Conservation Biology- Lecture 3 EXTINCTION

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Extinction – past and present

  • We are living in an age of mass extinction
  • The current extinction crisis has the highest recorded rate of speciesloss
  • We therefore need to examine geological history to place this in context and understand why we face these problems 

The age of bacteria

  • Earth is 4.55 billion years old
  • There has been life on earth for the last 3.8 billion
  • Bacteria dominated for the first 3.1 billion of these!

The primitive atmosphere

  • During this period the atmosphere comprised nitrogen, CO2, hydrogen and water vapour
  • This environment created a primordial ‘soup’ where Prokaryotes developed a range metabolic adaptations

The Atmospheric revolution

  • The arrival of cyanobacteria (2.6 Bn BP)
  • The exhaustion of mechanisms for absorbing excess oxygen
  • Atmospheric oxygen arrives..
  • Mass extinction follows!

Biodiversity through time

  • After this first global ‘catastrophe’ sees the rise of the Eukaryotes (which have mitochondria)
  • Diversity gradually increases over time and explodes during the Cambrian epoch
  • The rate of accumulation of diversity is not, however, constant…
  • Rapid periods of diversification are followed by stable periods, punctuated by periods of mass extinction

We can understand the trajectory of past species diversity through the fossil record 

  • The first species explosion occurred during the Cambrian 600 million BP:100 phyla appeared of which 32 survive today
  • 60 million years later another important diversification during the Paleozoic
  • The last major event occured at the Cretaceous/Tertiary boundary (extinction of dinosaurs – rise of the mammals)

Five Mass Extinctions

  • (500MA) Ordovician: 50% of animal families (e.g. trilobites)
  • (350MA) Devonian: 30% of animal families (fish, trilobites)
  • (250MA) Permian: 50% of animal families (95% marine life)
  • (180MA) Triassic: 35% of animal families (reptiles, molluscs)
  • (65MA) Cretaceous: dinosaurs, marine life 

The rate of current extinction 

  • We are living during the sixth mass extinction event
  • From the beginning of the Pleistocene era (2 million BP) increasingly drastic oscillations in global temperature (ice ages)
  • However, large animal extinctions coincide much better with the arrival of Homo sapiens..

Well known recent examples: Pleistocene megafauna: Smilodon- sabre toothed cat, Giant ground sloth

Island species very badly affected (Giant birds)

The last 150 years..

  • The known rate of extinction has soared
  • We know this best through birds and mammals
  • This rate of extinction is unprecedented

Other groups badly affected in the current wave:

  • Coral (reef bleaching)
  • Mass Amphibian extinctions
  • Loss of molluscs from island systems 

EXTINCT: Mammals (58), Birds (115), Molluscs (191), Other animals (120), Plants (517).

Species vulnerable to extinction


• A species can be rare…


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