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Food Webs and Energy Pyramids
Objectives
• Identification of the feeding relationships of
animals in an ecosystem
• Tracing the flow of energy and nutrients
through an ecosystem
• Understanding how organisms in an
ecosystem are interrelated
• Understanding the complex and dynamic
nature of an ecosystem.
Ecosystems
• Biotic Factors: Any living part of an environment.
• Abiotic Factors: Any non-living part of an environment.
Examples:
Feeding Strategies
• Autotroph - organisms that is able to capture energy from sunlight and
use it to produce its own food from inorganic compounds, also called a
producer.
• Heterotroph -organisms that obtain food by consuming other living things,
also called a consumer.
Feeding Strategies
• Producers/Autotroph- Sunlight is the main
energy source for life on Earth.
– Definition-organisms that can capture energy from
sunlight and use that energy to produce food.
– Examples:
Feeding Strategies
• Consumers/Heterotrophs
• Definition:-organisms that rely on other organisms for their energy and
food.
• Examples:
– Herbivores- such as cows, obtain energy by eating only plants.
– Carnivores- such as snakes, eat only animals.
– Omnivores- such as humans, eat both plants and animals.
– Detritivores- such as earthworms, feed on dead matter.
– Decomposers- such as fungus, break down organic matter.
– Scavengers- such as vultures, consume the carcass of other animals.
Trophic Levels
Energy, Producers, and Consumers
Trophic Levels
• Producers
• Definition- the beginning level in a food chain
that contains organisms that use energy
directly from the sun for life processes. For
example: Plants and other autotrophs use
sunlight to produce sugars and oxygen.
• Examples: plants, some protists (algae),
some bacteria (cyanobacteria)
Trophic Levels
• Primary Consumers
•
Definition- Organisms that obtain nutrients by consuming producers. They
indirectly use energy from the sun that was captured by the producers. For
example: when plants are eaten by animals.
• Examples: Rabbits, field mice, birds, and prairie dogs.
Trophic Levels
• Secondary Consumers
• Definition- Organisms that obtain nutrients by
consuming other consumers. They indirectly
use energy from the sun that was captured by
the producers and other consumers.
• For example: Foxes, birds, snakes
Trophic Levels
• Tertiary Consumers and Top Predator
Definition: Tertiary Consumers are carnivores /organisms that eat only
animals and they feed on secondary and primary consumers.
Examples: Harris’s Hawks, rattlesnakes, dogs, owls, bald eagles,
plankton-eating fish, shrew, lions and tigers.
Trophic Levels
• Detritivores
– Definition – organisms
that consume dead and
decaying organic matter
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Trophic Levels
• Decomposers
Definition: Organisms that break down and obtain energy from dead organic matter.
Examples: Bacteria, fungi, mushrooms, mites, gitterbug, millipede, slug, earthworm,
snail, and the dung beetle.
Trophic Levels
Trophic Levels
Food Chain vs. Food Web
A food chain is a series of steps in which organisms transfer energy by eating and being eaten.
Food Chain vs Food Web
A food web is a network of several interacting food chains.
Dynamic Nature of Ecosystems
Changes in Ecosystem
• Top Down
– Owls increase
– Mice decline
– Grass increases
Changes in Ecosystem
• Bottom up
– Add fertilizer- more grass
– More mice
– More owls
Energy Pyramid
Energy transfer is only 10% from
one trophic level to the next
higher trophic level
Lots of produces
Few top predators