Showing papers in "BioScience in 1997"

The Natural Flow Regime

Abstract: H umans have long been fascinated by the dynamism of free-flowing waters. Yet we have expended great effort to tame rivers for transportation, water supply, flood control, agriculture, and power generation. It is now recognized that harnessing of streams and rivers comes at great cost: Many rivers no longer support socially valued native species or sustain healthy ecosystems that provide important goods and services (Naiman et al. 1995, NRC 1992).

Hydraulic Limits to Tree Height and Tree Growth

Abstract: Examines what determines the height to which a tree will grow in a particular region and climate. The relationship between maximum tree height and the speed at which the tree grew when young; Mechanisms for growth including the respiration hypothesis, the nutrient limitation hypothesis, the maturation hypothesis and the hydraulic limitation hypothesis; Details about each hypothesis; Evidence for hydraulic limitation; Conclusions.

Economic and Environmental Benefits of Biodiversity

Abstract: A ll ecosystems and human societies depend on a healthy and productive natural environment that contains diverse plant and animal species. The earth's biota is composed of an estimated 10 million species of plants, animals, and microbes (Pimm et al. 1995). In the United States, there are an estimated 750,000 species, of which small organisms, such as arthropods and microbes, make up 95%.1 Although approximately 60% of the world's food supply comes from rice, wheat, and corn (Wilson 1988), as many as 20,000 other plant species have been used by humans as food. Some plants and animals provide humans with essential medicines and other diverse, useful products. For instance, some plants and microbes help to degrade chemical pollutants and organic wastes and recycle nutrients throughout the ecosystem. The rapidly growing world population and increased human activity threaten many of these species. The current extinction rate of species ranges from approximately 1000 to 10,000 times higher than natural extinction rates (Kellert and Wilson

Biological Corridors: Form, Function, and Efficacy

Abstract: H abitat loss and fragmentation are among the most pervasive threats to the conservation of biological diversity (Wilcove et al. 1986, Wilcox and Murphy 1985). Habitat fragmentation often leads to the isolation of small populations, which have higher extinctionrates (e.g., Pimm et al. 1988). Ultimately, the processes of isolation and population extinction lead to a reduction in biological diversity. Concern for this loss has motivated conservation biologists to discuss the actions that are needed to increase the effective size of local populations. Predominant among these possible str,ltegies has been the recommendation that corridors be induded in conservation plans (Figure 1) to increase the connectivity of otherwise isolated patches (Meffe and Carroll1994). The indusion of corridors in reserve designs has become an importa nt conservation tactic for protecting biological diversity. This strategy was motivated by theoretical and empirical observations demonstrating that increased interchange of in-

Ecosystem Expansion and Contraction in Streams Desert streams vary in both space and time and fluctuate dramatically in size

Abstract: St re

Pollinators, Flowering Plants, and Conservation Biology

Abstract: M ore than a century ago, Darwin (lg59) observed that "the number of bumblebees in any district depends in a great measure upon the number of fieldmice, which destroy their combs and nests ... che number of mice is largely Jependent, as everyone knows, on the number of cats .. .it is quite credible that the presence of a feline animal in large numbers in a district might uetermine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!" (p. -125). Dar\'{in recoglllzed the importance of interactions among organisms, specifically the role that pollinators play as links in communities. Yet, almost 140 years later, our understanding of pollination interactions is still rudimentary. The extent of dependence and linkage in pollination sys-

Leaf Form and Photosynthesis

Abstract: M orphological and anatomical features of plant leaves are commonly associated with metabolic type (e.g., Kranz anatomy of C4 species), amount of sun exposure (e.g., sun and shade leaves), or water stress (e.g., xeromorphism). However, although the primary function of the leaf is to absorb and process sunlight and carbon dioxide for photosynthesis, few structural features of leaves have been related mechanistically to these tasks. For example, it has been known for over a century that the internal anatomy of leaves is characterized by different cell layers (e.g., the palisade and spongy mesophyll) and that stomatal pores can be located on one or both sides of a leaf. Yet, only recently has any functional relationship between leaf form and photosynthetic performance been suggested. A variety of ecological studies have correlated numerous leaf structural parameters with photosynthetic performance (e.g., Abrams and Kubiske 1990, 1994, Hinckley et al. 1989,

Resurgence of the Irish Potato Famine Fungus

Abstract: rope and led to the Irish potato famine, the plant pathogenic fungus Phytophthora infestans is again creating a major plant health problem. Migrations of virulent and fungicide-resistant strains in the past two decades have caused a worldwide resurgence of the potato (and tomato) late blight disease. Epidemics in parts of the United States and Canada during the early 1990s were locally devastating, sometimes causing total crop loss and severe economic hardship for many potato and tomato growers. This resurgence supports the view that introduced pathogens and new variants of old ones present a real and immediate threat for plants as well as for animals and humans.

