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Ch. 19

Ch. 19 . Populations. Recall: A population is…. a group of organisms of the same species living in the same area at the same time. Population Properties. Population Spacing. Dispersal patterns within a population. clumped. random. uniform. Clumped – clustered together

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Ch. 19

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  1. Ch. 19 Populations

  2. Recall: A population is… • a group of organisms of the same species living in the same area at the same time

  3. Population Properties

  4. Population Spacing • Dispersal patterns within a population clumped random uniform

  5. Clumped – clustered together • Often occurs when resources are clustered or due to social behavior

  6. Clumped Pattern (most common)

  7. Uniform – separately by a fairly constant distance • May be due to social behavior

  8. Uniform May result from direct interactions between individuals in the population territoriality

  9. Random – each individual’s location is independent of other individuals

  10. Few populations; most show degree of clumping or uniformity

  11. Getting population size: • Counted directly – for immobile organisms like trees • Estimated – for abundant or widespread organisms • population sampling • Exp. If a small patch of land contains 25 oak trees, an area 10 times larger would likely contain 10x the number of oak trees • mark and recapture- marking a number of individuals in a population, returning them, and recapturing some of them as a basis for estimating the size of the population at the time of marking and release.

  12. All populations are dynamic • All populations change in size and composition over time!

  13. Four things affect population dynamincs: • Birth rate • Death rate • Life expectancy • Age structure

  14. Birth and Deaths • Birth Rate is the number of births in population in a certain time period; adds to population • Death Rate is the number of deaths in a population in a certain amount of time; subtracts form population

  15. Life expectancy – how long individuals are expected to live; longer life expectancies add to population • Age structure – distribution of individuals among different age groups; if higher percentage of young individuals there’s potential for rapid pop. growth

  16. Graphs of Age Structure and Effect on Population Growth High percentage of young individuals of reproductive age – rapid growth Small percentage of young individuals of reproductive age – negative growth

  17. Growth rate • amount by which a population’s size changes in time

  18. What does growth rate depend upon? • adding & removing individuals from a population • birth • death • immigration • emigration

  19. Population Equation • growth rate = birth rate – death rate • If birth rate > death rate, population size increases. • If birth rate < death rate, population size decreases

  20. Exponential Growth • Pattern of increase in # due to steady growth rate • J shape curve • Ideal conditions

  21. Exponential growth does not apply to most populations because of limiting factors. As the population grows, competition for shrinking supply of resources intensifies. Each individual gets a smaller share. Individuals’ ability to grow, reproduce, and fight off disease decreases. As a result, the population’s birth rate declines and death rate increases.

  22. Logistic Model • Builds on exponential model but accounts for limiting factors • Limiting factor – any factor that restrains population growth • food • space • waste accumulation • competition • predators • disease

  23. Logistic Model • Population grows, approaches carrying capacity and slows, stops when it reaches the carrying capacity • S shape

  24. Carrying capacity = number of individuals the environment can support over a long period of time Real populations may fit this pattern for some period of time but rarely remain stable; carrying capacity also can fluctuate.

  25. More on limiting factors:Density- independent vs. Density dependent

  26. Changes in Carrying Capacity • Population cycles • predator – prey interactions Populations rarely remain stable and can fluctuate!

  27. Why do we worry about small populations? • small populations are more vulnerable to extinction • disturbances can kill entire population • less organisms to survive and reproduce • less genetic variability

  28. Inbreeding in small populations may be a problem • decreases genetic variability even more • population less likely to adapt

  29. Human population growth • Developments that have contributed to the increase in human population growth: • Agriculture – stabilized and increased food supply • Hygiene • Sanitation • Diet • Medical care • Improved economic conditions

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