7.1 Population Characteristics A population is a group of individuals of the same species inhabiting the same area. Natality: The number of individuals added to a population through birth over a particular time period. Birth Rate = Humans born per 1,000 individuals per year. Mortality: The number of deaths in a population over a particular time period. Death Rate = Humans died per 1,000 individuals per year.

7.1 Population Characteristics Effect of birthrate and death rate on population size

7.1 Population Characteristics A survivorship curve shows the proportion of individuals likely to survive to each age. Three types of survivorship curves exist: Type 1:Species with high mortality in young. Type 2: Species with mortality equitable among age classes. Types 3: Species with mortality high only in old age.

Above: Type 1 Survivorship Above: Type 3 Survivorship Left: Type 2 Survivorship

Population Growth Curve Population growth rate is the birthrate minus the death rate. Example: In the US birthrate is 14/1000 individuals, deathrate is 8/1000 individuals Difference between the two is 6 per thousand Population growth rate= 0.6%

Sex Ratio and Age Distribution Sex ratio refers to the relative number of males and females in a population. The number of females is important because females determine the number of offspring produced in sexually reproducing populations. Age distribution is the number of individuals of each age in the population. Age distribution greatly influences the population growth rate.

7.1 Population Characteristics Age distribution in human populations

Population Density and Spatial Distribution Population density is the number of individuals per unit area. High population density injures all individuals within the population because they compete severely for necessary resources. Dispersal: Movement of individuals from densely populated locations to new areas. Emigration: Movement from an area. Immigration: Movement into an area.