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Lake Victoria is Africa's single most important source of inland fishery production. After it was initially fished down in the first half of the 20th century, Lake Victoria became home to a series of introduced food fishes, culminating in the eventual demographic dominance of the Nile perch, Lates niloticus. Simultaneously with the changes in fish stocks, Lake Victoria experienced dramatic changes in its ecology. The lake fishery during most of the 20th century was a multispecies fishery resting on a diverse lake ecosystem, in which native food fishes were targeted. The lake ended the century with a much more productive fishery, but one in which three species—two of them introduced—made up the majority of the catch. Although many fish stocks in Lake Victoria had declined before the expansion of the Nile perch population, a dramatic increase in the population size of Nile perch in the 1980s roughly coincided with the drastic decline or disappearance of many indigenous species. Now, two decades after the rise of Nile perch in Lake Victoria, this species has shown signs of being overfished, and some of the native species that were in retreat—or even thought extinct—are now reemerging. Data on the resurgence of the indigenous species suggest that heavy fishing of Nile perch may enhance biodiversity; this has spawned renewed interest in management options that promote both fishery sustainability and biodiversity conservation.
We introduce a collection of articles that proposes conceptual and methodological tools to advance the integrated study of ecological boundaries. A number of studies are germane to understanding the structure and function of boundaries over a wide array of ecological systems and scales. However, these studies have not been unified in a consistent theoretical framework. To integrate these seemingly disparate studies and to advance future research on boundaries, these articles present a common conceptual framework, a classification of the different types of boundaries and their potential functions, and statistical and modeling approaches that can be applied to a wide range of systems, processes, and scales. We summarize the themes that emerge from these articles and suggest questions to guide future research.
Ecologists use the term boundary to refer to a wide range of real and conceptual structures. Because imprecise terminology may impede the search for general patterns and theories about ecological boundaries, we present a classification of the attributes of ecological boundaries to aid in communication and theory development. Ecological boundaries may differ in their origin and maintenance, their spatial structure, their function, and their temporal dynamics. A classification system based on these attributes should help ecologists determine whether boundaries are truly comparable. This system can be applied when comparing empirical studies, comparing theories, and testing theoretical predictions against empirical results.
Habitat boundaries profoundly influence the structure and function of landscapes, influencing ecological processes both locally and over larger scales. In addition, boundaries themselves are dynamic entities whose changes can influence diverse populations, communities, and ecosystems by way of feedback effects. These two issues, scale dependence and spatiotemporal dynamics, underlie much of the now considerable attention that modelers and statisticians have devoted to the quantitative study of ecological edges and boundaries. We present the linkages between methods of delineating boundaries, monitoring boundary changes, and modeling edge-related dynamics. In the process, we clarify statistical and mathe-matical approaches to the study of ecological edges and boundaries, and we discuss important remaining issues in the area of quantitative edge research. In particular, we address conceptual and methodological problems faced by statisticians and modelers, while highlighting topics that would benefit from a collaborative approach.
Transitions between atmosphere and soil, and between soil and roots, are two examples of small-scale boundaries across which the nutrient, water, and gas dynamics of ecosystems are modulated. Most atmospheric inputs to ecosystems have to pass through the soil; thus, the atmosphere–soil boundary influences the type and amount of materials and energy entering the soil. Belowground plant inputs occur through the rhizosphere, the zone of soil immediately adjacent to the root. This soil boundary layer affects root inputs to soil and root extraction of water and nutrients from soil. We discuss how water, carbon, nitrogen, and oxygen dynamics are affected by atmosphere–soil and soil–root boundaries and how light, soil pH, and dust are affected by the atmosphere–soil boundary. (We also examine pH with regard to the root–soil boundary, but not in a separate section.) We examine the linkages between these small-scale boundaries and landscape ecology and discuss how the understanding of small-scale boundaries can contribute to the emerging field of boundary theory.
Boundaries are ubiquitous across a wide range of ecological systems and spatial scales. However, most research on boundaries has been scale and system specific. To promote the synthesis of boundary studies across the range of environments and scales they represent, we present an inclusive scope for boundary studies. Three linked tools make the scope operative: (1) a causal framework covering all types of boundaries, (2) a model template, and (3) a strategy for constructing hypothetical models of boundary function in any ecological system. The framework focuses on flows of organisms, materials, energy, or information in heterogenous mosaics; it specifies patch contrast, identity of the flow, and nature of the boundary as the concepts to quantify in any model. The model template arranges these components in a functional form to elucidate specific boundary relationships. From the model template, working models that are system and scale specific can be developed. We exemplify the use of the linked tools of framework, model template, and working model with an experimental study of forest–field boundary function.
Ranching is the dominant land use in much of the American West. Although a copious literature has examined the effects of various grazing practices on native ecosystems, we present here the idea that ranching has important impacts on the land independent of those caused by grazing itself. If biological conservation is to be successful on the western grasslands and shrublands, ranchers must be central to any plan. Focusing on the Great Plains of the United States, and on Wyoming in particular, we raise six points of concern that must be addressed before we can hope to restore or maintain native ecosystems on the range.
Although the Scopes trial remains the most famous court decision associated with the teaching of evolution, there have been many other more important court decisions associated with the teaching of evolution and creationism in public schools. An understanding of these decisions can help teachers answer students' questions about the teaching of evolution and creationism. Such an understanding can also be used to counter the antiscience attitudes and actions of creationist parents, school administrators, and colleagues.