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Island mammals



Jay Freeman wrote:

>...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. 

Hmmmm.

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

So. It doesn't look like even small mammals (such as feral rats and cats)
have much trouble displacing birds, just that they have a tougher time
reaching the islands to begin with.

Of course, in the Mesozoic, there would have been no "artificial" modes of
transports, as with human introduction.
I'd expect a Cretaceous "Galapagos" to look a lot like the modern one.
Plesiosaurs would have filled in the pinniped role, and sea birds and
pterosaurs would have filled in the roles that birds do today, with
sea-feeding generalists and terrestrial specialists adapting to whatever was
available. 

Hhhmmm.

>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 might be seen as an extension of the situation in Australia, where
reptiles remained (relatively speaking) more important as high-level
predators than is most other parts of the world. The varanid _Megalania_ was
far larger (22+ ft. or so) than any of the Australian mammalian predators,
though it undoubtedly filled a slightly different niche than the marsupial
carnivores.

Caitlin R. Kiernan