Population EcologyPopulation EcologySNC1L ScienceSNC1L Science

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Populations Change• A Population is all of the members of a

single species living in an area.• The various populations of different

species in one area are called a community.

• Population size depends on four factors:Births, Deaths,

Immigration, and Emigration.(migrating in) (migrating

out)

P = (N+I) – (M+E)

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Populations are limited• A limiting factor is any biotic or abiotic

factor that affects growth of a population. Too much or too little of any one is not good!

• Populations will grow or decline depending on their Biotic Potential

• This depends on:• Birth Potential• Capacity for Survival• Procreation• Reproductive Lifespan

BIOTIC ABIOTICFood resourcesPredationDiseaseCompetition

Level of lightTemperatureChemicalsWater Resources

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Birth Potential• Maximum Number of

offspring per birth• Humans have a much lower

birth potential than ducks, or salmon.

• Whooping Cranes only lay two eggs a year.

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• Number of offspring that survive to reproductive age

• Humans have a better chance at this than many other species...

• Female Clams release five million eggs at a time, but only 50 may survive.

• Sea Turtles lay 50 – 100 eggs, but few reach maturity.

• Parenting is not universal in nature!

Capacity for Survival

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Procreation• Number of times a species reproduces

each year.• Humans can only procreate once in a given year.• Mice can have a litter of 10 – 14 pups every 6 to 8

weeks.• Sparrows produce up to 3 broods of chicks annually.

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Reproductive Lifespan• Age of sexual maturity & how many

years reproduction is possible.• Humans need more than a decade to reach

sexual maturity.• African elephants need 15 years to mature,

but may reproduce to 90!• Dogs are mature at 1 year; they can

reproduce for the rest of their lives.

• Population sizes go up and down, but like to be stable

• Stability = when the population is in balance• Carrying Capacity = max # of individuals that the

ecosystem can support• Populations can exceed their environment’s

carrying capacity, but not for long.

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Carrying Capacity

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Carrying Capacity• Example: Fluctuations in Elk & Wolf

populations in Banff, Alberta

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Carrying Capacity• Example: Fluctuations in Snowshoe Hare &

Lynx populations, British Columbia

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Carrying Capacity• Example: Human population from prehistory

to modern day

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Population Density• Population size per unit area of habitat• Dense Populations = when there are a lot of

organisms in a limited area• Density determines population change, also.

Density Dependent

Factors

Density Independent

Factors

Food shortageCompetitionDiseaseInvasive speciesPredation

Flood, fire…Pesticide useClimate changeDroughtHabitat loss