human impacts

• climate change


  long term global increase in temperature and shifts in weather patterns
• causes of climate change

  burning of fossil fuels to create energy -> trapped in atmosphere -> temperature in certain areas slowly rise
• dryland salinity


  the accumulation of salt in soil and waterways to levels that are toxic to plants and animals
• causes of dryland salinity

  major contributor to dryland salinity is land clearing

  • causes saline groundwater to rise to surface and become more concentrated
• dryland salinity step by step

  1.native vegetation, plants with deep roots keep water tables low

  2. increased human population -> increased land clearing for agriculture and shallow rooted plants are planted, they don't reach the water tables -> water tables rise -> brings dissolved salts and other minerals

  3. lack of native vegetation allows water to evaporate at surface -> leaves behind dissolved salts -> salt is crystalised
• what does dryland salinity cause


  declining vegetation

  reduced biodiversity

  sick and dying trees
• eutrophication


  excessive amounts of nutrients in a body of water, usually cause by runoff from agricultural areas
• what does eutrophication cause

  decrease in oxygen supply

  death of plants and animals in ecosystem
• how does eutrophication occur

  1.nutrient runoff from agricultural fields into lakes and rivers

  2. rivers flow into ponds -> increased nutrients allows aquatic plants and algae population to increase

  3. competition increases -> the ecosystem in overcrowded and plants and animals that cannot overcome the competition die

  4. microbes feeding on dead organisms decompose plans and algae

  5. microbe population increases -> increased levels of oxygen is used for cellular respiration

  6. reduced oxygen concentration for other organisms = death (become hypoxic)
• habitat fragmentation


  land is cleared separating or isolating parts of habitat in the ecosystem

  • splits population = can't interbreed = no sharing of genetic diversity = loss of resilience
  • smaller population = less resilient and less likely to overcome change
• biomagnification


  substances that don't biodegrade entering waterways
• bioaccumulation


  organisms at lower trophic levels take substances into body tissue
• biomagnification step by step


  1.lower trophic level organisms take non-biodegradable waste into body tissue

  2. consumers eat tissue of lower trophic level organisms, substance accumulates at the next trophic level

  3. toxic levels of substances accumulates in tissue of higher order consumers -> causes illness and death
• pollution


  abiotic factor that is density independent and limits population growth

  • toxic discharge is washed directly into waterways
  • contributes to acid rain, the hole in the ozone layer, eutrophication and biomagnification
• acid rain (pollutant)


  very acidic rainwater

  • sulfur dioxide emitted during burning of fossil fuels combines with water vapor in atmosphere = formation of sulfuric acid -> rain falls as acid rain
  • acid takes minerals from soil
  • significant damage to conifers
  • changes the pH of freshwater ecosystems
• ozone (pollutant)


  ozone layer = screen that blocks UV light from 10-45km in stratosphere (doesn't block ALL light)

  1985 -> large thinning found over Antarctic -> grew each year

  • caused by chlorofluorocarbons (CFC's)
  • CFC use was restricted and the thinning started to slowly shrink
• introduced species


  introduced, non-native species that undergo exponential growth

  cause decline in native species due to

  • lack of predators
  • lack of disease
  • outcompeting native species
  • preying on native species
• deforestation


  total and permanent removal of standing forests

  contributes to increased greenhouse gases, climate change, desertification, soil erosion, flooding

  • loss of habitats
  • reduced biodiversity
• fire regimes

  natural fire regimes have been disrupted since european colonistation

  • introduced grasses create larger fuel load
  • less frequent fires allow tree density to increase and excess leaf litter to accumulate = more fuel for fires
  • more fuel load causes more intense fires
  • native vegetation does not survive high intensity fires because they have evolved to withstand many low intensity fires
  • loss of native vegetation
  • reduced biodiversity