I need help.......

[Kenelm Philip]

	Neil Jones said:

> The level of the population of a given butterfly species is determined
> by the resources available to the population.

Some people find this hard to believe--but an article in Nature back in the
1960s ('A Field's Capacity to support a Butterfly Population', Dethier &
MacArthur, 1964) provides support. 19,800 larvae of _Melitaea harrisii_
were introduced into a declining colony, which at that time had only
800 autumn larvae. The following autumn the colony had 400 larvae... The
extra adults had emigrated elsewhere (including back to the other colonies
from which the larvae had been taken).

	This does not mean that all introductions are doomed to fail.
Consider rabbits in Australia, or _P. rapae_ in North America. Furthermore,
ecosystems change, as do population levels. After a catastrophic loss
within a species, when the basic environment is unaltered, introduced
individuals can thrive--although the species will rebound on its own
given time. For instance, after yellowjackets knocked most taiga butter-
flies in the Fairbanks area down to 1 to 2% of their normal levels, I
would have expected that introduced individuals would have done very well.
As it was, however, populations recovered in a couple of years on their
own.

	But introducing individuals of a species which is slowly declining
in the attempt to reverse the decline does not seem to help. It's more
to the point to improve the habitat, rather than just throwing butterflies
at it.

							Ken Philip
fnkwp at uaf.edu