6.3.2 Populations

• Carrying capacity

  is the maximum population size that a habitat can support, defined by the presence of limiting factors
• Factors that limit the carrying capacity


  • food
  • water
  • light
  • oxygen
  • nesting sites
  • shelter
  • parasites
  • predators
• typical predator-prey relationship

  • prey is eaten by predator, predator population increases and prey population decreases
  • fewer prey results in increased competition for food, so predator population decreases
  • fewer predators means more prey survives, the cycle begins again
• interspecific competition - between different species


  • different species compete for the same resources
  • both have reduced resources, limiting growth and reproduction - populations decline
  • species distribution is effected - less well adapted species are out-competed and struggle to survive
• intraspecific competition - within a species


  • compete with eachother for the same resources
  • population varies around the carrying capacity
  • dependent on how resources compare to population size
  • density dependent factors
• Predation


  an organism kills and eats another organism
• Standard growth curve

  + critical phase

  A) Lag

  B) Exponential

  C) Stationary

  D) Carrying capacity

  
• Standard growth curve - lag phase


  • acclimatisation
  • micro-organisms switch on metabolic pathways
  • making shelter
  • finding food
  • low reproduction
• Standard growth curve - critical point

  • numbers have increased sufficiently
• Standard growth curve - log / exponential growth phase

  • population increases at regular intervals
  • rate depends on all factors, biotic and abiotic density dependent factors
  • biotic potential/intrinsic rate of increase - r
• Standard growth curve - stationary phase

  • death rate = birth rate
  • carrying capacity - k
  • population may vary around k
• Standard growth curve - death/decline phase


  • occurs in 'closed', limited habitat
• organism's niche


  its role in the ecosystem, includes its trophic level and all of its interactions with other organisms
• fundamental niche

  • the full range of environmental conditions that a species could occupy
  • limiting factors are not an issue, an ideal environment
  • large
• realised niche

  • part of a fundamental niche that an organism occupies
  • takes account of limiting factors present in their habitat
  • small
• R - strategist species


  • reproduce quickly
  • limiting factors don't have time to act
  • rapidly exploit habitat
  • environmental resistance causes a 'bust'
  • pioneer species/rats/bacteria
• K - strategist species

  • population size determined by k
  • gradual increase to k as limiting factors take effect
  • dominant competitors/climax species
• Competitive exclusion principle


  states that two species competing for the same resources cannot co-exist
• What is the definition of a fundamental niche?


  A fundamental niche refers to the full range of environmental conditions and resources a species could potentially use in the absence of competition.
• What are the key points about a fundamental niche?


  • It's a theoretical concept.
  • It's broader than actual usage.
  • It's determined by physiological tolerances.
• What are the components of an ecological niche?


  • Resources used
  • Habitat preferences
  • Interactions with other species
  • Impact on the environment