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Lecture 26 Chapter 36 Communities Learning Objectives Define disturbance Discuss the role of disturbance in communities Fire in Yellowstone Flood in Grand Canyon Contrast open and serotinous pine cones Recall what “NPS” & “USGS” stand for Disturbance A disruption in the community

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lecture 26

Lecture 26

Chapter 36


learning objectives
Learning Objectives
  • Define disturbance
  • Discuss the role of disturbance in communities
    • Fire in Yellowstone
    • Flood in Grand Canyon
  • Contrast open and serotinous pine cones
  • Recall what “NPS” & “USGS” stand for
  • A disruption in the community
  • Typically involves an abiotic force (we often call disasters)
    • Fires
    • Storms
    • Drought
    • Flood
    • Volcano
disturbance is natural
Disturbance is Natural
  • Despite “disaster” label, disturbance is natural, and often necessary
  • Example: prairies need fire every 2-3 years
    • Keeps trees from taking over
    • Recycles nutrients to soil
    • Clears away dead grass, allowing sunlight & air to penetrate
disturbance humans
Disturbance & Humans
  • People like to prevent “disasters” or natural disturbances
    • Put out forest fires
    • Dam rivers to control flooding
  • This can affect ecological communities negatively
natural fires in yellowstone park
Natural Fires in Yellowstone Park
  • A dozen natural fires in average year
  • Caused by lightning
  • Usually small “ground fires” (a few to 100 or so acres)
    • Patchy
    • Heat not too intense (many trees can survive)
benefits of fire
Benefits of Fire
  • Nutrients recycled
  • Undergrowth cleared
    • Allows sunlight to penetrate
  • Lush grass, flower growth encouraged
  • Bottom line: fire can beneficial
lodgepole pine
Lodgepole Pine
  • The dominant tree in Yellowstone
  • Makes 2 kinds of pine cones
    • Open cones:
      • Seeds fall out immediately
    • Serotinous cones:
      • Require fire to open
      • Cone coated in resin
      • Seeds stay inside until fire
      • Can stay on tree for years
      • Quickly reseed burnt areas
fire suppression
Fire Suppression
  • Fire suppression by National Park Service (NPS) began when park opened
    • Every fire quickly put out (natural or not)
    • Problem: fuel for fires accumulated year, after year, after year, then…
fire season of 1988
Fire Season of 1988
  • Summer 1988 park basically exploded!
    • Decades of fuel built up
    • Dry conditions, little rain
  • “Crown fires” in tops of trees
    • Too big, too hot to fight
aftermath of fire
Aftermath of Fire
  • Originally, thought to be great tragedy
    • Nature recovered
  • Park Service came under nation-wide scrutiny
    • Cost of fire suppression = 10X annual park budget (guess who pays)
grand canyon flooding
Grand Canyon Flooding
  • Flood disturbance was natural part of ecosystem
    • Maintained depth of river
    • Replenished sand on beaches
    • Cleared vegetation
dam disrupts flooding
Dam Disrupts Flooding
  • Dam in Glen Canyon region of Grand Canyon for flood control
  • Over time, environmentalists & anglers worried about habitat alteration
flood experiment
Flood Experiment
  • United States Geological Survey (USGS)
    • Decides to try “flood experiment”
    • March to April 1996, allows river to “flood” experimentally
    • River returned to more natural state
grand canyon floods
Grand Canyon Floods
  • USGS Websites
    • Rationale for experiment website 1
    • Grand Canyon Flows
    • Grand Canyon Sand
trophic level diet
Trophic Level & Diet
  • Primary producers = autotrophs, chemotrophs
  • Heterotrophs include:
    • Primary Consumers = herbivores
    • All carnivores, which include
      • Secondary consumers
      • Tertiary consumers
      • Quaternary consumers
  • There is an alga, eaten by a shrimp, eaten by a surfperch, eaten by a heron
  • Using trophic level terminology, how would you describe the surfperch?
  • What kind of heterotroph does not eat meat?
  • What is the lowest level heterotroph which eats meat?
problem with food chains
Problem with Food Chains
  • Food chains aren’t realistic
    • Few communities are so simple
    • Some species defy classification
      • Hawk can eat mice or snakes
      • Raccoons eat vegetation and meat
food webs
Food Webs
  • Food webs are more realistic depiction
  • Consist of several intertwined food chains
limited length of food chains webs
Limited Length of Food Chains/Webs
  • Remember 2nd Law of Thermodynamics
    • Some energy lost in every conversion
  • Metabolic efficiency typically 10%
    • 90% loss at each level
    • Only a few pyramid levels can be supported (3 to 5)
meat is energetically expensive
Meat is Energetically Expensive
  • Just as with any food chain, there is loss at every level
  • Meat requires greater land & water resources