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Ecosystems
Chapter 16
Overview
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Food Chains and Food Webs
Productivity
Ecological Pyramids
Biomagnification
Nutrient Cycles
Global Warming
Ecosystems
-The Community along
with:
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Nutrient Cycling
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Energy Flow
Energy Flow – Trophic Levels
The Food Chain
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Sunlight is captured by Autotrophs or
Producers using photosynthesis. selffeeders.
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Stored energy in autotrophs is transferred
to Heterotrophs – other feeders
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Includes Plants, Algae and Phytoplankton.
Also some chemosynthetic bacteria
Carnivores, omnivores
Decomposers use energy remaining in dead
organisms
Simple
Food Chains
Trophic Levels
Both
Marine and
Terrestrial
Productivity –Amount of food
in an ecosystem
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Primary productivity is growth of
producers
Gross productivity is the total amount of
food produced or ingested
Net productivity is amount available to
next trophic level, after respiration
Measured by weight or calories
See Table 2.1, pg. 26
Productivity
Amount of photosynthesis in an
ecosystemEquals amount of food
available for food chain
 Seasonal effects in north / south
seas
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Productivity rates:
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Kelp beds have highest productivity
Tropical rainforest highest per sq. meter
on land, but only covers 3.3 % of globe
Open ocean, one of the lowest, but
because it covers 65.0 % it equals
rainforest
Marsh lands nearly equal tropical
rainforest productivity
Summary of satellite data on global
primary productivity from 1997 to August
2000
Winter
NORTH
AMERICA
SPAIN
ATLANTIC OCEAN
AFRICA
Spring
Food Webs
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Energy transfer follows trophic
levels
Many animals eat at several trophic
levels
Omnivores: like most of us
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At salad bar you’re a herbivore
Eating a burger makes you a carnivore
marsh hawk
Higher
Trophic
Levels
crow
Sampling of connections in a
Tall grass prairie food web
upland
sandpiper
garter snake
frog
weasel
spider
Second
Trophic
Level
sparrow
earthworms, insects
First
Trophic
Level
badger coyote
prairie vole
grasses, composites
pocket gopher
ground squirrel
Energy Transfer in
Ecosystems Food / Energy
Pyramid
Primary Consumers eat producers,
incorporating the energy into the next
level.
 Only 10 % of energy consumed moves to
next level
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Animals loose 90% of the energy at each level
Why are Big Fierce Animals so Rare??
Consumers are Heterotrophs
Limited by Thermodynamcis
Energy Pyramid
Pyramid of Numbers
Nutrients Cycle
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Elements change form, but are not lost
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May be trapped in bio-inactive forms
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No more carbon now than when the
dinosaurs lived !!
Ice, fossil fuels
Held together in chemical bonds
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Breaking bonds – releases energy
Uses energy to form bonds
Nutrient cycles to learn:
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Water
Carbon
Nitrogen
Carbon Cycle
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Large reservoirs in rocks (99%), fossil
fuels
Marine component as well
Energy flows through carbon cycle as the
food chain
Associated with greenhouse effect
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Build up of CO2 , CH4 etc. in atmosphere
Raise sea levels – flooding islands, coasts
More severe weather ??
Nitrogen Cycle
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Largest pool is in atmosphere (80%) a
generally bio-inactive form
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Nitrogen fixing bacteria capture it from air
Many native plants have nitrogen fixing root
nodules
After water nitrogen is the most growthlimiting nutrient for plants
Nitrogen important for Autotrophs to make
proteins (enzymes)
Protein breakdown releases it back to
environment in urine
Nitrogen Cycle
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Always need to replenish agriculture
fields with fertilizer.
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Denitrifying bacteria release it back to
atmosphere
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Much of it is leached away, gets in drinking
water supplies, pollutes lakes
Now add antibacterial agents to fertilizers !
Tightly cycled in Ecosystems
Forests and Nitrogen Cycle
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Most of nitrogen tied up in a tree’s
Biomass
Soils tend to be nutrient poor
Burning trees releases nutrients
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Soil fertility only lasts a few seasons
Nitrogen is leached out with rains
Classic problem with Slash and
Burn
Hubbard Brook
Loss of Nitrate from a forest
after clear cutting
1620
1850
1850 (pocket only)
1990
Remaining virgin forest
Extent of deforestation in the United States