bluuebunny/crossref_metadata_2025 huggingface dataset:
Nest Building and Self-Assembling
Authors: Bonabeau Eric , Dorigo Marco , Theraulaz Guy
Published: November 2020

Social insect nest architectures can be complex, intricate structures. Stigmergy (see section 1.2.3), that is, the coordination of activities through the environment, is an important mechanism underlying nest construction in social insects. Two types of stigmergy are distinguished: quantitative, or continuous stigmergy, in which the different stimuli that trigger behavior are quantitatively different; and qualitative, or discrete stigmergy, in which stimuli can be classified into different classes that differ qualitatively. If quantitative stigmergy can explain the emergence of pillars in termites, the building behavior of the paper wasps Polistes dominulus seems to be better described by qualitative stigmergy. In this chapter, a simple agent-based model inspired by discrete stigmergy is introduced. In the model, agents move in a three-dimensional grid and drop elementary building blocks depending on the configuration of blocks in their neighborhood. From the viewpoint of bricks, this model is a model of self-assembly. The model generates a large proportion of random or space-filling forms, but some patterns appear to be structured. Some of the patterns even look like wasp nests. The properties of the structured shapes obtained with the model, and of the algorithms that generate them, are reviewed. Based on these properties, a fitness function is constructed so that structured architectures have a large fitness and unstructured patterns a small fitness. A genetic algorithm based on the fitness function is used to explore the space of architectures. Several examples of self-assembling systems in robotics, engineering, and architecture are described. Self-assembling or self-reconfigurable robotic systems, although they are not directly inspired by nest construction in social insects, could benefit from the discrete-stigmergy model of nest building. The method of evolutionary design, that is, the creation of new designs by computers using evolutionary algorithms, is a promising way of exploring the patterns that self-assembling models can produce. Many animals can produce very complex architectures that fulfill numerous functional and adaptive requirements (protection from predators, substrate of social life and reproductive activities, thermal regulation, etc.).
Where We Are, and How We Got Here
Authors: Lewis William M.
Published: November 2020

English is a subtle language with many words that offer fine shades of meaning, but it also can be blunt and unequivocal. Dictionaries were not made for words such as hairdo, ballpark, or pigpen. The law, however, as practiced by Americans, can mutate the meaning of even the humblest word. If the law concerns itself with pigpens, then we must know whether a pigpen still exists when the pigs are removed and, if so, for how long. We must know if a pen originally built for cattle can become a pigpen if occupied by pigs and if pigpens are the same in all parts of the nation. In short, we must have federal guidance, regional interpretations, legal specialists, and technical authorities on pigpens. So it is with wetlands. The chapters of this book will show how troublesome the definition of wetlands has become since the federal government began regulating them. In the meantime, it will suffice to define wetlands informally as those portions of a landscape that are not permanently inundated under deep water, but are still too wet most years to be used for the cultivation of upland crops such as corn or soybeans. Wetlands, in other words, coincide pretty well with the common conception of swamps, marshes, and bogs. Government has had its hand in wetlands for about 150 years. Between the 1850s and 1970s, the federal government was intent on eliminating wetlands. Since then, it has been equally intent on preserving them. An individual who behaved in this manner would seem at least irresponsible. Many critics of federal wetland policy have in fact given the government a sound thrashing for its inconsistency, but the shift from elimination to protection of wetlands has continued nevertheless. Blaming government is the duty of a free people, and also good sport. Even so, the obvious truth about wetland regulation is that government has merely reflected a change in public attitude toward wetlands. Most Americans now believe that wetlands should be saved throughout the nation, except possibly on their own property. Americans did not always feel this way. Most European colonists of North America came from homelands that were essentially tame.
Water Is as Water Does
Authors: Lewis William M.
Published: November 2020

