Population Ecology
Population
• All the organisms of a species that live in a an area at a certain time
• Populations change when –new members are added or –members leave or die
Birth
• The main way new members are added.• Birth Rate – number of births in a certain
amount of time–Example: births per year
Death
• Deaths are the main way members leave a population.
• Death rate = number of deaths in a certain amount of time Example: deaths per year
Immigration
• Organisms move in from another environment
• Causes a population to increase
Emigration
• Some organisms leave the environment to go somewhere else.
• Causes a population decrease
Population Change
Immigration
Births Deaths
Emigration
++ -
-
Population Density
• Measurement of population per unit area or unit volumeExamples: Wolves per square km.
Bacteria per ml.
• If a population increases or decreases in a given area, population density also increases or decreases
Calculate Population Density
• If Yellowstone National Park has 400 wolves and covers an area of 9000 square km., what is the population density of wolves in Yellowstone?
• _450 wolves = 0.05 wolves/km² 9000 km²
Limiting Factors
• Any factor that limits the growth of a population in an ecosystem
• May be biotic or abiotic• Examples– Climate– Food– Water– Space– Shelter
Carrying Capacity
• The maximum number of organisms that can survive in a particular ecosystem.
• When a population reaches its carrying capacity, it cannot grow any larger