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Chapter 55
Ecosystems
Ecosystem
• All the organisms and abiotic
factors in a community.
Ecosystem Studies
1. Energy Flow – the movement
of energy through trophic
levels.
2. Chemical Cycling – the
movement of matter from one
part of the ecosystem to
another.
Trophic Levels
• Division of an ecosystem
based on the source of
nutrition (energy).
Trophic Levels
1. Primary Producers
2. Primary Consumers
3. Secondary Consumers
4. Detritivores
Primary Producers
• Usually plants, capture energy
and store it in chemical bonds.
• Are the source of the energy
available to an ecosystem.
Primary Consumers
• Organisms that feed on the
producers.
• Ex: Herbivores
Secondary Consumers
• Organisms that feed on the
Primary Consumers.
• Ex: Carnivores
Comment
• There may be several layers of
Secondary Consumers in an
ecosystem.
Detritivores
• Get their energy
from the organic
waste produced
by all levels.
• Ex: bacteria and
fungi
Food Chain
• Linear
pathway of
who eats who
in an
ecosystem.
Food Webs
• Network
showing all
the feeding
relationships
in an
ecosystem.
Primary Productivity
• The rate at which light
energy is captured by
autotrophs or primary
producers.
• Gross PP – the maximum of
energy capture
• Net PP – the amount left
after Rs
Primary Productivity
• NPP = GPP – Rs
• GPP = NPP + Rs
• NPP = Net Primary
Productivity
• GPP = Gross Primary
Productivity
• Rs = Respiration
Available Energy
• Daily - 1022 joules of solar
radiation.
• 1% - captured by Ps.
• About 150 billion tons of
organic matter is created each
year.
Primary Producers
• 50 - 90% of GPP is lost to Rs by
the primary producers.
• NPP = 10 - 50%
• Animals - use only NPP, which
limits the food webs.
Limiting Factors
• Material or nutrient that is not
present in sufficient quantity
for the primary producers.
• Ex: N, P, K, Mg
Light, CO2
Energy Transfers
• Not 100% efficient.
• Why?
• Second law of
thermodynamics.
• Waste.
• Materials that can’t be
digested etc.
Energy Transfer
• Averages 10% with each
Trophic Level change.
• Exam expectations – may give
you data in energy units and
ask you to calculate the %.
Question ?
• Why do most ecosystems have
only 3 - 4 trophic levels?
• There isn’t enough energy
passed up through the food
web to support more levels.
Implications
• There has to be fewer high
level consumers in a food web.
• The higher level consumers
usually need a large
geographical area.
Question
• Which would support more
humans per area?
• Eating meat?
• Eating plants?
Pyramids
• Graphical representation of
relationships in ecosystems.
• Ex:
1. Productivity
2. Biomass
3. Numbers
Chemical Cycling
• Matter is recycled through
ecosystems.
• Ex: Biogeochemical Cycles
Matter Reservoirs
1. Organic Materials
2. Inorganic Materials
• Available  Unavailable
Representative Cycles
•
•
•
•
Water
Carbon
Nitrogen
Know one or more of these
cycles for an essay question.
Energy vs Matter
• Energy - flows through
ecosystems and is mostly
lost as heat.
• Matter - cycles in
ecosystems.
Question ?
• What is Man's influence on
Ecosystems ?
• Humans have had many
negative impacts.
Hubbard Brook
Biological Magnification
• The concentration of toxins in
successive levels of a food
web.
• Ex: DDT
Heavy metals
(Hg, Cd Pb)
Causes
• Not broken down by
digestion/decomposition.
• Lipophilic.
• Concentrates and effects the
upper levels of the food web.
Greenhouse Effects
• The trapping of heat by the
Earth's atmosphere. (CO2, H2O).
Carbon Dioxide Levels
• Prior 1850 - 274 ppm
1958 - 316 ppm
1992 - 351 ppm
• Point: the levels of CO2 are
rising. The cause is probably
due to humans.
Causes
• Industrialization.
• Burning of fossil fuels.
• Loss of forests.
Result
• Earth will heat up.
• Ice caps melt and sea levels
will rise.
• Climate shifts.
• Increased Ps (?)
Habitat Destruction
• Worst problem threatening
most species today.
Comment
• Man has a major impact on the
Biosphere.
• Man needs to learn how to
work with the Biosphere.
Summary
• Know the tropic levels of
ecosystems.
• Know an example of a food
chain and a food web.
• Know how energy moves
through an ecosystem.
Summary
• Know how matter moves
through an ecosystem.
• Know one or more examples
of matter cycling.
• Be able to discuss in detail a
human impact problem on
ecosystems.