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Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Predation is the consumption of one organism by another. Predation occurs when one organism benefits from killing another. Herbivores, parasites, and parasitoids can also be considered predators.

One of the standard interspecies interactions within a community is the concept of predation. This is the idea that one organism eats another, now you may think well I know of predators. There's the lions that eat the gazelle, there's the predator that goes after Arnold Schwarzenegger I know what a predator is. But in actuality it becomes a lot more complicated because life doesn't pay attention to our nice definitions, what most people think of when they talk about predation is what would be otherwise known as a true predator. That's where you hunt down some other organism and you kill it and eat it. Okay so lion eats gazelle good, but what about an herbivore? It hunts down and kills its prey but its preys are plants that doesn't sound so predatory but it is considered a form of predation.

Then it gets a little bit goofy because well what if I just take a bite out of it but I don't kill it? So then they start talking about grazing or browsing and that's where an organism eats part of another organism but doesn't kill it. Now you can probably think of some examples of browsers or grazers for example a cow. When it goes out into the field it grazes or browses on the grass. It's not killing grass, it's just nibbling parts of it and you know the grass can grow back. Sometimes though an ecologist might say well a mosquito it lands on you, bites you and eats parts of you but it doesn't kill you. But we don't really don't like to think of mosquitoes as being browsing or being predators of humans. This blends over into something called a parasite, a parasite is an organism that lives most or all of its time on or in another organism usually harming that organism but not technically killing it at least not immediately. So for example a tapeworm that lives inside of you, is getting its food from you.

Now you may not immediately show the effects but what's happening is that, it's taking away some of the food supply that you're using, thus harming you and eventually it may actually cause all sorts of problems as your immune system eventually starts trying to fight it. This also bleeds into something called a parasitoid and that's another of these examples where probably some student raise their in some ecology class and said "hey professor you've told me the definitions of a predator and a parasite what about this?" A parasitoid is probably another definition that somebody had to come up with because life is messy. And this is when one organism lays its eggs or its lava in another and eventually once the eggs hatch they come up out of that other organism and eventually kill it.

For example there's many wasps and they'll do this, they'll land and they'll sting like a caterpillar, or sting a spider wherever their intended target is. And they'll paralyze the caterpillar but not kill it and then they'll lay their eggs inside the caterpillar, and the caterpillar is still alive and the eggs hatch and the larvae arise and eat the caterpillar from the inside out and then it erupts and releases the wasps. It's kind of nasty but that's predation.