and tree strata rank lowest. The largest mainiual 

 populations occur in the subterranean and fjronnd 

 strata. 



In a l-'.iiropean oak-hornheani forest (Turcek 

 1951) 15 per cent of the bird species nested on the 

 ground, 2^ per cent in the herb and shrub strata. 31 

 per cent in or on the trunks of the trees, and 29 per 

 cent in the tree canopy. The largest number of indi- 

 viduals (52 per cent) occurred in the forest canopy, 

 although the bioniass of these birds constituted a 

 smaller percentage of the total (16 per cent) than did 

 the ground and herb population (67 per cent). In re- 

 spect to feeding, however, the distribution was differ- 

 ent : ^2 per cent found their food on the ground, 9 

 per cent in the herbs and shrubs, 10 per cent on the 

 tree trunks, 25 per cent in the tree foliage, and 6 per 

 cent in tiie open spaces between the canopy, trees, 

 and shrubs. 



Seasonal rhanpcs 



Outside of the tropics, the forest community 

 changes drastically with the seasons such that four 

 aspects may be recognized, each of which is divisible 

 into two or three different sectors. The total popu- 

 lation of the soil macrofauna in the temperate decidu- 

 ous forest is highest during the hiemal aspect because 

 of the migration of many foliage insects into this 

 stratum to hibernate. Forest species hibernate in 

 densities that vary randomly throughout the forest, 

 except where there are differences in topography or 

 substratum. Forest tracts adjacent to grass- or farm- 

 land, however, receive an influx of non-forest species 

 that hibernate principally on the forest-edge gen- 

 erally, and along the south edge in particular, where 

 exposure to solar radiation and protection from cold 

 northerly winds produces warmer temperatures 

 (Weese 1924). 



During the vernal aspect, insects and other in- 

 vertebrates come out of hibernation, and the adults 

 of forms variously frequenting the herb, shrub, and 

 tree foliage return to their characteristic stratum. 

 The population of ground animals remains relatively 

 high throughout the year, however, which can be at- 

 tributed to the reproduction of the geobionts and to 

 the fact that the immature stages of many foliage 

 arthropods, particularly Diptera, Coleoptera, and 

 Lepidoptera, occur in the ground. Various groups 

 of these geobionts and geophils reach their peak num- 

 bers at different times during the year (Pearse 1946). 



An insect species may show more than one popu- 

 lation peak during the year (Shelford 1951), depend- 

 ing on the number of generations produced and the 

 specific life-span. A species may appear, attain to 

 very large numbers, and disappear, all in a matter 





FLYING SQUICC?! 



MMl 



FIG. 9-12 Relation of 

 ilton and Cook 1940). 



nmals to the forest flo 



of a few days, or a few weeks at most. Considerable 

 variation also occurs from year to year in the popula- 

 tion fluctuations of individual species and of whole 

 groups, correlative with differences in weather, par- 

 ticularly temperature and moisture (Leopold and 

 Jones 1947). 



Bird populations in temperate zones reach peak 

 populations with the passage of transients during the 

 seasons of migration. These migration peaks are in- 

 conspicuous or absent in northern coniferous forests, 

 since most birds that arrive stay to nest. In the 

 tropics, birds are most abundant during the winter 

 period of the north temperate zone, since the fauna 

 then contains many migrant species from the north. 



Mammal populations in temperate regions com- 

 monly reach their maximum numbers in the autumn, 

 at the end of the breeding season. Populations de- 

 cline progressively as winter wanes, the result of 

 mortalities from severe weather, lack of food, and 

 predation. 



Comparison of animals 

 in different forest types 



There are more niches and microhabitats avail- 

 able in forest and forest-edge communities than in 

 any other type of terrestrial community. The strati- 

 fication and the diversification of plant forms are re- 

 sponsible for this. Many forest niches are much the 



TABLE 9-10 Stratal distribution of arthropod species in Missouri 

 (Dowdy 1951). 



Oak-hickory Red cedar 

 Distribution of species forest forest 



Grassland, forests, and forest-edges 137 



