Ecosystems and change over time (grade 6) · lesson

Resources living things need

💡 Every population depends on resources, and when a resource grows or shrinks, the population usually follows.

Resources are things living things need to survive. Some are living, like the plants a deer eats. Some are nonliving, like sunlight, water, air, and soil.

Resources are often linked. More rain means more grass. More grass means more food for animals that eat grass.

When a resource shrinks, fewer living things can survive. A lake that loses water can hold fewer fish.

🧠 Let's work it out

Follow the chain.
Rain → plants → animals that eat plants.
If a field gets more rain, it grows more grass, so it can support more grasshoppers.
If a dry year comes, there is less food, so the deer count drops.

What do you think comes next?

resource: something a living thing needs, like food or water
population: all the members of one species in one area

🔗 Khan Academy: Interactions in ecosystems · Khan Academy ↗

Competition

💡 When living things need the same limited resource, they compete, and each one gets less.

Competition happens when two or more living things need the same resource and there is not enough for all.

It can happen between different species, like rabbits and deer eating the same grass. It can also happen within one species, like crowded plants in one pot.

When a new animal moves in and eats the same food, the animals already there have less to eat.

🧠 Let's work it out

In a test, change only one thing.
Radish pots with 5, 10, 20, and 40 seeds got the same soil and water.
Only the number of seeds changed.
The crowded pots grew short plants.

What do you think comes next?

competition: when living things struggle for the same limited resource

Limits on population growth

💡 A population grows until it runs short of resources, then levels off near the carrying capacity.

With plenty of food and space, a population can grow fast. But resources always run short in time.

When they do, the population stops growing. It levels off.

The largest population an area can support over time is its carrying capacity. On a graph or table, it is where the numbers stop rising and stay about the same.

🧠 Let's work it out

Read the counts: 20, 60, 150, 200, 205, 198, 202.
The numbers climb, then bounce around 200.

What do you think comes next?

carrying capacity: the largest population an area can support over time

Predators and their food

💡 Predators depend on their prey, so when prey numbers change, predator numbers change too.

A predator hunts and eats other animals, called prey. Owls eat mice. Wolves eat moose.

When prey are plentiful, more predators can survive and raise young. When prey become scarce, the predators go hungry and their numbers drop.

Predator numbers often change a little after prey numbers change.

🧠 Let's work it out

Look at the order of events in a table.
Moose were plentiful in the early years.
The wolves grew in number during those years.

What do you think comes next?

predator: an animal that hunts other animals for food
prey: an animal that is hunted and eaten