1 / 34

Population Growth

Population Growth. December 7, 2010 Text p . 660-669. Population Dynamics. Populations always changing in size Deaths, births Main determinants (measured per unit time): Natality = number of births Mortality = number of deaths Emigration = # of individuals that move away

Télécharger la présentation

Population Growth

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Population Growth December 7, 2010 Text p. 660-669

  2. Population Dynamics • Populations always changing in size • Deaths, births • Main determinants (measured per unit time): • Natality = number of births • Mortality = number of deaths • Emigration = # of individuals that move away • Immigration = # of individuals that move into an existing population

  3. Effect on Determinants • The determinants vary from species to species • Environmental Conditions • Fecundity • Potential for a species to produce offspring in one lifetime vs.

  4. Limits on Fecundity • Fertility often less than fecundity • Food availability • Mating success • Disease • Human factors • Immigration/Emigration

  5. Survivorship • 3 patterns in survivorship of species • Type I • Low mortality rates until past reproductive years • Long life expectancy • Slow to reach sexual maturity, produce small numbers of offspring

  6. Type II • Uniform risk of mortality throughout life

  7. Type III • High mortality rates when they are young • Those that reach sexual maturity have reduced mortality rates

  8. Calculating Changes in Population Size Population Change = [(birth + immigration) – (deaths + emigration)] x 100 (%) initial population size (n) • Can be used to calculate growth rate of a population in a give time period • Positive Growth: Birth + Immigration > Death + Emigration • Negative Growth: Birth + Immigration <Death + Emigration

  9. Open/Closed Population • Growth can depend on type of population • Open: influenced by natality, mortality and migration • Closed: determined by natality and mortality alone

  10. Biotic Potential • The maximum rate a population can increase under ideal conditions • Or intrinsic rate of natural increase • Represented as r

  11. Carrying Capacity • Maximum number of organisms sustained by available resources • Represented as k

  12. Population Growth Models • Basic model • No inherent limit to growth Hypothetical model

  13. Geometric Growth Model • In humans, growth is continuous (deaths and births all times of year) • In other organisms deaths may be year round, but births may be restricted • Population typically grows rapidly during breeding season only • Growth rate is constant at fixed intervals of time (breeding seasons)

  14. Geometric Growth Model λ = the geometric growth rate N = population size t = time N (t + 1) = population size in year X λ = N (t + 1) or N(t + 1) = N(t) λ N (t) So... N(t) = N(0) λt

  15. Initial population of 2000 harp seals, gives birth to 950 pups, and during next 12 months 150 die Assuming geometric growth, what is the population in 2 years? Year 1, Population Change = 950 births – 150 deaths = 800 Initial Population N(0) = 2000 Population at end of Year 1, N(1) = 2000 + 950 – 150 Geometric Growth Rate (λ) = 2800 = 1.4 2000 Year 2 (t = 2): N(t) = N(0) λt N(2) = (2000) (1.4)2 = 3920

  16. Exponential Growth Model • Populations growing continuously at a fixed rate in a fixed time interval • The chosen time interval is not restricted to a particular reproductive cycle • Can determine the instantaneous growth rate, which is the intrinsic (per capita) growth rate

  17. Intrinsic growth rate (r) N = population size dN = instantaneous growth rate of population dt Population Growth Rate: dN = rN dt Population’s Doubling time (td) = 0.69 r

  18. 2500 yeast cells growing exponentially. Intrinsic growth rate (r) is 0.030 per hour Initial instantaneous growth rate: dN = rN dt = 0.030 x 2500 = 75 per hour Amount of time for population to double in size: Td = 0.69 = 0.69 = 23 hrs r 0.030

  19. Population size after each of 4 doubling times: Td = 23 hrs, initial population = 2500

  20. Curve Shapes Exponential = J-shaped curve Smooth vs. geometric, which fluctuates

  21. Logistic Growth Model • Geometric and exponential assume population will grow at same rate indefinitely • This means intrinsic growth rate (r) is a maximum (rmax) • In reality, resources become limited over time • Population nears the ecosystem’s carrying capacity, and growth rate drops below rmax

  22. Logistic Growth Model • Growth levels off as size of population approaches its carrying capacity Instantaneous growth rate: rmax: maximum intrinsic growth rate N: population size at any given time K: carrying capacity of the environment

  23. Logistic Growth Curve • S-shaped curve (sigmoidal) • 3 phases • Lag, Log, Stationary • At stationary phase, population is in dynamic equilibrium

  24. Useful model for predictions • Fits few natural populations perfectly

  25. r & K Selection • Species can be characterized by their relative importance of r and K in their life cycle

  26. r-Selected Species Carrying capacity, K • Rarely reach K • High biotic potential • Early growth • Rapid development • Fast population growth Population numbers (N) r-selected species Time

  27. K-Selected Species Carrying capacity, K • Exist near K most of the time • Competition for resources important • Fewer offspring • Longer lives K-selected species Population numbers (N) Time

  28. Work: Text Page 669, # 1-5

More Related