[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: mammal mystery



> Can anyone think of an extant island ecosystem, an island that did not
> originate by breaking away from a larger land mass (so never mind Madagascar
> and Tasmania and such), where mammals are the dominate tetrapods?

> Birds and reptiles (and mostly birds) seem to win out.
                                                ^^^^^^^
  If you are using "win out" in a strict sense, and suggesting that
the reason why birds and reptiles dominate is pure competition, surely
there is another issue, one of transport.  Birds -- quite large birds
-- can easily reach any island in the world.  Non-marine mammals and
non-marine reptiles have it tough.  With a large bird already well
along the route of filling the large-predator niche, any mammalian
arrival would likely have a difficult time establishing itself, much
less evolving larger descendents to fill other niches.  The mechanics
of transport probably favor small-mammal introductions over large
ones, at long over-water distances, and also probably favor non-bird
reptiles over mammals (on grounds of less requirement for food and
water, and better ability to cope with temperature extremes, all en
route).

  Of course, in modern times, mammals are devastatingly successful
competitors on essentially all oceanic islands where humans have
introduced them -- it's not that they can't compete, it is that
geography has never given them the opportunity to do so.

  The only island ecosystem I can think of, in which the top predator
prior to human intervention is a non-avian tetrapod that seems
substantially to have evolved in place (rather than being a small
modification of something that came with the island, as in Tasmania or
Madagascar), is Komodo, which is not oceanic, and which is evidently
rather atypical.  (Though it's kind of nice that there is still one
place in the world where a bold adventurer can get eaten by a dragon
without intending to.)

                                                --  Jay Freeman