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why is it difficult to estimate current rate of extinction?

  • difficult to say w/ certainty that a species is extinct
  • most species unknown to scientists, therefore extinct species also unknown


cycles that generate climate changes short term

  • earth revolves on its axis leading to alternating cooling and warming w/ solar radiation
  • earth orbits sun, tilted axis generates annual climactic cycles b/w northern hemisphere tilted toward sun during half of the orbit, southern hemisphere tilted toward sun other half
    • diurnal-nocturnal behaviour of animals
    • seasonal growth and death of annual plants


cycles that generate climate changes long term

  • variaration of tilt of earth's axis
  • variation of shape of earth's orbit around sun
  • procession of equinoxes: distance form earth to sun cna either accentuate or ameliorite effects of axial tilt on weather


3 concerning observations re:global warming

  • greenhouse gases lead greenhouse effect
  • increased concentration of gg lead to increase greenhouse effect
  • mean global temperature has increased


greenhouse gases

water vapor, carbon dioxide, methane, etc.


greenhouse effect

gg allow solar radiation to penetrate atmosphere and warm earth's surface and inhibit reradiation of energy back to space


causes of global warming

  • increased consumption of fossil fuels
  • devasation of ecosystems (release gg)
  • astronomical factors, increased photosynthesis (unpopular)


will organisms be able to adapt to future climate change?

  • have been able to adapt well in past but maybe not in future
    • current pops. already stressed by habitat degradation and overexploitation
    • stressed pops. are small and therefore have lower chance to produce offspring
    • human alteration of landscapes has reduced quantity of suitable habitats and fragmented landscapes by roads, etc. decreasing odds of individuals arriving in new suitable habitat
  • possible temps will rise to unprecedented levels
  • melting ice caps reduce shoreline 
  • unprecedented rate of increase in temp


why are rare species more vulnerable to extinction than common species?

  • greater chance of pushed to extinction by environmental change
    • environmental event may encompass species' entire range
  • demographic problems
    • unbalanced sex ratio can limit birth rate
    • more likely to happen to small pops.
  • genetic problems
    • inbreeding
    • genetic drift
    • bottlenecks
    • restricted ability to adapt



why are some species particularly sensitive to human-induced threats?

  • limited adaptability and resilience
    • may be due to low reproductive capacity, limited dispersal capabilities, inflexible habitat requirements, etc.
  • human attention
    • may be edible, extremely unpopular (e.g. bats)
  • ecological overlap
    • tied to human-preferred ecosystems (e.g. w/ fertile soil and benign climates)
  • large home-range requirements
    • cannot fit in among humans



groups of individuals of some species occupying a defined area at same time


meta populations

group of diff. patch pops.



subpopulations appearing and disappearing due to colonization and local extinction


population visibility analysis (PVA)

any systematic attempt to understand processes that make pop. vulnerable to extinction, technique used to measure minimum viable population


4 interacting factors that might contribute to pop's extinction

  • demographic stochasticity
    • =uncertainty resulting from random variation in reproductive success and survivorship at individual level
  • environmental stochasiticity
    • =random variations in components of habitat quality
    • e.g. climate, nutrients, water
  • catastrophes
    • =dramatic events that occur at random intervals
    • e.g. droughts, hurricanes 
  • genetic stochasticity
    • random variation in gene frequencies of a pop. resulting from genetic drift, bottlenecks, inbreeding, etc.


habitat degradation

process by which habitat quality for a given species is diminished


habitat loss

habitat quality so low that environment is no longer usable by given species


ecosystem degradation

alterations to an ecosystem degrade/destroy habitat for many of the species that constitute the ecosystem


ecosystem loss

changes to ecosystem so profound to so many species (esp. dominant species) are lost so that ecosystem converted to another type (e.g. deforestation)


contamination: air pollution

  • extensive research on effects on human and domesticated species, less on wild species
  • destroy plant species downwind from factories
  • eradicate lichen species
  • diminish individuals' health and ability to reproduce
  • can make aquatic habitats more acidic


contamination: water pollution

  • aquatic species more vulnerable than land species
  • extinction of species in one place can lead to entire extinction b/c only found in one place
  • less likely to cause extinction if in marine habitats
  • eutrophication and harmful algal blooms


contamination: pesticides

  • some benign and break down quickly, others wreak havoc (e.g. DDT)
  • biomagnification = pesticides concentrate at top of ecosystem


human structures: roads

  • curbs/lanes dividers absolute barriers to small, flightless mammals, etc.
  • animals run down even if can cross
  • provide access to habitats to people who want to exploit ecosystem
  • may provide access for exotic species to infiltrate habitat


human structures: dams

  • limits species' ability to move up/down stream during mating season
  • e.g. salmon populations eliminated by dams


soil erosion

  • natural process accelerated by humans (e.g. agriculture)
  • leads to habitat degradation and decreased productivity of land


fire regimes

  • severe human fires can destroy habitats
  • campaigns to prevent fire also too effective - low intensity fires suppressed, leads to accumulation of fuel


water use

  • mostly used for agriculture than industry, domestic uses and reservior expansion
  • when remove large quantity of water, biota affected



  • forests grow in places w/ fertile soil so desireable for agriculture
  • slowed, stopped or reversed in some areas
  • demand for forest in developed countries decreased b/c pop stabilised or shift away from agro
  • still issue in tropical regions
  • damages diverse ecosystems



  • grasslands/woodlands being degraded until dominated by sparse unproductive veg.
  • usually associated w/ overgrazing and cultivation


why do large fragements have more species than small ones?

  • greater variety of environments
    • provides niches for additional species
  • likely to have common and uncommon species
    • small fragment likely to only have common species
  • larger samples have more species