# Variables and Parameters

What is the difference between a variable and a parameter?

In the context of these population-modeling equations, a *variable* represents the level of a particular population. In the mutualism section, there are two variables, *x* and *y*, which represent the two species that are helping each ot
her. When we write x' or dx/dt we mean the rate of change of population x.
A *parameter*, on the other hand, determines how much of an effect a particular phenomenon has on the populations.

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