Biology Chapter 4 Population Biology

4.1 Population Growth If you graph population vs. time, there are some common patterns visible Initially, your graph will be a “J” shaped curve, showing exponential growth Eventually, your graph will be an “S” shaped curve, when your population reaches its carrying capacity

4.1 Exponential Growth Exponential growth occurs when population increases faster over time An example of this would be the population doubling each year. This would result in exponential growth This creates the “J” shaped portion of a population curve yearPopulation

4.1 Carrying Capacity Carrying capacity- the number of organisms that an environment can support indefinitely When a population reaches its carrying capacity, it stops increasing This leads to the “S” shape on a population graph This is due to an increase in the death rate, rather than a decrease in the birth rate The death rate increases are due to limiting factors such as disease, lack of food, predators, or lack of space

4.1 Life History Patterns There are 2 types of life history patterns: Rapid (examples: bacteria, soybeans) Common among organisms with unstable environments These organisms have small body size, mature rapidly, reproduce early, and have a short life-span Slow (examples: humans, trees) Common among organisms with fairly stable environments These organisms generally have large body size, reproduce later in life, mature slowly and have a long life span

4.1 Population Density There are 2 types of limiting factors related to population: Density dependent- have a bigger impact on bigger populations Includes predation, disease, competition, parasites, and food availability Density independent- the impact is not related to the size of the population Includes storms, floods, drought, temperature and other major habitat destruction

4.1 Other Limiting Factors Predation- if the population of a prey species increases, then more predators can eat, increasing the predator population then as the prey population declines, there is less food for the predators, so their population declines (this cycle repeats) Competition- when multiple populations compete for the same resources, the amount of available resources decreases, then the population decreases Then there is less competition and the resources increase, allowing the populations to increase again (this cycle repeats) Crowding- Overcrowding leads to stress, which can decrease populations by increasing aggression, decreasing parenting, decreased fertility, and decreased disease resistance

4.2 Human Population Growth Demography- the study of human population size, density & distribution, movement, and its birth and death rates Current world population is approximately 6.5 billion people Human population growth differs from that of other organisms because we possess the ability to change our environment This generally results in increased population growth

4.2 Calculating Population Growth Birth rate- the number of live births per 1000 population per year Death rate- the number of deaths per 1000 population per year Immigration- the movement into a population Emigration- the movement out of a population PGR = population growth rate PGR = (birth rate + immigration) - (death rate + emigration) Simplified: PGR = birth rate – death rate (immigration and emigration are ignored because they are often inaccurate)

4.2 Population Growth Rates If PGR > 0, a population is increasing There are more births per 1000 than deaths per 1000 If PGR = 0, the birth rate and death rate are equal, so overall population is not changing If PGR < 0, a population is decreasing There are more deaths per 1000 than births per 1000

4.2 Doubling Time Doubling time- the time needed for a population to double in size If the doubling time is short, the country is generally labeled as developing If the doubling time is long, the country is generally labeled as developed Doubling time is calculated by dividing 70 by the growth rate

4.2 Age Structure Age structure is the proportions of the population that are in different age levels It can also indicate gender of the population The shape of the age structure can indicate approximate growth rates stable growth rapid growth slow growth