The human population and the environment Chapter 4 AP Environmental The human population and the environment Chapter 4

Population Dynamics Population: Species: Population dynamics A group of individuals of the same species living in the same area of interbreeding and sharing genetic information. Species: All individuals that are capable of interbreeding. Made up of populations Population dynamics The general study of population changes.

Population Dynamics Formula to represent population change: Human population is usually presented as a crude rate which is a given number per 1000. Example: If the crude death rate is 9 then that represents 9 out of every 1000 people died in that given time frame. Expressed as a percentage this would equal 0.9%. Crude growth = crude birth rate – crude death rate ( g = b-d) and represents a net change in the population P1 = number of individuals at a given time P2 = number of individuals at a later time P2 = P1 + (B – D) + (I – E)

Population Dynamics Growth rates can be determined using a series of equations that factor in the number of births or deaths in a population with a known population size (N). birth rate (b)= B/N death rate (d) = D/N Growth rate (g) = (B-D)/N

Age Structure Population age structure: The proportion of the population in each age class Affects current and future birth rates, death rates and growth rates Has an impact on the environment Has complications for current and future social and economic status.

Age Structure

History of Human Population Hunters and gatherers The world’s population was probably less than a few million Early, pre-industrial agriculture Allowed a much greater density of people The first major increase in human population Machine age Industrial revolution led to rapid increase in human population The Modern era Rate of population has slowed in wealthy nations but continues to increase rapidly in poorer, less developed nations.

Population Changes Exponential growth represents a constant net rate of increase. The rate of net increase for the human population in the graph has exceeded the exponential rate Factors like a decline in death rate have caused the growth in the net rate of increase

Where do you see population trends increasing? Why? Population Changes Where do you see population trends increasing? Why?

Population Changes

Exponential growth and doubling time The current growth rate for the human population falls between 1-2% so doubling time is expected to be between 35-70 years. *Remember: doubling time = 70/R No population can sustain exponential growth rate indefinitely because of resource constraints within the environment

Logistic Growth The logistic growth curve Logistic carrying capacity “S” shaped curve that is generated by the logistic growth equation. A small population grows rapidly But the growth rate slows down The population eventually reaches a constant size. Logistic carrying capacity The population size at which births equal deaths and there is no net change in population *There is very little evidence that animal populations actually follow true logistic growth patterns

Logistic Growth

Growth Factors Total Fertility Rate (TFR) is a major factor in the growth or maintenance of a population over time. Total fertility refers to the average number of children that could be born to a woman if she follows the normal rates of fertility and survives from birth through her reproductive years. In populations an important figure in fertility is called Replacement Level Fertility. Replacement level fertility means that a woman produces enough children to maintain the current population levels

Growth Factors Fertility rates are generally higher in developing countries because of a need for labor and caregivers within the household, a lack of education in birth control, and cultural beliefs Worldwide fertility rates are dropping due to higher levels of urbanization, especially in developing countries If fertility rates were to drop below replacement levels then the population could stabilize

Demographic Transition Three-stage pattern of change in birth rates and death rates. Occurred during the process of industrial and economic development of Western nations. Leads to a decline in population growth. Stage I: Decline in death rate Stage II: High growth rate Stage III: Birth rate drops toward the death rate, leading to low or zero growth rate

Demographic Transition

Demographic Transition

Effects of the Human Population The total impact of the human population on the environment is: the average impact of an individual multiplied by the total number of individuals For individuals, the impact is determined by the amount of the environment that is considered necessary to support a particular lifestyle. This is also called an ecological footprint. T = P x I

Effects of the Human Population Human carrying capacity The number of people that can live on Earth at the same time? To determine: Extrapolate from past growth The “Packing Problem” approach Considers how many people might be packed onto Earth, not taking into sufficient account the need for lands and oceans to provide food, water, energy, construction materials, and scenic beauty and the need to maintain biological diversity

Nature’s effect on Humans Acute or epidemic disease Appears rapidly in the population, Affects a comparatively large percentage of it, Declines then almost disappears, only to reappear later Chronic disease Is always present in a population Typically occurs in a relatively small but relatively constant presentation of the population Examples include heart disease, cancer, and stroke

Nature’s effect on Humans Maximum lifetime: The genetically determined maximum possible age to which an individual of a species can live Life expectancy: The average number of years an individual can expect to live given the individual’s present age

Nature’s effect on Humans Short-term factors Those that affect a population during the year in which they become limiting Intermediate-term factors Those whose effects are apparent after one year but before ten years Long-term factors Those whose effects are not apparent for ten years Some factors fit into more than one category

Population Solutions: Zero Population Growth Delay the age of first childbearing by women Birth control Biological and Social Breast-feeding, which can delay resumption of ovulation Abstinence Induction of sterility with natural agents Contraceptive devices National Programs to Reduce Birth Rates Formal family planning programs to explain the problems arising from rapid population growth Describe the benefits to individuals of reduced population growth.