Populations
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Populations. SNC1D0. Populations. Population size is affected by four main factors Natality Rate How many births there are per year Mortality Rate How many deaths there are per year Immigration The number of individuals that have moved into the area Emigration

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Populations

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Populations

Populations

SNC1D0


Populations1

Populations

  • Population size is affected by four main factors

  • Natality Rate

    • How many births there are per year

  • Mortality Rate

    • How many deaths there are per year

  • Immigration

    • The number of individuals that have moved into the area

  • Emigration

    • The number of individuals that have moved out of the area


Natality and mortality

Natality and Mortality

  • What factors might affect the natality rate?

    • # of children produced per pregnancy

    • Frequency of child birth

    • Length of pregnancy

  • What factors might affect the mortality rate?

    • # of predators

    • Amount of available food

    • Weather (cold, hot, too much rain, too little rain, etc...)

    • Disease

    • Hunting

    • Loss of habitat


Salmon and pandas

Salmon and Pandas

  • Salmon have a high reproduction rate

    • Mate every 2 years

    • Lay 1000 – 2000 eggs each

  • Giant Panda

    • Can mate once per year

    • Produce ~1 child every two years


Limits on populations

Limits on Populations

  • There are several limiting factors on populations

    • Some are biotic and some are abiotic

    • These factors prevent populations from becoming too large

  • Influence of biotic factors

    • Competition (for food, habitat, mates, etc...)

    • Predation

    • Disease

    • Mutualism

    • Parasitism

    • Commensalism


Competition

Competition

  • When two different species compete over

    • Food

    • Shelter

  • Eg: Foxes and coyotes often compete over food (mice, rabbits, etc...)

  • Eg: Humans compete with insects over crops


Predation

Predation

  • Some organisms eat others for food

    • Eg: Lynx prey on hares

    • One is the predator, one is the prey


Mutualism

Mutualism

  • Sometimes, two species benefit each other

    • Eg: nitrogen-fixing bacteria live in the roots of some plants and provide them with nutrients

    • Eg: E. coli bacteria live in the colon of humans and provide us with vitamins


Parasitism

Parasitism

  • When one organism lives on/in another and feeds on it

    • Only one organism benefits

    • Eg: tapeworms

    • Mosquitoes


Commensalism

Commensalism

  • When one organism benefits and the other neither benefits or is harmed

    • Eg: barnacles and whales

    • Remora fish on sharks


Effect of biotic factors

Effect of Biotic Factors

  • Analyze the population trends of lynx and hare in the same ecosystem


Abiotic factors

Abiotic Factors

  • The abiotic factors in an ecosystem also limit the population

  • All organisms have a tolerance range

    • A range in which they can comfortably live

  • This applies to all abiotic factors

    • Temperature

    • Acidity

    • Nutrients

    • Salinity (amount of salt)

    • Light availability

    • Etc...


Tolerance range

Tolerance Range

  • In the optimum range the largest possible population can exist

    • Outside this range there can only be a small #, or no individuals living

Optimum Range

Abiotic Factor


Carrying capacity

Carrying Capacity

  • For every population there is a maximum size that can be sustained by its ecosystem

    • This is called the carrying capacity

    • It is constrained by the specific biotic and abiotic factors in the ecosystem


Homework

Homework

  • Pg 55 # 1 – 8


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