From an Aeon piece by Bill Adams about the inability of nature preserves to stem the loss of biological diversity:

“Part of the problem is biological. Protected areas such as national parks do help preserve the animals and plants inside them, if the areas are large enough. Yet, despite the fact that there has been a huge increase in both the number and extent of protected areas through the 20th century, biodiversity loss has continued apace, accelerating in many regions. What is going wrong?

The problem is that protected areas become ecological islands. In the 1960s, a famous series of experiments on patterns of extinction and immigration were conducted in the islets of the Florida Keys by EO Wilson and his student Daniel Simberloff. Their findings became the basis of the ‘theory of island biogeography.’ Simply put, islands lose species: the smaller the island, the faster they are lost. Since then, ecologists have recognised that these islands of habitat need not be surrounded by a sea of water. In Amazonia, ecologists conducted experiments on land that had been converted from forest to farms: islands of trees in a sea of dirt. They preserved square blocks of forest of different dimensions and studied the effect on diversity. Edge effects — the increase of sun, wind and weeds at the boundary between forest and cleared land — changed the microclimate of the forest, and species were lost. The smaller the remnant forest patch, the faster the species disappeared.”