Hardpan: 



and chernozemic soils, 172 



and rooting of grassland vegetation, 

 325 



conditions of formation of, 170-171 

 Hardy- Weinberg Law, 259 

 Herbivores (sec also Carnivores): 



adaptations of teeth of for food- 

 getting, 188 



and plants similar to predators 

 and prey, 241 



as more specific than carnivores 

 in range of food selection, 194 



as most numerous organisms in 

 food chain, 230 



as primary consumers in second 

 trophic level, 196 



classification of in respect to 

 diversity of food, 195 



cycles of and variations in mineral 

 salts of plants, 241 



cycles of as basic to other cycles, 

 241 



effect of variations in abundance 

 of on carnivores, 192 



enzymes of and food palatability, 

 190 



food behavior of in streams, 55 



food coactions among in arctic 

 tundra, 320 



large ungulate populations of as 

 developing best in grassland, 

 328 



ratio of to carnivores in coral reef 

 biome, 367 



size of food not of major im- 

 portance to. 191 



species included in, 187 



toleration of grasses to consider- 

 able grazing by, 325 



wide choice of food for, 195 

 Heredity, as factor in determining 

 responses to environment, 13 

 Humidity: 



absolute, 97 



as factor in species of ants in 

 sand, 109 



compared in grassland, forest- 

 edge, and forest interior, 121 



compared on north and south fac- 

 ing slopes of grasslands, 124 



in alpine tundra, 316 



in arctic regions of North 

 America, 315 



in deserts, 332 



in sand dune habitat, 106 



in tropical biomes, 341 



low relative, as barrier to dis- 

 persal of moist- skinned 

 creatures, 148-149 



of temperate deciduous forest 



biome in North America, 293 

 relative, 97 



Humidity (Continued) 

 vertical gradients of in forests, 



123 

 Humus: 

 amount of in soil, 165 

 and degree of maturity of soil 



profile, 170 

 and mineral content of leaf fall, 



165 

 and production of black soils, 163- 



164 

 as food for earthworms, 132-134 

 ilefnied. 165 

 dry weight of material constituting, 



165 

 effect of on number and kinds of 



animals in soil, 121 

 formation of and animal excreta, 



165-166 

 formation of and respiration of 



plant parts and animals under- 

 ground, 165 

 functions of layers of, 165 

 kind of dependent on whether leaves 



are coniferous or deciduous, 138 

 mor, defined. 171 

 mull, defined. 171 

 occurrence of mor layer of, 171 

 of burned forest, animals in, 130 

 peat soil not classified as, 165 

 quick oxidation of in latosolic 



soils, 172 

 use of by animals in forests, 299 

 variations in rate of absorption of 



organic content of in serai and 



climax forests, 165 

 Hybridization: 

 and more pronounced niche segre- 

 gation, 264 

 and variety of habitats as causing 



introgression, 264 

 detection of difficult because of 



introgression, 263-264 

 factors in natural selection 



a,K'nnist products of, 264 

 occurrence of and necessity for 



intermediate habitats, 264 

 occurrence of as indication that 



speciation does not yet exist, 



263-264 

 products of as superior to parents 



and consequent selection for in 



evolution, 264 

 Hydrosphere, 6 



Imitation: 

 and transmission of behavior 



patterns, 251 

 as form of learning, 15 



Imprinting: 



and transmission of behavior 

 patterns, 251 



in birds, as form of learning, 15 

 Innate Behavior (sec also Behavior 

 Patterns): 



aggressiveness as form of and 

 position in social hierarchy, 183 



and emigration among insects, 228 



and releasers, 14 



as rooted in nervous system, 251 



as subject to evolutionary develop- 

 ment, 251 



building of termite nests as exam- 

 ple of, 251 



demonstrated in spinning of flour 

 moth, 251 



endogenous periodic rhythms as, 

 100-101 



evidence for existence of, 251 



in choice of kind of forest com- 

 munity by birds, 250 



in choosing niche as saver of 

 energy and time of animal, 254 



in cricket hybrids as intermediate 

 between that of parents, 251 



in habitat preferences of laboratory 

 animals, 251 



in toad hybrids as intermediate 

 between that of parents, 251 



type of nest built as, 248 



types of, 13 

 Insects (see also Measurement of 

 Populations; Populations): 



activities of and temperature of 

 sand dunes, 106-107 



adaptation of mouth parts of for 

 food- getting, 188 



annual local migrations of, 158-159 



as destroyers of coniferous forest, 

 309-310 



as grazing animals, 126-127 



behavior of in experimental 

 gradients, 123-124 



changes in populations of in grass- 

 lands from overgrazing, 128 



daily migration of deciduous 

 forest species, 159 



density of populations of in air, 147 



emigration of and inherited 

 behavior, 228 



evolution of DDT-resistant kinds 

 of, 265 



foliage: 

 censusing of, 37-38 

 in forest communities, 135 

 species composition of in conif- 

 erous forest as similar to that 

 of deciduous forest, 305-306 



in abandoned field sub- seres, 115 



in American tropics, 347 



in arctic tundra, 319 



in floodplain seres, 114 



Index 423 



