Energy Flow Through Trophic Levels
Biology 12(C)
Energy Flow Through Trophic Levels
Learning Objectives
• Analyze the flow of matter and energy through trophic
levels using various models, including food chains, food
webs, and ecological pyramids
Energy Flow Through Trophic Levels
Individual organisms within a community survive by:
• Producing food
• Feeding on other organisms
Flow of matter and energy – energy in food is transferred
from one organism to another
• Organized system of energy flow through ecosystem
Trophic Levels
Trophic level – distinct level of feeding within ecosystem
• Species at each level vary in different communities
Trophic levels:
• Producer
• Consumer
– Primary
– Secondary
– Tertiary (or top)
• Decomposer
Trophic Levels
Producer – produce own
food, first or lowest
trophic level
• Example: plants
Primary consumer – firstorder consumer, eats a
producer
• Example: grasshopper
Trophic Levels
Primary consumer –
first-order consumer,
eats a producer
• Example: grasshopper
Secondary consumer –
second-order consumer,
eats primary consumer
• Example: lizard
Trophic Levels
Secondary consumer –
second-order consumer,
eats primary consumer
• Example: lizard
Tertiary consumer – thirdorder consumer, eats
secondary consumer
• Example: snake
Trophic Levels
Decomposer (saprobe) – breaks down dead plant and animal
matter and returns nutrients to soil
– Examples: bacteria and fungi
Trophic Levels
Sometimes consumers are referred to by type of food they
eat rather than trophic level:
• Herbivore – eats only plants
– Examples: deer, rabbit
• Carnivore – eats only animals
– Examples: lion, shark
• Omnivore – eats plants and animals
– Examples: bear, human
• Scavenger – feed only on dead organisms
– Examples: vulture, hyena
Food Chains
Food chain – sequence of organisms feeding on one another
at a lower trophic level
Producer
Primary Consumer
Secondary Consumer
Food Webs
Food web – network of interacting food chains
• Most organisms eat more than one food type
• Ecosystems usually contain more than one food chain
• Complex relationships between trophic levels
Food Webs
Highest Trophic Level
Lowest Trophic Level
Food Webs
• Which organisms are the
producers?
– Pond weed and algae
• Which organisms are the
secondary consumers?
– Perch, minnow, and
dragonfly
• Which organisms do
frogs eat?
– Minnow and dragonfly
Complex Food Web
Food Webs
• Which consumers feed on bivalves?
– Sea ducks, tundra swans, and herbivorous ducks
• Which consumers feed on zooplankton?
– Small fish, bivalves
Ecological Pyramids
Ecological pyramid – used to visualize food chains
• Pyramid of energy – amount of energy in bodies of
organisms at each trophic level
• Pyramid of numbers – number of organisms feeding at
each trophic level
• Pyramid of biomass – total mass of dry, organic matter at
each trophic level
Pyramid of Energy
Energy decreases up the
pyramid:
• Grass captures sun’s
energy
• Rabbit obtains 10% of
stored energy in grass
• Snake obtains 10% of
stored energy in rabbit
• Eagle receives 10% of
stored energy snake
Pyramid of Energy
1 kcal
10 kcal
100 kcal
1000 kcal
Pyramid of Numbers
Numbers decrease up the
pyramid:
• More individual
organisms at lower
trophic levels
• Fewer individuals at
higher trophic levels
Pyramid of Numbers
Pyramid of Biomass
Biomass decreases up the
pyramid:
• Greatest biomass at
producer level
• Least biomass at tertiary
consumer level
Pyramid of Biomass
Tertiary Consumer
(1.5 grams/square meter)
Secondary Consumer
(11 grams/square meter)
Decomposer
5 grams/square meter
Primary Consumer
(37 grams/square meter)
Producers
807 grams/square meter
Pyramid of Biomass
Planktonic ecosystem
dominated by small,
floating organisms
• Zooplankton consume
phytoplankton rapidly
• Producers population
can never become large
• Phytoplankton
reproduce rapidly
Inverted Pyramid of
Biomass of Aquatic
Ecosystem
Zooplankton
21 grams/square meter
Phytoplankton
4 grams/square
meter
Energy Flow Through Trophic Levels
• Matter of one organism passed to another when eaten
– Cycles through ecosystem
• Energy stored in organism passed to another when eaten
– Enters from sun
– Flows through trophic levels
– Lost as work and energy
Energy Flow Through Trophic Levels
Learning Objectives
• Analyze the flow of matter and energy through trophic
levels using various models, including food chains, food
webs, and ecological pyramids