Population ecology intro


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Population ecology intro

  1. 1. What is population?• Group of individuals of the same species that live in the same area
  2. 2. Does population change?• Sea otters, kelp, and sea urchins
  3. 3. •Kelp forests offer a habitat for sea otters•Sea urchins feed on kelp•Sea otters feed on sea urchins
  4. 4. • What do you think happens when sea otters are hunted? – Sea urchins increase or decrease? – Kelp forest increase or decrease?• Sea otters are then placed on the endangered species list• So now what happens to the population of sea otter? – Starts to increase• How does this affect the kelp and the sea urchins? – Sea urchins start to get eaten again=decrease in # – Kelp increases b/c less sea urchins to eat them
  5. 5. But now we have a new hunter….
  6. 6. What happens to the sea otter, kelp, and sea urchins?
  7. 7. What does this tell us about population?• Population changes• There are many factors that influence a population – Natural – Unnatural• Population density has a great impact on ecosystems
  8. 8. 3 important characteristics of Population• Geographic Distribution• Density• Growth Rate –Birthrate, death rate, individuals entering/leaving***Population Age structure is also an important characteristic
  9. 9. Geographic Distribution• AKA Range• Describes an area inhabited by a population• Can vary –Few cubic centimeters –Kilometers of the ocean
  10. 10. Density• # of individuals per unit area• Low density –Cactus in desert• High density –Other desert plants and succulents
  11. 11. Math Time• Formula for calculating population density• Population density=Number of individuals units area• Problem: Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population?• 50 bullfrogs per square kilometer
  12. 12. Growth Rate• Many factors affect growth rate
  13. 13. 3 Factors that affect population size• # of births• # of deaths• # of individuals that enter or leave population Population will increase or decrease depending on # of individuals added or removed
  14. 14. What happens to the population when we….• Have more births than deaths? – Population increases• Have more deaths than births? – Population decreases• Have equal amounts of births and deaths? – Population remains constant
  15. 15. Immigration• “im”= in• Migrate= to move from one place to another• Immigration is the individual movement into an area• Animals in search of mates and food in new areas
  16. 16. Emigration• “E” means „out‟• Migrate means to move from one place to another• Emigrate means individuals moving out of one place and into another• Young wolves and bears leaving as they mature• Shortage of food
  17. 17. Sampling Techniques• How would we measure the population of a species?• Impractical to count each and every one• Variety of sampling techniques – Quadrants – Indirect counting – Mark-Recapture
  18. 18. Quadrants• Involves marking off specific area, boundary• Count specific species within the boundary• Repeat in several locations within desired ecosystem• Average the results to determine population density• More quadrants sampled=more accurate
  19. 19. Indirect Counting• Used for species that are too difficult to see or move around too quickly• Does not involve counting organisms themselves – Count nests, burrows, tracks
  20. 20. Mark-Recapture• Most common• Choose a study area• Trap/capture animals• Mark the captured animals and release back into habitat – Markings are not to disturb organism• After a period of time, recapture animals in the same study area• Count marked and unmarked organisms
  21. 21. How to Estimate Population from Mark-Recapture MethodTotal population= (# in first capture) x (# in second capture) number of marked animals RECAPTURED
  22. 22. Limits to Accuracy• Involve making assumptions about populations – Assumptions not valid=estimate not accurate• Quadrant – Assumption: • Organisms distributed evenly in study area – Problems • “Clumps” • Quadrant with clump vs quadrant without clump – Minimize problem • Analyze how study population is distributed in order to choose appropriate quadrant size• Mark-Recapture – Assumption: • Both marked and unmarked animals have same chance of surviving and being recaptured in second trial – Problem • After being captured once, how do you think animals will behave? • Leads to overestimating population size – Minimize problem • Minimize effects of trapping on organisms
  23. 23. Two types of growth• Exponential growth – Individuals reproduce at a constant rate – Population multiplies by constant FACTOR over constant time interval• Logistic growth – Occurs when a populations growth slows or stops after a period of exponential growth – As population approaches carrying capacity, BR may decrease, DR may increase or both, until equal
  24. 24. Exponential Growth• Occurs under ideal conditions with unlimited resources• Think about exponents in math….• Starts slowly then sky rockets to infinity• Our graph will look like a J• Bacteria
  25. 25. Lets look at bacteria…• Bacteria reproduce by splitting in half• Bacteria have a doubling time of 30 minutes• If you start will one bacterium, how many bacteria will there be after the first 30 minutes? – 2• After an hour? – 4• After an hour and a half? – 8• After two hours? – 16• After 15 hours? – Over a billion
  26. 26. Logistic Growth• As resources become less available, the growth of the population slows or stops• S-shape curve• No net increase or decrease in population• What we usually see in nature
  27. 27. Carrying Capacity• The largest number of individuals that a given environment can support• The part of the logistic graph after the exponential growth…the flattening out• The point at which this flat line reaches the y- axis is the size of the population when the growth rate reaches zero• This doesn‟t mean the population stops growing• Many factors slow the growth of plants and animals…
  28. 28. Limiting Factor• Condition that can restrict a population‟s growth• Could be: – Space – Disease – Availability of food
  29. 29. Factors Affecting Population Growth • Density-dependent • Density-Independent Factors Factors • Factor that limits • Factors that affect population as population population but are density increases unrelated to population – Competition density; affect population regardless of size – Predation • Insects vulnerable to this – Disease – Weather /Natural – Parasitism disasters – Crowding and – Human activities Stress – Fires – deforestation
  30. 30. Boom and Bust Growth Cycles• Increase rapidly for a period of time followed by a sharp decrease in population for a brief period of time• Still not completely understood• Hypothesis: – Changes in food supply – Stress from overcrowding – Other organisms influence on population
  31. 31. -Involves more than one population-Rapid increase and decrease in populations