The emergence of invasive species or excessive population growth of some species may raise concern about negative side effects. Examples are geese populations feeding on agricultural lands and musk rats digging holes in dikes used to control water levels. We are asked regularly whether these populations can be managed and what their effects may be on biodiversity and possible damage. A&W invests in the development of models, since these are an effective tool for a quantitative approach and help to generate hypotheses and objective estimates. Also genetics provide opportunities to get information, in particular on the origin and size of populations. In some cases, this may be preferable to other methods.