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 10 own raft DHJanzen101223.jpg high resolution
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| Some organisms are their own raft. These seeds (and a fruit, the coconut on the lower left) were found washed up on the beach in Costa Rica, but could just as well have been found on any island beach around the tropics (and indeed, as far north as Newfoundland and England). Some of such seeds, like the coconut (see below) are sea-dispersed and for them the island is just more habitat, rather than an island habitat that they tenuously occupy. The large pink Mora megistosperma seed (Fabaceae) is also sea-dispersed from mangrove swamp to mangrove swamp on the Pacific coast of Costa Rica (actually, it needs a mangrove swamp rather than a beach on which to survive, so washed up on an island beach it is effectly a dead waif. The others, and many other species as well, are indeed waifs that serendipituously ended up in a river that carried them to sea, where they float until the saltwater eventually kills them, or a storm deposits them on a beach (or better yet for them) above the high tide line. If the sea has not killed them by the time they are deposited above the high tide line, they have some minimal chance of becoming established, and this is presumably the origin of most natural populations of plants on oceanic islands (the other is to have been brought as domesticates or contaminants by people). | ||
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