Have you ever watched a show about the wild?  A pair of deer butt horns!  A shark eats a seal!  Lions run down a gazelle!  Is all nature like that?  All about eating and blood and guts?  Or is that just what keeps our eyes glued to the TV screen?  Let's look at some living things who work with each other rather than rip each other apart.  These are the type of things that might not make it on TV.  We will start with the not so nice ones and work our way to the nicest.  Maybe this will make us think better of the natural world.

When a lion kills a gazelle, it wants to eat as much as it can and maybe share the rest with its family.  Then there are some living things that will take small pieces of another living thing's body.  They usually are much smaller than the thing they are taking from.  Parasitism is when one living thing gets its energy from another living thing, does not give anything back, and hurts the thing it's taking things from.  You have seen them before.  Have you ever slapped a mosquito?  Ever had a tick?  Those are parasites.  These little robbers do not want to kill their host.  If they did, what would they eat?  A mosquito nipping at your arm may be annoying, but that's a lot better than a lion gnawing on your arm. 

Who are you calling a parasite!

Now let's get a little nicer.  Sometimes a living thing will live off the body of another living thing without hurting it.  They do not steal anything.  They do not bite.  They just think the body of another living thing is a great place to hang out.  Commensalism is when two living things live together and one gets good things out of it while the other is not hurt by it.  Have you seen a picture of a whale with rocky white things stuck to its skin?  Those are barnacles, living things that attach themselves to the whale.  Living on a whale does two good things for them.  First, nothing will try to eat them.  They are on a whale!  Also, they can eat things that float by.  They may make the whale's skin a little itchy, but they do not hurt it.  Unless, of course, the whale wants to go on a date.  Barnacles do not look very pretty.

Stick with me guys and I'll take you places.

Now let's get really nice.  While sharks are biting and elk are fighting, are there any animals that just get along?  Yes!  Actually, there are many.  Mutualism is when two living things work together and both get good things out of it.  Bees and flowers are the most common example.  Without flowers, bees could not make honey.  Without bees, flowers could not make new seeds.  It's win-win for these two.  There are lots of animals that get along.  Birds will live on the backs of zebras and eat the ticks that are drinking the zebra's blood.  The bird gets food.  The zebra gets its ticks taken away.  In some of these cases, one animal could not live without the other.  So, lions, eat your hearts out.  No, not that other animal's heart.

This works out great. I get what I want and you get what you want.

There's a word that we use for all of these kinds of relationships.  Symbiotic is when two living things live together and change how the other one lives.  Sometimes it's good for one and bad for the other.  Sometimes it's just good for one.  Sometimes it's even good for both.  These relationships do not end with animals living with animals.  Look at humans and dogs.  The dog gets food and love.  The human gets a friend and a guard.  If you see two living things living together, think about whether one is getting a better deal than the other. 

If you feed me I'll be your best friend.

A bird sits on a zebra.  A barnacle sticks to a whale.  A tick steals a little blood.  These are not as exciting as watching a shark hunt or a lion roar.  However, it is nice to know that there are some living things out there that are finding ways to live together.  We could take note of the animals that do not always make it on TV.


NECSI.  "Mutualistic Relationships."  NECSI, 2011.  <http://www.necsi.edu/projects/evolution/co-evolution/mutualistic/co-evolution_mutualistic.html>

NECSI.  "Parasitic Relationships."  NECSI, 2011.  <http://necsi.edu/projects/evolution/co-evolution/parasites/co-evolution_parasite.html>

CBU.  "Examples of Commensalism."  CBU, 2010.  <http://facstaff.cbu.edu/~seisen/ExamplesOfCommensalism.htm>