## Twosex Models

Pollack (1986) lists three different categories for questions regarding the two sexes. These are i) sexual reproduction ii) sex ratio at birth and iii) demography's two-sex problem, i.e., the population consequences of sex-specific birth, death, and mating. The concern here is with the last category of questions concerning the demographic implications of sex-specific differences in vital rates. The major books and papers addressing the two-sex problem in demography include those by Karmel...

## Bibliography

S. (1925) A method of computing the effectiveness of an insecticide. J. Econ. Entomol. 18 265-267. Back, E. A., and C. E. Pemberton (1916) Effect of cold-storage temperatures upon the Mediterranean fruit fly. J. Agric. Res. 5 657-666. Beddington, J. R., and D. B. Taylor (1973) Optimum age-specific harvesting of a population. Biometrics 29 801-809. Bellows, T. S., and M. H. Birley (1981) Estimating developmental and mortality rates and stage recruitment from insect stage-frequency...

## Introduction

All biological populations obey the immutable rule that, migration withstanding, the difference between their birth and death rates determines the direction and size of their growth rate. This relationship provides the foundation for demography the study of populations and the processes that shape them (Pressat, 1985). Demography began as the study of human populations and literally means description of the people. The word is derived from the Greek root demos, meaning the people, and was...

## The Abridged Life Table

The complete life table has two disadvantages that can be removed by constructing an abridged table. First, it is sometimes not possible to monitor daily mortality of individuals in a cohort over their entire life course. For example, it is extremely difficult to determine the precise time of death for eggs and pupae for most insects. Thus the practical solution for determining cohort mortality for these stages is to note the number entering and the number surviving through the stage, which...

## The Multiple Decrement Life Table

The multiple decrement life table is used widely in human actuarial studies to address questions concerning the frequency of occurrence for causes of death and how life expectancy might change if certain causes were eliminated. The conventional single decrement life table shows the probability of survivorship of an individual subject to the one undifferentiated hazard of death. In multiple decrement tables the individual is subject to a number of mutually exclusive hazards, such as disease,...

## Zy

Population Curve The Logistic Equation Parameters for the logistic equation can be determined from only three population samples taken at equidistant times by formulating three equations in three unknowns. The solution for the logistic differential equation is set equal to the population levels at each of the three sample dates, which creates the three simultaneous equations. The three unknowns are the initial number N0 , the growth rate parameter r , and the carrying capacity K . The...

## G

Taking natural logs of the age-specific mortality rates for each sex and estimating the slope of the best fitting straight line through these points from ages 0 through 14 days yields a 2-week exponential rate of change of G .2270 for males and G .2936 for females. Using the formula for MRDT given above yields a mortality rate doubling time of 3.1 days for males and 2.4 days for females. Or expressed another way, the mortality of young females increased by 16-fold in approximately the same time...