Communities

1
Lecture 26

• Chapter 36
• Communities

2
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

3
Disturbance

• A disruption in the community
• Typically involves an abiotic force (we often
  call disasters)
• Fires
• Storms
• Drought
• Flood
• Volcano

4
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

5
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

6
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)

7
Benefits of Fire

• Nutrients recycled
• Undergrowth cleared
• Allows sunlight to penetrate
• Lush grass, flower growth encouraged
• Bottom line fire can beneficial

8
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

9
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

10
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

11
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)

12
Grand Canyon Flooding

• Flood disturbance was natural part of ecosystem
• Maintained depth of river
• Replenished sand on beaches
• Cleared vegetation

13
Dam Disrupts Flooding

• Dam in Glen Canyon region of Grand Canyon for
  flood control
• Over time, environmentalists anglers worried
  about habitat alteration

14
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

15
Grand Canyon Floods

• USGS Websites
• Rationale for experiment website 1
• Grand Canyon Flows
• Grand Canyon Sand

16
Trophic Level Diet

• Primary producers autotrophs, chemotrophs
• Heterotrophs include
• Primary Consumers herbivores
• All carnivores, which include
• Secondary consumers
• Tertiary consumers
• Quaternary consumers

17
Question

• 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?

18
Question

• What kind of heterotroph does not eat meat?

19
Question

• What is the lowest level heterotroph which eats
  meat?

20
Problem with Food Chains

• Food chains arent realistic
• Few communities are so simple
• Some species defy classification
• Hawk can eat mice or snakes
• Raccoons eat vegetation and meat

21
Food Webs

• Food webs are more realistic depiction
• Consist of several intertwined food chains

22
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)

23
Meat is Energetically Expensive

• Just as with any food chain, there is loss at
  every level
• Meat requires greater land water resources