Abstract
A recent experimental study of the effect of and individual selection on population size in the flour beetle, Tribolium castaneum (Wade, 1976, 1977) showed that both the and individual selection treatments resulted in changes in the mean numbers of adult beetles. These changes in mean adult numbers occurred rapidly, often within two or three generations, and were large in magnitude, the population size in the selection treatments differing from that of the control by over 50%. In this paper I will elucidate the genetic and ecological mechanisms responsible for the observed changes in population size. I begin by reviewing briefly the major populational results and notation of the selection experiments, because all of the data reported here will be discussed in the context of the earlier study. The selection experiment (Wade, 1976, 1977) consisted of four treatments (48 populations per treatment) labelled for purpose of discussion as follows: Treatment Aselection by the differential extinction and recolonization of populations, i.e., selection, for greater numbers of adults per population; Treatment B-group selection for fewer numbers of adults per population; Treatment C-no selection, individual selection within populations was allowed to determine the numbers of adults; Treatment D-random selection, selection and recolonization of populations were carried out by means of a table of random numbers (cf. Wade, 1976, 1977, for details of the experimental design). After nine generations of selection, the average adult population sizes and the standard errors of the means were 178 ? 8.23 for the A treatment, 20 ? .58 for B, 49 + 5.92 for C, and 69 + 6.35 for D. The relationship among the means of A> D> C > B was highly significant (P < .005, Kruskal-Wallis rank sum test, 48 observations per treatment). In this paper I present the results of experiments designed to reveal treatment similarities and dissimilarities with respect to those primary (cf. 1 through 4 below) and group interactions (cf. 5 below) (Park et al., 1961) which are known to influence population size in Tribolium (cf. King and Dawson, 1972; Mertz, 1972; Sokoloff, 1974; for detailed and comprehensive reviews). The characteristics assayed from populations of each of the four treatments were as follows:
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