Populations Three important characteristics of a population are

Populations

Three important characteristics of a population are … 1) Population Density Number of individuals per unit area 2) Geographic Distribution Describes the area inhabited by a population 3) Growth Rate How fast a population can grow

Population Growth is affected by: Number of births Number of deaths Number of individuals that enter or leave Immigration Emigration

Immigration movement of individuals into an area (causes population growth) Emigration movement of individuals out of a population (causes population to decrease) Think “in” for Immigration Think “exit” for Emigration

Population Growth Exponential growth Individuals reproduce at a constant rate Occurs under ideal conditions including unlimited resources A population’s growth rate is small when the population is small and continues to increase as the population size increases

Population Growth Logistic Growth When a population’s growth slows or stops following a period of exponential growth Takes into account environmental factors that limit population growth Occurs when there is steady population growth Occurs after a period of exponential growth

Population Growth Population size increases until it reaches Carrying Capacity The largest number of individuals that an environment can support.

Population Growth Exponential Growth Represented by a J-shaped curve Logistic Growth Looks like an S-shaped curve

Exponential Growth

Logistic Growth

Limiting Factors What are limiting factors? Any abiotic or biotic factor that restricts the numbers, reproduction, or distribution of a population Two Types: Density-Dependent Density-Independent

Limiting Factors Density-Dependent: Competition Predation Parasitism Disease

Limiting Factors Density-Independent: Unusual weather Natural disasters Seasonal difference Human activities

Things to Think About How has the human population been growing? Human Population has been growing exponentially for centuries Has the human population’s death rate increased or decreased? Why…because of technological OR biological attributes? Technological, rather than biological attributes of our species have lowered death rates

Things to Think About What has caused a rise in earth’s carrying capacity? Technology has raised earth’s carrying capacity What population can continue to grow exponentially? No population can continue to grow indefinitely