Page 673 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 19 ecosystem essentials 637
derived from all living and recently living organisms and is measured as the net dry weight of organic material. Net primary productivity produces the energy needed for consumers—generally animals (including zooplankton in aquatic ecosystems)—that depend on producers as their carbon source.
producer (p. 607)
vascular plant (p. 608)
stomata (p. 608)
photosynthesis (p. 608) chlorophyll (p. 608)
respiration (p. 609)
net primary productivity (p. 609) biomass (p. 609)
consumer (p. 609)
4. Define a vascular plant. How many plant species are there on Earth?
5. How do plants function to link the Sun’s energy to living organisms? What is formed within the light- responsive cells of plants?
6. Compare photosynthesis and respiration with regard to the concept of net photosynthesis, which is the result of deducting respiration from photosynthesis. What is the importance of knowing the net primary productivity of an ecosystem and how much biomass an ecosystem has accumulated?
7. Briefly describe the global pattern of net primary productivity.
■ Discuss the oxygen, carbon, and nitrogen cycles, and explain trophic relationships.
Life is sustained by biogeochemical cycles, through which circulate the gases and nutrients necessary for growth and development of living organisms. Excessive nutrient inputs into oceans or lakes can create dead zones in the water, areas with low-oxygen conditions that limit underwater life.
Energy in an ecosystem flows through trophic levels, or feeding levels, which are the links that make up a food chain, the linear energy flow from producers through various consumers. Producers, at the lowest trophic level, build sugars (using sunlight, carbon dioxide, and water) to use for energy and tissue components. Within ecosys- tems, the feeding relationships are arranged in a complex network of interconnected food chains called a food web.
Herbivores (plant eaters) are primary consumers. Carnivores (meat eaters) are secondary consumers. A consumer that eats both producers and other con- sumers is an omnivore—a role occupied by humans. Detritivores are detritus feeders (including worms, mites, termites, and centipedes) that ingest dead or- ganic material and waste products, and release simple inorganic compounds and nutrients. Decomposers are the bacteria and fungi that process organic debris out- side their bodies and absorb nutrients in the process, producing the rotting action that breaks down detritus. Energy and biomass pyramids illustrate the flow of en- ergy between trophic levels; energy always decreases
with movement from lower to higher feeding levels in an ecosystem.
biogeochemical cycle (p. 611) dead zone (p. 613)
food chain (p. 616)
food web (p. 616)
detritivore (p. 617) decomposer (p. 617) herbivore (p. 617) carnivore (p. 617) omnivore (p. 617)
8. What are biogeochemical cycles? Describe several of the essential cycles.
9. What roles are played in an ecosystem by producers and consumers?
10. Describe the usual trophic relationships between producers, consumers, and detritivores in an eco- system. What is the place of humans in a trophic system?
11. What is an energy pyramid? Describe how it relates to the nature of trophic levels.
■ Describe communities and ecological niches, and list several limiting factors on species distributions.
A community is formed by the interactions among popula- tions of living animals and plants. Within a community, a habitat is the specific physical location of an organism—its address. An ecological niche is the function or operation of a life form within a given community—its profession.
Light, temperature, water, and nutrients constitute the life-supporting abiotic components of ecosystems. The zonation of plants and animal communities with alti- tude is the life zone concept, based on visible differences between ecosystems at different elevations. Each species has a range of tolerance that determines distribution. Spe- cies populations are stabilized by limiting factors, which may be physical, chemical, or biological characteristics of the environment.
community (p. 619) habitat (p. 619) ecological niche (p. 619) life zone (p. 621) limiting factor (p. 622)
12. Define a community within an ecosystem.
13. What do the concepts of habitat and niche involve?
Relate them to some specific plant and animal
communities.
14. Describe mutualistic and parasitic relationships in
nature. Draw an analogy between these relation- ships and the relationship of humans to our planet. Explain.
15. Discuss several abiotic influences on the function and distribution of species and communities.
16. Describe what Alexander von Humboldt found that led him to propose the life zone concept. What are life zones? Explain the interaction between elevation, latitude, and the types of communities that develop.