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Populations

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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  1. Populations SNC1D0

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Predation • Some organisms eat others for food • Eg: Lynx prey on hares • One is the predator, one is the prey

  8. 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

  9. Parasitism • When one organism lives on/in another and feeds on it • Only one organism benefits • Eg: tapeworms • Mosquitoes

  10. Commensalism • When one organism benefits and the other neither benefits or is harmed • Eg: barnacles and whales • Remora fish on sharks

  11. Effect of Biotic Factors • Analyze the population trends of lynx and hare in the same ecosystem

  12. 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...

  13. 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

  14. 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

  15. Homework • Pg 55 # 1 – 8

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