Tundra (Continued) 



penetration of grassland species 



into, 317 

 precipitation in, 316 

 protection from cold by animals 



of, 322 

 range of temperatures in, 316 

 rarity of reptiles and amphibians 



in North American, 322 

 rugged terrain of compared to 



that of Arctic, 316 

 species of as dispersing from 



Tibet Plateau, 321 

 species of Tibetan faciation of 



conspecific with those of North 



America, 321 

 taxonomic composition of vege- 

 tation of, 317 

 uses of by man, 323 

 white coloring of animals in, 322 

 antarctic: 

 absence of plankton in during 



winter, 319 

 abundance of aquatic organisms 



in, 319 

 limited fauna of, 319 

 nutritive salt accumulation and 



population abundance in, 319 

 shores of as more abundant food 



areas in, 319 

 arctic: 

 animal adjustments of to severe 



cold, 320 

 aspection in, 320 

 bush or mat type, 316 

 colonization of alpine slopes by 



species of as interrupted by 



forests, 317 

 dispersal of species of southward 



in post- Pleistocene era, 317 

 effects of freezing and thawing 



on soil of, 315 

 Eskimos in, 321 

 failure of breeding in, 320 

 fearlessness of animals of before 



man, 321 

 flight songs of birds In, 320-321 

 food coactions in among herbi- 

 vores, 320 

 freezing of lakes of during 



winter, 315 

 grass type, 316-317 

 importance of cryoplanation in, 



315 

 Lapps in, 321 



length of photoperiods in, 316 

 lichen- mass barrens type, 316- 



317 

 migration in, 320 

 mingling of species of with grass- 

 land species, 317 

 oscillations in abundance of 



animals in, 320 



Tundra Arctic (Continued) 



periods of rest of animals in 



during summer, 320-321 

 permafrost in, 315 

 perpetual snow and ice type, 



316-317 

 precipitation in, 315 

 soil temperature below surface, 



315-316 

 soil temperature on surface in 

 spring and animal activity, 

 315-316 

 temperature in, 315 

 use of by man, 321 

 white coloration of animals as 

 protective device in, 320 

 arctic and alpine biociations of, 



compared, 319 

 typical extension of, 315 

 arctic biociation of: 

 aquatic nature of birds of, 319 

 as including both North America 



and Eurasia, 318 

 birds in found in North America 



and Eurasia, 318 

 birds in North American faciation 



of, 318-319 

 evolution of fauna in from forms 

 able to tolerate cold climates, 

 318 

 insects found in, 319 

 invasion of Eurasian forms into 

 North America and evolution of 

 fauna of, 318 

 lake animals of, 319 

 mammals in common to both 

 Eurasia and North America, 

 318 

 most abundant mammals in, 318 

 pond animals of, 319 

 richness of species of in North 

 America, 318 

 as representing southward disper- 

 sal of Arcto-tertiary flora, ,313 

 continuous distribution of species 

 of from North to Rockies in 

 post- Pleistocene era, 317 

 description of vegetation of, 316 

 factors in composition of serai 



vegetation of, 316 

 flora of possibly segregates of 



Arcto-tertiary flora, 317 

 kinds of vegetation in, 316 

 nature of climax in unknown, 316 

 perrenial nature of plants of, 316 

 regions of during interglacial 



periods, 317 

 seed germination in, 316 

 species characteristic of in bio- 

 ciation of North American 

 boreal forests, 306 

 survival of flora of during Pleisto- 

 cene glaciation, 317 



U 



Ubiquitous Species: 

 as basis for ecological classifica- 

 tion, 20 

 of microscopic animals in muddy- 

 bottom marine habitats, 356 

 of oceans and polar regions, 370 



Variation(s) in Population Charac- 

 teristics (stf also Populations): 



and Baldwin effect, 261 



and exploitation of environment, 

 261-262 



and genetic homeostasis, 261- 

 262 



and natural selection, 264-265 



as caused by genotypes of survivors 

 of population reductions, 262 



due to occurrence of mutations, 

 262-263 



expression of through gene com- 

 binations, 262 



genetic drift or Sewall Wright 

 effect, defined. 262 



having adaptive significance to 

 food consumed at genus level, 

 262 



inbreeding and consequent restric- 

 tion of genotypes as causing, 

 262 



occurrence of over many genera- 

 tions as causing species 

 identity, 260 



of asexual and self- fertilizing 

 forms, 264 



polymorphism, described. 261 



preadaptation as, 266 



relativity in adaptivity of, 265- 

 266 



through hybridizations, 263-264 



through panmixia, 261-262 



through phenotypic adaptations not 

 genetically heritable, 261 



through polymorphism, conditions 

 of occurrence of, 261 

 Vertebrates: 



as successful colonizers of land, 

 367-368 



cold-blooded, dispersal of, 151- 

 153 



competition between individuals 

 at low population level among, 

 231 



conditions of susceptibility to 

 predation among, 231 



in antarctic, 319 



in forest soil, 135 



in grassland communities, 125 



in sand seres, 109-110 



Index 447 



