Ecological Society

                                                        Chicago 12/31/47

 
                            F!UND-TA.TBL DISCUSSIONT 
                     Game and Fur Population Mechanisms 
 
                         Introduction by Aldo Leopold 
 
 
This discussion is intended to illustrate three points: 
 
     1. The causes of fluctuation in p;opulation levels are not yet understood.

 
     2. The possible causes are so numerous that they must be narrowed down

         before the final search can begin. 
 
     3. Age and sex composition promises to accomplish the needed narrowing.

 
                       Fluctuations Are HTot Understood. 
 
A decade Pgo we wildlife managers thought we understood all major fluctuations

except cycles; that is to say we were sure that food, cover, predation, weather

and other "visible factors would ulti.mately exnlain all major changes
except 
that rhythmic fluctuation characteristic of northern grouse, hares, and rabbits.

 
Today unexplained fluctuations are occurring in grou-s we once thought of
as well 
understood. Heee are some of the recont events which seem dif-ficult to explain

in the temns with which we are familiar. 
 
The Pheasant Low. During the last thr-ee ye, rs the. bottom has fallen out
of this 
species. The decline was siumiltaneous iL timing, and nearly transcontinental

in extent. Wen the fabulous Dakotas felt the pinch. 
 
It seems unlikely that either nreda.tion, or v-eather in the ordinary sense,
or 
agricultural changes would operate so uniformly in either space or time.
Has 
the pheasant beco>ýe cyclic?  It is too early, of course, to answer
this question. 
We imow only that the decline coincided in time with the cyclic decline in
grouse, 
and lacked the geographic spottiness characteristic of ordinary local ups
and 
downs. 
 
The Fox High. During the last three years there has been an u)surge of foxes,

nearly transcontinental in scope. It still prevails in many states. Fox highs'

have occurred berfore, but transcontinental synchronism is either new sou~th
of 
Cana-da, or was not oreviously detected. A 10-year fox cycle has been supposed
to 
prevail in Canada, at least since 1900. Is the Canqdian fox cycle spreading

southward? 
 
Recessions. A peculiar population behavior, not yet named but here called

recession, seems to take place in gallinaceous birds. It is confined to new

transplantations or newly invaded ranges. Thus Thbasants in parts of western

New York collapsed in 1936 and have never regained previous levels. It is

alleged that a similar recession followed their introduction to Oregon in
189l: 
they are said to have flared to great high and then receded to a lower level.

Hungarian partridge in the Lake States, at first successful on certain soils,

receded to a low level after 1936, (but there are now signs of recovery,
so this 
may not be a recession). Pinnated grouse have invaded the Upper Peninsula
of 
Michigan during the last two decades. They flared up and later receded, some-

times to the point of extinction, in a kind of west-to-east wave. A wave
of