Water Resources: Agriculture, the Environment, and Society

Abstract: This paper analyzes consumption of water by individuals agriculture and energy production by assessing the status of water resources. Furthermore it examines the relationship between water availability and biodiversity. The availability and quality of fresh water has become a major international problem. Limited water resources and inefficient water use combined with a rapidly growing population endanger the worlds finite fresh water supply. In many parts of the world per capita freshwater resources available for food production and for other human needs are declining and are becoming scarce in the arid regions. In fact agricultural productions account for approximately 87% of the worlds freshwater consumption. Moreover most of human activities adversely affect the quality of freshwater resources. Chemical and pathogen pollution of water supplies not only diminishes the quality of water but causes human health problems. Given these scenarios the freshwater problem can be prevented by 1) encouraging conservation and increasing efficiency of irrigation water by eliminating freshwater subsidies and encouraging developments in irrigation technologies; 2) giving farmers incentives to conserve water and soil resources; 3) controlling soil erosion; 4) protecting forests and other biological resources; and 4) preventing water pollution.

Commercialization of Transgenic Plants: Potential Ecological Risks

Abstract: transgenic crop varieties is increasing exponentially (Figure 1). As of 1996, several transgenic crop plants have already been approved for commercial release in the United States, including disease-resistant squash, herbicide-resistant soybean, and insect-resistant potato and cotton. Many more crop varieties are nearly ready for commercialization. At this rate of development, the majority of all widely cultivated plants in the United States may possess genetically engineered traits within the next few decades.

Feasibility of Large-Scale Biofuel Production

Abstract: iofuels are widely seen as a feasible alternative to oil. Indeed, in 1995 the Clinton Administration proposed amendments to the Clean Air Act that would require gasoline sold in the nine most polluted US cities to contain additives from renewable sources, such as grain alcohol. This move, even if blocked by a three-judge panel of the US Court of Appeals in Washington, DC (Southerland 1995), has helped to focus attention on the question of whether research and development in biofuel production from agricultural crops should be increased (e.g., Abelson 1995). In Europe, similar fiscal and regulatory provisions have already been introduced (Chartier and Savanne 1992, Sourie et al. 1992). These policies assume that biofuels have the potential to reduce current dependence of industrialized societies on rapidly disappearing fossil energy stocks and that biofuels are desirable from an ecological point of view. But are these assumptions correct?

Monitoring environmental quality at the landscape scale

Abstract: ver the past century, technological advances have greatly improved the standard of living in the United States. But these same advances have caused sweeping environmental changes, often unforeseen and potentially irreparable. Ethical stewardship of the environment requires that society monitor and assess environmental changes at the national scale with a view toward the conservation and wise management of our natural resources. Some of the most important environmental changes occur a t the spatial scale of landscapes. Obvious examples include clearcutting for lumber, urbanization, the loss of wetlands, and the conversion of forest and prairies into crop and grazing systems. Decisions about how to change land cover may be made by individual landowners, but their im-

Plant Production and Emission of Volatile Organic Compounds

Abstract: \AI ways in which plant proV cesses influence the atmosphere, most biologists first think of photosynthetic oxygen production and carbon dioxide uptake. Given a few more minutes, many will also point out that plant transpiration of water plays a role in the chemistry of the troposphere (the lower 10 km of the atmosphere). Few, however, are aware that plant processes play key roles in ozone production, methane oxidation, and the global carbon monoxide budget. Several biologists and atmospheric chemists have recognized the effects of plants on the atmosphere (Rasmussen 1972, Tyson et al. 1974, Went 1960), but only recently has research into chemical emissions from plants advanced beyond a curiosity of interest to only a handful of environmental scientists. The topic of plant chemical emissions and their role in

Large Animals and System-Level Characteristics in River Corridors Implications for river management

Abstract: rocesses structuring riparian corridors can be viewed as a hierarchy, in which primary factors (such as matter, energy, and water) create a spatially extensive and temporally variable physical environment, which becomes habitat for plants and animals. The habitat is further modified by the activities of large animals as they selectively eat vegetation, burrow and wallow in soils, and build dams on streams, among other activities. As a result, the variety of habitats, or "patches," is increased. The vegetation and microorganisms living on the increased variety of habitat patches largely determine the eventual distribution and cycling rates of elements (e.g., nitrogen and phosphorus) as basic population and community processes are carried out (Table 1). In general, ecologists understand how interactions among water, energy, and matter shape the physical characteristics and habitat patches of river corridors, and how vegetation and microbes cycle elements, grow, reproduce, compete, and otherwise function. However, there has been little recognition of the equal importance of large animals in shap-

