You are not currently logged in.
Access your personal account or get JSTOR access through your library or other institution:
If You Use a Screen ReaderThis content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Trends in Geographical Variation in Palaerctic Members of the Genus Parus
D. W. Snow
Vol. 8, No. 1 (Mar., 1954), pp. 19-28
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2405662
Page Count: 10
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Preview not available
1. In the genus Parus in the Palaearctic Region geographical variation is closely related to climate. Bergmann's rule is general, but it is modified to a greater or lesser extent by a 'latitude effect,' size being greater at lower than at higher latitudes for equivalent winter temperatures. In nearly all the species, relative tail-length increases and the relative lengths of beak and tarsus decrease in the colder parts of the range (Allen's rule). In continuous populations colour variation follows differences in temperature and humidity. 2. The rules for variation in colour and tail-length seem to carry with them no concomitant disadvantages, but Bergmann's and Allen's rules may at times conflict with other ecological requirements. 3. Until the geographical variation of a whole genus has been analysed with respect to climate, subspecific differences cannot be safely interpreted as adaptations to habitat or to the presence or absence of competitors, nor can they be used as clues to past history.
Evolution © 1954 Society for the Study of Evolution