Necessary materials: PowerPoint Guide

If teacher has internet access, the following YouTube video would be a good tool at Slide 12 “Trophic Level Cascades Complete” at http://www.youtube.com/watch?

v=yg5ieYKvYI8

Teacher Information!

Ecosystem Productivity

Principles of Ecology

Students will be able to… Discuss trophic levels and energy flow in

ecosystems

Food chains Definitions reviewed:

Producers autotrophs make up the base of an ecosystem

Consumers eat other living organisms Detrivores/decomposers consume dead

organisms and fecal wastes

Primary productivity The rate at which producers capture & store

energy in their tissues Gross = total Net = after respiration The most productive ecosystems in the world

estuaries, swamps, marshes, tropical rain forest

Net primary production per unit area of the world’s common ecosystems

Factors influencing primary productivity Climate & nutrients Morphology & size of organism Rainfall Temperature Season Soil (mineral & nutrient availability)

Pathways of energy flow Energy from primary productivity can flow

through 2 categories of food webs Grazing food webs

Producer Primary consumer Secondary consumer tertiary consumer…

Detrital food webs Energy flows from producers to detrivores &

decomposers

Trophic levels Feeding levels with respect to primary source

of energy Producers & consumers each occupy a

different trophic level Energy is lost at each level

Biomass The total weight of all living organisms Biomass at each trophic level biomass

pyramid

Biomass pyramid(grams/m2)

809

37

11

1.5

Producers

Herbivores

Primary carnivores

Top carnivores

Detrivores/decomposers5

Energy flow pyramid The amount of energy in each trophic level

can also be estimated and plotted in a pyramid

Energy flow pyramid(kcal/m2/year)

20,810

3,368

383

21

Producers

Herbivores

Primary carnivores

Top carnivores

Detrivores/decomposers

5,060

Why do energy and biomass decrease at higher trophic levels? Not all biomass is consumed from one

trophic level to next Not all that is consumed is turned into

biomass Shorter food chain/web = less loss of energy

Supports idea that vegetarianism is the best way to feed a large population…

Vegetarianism Results in a decrease of human position on

food chain This won’t solve world hunger

Only 25% of earth’s land can be farmed We need ruminants

The “Cellulose Dichotomy” Cellulose most abundant, naturally-occuring organic

molecule on earth Humans can’t digest it Ruminants can digest it

Cattle, sheep, goats Deer, bison, antelope, moose, elk

“Hind-gut fermentors” can digest cellulose Horses, rabbits, some rodents cellulose

Review Discuss trophic levels and energy flow in

ecosystems