Ecosystems: Trophic
Relationships
Metabolism
Photosynthesis fixes carbon into sugars
Respiration breaks down sugars and
releases energy
Aerobic respiration occurs in the presence
of oxygen
Anaerobic respiration or fermentation
occurs in the absence of oxygen
Producers
Autotrophs synthesize sugars using
energy from the sun or chemicals
Plants, algae, and bacteria on land
Lichen in early succession and tundra
Phytoplankton in the oceans
Primary Consumers
Herbivores
Zooplankton
Secondary Consumers
Carnivores
Tertiary Consumers
Top Carnivore
Omnivores
Most humans
Bears
Decomposers
Bacteria
Fungi
Break down decaying material
Detrivores
Feed on waste or
dead bodies
Insects and scavengers
Energy Flow
Ecosystems recycle matter but energy
flows one way
Decomposers break down nutrients so
that they may be used by producers
Food Chain
Shows the path of energy from
producer to consumer
Arrows show direction of energy flow
Trophic Levels
Other Pyramids
Ecological Efficiency
Ranges from 2-40%
Typically estimated at 10%
Ninety percent loss due to entropy
(mostly heat)
Primary Productivity
Gross Primary Productivity (GPP) is the
rate at which solar energy is converted
to biomass
Net Primary Productivity (NPP) is the
energy stored minus the energy used
for metabolism
Measured in kcal/m2/yr
NPP by Ecosystem Type
Total NPP by Ecosystem Type
Food Web
Trophic Level Question
Each week, an owl must eat an average of
five mice weighing 10 grams each in order to
survive. How much plant material would each
mouse have consumed?
Solve this problem, and include set up and
units.
Explain how this scenario relates to trophic
levels.
Assume that energy and mass are
proportional with the same constant of
proportionality for each of these organisms.
The Answer…
It is estimated that only 10 percent of
the energy at each trophic level is
available to organisms at the next
higher level
One owl must consume five mice per
week in order to survive.
More Answer…
Entropy occurs and not all of the grass
is converted to biomass.
A 10-gram mouse would convert 10
percent of the plant material, so each
mouse would have to consume 100
grams in order to survive.
More Answer…
The mouse utilizes some of this grass
for normal living functions, plus
releases some as waste material.
Grass is at the producer level. It makes
up the greatest biomass, it is the most
numerous, and it has the greatest
combined energy of the system.
More Answer.
As herbivores, mice would make up the
next trophic level, and have less
biomass, fewer individuals, and less
stored energy than the trophic level
below it.