Moisture (Coiilhtued) 



and saturation deficit, 97 

 factors in, 97 



measurement of rate of, 97 

 in food, as "free water," 97 

 in soil: 

 addition of and re- activation of 



soil animals, 107 

 as causing activity in inverte- 

 brates, 313 

 content of, 165 

 drying of and decrease in soil 



animal population, 13-1 

 organisms active in, 131 

 lack of in deserts: 

 adaptation of plants to, 333 

 as critical environmental factor, 

 338 

 loss of: 

 decrease in through evolution of 

 internal moist membranes, 99 

 prevention of by body surfaces, 



97-98 

 through excretory organs, 97-98 

 through feces, 97-98 

 through respiratory surfaces, 

 97-98 

 metabolic water, 97 

 role of in formation of plaiit seres 



on rock, 102-104 

 sources of for desert animals, 338 

 to organisms, methods of, 97 

 Morphological Adaptations {sec also 

 Adjustment(s) to Terrestrial 

 Habitats; Food; Food- getting): 

 and relation to strata of communi- 

 ties, 8 

 as basis for division of aquatic 



organisms, 66 

 as causing restriction of animals 



to particular food, 195 

 establishment of through natural 



selection, 9 

 for food-getting, 188-189 

 for predation and competition, 9 

 influence of temperature on, 9 

 in reproductive system, 9 

 interplay of genetics and environ- 

 ment in inheritance of, 7 

 of insects for living in grasslands, 



125 

 of parasites in being restricted to 



special niches, 180 

 sessility and motility as considera- 

 tions in, 7 

 variety of for food- getting, 8 

 Morphology, 3, 16 

 Mortality: 

 and mean length of life for wild 



populations, 215-216 

 at end of cycles due to exhaustion 

 of adrenopituitary system, 241 



Mortality (Continued) 

 causes of in primitive herds of 



bison, 328 

 environment as cause of and repro- 

 duction of females of species, 

 217 

 expression of in life tables, 212- 



214 

 in shallow marine waters due to 



severe cold, 354 

 of coral reef polyps and building 



of reefs, 366 

 of lemmings during population 

 declines and state of vegetation, 

 241 

 of rabbit populations through intro- 

 duction of myxomatosis, 235 

 oi snowshoe rabbit young, 224 

 of white man in tropics, 349 

 of young and overcrowding, 224- 



225 

 rate of: 

 as high among young and adult- 

 young ratios, 216 

 as high in epizootics, 228 

 as influenced by number of young 

 and carrying capacity of habitat, 

 211 

 direct variation in with density 



of population, 219-220 

 for animals in captivity, 215 

 in rose thrip and climatic factors, 



231-232 

 in young and parental care, 211 

 variation in from one age level 



to another, 216 

 variations in between sexes, 215- 

 216 

 Motile Organisms: 

 and kineses, 12 

 and taxes, 12 

 and tropisms, 12 



in grassland, variations in micro- 

 habitat of, 123-124 

 in intertidal habitats as achieving 



proper zonation, 362-363 

 morphological changes in induced 

 by habitat, 7 

 Motility, as consideration in mor- 

 phological adaptation, 7 

 Mutations: 

 as affecting period of time re- 

 quired for evolution, 267 

 behavior patterns subject to, 13 

 cause of, 263 

 factors in establishment of in 



populations, 263 

 haphazard nature of, 262-263 

 in asexual and self- fertilizing 



forms, 264 

 independence of from environ- 

 mental conditions, 9 



Mutations (Coiiliiiiwd) 

 permanent fixing of as described 



in Baldwin effect, 261 

 rate of occurrence of, 262-263 

 recessive character of those upon 



which natural selection works, 



265 

 Mutualism: 

 and animal browsing on trees and 



shrubs, 177 

 as demonstrated between plants, 



176 

 as demonstrated by protozoa and 



termites, 177 

 between plants and animals, 177 



defined. 176 

 differences from symbiosis, 176 



defined. 176 

 nut-burying by squirrels as, 177 



defined. 176 

 through animal transportation of 



ingested seeds, 177 

 through improvement of seed 



germination by animal diges- 

 tion, 177 



N 



Natural Selection (see Evolution) 

 Nekton {see Biocies, Lake; Lakes; 



Sea) 

 Niche(s) {see also Aspection; Diur- 

 nation; Microhabitat(s); Shelter): 

 adaptations to and rate of repro- 

 duction, 217 

 advantages to animals of segrega- 

 tion into, 254 

 as center of origin for spread of 



new species, 26 

 as defined by Charles Elton in 



1927, 245 

 availability of each kind in tropical 



rain forest limited, 345-346 

 bill adaptations of birds for feed- 

 ing in, 188 

 choice of: 

 according to food preference 

 determined by differences in 

 size of related species, 249 

 as determined by vegetation, 29 

 aspection as factor in, 247 

 as sometimes a random matter, 



249 

 by birds according to foot- span, 



248-249 

 by birds according to strata of 



vegetation, 248 

 by mammals according to strata, 



248 

 by warblers in evergreen forests, 

 248 



Index 429 