The greatest subtlety of wetlands lies in their hydrology. This is unfortunate, given that the very name wetland invokes images of water on the land. In fact, those who have been impatient with the thicket of indicators by which federal agencies identify wetlands have at times demanded a return to basics in the form of simple inspection for water. One Washington insider even suggested that we might send out her Uncle Dennis to delineate wetlands. If Uncle Dennis, who has a propensity to sit down, returns with a wet bottom, he has been in a wetland; otherwise he has not. The truth is that Uncle Dennis could sometimes wet his shorts in an upland forest or grassland, yet at other times sit comfortably dry on a certified wetland. The hydrologic conditions that separate wetlands from uplands in fact involve four phenomena related to saturation: proximity to the surface, time of year, duration, and frequency. Proximity of saturation to the soil surface is one of the most widely misunderstood aspects of wetlands. In many wetlands, water stands on the surface for extended intervals or, in a few cases, continuously. The significance of standing water (inundation), however, is easily overrated. Inundation is neither necessary nor sufficient for a wetland. Recurrent and prolonged saturation of soil near the surface is sufficient to create and maintain a wetland, even if water never actually stands on the surface. The exact distance within which saturation must approach the surface varies from one region or one wetland type to another but by rule of thumb is about one foot or, scientifically speaking, 30 cm. While plant roots often extend beyond one foot, prolonged saturation of the upper foot blocks penetration of oxygen into the soil, and thus to roots, so completely that most plants cannot survive. Plants that tolerate or thrive in saturated soils are called hydrophytes; they are characteristic of wetlands. Thus, the critical depth for saturation is determined by the differential responses of hydrophytes and non-hydrophytes to prolonged immersion of roots in water. The upper one foot of soil is also the zone of most intense microbial metabolism in soil.
Once and Future Wetlands
Authors: Lewis William M.
Published: November 2020

A societal conflict as prolonged and complex as the reversal of national policy on wetlands in the United States must contain some lessons for the future. Perhaps we are still too close to the issues to have everything in perspective historically, but two lessons seem obvious. One of these has to do with the channelizing effect of change in public attitudes toward wetlands and the other with the stabilizing effect of science on regulations and policies intended for the protection of wetlands. A look back at the previous chapters suggests that the history of wetland policy in the United States can be divided into three eras: a classical era during which removal was the policy; a modern era during which protection was the policy; and a new era, which appears to be postmodern in the sense that we adjust protection qualitatively in an attempt to make our coexistence with wetlands more comfortable. Politics of the removal era appear to have been relatively tranquil, as congressional action surrounding wetlands developed almost entirely through consultation with a single interest group (i.e., those who saw some economically beneficial potential in federal progams subsidizing or encouraging the removal of wetlands; Tzoumis 1998). The desire for protection, although present in some circles much earlier, became politically potent in parallel with the growth of general public support for environmental legislation. From that time forward, legislation and national policy have consistently been formed in an atmosphere of strongly opposing viewpoints, but the protectionist impulse has prevailed. It seems doubtful now that an open legislative assault on wetland protection would be successful, simply because the public has fully absorbed the idea of protection for about a generation. The fundamental intent of protectionism, however, still could be subverted judicially or administratively; this is the main issue for the future. From 1970 to the present, the politics of wetlands has seemed unstable and even chaotic. Participants in the contest over wetlands typically have viewed the future with a high degree of pessimism. This is especially true for the defenders of wetlands, who fear, and in some cases almost anticipate, reactionary backsliding.
Synthetic Peptides: Beginning the Twenty-first Century
Authors: Grant Gregory A.
Published: November 2020

This second edition of Synthetic Peptides is being published at the beginning of the twenty-first century and marks nearly 100 years since the beginnings of the chemical synthesis of peptides. From the first decade of the twentieth century up to the present time, the evolution of the development, analysis, and use of synthetic peptides has been steady and remarkable. It has been about 10 years since the first edition of this book was published. Much remains unchanged, such as the basic principles of peptide structure, the basic chemistry for assembling a peptide chain, and many of the techniques used to evaluate synthetic peptides. However, during that time we have seen a switch from primarily the use of Boc chemistry for routine synthesis to that of Fmoc chemistry. Mass spectrometry has also matured with the development of more user-friendly and affordable instrumentation to the point that it is now the premier analytic method for synthetic peptides. Methods for the production of very long peptides, such as chemoselective ligation, are maturing, although they are still not an everyday thing for most peptide chemists, and better chemistries for producing peptides with “posttranslational modifications,” such as phosphates, sugars, and specific disulfide bonds, are now well within reach. As a result, you will find many sections of this book largely unchanged, but you will also find many new sections that document the developments of the last ten years with the inclusion of new information and methodologies. However, a good feeling for what the beginning of the twenty-first century offers can best be appreciated by considering the developments that have led to this point. Emil Fischer introduced the concept of peptides and polypeptides and presented protocols for their synthesis in the early 1900s (Fischer, 1902, 1903, 1906). Although others also made contributions in those days, most notably Theodor Curtius, the work of Fischer and his colleagues stands out, and he is generally regarded as the father of peptide chemistry.
Peptide Design Considerations
Authors: Moore Michael L. , Grant Gregory A.
Published: November 2020

