BIO372 : Extinction : Pattern & Opportunity : Lesson

I. Competition and Adaptive Radiation

1. Niche
   • Ranges of environmental factors in which an organism can live, e.g., temperature and humidity
   • Role played by the organism in its habitat, e.g., herbivore
2. Competition
   • Two individuals share a resource which is in short supply
     • Head-to-head confrontation, e.g., defending a territory: birds, lions, hyenas, wolves, lizards, bees
     • More often, one individual uses a resource before another individual gets to it, and thereby deprives the other of something it needs
   • If niches of the competing individuals are different enough, they can coexist; otherwise, one individual locally eliminates the other
3. Adaptive radiation into empty niches
   • When dominant species are eliminated, inferior competitors invade their niches, e.g., after a mass extinction episode: 5 major extinctions in geologic time
   • New adaptations allow species to invade previously unoccupied niches: bird and insect flight, human technology

II. The Mother of Mass Extinctions

1. Overview
   • End of Permian period, 250 million years ago
   • Staggering death toll: 90% of marine species, 67% of reptiles and amphibians, 30% of insects (their only mass extinction known)
   • Marine sessile life forms replaced by new lineages of mobile and predatory relatives of fish, squid, snails, and crabs

2. Clues from rock layers and fossils
   • Extensive drop in sea level during late Permian
   • Environmentally sensitive species died off rapidly
   • Duration of extinction similar to others: approximately 1 million years
   • Greater loss of taxa than other extinctions: 80-95%; 57% marine genera in Ordovician; 45% at K-T boundary
   • Some animal groups harder hit than others
   • Plants seem to have suffered

3. Extinction traps
   • Extensive volcanism
     • Dust and sulfates ejected into stratosphere lead to atmospheric cooling
     • Acid rain
     • Wildfires
     • Release of poisonous trace elements
     • Depletion of ozone layer resulting in increased UV radiation
     • Global warming from increased CO₂

4. Geochemistry
   • Shift in carbon isotope ratios (carbon 12 to carbon 13): organic matter was buried
   • Continents merged into Pangea
   • Sea level fell
     • Reduced area of continental shelf
     • Increased erosion and oxidation of organic matter
     • Atmospheric oxygen reduced and CO₂ increased
   • Subsequent rise in sea level flooded coastal communities
   • Water becomes anoxic

5. Recovery
   • Survivors
     • Long recovery time
     • Few remaining species were abundant and widespread
       • Lystrosaurus, a mammal ancestor, was found througout Pangea
     • Lazarus taxa reemerged
   • New adaptations opened new niches
     • More mobile, predatory species dominated the oceans
     • Burrowing animals prevalent
     • Skeletal changes for predation and avoiding predation
     • Insects shifted from dragonflies to more flexible forms with complete metamorphosis

6. Hypotheses
   • Survivors possessed specific adaptations for these environmental changes
   • Survivors were those that happened to be in protected locations

1. Large animals (megafauna) hunted to extinction by human tribes: dodo bird, mammoth
2. Current extinction rate from habitat destruction is similar to a mass extinction

When you have completed this lesson, go on to Review Questions