Not all islands are surrounded by water. Some are ringed by wheat fields, highways, fences, suburbs and municipal boundaries. For the creatures trapped inside them, survival depends on connection.

Islands may be chunks of land surrounded by water, but they don't have to be. Think traffic island. A bit of grass, maybe a tree. A bird or two can come and go. But anything not able to fly is marooned. Wiggle or walk off the edge and you're history.

That's a good analogy for what we're doing to the planet.

The mountains of the Cape Peninsula are quite literally a traffic island surrounded by a sea, roads and people. For the baboons, caracals and maybe a leopard or two as well as other creatures without wings there's no escape across the Cape Flats. We've islanded them. A disease or a fire that traps them and they're gone.

Take the wheat fields of the Western Cape. They used to be renosterveld, but what remains is often confined to valleys, rocky slopes or hilltops not suitable for cultivation. Maybe 5% is left. The walking, crawling creatures of the renosterveld cannot cross the wheat fields without being picked off. We've islanded them too. What wild things need in a hyper-humanised world is escape routes.

There's solid science behind the idea.

It was the Prussian naturalist Alexander Humboldt who laid the foundations...