Peptides have become an increasingly important class of molecules in biochemistry, medicinal chemistry, and physiology. Many naturally occurring, physiologically relevant peptides function as hormones, neurotransmitters, cytokines, and growth factors. Peptide analogs that possess agonist or antagonist activity are useful as tools to study the biochemistry, physiology, and pharmacology of these peptides, to characterize their receptor(s), and to study their biosynthesis, metabolism, and degradation. Radiolabeled analogs and analogs bearing affinity labels have been used for receptor characterization and isolation. Peptide substrates of proteases, kinases, phosphatases, and aminoacyl or glycosyl transferases are used to study enzyme kinetics, mechanism of action, and biochemical and physiological roles and to aid in the isolation of enzymes and in the design of inhibitors. Peptides are also used as synthetic antigens for the preparation of polyclonal or monoclonal antibodies targeted to specific sequences. Epitope mapping with synthetic peptides can be used to identify specific antigenic peptides for the preparation of synthetic vaccines, to determine protein sequence regions that are important for biological action, and to design small peptide mimetics of protein structure or function. A number of peptide hormones or analogs thereof, including arginine vasopressin, oxytocin, luteinizing hormone releasing hormone (LHRH), adrenocorticotropic hormone (ACTH), and calcitonin, have already found use as therapeutic agents, and many more are being investigated actively. Peptide-based inhibitors of proteolytic enzymes, such as angiotensin converting enzyme (ACE) and human immunodeficiency virus (HIV) protease, have widespread clinical use, and inhibitors of renin and elastase are also being investigated for therapeutic use. Finally, peptides designed to block the interaction of protein molecules by mimicking the combining site of one of the proteins, such as the fibrinogen receptor antagonists, show great therapeutic potential as well. With the development of solid-phase peptide synthesis by Bruce Merrifield (1963) and the optimization of supports, protecting groups, and coupling and deprotection chemistries by a large number of researchers, it has become possible to obtain useful amounts of peptides on a more or less routine basis.
Diurnal Mountain Winds
Authors: Whiteman C. David
Published: November 2020

Diurnal mountain winds develop over complex topography of all scales, from small hills to large mountain massifs and are characterized by a reversal of wind direction twice per day. As a rule, winds flow upslope, up-valley, and from the plain to the mountain massif during daytime. During nighttime, they flow downslope, down-valley, and from the mountain massif to the plain. Diurnal mountain winds are strongest when skies are clear and winds aloft are weak. Diurnal mountain winds are produced by horizontal temperature differences that develop daily in complex terrain. The resulting horizontal pressure differences cause winds near the surface of the earth to blow from areas with lower temperatures and higher pressures toward areas with higher temperatures and lower pressures. The circulations are closed by return, or compensatory, flows higher in the atmosphere. Four wind systems comprise the mountain wind system, which carries air into a mountain massif at low levels during daytime and out of a mountain massif during nighttime. The slope wind system (upslope winds and downslope winds) is driven by horizontal temperature contrasts between the air over the valley sidewalls and the air over the center of the valley. The along-valley wind system (up-valley winds and down-valley winds) is driven by horizontal temperature contrasts along a valley’s axis or between the air in a valley and the air over the adjacent plain. The cross-valley wind system results from horizontal temperature differences between the air over one valley sidewall and the air over the opposing sidewall, producing winds that blow perpendicular to the valley axis and toward the more strongly heated sidewall. The mountain-plain wind system results from horizontal temperature differences between the air over a mountain massif and the air over the surrounding plains, producing large-scale winds that blow up or down the outer slopes of a mountain massif. The mountain-plain circulation and its upper level return flow are not confined by the topography but are carried over deep layers of the atmosphere above the mountain slopes. Because diurnal mountain winds are driven by horizontal temperature differences, the regular evolution of the winds in a given valley is closely tied to the thermal structure of the atmospheric boundary layer within the valley, which is characterized by a diurnal cycle of buildup and breakdown of a temperature inversion.
Rocky-Shore Fishes
Authors: Thomson Donald A. , Gilligan Matthew R.
Published: November 2020

