Re: My last word
Fri, 23 Apr 1999 22:17:45 EDT

In a message dated 4/23/99 3:04:39 PM Mountain Daylight Time, writes:

> >
> > Look again at what I said: I said the place matters little, I didn't
> > it didn't matter at all.
> OK. Nevertheless, it seems that Majerus disagrees:
> #"If the relative fitness of the morphs of the peppered moth does depend
> #on their crypsis, the resting position is crucially important to the
> #estimation
> #of fitness differences between the morphs. This is particularly the case
> #in changing or intermediate habitats with respect to pollution, because in
> #such habits the distribution of lichens on trees is likely to be more
> #heterogeneous than in very unpolluted or very polluted habitats. It is
> #therefore valuable to consider, albeit briefly, on which parts of trees
> #lichens of different types seem to grow in different situations."
> # -- Majerus p. 123

Since I do not have a copy of Majerus' book, I can only speculate as the the
context of that quote. It sounds like Majerus is discussing the relationship
of lichen coverage to crypsis. In that case, place would have an effect ONLY
if crypsis were largely dependent upon lichen coverage and ONLY if lichen
coverage varied from place to place. According to Don's posts (including
reprints of posts sent to him by Majerus) crypsis is not necessarily
dependent upon lichen coverage, though it was undoubtably a factor in
England. Yet considering that Majerus is convinced that "that the rise and
fall of the carbonaria form of the peppered moth has resulted from changes in
the environments in which this moth lives", that these changes "have come
about as a result of changes in pollution levels which have altered the
relative crypsis of the forms of this moth", and that the "main, if not the
only selective factor that has lead to changes in the frequencies of the
forms over time is differential bird predation", it would seem to me that
even if lichen grows differently on branches than on trunks, the research
presented by Majerus in his book (according to Don Frack and Majerus) show
that they played only a very small role in crypsis, and that place indeed
played little or no role in the fitness of the morphs. This leads me to
believe that the quote you give above is the beginning of a discussion that
will ultimately conclude with something like "in fact the resting place is
not crucial to fitness estimation after all." Otherwise Majerus' strong
claim connecting crypsis, pollution and bird predation -- without adding
resting place qualifiers -- makes no sense. And it makes even less sense
when you consider that Majerus is the leading proponent of the canopy as the
normal resting place of the moth. Obviously he must believe that crypsis and
selective bird predation is just as important there as on the trunk. But you
have his book; what does he say?

> >> Has anyone demonstrated
> >> empirically that selective predation occurs where moths normally
> >> rest?
> >>
> >
> > According to Majerus, yes; the details and references are in his book.
> >
> Perhaps you could help me out a little. What I've found so far seems
> to contradict what you say. For example:
> #"Although observations of peppered moths being taken from natural resting
> #positions are still lacking and are urgently needed, it is highly probable
> #that predation levels are significant." -- Majerus
> and then a little later on the same page:
> #"Yet, surprisingly, experiments to show formally that the degree of
> #of the different peppered moth forms does affect the level of predation
> #inflicted on them by birds have never been carried out." --Majerus

This is what Don Frack said in his first post on the peppered moth, posted by
me under the title "Peppered Moths - in black and white (part 1 of 2)":
"Finally, Coyne's reference to a 'mystery' of where peppered moths rest
appears to contradict Majerus, who refers to his and others experiments on
branch-related resting sites - apparently the most common location.
Experiments with moths attached to these locations support the cryptic
advantage of earlier studies from trunks." In other words, Don is saying
that Majerus is saying that there have been experiments done on branch
resting sites and that these experiments confirm those of the trunk resting
sites. They may not be "formal" experiments in which direct observation of
birds taking moths from branches confirm the experimental setup, but they
seem good enough for Majerus.

> >>
> >> As another possible influence of location, would you happen to
> >> know off hand whether lichens grow better on tree trunks as opposed
> >> to branches?
> >>
> >
> >It depends upon the species, but generally no.
> >
> Once again, it seems that you disagree with Majerus.

Maybe, maybe not. The above quote merely raises the possibility that lichens
might grow differently on different parts of the tree, and you cut off the
quote right at the point where he is just about to reveal if that was true
and to what extent it was true. And these lichens may be one of those
species that does grow differently in different places (Majerus is not making
a general statement about all lichens). Also, if you look more closely at
what Majerus said, the only time you would expect lichen coverage to be
heterogeneous is when the tree was in transition between a very unpolluted
state and a very polluted state. Even so, since Majerus is convinced by the
research that crypsis and selective bird predation plays as important a role
in the canopy resting places as it does on the trunk, he must also believe
that even if lichen coverage is heterogeneous, it has little affect on
fitness as determined by crypsis.

Kevin L. O'Brien