Subject: 'Ehrlich experiment'

From: Kenelm Philip <[email-masked]>
Date: Mon, 25 Mar 1996 12:35:06 -0900

Now that we have a published reference to the so-called 'Ehrlich
experiment' (see my recent post: 'Ehrlich experiment--a reference at last'),
I would like to comment on what it may mean to the ongoing  discussion about
collecting.

        I always like to consider the extreme cases of a problem--then
you're pretty sure everything will fall between them. As far as butterfly
collecting goes, I can think of two extreme situations regarding the
application of _intensive_ collecting to a colony:

1. Collecting every female from a colony before oviposition, or collecting
every male before mating, will destroy the colony in one year (for butter-
flies with a two-year life cycle, this may have to be done two summers in
a row).

2. Collecting every male from a colony after mating, or every female after
oviposition, will have no effect on the colony (at least to first order.
There could be second-order effects where the absence of adults could some-
how alter predation on the next-generation larvae...).

I would imagine that most contributors to the collecting thread would agree
with both of the above statements. By doing so, people in favor of unres-
tricted collecting have agreed with the idea that, in theory, collecting
can totally destroy a population, provided that all males and/or all females
can indeed be found and collected at the appropriate times. On the other
hand, people in favor of severely restricted (or no) collecting have agreed
with the idea that even very heavy collecting can, under the right cond-
itions, cause no appreciable damage to a population.

        Most ordinary collecting will fall somewhere between these two
extreme cases, firstly because of timing, and secondly because only a
small fraction of the population is taken.

        Where does the 'Ehrlich experiment' fall? Obviously much closer to
#2 than #1, since they estimated that only 5% to 25% of the females were
taken. 75% to 95% of the females were thus unaffected, and presuming that
the remaining males were able to fertilize them, the resulting decrease in
colony numbers could easily be made up in one season. The fact that the
experiment produced no significant decrease in the colony population is
thus not surprising. Note that in Interior Alaska in 1992 to 1993, butterfly
numbers recovered in one generation from a drop to around 10-15% of the
normal population levels. This drop was area-wide, so the recovery could
not have been due to recruitment from other populations.

        The Ehrlich experiment was a deliberate attempt to overcollect a
colony of a few hundred to a few thousand adults. Normal scientific col-
lecting for taxonomic purposes is less severe, and in many cases (like the
Ehrlich experiment) has much less impact on females than males. (I remember
some years ago when Denali National Park required me to submit an environ-
mental impact statement before allowing the ALS to run volunteer collectors
in the park--and I informed them that in previous years the volunteers I
had had in the park had submitted between 100 and 200 specimens each year,
of which about 10% were females. This from a population estimated to be in
the many millions, in an area larger than Massachusetts. Not a serious
problem...)

        The dangerous cases obviously are when a small and concentrated
population receives concentrated collecting--but the collecting would
appear to have to be more efficient than Ehrlich's experiment to cause
much damage. This might occur for cases of commercial collecting when the
collector does not wish to preserve the colony, and has special collecting
techniques to obtain all females, or all males prior to mating. It might
occur for scientific or hobby collecting in the case when _many_ collectors
visit the same site, each collector doing little harm individually. It
might also occur when the number of adults in the colony is exceedingly
small and the females are more conspicuous than usual. Finally, there may
be cumulative effects when a colony is hit many years in a row.

        It seems to me that there is (at least in theory--in practice our
limited resources for wildlife management might rule against this) one
way to allow collecting of almost any population and yet have little or no
impact. If mark-release-recapture is used to monitor the size of the pop-
ulation, one can set bag limits for males (no females) early in the flight
season, and then (lower) bag limits for females later in the flight season
after the bulk of oviposition has occurred. This should allow fairly high
levels of collecting to occur, at conditions near case #2 above.

        In the meantime, the Ehrlich experiment suggests that most popu-
lations are at little danger from 'reasonable' levels of collecting--and
since endangered and threatened populations require collecting permits in
many countries, it would not appear that legal collecting is a significant
problem unless you have a country in which almost no populations are
legally protected (in which case the collectors are not the whole problem).
When populations are known to consist of only a few adults, or a few tens
of adults, they would normally be protected in some manner--unless we
have a
widespread species that normally occurs in many such small colonies.

        It would also appear that even _illegal_ collecting in many cases
is not actually very much of a threat to populations or species, despite
the point of view so skillfully (and in my opinion erroneously) upheld by
Ted Williams in Audubon magazine.

                                                        Ken Philip
[email-masked]

P.S. Sorry this got so long...