Evolution of litter size |
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Authors: | Yosiaki It? and Yoh Iwasa |
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Institution: | (1) Laboratory of Applied Entomology and Nematology, Nagoya University, 464 Nagoya, Japan;(2) Department of Biophysics, Kyoto University, 606 Kyoto, Japan;(3) Present address: Department of Biological Sciences, Stanford University, 94305 Stanford, California, USA |
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Abstract: | Summary Theories on the evolution of litter size among organisms were reexamined. The competition theories, including that based on
ther−K-selection hypothesis, could not explain well why low-fecundity strategies have often evolved in stressful environments such
as mountain streams, deep sea and the antarctic, where interspecies competition is considered to be lax. The theory, based
on It?'s (1980) concept of theprocurability of food by the young, was considered to have greater generality because it could explain not only the above-mentioned cases but also those where
small litter size is observed in habitats with high species diversity (where interspecific competition may be keen), such
as tropical rain forest. Examination of the process of selection of high-fecundity and low-fecundity genotypes also suggested
that the procurability of food by the young can best explain the evolution of low-fecundity. The concept of density-induced
dispersal and a distinction between density-dependent and density-independent predation pressures should be incorporated into
our discussions on the evolution of reproductive rates.
This work was supported in part by Grant-in-Aid No. 439017 from the Ministry of Education, Science and Culture. |
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