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The modification of the physical environment by organisms is a critical interaction in most ecosystems. The concept of ecosystem engineering acknowledges this fact and allows ecologists to develop the conceptual tools for uncovering general patterns and building broadly applicable models. Although the concept has occasioned some controversy during its development, it is quickly gaining acceptance among ecologists. We outline the nature of some of these controversies and describe some of the major insights gained by viewing ecological systems through the lens of ecosystem engineering. We close by discussing areas of research where we believe the concept of organisms as ecosystem engineers will be most likely to lead to significant insights into the structure and function of ecological systems.
Ecosystem engineers are organisms whose presence or activity alters their physical surroundings or changes the flow of resources, thereby creating or modifying habitats. Because ecosystem engineers affect communities through environmentally mediated interactions, their impact and importance are likely to shift across environmental stress gradients. We hypothesize that in extreme physical environments, ecosystem engineers that ameliorate physical stress are essential for ecosystem function, whereas in physically benign environments where competitor and consumer pressure is typically high, engineers support ecosystem processes by providing competitor- or predator-free space. Important ecosystem engineers alleviate limiting abiotic and biotic stresses, expanding distributional limits for numerous species, and often form the foundation for community development. Because managing important engineers can protect numerous associated species and functions, we advocate using these organisms as conservation targets, harnessing the benefits of ecosystem engineers in various environments. Developing a predictive understanding of engineering across environmental gradients is important for furthering our conceptual understanding of ecosystem structure and function, and could aid in directing limited management resources to critical ecosystem engineers.
The impact of organisms on oxygen is one of the most dramatic examples of ecosystem engineering on Earth. In aquatic systems, which have much lower oxygen concentrations than the atmosphere, vascular aquatic plants can affect oxygen concentrations significantly not only on long time scales but also on time scales of less than a day. Aquatic plants are generally thought of as adding oxygen to aquatic systems through photosynthesis, but the impact of vascular aquatic plants on oxygen varies greatly with plant morphology. Floating-leaved plants that vent oxygen to the atmosphere can strongly deplete oxygen. In some ecosystems where floating-leaved plants have replaced submersed vegetation, oxygen concentrations have been substantially reduced. These oxygen changes can have cascading impacts on nutrient and trace gas chemistry and on the suitability of plant beds as habitat for invertebrates and fishes.
Physical ecosystem engineers are organisms that physically modify the abiotic environment. They can affect biogeochemical processing by changing the availability of resources for microbes (e.g., carbon, nutrients) or by changing abiotic conditions affecting microbial process rates (e.g., soil moisture or temperature). Physical ecosystem engineers can therefore create biogeochemical heterogeneity in soils and sediments. They do so via general mechanisms influencing the flows of materials (i.e., modification of fluid dynamic properties, fluid pumping, and material transport) or the transfer of heat (i.e., modification of heat transfer properties, direct heat transfer, and convective forcing). The consequences of physical ecosystem engineering for biogeochemical processes can be predicted by considering the resources or abiotic conditions that limit or promote a reaction, and the effect of physical ecosystem engineering on these resources or abiotic conditions via the control they exert on material flows and heat transfer.
An impressive array of animals function as ecosystem engineers in streams through a variety of activities, ranging from nest digging by anadromous salmon to benthic foraging by South American fishes, from the burrowing of aquatic insects to the trampling of hippos. These ecosystem engineers have local impacts on benthic habitat and also strongly affect downstream fluxes of nutrients and other resources. The impacts of ecosystem engineers are most likely some function of their behavior, size, and population density, modulated by the abiotic conditions of the stream. In streams, subsidies often control the body size and density of ecosystem engineers, while hydrologic energy controls their distribution, density, and life-history attributes, the habitats they create, and the resources and organisms they affect. Because ecosystem engineers can profoundly affect stream ecosystems, and because they themselves can be significantly affected positively or negatively by human activities, understanding ecosystem engineering in streams is increasingly important for the management of these ecosystems.
News media coverage of the controversy surrounding recent attempts to insert creationism into public school science curricula—this time in the form of “intelligent design”—has generated miles of copy and hours of television footage. The quality of that reporting varies widely, depending on the media outlet. Often, reporters with no scientific training are assigned to report on evolution–creationism controversies, which inevitably leads to distortions of the relevant science. A misconceived concern for balance frequently results in equal time being accorded to biologists and creationists, creating the illusion of scientific equivalence. At other times, a clear bias toward creationism is revealed, especially on cable television. Focusing mainly on recent treatments, this article analyzes and critiques specific stories, as well as trends and patterns in coverage in newspapers, magazines, and television; it concludes with suggestions of ways in which scientists can be more effective in dealing with the media.
The loss of large carnivores at the edges of parks, preserves, and human habitations threatens the conservation of many species. Thus, effective predation management is a conservation issue, and tools to mitigate conflicts between humans and predators are required. Both disruptive-stimulus (e.g., fladry, Electronic Guards, radio-activated guards) and aversive-stimulus (e.g., electronic training collars, less-than-lethal ammunition) approaches are useful, and technological advances have led to many new, commercially available methods. Evaluating the biological and economic efficiency of these methods is important. However, social and psychological effects should also be considered. The management of animal damage to human property is necessary, and methods that allow the coexistence of livestock and large predators must be employed. With further research and development that includes interdisciplinary approaches to management methods, biologists may be better able to conserve large carnivore species by ameliorating human conflicts with them.