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CHAPTER
2
Interactions in Ecosystems
• 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
CHAPTER
2
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.
CHAPTER
2
Interactions in Ecosystems
Activity
Using the food web on
the right, predict what
might happen if a
disease killed all the krill
in the ecosystem. Which
species would be
affected, and how? Try
drawing a new food web.
You can find more
information on food
chains and webs on
pages 34–36 in the
student book.
CHAPTER
2
Interactions in Ecosystems
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.
2.1
Biotic and Abiotic Factors in Ecosystems
• 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.
VOCABULARY
ecology
organism
habitat
population
community
ecosystem
biosphere
biotic factor
abiotic factor
dynamic equilibrium
limiting factor
2.2
Ecological Roles and Relationships
• 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.
VOCABULARY
nutrients
producer
autotroph
phytoplankton
consumer
heterotroph
herbivores
primary consumer
zooplankton
carnivore
omnivore
detrivore
decomposer
biodegradation
predation
predator
prey
predator–prey cycle
2.3
Symbiosis
• Symbiosis refers to any close relationship between
two different species. There are three types of
symbiotic relationships:
VOCABULARY
symbiosis
mutualism
commensalism
parasitism
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).
host
parasite