3.1 What Is Ecology?

Ecology is the scientific study of interactions among organisms and between organisms and their physical environment.

The biological influences on organisms are called biotic factors.

Physical components of an ecosystem are called abiotic factors.

Modern ecologists use three methods in their work: observation, experimentation, and modeling. Each of these approaches relies on scientific methodology to guide inquiry.

• biosphere (64)

• ecosystem (65)

• species (64)

• biome (65)

• population (64)

• biotic factor (66)

• community (64)

• abiotic factor (66)

• ecology (65)

3.2 Energy, Producers, and Consumers

Primary producers are the first producers of energy-rich compounds that are later used by other organisms.

Organisms that rely on other organisms for energy and nutrients are called consumers.

• autotroph (69)

• carnivore (71)

• primary producer (69)

• herbivore (71)

• photosynthesis (70)

• scavenger (71)

• chemosynthesis (70)

• omnivore (71)

• heterotroph (71)

• decomposer (71)

• consumer (71)

• detritivore (71)

3.3 Energy Flow in Ecosystems

Energy flows through an ecosystem in a one-way stream, from primary producers to various consumers.

Pyramids of energy show the relative amount of energy available at each trophic level of a food chain or food web. A pyramid of biomass illustrates the relative amount of living organic matter available at each trophic level of an ecosystem. A pyramid of numbers shows the relative number of individual organisms at each trophic level in an ecosystem.

• food chain (73)

• trophic level (77)

• phytoplankton (73)

• ecological pyramid (77)

• food web (74)

• biomass (78)

• zooplankton (76)

3.4 Cycles of Matter

Unlike the one-way flow of energy, matter is recycled within and between ecosystems.

Water continuously moves between the oceans, the atmosphere, and land—sometimes outside living organisms and sometimes inside them.

Every organism needs nutrients to build tissues and carry out life functions. Like water, nutrients pass through organisms and the environment through biogeochemical cycles. The carbon, nitrogen, and phosphorus cycles are especially critical for life.

If ample sunlight and water are available, the primary productivity of an ecosystem may be limited by the availability of nutrients.

• biogeochemical cycle (79)

• denitrification (84)

• nutrient (82)

• limiting nutrient (85)

• nitrogen fixation (84)

Think Visually Using information from this chapter, complete the following flowchart:

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