A different process goes on when an island forms by splintering. Here, the ecosystem is pre-existing: the island is created with a set of residents already in place. But it is now too small to support them all.

What happens next is a kind of unraveling, a fraying, a disassembling such that the ecosystem becomes simpler, so as to fit the space that is now available. On those recently-created islands of Indonesia, for example, the smallest islands are home to many fewer species than the largest islands. And, as you’d expect, you don’t find big animals on the smallest islands either.

When we humans burn tracts of forest, or make islands in some similar way, the immediate impacts depend on a suite of factors, including how many islands there are, how big they are, and how close they are together. It also matters what is between them. Fields may be more hospitable to wildlife than roads or water; under some circumstances, life forms may be able to flit from one fragment to another, and the “island” nature of the fragments will be reduced. Perhaps we can use such patterns to shape how we use land, to try and minimize the impact we have.

Perhaps.

The once-mighty longleaf pine ecology that spread from eastern Virginia to east Texas now only exists in tiny islands separated by cities, fields, and roads. Maybe we should preserve the few patches that are left. This isn’t just about plants and animals, you know, it’s also about flood control, food supply, and living conditions.

Half a century ago we overused pesticides, in particular DDT, which caused birds’ eggs to become too fragile. Bald eagles vanished from many places. But sometimes they come back, when we stop poisoning them and instead save some habitat.

The eagle pictured was just sitting beside the road as we drove by. There are more in nearby counties. Picture by Gretchen Quarterman, 23 March 2010.