AP Bio Unit Topics 3 & 4

• population: a group of individuals of the same species living in an area
• population ecology: analyzes the factors that affect population size and how and why it changes over time
• density: the number of individuals per unit area
• density can be determined by:

  • counting the number of individuals in the population (rarely done)
  • sampling techniques (count small areas, average the areas, and then use the averages to estimate total population size)
• knowing a population's density provides more information about its relationship to the resources it uses
• dispersion: the pattern of spacing among individuals within a population
• types of dispersion: clumped, uniform, random
• clumped dispersion: individuals gather in patches
• uniform dispersion: evenly spaced individuals in a population

  • can be due to territoriality
• random dispersion: unpredictable spacing; uncommon
• the size of a population is not static, affected by:

  • births/deaths
  • emigration/immigration
  • demography
• Demography: the study of the vital statistics of populations and how they change over time
• life table: an age-specific summary of the survival pattern of a population
• life table is represented by a survivorship curve
• type 1 curve: low death rate during early/middle life and high death rate later in life
• type 2 curve: constant death rate over the lifespan of the organism
• type 3 curve: high death rate early in life, lower death rate (for those that survive early life)
• exponential growth model: a population living under ideal conditions (ie easy access to food, abundant food, free to reproduce etc)

  • population grows rapidly
• a population growing exponentially grows at a constant rate

  • J shaped curve
• logistic growth model: the per capita rate of increase approaches 0 as the population size nears its carrying capacity

  • the density of individuals exceeds the systems resource availability
• populations are influenced by natural selection and environmental factors
• life history: the traits that affect an organism's schedule of reproduction and survival
• three variables affect life history

  • when reproduction begins
  • how often the organism can reproduce
  • the number of offspring produced per reproductive episode
• k-selection (density-dependent selection): seen in high density populations that are close to carrying capacity (K)
• r-selected (density-independent selection): seen in low density populations with little competition
• density-dependent regulation: as a population increases, factors can slow or stop growth by decreasing birth rate and increasing death rate
• examples of density-dependent regulation: competition, predation, toxic wastes, territoriality, disease, intrinsic factors (ie reproduction rates)
• density-independent regulation: factors that exert their influence on population size, but the birth/death rate of a population does not change
• examples of density-independent regulation: weather, climate, natural disasters