Marine systems have provided little empirical or theoretical support for the equilibrium theory of island biogeography introduced by MacArthur and Wilson (1967; hereafter referred to as MacArthur-Wilson equilibria). In particular, although marine islands represent isolated habitats for shoreline-restricted marine organisms, it is clear that they do not have impoverished biotas relative to adjacent mainland shores as do their terrestrial counterparts. Additionally, it is not clear that colonization rates based on distance from propagule sources, and extinction rates based on island size, play a substantial role in determining the number and kind of species that may exist here. In this chapter we ask whether the gulf islands are biogeographic islands to rockyshore fishes as they are to terrestrial plants and animals. Although the adults and juveniles of most marine shore fishes cannot readily cross the deep waters separating landmasses, most marine fishes have pelagic eggs and larvae which are often found great distances from shore (Leis and Miller 1976; Leis 1991). Certain families of teleostean fishes (e.g., the blennioids and gobioids) have demersal eggs that are attached to a substrate, and only the larvae are dispersed by ocean currents. Some of these fishes have short-lived larvae that are normally found only close to shore (Brogan 1994). Considering such different types of dispersal mechanisms, one must conclude that distance over open water must be as formidable a barrier to dispersal in some fishes as it is to terrestrial organisms. In line with this conclusion, shore-fish faunas of oceanic islands show high degrees of endemism—for example, 23% in Galapagos shore fishes (Walker 1966), 23.1% and 22.2% in Hawaiian and Easter Island fishes, respectively (Randall 1998). It is well known that the marine insular environment differs considerably from the mainland or continental environment (Robins 1971). Essentially, the former is characterized by a more stable, predictable physical regime with moderate fluctuations in physical factors such as sea temperature, salinity, and turbidity, whereas the latter usually has wider and more unpredictable fluctuations in physical parameters. Robins (1971) compared the difference in species richness between insular and continental fish faunas of the tropical western Atlantic to that between a tropical and a temperate forest, respectively.
Reptiles: Ecology
Authors: Case Ted J.
Published: November 2020

The reptiles of the islands of the Sea of Cortés have provided many opportunities to test ecological and biogeographical hypotheses because they support a diverse fauna with much insular endemism; are numerous and of varying ages and degrees of isolation; are relatively undisturbed by human activity and introduced species; and have a relatively well-understood geological history (see chap. 2). In particular, contrasts of mainland and island reptile populations in the region have resulted in significant progress in testing theories of island biogeography, principles of ecological character displacement, ecological release, density compensation, and vicariance biogeography (see chap. 8). The reptiles, being conspicuous in these arid habitats, have attracted relatively more research attention than other vertebrates, and today we have a reasonably complete picture of at least which species are on which islands. Since the first edition of this book, nearly 20 years ago, there have been only 15 new records for the major islands, of which all but one are of snakes. In this chapter I review the basic elements of reptilian island biogeography in the Sea of Cortés with an emphasis on ecological factors shaping distributions and evolutionary trajectories. I first examine the patterns of species diversity and association across islands. I then take a closer look at some particular island forms, reviewing features of their life history that seem divergent from mainland relatives. In this regard I present some new data from a long-term study of two insular species of chuckwallas. Finally, I review patterns of population density across islands and their possible determinants. A recurrent debate in island biogeography centers on the relative importance of contemporary and ongoing ecological factors relative to historical circumstances in accounting for the number and the identities of species on islands. Historical biogeographers typically view the number of species on an island as being determined by the availability of appropriate habitats. They see changes in species composition chiefly as a consequence of alteration of the mix of habitats due to climatic change (e.g., Pregill and Olson 1980; Olson and Hilgartner 1982); extinctions are posited to occur in waves, as old habitats disappear and new ones become available.
Anemometry
Authors: Brock Fred V. , Richardson Scott J.
Published: November 2020

The function of an anemometer (sometimes with a wind vane) is to measure some or all components of the wind velocity vector. It is common to express the wind as a two-dimensional horizontal vector since the vertical component of the wind speed is usually small near the earth’s surface. In some cases, the vertical component is important and then we think of the wind vector as being three-dimensional. The vector can be written as orthogonal components (u, v, and sometimes w] where each component is the wind speed component blowing in the North, East, or vertically up direction. Alternatively, the vector can be written as a speed and a direction. In the horizontal case, the wind direction is the direction from which the wind is blowing measured in degrees clockwise from North. The wind vector can be expressed in three dimensions as the speed, direction in the horizontal plane as above, and the elevation angle. Standard units for wind speed (a scalar component of the velocity) are m s-1 and knots (nautical miles per hour). Some conversion factors are shown in table 7-1. Wind velocity is turbulent; that is, it is subject to variations in speed, direction, and period. The wind vector can be described in terms of mean flow and gustiness or variation about the mean. The WMO standard defines the mean as the average over 10 minutes. The ideal wind-measuring instrument would respond to the slightest breeze yet be rugged enough to withstand hurricane-force winds, respond to rapidly changing turbulent fluctuations, have a linear output, and exhibit simple dynamic performance characteristics. It is difficult to build sensors that will continue to respond to wind speeds as they approach zero or will survive as wind speeds become very large. Thus a variety of wind sensor designs and, even within a design type, a spectrum of implementations have evolved to meet our needs.
Solar and Earth Radiation
Authors: Brock Fred V. , Richardson Scott J.
Published: November 2020

