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[Vol. 88 
ing on their nutritional value, and can differ from a branch with a 
few aphids to a large homopteran population which provides most 
of a colony’s food intake. The degree to which a colony depends 
upon persistent resources will approximately determine the intensity 
of their defense. Formica fusca tends only a very few aphids and can 
be chased from them relatively easily (Brian 1955), while F. rufa 
colonies regularly destroy each other in battles for the control of 
specific trees (Elton 1932, Skinner 1980). Therefore, the removal of 
persistent resources can affect colonies differently; some nests will 
die if they are deprived of them (Elton 1932). In this section we will 
only consider species which are dependent, at least in part, upon 
such resources (Groups II & III, in part, Oster and Wilson 1978). 
Most studies on the defense of persistent resources concern the 
genera Formica and Pogonomyrmex. The patterns of their nest 
distribution depends upon colony structure, nest site requirements 
and habitat complexity. Most Formica nest distributions are the 
result of the interaction between the need for high insolation of the 
nest and the proximity of trees or bushes which are suitable for 
tending aphids. Many species nest along the ecotones between fields 
and forests, in forests, and in forest clearings (F. lugubris, F. 
schaufussi, F. exsectoides, F. polyctena, F. rufa, F. ulkei). These 
species will be found in overdispersed arrays only if habitat patches 
are found in rather predictable patterns. These are clearly special 
cases and explain some of the variation between authors for some 
species (see for example, F. lugubris, Table 1). We expect the linear 
distance along the ecotone to be relatively even in this case, but we 
have no data to test this hypothesis. Casual observations on F. 
schaufussi tend to support this (Traniello, personal observations). 
Formica species which nest in fields should be found in overdis- 
persed arrays; the few reports that exist indicate that they are (F. 
uralensis, F. opaciventris, F. fusca, F. pratensis, Table 1). In 
addition, Pogonomyrmex species which defend patches of seeds are 
found in overdispersed arrays. These and other species that defend 
persistent resources and are not nest site limited are in general found 
in overdispersed arrays ( Atta spp., Acromyrmex octospinosus, 
Lasius niger, etc., Table 1). 
Colonies which depend upon persistent resources frequently 
organize resource defense and utilization with trunk trails. Trunk 
trails are long term routes which are marked with persistent trail 
