Migration strategies

[Kenelm Philip]

> can migration occur in one direction only?
 
Here's an example (no doubt only one among many) of what has been said on
this topic in the past.
 
        From 'Migration & Dispersal of Insects by Flight', C. G. Johnson,
Methuen, 1969. In the Contents, we have:
 
"3. Classes of Migration
        Introduction
        Class I - Emigration, without return, usually by relatively short-
        lived adults
        Class II - Emigration and return by the same, relatively short-
        lived individuals within a season
        Class III - Emigration to hibernation or aestivation sites and
        return by the same individuals after imaginal diapause"
 
The author then points out that these classes grade into each other, and
breaks Class I into 5 subclasses, and Class III into 3 subclasses (the
last of which includes the North American Monarch migrations).
 
        He also defines 'migration' as synonymous with 'adaptive dispersal',
thus short-circuiting the discussion about dispersal as compared to
migration.
 
        And this author does seem to have applied some 'taxonomy' to the
subject.
 
        In case anyone interprets the above, as some may have for my prev-
ious posting re extinction, as an attempt to claim that this is the only
correct way to look at these terms--nothing could be farther from my
intention. All I want to do is point out that one or more knowledgeable
people in the field have used these terms thus in the past. How other
people may have used them, or how they _should_ be used in the future, is
another matter.
 
        I would, however, guess that the book above (as with the Dictionary
I referred to for 'extinction') could be considered a representative
reference in its field. I will agree with Ron Gatrelle that you can probably
extract a different definition of such terms from almost every book on
the subject one picks up. But one has to start _somewhere_...
 
                                                        Ken Philip
fnkwp at uaf.edu
 
 
 
 
 
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