This chapter is concerned with the measurement of solar radiation that reaches the earth’s surface and with the measurement of earth radiation, the long wave band of radiation emitted by the earth. The unit of radiation used in this chapter is the Wm-2. Table 10-1 lists some conversion factors. Radiant flux is the amount of radiation coming from a source per unit time in W. Radiant intensity is the radiant flux leaving a point on the source, per unit solid angle of space surrounding the point, in W sr-1 (sr is a steradian, a solid angle unit). Radiance is the radiant flux emitted by a unit area of a source or scattered by a unit area of a surface in Wm-2 sr-1. Irradiance is the radiant flux incident on a receiving surface from all directions, per unit area of surface, in Wm-2. Absorptance, reflectance, and transmittance are the fractions of the incident flux that are absorbed, reflected, or transmitted by a medium. Global solar radiation is the solar irradiance received on a horizontal surface, Wm-2. This is the sum of the direct solar beam plus the diffuse component of skylight, and is the physical quantity measured by a pyranometer. Direct solar radiation is the radiation emitted from the solid angle of the sun’s disc, received on a surface perpendicular to the axis of this cone, comprising mainly unscattered and unreflected solar radiation in Wm-2. At the top of the atmosphere this is usually taken to be 1367 W m-2 ± 3% due to changes in the earth orbit and due to sunspots. The direct beam is attenuated by absorption and scattering in the atmosphere. The direct solar radiation at the earth’s surface is the physical quantity measured by a pyrheliometer. Diffuse solar radiation (sky radiation) is the downward scattered and reflected radiation coming from the whole hemisphere, with the exception of the solid angle subtended by the sun’s disc in Wm-2. Diffuse radiation can be measured by a pyranometer mounted in a shadow band, or it can be calculated using global solar radiation and direct solar radiation.
Upper Air Measurements
Authors: Brock Fred V. , Richardson Scott J.
Published: November 2020

Measurements of atmospheric properties become progressively more difficult with altitude above the surface of the earth, and even surface measurements are difficult over the oceans. First balloons, then airplanes and rockets, were used to carry instruments aloft to make in-situ measurements. Now remote sensors, both ground-based and satellite-borne, are used to monitor the atmosphere. In this context, upper air means all of the troposphere above the first hundred meters or so and, in some cases, the stratosphere. There are many uncertainties associated with remote sensing, so there is a demand for in-situ sensors to verify remote measurements. In addition, the balloon- borne instrument package is relatively inexpensive. However, it should be noted that cost is a matter of perspective; a satellite with its instrumentation, ground station, etc. may be cost-effective when the mission is to make measurements all over the world with good space and time resolution, as synoptic meteorology demands. Upper air measurements of pressure, temperature, water vapor, and winds can be made using in-situ instrument packages (carried aloft by balloons, rockets, or airplanes) and by remote sensors. Remote sensors can be classified as active (energy emitters like radar or lidar) or passive (receiving only, like microwave radiometers), and by whether they “look” up from the ground or down from a satellite. Remote sensors are surveyed briefly before discussing in-situ instruments. Profiles of temperature, humidity, density, etc. can be estimated from satellites using multiple narrow-band radiometers. These are passive sensors that measure longwave radiation upwelling from the atmosphere. For example, temperature profiles can be estimated from satellites by measuring infrared radiation emitted by CO2 (bands around 5000 μm) and O2 (bands around 3.4μm and 15μm) in the atmosphere. Winds can be estimated from cloud movements or by using the Doppler frequency shift due to some component of the atmosphere being carried along with the wind. An active sensor (radar) is used to estimate precipitation and, if it is a Doppler radar, determine winds. The great advantage of satellite-borne instruments is that they can cover the whole earth with excellent spatial resolution.
What Made El Niño 1997-1998 Famous?: The Key Events Associated with a Unique Climatic Event
Authors: Changnon Stanley A.
Published: November 2020

