Problems with Energy Flowthrough Ecosystems

Energy transfer between trophic levels is inefficient

• Only 10% of the energy present in a given trophic level can be found in the next level.

• So the number of organisms that can be supported at each level also goes down each time

• What happens to toxins?

Biological Magnification

• Harmful substances like pesticides accumulate in higher concentrations in higher trophic levels

• Many such toxins accumulate in fat because they are lipid-soluble

• E.g. DDT accumulation in birds affects ability to deposit calcium in eggshells, even found in human breast-milk!

Energy Flow vs. Nutrient Cycling

• Energy flows through ecosystems - that is, it enters the ecosystem via sunlight, is stored temporarily in complex molecules, and ultimately leaves it in the form of heat.

• Nutrients cycle within ecosystems - that is, they are atoms (Carbon, Nitrogen, Phosphorous…) that stay within the ecosystem and are found at different times in different parts of the system.

The Big Picture: Energy Flow and Nutrient Cycling