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Population Dynamics Day 4

Population Dynamics Day 4. Population Characteristics. Population Density: The number of organisms per unit area Dispersion: The pattern of spacing a population within an area 3 main types of dispersion Clumped Uniform Random Resource availability determines dispersion patterns.

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Population Dynamics Day 4

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  1. Population DynamicsDay 4

  2. Population Characteristics • Population Density: • The number of organisms per unit area • Dispersion: • The pattern of spacing a population within an area • 3 main types of dispersion • Clumped • Uniform • Random • Resource availability determines dispersion patterns

  3. Population Limiting Factors 1) Density-independent factors • Factors that limit population size, regardless of population density. • usually abiotic • include natural phenomena • Ex. drought, flood, fire extreme temperature, tornadoes, etc.

  4. Population Limiting Factors (cont.) 2) Density-dependent factors • Any environmental factor that depends on the density of the population • Usually biotic • For ex. • Predation • Disease • Parasites • Competition

  5. Population Limiting Factors (cont.) 3) Population growth rate • How fast a population grows • Factors that influence this are: • Natality (____ rate) • Mortality (_____ rate) • Emigration (the number of individuals moving _________ a population) • Immigration (the number of individuals _________ a population) birth death away from moving to

  6. Understanding Exponentials • Put your pens down for a minute & think about this: • An employer offers you two equal jobs for one hour each day for fourteen days. • The first pays $10 an hour. • The second pays only 1 cent a day, but the rate doubles each day. • Which job will you accept?

  7. Understanding Exponentials Now, how much would your employer owe you if you stayed at this job for another 2 weeks? Job 2 lags for a long time before exponential growth kicks in! What would happen if this type of growth took place within a population?

  8. Population Growth Models 1) Exponential growth model • Also called geometric growth or J-shaped growth. • First growth phase is slow and called the lag phase • Second growth phase is rapid and called the exponential growth phase • Bacteria can grow at this rate, so why aren’t we up to our ears in bacterial cells?

  9. Population Growth Models (cont.) • Limits to exponential growth • As population density increases, competition follows as nutrients and resources are used up • The limit to population size that a particular environment can support is called carrying capacity (k) • When you’re done writing, put your pens down…

  10. What population do you think this is?

  11. So, what do you think is going to happen to the human population? • We will probably reach our carrying capacity. • Our growth rate will start to look like most organisms, which is the Logistic Growth Model Carrying Capacity (k) What letter does this curve kind of look like?

  12. Population Growth Models (cont.) 2) Logistical growth model • Often called the S-shaped growth curve • Growth slows or stops following exponential growth at the population’s carrying capacity • Populations stop increasing when: Birth rate < Death rate Emigration > Immigration • Carrying capacity can be raised or lowered. How? Ex. 1: Artificial fertilizers have raised Ex. 2: Decreased habitat can lower k

  13. Community Dynamics Day 5

  14. Communities • Review: • A community is a group of interacting populations that occupy the same area at the same time.

  15. Limiting Factors of Communities Any abiotic or biotic factor that restricts the numbers, reproduction, or distribution of organisms.

  16. Range of Tolerance Upper and lower limit of conditions in which an organism can survive. Ex. Temperature, Salinity, pH

  17. Ecological Succession The change in an ecosystem that happens when one community replaces another as a result of changing biotic and abiotic factors

  18. Ecological Succession (cont.) 2 types: 10 Primary Succession 20 Secondary Succession

  19. Primary Succession • In primary succession (10), the community establishes in an area of exposed rock (no soil) It occurs very slowly at first

  20. Primary Succession (cont.) • Pioneer species, or the first organisms to arrive, are usually lichens or mosses • They secrete acids that can break down rock, creating soil.

  21. Primary Succession (cont.) • Small weedy plants and other organisms become established. • As they die, more soil is made

  22. Primary Succession (cont.) • Animals, water and wind bring seeds that sprout • Eventually there is enough soil for shrubs and trees to grow.

  23. Primary Succession (cont.) • The stable, mature community that eventually develops from bare rock is called a climax community.

  24. Secondary (20) Succession • Disturbances (fire, flood, windstorms) can disrupt a community. • After a disturbance, new species of plants and animals might occupy the habitat.

  25. Secondary Succession (cont.) • Pioneer species in 20 succession are usually plants that grow in disturbed area. • Much fasterthan 10succession

  26. Succession End point? • Cannot be predicted • Different rates of growth &human involvementmake it impossible toknow if a true climaxcommunity has beenreached.

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