• The components of an ecosystem一 the community of interacting species present in a region, along with the abiotic components of the soil, water, and atmosphere-are linked by the flow of energy and the cycling of nutrients needed to sustain life.

• Further, ecosystems are themselves linked by the global exchange of energy and nutrients throughout the biosphere, the thin zone of soil, water, and atmosphere surrounding Earth where all life exists.

53.1 How Does Energy Flow Through Ecosystems?

• Energy enters ecosystems via primary producers, also called autotrophs (literally, “self-feeders”)-organisms that can synthesize their own food from inorganic sources.

• The total amount of chemical energy produced in a given area and time period is called gross primary productivity (GPP).

• Energy that is invested by primary producers in building new tissue or offspring is called net primary productivity (NPP).

  • NPP represents the total amount of chemical energy that is stored in organic material, or biomass.

• Consumers eat living organisms.

  • Primary consumers eat primary producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers; and so on.

• Decomposers, or detritivores, obtain energy by feeding on the remains of other organisms or waste products.

  • Dead animals and dead plant tissues (“plant litter”) are collectively known as detritus.

• Organisms that obtained energy from the same type of source were said to occupy the same trophic (“feeding”) level.

• A food chain focuses on one possible pathway of energy flow among trophic levels in an ecosystem.

• At the second trophic level, the decomposer food chain has a primary decomposer, which feeds on plant detritus, rather than a primary consumer.

• Because most consumers feed on a wide array of organisms and at multiple trophic levels, food chains are embedded in more complex food webs.

• Mercury and POPs undergo biomagnification-meaning that they increase in concentration in consumers at higher levels in a food chain.

53.2 How Do Nutrients Cycle Through Ecosystems?

• Tissues also contain carbon (C), nitrogen (N), phosphorus (P), sulfur (S), calcium (Ca), and other elements considered nutrients because they are essential for normal metabolism, growth, and reproduction.

• The path an element takes as it moves from abiotic systems through producers, consumers, and decomposers and back again is referred to as its biogeochemical cycle.

• These microscopic decomposers and the carbon-containing compounds that they release combine to form what biologists call soil organic matter, a complex mixture of partially and completely decomposed detritus.

  • When the detritus becomes completely decayed, it is called humus because it is rich in a family of carbon-containing molecules called humic acids.

• A group of researchers led by Likens and Bormann began by choosing two similar watersheds-areas drained by a single stream-for study.

• Most groundwater is stored in aquifers-layers of porous rock, sand, or gravel that are saturated with water.

  • Aquifers are said to be closed (contained) when nonporous rock layers overlie them, and open (uncontained) when they can be recharged by water percolating down from the surface.

• The water table-the upper limit of the underground layer of soil that is saturated with stored water-is dropping on every continent.

• The global nitrogen cycle tracks the movement of nitrogen among terrestrial and aquatic ecosystems.

• The global phosphorus cycle tracks the movement of phosphorus among terrestrial and aquatic ecosystems.

• The global carbon cycle documents the movement of carbon among terrestrial ecosystems, the oceans, sediments, and the atmosphere.

53.3 Global Climate Change

• Global warming refers to the increase in the average temperature of the planet.

  • The average temperature is very important in determining physical, chemical, and biological processes.

• Global climate change refers to the sum of all the changes in local temperature and precipitation patterns that result from global warming-including the frequency and intensity of storms, droughts, and other events.

  • The effects of global warming vary depending on geography, local weather patterns, ocean currents, and other factors.

  • But averaged over the entire planet and over time, the Earth is already much warmer than it was just a few decades ago and is projected to get even warmer.

• Carbon dioxide is a greenhouse gas: It traps heat that has been radiated from Earth and keeps it from being lost to space, similar to the way the glass of a greenhouse traps heat, causing a greenhouse effect.

• The timing of seasonal events, or phenology, is changing in many biomes.