. L'écologie animale. L'écologie animale. Le taux de croissance intrinsèque des espèces par jour (r) la longévité moyenne en jours T taux de production nette courte queue vole 0,0125 141,75 0,0147 1,772 5,90 rat de Norvège 217,57 25,66 3,198 0,101 5,616 55,6 Farine 275,00 0,109 4,731 43,4 charançon du riz 113,56 pou humain O.Ul 30,92 30,93 3,432 jeunes et niiddle-âgés de cours sont plus ou moins égaux en nombre, la diminution de la taille se produisant progressivement au cours de la vie. Adapter.tion à des créneaux dans les population de toute espèce, quel que soit le nombre d'oeufs ou de jeunes produits par paire d'adultes, le nombre de rejetons rea

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. Animal Ecology. Animal ecology. Species Intrinsic growth rate per day (r) Average longevity in days T Net produc- tion rate Short-tailed vole 0.0125 141.75 1.772 5.90 Norway rat 0.0147 217.57 3.198 25.66 Flour beetle 0.101 55.6 5.616 275.00 Rice weevil 0.109 43.4 4.731 113.56 Human louse O.Ul 30.92 3.432 30.93 young and niiddle-aged classes are more or less equal in numbers, the decline in size occurring progressively throughout life. ADAPT.TION TO NICHE In the stabilized population of any species, whatever the number of eggs or young produced per pair of adults, the number of offspring reaching re- productive status can never be greater than two in sexual forms, which is the number required to replace the parents on their death. With each new generation there is, therefore, a population turnover, with newly born individuals replacing the adults that die. In a stabilized population, the rate of increase of a popu- lation through the course of several reproductive cycles must equal the death-rate, so that the value of one factor is also a measure of the other. Either factor is indicative both of the rate of population turnover and of the intensity of environmental resistance. The intrinsic growth rates for populations of sev- eral species under optimum conditions is given in Table 1S-7 by the factor r. which represents the mean rate of increase per individual per day. There is a general inverse relation between growth rate and longevity, T. However, if growth rate were depend- ent only on the longevity of the species, then rT would equal a constant. Obviously this is not true. It appears that difTerent growth rates may correlate with various intensities of environmental resistance in the different habitats occupied by different species. If there were a habitat offering no environmental re- sistance, and all offspring therefore survived, then a female would need to produce only one female off- spring to replace herself when she died. This would be the net productio

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