Chapter 7 Desert Ecosystems
Chapter Outline
Introduction
Ecosystems
Nutrient cycling
Energy flow
Net Primary Productivity
Spatial and temporal variability in net primary
production
Cryptogamic soil crusts as producers
Factors limiting net primary productivity
Food Webs
Importance of detritus
Animals as consumers
Trophic levels
Looping in food webs
Production efficiencies and length of food chains
Plant and animal biomass
Ecosystem Structure
Role of abiotic and biotic factors
Evidence that biotic interactions regulate
populations
Succession in the desert?
Similarities among deserts
Web Resources
Biological Soil Crusts describes the ecology of cryptogamic soil crusts and also provides a link to a 90 page technical reference (look for the "advanced" link). By BLM, USGS, and NPS.
Study Questions
1. The net primary productivity (NPP) is low in the desert. a) Define NPP. b) Compare NPP in the desert with that of other biomes. c) Studies in the Chihuahuan Desert found that monthly applications of 25 millimeters of water had no effect on productivity while weekly sprinklings of 6 millimeters of water more than doubled productivity. Explain these results.
2. How might detritus lead to some stability to desert food webs. Be complete by first defining detritus and its role in desert food webs.
3. The desert is a land of generalists and opportunists. How does this lead to food web complexity?
4. Despite the low amount of energy passing through desert food webs, energy passes through more trophic links in deserts than elsewhere. a) Explain why the number of trophic links in any food web is limited. b) How is it that energy can pass through more trophic links in desert food webs?
5. It has been stated that desert populations are regulated primarily by abiotic constraints rather than biotic ones. Provide arguments for and against this dogma.
6. Explain why secondary succession in the desert may have fewer seres yet take longer than succession in adjacent regions. Start by defining secondary succession.
7. Similarities in desert organisms and communities around the globe help us identify and understand those traits that are actually adaptations to the desert environment. Explain and provide examples to support your explanation.
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Copyright © 2001-2013 John Sowell