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)

nutrientcycling

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

• Parasites

• Omnivores

• Decomposers

• Detritivores

SPRING

rodents, rabbits

fruits

insects

birds

SUMMER

rodents, rabbits

fruits

insects

birds

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

OmnivoresAnimal 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 fruit-bearing 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

• A straight line

sequence of who eats

whom

• Simple food chains

are rare in nature

MARSH HAWK

UPLAND SANDPIPER

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

FoodWeb

http://www.vtaide.com/png/oceanchain.htm

Two Types of Food Webs

Producers (photosynthesizers)

Producers (photosynthesizers)

herbivores

carnivores

decomposers

decomposers

detritivores

ENERGY OUTPUT ENERGY OUTPUT

Grazing Food Web Detrital Food Web

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

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

Trophic Levels - Definitions

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

detritivores

21

383

3,368

20,810 kilocalories/square meter/year

top carnivores

carnivores

herbivores

producers

decomposers

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_environment.htm

• http://www.globalchange.umich.edu/gctext/Inquiries/Inquiries_by_Unit/Unit_4.htm