Showing papers by "Robert R. Sokal published in 1976"

Oscillations in Housefly Population Sizes Due to Time Lags

Abstract: Oscillations of animal population size can be caused by time delays due to development. Mathematical representations of this have been studied by previous workers. We investigated the applicability of their models to laboratory populations of houseflies. Estimates of the necessary parameters-death rate, oviposition rate, development time, and the association of larval survivorship with density-were obtained from various experiments. A stability analysis of the model by the method of Maynard Smith predicted oscillations in adult population size for these parameter values. This was also predicted by numerical solutions to the equations of the model. Four population cages of houseflies maintained for periods up to 2.5 yr showed the predicted pattern. The populations fluctuated markedly and regularly in adult size, generally between 200 and 1,600, with a periodicity of 5-6 wk. The correspon- dence between prediction and observation was reasonably close and was improved when further complications were considered and the behavior of the populations was simulated on a computer. In another cage maintained under different conditions of husbandry, where ovi- position was less but other parameters were the same, the stability and population size differed in a manner predicted by the model. Of several theories that might explain oscillations, only that of time delays is likely to be appropriate for these populations.

The Kluge-Kerfoot Phenomenon Reexamined

Abstract: Kluge and Kerfoot (1973) reported from several vertebrate data sets that interlocality character differentiation was positively correlated with intralocality variability for the same characters. Their method of analysis is criticized since it would give functional dependence in the null case of no geographic distribution. An alternative method of analysis is proposed based on coefficients of variation among and within localities. When Kluge and Kerfoot's data sets are reexamined by this method, the relationship is not as high or as regular as reported by these authors. The first invertebrate data (from aphids, flies, snails, and protozoa) are analyzed and yield results comparable to the findings on vertebrates.

Selection at two levels in hybrid populations of musca domestica.

Abstract: This study is an account of the genetic changes in a population of houseflies under specified conditions of husbandry. It is an attempt to test and interrelate two generalizations from past studies of ecological genetics. First is the generalization that the dynamics of populations depend on their genetic structure. To our knowledge, strain differences in life histories are evident in every species that has been studied in the laboratory or in sample plots (e.g. Clausen, Keck, and Heisey, 1948; Sullivan and Sokal, 1963; Sokal and Karten, 1964; Birch et al., 1963). Polymorphic populations of Drosophila pseudoobscura show a higher carrying capacity (Beardmore, Dobzhansky, and Pavlovsky, 1960) and a higher intrinsic rate of increase than do monomorphic populations (Dobzhansky, Lewontin, and Pavlovsky, 1964). Also, the outcome of competition between species of Tribolium depends on their genotype (Lerner and Ho, 1961; Park, Leslie, and Mertz, 1964). The second generalization is that gene frequencies usually change in complex ways, indicating widespread frequencydependent selection, interaction between loci, or both. Single locus models of gene frequency change may be useful for their