Populations

• Ecology


  The study of the interrelationships between organisms and their abiotic and biotic environment
• Ecosystem


  A characteristic community of independent species interacting with the abiotic components of their habitat
• Community


  Interacting populations of two or more species in the same habitat at the same time
• Habitat


  The place in which an organism lives
• Population


  An interbreeding group of organisms of the same species occupying a particular habitat
• Abiotic environment


  The non-living conditions affecting a community or an organism (e.g., temperature, soil, pH, light intensity)
• Biotic environment


  The living conditions affecting a community or an organism (e.g., competition, predation, disease)
• Niche


  The role and position a species have in its environment, including all interactions with the biotic and abiotic factors of its environment
• Ecosystems


  • The intensity of energy flowing through the ecosystem varies
  • Biological cycles vary the mineral availability
  • Habitats changes over time as succession occurs
  • New species arrive and some species are no longer present
• Birth rate


  The reproductive capacity of a population. It is the number of new individuals derived from reproduction per unit time
• Death rate


  The ratio of deaths in a population compared to the total population
• Immigration


  The movement of individuals into a population of the same species
• Emigration


  The movement of individuals out of a population of the same species
• Birth rates, death rates, immigration and emigration

  Affect population size
• Calculating population size


  Population size = (birth rate + immigration) - (death rate + emigration)
• Factors that slow down population growth

  • Low availability of nutrient or food
  • Competition
  • Disease and parasitism
  • Overcrowding
  • Predation
  • Accumulation of toxic waste
  • Change in climate
  • Change in temperature
• Factors that cause a population crash

  • Intraspecific competition for food mates, shelter etc
  • Predation
  • Climate change
  • Disease outbreaks
• One step growth curve

  1. Lag phase

  2. Exponential phase

  3. Stationary phase

  4. Death phase
• Lag phase


  A period of slow growth, reproduction, or cell division
• Exponential phase


  As numbers increase, there are more individuals available for reproduction, so the rate of reproduction increases rapidly
• Stationary phase


  • When birth rate is equal to the death rate
  • The carrying capacity for the population has been reached
  • The population is not absolutely constant as it fluctuates around the carrying capacity depending on factors such as the number of predators, availability of food etc
• Death phase


  Factors that slow down population growth become more significant, and the population size decreases until the death rate is greater than the birth rate
• Populations are sometimes plotted on logarithmic graphs because when a population increase is very large (e.g., bacteria), the range of numbers is too great to plot on a linear scale
• Carrying Capacity

  
  

  1. The maximum number around which a population fluctuates in a given environment.
  2. Limiting factors (e.g., low food availability, overcrowding, predation) cause population to fluctuate around this number.
• Intraspecific competition


  Competition between individuals from the same species
• Density-Dependent Factors:

  Factors affecting more of the population in denser conditions. Biotic, including disease, parasitism, and food depletion.
• Density-Independent Factors:

  Abiotic factors; effect is consistent regardless of population density. Often due to sudden changes like fire or flood.
• Negative Feedback in Population Dynamics

  
  

  1. If population rises above the set point, density-dependent factors increase mortality or reduce breeding, causing population to decline.
  2. If population is temporarily relieved, it can rise again.
• Abundance


  The number of individuals in a species in a given area
• Estimating abundance


  1. Mark-release-recapture

  2. Kick sampling

  3. Using a quadrat
• Measuring plant abundance using a quadrat

  Calculate the mean number per area (i.e., the density number/m2), estimating the percentage cover of a plant or estimating the percentage frequency
• Distribution


  The area or volume in which the organisms of a species are found
• Analysing distribution in a non-uniform habitat

  Use a transect
• The most significant energy source for ecosystems is light energy, radiating from the sun because light is the energy source for photosynthesis
• Food chains


  A means of transferring biomass
• Trophic level


  A feeding level. It is the number of times that energy has been transferred between the Sun and successive organisms along a food chain
• Biomass


  The mass of biological material in living, or recently living organisms
• Producers


  Green plants, cyanobacteria and some Protoctista are producers as they incorporate the suns energy into carbohydrates, which are the food and energy source for successive organisms in the food chain
• Only a small proportion of the total energy that reaches the plant as light is incorporated into the plant's tissues
• Carnivores


  Secondary, tertiary ad higher consumers