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Designating areas as protected spaces for wildlife is a common strategy for preserving biodiversity, but heavy human development around those areas may largely counteract the benefit of those protections.

This phenomenon is described in a new study using camera-trap data to evaluate the effectiveness of hundreds of protected areas across China. Co-author Roland Kays, research professor at North Carolina State University and scientist at the N.C. Museum of Natural Sciences, said that researchers found major losses in biodiversity where protected areas were hemmed in by people. The study is in the journal Current Biology.

These losses often began with large predators like tigers, which saw large reductions in population when their movement was limited by the presence of people. The areas between two preserves, which scientists call a matrix, play an important part in allowing those large species to move freely. When that matrix becomes difficult to traverse, usually due to human development or deforestation, apex predators are often the first to suffer.

"Larger species are going to need more space, and one way they can get that is to move from one protected area to another. The other way is to just use areas outside of protected areas," Kays said. "As those spaces get more and more developed, these larger species just aren't going to be able to move around in the way they need to, and you will start to lose them."

Researchers found that apex predators had gone completely extinct in about 84% of protected areas, correlating closely with the extent of human development nearby. In some cases, researchers found, preserves may have even been established too late, after large predator species had already died off. The effects were clear; areas without these large species were significantly less biodiverse, mostly dominated by increasing populations of wild boars and other medium-sized predators.

The rate of species loss significantly outpaced what might be expected from natural, random extinctions, said lead author Junjie Liu, a Ph.D. student in the Guangxi University Key Laboratory of Forest Ecology and Conservation.

"My initial hypothesis was that current protected area networks would support higher network complexity compared to a model simulating random species loss," Liu said. "I was surprised to find that the network complexity of current communities was significantly lower than that of the extinction scenario, which was largely due to the loss of apex predators."

As China experiences a decline in human population, an opportunity may arise to reclaim some wild spaces and reintroduce apex predator species, Kays said. This would present a significant opportunity to revitalize biodiversity in China, and a strategy which could be applied to other areas experiencing similar losses worldwide.