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2011-12-11 23:17:28
population ecology

BIOL 1215-18 Population Ecology
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  1. Populations Ecology:
    Study of populations relative to environment
  2. Environmental Influencing:
    • Density
    • Distribution
    • Age Structure
    • Population Size
  3. Population:
    Group of individuals of single species living in same area.
  4. Density:
    • Number of individuals per unit area or volume.
    • Result of processes that add or remove inividuals from population.
  5. Dispersion:
    • Pattern of spacing of individuals in boundaries of population.
    • Influenced by environmental and social factors.
  6. Calculating Density:
    • Impractical or impossible to count all individuals in a population.
    • Sampling techniques estimate density and total population size.
    • Population size estimated from small samples, index of population size, or mark-recapture method.
  7. Three Methods for Marking:
    • Bands on Feet (Birds)
    • Radio Collars (Wolves)
    • Recognizing Individual Uniqueness (Dorsal fin on Whales)
  8. Assumption for Marking Techniques:
    Method will not affect organisms way of life.
  9. Processes that Change a Population Size:
    • Immigration - Influx of new individuals from other areas
    • Emigration - Movement of individuals out of a population
  10. Clumped Dispersion:
    • Individuals aggregate in patches.
    • Influenced by resource availability and behavior.
  11. Uniform Dispersion:
    • Individuals are evenly distributed.
    • Influenced by social interactions like territoriality.
  12. Random Dispersion:
    • Position of each individual is independent of others.
    • Occurs in absence of strong attractions or repulsions.
  13. Demographics:
    • Study of vital statistics of a population and change over time.
    • Death rates and birth rates are important to demographers.
    • Life tables to study death rates.
    • Reproductive tables to study birth rates.
  14. Life Tables:
    • Age-specific summary of the survival pattern of population.
    • Best by following fate of cohorts.
  15. Cohorts:
    A group of individuals of the same age.
  16. Calculation of Death Rate:
    [(Deaths During Year)/(Alive At Start)] = Death Rate
  17. Survivorship Curve:
    Graphic way of representing data in a life table.
  18. Survivorship Curve Classification:
    • Type I - low death rates early-mid life, increase in older age.
    • Type II - constant death rate.
    • Type III - high death rates early, lower death rate for survivors.
  19. Reproductive Rates:
    Species with sexual reproduction, concentrate on females.
  20. Reproductive Table:
    • Also called a Fertility Schedule.
    • Age-specific summary of reproductive rates in population.
    • Describes reproductive pattern of population.
  21. Calculation of Average Number of Female Offspring:
    [(Females Weaning a Litter)X(Females in Litter)] = Female Offspring
  22. Traits Affecting Reproduction and Survival Schedule:
    • Age which reproduction begins.
    • How often organism reproduces.
    • How many offspring produced during reproductive cycle.
  23. Life History Traits:
    Evolutionary development in physiology and behavior of organism.
  24. Semelparity:
    • Big-bang reproduction.
    • Reproduce once and die.
    • Variable or unpredictable environments favor big-bang reproduction.
  25. Iteroparity:
    • Repeated reproduction.
    • Produce offspring repeatedly.
    • Dependable environments favor repeated reproduction.
  26. Survival and Reproduction:
    Finite resources lead to trade-offs.
  27. For Finite Resources:
    • Reduced brood size has higher survivability because there of lower population of species (less consumption and more dispersion of resources)
    • Enlarged brood size has lower survivability because there of higher population of species (more consumption and less dispersion of resources)
  28. Survival:
    • Parental care of smaller broods facilitate survival of offspring.
    • Some plants have many small seeds ensuring growth and reproduction.
    • Other plants have few large seeds giving large energy store to help seedlings.
  29. Modeling Population Growth:
    • Change in population size = Births + Immigrants - Deaths - Emigrants
    • Ignoring immigration and emigration, population's growth rate (per capita increase) equals birth rate minus death rate.
  30. Per capita rate of increase(r):
    • Difference of per capita birth rate(b) and per capita death rate(d)
    • r = b-d
    • Increasing if birth rate is higher than death rate (r>0).
    • Decreasing when birth rate is lower than death rate (r<0).
    • Zero population growth if birth rate equals the death rate (r=0).
