The United Nations recently agreed to major expansions of global protected areas (PAs) to slow biodiversity declines1. However, although reserves often reduce habitat loss, their efficacy at preserving animal diversity and their influence on biodiversity in surrounding unprotected areas remain unclear2-5. Unregulated hunting can empty PAs of large animals6, illegal tree felling can degrade habitat quality7, and parks can simply displace disturbances such as logging and hunting to unprotected areas of the landscape8 (a phenomenon called leakage). Alternatively, well-functioning PAs could enhance animal diversity within reserves as well as in nearby unprotected sites9 (an effect called spillover). Here we test whether PAs across mega-diverse Southeast Asia contribute to vertebrate conservation inside and outside their boundaries. Reserves increased all facets of bird diversity. Large reserves were also associated with substantially enhanced mammal diversity in the adjacent unprotected landscape. Rather than PAs generating leakage that deteriorated ecological conditions elsewhere, our results are consistent with PAs inducing spillover that benefits biodiversity in surrounding areas. These findings support the United Nations goal of achieving 30% PA coverage by 2030 by demonstrating that PAs are associated with higher vertebrate diversity both inside their boundaries and in the broader landscape.
Sarawak, on the island of Borneo, is known internationally for its rich rain forests, flora and fauna. Its rain forests, occupying two-thirds of its geographical area shelters 2500 tree species, 5500 flowering plants and over 20 000 different kinds of animals and insects. Such abundance of plants, and in particular, in the variety thereof, have attracted the attention of scientists involved in the field of research into their potential medicinal value. Recent discovery that two species of Calophyllum tree in the rain forests of Sarawak produce active anti-HIV agents, has, no doubt, intensified interest in the State's plant resources for scientific research.