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What is a Population?

What is a Population?. Population Ecology. - The study of changes in population size and the factors that regulate it. Population. - group of individuals of a single species that occupy the same general area. 1. Rely on same resources. 2. Influenced by the same biotic and abiotic factors.

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What is a Population?

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  1. What is a Population? Population Ecology - The study of changes in population size and the factors that regulate it. Population - group of individuals of a single species that occupy the same general area 1. Rely on same resources 2. Influenced by the same biotic and abiotic factors 3. High likelihood of interbreeding

  2. How do scientists describe population growth? Let’s look at population growth of bacteria starting from a single bacterium - binary fission every 20 minutes under ideal conditions Q: How many will there be after 36 hours?

  3. How do scientists describe population growth? 2n Where n = # of divisions Let’s look at population growth of bacteria starting from a single bacterium - binary fission every 20 minutes under ideal conditions Q: How many will there be after 36 hours? A: 2108 (enough to cover the planet one foot deep) Graph it:

  4. How do scientists describe population growth? 1. Exponential Growth Model (J-shaped curve) Unlimited resources Absence of predation No disease So why is Earth not covered in bacteria?

  5. How do scientists describe population growth? Ex. Fur seals on St. Paul Island 1. Uncontrolled hunting until 1925 2. Population jumped until 1935 - Almost exponential 3. Population stabilized - Some hunting - limited breeding grounds

  6. How do scientists describe population growth? 3. Logistic Growth Model (S - shaped curve) Q: How does the logistic model differ from the exponential model?

  7. How do scientists describe population growth? Carrying capacity (K) - The max. population the environment can support. Determined by: The species itself and the environment (resources available, predation, etc…)

  8. How do scientists describe population growth? 3. Logistic Growth Model When is growth rate the lowest? 1. When population is small or large When is it the highest? 1. Population at intermediate level relative to carrying capacity. What factors would cause a population to stop growing?

  9. What is a limiting Factor? 2. Population limiting factors - environmental factors that restrict population growth There are many factors that limit a population from getting to large. - Competition for food or space. - Disease - Predation - Stress levels - Climate/ weather - Major disasters (freak events)

  10. What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors a. Competition among members (intraspecific) - food supply, water, space, energy (oil), mates, etc… Song Sparrow Population Experiment (small island in British Columbia) - add food - Clutch size increased Fig. 35.4A

  11. What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors a. Competition among members (intraspecific) i. food supply ii. space (territory) A. Dispersion patterns 1. clumped 2. uniform 3. random

  12. What are some of the factors that limit population growth? Dispersion patterns

  13. What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors b. Health - increased spread of disease with increased pop. density - accumulation of waste

  14. What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors c. Predation As the hare population increases, so does the Lynx population, which will cause the hare population to decrease and in turn the lynx population decreases, etc… “boom-and-bust” cycles Fig. 35.5

  15. What is happening to the moose and wolf populations? • Red is moose • Blue is wolves • 1955 to 1995

  16. What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors d. Physiological factors White-footed mouse experiment 1. Enclose in a small field 2. Reproduce quickly to 30 or 40 3. Reproduction declines and pop. stabilizes around 40 4. Add more food and water - no change RESULT: high population induces stress syndrome (hormonal changes) - sexual maturity delayed, reproductive organs shrink, depressed immune system

  17. What are some of the factors that limit population growth? Population limiting factors 2. Abiotic factors a. Climate and weather Ex. Aphids Fig. 35.4B - insects that feed on phloem sap of plants 1. Exponential growth in spring 2. Rapid die out in hot, dry summer 3. A few individuals survive and reproduce when conditions improve

  18. What are some of the factors that limit population growth? Population limiting factors 2. Abiotic factors b. Fire, flood, etc…

  19. Human Population Growth Human population growthIs there a Carrying Capacity for Homo sapiens? Section 5-3 Industrial Revolution begins Agriculture begins Bubonic plague Plowing and irrigation

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