Lecture 26

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 aren’t 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