There Are Many Types of Islands

IMAGINE a world without islands.

Biologists often use the word 'island' to mean something other than just a piece of land surrounded by water. From the point of view of a freshwater fish, a lake is an island: an island of habitable water surrounded by inhospitable land. From the point of view of an Alpine beetle, incapable of flourishing below a certain altitude, each high peak is an island, with almost impassable valleys between. There are tiny nematode worms (related to the elegant Caenorhabditis) which live inside leaves (as many as 10,000 of them in a single badly infected leaf), diving into them through the stomata, which are the microscopic holes through which leaves take in carbon dioxide and release oxygen. To a leaf-dwelling nematode worm such as Aphelencoides, a single foxglove is an island. To a louse, a single human head or crotch might be an island. There must be lots of animals and plants that regard an oasis in a desert as an island of cool, green habitability surrounded by a hostile sea of sand. And, while we are redefining words from an animal's point of view, since an archipelago is a chain or cluster of islands, I suppose a freshwater fish might define an archipelago as a chain or cluster of lakes, such as the lakes along the Great Rift Valley in Africa. An Alpine marmot might define a chain of mountain peaks separated by valleys as an archipelago. A leaf-mining insect might regard an avenue of trees as an archipelago. A botfly might regard a herd of cattle as a moving archipelago.

Creating many ways for species to evolve divergently.