There are certain jobs, like digesting a certain nutrient or carrying out a specific metabolic trick, that are always filled by some microbe – just not always the same one. You see the same trend on a bigger scale. In New Zealand, kiwis root through leaf litter in search of worms, doing what a badger might do in England. Tigers and clouded leopards stalk the forests of Sumatra but in cat-free Madagascar that same niche is filled by a giant killer mongoose called the fossa; meanwhile, in Komodo, a huge lizard claims the top predator role. Different islands, different species, same jobs. The
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