POPULATOPN

• Population ecology


  The study of how and why populations change
• Population


  Group of individuals of a single species that occupy the same general area, rely on the same resources, are influenced by the same environmental factors, and are likely to interact and breed with one another
• Population ecology


  • Concerned with changes in population size and the factors that regulate populations over time
  • Population ecologists might use statistics (number and distribution of individuals) to describe a population
• Population dynamics


  The interactions between biotic and abiotic factors that cause variation in population sizes
• Population growth is an important aspect of population dynamics
• Births and immigration increase population, deaths and emigration decrease population
• Population ecology plays a key role in applied research, such as managing wildlife populations, developing sustainable fisheries, and controlling the spread of pests and pathogens
• Conservationists use population ecology concepts to help identify and save endangered species
• Population density


  The number of individuals of a species per unit area or volume
• Estimating population density


  1. Total count method

  2. Sampling method
• Quadrat sampling method


  Widely used in plant studies
• Mark-recapture method


  Used for very mobile or elusive species

  
• Dispersion pattern


  The way individuals are spaced within their area
• Dispersion patterns


  • Clumped
  • Uniform
  • Random
• Estimates of population density and dispersion patterns enable researchers to monitor changes in a population and to compare and contrast the growth and stability of populations in different areas
• Life tables


  Track survivorship, the chance of an individual in a given population surviving to various ages
• Survivorship curves


  Plots of the number of survivors versus relative age
• Survivorship curve types


  • Type I
  • Type II
  • Type III
• Population change


  N = (B + I) - (D + E), where N is the change in population, B is births, I is immigration, D is deaths, and E is emigration
• The exponential growth model describes the rate of population increase under ideal conditions
• Exponential growth model


  G = rN, where G is the growth rate, r is the per capita rate of increase, and N is the population size
• The exponential growth model assumes unlimited resources and space, but in nature, limiting factors lead to the logistic growth model
• r


  Per capita rate of increase (the average contribution of each individual to population growth for the time interval)
• Rabbits have a higher r than elephants


  Bacteria have a higher r than rabbits
• When a population is expanding without limits, r remains constant and the rate of population growth depends on the number of individuals already in the population (N)
• The larger the population size, the more new individuals are added during each time interval
• Exponential growth model


  Gives an idealized picture of unlimited population growth, where the population grows extremely rapidly and at a constant rate if a population has a constant birth rate through time and is never limited by food or disease
• Even elephants, the slowest breeders on the planet, would increase exponentially if enough resources were available
• Limiting factor


  Environmental factors that restrict population growth rate
• Logistic growth


  A description of idealized population growth that is slowed by limiting factors as the population size increases
• Carrying capacity


  The maximum population size that a particular environment can sustain
• Logistic growth model formula

  G = rN(K-N)/K

  Where:

  G = growth rate of population

  N = population size

  r = per capita rate of increase

  K = carrying capacity
• The value of K varies, depending on the species and the resources available in the habitat
• Organisms interact with other organisms in their communities, including predators, parasites, and food resources, that may affect Carrying Capacity
• Changes in abiotic factors may also increase or decrease carrying capacity
• The concept of carrying capacity expresses an essential fact of nature: Resources are finite!
• Density-dependent factors


  Limiting factors whose intensity is related to population density
• Density-dependent factors


  • Appear to restrict growth in natural populations

  Examples: Intraspecific competition, availability of space
• Density-independent factors


  A population-limiting factor whose intensity is unrelated to population density, affected by abiotic factors such as weather, climate, and disturbances
• Life history


  The traits that affect an organism's schedule of reproduction and death