Desert Ecology Chapter 7

Chapter 7 Desert Ecosystems

Chapter Outline | Web Resources | Study Questions

Chapter Outline

Each of the North American deserts has their unique species. Cirios are unusual plants that look like large, upside-down carrots. They are endemic to the southern Sonoran Desert. Along with their uniqueness, the deserts do have similarities in ecosystem structure and function.

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.

Cryptogamic crust darkens this soil in Canyonlands National Park in Utah. Photosynthetic cyanobacteria, algae, and lichens contribute to primary production, and nitrogen-fixing cyanobacteria also enhance the fertility of the soil. Importantly, the crust retards soil erosion if left undisturbed.

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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