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Flow of Energy and
Relationships
The Structure of Ecosystems
• Trophic categories
• Trophic relationships: food chains, food webs,
trophic levels.
• Nonfeeding relationships: symbiosis
• Abiotic factors
Autotrophs = Producers = Self feeders
Consumers = Heterotrophs
• Primary consumers =
herbivores = rabbit: eat
plant material
• Secondary consumers =
carnivores = predators =
coyotes: prey are
herbivores and other
animals.
• Detrivores – feed on
dead material (detritus)
Consumers = Heterotrophs
• Parasites = predator = either plant or animal:
prey are plants or animals.
Detritus Food Web
Trophic Relationships: Food Chain
Third-order Consumer
Secondary Consumer
Primary Consumer
Producer
Match Organisms with Trophic Level(s)
Trophic Levels
Organisms
Secondary
Consumer
ThirdOrder
Consumer
Snakes
X
X
Owls
X
X
X
X
Plants
Producer
X
Rabbits
Bacteria
Primary
Consumer
X
X
X
Match Trophic Categories with Trophic Level(s)
Trophic Levels
Category
Autotrophs
Producer
Primary
Consumer
Secondary
Consumer
Third-Order
Consumer
X
X
X
X
X
X
X
X
X
Herbivores
X
Carnivores
Omnivores
Parasites
X
Trophic Relationships Among Producers and
Consumers
Food Webs = Food Chain Interrelationships
Keystone Species
• Role in the community is
critical to the
community’s survival
• Importance can be
greater than their
abundance suggests
• Can be predators, prey,
producers, or mutualistic
species
Keystone Species
• Are often involved in predator-mediated competition
– Predators thin the numbers of highly competitive species,
allowing other species to survive
– Removal of a predator can cause a trophic cascade
• Lower levels of the food chain grow out of control then crash
• Can be ecosystem engineers
– Alter and create habitat for other organisms
Trophic Level Energy Flow
Third-order Consumer 1Kcal
Secondary Consumer 10 Kcal
Primary Consumer 100 Kcal
Producer 10,000 Kcal
Biomass Pyramid
Trophic Levels: Pyramid of Biomass
5
4
3
2
1
Which level is occupied by:
producers?
primary consumers?
secondary consumers?
third-order consumers?
Trophic Levels: Pyramid of Energy
5
4
3
2
1
Which level is occupied by:
producers?
primary consumers?
secondary consumers?
third-order consumers?
Nutrient Cycles and Energy Flow
Nonfeeding (Symbiotic) Relationships
• + And + = Mutualism. Both species benefit by the
interaction between the two species. Honey bee
and flower
• + And 0 = Commensalism. One species benefits
from the interaction and the other is unaffected.
Remora fish and shark
Nonfeeding (Symbiotic) Relationships
• + And - = One species benefits from the interaction
and the other is adversely affected. Examples are
predation, parasitism, and disease.
• - And - = Competition. Both species are adversely
affected by the interaction.
Resource Partitioning: Reducing Competition