Chapter 5 Populations Biotic Potential: The size a population would reach if all offspring were to survive and reproduce • Conditions have to be idealenough food and living space Population Density- Number of individuals in an area • What Determines density and distribution? • Geographic Distribution- range- the area the population inhabits Population Growth • Affected by -Birth rate (natality) -Death rate (mortality) -Immigration- entering an area -Emigration- leaving an area Populations increase if births exceed deaths and immigration exceeds emigration Exponential Growth • Exponential Growth occurs when the individuals in a population increase at a constant rate • Look at graph on p.121 -under ideal conditions -population grows slowly at first -rises to an infinitely large size -J-shaped curve Logistic Growth • Logistic growth occurs when a population’s growth slows or stops following a period of exponential growth. • S-shaped curve-graph levels off • Carrying capacity- Usually population fluctuates around this point- s-shape • Look at graph on p. 122 Carrying Capacity • The number of individuals an area can support without ruining the area. Limiting Factors • Something that causes population growth to decrease • Density dependent • Density independent Density- Dependent Factors • Limit a population when the number of individuals reach a certain level • Competition for food, water, space, sunlight, etc. • Predation • Parasitism + disease Wolf/Moose graph Density -Independent Factors • Affect all populations regardless of size • Weather, natural disasters, seasonal change, human interventions (dams,logging, housing developments) • Populations usually decrease dramatically after such an event • Can be permanent + cause extinction Human Population Growth • Slow growth historically • Now, exponential growth- 6-7 billion • Current World Population • Some countries have higher growth rates than others Demographic Transition • Dramatic change in birth and death rates • Nutrition, medicine, clean water supplies increase survival rates • Some countries, population stabilizes, but for a while, births may exceed deaths Age diagram • In some cases, populations may even decrease- U.S., Japan, Europe • Some countries are still growing exponentially • Parts of Africa, Mexico, India • Many young people, of an age where they will still be having children • 9 billion predicted by 2050 • What will stop/slow the growth?