This NetLogo simulation, developed at Northwestern University, models three initial populations (grass, bugs, birds) within an ecosystem over time. Settings within the simulation help students to make sense of how disruptions, such as an invasive species (mice), disease (reduction in number of bugs), and fire (burning of grass), may impact population dynamics and ecosystem stability over time. By manipulating these settings, students can ask questions and then look for evidence using mathematical representation to support their thinking about what factors affect biodiversity and cause populations to be either stable or unstable over time. Instructional supports include background information, instructions for using the simulation, and suggestions for extending the simulation. Although the downloaded version is recommended by the creators, a web version is also available at http://bit.ly/NetLogoSimulation.