El Niño 97-98 provided one of the most interesting and widely known climatic events of this century. It garnered enormous attention not only in the scientific community but also in the media and from the American public. El Niño developed rapidly in the tropical Pacific during May 1997, and by October “El Niño “had become a household phrase across America. Television and radio, newspapers and magazines pummeled America with the dire tales of El Niño during the fall of 1997 as the climate disruption battered the West Coast and the southern United States with storm after storm. Worried families changed vacation plans, and insurance executives pondered losses and raised rates. Victims of every type of severe weather blamed El Niño . After a winter filled with unusual weather, the head of the National Oceanic and Atmospheric Administration (NOAA) declared, “This winter’s El Niño ranks as one of the major climatic events of this century.” It was the first El Niño observed and forecast from start to finish. The event was noteworthy from several perspectives. • First, it became the largest and warmest El Niño to develop in the Pacific Ocean during the past 100 years. • Second, the news media gave great attention to the event, and El Niño received more attention at all levels than had any previous climate event. • Third, scientists were able to use El Niño conditions to successfully predict the climate conditions of the winter six months in advance. • Fourth, the predictive successes brought new credibility to the science of long-range prediction and, in general, acted to increase the public’s understanding of the climate and oceanic sciences. • Fifth, there were notable differences in how weather-sensitive decision makers reacted to the predictions, some used them for great gain, while others, fearing failure, did not. • Sixth, the great strength of El Niño brought forth claims that the phenomenon was the result of anthropogenic-induced global warming. This possibility was debated and added to the scientific-policy debates surrounding climate change. • Seventh, the net effect of the El Niño -influenced weather on the United States was an economic benefit, after early fears and predictions of great damages.
Was El Niño A Weather Metaphor—A Signal For Global Warming?
Authors: Wilkins Lee
Published: November 2020

This chapter reviews media coverage of El Niño 97-98 and identifies some significant trends within that coverage. The coverage analyzed includes that provided by the major American television networks, the elite press, and significant regional newspapers. During the early months of the study period, news coverage of El Niño was focused on the science of the prediction and was framed as an issue of risk with appropriate uncertainty. However, as the predictions themselves were borne out in real-world phenomena, coverage of El Niño became event driven, and the phenomenon itself was treated as certainty. The risks of climate change attributed to El Niño outweighed the potential benefits in many media reports. Coverage of El Niño was extensive, particularly on the West Coast of the United States, where many individual weather events were connected with the larger phenomenon. The chapter then explores the possibility that the totality of the media coverage may have two lasting impacts. First, on the basis of existing scholarship on mass communication and risk communication, it is reasonable to suggest that the extensive news coverage of El Niño may have had some influence on public perception of climate change, particularly the salience of climate change in discrete regions of the nation. Second, the chapter suggests that the mediated reality of the 1997-1998 event will serve as a signal event for popular and political understanding of the consequences of global warming. Historically, journalism has been both hampered and helped by its definition of news. Previous studies of media coverage of a variety of “risky” events have noted that news accounts tend to be event focused, lack context, and treat science as a matter of dueling opinions, rather than a process of knowledge acquisition. These scholarly findings, which are long-standing, have had some impact on the professional community, particularly among science writers, who over the past two decades have become both better trained in science and more aware of the limitations of the concept of “news”—at least when it comes to reporting certain sorts of events. Media coverage of El Niño , in general, reflected these previously documented trends.
A Genetic Algorithm to Design Optimal Patch Configurations Using Raster Data Structures
Authors: Brooks Christopher
Published: November 2020

The design of optimal patch configurations is a generic problem relevant to many spatial planning exercises. Spatial pattern affects processes in the natural and manufacture of environment and should be incorporated as a criterion in planning. Currently, while geographic inormation systems (GISs) are adequate for data storage, analysis, and visualization they do not provide sophisticated spatial decision-making functions. With the help of GISs, pattern can be incorporated into spatial decision-making explicitly, using ad hoc procedures, or implicitly, through visualization of alternative plans. Other computer technologies like remote sensing and decision support systems facilitate decision-making by supplying timely data and techniques for solving multi-criteria evaluation problems. There are now a number of artificial intelligence techniques that can be coupled with GIS to address a variety of hard spatial problems. Genetic algorithms are particularly attractive for optimization problems because they are efficient and effective in complex search spaces. Landscape ecologists use the twin concepts of patch and matrix to describe the spatial structure of the environment (McGarigal & Marks, 1994). The matrix is the dominant landscape element and patches are distributed within it. Patches can be crisp objects with well-defined boundaries, such as administrative areas, or inferred objects with fuzzy boundaries, such as vegetation or habitat patches in natural environments. In the former case, patches can be adequately represented by polygons in a vector GIS. In the second case patches are inferred from a continuous spatial distribution of attribute values. The raster data model is the most common representation of continuous fields within a GIS and is preferred to vector models in environmental applications because it is a better representation of the continuous variation characteristic of natural phenomena. There is a need for decision support tools that use raster GISs when spatial criteria relate to natural phenomena. Patch design involves many complexities: in a raster GIS it is also a complex problem in spatial geometry. This chapter describes a genetic algorithm for designing patch configurations in raster GISs. The genetic algorithm is coupled with GIS and multicriteria evaluation functions to build an autonomous system that explicitly includes pattern as a criterion in the design of patch networks. Conceptually, the problem is to extract from an infinite set of possible spatial patterns a single pattern that is optimal by some criterion.
The Shortgrass Steppe: The Region and Research Sites
Authors: Lauenroth William K. , Burke Ingrid C.
Published: November 2020

