Population dynamics


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  • A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring
  • Compare birth rate to death rate
  • dN/dt = change in number of individuals per unit time
  • dN/dt = change in number of individuals per unit time
  • dN/dt = change in number of individuals per unit time
  • Kaibob deer – in AZ, kill predators to protect deer, but then grew rapidly, until ate resources and began to starve.
  • Population dynamics

    1. 1. Population Dynamics Populations.ppt
    2. 2. Vocabulary <ul><li>Population </li></ul><ul><li>Biotic Potential </li></ul><ul><li>Carrying Capacity </li></ul><ul><li>r-Selection </li></ul><ul><li>K-Selection </li></ul><ul><li>Survivorship Curve </li></ul>Populations.ppt
    3. 3. Population <ul><li>number of individuals of a species in a defined place and time. </li></ul>Populations.ppt Dynamic characteristics of populations
    4. 4. Dynamic characteristics of populations <ul><li>Population size, number of individuals (N) </li></ul><ul><li>Density (N/ area) </li></ul><ul><li>Dispersion </li></ul><ul><ul><li>Random </li></ul></ul><ul><ul><li>Uniform </li></ul></ul><ul><ul><li>Clumped </li></ul></ul>Populations.ppt
    5. 5. Dynamic characteristics of populations <ul><li>Age distribution, </li></ul><ul><ul><li>proportions of young, middle-aged, old </li></ul></ul><ul><ul><li>Differs in growing, stable, decreasing populations </li></ul></ul>Populations.ppt
    6. 6. Changes in populations <ul><li>Growth </li></ul><ul><ul><li>Expansion of species’ populations may lead to evolution of new species </li></ul></ul><ul><li>Decline </li></ul><ul><ul><li>Shrinking species’ populations may lead to extinction </li></ul></ul><ul><ul><ul><li>Small populations </li></ul></ul></ul><ul><ul><ul><li>Narrowly specialized species </li></ul></ul></ul>Populations.ppt
    7. 7. Changes in populations <ul><li>Δ N = +B +I –D –E </li></ul><ul><ul><li>+B = births (birth rate) </li></ul></ul><ul><ul><li>+I = immigrants (immigration rate) </li></ul></ul><ul><ul><li>– D = deaths (death rate) </li></ul></ul><ul><ul><li>– E = emigrants (emigration rate) </li></ul></ul><ul><ul><li>(For many [most] natural populations I and E are minimal.) </li></ul></ul>Populations.ppt
    8. 8. Population growth <ul><ul><li>B > D </li></ul></ul><ul><ul><li>Exponential growth, dN/dt = rN </li></ul></ul><ul><ul><ul><li>N = number, pop.size </li></ul></ul></ul><ul><ul><ul><li>r = biotic potential (maximum reproductive capacity of an organism if resources are unlimited) </li></ul></ul></ul>Populations.ppt
    9. 9. Population growth <ul><li>Exponential growth unlimited </li></ul><ul><ul><li>dN/dt = rN </li></ul></ul><ul><li>Unrealistic </li></ul>
    10. 10. Carrying Capacity <ul><li>The population size that the environment can sustain for a long period of time. </li></ul><ul><li>Determined by </li></ul><ul><ul><li>Renewable resources (water, light, etc) </li></ul></ul><ul><ul><li>Nonrenewable resources (land) </li></ul></ul>
    11. 11. Population growth <ul><li>Logistic growth, </li></ul><ul><ul><li>dN/dt = rN (1 - N/K) </li></ul></ul><ul><ul><ul><li>N = number, population size </li></ul></ul></ul><ul><ul><ul><li>r = biotic potential </li></ul></ul></ul><ul><ul><ul><li>K = carrying capacity </li></ul></ul></ul><ul><ul><li>Better represents real populations </li></ul></ul>
    12. 12. Population growth <ul><li>Logistic growth, </li></ul><ul><ul><li>dN/dt = rN (1 - N/K) </li></ul></ul><ul><ul><ul><li>N = number, population size </li></ul></ul></ul><ul><ul><ul><li>r = biotic potential, “intrinsic rate of increase.” </li></ul></ul></ul><ul><ul><ul><li>K = carrying capacity </li></ul></ul></ul><ul><ul><li>Better represents real populations </li></ul></ul>
    13. 13. Logistic model <ul><li>Logistic model works, to a point. </li></ul><ul><ul><li>Real organisms have time lags for growth, time to develop eggs, flowers, etc. </li></ul></ul><ul><ul><li>Real populations may exceed carrying capacity. </li></ul></ul><ul><ul><ul><li>Kaibab Deer </li></ul></ul></ul>Populations.ppt
    14. 14. Various species have various strategies for coping with a variable world. Populations.ppt
    15. 15. Two general types of Reproductive Strategies
    16. 17. Survivorship Curves <ul><ul><li>• Plots surviving individuals at different age groups </li></ul></ul><ul><ul><li>r-strategists have Type III </li></ul></ul><ul><ul><li>K-strategists have Type I </li></ul></ul>Populations.ppt
    17. 18. Survivorship Curves Populations.ppt Type I survivorship curves are characterized by high survival in early and middle life, followed a rapid decline in survivorship in later life. Humans are one species that show this pattern of survivorship. Type II curves are an intermediate between Type I and III, where roughly constant mortality rate is experienced regardless of age. Some birds follow this pattern of survival. In Type III curves, the greatest mortality is experienced early on in life, with relatively low rates of death for those surviving this bottleneck. This type of curve is characteristic of species that produce a large number of offspring. One example of a species that follows this type of survivorship curve is the cockroach.