III. Early Loss Typical of species that have great numbers of
offspring and reproduce for most of their
lifetime. Death is prevalent for younger members
of the species (environmental loss and predation)
and declines with age. Examples: sea turtles,
trees, internal parasites, fish, and oysters.HUMAN POPULATION DYNAMICS
Many different factors affect the human population: historical population sizes,
population distribution, fertility rates, and growth rates and doubling times. Age-
structure diagrams act as indicators of future population trends.
Historical Population Sizes
The rapid growth of the world’s human population over the past 100 years has
been due primarily to a decrease in death rates. In 1900, the overall death rate in
the United States was 1.7%. In 2000, the death rate had dropped to 0.9% (almost
half). Children in 1900 were 10 times more likely to die than children in 2000.
Several factors have reduced human death rates: ■ Increased food and more
efficient distribution that result in better nutrition ■ Improvements in medical
and public health technology ■ Improvements in sanitation and personal
hygiene ■ Safer water supplies
Figure 6.5 Global birth and death rates (1950–2050)