Functional connectivity of the world’s protected areas

But even protected areas have shortfalls that make them unlikely to stop biodiversity loss. Because more than 90% of all terrestrial protected areas are embedded within human-modified land, protected areas are essentially becoming islands in a sea of human-dominated land uses that can significantly hinder animal movement. Not only are they becoming disconnected from one another, many protected areas by themselves are not large enough to encompass the life history needs of many species.

For these reasons we embarked on a two and half year-long research project aimed at measuring how isolated each of the world’s protected areas are from one another, from the perspective of moving mammals. We also set out to identify the places where mitigating human pressures on the environment is most important for maintaining the global flow of mammals between protected areas.

We did all of this by characterizing the ‘functional’ connectivity of the world’s terrestrial protected areas. Unlike ‘structural’ connectivity, which assesses how connected landscape elements are, functional connectivity measures the degree to which landscape elements actually contribute to animal movement. To characterize functional connectivity, we used a 2018 analysis of mammal movement in relation to the global human footprint index to model resistance-to-movement across the world’s terrestrial surface. Then, using the World Database on Protected Areas, we applied circuit theory to model the net probability of individuals moving through each grid cell as they travel between protected areas.

Two key outcomes emerged from our study. One: we developed the first ever global metric for measuring the functional connectivity of Earth’s terrestrial protected areas – i.e., connectivity from the perspective of moving mammals. We showed how this metric can be aggregated to the national level, so that signatory nations to the Convention on Biological Diversity (CBD) could monitor their progress towards meeting global conservation targets aimed at connecting protected areas. These and other targets will be updated in December 2022 at the 15^th Conference of the Parties for the CBD (Montreal, Canada) and are likely to guide the conservation agenda for at least the next decade.

Two: we mapped the world’s most critical areas for connectivity, finding that two-thirds of these areas are unprotected, with 6% occurring on land with moderate to high human modification and 23% occurring on land suitable for future agricultural expansion. If these areas are developed or otherwise disrupted, connectivity between protected areas could be diminished or lost. Our map of critical connectivity areas can be incorporated into conservation blueprints to capture a vital dimension of biodiversity not previously considered in global conservation priorities.

However, formal land protections are not the only way to preserve connectivity. We found that, at the national level, mitigating human pressures on the environment was twice as important to protected area connectivity than the size of a country’s protected area estate. This suggests we have a lot of options to manage permeable landscapes, such as retaining natural habitats within agricultural areas, removing fences, building highway overpasses or underpasses, and restoring greenways and other stepping stones between parks. Our future and the future of biodiversity depends on the maintenance of healthy ecosystems, which in turn relies on continued animal movement and gene flow among connected populations.

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