is temp the limiting factor on range

[Michael Gochfeld]

With regard to the Queen of the Carolinas thread, Ron wrote about the
"possibillity of overwintering in sheltered situations on the Carolina
coast itself in the mildest years."

I have made what I assume is the same assumption that winter temperature
(or perhaps snow cover) limits the overwintering of southern species in
the northern part of their range (or north of their normal range).

The assumption follows that this accounts for the die off of species in
the fall, and the re-invasion the following year (or at longer
intervals) of southern species into (for example, NJ or New England).

If this were the case, the overwintering stage of a species should be
temperature sensitive with cold temp either killing outright or delaying
development.

But I wonder for how many of these northward invading species there is
actual experimental evidence that cold in winter IS the proximate
limiting factor.  We do see adult survival limited by the early or
delayed arrival of winter (but that seems to be a different question).

For example, My wife, Joanna Burger, showed experimentally that summer
temperature influencing incubation and development (rather than winter
temperature influencing adult survival) might impose the northern range
limit on a snake species.

Or, how often do we see survival in the north  (and early spring
emergence) of such species after truly warm (snowless) winters (i.e.
after 1999-2000 or 1998-1999).

Mike Gochfeld


 
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