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07 pop bio


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  • 1. Barbara J. King , Department of Anthropology, College of William and Mary "Apes, Elephants and the Relational Self:  Thinking Through Animal Personhood” Tuesday, March 15, 4:00pm Knight Auditorium, Spurlock Museum, 600 S. Gregory, Urbana. Barbara J. King is the author of Being With Animals:  Why We Are Obsessed with the Furry, Scaly, Feathered Creatures Who Populate Our World  Announcements: Feb 14, 2011
  • 2. Do all species matter? Is there redundancy in communities? Paul Ehrlich made an analogy between species in communities and rivets on the wing of an airplane. Removing a few rivets from an airplane is undoubtedly safe. How many are you willing to remove? On average, there are only 2 degrees of separation between any two species in a food web.
  • 3. Percentage of threatened or endangered species in the U.S. imperiled by: Why are species declining? Disease - 3% Overexploitation - 17% Pollution - 24% Invasive species - 49% Habitat degradation and loss - 85% Dave Wilcove et al. 1998 BioScience
  • 4. Population Biology 10 February 2010 Lecture Objectives: 1. Learn the population characteristics that determine population growth rate 3. Understand the different types of population growth curves and life history traits 2. Understand why the number of individuals in a population may change over time
  • 5. World Wildlife Fund launches campaign to save tigers Feb 10, 2010 * Number of tigers in the wild has dropped to 3,200 from 100,000 in 1900, group says * Poaching, habitat loss, development, illegal trafficking threaten tigers, WWF says * There are now more tigers in captivity in the United States, about 5,000, than there are in the wild worldwide, the group said. CNN
  • 6. Population Characteristics Population – All organisms of the same species found within a specific geographic region Different populations can differ in: *Birthrate *Death rate *Sex ratio *Age distribution *Density *Population growth rate
  • 7. Birthrate (Natality)
        • Birthrate (b) —Number of individuals added through reproduction over a particular time period.
    In many species, birthrate is influenced by the amount of food available Sexually reproducing species must also find mates In humans, expressed as # of babies/1000 individuals/year
  • 8. Asexual Reproduction Females that reproduce asexually do not need to find a mate New Mexico Whiptail Daphnia
  • 9. Death rate (Mortality) Mortality (d) — Number of individuals removed via death For many species, predation is a major contributor to death rate In human populations, talk about # of people who die/1000 individuals/year
  • 10. Mortality Survivorship curve – a graph showing the proportion of individuals likely to survive to each age Three main types: Type I Type II Type III
  • 11. Type I survivorship curve Survival is high until old age
    • Examples:
    • Dall sheep
    • Humans in developed countries
  • 12. Type II survivorship curve Mortality is spread evenly among all age groups
    • Example:
    • Many species of birds
  • 13. Type III survivorship curve Very high mortality among the young
    • Examples:
    • Plants
    • Animals that produce many offspring
  • 14. Survivorship curves (continued) One major factor determining the shape of the survivorship curve is the degree of parental care How long do parents care for the offspring after they are born?
  • 15. Population growth rate Population growth rate (r) – the rate at which the size of the population changes r = b - d Assumes no immigration or emigration—when this happens population growth rate is then more generally, (birth + immigration) – (death + emigration)
  • 16. Exponential Growth Note: This equation is provided only to help. You do not need to memorize it. You will not be asked about the equation on a test. Change in number over time Population growth rate Number of individuals The number of individuals in each generation is a multiple of the previous generation
  • 17. Example of exponential growth
  • 18. Populations do not grow exponentially forever
  • 19. r r r Example for a population of algae
  • 20. r >0 r=0 r<0 Example for a population of algae
  • 21. r r r Example for a population of algae In the red region, what might cause N to decline? What information do you need to answer this question fully?
  • 22. Sex Ratio In many sexually reproducing species, with separate sexes, sex ratio is 1:1 Other factors influencing population growth rate In other species (e.g., asexuals, social insects) can have far more females than males
      • Sex Ratio— Relative number of males and females in a population.
  • 23. Age Distribution (Age Structure)
      • Age Distribution —Number of individuals of each age in the population.
        • Greatly influences reproductive rate of a population.
    Other factors influencing population growth rate
  • 24. How does the age distribution differ among these populations?
        • Why does age distribution influence reproductive rate of a population?
  • 25.
    • Dispersal: Movement of individuals
    • Emigration : leaving a population, often from crowded areas or in response to environmental change
    • Immigration : emigrating individuals become immigrants in a new population (joining a population)
    Other factors influencing population growth rate
  • 26. Summary of factors influencing population growth rate Birthrate Death rate Sex Ratio Age distribution Immigration Emigration How many individuals are in a population at any given time?
  • 27.  
  • 28. Population Density (N) —Number of individuals per unit area.
      • High population density may lead to increased competition for resources.
    Population Density Population 1 N = 4 flowers/m 2 N = 12 flowers/m 2 Population 2
  • 29. Population Growth Curve
    • Biotic Potential —Inherent reproductive capacity.
      • Generally, biotic potential is much above replacement level.
        • Natural tendency for increase.
    How to combine number of individuals (N) and population growth rate (r)? When not limited, populations tend to grow exponentially
  • 30. Population Growth Curve
  • 31. Typical Growth Curve
    • Lag Phase —First portion of the curve; slow population growth.
    • Exponential Growth Phase —More organisms reproducing causing accelerated growth; continues as long as birth rate exceeds death rate.
    • Stable Equilibrium Phase —Death rate and birth rate equilibrate; population stops growing.
    If death rate exceeds birth rate, population crashes
  • 32. Carrying Capacity (K)
    • Carrying Capacity —Number of individuals of a species that can be indefinitely sustained in a given area.
  • 33. Carrying Capacity
  • 34. Environmental Resistance
    • Environmental Resistance —Any factor (limiting factor) in the environment influencing carrying capacity. Four main factors:
      • Raw material availability
      • Energy availability
      • Waste accumulation and disposal
      • Organism interaction
  • 35. Logistic Equation Note: This equation is provided only to help. You do not need to memorize it. You will not be asked about the equation on a test. Logistic growth describes this “S” shaped growth curve.
  • 36. Population cycling due to organism interactions Hare population: birth rate limited by food availability death rate determined by predators, food Lynx population: birth and death rate determined by food availability (hares)
  • 37. Population Cycles
  • 38. Remember: Several factors influence population growth rate: Birthrate Death rate Sex Ratio Age Distribution Immigration Emigration But, there are also additional things about the individuals that influence how the population grows
  • 39. Life history traits – characteristics of an individual that influence survival and reproduction Age at maturity 11 - 20 years 3-6 years Atlantic Salmon African elephant 2 months House Mouse
  • 40. Life history traits – characteristics of an individual that influence survival and reproduction Atlantic Salmon African elephant House Mouse 1 calf every 3-8 years 1,500 to 8,000 eggs once 5-8 young every month Number of offspring produced
  • 41. Life history traits – characteristics of an individual that influence survival and reproduction Atlantic Salmon African elephant House Mouse Number of reproductive events ~3 - 10 1 ~6-12
  • 42. Life history traits – characteristics of an individual that influence survival and reproduction Atlantic Salmon African elephant House Mouse Lifespan 60 - 70 years 3-6 years ~2 years
  • 43. By the end of this lecture you should be able to:
    • Explain the three types of survivorship curves.
    • List the factors that influence population growth rates and population density.
    • Describe the difference between exponential and logistic growth and why populations don ’ t grow exponentially forever.
    • Tell the four main factors determining carrying capacity.
    • Explain why populations cycle.
    • Know the key life history traits.