Limit Factors

• Limiting Factor


  Anything that drives a population's size and slows or stops it from growing
• Types of limiting factors

  • Biotic
  • Abiotic
• Carrying capacity


  The maximum size of the population a habitat can support
• Shelford's Law states that the abundance or distribution of an organism can be controlled by certain factors
• Shelford's Law


  Organisms can tolerate (or survive within) a certain range of a particular factor, but cannot survive if there is too much or too little of the factor
• Population


  A group of individuals of the same species that live together in a region
• Population dynamics


  Changes that are predicted to occur in the members of the population
• Population dynamics


  Can be measured in terms of size, age structure, and dispersion
• Factors affecting population size

  • Natality
  • Mortality
  • Immigration
  • Emigration
• Natality


  The number of individuals who are born alive
• Mortality


  The number of individuals who die
• Immigration


  The number of individuals that enters a population
• Emigration


  The number of individuals that move out of a population
• Population growth rate


  The amount by which a population’s size changes in a given time
• Population growth rate


  (Birth rate + Immigration) – (Death rate + Emigration) = growth rate
• Age Structure


  The number or percentage of males and females in young, middle, and older groups
• Age Structure groups


  • Pre-reproductive (ages 0-14)
  • Reproductive (ages 15-44)
  • Post-reproductive (ages 45 and older)
• Dispersion


  Describes the distribution of individuals within the population
• Dispersion types


  • Clumped
  • Uniform
  • Random
• Population Growth Patterns

  • Exponential growth pattern (J curve) occurs in an ideal, unlimited environment
  • Logistic growth pattern (S curve) occurs when environmental pressures slow the rate of growth
• Population Density


  The measure of how crowded the population is or the number of individuals in a given space
• For example, the 2019 population density in the Philippines is 363 people per sq km calculated on a total land area of 298,170 sq km
• Types of limiting factors

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


  • Natural catastrophes
• Reproductive Strategies


  • R-selected: lives in unstable and unpredictable environments, produces many offspring with short life expectancy
  • K-selected: lives in more stable environments, few but long-lived offspring
• Ecological Succession


  The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process
• Environmental Problems Related to Population Growth: Overpopulation, Overconsumption, Technological advances
• Population Dynamics and Sustainable Goals

  The population, consisting of people all over the world, is at the center of sustainable development
• UN Population Growth and Challenges: World population projected to reach 11 billion by 2021, with rapid growth rates varying across regions