62 ANIMAL LIFE AND SOCIAL GROWTH 



migrants take shelter under leaves and grasses 

 and burrow into the soil and are joined in this 

 migration by insects that spend the growing season 

 on the upper levels of the forest margin trees and 

 shrubs. 



Some of the important relationships within these 

 communities are suggested by the diagrams given 

 in Fig. 2, which outline some of the interactions 

 between and within the communities of the aspen 

 parkland. The arrows point from the aggressor 

 to the plant or animal which is eaten. This chart 

 helps us to understand the way in which distinct 

 communities are united into a larger web-of-life 

 since we can see here that there are inter-commu- 

 nity activities that tend to unify the whole. The 

 food-web interactions within a single community 

 are also illustrated. 



Like the communities in fragments of Illinois 

 woodlands which were discussed earlier in the 

 chapter, the animal communities of the aspen 

 parklands consist of a permanent nucleus of 

 perennially important animals, mostly vertebrates, 

 to which are added others, mainly birds and 

 insects that are present or active only during the 

 summer season. In these parkland communities 

 the seasonal sub-communities are characterized 

 by birds that pass through in their spring and fall 

 migrations, or are summer or winter residents, 



