7,000th post: Evolutionary Niches (Lemurs the size of gorillas with eyes like dinner plates!)
Any verdant and fairly temperate Earth environment offers a set of animal "job openings" that evolution will fill working with whatever genes are around to work with.
In the age of dinosaurs there were dinosaurs filling the same niches we have today. (Or had recently, before mankind busted out of Africa and wiped out most very large non-African mammals that hadn't evolved alongside man and thus had no instinctual clue how dangerous we could be.)
There are huge vegetarians, like brontosaurs and elephants. Large predators like T Rexes and tigers, and the grazing herd animals they hunt. Little vegetarians like squirrels that run around in the trees. Fairly little predators like cats to eat them.
Back then, they were all reptiles. Today most of the larger land animals are mammals. But they overall circle of animals to eat different types of plant, and animals to eat those animals, and bigger animals those predators can't get, and larger predators to get those, and so on...
In southern florida it seldom gets cold, and thus reptile metabolism can be pretty high there. Instead of squirrels, lizards run back and forth across your lawn all day. They have alligators as the primary predator. (It's wild that a few Americans a year are eaten by reptiles.)
Islands can get pretty weird because they sometimes have limited genes to work with. Environmental niches for large animals WILL be filled. If there is food something evolves to eat it. Madagascar today has lemurs that tend to be small and nocturnal, but prehistoric Madagascar (before man arrived) had a lot more types of lemurs, with lemurs filling both nocturnal and diurnal niches. There were nocturnal lemurs as big as gorillas, with eyes the size of dinner plates. We have their skeletons.
We are aces at killing off big animals, or very sharply restricting their range. One rule-proving exception is the vast herds of Bison Europeans encountered in the American west... or is it? The Bison had managed to survive mankind by getter smaller and breeding faster. (Prehistoric bison were much larger) And then, out of nowhere, the Bison's great predator, the Native American, was mostly wiped out by smallpox. Then a couple of hundred years later Europeans make it inland far enough to encounter herds of bison supposedly stretching from horizon to horizon.
No delicious animal is able to form herds that big! Predators will evolve to eat them. But the pre-Indians had killed off most things that could eat a lot of bison... except man. But that's fine... man was doing well having killed off bison eating predators (sabre toothed cats, huge prehistoric species of wolf, etc.) and stepped into there bison-hunting niche. Then a plague from nowhere leaves the bison with nothing but (small) wolves to worry about.
How much western desert was created by out of control bison populations? I don't know... but I know that most of the American west we see today could not plausibly support herds of bison stretching to the horizons.
Anyway, what reminded me of this is the story about cats threatening bird populations in New Zealand. Birds in New Zealand are an odd story. New Zealand, being so isolated, had little else but birds to work with and filled the niches with birds, just as the Jurassic era filled them with reptiles. There were Moas, considerably bigger than ostriches with thick legs and huge beaks... quite dangerous. And there were gigantic eagles that could fly off with a sheep... if there had been any sheep.
We know these giant birds of New Zealand only from their bones. They were extinct before Europeans got to New Zealand, having been killed off by the human population... and the rats the brought with them. (egg eaters) Everywhere humans went we appear to have wiped out a lot of large animals. Larger animals have smaller populations, longer gestation periods and fewer places to hide. They are pretty easy to kill off.
Funny thing about New Zealand, though... some of the bones of giant birds aren't all that old. The Maori only beat Europeans to New Zealand by a few hundred years! But it didn't take long for we humans to get rid of the large species. In New Zealand's case, since humans were so recent to the island, we know that it happened in mere centuries, and without modern weapons.
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