About this video
Organisms need resources such as food, water, shelter and space, and most of these are limited. When resources are plentiful, populations grow, but as populations get bigger, competition increases and growth slows, stops or even reverses. Locust plagues show this pattern: heavy rain brings lots of food, locusts multiply and swarm, then crash when the food runs out.
You'll be able to
- explain what a resource is and give biotic and abiotic examples.
- describe how population size changes when resources are plentiful or limited.
- explain why competition increases as a population grows.
- use resource availability to explain a locust plague.
Key words
- resource
- Anything an organism needs to live, like food, water, shelter or space.
- limited resource
- A resource that is not available in an endless supply.
- competition
- What happens when many organisms depend on the same limited resources.
- population
- A group of the same kind of organism living in the same area.
Transcript
- [Narrator] For thousands of years, people have written about huge swarms of locusts appearing out of nowhere, eating entire fields of crops, and then just disappearing just as quickly. What causes something like that to happen? The answer is resources. All living things need resources to survive and reproduce, but what exactly is a resource?
Well, resource is anything an organism needs to live. Some resources come from living things, like food, we call them biotic factors, while others come from non-living parts of the environment, like water, air, shelter, and space. We call them abiotic factors.
When organisms have enough of these resources, they're more likely to stay healthy and grow and produce offsprings. And when many organisms have enough resources, their population can grow. But there's an important catch: most resources are limited. They're not available in an endless supply.
Think about it. A field, for example, can only grow so much food, a pond can only hold so much water, and a forest can only have so many places to live. So the question is what happens when a population gets bigger and bigger, but the amount of resources stays the same?
To answer that question, let's imagine a small group of rabbits living in a meadow. At first, there's plenty of grass, water, and space for all of them. The rabbits have enough to eat, so many survive and have babies, and so the rabbit population starts to grow.
But as more and more rabbits live in the same meadow, they all need to share the same grass and the same water. Eventually, there isn't enough for everyone. So what happens next? Competition. These rabbits begin competing for grass, for water, for space. Some rabbits may not get enough food or space to survive, and so fewer babies are born, and as a result, the growth of the rabbit population slows down.
It may even shrink. And this is not just the story of rabbits. This is a common pattern we find everywhere in nature. When there is plenty of resources, organisms thrive and the population grows, but as populations grow larger and larger, resources start becoming limited.
As a result, competition increases and the population growth slows down, or it can even stop. And by the way, competition can also happen between different species. For example, a bird and a squirrel might compete for the same seeds, or different kinds of plants might compete for the same sunlight and water.
And this competition is not about animals being mean to each other or being aggressive to each other. No, no, no, it's simply what happens when many organisms depend on the same limited resources. As a result, this competition affects which organisms survive and reproduce.
Now, let's return to the locusts. Locust plagues often begin after a period of heavy rainfall. Why? Because the rains help plants grow very quickly, which creates lots of food for locusts. With so much food available, locust populations grow very fast, and locusts have a special ability that most of the organisms don't really show in the same way.
When their numbers get very high and they become crowded together, their bodies and behavior change. They shift from living alone to actively seeking each other out, gathering in huge groups and moving together as swarms. These swarms devour crops and fields. That's what turns ordinary population growth into massive locust plagues people have feared for centuries.
But that growth doesn't last forever. As the locust population gets larger, they begin to use up the available plants. Eventually, there isn't enough food to support such a huge number. Competition for resources increases and the population crashes back down, making the swarms disappear.
This is why population growth and the resources are always connected. Organisms need resources to live. These resources, like food, water, oxygen, shelter, space, sunlight, they're often limited. When they appear plentiful, populations can grow, but as the populations grow, individuals must share those limited resources, making the resources scarce.
And when the resources are scarce, population growth slows or even stops. And so, look, the availability of resources helps determine how big or small a population can become.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.