Module 5

• Microorganisms are known to be key drivers of global biogeochemical cycles for their roles in fixing both carbon and nitrogen into organic matter
• The human population contributes to global change by altering biogeochemical cycles
• Demographic factors


  Birth, death, immigration, and emigration
• Members of a population enter through birth and immigration, and exit through death and emigration
• Visual records of demographic factors

  • Life tables
  • Survivorship curves
  • Age structures
• Exponential growth model


  Continuous population increase in an unlimited environment and yields a J-shaped curve
• Logistic growth model


  Population growth rate plateaus when resources get diminished and produces an S-shaped population growth curve
• Carrying capacity


  The total number of individuals that the environment can support
• Environmental checks on population growth

  • Density-dependent factors
  • Density-independent factors
• Density-dependent factors


  Biotic factors like disease, competition and predation which limit population growth
• Density-independent factors


  Abiotic factors like temperature, weather, light intensity that exert the same influence on the population regardless of population size
• Knowledge of population dynamics can help relate the complex interwoven connections between population ecology and the sustainable use of biological resources
• Demographic transition is the transition from high birth and death rates to low birth and death rates as a country develops
• The population of Manila is growing rapidly, reaching over 20 million people
• Life tables are a record of the birth and death rates for organisms at different life stages.
• A simplified graphical presentation of elements of the life table that shows what fraction of a population survives from age to next is called a survivorship curve.
• The age structure is literally a “groufie” of a population at a specific moment in time. Members of this population are clustered according to age and sex categories.
• Environmental resistance factors

  • Food
  • Diseases
  • Predators
• Type I Survivorship

  • Convex Curve
  • Late loss
  • Majority reaches maturity
  • Typical of k selected species
  • Elephants, humans, annual plants
• Type II Survivorship

  • Diagonal Curve
  • Constant loss
  • Independent of Age
  • Birds, rodents, hydra, perennial plants
• Type III Survivorship:

  • Early loss
  • Low mortality after maturity
  • Typical of r-selected species
  • Oysters, small fish, trees