 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 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/m 2 ) Producers Herbivores Primary carnivores Top carnivores Detrivores/ decomposers 5

Energy flow pyramid  The amount of energy in each trophic level can also be estimated and plotted in a pyramid Energy flow pyramid (kcal/m 2 /year) 20,810 3, 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