The goal of conservation biology is to maintain healthy and diverse populations of native species of organisms. Those include plants, animals, fungi, and microorganisms. The human landscape damages natural habitats and reduces populations of many species. But in suburban and urban environments that are already disrupted, we are interested in preserving the wildlife that we can. Small backyard ponds can help. They provide habitat for aquatic invertebrates, may be sources or sinks for some amphibians, and provide access to water and food for some larger animals. In these mesocosms, we are trying to maintain as many native species as we can. For most, these are ecological ‘sources’ or are neither a ‘source’ or a ‘sink’. We have to hope that there are few or no species for which these ponds are a ‘sink’.