Question

How does carrying capacity affect the number of organisms in an ecosystem?

Answer 1

One of ways to understand how many organisms can grow in an ecosystem is to look at the very basics.

You have seen and heard about ecosystems as expressed a pyramid: a large base with layers above that are smaller and smaller.

The base of all ecosystems are the producers or what we call plants such as trees, grass, shrubs, herbs and algae. These use sunlight and carbon dioxide and water to make food for their growth, reproduction and repair.

Of all of the production made by those producers, only 10% is left over for the second level of the pyramid.

The second level eats or consumes that 10% of first level and these are called primary consumers or herbivores (herb eaters).
After using the food from the first level for growth, reproduction and repair, only 10% of that first 10% is available for the next level.

That gives the last level 1% from that first level to grow, reproduce and repair. This third level contains secondary consumers.

Each step up the pyramid, the number that can be supported is reduced by 90%. Fewer herbivores, then even fewer carnivores.
Most ecosystems can only support 4 levels.
Only two can support 5: tropical and temperate rainforests.