THE INSECT ASSOCIATION OF A LOCAL ENVIRONMENTAL COMPLEX. 43 
for a given terrestrial environment the animal and plant association is co-extensive, 
and that the boundaries of the one roughly coincide with the other, the whole 
forming what Has been defined as a biota composed of animal and plant assemblages. 
This relationship, which must as yet be considered hypothetical when regarded 
broadly, has been here constantly kept in view, and the tables in which the various 
insect species have been listed are meant to indicate this basic principle. The plant 
ecologist recognises various kinds of association which have been designated by the 
name of the dominant type of vegetation, such as pine association, moorland associa- 
tion, etc. In our study the association which is recognised as rather heterogeneous 
belongs to the grassland -j- mixed wood type. Being a strictly local complex, the 
conditions must be referred to as dependent primarily on soil or edaphic, as con- 
trasted with climatic factors which determine the kind of vegetation over wide areas, 
such as deciduous forest and steppe. 
For the determination of the various species of an association, their abundance 
and grouping, the botanist has devised the quadrat method. By this means the 
most accurate information can be obtained of the facts as they exist within a definite 
square area. Although the space covered is minute, valuable data can be obtained, 
from which conclusions of a general nature can be deduced applying to the whole 
association of which the smaller area selected is representative. Such detail and 
thoroughness is scarcely required for our purposes, and only a general idea of the 
relative abundance of plant species has been attempted, expressed as common, fairly 
common, very common (cf. Tables X, XI). 
By reason of their sessile habits the individuals of a plant association can be 
more easily studied than those of the more motile species of an animal association. 
It is often a very difficult matter to settle what species are peculiar to the association 
and what are merely invaders, temporarily or permanently. The clue to an insect’s 
real habitat is the test of where it breeds. This may also be the situation where it 
feeds, but in a great many cases the two places are not the same. A knowledge 
of the larval habits is therefore essential as giving an indication of the animal’s 
real habitat. 
Physical Factors of the Environment. 
The environment or habitat may be defined as the result of the action and inter- 
action of the combined forces or factors present in any given, region, and, according 
to Vestal,* who quotes Schimper, have been classified into two groups — climatic 
(geographic) factors which operate over very broad areas, and edaphic (local) factors 
which effect local modifications of the plant life (and the animal as well) within any 
such broad region. The composition of the animal association is primarily de- 
pendent upon the ecological type of the vegetation, which is again dependent upon 
various factors, enumerated by Clements t as water-content, humidity, light, 
* Op. cit. t Op. cit. p. 18. 
