Have you ever watched a show about the wild? A shark (鲨鱼) eats a seal! Lions run down a gazelle! Is all nature like that? All about eating and blood? Or is that just what keeps our eyes glued to the TV screen? Let's look at sonic living things who work with each other instead of ripping each other apart.
When a lion kills a gazelle, it wants to eat as much as it can and maybe share the rest with its family. There are some living things that will take small pieces of another living thing's body. 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.
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. 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 (鲸) with rocky white things stuck to its skin? Those are barnacles(藤壶). They attach themselves to the whale, so nothing will try to eat them and they can eat things that float by.
Now let's get really nice. While sharks are biting and lions 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.
We use the word "Symbiotic (共生的)" for all of these kinds of relationships. 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. So, it is nice to know that there are some living things out there that are finding ways to live together. We could pay attention to the animals that do not always make it on TV.