The central grassland region of North America (Fig. 1.1) is the largest contiguous grassland environment on earth. Prior to European settlement, it was a vast, treeless area characterized by dense head-high grasses in the wet eastern portion, and very short sparse grasses in the dry west. As settlers swept across the area, they replaced native grasslands with croplands, most intensively in the east, and less so in the west (Fig. 1.2). The most drought-prone and least productive areas have survived as native grasslands, and the shortgrass steppe occupies the warmest, driest, least productive locations. James Michener (1974) provided an apt description of the harshness of the shortgrass region in his book Centennial:… It is not a hospitable land, like that farther east in Kansas or back near the Appalachians. It is mean and gravelly and hard to work. It lacks an adequate topsoil for plowing. It is devoid of trees or easy shelter. A family could wander for weeks and never 4 nd enough wood to build a house. (p. 64)… The objective of this chapter is to introduce the shortgrass steppe (Fig. 1.3) and its record of ecological research. First we present an ecological history of the shortgrass steppe since the Tertiary, and provide the geographic and climatic context for the region. Second we describe the major research sites, and the history of the three major entities or programs that have shaped much of the science done in the shortgrass steppe: the U.S. Department of Agriculture (USDA)–Agricultural Research Service (ARS), the International Biological Programme (IBP), and the Long-Term Ecological Research (LTER) Program. Grasses have been an important component of the shortgrass steppe of North America since the Miocene (5–24 million years ago) (Axelrod, 1985; Stebbins, 1981). Before that, during the Paleocene and Eocene (34–65 million years ago), the vegetation was a mixture of temperate and tropical mesophytic forests. Two causes have been proposed as explanations for this ancient change from forest to grassland. First, global temperatures decreased rapidly during the Oligocene (24–34 million years ago), creating conditions for a drier climate. These drier conditions, combined with a renewal of the uplift of the Rocky Mountains that had begun during the Paleocene, left the Great Plains in a rain shadow.
Land-Use History on the Shortgrass Steppe
Authors: Hart Richard H.
Published: November 2020

As described in chapter 1 of this volume, the grasslands of central North America began to expand at the end of the Wisconsin period (about 10,000 years BP), and continued their expansion through the warming trend that persisted until about 3000 years BP, occupying their maximum territory at that time (Dix, 1964). Currently, the region still supports trees on escarpments, along streams, and at other sites protected from fire, but centuries ago, fires caused by lightning or kindled by Native Americans may have eliminated relict stands of forest and savanna on the open plains. Large browsers and grazers also may have played a part in eliminating trees as well as grasses sensitive to grazing pressure (Axelrod, 1985). Throughout millennia, bison in particular were likely to have shaped the plant communities of the shortgrass steppe, and thus were an essential component of the system (Larson, 1940). Bison appeared as early as 300,000 years BP; bison, mammoths, mastodons, camels, horses, and other grazers were numerous by 20,000 years BP. Humans arrived in North America perhaps as early as 60,000 years BP, but certainly by 15,000 years ago. Fires and bison may have achieved maximum impact as recently as the past 500 years (Axelrod, 1985; Looman, 1977). The roles of climate, fire, and grazing in the development of North American grasslands have been examined by Ellison (1960), Coupland (1979), Dyer et al. (1982), Anderson (1982), and Tetlyanova et al. (1990). The earliest known human sites on the shortgrass steppe date to about 13,000 years BP (Wedel, 1 979) and a re f ound i n the vicinity o f fossil g lacial l akes. The population of these mammoth hunters was apparently sparse and scattered. Soon after 11,000 years BP, many of the large mammalian species such as the mammoth, native horse, camel, and ground sloth vanished, and the hunters turned to bison. Bone beds representing mass kills of bison have been found below buffalo jumps (Fig. 4.1) and even in the remains of wood or stone corrals, but single kills must have been much more common.
Simulation of Disturbances and Recovery in Shortgrass Steppe Plant Communities
Authors: Peters Debra P. C. , Lauenroth William K.
Published: November 2020

