• An ecosystem is made up of a community of organisms and the non-living environment.

• The living components of the ecosystem are called biotic factors, which include plants, fish, invertebrates, and single-celled organisms.

• The non-living components, or abiotic factors, include the physical and chemical components in the environment—temperature, wind, water, sunlight, and oxygen.

• Biotic and abiotic factors influence each other in an always changing balance called dynamic equilibrium.

Biotic and Abiotic Factors in Ecosystems2.1

VOCABULARY

ecology

organism

habitat

population

community

ecosystem

biosphere

biotic factor

abiotic factor

dynamic equilibrium

limiting factor

Ecological Roles and Relationships2.2

VOCABULARYnutrients

producer

autotroph

phytoplankton

consumer

heterotroph

herbivores

primary consumer

zooplankton

carnivore

omnivore

detrivore

decomposer

biodegradation

predation

predator

prey

predator–prey cycle

• An ecosystem is a complex network of interactions.

• All organisms must take in water, food, and nutrients. Nutrients are elements and compounds that organisms need to live and grow.

• Organisms can be producers, consumers, herbivores, carnivores, or decomposers in ecosystems.

• Eventually nutrients cycle back into the ecosystem for the producers.

Symbiosis2.3

VOCABULARY

symbiosis

mutualism

commensalism

parasitism

host

parasite

• Symbiosis refers to any close relationship between

two different species. There are three types of

symbiotic relationships:

1. Mutualism is a relationship in which both species

obtain some benefit from the interaction.

2. Commensalism is an interaction in which one

organism benefits while the other is unaffected.

3. Parasitism occurs when one organism (the

parasite) lives and feeds on, or in, the body of

another organism (the host).

• Nutrients are cycled back into the ecosystem, but energy only moves in one direction through the community from producers to herbivores to carnivores.

• Trophic level describes the position of the organism in relation to the order of nutrient and energy transfers in an ecosystem. Organisms that eat the same type of food belong to the same trophic level.

• Food chains show a single pathway taken by nutrients and energy through the trophic levels.

• In reality, ecosystems have more complex food webs, showing the different cross-linked food chains.

Trophic Levels and Energy Flow2.4

VOCABULARY

trophic level

food chain

food web

• Ecologists use three different types of ecological

pyramids to illustrate ecosystems:

1. Pyramid of energy: represents

how much energy is available

in each trophic level

2. Pyramid of numbers: represents the actual number

of organisms present in each trophic level

3. Pyramid of biomass: represents

the total mass of living things in

each trophic level

Ecological Pyramids2.5

VOCABULARY

ecological pyramid

food pyramid

pyramid of energy

pyramid of numbers

pyramid of biomass

Interactions in Ecosystems2CHAPTER

• Ecosystems are made up of living

things (biotic factors) and non-living

things (abiotic factors), which are

connected to each other in complex

interrelationships.

• Nutrients are cycled within an ecosystem.

producers consumers decomposers producers

Interactions in Ecosystems

• Energy flows through ecosystems.

• This energy comes from an outside source: the Sun.

• Ecologists represent food and energy

flows in food chain, food web, and pyramid

diagrams.

2CHAPTER

Interactions in Ecosystems2

Key Ideas

• Living things are connected to each other in complex

interrelationships.

• Biotic and abiotic factors are responsible for shaping a

community of living things.

• Nutrients cycle within ecosystems.

• Energy flows through ecosystems.

CHAPTER