1. Problems with Energy Flow through Ecosystems

2. 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?

3. 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!

4. 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.

5. The Big Picture: Energy Flow and Nutrient Cycling