Lower (or higher) mortality might induce lower (or higher) fertility, but it is well established that higher birth rates lead to higher infant and child mortality. This higher mortality is related to the effect on infants and children of earlier weaning and reduced care from mothers.

Fertility is the number of children born to a woman, while fecundity is her physiological potential to bear children. Fertility is often used as measure of fitness, and fecundity is related to reproductive value.

Fertility, mortality and migration are principal determinants of population growth. Population change depends on the natural increase changes seen in birth rates and the change seen in migration. Changes in population size can be predicted based on changes in fertility (births), mortality (deaths) and migration rates.

The death of more infants compels the parents to bear more children due to lack of confidence of their survival. It causes the population growth in the family. Consequently, the whole population increases. In this way high infant mortality rate increases the population.

Among these factors, age at first marriage, perceived ideal number of children, literacy status, mass media exposure, wealth status, and experience of child death are important and strong predictors that affect fertility.

Factors Affecting Mortality:

• Infectious, parasitic and respiratory diseases.
• Cancer.
• Diseases of the circulatory system.
• Violence and accidents. ADVERTISEMENTS:
• All other causes such as diseases of the digestive system.

The most commonly used metric is the Total Fertility Rate (TFR) – or often simply ‘fertility rate’ – which measures the average number of children per woman. In the pre-modern era fertility rates of 4.5 to 7 children per woman were common. At that time the very high mortality at a young age kept population growth low.

18.5 births per 1,000

The age-specific fecundity (mx) is calculated as the average number of offspring per female in age-class x. The sum of this column tracks the reproductive output of a hypothetical female that lives to the maximum observed age. This sum is called the gross reprouctive ratio (GRR).

The meaning of fecundity is the reproductive rate (fecundity rate) or the performance of an individual or the population. Fecundity is the estimate of the number of gametes produced by an individual. In simpler terms, fecundity is the quantification of the number of individuals added to the population.

Fecundity is the ability to produce offspring. It can also describe the reproductive rate of an individual organism. Having high fecundity is an adaptation of many wildlife species. It is unusual for humans to have more than one baby at a time.

Fecundity. As age structure suggests, some individuals within a population have a greater impact on population-level processes, such as growth. Fecundity describes the number of offspring an individual or a population is able to produce during a given period of time (Martin 1995) (Figure 4).

Why can’t a female lizard have both high fecundity and high survival? The more energy the female devotes to offspring, the less that can be devoted to her survival.