Feeding Relationships
Ecosystem
An association of
organisms and
their physical
environment,
interconnected
by ongoing flow
of energy and a
cycling of
materials
energy input
from sun
PHOTOAUTOTROPHS
(plants, other producers)
nutrient
cycling
HETEROTROPHS
(consumers, decomposers)
energy output (mainly heat)
http://www.eduweb.com/portfolio/earthsystems
/food/foodweb2.html
Important Terminology:
Modes of Nutrition
• Autotrophs
– Capture sunlight or chemical energy
– Producers
• Heterotrophs
– Extract energy from other organisms or
organic wastes
– Consumers, decomposers, detritivores
Photosynthesis is the process by which
plants convert energy from the sun to
usable energy for humans
Human survival depends on the stored
energy in agricultural ecosystems
Consumers
• Herbivores
• Carnivores
insects
rodents,
rabbits
• Parasites
birds
• Omnivores
• Decomposers
SPRING
fruits
SUMMER
fruits
rodents,
rabbits
insects
birds
• Detritivores
Seasonal variation in the diet of an
omnivore (red fox)
Consumers
• Herbivores
“plant eaters”
• Carnivores
“meat eaters”
• Parasites
“living eaters”
• Omnivores
“all eaters”
• Decomposers “dead thing/waste eaters”
• Detritivores
“eat materials from living things”
Herbivores
Animals that get energy from
eating plants
• Possess special
digestive systems
for digesting all
kinds of plants
• Need a lot of
energy to stay
alive
• May eat all day
long
Omnivores
Animal that eats either other
animals or plants
• Some will hunt and
others will
scavenge for dead
matter or eggs of
other animals
• Generally eat only
the fruits and
vegetation of fruitbearing plants
Carnivores
Generally eat
herbivores, but
will also eat
omnivores
• Require large amounts of energy in order to
hunt and kill
• The bigger the carnivore, the more it has to eat.
• Important to the ecosystem because they keep
other species from becoming overpopulated.
Decomposers
Food Chain
MARSH
HAWK
• A straight line
sequence of who eats
whom
UPLAND
SANDPIPER
• Simple food chains
are rare in nature
GARTER
SNAKE
CUTWORM
Decomposer Food Chains
• Organisms that receive energy from dead
plant and animal material
• Make up majority of food chains
• Scavengers eat the remaining energy in
large dead organisms
– Ex: Vultures eat the carcasses of dead animals
Food
Web
http://www.vtaide.com/png/oceanchain.htm
Two Types of Food Webs
Grazing Food Web
Producers
(photosynthesizers)
Detrital Food Web
Producers
(photosynthesizers)
herbivores
decomposers
carnivores
detritivores
decomposers
ENERGY OUTPUT
ENERGY OUTPUT
Feeding Levels
• Important terms:
– Trophic levels
– Detrivores
– Decomposers
– Pyramid of Numbers
– Pyramid of Biomass
– Pyramid of Energy Flow
Trophic Levels
Trophic Levels
• The source of energy (input) for all
ecosystems is the sun
• All the organisms at a trophic level are the
same number of steps away from the
energy input into the system
• Producers are closest to the energy input
and are the first trophic level
Feeding Levels
• First trophic level
– always plants
• Second trophic level
– primary
consumers
• Third trophic level
– secondary
consumers
Trophic Levels - Definitions
1. Primary Producer = Autotrophs
support all other trophic levels by
synthesizing sugars and other organic molecules
using light energy.
2. Primary Consumers = Herbivores
consume primary producers.
3. Secondary Consumers = Carnivores
eat herbivores.
4. Tertiary Consumers = Carnivores
eat other carnivores.
5. Detritivores = Consumers
derive energy from organic wastes and dead organisms
Energy Losses
• Energy transfers are never 100 percent
efficient
• Some energy is lost at each step
• Limits the number of trophic levels in an
ecosystem
• Energy flows through the food chain but only
about 10% of the energy is passed on from one
trophic level to the next.
– Ex: Plant has 100kJ, caterpillar uses 10% for life
processes, 90% is lost as heat or waste
All Heat in the End
• At each trophic level, the bulk of the
energy received from the previous
level is used in metabolism
• This energy is released as heat energy
and lost to the ecosystem
• Eventually, all energy is released as
heat
Environmental Pyramids
• Food chains are useful for describing
basic feeding relationships among
organisms
• Pyramids illustrate different feeding
relationships
– visual comparisons among organisms at
different trophic levels within the same
pyramid and between pyramids
• Pyramid of Numbers
• Pyramid of Biomass
• Pyramid of Energy
Pyramid of Numbers
• Shows the numbers of organisms that are
required to feed the next trophic level.
• The greatest number of organisms is in the
first trophic level, least number on top of the
trophic level
Pyramid of Biomass
• Shows the relative mass of the
organisms at each trophic level
• Shows the energy available in each
trophic level
• More useful than pyramid of numbers
because it takes into account the size
of the organism
Pyramid of Energy Flow
• Shows the amount of nutrient energy at
each trophic level (difficult to measure
• Shows how the energy available at each
trophic level is greatest at the bottom of
the food chain and least at the top
• Pyramid of energy is always upright and
cannot be inverted, the other pyramids
can be
Pyramid of Energy
Pyramid of Energy Flow
• Primary producers trapped about 1.2 percent
of the solar energy that entered the
ecosystem
• 6-16% passed on to next level
top carnivores
21
carnivores
herbivores
383
decomposers
3,368
producers
20,810 kilocalories/square meter/year
detritivores
Food and Population Size
• The closer humans are to the
producer, the more usable energy we
consume
• The further we are down the food
chain, the less energy we receive from
the producers
• Fig 1.23 pg 28
Food and Competitors
• Monocultures – where humans mass
produce a particular type of food
• This decreases biodiversity and
increases pests
– Ex: Population of aphids can become out
of control when their food source is grown
as a monoculture
– Ex: Wheat Rust article
• By selecting plants with desired
characteristics, scientists have been able to
produce also reduced the genetic variety of
crops.
• Historically, humans relied on about 200
different species of plants.
• Today we rely heavily on about 20 different
species – wheat rice, corn, and potatoes being
the most common.
• Plants selected for rapid growth and desired
aesthetic qualities may not be ideally suited to
withstand disease an other negative
environmental conditions
Poisons in Food Chains
• Pesticides are used to kill pests but
are designed to not harm plants or
humans
• Biological Magnification:
– once pesticides enter a food chain, its
concentration increases as it moves
through the food chain
– Ex: DDT in food chain (pg 30-31)
Biological Magnification
A nondegradable or slowly degradable
substance becomes more and more
concentrated in the tissues of
organisms at higher trophic levels of a
food web
DDT in Food Webs
• Synthetic pesticide
banned in the United
States since the 1970s
• Birds that were top
carnivores accumulated
DDT in their tissues
Consuming the Planet
• Human population is increasing rapidly!
– Due to decrease in death rate with medical and
scientific advancements
• We are consuming the earth’s natural
environment to feed ourselves
• We are also using up resources for
convenience
– Ex: cotton, tobacco, domestic pets (birds, fish,
etc)
• We are destroying natural ecosystems
– Burn forests, drain wetlands, pave highways,
build golf courses
References/Resources
• http://faculty.southwest.tn.edu/rburkett/
ES%20%20%20understanding_the_environm
ent.htm
• http://www.globalchange.umich.edu/gc
text/Inquiries/Inquiries_by_Unit/Unit_4.
htm