Population Dynamics

POPULATION

  • A group of individuals of a single species inhabiting a specific area at the same time

Population Dynamics

  • Area in population ecology concerned with factors influencing the expansion, decline, or maintenance of populations
  • Includes the effects of: births, deaths, immigration, and emigration

Importance of the Study of Population Dynamics

  • For the Conservation of diverse plants and animals
    •  Determines whether or not a species is going extinct
  • For the Control of noxious pests, including human parasites and pathogens
  • For the Maintenance of economically important animal and plant populations

   

DEMOGRAPHY

  • Describes changes in population throughout the life cycle of the organism
  • Commonly used in human population, but can also be used for general purposes
  • Populations are affected by:
    • Birth (Natality)
    • Death (Mortality)
    • Immigration → new members of the population entering the population but not through birth
    • Emigration → leaving the population and decreasing population size
    • Emigration happens due to some dispersal mechanisms of certain populations
      • Ex: Spiderlings → produce silk and hang on to the tips of leaves, waiting for wind to take them to other places (they balloon themselves to occupy new environments)
      • Allows for the species to be dispersed and prevents competition
    • Dispersal can either increase or decrease local population densities
      • Can lead to population expansion, resulting to an increase in their geographic range
      • Normally happens when environmental conditions in the original habitat become unfavorable
  • Biotic Potential
    • Property or capacity of populations to multiply; maximum reproductive rate of an organism
    • Normally high in most species
    • Influenced by sex ratio and age distribution
    • Favorable environmental conditions enable species to realize their full biotic potential → leads to population increase

Population Growth Models

  • Exponential Growth Model
    • Represents growth of a population without environmental resistance factors
    • No limits to population growth (such as predators, food, etc.)
    • A continuous population increase in an unlimited environment
    • Represented by a J-shaped curve
    • Exponentially rises
  • Logistic Growth Model
    • Shows that when resources are diminished, population growth rate will ultimately plateau
    • Takes into consideration Carrying Capacity
    • The total number of individuals the environment can support
    • Represented by an S-shaped curve
    • Lag-Phase
      • Population size small, resources abundant
    • Log (Exponential) Phase
      • Rapid growth and fast resource utilization
    • Stationary Phase
      • Zero population growth; carrying capacity is reached
    • Death (Decline) Phase
      • Population has exceeded carrying capacity and slowly decreases

Environmental Resistance Factors

  • Limiting factors (ex: raw materials, energy supply and accumulation of waste products)
  • Influenced by the Carrying Capacity of the environment
  • Density-dependent factors
    • Biotic factors, such as diseases and predation, that limit population growth
  • Density-independent factors
    • Abiotic factors, such as temperature and weather, that also influence population growth