. Animal Ecology. Animal ecology. \i)n-hcritahli' variations Nut all \ariatioiis of organisms are of direct significance in spcciation. \'on-lieritai)le changes in hocly structures, functions, and behavior are coninion. If muscles are used continually and intensively, they become thicker and stronger; if one kidney is re- moved, the other becomes hypertrophied; skin sub- jected to frequent rubliing or pressure thickens and becomes horny: and so on through a lengthy catalog. Animals progressively exposed to ever more severe temperatures or lower oxygen concentrations will tol- erate extreme con
. Animal Ecology. Animal ecology. \i)n-hcritahli' variations Nut all \ariatioiis of organisms are of direct significance in spcciation. \'on-lieritai)le changes in hocly structures, functions, and behavior are coninion. If muscles are used continually and intensively, they become thicker and stronger; if one kidney is re- moved, the other becomes hypertrophied; skin sub- jected to frequent rubliing or pressure thickens and becomes horny: and so on through a lengthy catalog. Animals progressively exposed to ever more severe temperatures or lower oxygen concentrations will tol- erate extreme conditions, which, had they been sud- denly presented, would have been fatal. Insect larvae transferred to a new type of food often become so conditioned to it that they produce a strain that pre- fers that food to other more usual food of the species. Chimney swifts in wilderness North America nested in hollow trees, but with settlement of the country and the construction of chimnied buildings during the last two centuries, the species has changed its behavior almost completely, accepting chimneys as a satisfactory nest-site location. Many phenotypic adaptations persist genera- tion to generation, either as similar responses made by each generation to constant environmental condi- tions : as the result of imitation of parents, condi- tioning of young, or imprinting (Gushing 1941, 1944, Thorpe 1945) : or because the particular genes re- sponsible for these characteristics have been sorted out (canalized) from the general gene pool of the sjiecies (^^'addington 1957). One would expect a change in behavior or function, arisen in consequence of exposure to the new conditions, usually to presage the evolutional development of a new structure, for natural selection cannot bring about the structural adaptation or perfection of an organ unless the organ is already being used for the new purpose (Prosser 1957). According to the so-called Baldtvin effect, a mutation which afTects establish
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
