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This article presents a synthesis of what is known about areas of rapid land-cover change around the world over the past two decades, based on data compiled from remote sensing and censuses, as well as expert opinion. Asia currently has the greatest concentration of areas of rapid land-cover changes, and dryland degradation in particular. The Amazon basin remains a major hotspot of tropical deforestation. Rapid cropland increase, often associated with large-scale deforestation, is prominent in Southeast Asia. Forest degradation in Siberia, mostly related to logging activities, is increasing rapidly. The southeastern United States and eastern China are experiencing rapid cropland decrease. Existing data do not support the claim that the African Sahel is a desertification hotspot. Many of the most populated and rapidly changing cities are found in the tropics.
Coloration is a diagnostic tool for identifying mammals, but inquiry into its function has lain dormant for almost a century. Recently, the topic has been revived and modern phylogenetic methods have been applied to large data sets, allowing researchers to assess, for the first time, the relative importance of three classic hypotheses for the function of coloration in mammals: concealment, communication, and regulation of physiological processes. Camouflage appears to be the single most important evolutionary force in explaining overall coloration in mammals, whereas patches of colored fur are used for intraspecific signaling. Sexual selection is associated with flamboyant ornamentation in a minority of primates and other restricted mammalian taxa, but to a far lesser extent than in birds. Interspecific signaling among mammals includes aposematic coloration, exaggeration of signals to deter pursuit, and lures for misdirecting predatory attack. Physiological causes of coloration, including melanism, are evident but poorly researched. The relative importance of evolutionary forces responsible for external coloration varies greatly between vertebrate taxa, but the reasons for this variation are not yet understood.
Material accumulates at the water–air interface of all natural water bodies to form a surface film. The interface is a dynamic environment, so surface films are altered by water movements, solar radiation, and biological processes. These films consist of a complex of organic matter and microorganisms, some of which are harmful. Researchers have often overlooked surface films when studying water bodies, and their importance is only now being recognized.
We analyzed the threats to imperiled vertebrate species in China and compared our results with those from a similar study conducted in the United States. Overexploitation is the most pervasive threat to Chinese vertebrates, contributing to the endangerment of 78% of imperiled species, followed by habitat destruction (70%), pollution (20%), alien species (3%), and disease (< 1%). Harvest for food and use in traditional Chinese medicines are the two main forms of overexploitation, while logging is the most pervasive form of habitat destruction. Threats to vertebrate species are strikingly different in the United States, where habitat destruction affects 92% of imperiled vertebrate species, followed by alien species (47%), pollution (46%), overexploitation (27%), and disease (11%). The greater frequency of overexploitation in China stems from China's larger, poorer, and more rural population, along with widespread trade in wildlife products. The apparent lower frequency of alien species in China may reflect neglect of this issue by Chinese scientists.
Ecologists increasingly recognize the need to understand how landscapes and food webs interact. Reservoir ecosystems are heavily subsidized by nutrients and detritus from surrounding watersheds, and often contain abundant populations of gizzard shad, an omnivorous fish that consumes plankton and detritus. Gizzard shad link terrestrial landscapes and pelagic reservoir food webs by consuming detritus, translocating nutrients from sediment detritus to the water column, and consuming zooplankton. The abundance of gizzard shad increases with watershed agriculturalization, most likely through a variety of mechanisms operating on larval and adult life stages. Gizzard shad have myriad effects on reservoirs, including impacts on nutrients, phytoplankton, zooplankton, and fish, and many of their effects vary with ecosystem productivity (i.e., watershed land use). Interactive feedbacks among watersheds, gizzard shad populations, and reservoir food webs operate to maintain dominance of gizzard shad in highly productive systems. Thus, effective stewardship of reservoir ecosystems must incorporate both watershed and food-web perspectives.
Obsolescence of environmental laws and regulations is unavoidable, and policies dealing with endangered species and ecosystem conservation often lag decades behind the relevant science. For example, endangered species laws and regulations and other conservation statutes typically fail to consider the interactions of strongly interacting species, probably because the importance of such interactions was not well understood when the laws were drafted. By failing to consider current knowledge, therefore, natural resource scientists and managers may be harming the species and systems they are charged with protecting. Most ecologists agree that the conservation of biodiversity is facilitated by maintaining population densities and distributions of strongly interactive species above estimable thresholds for ecological effectiveness. Assuming that conservation biologists and natural resource managers are “physicians to nature,” we therefore propose they are obligated to adhere to a doctrine of “best conservation practices based on the best science,” applying a more rigorous standard for the management of relatively interactive species than may be mandated by older statutes and effected by current practice and convention.