. Animal Ecology. Animal ecology. MAR APR MAY JUN JUL AUG SEP OCT FIG. 19-3 Seasonal changes In relative frequency of the third chromosome with the standard (black), arrowhead (stippled), and Chiricahua (cross-hatched) gene arrangements in a natural population of Drosophila pseudoobicura (Dobzhansky 1951). species, these genes may be arranged in all sorts of combinations to form an almost infinite mixture of character modifications (Caspari 1951). Heterozy- gotes are, therefore, much more in adaptively responding to the environment than are homozygotes. The more characters for which
. Animal Ecology. Animal ecology. MAR APR MAY JUN JUL AUG SEP OCT FIG. 19-3 Seasonal changes In relative frequency of the third chromosome with the standard (black), arrowhead (stippled), and Chiricahua (cross-hatched) gene arrangements in a natural population of Drosophila pseudoobicura (Dobzhansky 1951). species, these genes may be arranged in all sorts of combinations to form an almost infinite mixture of character modifications (Caspari 1951). Heterozy- gotes are, therefore, much more in adaptively responding to the environment than are homozygotes. The more characters for which an individual is het- erozygous, the more adaptable its offspring are likely to be. Adaptive polymorphic populations are more efficient in exploiting the environment than are ge- netically uniform ones. Conversely, species that are widespread geographically through many habitats are genetically more diversified than are those restricted to few or specialized habitats. There are limits, how- ever, beyond which a character cannot change. The continual tendency for characters to fluctuate around a mean or intermediate condition gives a population r/enctic homeostasis (Lerner 1954). Genetic drift Although certain characters may result from the action of a single gene or pair of genes, many, perhaps most, characters within a species are poly- genic ; , they are aifected by a multiplicity of genes. The exact form in which a character is expressed de- pends on the particular combination of genes which the individual or population possesses (Waddington 1957). If a fertilized female, a single pair of animals, or at most a few hundred individuals become separated from the rest of the species, there will be represented in them a considerable decrease in the number of genes available to the main body of the species, since no individual or small group of individuals can pos- sess all the genes that occur within the species' pool. Inbreeding within small isolated populations may thus bri
Size: 1067px × 2343px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