  31. Calculating population size (N):
    Nt+1 = rNt + Nt
  32. Population growth over many time intervals:
    • ΔN/ Δt = rN
    • Discrete time interval, no immigration or emigration.
  33. Population Growth Instantaneously:
    • dN / dt = rinstN
    • rinst is the instantaneous per capita rate of increase.
  34. Exponential Growth Model:
    • To study population growth in idealized situation.
    • Ideal situations help us understand capacity and factors of species to grow.
  35. Exponential Population Growth:
    • Population increase under ideal conditions.
    • Rate of reproduction is at maximum (intrinsic rate of increase).
    • dN = rmaxN
    • dt
    • If r > 0, population increase is rapid.
  36. J-Shaped Curve:
    • Result of exponential population growth.
    • Population growth depends on the value of N and r,.
    • Thus population increase is greater as time passes.
    • Characterizes some rebounding populations.
  37. Logistic Growth Model:
    • Exponential growth cannot be sustained for long in any population.
    • Realistic population model limits growth by using carrying capacity.
    • Fit few real populations but useful for potential growth.
    • Carrying capacity(K) is max population size environment can support.
    • Per capita rate of increase declines as carrying capacity reached.
    • dN = rmax N(K-N)
    • .dt _ _____ _ K
    • (K-N)/K close to 1, per capita rate of increase approaches maximum rate.
    • (K-N)/K is close to 0, per capita rate of increase is small.
  38. Sigmoid Curve:
    • Result of logistic model of population growth.
    • Some overshoot K before settling down to stable density.
    • Some fluctuate greatly and difficult to define K.
    • Some show an Allee effect.
  39. Allee Effect:
    Difficult time surviving/reproducing if population size is small.
  40. Logistic Model and Life Histories:
    • Life history traits favored by natural selection vary with population density and environmental conditions.
    • K-selection and r-selection are oversimplifications but stimulated alternative hypotheses of life history evolution.
  41. K-selection:
    • Density-Dependent selection.
    • Selects life history traits sensitive to population density.
  42. r-selection:
    • Density-Independent selection.
    • Selects life history traits maximizing reproduction.
  43. Factors Affecting Population Growth:
    • Environmental factors that stop a population from growing.
    • Radical Fluctuations in size over time.
  44. Density-Independent Populations:
    Birth rate and death rate do not change with population density.
  45. Density-Dependent Populations:
    • Birth rates fall and death rates rise with population density.
    • Negative feedback that regulates population growth.
    • Affected by competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors.
  46. Competition for Resources:
    Crowded populations intensifies competition for resources resulting in lower birth rates.
  47. Territoriality:
    • In vertebrates and invertebrates competition for territory limit density.
    • Cheetahs use chemical communication to warn other cheetahs of their boundaries.
    • Oceanic birds exhibit territoriality in nesting behavior.
  48. Disease:
    • Influences the health and survival of organisms.
    • Pathogens can spread more rapidly in dense populations.
  49. Predation:
    Population growth attracts predator preferential.
  50. Toxic Wastes:
    Accumulation contribute to density-dependent regulation of population size.
  51. Intrinsic Factors:
    Physiological factors regulate population size.
  52. Population Dynamics:
    • Challenged hypothesis that large mammal populations are relatively stable.
    • Biotic and abiotic factors influence population size.
    • Some undergo regular booms-and-bursts cycles.
  53. Global Human Population:
    • No population can grow indefinitely.
    • Increased slowly until 1650 and began to grow exponentially.
    • Still growing but began to slow during the 1960s.
  54. Regional Human Population Configurations:
    • Zero population growth = High birth rate & High death rate
    • Zero population growth = Low birth rate & Low death rate
    • Demographic transition goes from first state toward second state.
    • Associated increase in quality of health education.
    • Most global population growth concentrated in developing countries.
  55. Age Structure:
    • Relative number of individuals at each age.
    • Age structure diagrams predict population's growth trends.
    • Illuminates social conditions and help plan for the future.
    • Infant mortality and life expectancy at birth vary greatly.
  56. Global Carrying Capacity:
    • Carrying capacity of humans on Earth uncertain.
    • Average estimate is 10-15 billion.
    • Ecological footprint concept summarizes land and water needed to sustain a nation.
    • Measures proximity to carrying capacity of Earth.
    • Great footprint size and ecological capacity variation.