Understanding What Organisms Eat with Stable Isotopes
WHAT ARE STABLE ISOTOPES?
I use stable isotopes to determine what organisms are eating. Remember isotopes from middle school chemistry? They're elements with same number of protons but different numbers of neutrons. They're unlike radioactive elements like carbon-14 because they don't decay. They are stable isotopes!
ISOTOPE FRACTIONATION
Carbon-12
Carbon-13
Nitrogen-14
Nitrogen-15
When you eat some food with carbon and nitrogen, your body preferentially metabolizes the lighter isotopes because the bonds are easier to break. I think of it like a game of red rover. If you have an option between breaking through the hands of two small children or one small child and one large child, you would choose the two small children. The same is true with isotopes. Your body preferentially breaks the bonds between the two lighter atoms.
ISOTOPES IN FOOD WEBS
Organisms preferentially break the bonds between the lighter isotopes and leave the heavier isotopes in their bodies. When a predator comes eats that organism, they are eating more heavy isotopes than that first organism. So as you move up the food chain, the organisms have more heavy isotopes.
