# Carrying capacity

Let's start with the last possibility: there are only a limited number of resources (rotten bananas and such) in the environment, which induces a **carrying capacity **.

Here's how a carrying capacity works. Let's say that 1 banana can support 100 flies, and in my house I have exactly one banana. If there are :

**2 flies (very small population)** : everybody gets lots to eat, and achieves their full reproductive potential. But since we only started with a couple of flies, the population doesn't grow too much.

**50 flies (well below carrying capacity) :** each fly gets plenty to eat. There are a good number of flies, and they reproduce like crazy. The population starts to take off.

**90 flies (almost at carrying capacity) :** everybody gets just a little more than they need to eat. The population grows, but only a little.

**100 flies (carrying capacity) : **each fly gets exactly enough to eat to be able to reproduce itself, so that next month there will be exactly the same number of flies.

**110 flies** **(just above carrying capacity) : **each fly get a little less than it needs. On average the reproductive rate goes below replacement, and the population declines.

**200 flies** **(way above carrying capacity) :** each fly is grossly underfed, spindly, and malnourished, and can barely get up the energy to -- never mind. The population crashes. Only a few survivors, if any, are left to pick up the pieces.

Copyright University of Maryland, 2007

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