Chapter 24

• Carrying capacity

  maximum size of a population
• Label the phases in a population growth curve

  A) slow growth

  B) rapid growth

  C) stable state, no growth

  D) carrying capacity

  
• Explain phase 1 of a population growth curve

  • slow growth
  • small number of individuals present reproduce increasing the total population - birth rate higher than death rate so pop increases
• Explain phase 2 of a population growth curve

  • rapid growth
  • as number of breeding individuals increases, total population multiplies exponentially
  • no constraints act to limit the population explosion
• Explain phase 3 of a population growth curve

  • stable state
  • further growth is prevented by external constraints
  • birth rates & death rates are approximately equal
  • slight increases & decreases can be accounted for by fluctuations in limiting factors (e.g. presence of predators)
• Limiting factors

  determine the size to which a population can grow
• Examples of abiotic limiting factors

  • temperature
  • light
  • pH
  • availability of water or oxygen
  • humidity
• Examples of biotic limiting factors

  • predators
  • disease
  • competition
  • migration
• Immigration 


  • movement of individual organisms into a particular area
  • increases population size
• Emigration 


  • movement of individual organism away from a particular area
  • decreases population size
• Density independent factors 


  • affect a whole population regardless of its size
  • include earthquakes, fires, volcanic eruptions & storms
  • can dramatically change population size & in some cases can remove whole populations of a species from a region
• Interspecific competition


  • competition between different species for the same resource
  • results in reduction of resource available to both populations
  • less well adapted species is likely to be outcompeted - if conditions remain the same the less well adapted species will decline in number until it can no longer exist in habitat alongside the better adapted species
• Competitive exclusion principle 


  where 2 species are competing for limited resources, the one that uses the resources more effectively will ultimately eliminate the other
• Intraspecific competition 


  • members of the same species compete for the same resource
  • availability of resource determines population size - greater availability = larger population can be supported
• Effects of intraspecific competition

  fluctuations in number of organisms present in a population over time

  1. when resource is plentiful in a habitat, all organisms have enough of resource to survive & reproduce - increases population size
  2. as result of increased population, resources are now limited & there is not enough available for all organisms to survive - population decreases
  3. smaller population means less competition exists, so more organisms survive & reproduce - population increases

  
• Predator-prey relationships

  • stage 1: increase in prey population provides more food for predators, so more survive & reproduce - increase in predator population
  • stage 2: increased predator population eats more prey organisms - decreases prey population
  • stage 3: reduced prey population can no longer support large predator population, intraspecific competition for food increases - decrease in predator population
  • stage 4: reduced predator population results in less prey population being killed, more prey survive & reproduce - increase prey population

  
• Conservation

  maintenance of biodiversity through human action or management - also involves restoring ecosystems that have been damaged or destroyed
• Preservation

  protection of an area by restricting or banning human interference, so the ecosystem is kept in its original state
• Reasons for conservation

  • economic - provide resources that humans need to survive & provide an income
  • social - people enjoy the natural beauty of wild ecosystems as well as using them for relaxation & exercise
  • ethical - all organisms have right to exist & most play an important role within organisms - should not have right to decide which organisms can survive, and which we can live w/out
• What is a sustainable resource?

  a renewable resource that is being economically exploited in such a way that it will not diminish or run out
• Aims of sustainability

  • preserve the environment
  • ensure resources are available for future generations
  • allow humans in all societies to live comfortably
  • enable less economically developed countries (LEDCs) to develop through exploiting their natural resources
  • create a more even balance in consumption of these resources between more economically developed countries (MEDCs) & LEDCs
• How does small-scale timber production provide resources in a sustainable way?

  • coppicing - tree trunk cut close to ground, new shoots form from cut surface & mature, shots are cut & in their place more produced
  • rotational coppicing used - woodland divided into sections, allowing previously coppiced sections to regrow before repeating cycle - maintains biodiversity as the trees never grow enough to block out the light - succession cannot occur & more species can survive
  • pollarding may also be used - trunk is cut higher up so animals cannot eat new shoots as they appear
• How does large-scale timber production ensure sustainable production?

  • practise selective cutting - remove only the largest trees
  • replace trees through replanting rather than waiting for natural regeneration - also helps ensure biodiversity & mineral & water cycles maintained
  • plant trees an optimal distance apart to reduce competition = higher yields
  • manage pests & pathogens to maximise yields
  • ensure areas of forest remain for indigenous people
• Disadvantage of large-scale timber production

  • habitats are destroyed
  • soil & minerals reduced
  • bare soil which is left is susceptible to erosion
  • trees are important for binding soil together, removing water from soil & maintaining nutrient levels through role in carbon & nitrogen cycles
• How is fishing made sustainable?

  • fishing quotas provide limits on the numbers of certain species of fish that are allowed to be caught in a particular area
  • use of nets w diff mesh sizes
  • commercial & recreational fishing allowed only at certain times - protects breeding season of some fish species & allows fish levels to increase back to sustainable level
  • fish farming introduced to maintain supply of protein food whilst preventing loss of wild species