Chapter 4

• Population Ecology


  Focuses on the factors that influence the population's size, growth rate, density, and structure
• Population


  A group of individuals of the same species living in a given area at a given time
• Demographics or Vital Statistics of Populations

  • Population Density
  • Population Size
  • Distribution
  • Age Structure
• Population Density


  The number of individuals of a species per unit area or volume
• Patterns of Dispersion


  • Clumped Pattern
  • Uniform Pattern
  • Random Dispersion
• Clumped Pattern


  Individuals are aggregated in patches
• Uniform Pattern


  Dispersion often results from interactions among the individuals and exhibits an even or homogeneous pattern
• Random Dispersion


  Individuals in a population are spaced in a patternless, unpredictable way
• Factors affecting Population Size

  • Natality (births)
  • Mortality (deaths)
  • Annual Immigration
  • Emigration
• Zero Population Growth


  Interval in which the number of births is balanced by the number of deaths, so the population remains the same
• 2000 mice in one month produces 1000 offspring, 200 mice die in that month
• Exponential Growth


  Occurs in populations that produce offspring throughout the year
• Biotic Potential


  The highest possible growth rate achieved when resources are unlimited
• Factors affecting Biotic Potential

  • Usual number of offspring per reproduction
  • Chances of survival age of reproduction
  • How often each individual reproduces
  • Age at which reproduction begins
• Survivorship Curve


  Probability of cohort members surviving to particular ages
• Types of Survivorship Curves

  • Type I (Mammals, humans)
  • Type II (Hydras, songbirds, small mammals, some invertebrates)
  • Type III (Oysters, many invertebrates, fishes, humans in less developed countries)
• Age Structure


  • Pre-reproductive (0-14 years)
  • Reproductive (15-64 years)
  • Post-reproductive (65 and above)
• Patterns of Age Structure Diagram

  • Pyramid shaped
  • Bell shaped
  • Urn shaped
• Population Growth


  dN/dt = rN (Change in numbers per change in time equals the rate of growth times the number of individuals)
• If r is less than 1, the population is shrinking. If r is exactly 1, there is no change. If r is greater than 1, the population is growing.
• Logistic Growth


  Occurs in populations that produce a single batch of offspring in a year (e.g. insects)
• Carrying Capacity


  The maximum number of individuals determined by the balance between environmental goods/services required and provided
• Carrying capacity is critical to a given area of the environment because the availability of environmental goods and services varies with the type of ecosystem
• Carrying capacity refers to the ability of an ecosystem to provide the same quantity and quality of environmental goods and services over time
• Density-independent factors are factors that affect population growth but are not related to population size, often abiotic factors like weather and natural disasters
• Density-dependent factors are factors related to population size, like predators, parasites and pathogens
• 1. adapted species


  Tend to have rapid reproduction and high mortality of offspring, may frequently overshoot carrying capacity and die back, occupy low trophic levels or be successional pioneers, invest little in individual offspring
• 1. adapted species


  Larger, live longer, mature slowly, produce fewer offspring, have fewer natural predators than species below them in the ecological hierarchy
• Population of the Philippines: 113,955,183 as of July 5, 2023, 119,112,300 as of July 5, 2024, 108,149,143 as of July 10, 2019, 108,450,027 as of September 25, 2019
• The 2019 population is 108.12 million, according to the latest UN estimates
• Population growth rate: 1.72% between 2010 and 2015
• Birth rate: 24.62 births / 1000 population (2013 est.)
• Death rate: 4.95 deaths / 1000 population (2013 est.)
• Age Structure of Philippines Population

  • 0-14 years 34.6%
  • 65 and over 4.3%