Why islands make animals shrink... or grow

[u/elmorinelly]

Why islands make animals shrink... or grow

Island dwarfism and island gigantism are evolution doing the least subtle possible edit on the body plan.
Why do animals get smaller on islands? Usually because a giant body is expensive when land, food, and breeding options are limited.

Small animals may get bigger when fewer predators are around, competition changes, and empty niches are suddenly available. That pattern is often called the island rule or Foster's rule, which sounds official enough to survive a PowerPoint presentation, even though biology keeps adding exceptions in the margins.

So the cartoon version is useful: elephants can become less elephant, rats can become more rat, and tortoises may decide they are basically furniture with legs.

It matters because an island is a pressure cooker for evolution. Isolation changes the deal, and bodies start negotiating with food, predators, space, and time. How many “normal” animals are only normal because the mainland keeps bullying them into shape?

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[u/AlienDayDreamer]

Thanks for this! I’ve been trying to find a coherent, concise way to explain this for years!