmental challenges, have substantial importance for international cooperation and conflict resolution. According to population data from WorldPop (Tatem 2017; WorldPop and CIESIN 2018), an estimated 2.1 million people reside within non-determined legal status territories, while around 936 million people live in areas marked by fragile and conflict situations. Furthermore, over 3.5 billion people inhabit regions dependent on shared water resources in transboundary river basins, underlining the complex interplay between population distribution and resource management in these geopolitically sensitive and overlapping areas. Figure 4 illustrates the log human population density in transboundary river basins across the world.

# **The Role of Human Population Density**

Understanding the relationship between biodiversity and human population density is crucial for addressing the ongoing biodiversity crisis. As human populations grow and expand, the pressure on ecosystems intensifies, making it essential to explore how population density impacts biodiversity conservation. Human activities, particularly in densely populated areas, have been a major driver of ecosystem alteration, from habitat loss and fragmentation to overexploitation of resources. The clearing of forests and wetlands for agriculture, urban development, and infrastructure projects has directly contributed to the decline in species diversity and the disruption of critical ecological processes.

Human population density often correlates with higher levels of resource consumption, which in turn often leads to greater environmental degradation. For example, densely populated urban areas tend to have higher pollution levels, increased waste production, and more extensive land conversion. These factors not only stress the natural environment, but also create challenges for species survival. As human settlements encroach on natural habitats, conflicts between humans and wildlife frequently emerge, exacerbating threats to biodiversity. Farmers may face crop damage from wildlife, leading to retaliatory killings, while wildlife may lose their habitats or be forced to migrate into more dangerous or fragmented areas. These interactions highlight the urgent need to assess how human population density contributes to habitat loss and species endangerment.

At the same time, understanding population density's effects on biodiversity can inform strategies for fostering human-wildlife coexistence. Regions with higher population densities require innovative solutions, such as effective land-use planning, the establishment of wildlife corridors, 11