1914J 
Jackson: Land Vertebrates of Ridgeway Bog 
33 
as the plants are concerned, last indefinitely. This is theoretically 
true of all climax or geographic formations, and has been estab- 
lished for the beech and maple forest of eastern North America’’ 
(Shelf ord, 1913, p. 308). Shelf ord has well modified this state- 
ment by the clause ‘so far as the plants are concerned.’ Indeed 
it is 'hazardous to state that any association of formation is cli- 
max in the sense that climax means final, so plastic is the biota, 
so frequent the changes, and so little known their causes. Could 
we eliminate the possible physiographic, climatic, physical, and 
chemical changes, not all brought about directly by the plant itself, 
the problem would be in a measure simplified. As it is, we can 
with reasonable certainty, in regions where succession has been 
studied, determine the climax forest association as it is effected 
through purely plant ecological processes; when changes, brought 
about through such agencies as, perhaps, drought, wind, or drain- 
age occur, they may disrupt the ecological balance and a new 
succession may begin. Such changes are probably few and affect 
the association more than they do the formation; the effect in 
most cases is probably more to delay than to destroy the climax 
association. When operative over large regions and for consid- 
erable time their effect is geological rather than ecological, as 
witnesses, for example, each ice sheet of the glacial epoch. Un- 
fortunately, in the case of animals we have little experimental 
evidence, except with aquatic invertebrates (Hogg, 1854; Vernon, 
1895; Warren, 1900; Colton, 1908), of the ecological effect of the 
continuous existence of a species in a habitat. 
The latest ecological change in Ridgeway Bog is that of the 
Roadside Association, brought about indirectly by the clearing 
of a narrow tract through the Cedar-Balsam-Hemlock and Tama- 
rack-Spruce Associations; the Roadside Association will be dis- 
cussed more fully in succeeding paragraphs. The general relation 
of the different associations to each other can best be understood 
by reference to figure 1, and to tables 1 and 2 which represent 
respectively the distributions of the plants and the vertebrates 
in the bog and their relative abundance. In determining relative 
abundance I have endeavored not only to compare the abundance 
of a given species within the different associations, but also to 
compare the abundance of different species within a given asso- 
ciation. I have used the terms common (c), few (f), and rare 
(r) to indicate this. 
