Chapter 29 How Do Ecosystems Work?

Fig. 29-1 HEAT producers Energy from sunlight HEAT NUTRIENTS primary consumers detritus feeders and decomposers HEAT solar energy heat energy higher-level consumers energy stored in chemical bonds nutrients HEAT Fig. 29-1

29.2 How Does Energy Flow Through Ecosystems? Energy enters ecosystems mainly through photosynthesis. During photosynthesis, solar energy powers reactions that store energy in the chemical bonds of sugar and other high-energy molecules. Photosynthetic organisms produce food for themselves, using nonliving nutrients and sunlight. Organisms that can produce their own food are called autotrophs, or producers.

29.2 How Does Energy Flow Through Ecosystems? As producers manufacture food for themselves, they directly or indirectly produce food for nearly all other organisms as well. Organisms that cannot produce their own food are called heterotrophs, or consumers. Heterotrophs must acquire energy and many of their nutrients from the bodies of other organisms.

29.2 How Does Energy Flow Through Ecosystems? Energy passes from one trophic level to another. Energy flows through communities from producers, which are the first trophic level, through several levels of consumers. Primary consumers, or herbivores, feed directly on the producers and form the second trophic level. The third and fourth trophic levels are the secondary and tertiary consumers, and consist of meat-eating predators.

29.2 How Does Energy Flow Through Ecosystems? Feeding relationships within ecosystems form chains and webs. It is common to identify a representative of each trophic level such that each representative species eats another on the level below it. This linear feeding relationship is called a food chain. Different ecosystems have radically different food chains.

29.2 How Does Energy Flow Through Ecosystems? A simple terrestrial food chain TERTIARY CONSUMER (4th trophic level) PRIMARY CONSUMER (2nd trophic level) SECONDARY CONSUMER (3rd trophic level) PRODUCER (1st trophic level) (a) A simple terrestrial food chain Fig. 29-4a

29.2 How Does Energy Flow Through Ecosystems? A simple marine food chain SECONDARY CONSUMER (3rd trophic level) Phytoplankton PRODUCER (1st trophic level) Zooplankton PRIMARY CONSUMER (2nd trophic level) TERTIARY CONSUMER (4th trophic level) (b) A simple marine food chain Fig. 29-4b

29.3 How Do Nutrients Move Within And Among Ecosystems? Carbon cycles through the atmosphere, oceans, and communities. Carbon enters the living part of the ecosystem when producers capture CO2 during photosynthesis and incorporate its carbon atoms in organic molecules. Primary consumers, such as rabbits, shrimp, and grasshoppers, eat the producers and acquire the carbon stored in their tissues. Producers and consumers die, and the carbon in their bodies is returned to the reservoirs by decomposers.

burning of fossil fuels CO2 dissolved in the ocean fire reservoirs processes CO2 in the atmosphere trophic levels photosynthesis respiration burning of fossil fuels CO2 dissolved in the ocean fire producers consumers decomposition of wastes and dead bodies fossil fuels limestone soil bacteria and detritus feeders Fig. 29-8

29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the carbon cycle contributes to global warming. Much of Earth’s carbon is in long-term storage in reservoirs such as fossil fuels, which are formed from the buried remains of plants and animals. Over millions of years, the carbon in the organic molecules of these organisms is transformed by high temperature and pressure into coal, oil, or natural gas. Burning fossil fuels transfers the carbon locked in these reservoirs into atmospheric CO2.

29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the carbon cycle contributes to global warming (continued). Since the Industrial Revolution, humans have increasingly relied on the energy stored in fossil fuels. When we burn them in our power plants, factories, and cars, CO2 is released into the atmosphere. The amount of CO2 in the atmosphere has increased by more than 36% since 1850, from 280 parts per million (ppm) to 381 ppm.

29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the carbon cycle contributes to global warming (continued). Deforestation also adds CO2 to the atmosphere. When forests are cut and burned, the carbon stored in the bodies of the trees returns to the atmosphere. Altogether, humans release almost 7 billion tons of CO2 into the atmosphere each year, much of which fuels global warming.

heat radiated into space sun sunlight CO2 methane nitrous oxide atmosphere deforestation forest fires heat trapped in the atmosphere power plants and factories vehicle emissions homes and buildings agricultural activities Fig. 29-14

29.4 What Happens When Humans Disrupt Nutrient Cycles? Greenhouse gases trap heat in the atmosphere. Atmospheric CO2 acts like glass in a greenhouse—it allows solar energy to pass through it to reach Earth’s surface, but does not allow much of it to be released back into space, thus increasing the heat content of the atmosphere as a result. Most climate scientists have concluded that this greenhouse effect has been intensified by human activities that produce CO2 and other greenhouse gases, such as methane.

29.4 What Happens When Humans Disrupt Nutrient Cycles? A global meltdown is underway. Throughout the world, ice is melting; glaciers are retreating and disappearing. In Glacier National Park, where 150 glaciers once occurred, only 35 remain, and scientists estimate that none will remain in 30 years from now.

29.4 What Happens When Humans Disrupt Nutrient Cycles? Glaciers are melting. Fig. 29-16

29.4 What Happens When Humans Disrupt Nutrient Cycles? Weather is growing more extreme. Scientists predict that global warming will increase the severity of extreme weather events. During the past 35 years, both the intensity and duration of hurricanes has increased by 50%. As the world warms further, droughts in certain areas will last longer and be more severe, disrupting agriculture.

29.4 What Happens When Humans Disrupt Nutrient Cycles? Our decisions make a difference. What can individuals do to help reduce the impact of global warming? Use fuel-efficient vehicles, car pools, and public transportation. Conserve electricity. Improve the energy-efficiency of housing. Recycle.