When University of Minnesota professor Donald Alstad created Populus more than 20 years ago, he had no idea of the wide-spread impact it would have in the fields of ecology and evolutionary biology. Now the software has been downloaded more than 200,000 times by hundreds of universities all over the world. Tim Mousseau, a professor of biology at the University of South Carolina, said Populus allows students to see the consequences of a changing environment on different populations of animals. Students can explore in real-time the effects of mutation, different levels of competition and what can result from interactions between species. The software shows how all these things affect the natural environment, he said. âÄúIt had a profound influence on educating our students at all levels, undergraduate and graduates,âÄù Mousseau said. Alstad, a professor in the Department of Ecology, Evolution and Behavior, began work on Populus in the 1980s through grants from the National Science Foundation and IBM. The name Populus is a combination of the words population and calculus. Through Populus students can watch how growth of a population changes by introducing or removing an element. The software allows students to play with values and experiment. Alstad had already been teaching ecology and evolution at the University for several years before he began working on Populus. He, along with other professors in the department, knew students were struggling with the mathematical models used in class. With Populus, the students could now visualize these abstract and difficult models, Alstad said. A model can involve a situation with a predator and prey and how they interact in nature. Students can change the growth rate of one and see how it affects the other species. Students can even change how much prey a predator has to eat. âÄúIt allows us then to predict interesting things about how these species are going to interact in the wild,âÄù Alstad said. By 1991 Alstad had sent the program out to more than 600 universities, charging only the price of the disc the software was on. Alstad started distributing it through the Web in the mid-1990s. Now it can be downloaded free off its Web site. A download counter was put on the Web site in 2003. Since then, the counter has recorded over 200,000 downloads of the software. Though Alstad received funding early on, the project was not given funding for continued development, said Aaron Ellison, a senior ecologist at Harvard University. âÄúDon has really done this as a labor of love for the last 20 years of his career,âÄù Ellison said. âÄúItâÄôs pretty bullet proof at this point and heâÄôs done that on the cheap.âÄù Earlier on, Alstad worked with undergraduate programmers from the Institute of Technology who helped him update the program, including making the format more user-friendly. Ellison first learned about the software when he was teaching at Mount Holyoke College in Massachusetts in the Department of Biological Sciences. He used the software from 1991 until he stopped teaching 10 years later. Populus helps biology, ecology and environmental science students explore complex mathematical ideas involved with ecological systems, Ellison said. The students do not have to solve tough equations because the software does it for them based on the information the students give it. âÄúSo what Populus lets you do is see how these models work without you having to take three semesters of calculus,âÄù Ellison said. âÄúIn a sense, what it is is an open-ended equation solver for people who donâÄôt understand equations.âÄù It is not a traditional science lab tool by any means, Ellison said. âÄúThe students have to actually think about what theyâÄôre doing and the results can be unpredictable and so it really lets the students learn how processes work,âÄù he said.