Picture a polar bear... in the desert. No, what you're imagining is way too cute. Take off the sunglasses the swim trunks. There, he's hot, he's hungry, he's downright miserable. Why is he such a grumpy bear? Well, it's because he's not where he belongs. There aren't any tasty seals to eat, no cold water to enjoy and no snow to sleep in. The desert isn't his habitat.

You know that a habitat is the area where something lives, but from polar bears to porcupines, animals don't just need a place to live. They also rely on the other living and non-living things around them to survive, and life looks different in different places around the world. So, what makes a habitat a home? 

Well, what do you need? I need sandwiches, pancakes, carrots, maybe some nice peaches - so I need food, and I need water. I need a place to live, and I need a place to film Crash Course videos. You could say this is my habitat.

Animals need these things too: food, water, shelter, and space to live. For animals, their food comes from their neighbors - the other living things in their habitat. You know that plants and animals all fall somewhere along the food chain which is a model we use to describe the flow of energy between living things. But the real world is made up of lots and lots of food chains and those chains can get kind of messy. 

I mean, look at our polar bear. Sure, his favorite food is seal but in a pinch, he'll eat walrus, dead whales, birds' eggs, and if he has absolutely no other choice, plants. The polar bear is at the top of multiple food chains, and that's not unusual most animals don't just eat one thing and neither do I. I'm at the top of the pancake food chain and the carrot food chain. It just so happens I prefer pancakes. 

So you can see how food chains are actually all tangled around with each other, with many different ones overlapping kind of like a web, so we call this a food web. Food webs are big tangled systems that include every plant and animal in a habitat, and as you might guess, all food webs are different. Let's compare two different habitats to see how the food webs play out. 

First, we'll go back to our old stomping ground - the forest. Let's begin with, you know this people, the plants. Trees, grass, and other plants that change energy from the sun into sugar. But then you have some animals that eat other animals. This is where things get a little more complicated. Today an owl makes a mouse his lunch, but tomorrow it may be a rabbit. Today a snake snacks on a squirrel, but a few days later our owl friend might make a meal of another meat-eater like the snake.

Finally, the decomposers - insects, fungi, and bacteria are breaking down whatever's leftover, from uneaten rotten fruit to leftover animal carcasses. As they break down matter, they provide more nutrients for the plants. 

It's a bit of a different story up in the Arctic, I mean look at all that ice. I know what you're thinking, where are the plants? How do we have a food web without plants? Zoom in on the seawater, zoom way in, further, further, stop! Can you see those tiny plants? They're called phytoplankton, and just like plants on land, they convert energy from the sun. Really small creatures called zooplankton eat the phytoplankton, and all kinds of small fish dine on the zooplankton. Larger fish eat the smaller fish. There are big marine mammals too, beluga whales eat fish while humpback whales eat the tiny plankton and krill.

And what else eats fish? Seals. That's our polar bear's favorite food, but up here you can't afford to be picky, so he may have to nibble on some whale carcass if necessary. As for decomposers, there aren't many bugs or earthworms in this cold climate, there are bacteria but since it's so cold the decomposers break down matter much more slowly than in the forest. 

 
So you can see, food webs and the ecosystems that support them look different in different parts of the world depending on the habitat conditions. Flat or mountainous land, more or less water, these seemingly small changes in habitats affect what kind of plants and animals live there. 

Up in the Arctic, a polar bear has the right conditions to keep him happy. First, he fits into his food web perfectly. The food that's available to him has enough fat and protein to keep his energy up. Second, he fits into his habitat perfectly. He has the body adaptations to not just survive, but feel really comfortable in the super cold. A polar bear isn't built to survive in the desert or the forest. So let's put out poor polar bear back where he belongs. I was starting to feel bad for the guy.