Chapter Summary

• An ecosystem includes all the organisms in a given area and their physical and chemical environment.

• Energy flowing through ecosystems originates with sunlight and inorganic and organic compounds. It involves the processes of photosynthesis, chemosynthesis, and secondary production. Review Focus: Key Figure 57.1, Activity 57.1

• Energy is lost from ecosystems as metabolic heat.

• Nutrients originate in soil, water, and the atmosphere and cycle through ecosystems via the processes of production and decomposition.

• Net primary production (NPP) is the amount of carbon remaining in plants after respiration, and varies with latitude and ecosystem type. Review Figures 57.2, 57.4

• Terrestrial NPP is highest in the tropics where temperatures are high year-round and rainfall is abundant. Review Figures 57.3A, 57.5

• Oceanic NPP varies little with latitude but peaks at mid-latitudes and in coastal zones and areas of upwelling where the main primary producers—primarily ATP—phytoplankton and algae—primarily ATP—have access to light and nutrients. Review Figure 57.3B

• In aquatic systems, nutrient runoff from agriculture and wastewater can cause eutrophication, resulting in algal blooms and low oxygen conditions (hypoxia) for aquatic life.

• Once energy captured by primary producers is fixed as NPP, consumption by heterotrophs transfers a fraction of that energy to higher trophic levels, creating net secondary production. Review Figure 57.8

• Organisms differ in their production efficiency, or the percentage of energy stored in assimilated food that is used to produce new biomass. Review Figure 57.8, Table 57.1

• The amount of energy transferred within food webs depends on trophic efficiency, or the amount of energy used at one trophic level divided by the amount used at the trophic level below it. Review Figure 57.9

• The flow of energy in food webs is influenced by the number of trophic levels and the relative contribution of bottom-up (NPP passing up the food web) and top-down (consumers regulating NPP) forces. Review Figure 57.10A

• Most food webs have just three or four trophic levels because of energy limitations at higher trophic levels, the effects of disturbance, or the evolutionary constraints on top predators.

• Nutrients move through the biotic parts of ecosystems via production and decomposition. Review Figure 57.11

• At a global scale, nutrients move through geological, atmospheric, and biological pools, making up biogeochemical cycles.

• Water cycles rapidly through the globe as part of the hydrologic cycle, transporting nutrients and serving as an essential requirement for organisms. Review Figure 57.12, Animation 57.1

• Carbon moves through biological systems and returns to the atmosphere through respiration. Review Figure 57.13, Animation 57.2

• Burning of fossil fuels increases the carbon dioxide and sulfur in the atmosphere, causing global warming and acidic conditions in oceans and lakes. Review Figures 57.14, 57.15, Investigating Life: Food Webs in an Acidic and Warming Ocean

• The nitrogen cycle is dominated by biotic transformations controlled by bacteria, whereas the phosphorus and sulfur cycles are dominated by geochemical processes. Review Figures 57.16, 57.17, Animation 57.3

• Ecosystem services benefit humans and can be categorized as those that provide provisioning, regulating, supporting, or cultural services.

• Most ecosystem services are either irreplaceable or prohibitively expensive to replace.

• Ecosystem values are measures of how important ecosystem services are to people—that is, what they are worth. Review Figure 57.18

• Ecosystem services can be valued by determining the market value or the willingness of people to pay for the services. Review Figure 57.19