アジアゾウの孤立化が進行、社会的ネットワークの分断が明らかに（Elephants Found to be Increasingly Isolated, Leading to Fractured Social Networks）

Animal societies can maintain their structure despite changes in membership, but gradual demographic losses may accumulate until they trigger abrupt changes in social organization. This study tracked demographic turnover and social network dynamics over 12 years in 443 wild female Asian elephants in Udawalawe National Park, Sri Lanka. The researchers found that deaths and permanent departures increasingly outpaced new arrivals. As these changes accumulated, previously large and densely connected communities fractured into smaller, more isolated social groups. This fragmentation was driven not only by the disappearance of individuals but also by the rewiring of relationships among surviving elephants, including the loss of weaker social connections. The findings provide empirical evidence that gradual demographic change can push the social networks of a long-lived mammal past a critical tipping point, resulting in a less cohesive and potentially less resilient social structure. The study highlights the importance of monitoring social relationships alongside population numbers in wildlife conservation, as the erosion of social connectivity may undermine the resilience and recovery of animal populations.