# The Lotka–Volterra Equations

### Sunday May 31, 2020

###### •  mathematics • differential equations •  ecology •  environmental science •  CMNA •

My favorite set of differential equations are the Lotka-Volterra equations. These equations describe predator-prey relationships. What impresses me the most about them are their complete simplicity:

\begin{align} \frac{dx}{dt} &= \alpha x - \beta x \text{, and} \\ \frac{dy}{dt} &= \delta x y - \gamma y \end{align}

In these equations, $x$ and $y$ are the population counts of some prey species and some predator species. $\frac{dx}{dt}$ and $\frac{dy}{dt}$ are their respective growth rates. The Greek describes the relationship between the two. Obviously, this is a bit simpler than we might imagine the reality, but it is, after all, only a model. But I think it is a powerful demonstration of how differential equations can model dynamic systems with elegance and beauty.

The Python agent-based modelling platform, Mesa, includes a dynamic system that models the Lotka-Volterra equations in a different way, but show the relationship through a population of sheep and wolves. Here’s a video of a typical run: