Population ecology intro

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  • 1. What is population?• Group of individuals of the same species that live in the same area
  • 2. Does population change?• Sea otters, kelp, and sea urchins
  • 3. •Kelp forests offer a habitat for sea otters•Sea urchins feed on kelp•Sea otters feed on sea urchins
  • 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. But now we have a new hunter….
  • 6. What happens to the sea otter, kelp, and sea urchins?
  • 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. 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. Geographic Distribution• AKA Range• Describes an area inhabited by a population• Can vary –Few cubic centimeters –Kilometers of the ocean
  • 10. Density• # of individuals per unit area• Low density –Cactus in desert• High density –Other desert plants and succulents
  • 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. Growth Rate• Many factors affect growth rate
  • 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. 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. 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. 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. 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. 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. 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. 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. How to Estimate Population from Mark-Recapture MethodTotal population= (# in first capture) x (# in second capture) number of marked animals RECAPTURED
  • 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. 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. 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. 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. 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. 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. Limiting Factor• Condition that can restrict a population‟s growth• Could be: – Space – Disease – Availability of food
  • 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. 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. -Involves more than one population-Rapid increase and decrease in populations