Search

This article is a primer on mortgage finance. It discusses the basics of the mortgage market and mortgage finance. In so doing, it provides useful information that can aid individuals [...]

Two groups of Tribolium confusum populations were observed in population cages for 80 weeks. Upon reaching equilibrium the numbers and sizes of adults and pupae were greater in one group than in the other. In the larger populations, natalities were estimated to be higher and adult life spans shorter, and, in separate experiments, the two population groups were also found to differ in the interaction between fecundity and adult density. The latter response was proposed as a possible cause of the other population differences. The presence of characteristics leading to density dependent control of population size, was construed as an adaptation to a stable, undisturbed environment. Variations in these characteristics, generated initially by genetic differences and possibly amplified by population interactions, suggest retention by the species of the adaptive variability necessary for the maintenance of population fitness.

In an environment where resources are gradually depleted, genetic differences in the survival capacity of Tribolium confusum populations can be found, but the biological basis for the differences remains obscure. When compared with two homozygous populations, a heterozygous population proves to have the greatest survival capacity, regardless of turnover rate, and emerges as the fittest of the three populations studied. Within each population the biological basis for survival can be determined in part, for then it is possible to detect correlations between population characteristics and survival. Increasing adult population size shortens duration, while increasing efficiency in utilization of resources lengthens duration. Other characteristics, such as egg supply, the rate of recovery following decimation, and pupal biomass, appear to have no impact on duration. However, the number of pupae at an early period, while not directly correlated with duration, influences it indirectly, for an increase in the number of pupae results in a larger adult population and this shortens duration.

The size of a population (number of live adults) is a characteristic presumably important to the population's fitness. A wild strain was found to control this characteristic more closely than did a mutant strain. A wild strain formed the same sized population regardless of whether a small or large number of insects were used as founders. The size of the mutant population varied with the number of founders. Population size influenced population fitness, defined as the ability to survive longer a period of environmental stress. Under the stress generated by failing to renew the medium, some wild-type populations continued to exist after all the mutant populations were extinct. A negative correlation existed between population size and survival.

The size of the population formed by the flour beetle Tribolium confusum has been found to depend on the volume of the environment rather than the amount of nutrient provided. This was determined by mixing powdered polyethylene with the flour medium, to vary the volume while holding the amount of nutrient constant. The polyethylene is probably not injurious to the adults for it appears to have no major effect on death rate. However, polyethylene and flour mixtures do alter some individual and population characteristics, probably those involved in cannibalism and egg production.

The mobility of adult—flour beetles in their natural environment (a flour medium) was measured for 2 genetic strains and both sexes of Tribolium confusum. (When the sexes were observed separately, the mobility of a mutant and a wild strain did not differ in the males, but in females the mutants were nearly 10 times as mobile as the wild individuals. If males and females of the wild strain are observed together, the mobility of the males appears to approach that of the females.