Charged with describing the current state of the environment, scientists worldwide collaborated to produce the Millennium Ecosystem Assessment. In seven synthesis reports and other technical documents, the assessment summarizes the Earth's present condition and the impacts humans have on critical ecosystem services.

Mycorrhizae occur in nearly all terrestrial ecosystems. Resource exchange between host plants and mycorrhizal fungi influences community, ecosystem, and even global patterns and processes. Understanding the mechanisms and consequences of mycorrhizal symbioses across a hierarchy of scales will help predict system responses to environmental change and facilitate the management of these responses for sustainability and productivity. Conceptual and mathematical models have been developed to help understand and predict mycorrhizal functions. These models are most developed for individual- and population-scale processes, but models at community, ecosystem, and global scales are also beginning to emerge. We review seven types of mycorrhizal models that vary in their scale of resolution and dynamics, and discuss approaches for integrating these models with each other and with general models of terrestrial ecosystems.

We quantified the threats facing 488 species in Canada, categorized by COSEWIC (Committee on the Status of Endangered Wildlife in Canada) as extinct, extirpated, endangered, threatened, or of special concern. Habitat loss is the most prevalent threat (84%), followed by overexploitation (32%), native species interactions (31%), natural causes (27%), pollution (26%), and introduced species (22%). Agriculture (46%) and urbanization (44%) are the most common human activities causing habitat loss and pollution. For extant species, the number of threats per species increases with the level of endangerment. The prevalence of threat types varies among major habitats, with overexploitation being particularly important, and introduced species particularly unimportant, for marine species. Introduced species are a much less important threat in Canada than in the United States, but the causes of endangerment are broadly similar for Canadian and globally endangered species.

Conservation biologists struggle to decide how many animals to save. In this article, I outline 18 approaches to setting population target levels (PTLs) for animals, with rules of thumb and analytical recommendations for each approach. Minimally viable populations, the most common target level, are necessary but not sufficient for most efforts, given the range of values that bear on conservation. Reference ecosystems, either extant or historical, are key for setting practical target levels. Setting PTLs sufficient for conserved populations to be animals in all respects (including functional, social, landscape, ethical, aesthetic, and spiritual aspects) is a critical consensus point. In many cases densities as well as overall population size will need to be specified. I suggest a four-tiered system of setting incrementally higher population target levels such that conservation provides first for demographic sustainability, then ecological integrity, then sustainable use, and finally restoration of historical numbers of wildlife, based on times when human beings had less impact on the planet than we do today.

In 2005 and 2006, highly pathogenic avian influenza H5N1 infected wild birds or poultry in at least 55 countries in Asia, Europe, and Africa. Scientists still have limited understanding of how these wild birds were infected and of how the virus behaves in a field setting. Better ecological and ornithological data are essential to resolve these uncertainties. At present, information on species identity, location and habitat, and sampling and capture methodology, as well as details of the affected bird populations, are inadequate or lacking for most incidents of H5N1 in wild birds. Greater involvement by ornithologists and ecologists, who have extensive experience in conducting field research on wild animals, is vital to improve our ability to predict outbreaks and reduce the environmental and socioeconomic impacts of H5N1 avian influenza.

Estimates of the economic impacts of nonnative nuisance (“invasive”) species must rely on both a sound ecological understanding and the proper application of economic methods. Focusing on the example of the invasive European green crab (Carcinus maenas), we show that the crab's estimated economic impact—which has been used to help justify recent public policy—is based on data taken from the wrong geographic location. Furthermore, the predictions of ecological effects appear to rest on loose footing, and economic methods have been misapplied in constructing the estimate. Our purpose is to call attention to the need for the more careful application of science and economics in managing this pressing environmental issue.