I wasn’t sure if this was a General Question or the beginning of a Great Debate. I finally decided to come here, as this commentary seemed likely to draw more questions than answers.
There was just a special about birds on PBS. One of the themes was that flying is expensive, and that, when lack of predators makes it possible, birds will happily give it up, and become flightless.
Now, every even approximately oceanic island lacks a native predator population (aside from a few eagles and snakes), so every e.a.o.i. has (or had, prior to their occupation by humans) its flightless birds – rails, ducks, ratites, etc. It seems that predators don’t get to, or don’t survive on, islands – even New Zealand lacks native predators. Until you get to Australia, whether it is to be considered an island or a continent, there just isn’t a predator population (and Tasmanian devils, despite their reputation, aren’t very impressive predators). It would seem that several million square kilometers are the minimum size for a predator population to evolve and survive.
But, wait, there’s more…
The breakup of Pangaea into Laurentia and Gondwanaland seems to have led to two very different types of fauna: ratites, marsupials, edentates, and primates in Gondwanaland; miacids and ungulates in Laurentia; and (excepting the stunning, but so far short-term, success of humans) Laurentian fauna seem to invariably have the upper hand when they come into conflict.
Is this solely due to the fragmentation of Gondwanaland into pieces too small (South America, Australia, etc.) to support a really competitive fauna, or is there something deeper at work here?
“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”