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>> I don`t know much about La Brea, but I can`t see how any determination of
extinction by climate change can be made by studying one site alone. Sure,
one may see that a species was in decline in that area. Sure, one can also
see that climate was perhaps "deteriorating" in direct correlation at that
particular site. But what is to say that the species in question didn`t just
migrate out of there?<<
Permit me a guess:
--species have a range, defined as the area with sufficient survival
--the total population of the species increases until it reaches an optimal
number throughout the range.
If a population of a species already at the optimal number throughout its
range migrates out of its portion of the range into another portion, there
will be competition until the population has been reduced to the optimal
number again in that area. The net result of migration would be a reduction
in the total number of individuals of the given species.
Seems logical, no?