Re: species flock -Reply -Reply

[Mike & Diane Wise <apistowise@bewellnet.com>]

William Vannerson wrote:

> I know that the SA continent has had large lakes and seas recede as well as
> different rivers altering courses.  These geological events could produce
> "flocks" similar to the African cichlids.  Even for Apisto species that
> currently are not part of the same river courses.

I find the paleogeography of South America over the past 5 million years to be
very interesting. Before the rise of the Andes, about 5 million years ago, the
Amazon River drained into the Pacific Ocean. As the mountain chain rose, this
mouth of the Amazon was blocked and a vast lake temporarily filled the Amazon
Basin until it found a new outlet. It flowed northward along the eastern flanks
of the Andes where it joined the Orinoco and flowed into the Caribbean. At about
the same time the Guiana/Brazilian Highlands were breached and waters finally
flowed eastward into the Atlantic.

During the Pleistocene Epoch (2 million - 10,000 years before present) the Amazon
Basin went through repeated wet and dry cycles roughly corresponding with the Ice
Ages occurring in the northern hemisphere. During periods of maximum glaciation
in the north, sea level lowered 100 m (330 ft) worldwide and the Amazon Basin
dried out. The rain forest was replaced by a broad grassy plain. The rain forest
survived only in small localized areas where the orographic effects of mountains
and highlands provided enough rainfall to supply their needs. These "refugia", as
they've been called, are in many cases the focal points for many of the
Apistogramma species-groups. During the wetter/warmer interglacial periods the
Amazon Basin again turned to rain forests, and allowed species to migrate from
their refugia and expand into new areas. This occurred several times. I imagine
that the apistos evolved into the various species-groups during the these dry
periods while isolated in widely separated refugia.

Mike Wise

> Again, this would be a yfascinating graduate study topic for any
> students lurking on the list.  hint. hint. ;-)
>
> Bill Vannerson
> http://ourworld.compuserve.com/homepages/william_vannerson
>
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