Forest Response to Disturbance and Anthropogenic Stress Rethinking the 1938 Hurricane and the impact of physical disturbance vs. chemical and climate stress on forest ecosystems

Abstract: emperate forests of the northeastern United States are dynamic ecosystems that have been shaped through geological and historical time by climate change, natural disturbance, and human activity (Davis 1986, Peterken 1993, Whitney 1994). Particularly noticeable through a retrospective view is the remarkable resiliency of these forests to a wide range of physical disturbances, including windthrow, fire, and land clearance (Boose et al. 1993, Foster 1994, Motzkin et al. 1996, Raup 1964). Despite this resiliency, novel environmental stresses may surpass the ability of these forests to control important ecosystem processes (Likens et al. 1996). For instance, changes in the global earthatmosphere system resulting from industrial and human land-use ac-

Fires, Hurricanes, and Volcanoes: Comparing Large Disturbances

Abstract: T he importance of natural disturbances in shaping landscapes and influencing ecosystems is now well recognized in ecology (e.g., Pickett and White 1985, Turner 1987, White 1979). Disturbance can be defined generally as any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resource or substrate availability or the physical environment (White and Pickett 1985). In recent years, ecologists have learned a great deal about the dynamics and effects of relatively small, frequent disturbances. Exten-

Genome Resource Banks

Abstract: B iological diversity is the key to maintaining life as we know it (Wilson 1992). However, rapidly growing human populations place extraordinary pressures on ecosystems, such as large-scale environmental destruction, habitat conversion, habitat fragmentation, and pollution. One reaction to these problems has been the emergence of conservation biology, an assemblage of scientific disciplines that are focused on sustaining biodiversity through a cooperative synthesis of ideas, information, and approaches. Virtually all conservation biologists agree that habitat preservation is the best way to conserve biodiversity. Setting aside large tracts of land so that they are free from human interference can protect many species, but this approach has also been charac-

Natural Resource Management in the Brazilian Amazon An integrated research approach

Abstract: he Amazon region of Brazil contains billions of cubic meters of high-quality wood whose overall value after sawing would be several trillion dollars. Given this timber wealth, it is common to consider forestry as the natural vocation for Amazonia (Pandolfo 1974). Already, well over half of the wood consumed in Brazil comes from Amazonia, and this domestic demand for Amazonian roundwood is expected to grow (Verissimo et al. 1992). Foreign consumption of Amazonian wood, although low at present, is also likely to increase as Asian tropical hardwood stocks decline. Brazil, which possesses almost one-third of the world's rain forest

Bios-3: Siberian experiments in bioregenerative life support.

Abstract: The Russian experience with the bioregenerative life support system Bios-3 at Krasnoyarsk, Siberia, is reviewed. A brief review of other bioregenerative systems examines Biosphere 2 in Oracle, Arizona, and the Bios-1 and Bios-2 systems that preceded Bios-3. Physical details of the Bios-3 facility are provided. The use of Chlorella and higher plants for gas exchange is examined. Long-term studies of human habitation are discussed. Other topics include microflora in Bios-3, the theory of closed systems, and problems for the future.

Kinship and Cannibalism

Abstract: annibalism-the ingestion of all or part of a conspecificis common, occurring in nearly every major vertebrate and invertebrate group (Elgar and Crespi 1992). In some species, certain individuals even develop specialized weaponry to facilitate the capture and consumption of conspecifics (Figure 1). One consequence of cannibalism is that cannibals may occasionally have to choose between eating a relative or a nonrelative. Do cannibals discriminate among potential prey? In particular, do they avoid eating relatives? In this article, I address these issues by reviewing both the theory of how kinship should affect prey choices and the evidence bearing on these predictions. I also explore the behavioral mechanisms used by animals to identify kin. Interest in kinship and cannibalism stems from the advent of modern

The Decoupling of Terrestrial Carbon and Nitrogen Cycles

Abstract: approach has proven valuable in understanding not only marine biogeochemistry (Broecker et al. 1979, Howarth 1988), but also carbon and nutrient cycles on land (Bolin and Cook 1983, Melillo and Gosz 1983, Reiners 1986, Rosswall 1981, Vitousek 1982). Both plant species diversity and their ability to produce varying amounts of structural material cause greater variation in carbon to nutrient ratios within terrestrial biomass than is found in the ocean (Vitousek et al. 1988). Yet nutrient limitation of net terrestrial

