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Dr Musgrave's 2nd Reply
(Received by A. S. Lodge from Dave Thomas on April 23, 2002)
Once again, in his response Wells fails to distinguish adequately between exposed trunks and trunks in general, as well as actual data and claims arising from this data. Let me remind readers that Wells has in his book a section titled "Peppered moths don't rest on tree trunks" where he wrote "...evidence has accumulated showing that peppered moths do not normally rest on tree trunks." In his reply at http://members.tripod.com/aslodge/id67.htm, Wells writes "The clear conclusion that emerges from all of them is that peppered moths do not normally rest on tree trunks in the wild". In his response, Wells has not adequately distinguished between tree trunks in total and exposed tree trunks in his writings. This is important as Wells has claimed that critics of his writing have engaged in data manipulation. Healthy dialog would be encouraged if Wells retracts the claims of data manipulation.
In my response to Arthur Lodge, I wrote "if our question is 'Do peppered moths, in the wild, often settle on tree trunks,' then the data from Majerus, the largest and best study of moth resting places in the wild, is a resounding 'yes.' If the question is 'Do peppered moths, in the wild, often settle on exposed tree trunks' then the answer is a qualified yes, depending on whether one feels at least one moth in 10 resting on exposed trunks is 'often' (it is certainly non-trivial). This latter question is of less relevance as the majority of Kettlewell's experiments were not performed with moths resting exclusively on exposed trunks, but on shaded trunks and branches more representative of the moths' natural resting places."
Wells, in his response has chosen a title that suggests it responds to the second question, yet mostly fails to address the issue at all. For example, he quotes Mikkola's claims that moths only exceptionally rest on trunks (Mikkola was not addressing the exposed non-exposed distinction, which is supposedly the focus of this response), yet Mikkola's own data show that a significant numbers of moths rested on trunks; and, of those that were on his experimental tree segments, 40% rested on trunks compared to branches. Observational studies from the wild show that 25% of moths rest on trunks, even more if we take note of the fact that moths categorized as resting at trunk/branch junctions are actually resting on the trunk below the branch. This data is incompatible with Mikkola's claim.
Liebert and Brakefield call for experiments that test the differences in predation in various resting places. The quote does not address the issue of whether moths rest in exposed positions in significant numbers. This is precisely what Majerus has done, yet Wells feels that he can dismiss this direct experimental evidence that there is differential predation in both non-exposed and exposed sites as "just a pilot study." Everyone, especially Majerus, would agree more data are needed, especially if we want accurate quantitative data. However, the results from Majerus's study and the results from Kettlewell's mark-release experiments where moths were on un-exposed branches and trunks (in distinction to the direct, filmed experiments where exclusively exposed trunks were used) are strong evidence
that Kettlewell's results are qualitatively correct. In contrast, there is no experimental support of any kind for the proposition that there is no differential predation of pale or dark moths in polluted woods, and that Kettlewell's results are invalid.
To summarize, Mikkola had suggested that moths do not rest on trunks in any numbers, based on extrapolation from an experiment where significant numbers of moths rested on trunks, and that differential predation should be re-evaluated. Majerus has shown that significant numbers of moths do rest on trunks in the wild, and has re-evaluated differential predation, showing that it occurs in both exposed and unexposed locations. I would like to finish with a quote from Majerus, the person who has done the most to quantitate where moths rest, and to quantitate actual predation. I normally don't engage in dueling quotes on complex issues, but Majerus is quoted by Wells in support of Wells's claim that scientists know that Kettlewell's work is invalid. "My view is of the rise and fall of the melanic peppered moth is that differential bird predation in more or less polluted regions, together with migration, are primarily responsible, almost to the exclusion of other factors." Majerus M, Melanism, page 155.
Again, I encourage people not to take my word for this, but to read the actual articles themselves. Many will be hard to find outside of a University research library, but Majerus's book should be available from any large municipal library.