The Disappearance of Guam's Wildlife New insights for herpetology, evolutionary ecology, and conservation

Abstract: nesia, an archipelago of "micro" islands in the middle of the western Pacific Ocean. The largest island of Micronesia, Guam covers only 541 km2. It is shaped like an elongated peanut, 4 km across the narrow waist and 45 km long. The closest larger island is Manus, which is 1740 km to the south, across the equator and north of New Guinea. Few species are found on small, remote islands such as Guam. To reach

The evolution and genetics of aphid endosymbionts

Abstract: O ne of the striking attribute.s of prokaryotes (boch Bacteria and Archaea) is the dlversity of thei! catabolic pathways and ehe ir biosynthetic capabilities (Brock er al. 1994). Many prnkaryores are able co L1se unusual substrates for growth and synthesize a11 of the constituenes of cells from relative!y simple compounds. In contrast, many eukaryotcs lack such capa bi litics and ha ve developed elose associations in which they take advantage of thc metabolie versatility of prokaryotes. In some of these associations, the organisms live in elose contace bm remain separate. In orher cases, called endosymbioses, the prokaryote i5 scqucstered \vithin the eukaryotic eell. The c1assicaJ eompilation of endosymbiotic assoClations is that of suchner (1965). Inseets are particularly prone ta endosymbiotic associatiom .. Such associ~tions are widespread among members of the orders Homoptera (a phids, whiteflies, mealybugs, psylIid!>, and cicadas), Blattaria (cock-

Himalayan Forests and Ecological Generalizations

Abstract: E cological measurements, as traditionally made, represent small areas. However, in response to worldwide concern about environmental quality, ecologists have expanded their focus to encompass the earth (e.g., Field et al. 1995, Frank and Inouye 1994, Neilson and Marks 1994, Wessman 1992). Analyzing and predicting processes at the scale of the biosphere require that information-including data about geographic regions and biological systems that are not well represented in widely available data basesbe integrated at the appropriate scale. To obtain the information that is required to draw conclusions at the scale of the biosphere, ecologists must make new measurements at broader scales and in regions for which data are currently sparse, must extrapolate from the existing data, or must search for less well known data that are reliable and appropriate. The first option-large-scale collection of field data-is expensive

Causes and Implications of Species Restoration in Altered Ecosystems

Abstract: gered Species Act of 1973 one year after passage. Since that time, natural recolonization and population recovery of wolves in the western Great Lakes region of the United States (the Lake States-Minnesota, Wisconsin, and Michigan) has been a notable success of the Act (Refsnider 1994). At the time of listing, the wolf was extirpated throughout the United States outside Alaska except for remnant populations in northeast Minnesota and on Isle Royale, in Lake Superior (Mech 1970). Since protection under the Act, the wolf population has in-

On the Tails of Birds

Abstract: rations in some sexually dimorphic species (Andersson 1994, Balmford et al. 1993a, 1994, Evans and Thomas 1992, Norberg 1995, Winquist and Lemon 1994). For example, the long-tailed widow bird Euplectes progne, a bird a little larger than a starling, has a tail more than 1 m long; the lyre-tailed nightjar Uropsalis lyra has a tail eight times as long as its body, giving it-in relative terms-the largest tail of any bird; and the marvelous spatule-tailed hummingbird Loddigesia mirabilis has a tail that is elongated into bizarre crossed wirelike structures with "flags" at the ends that are as long as its body (Figure 1). Other species, such as the spinetail swifts (Neafrapus cassini), have tails consisting of just a few spiny barbs. Between these extremes, bird tails exhibit a wide range of morphologies (Figure 2; Norberg 1989, Thomas 1993a, Thomas and Balmford 1995). In this article, I describe recent work that uses aerodynamic analyses to investigate the evolutionary forces responsible for the morphologies of birds' tails.

The Evolution of Cooperation.

Abstract: The ants and termites have renounced the 'Hobbesian war,' and they are the better for it. Their wonderful nests, their buildings, superior in size relative to man; their paved roads and overground vaulted galleries; their spacious halls and granaries; their cornfields, harvesting and 'malting' grain; their rational method of nursing eggs and larvae, and of building special nests for rearing aphids whom Linnaeus so picturesquely describes as 'the cows of the ants' and finally, their courage, pluck and superior intelligence-all these are the normal outcome of the mutual aid