Simulation modeling is a complementary tool to field observation and experimentation in understanding ecological systems (Lauenroth et a l., 1998). The overall objective of our plant community modeling is to allow us to evaluate the importance of gap dynamics concepts of succession for understanding shortgrass plant community recovery after disturbances. A gap dynamics approach focuses on individual plants, and the interactions between disturbance characteristics and plant life history traits in explaining successional patterns (Watt, 1947). Simulation models have been used extensively to evaluate the importance of gap dynamics processes to short- and long-term vegetation dynamics in temperate and tropical forests (e.g., Botkin et al., 1972; Shugart, 1984). We developed a gap dynamics model for shortgrass steppe plant communities (STEPPE [Coffin and Lauenroth, 1990]) based upon the conceptual and modeling framework provided by forest models, modifying it to represent Great Plains grasslands (Coffin and Lauenroth, 1996; Coffin and Urban, 1993). We used STEPPE in several capacities: (1) to synthesize and integrate existing knowledge to improve our understanding of recovery processes after disturbance, (2) to identify key processes limiting recovery, and (3) to predict long-term recovery dynamics for different climate and disturbance characteristics—in particular, soil texture and disturbance size. Our approach to modeling shortgrass community dynamics was to incorporate only the most important processes needed to address specific research questions. We added processes through time either because the model did not sufficiently represent ecosystem dynamics or because we posed more complicated research questions. STEPPE simulates the recruitment, growth, and mortality of individual plants on a small plot through time at an annual time step (Fig. 7.1) (Coffin and Lauenroth, 1990). Recruitment and mortality both have stochastic elements. Growth is deterministic and is based upon competition for resources among plants. A key difference between STEPPE and the forest models from which it was derived is that belowground resources are the most frequently limiting resources in semiarid grasslands compared with aboveground resources (light) in forests (Lauenroth and Coffin, 1992).
Insect Populations, Community Interactions, and Ecosystem Processes in the Shortgrass Steppe
Authors: Crist Thomas O.
Published: November 2020

Insects are diverse, abundant, and have numerous roles in rangeland ecosystems. More than 1600 species representing 238 families of insects have been recorded in the shortgrass steppe of northeastern Colorado (Kumar et al., 1976). Of this large assemblage, a much smaller subset—perhaps fewer than 50 species—is highly abundant with a large influence on community and ecosystem processes (Lauenroth and Milchunas, 1992). Even within abundant insect groups, such as grasshoppers, some species have far greater effects than others as herbivores (Capinera, 1987). In this chapter I consider a small number of insect groups that have various in) uences in shortgrass steppe ecosystems (Table 10.1). I focus on three insect taxa—grasshoppers, beetles, and ants—that are widespread, abundant, and ecologically important in semiarid environments. I also draw attention to neglected groups, such as termites and spiders, for their potentially important roles in the shortgrass steppe. My primary objective is to emphasize the linkages among insect populations, community interactions, and ecosystem function. From this approach stems several related issues: how population distributions affect community interactions, how population abundance affects the processing and redistribution of energy and nutrients in ecosystems, and how abundance and species diversity are important to the functional roles of species in ecosystems. I skirt issues of population regulation in insects, which are reviewed elsewhere (Cappuccino and Price, 1995), and instead consider how temporal and spatial patterns in insect populations relate to community and ecosystem processes. Understanding relationships among populations, communities, and ecosystems requires approaches that link patterns and processes across scales. Much of what is known about the roles of insects in the shortgrass steppe is based on studies conducted at relatively fine scales. To link insect population studies to community and ecosystem processes, however, I suggest that insect populations should also be studied across broader scales that encompass topographic variation. The rolling topography in the shortgrass steppe produces a gradient in soil texture, water availability, and nutrient retention from uplands to lowlands (Clark and Woodmansee, 1992; Schimel et al., 1985). Plant community structure also varies with topography in spatially repeating patterns across the landscape (Milchunas et al., 1989).
Net Primary Production in the Shortgrass Steppe
Authors: Lauenroth William K. , Milchunas Daniel G.
Published: November 2020

Net primary production (NPP), the amount of carbon or energy fixed by green plants in excess of their respiratory needs, is the fundamental quantity upon which all heterotrophs and the ecosystem processes they are associated with depend. Understanding NPP is therefore a prerequisite to understanding ecosystem dynamics. Our objectives for this chapter are to describe the current state of our knowledge about the temporal and spatial patterns of NPP in the shortgrass steppe, to evaluate the important variables that control NPP, and to discuss the future of NPP in the shortgrass steppe given current hypotheses about global change. Most of the data available for NPP in the shortgrass steppe are for aboveground net primary production (ANPP), so most of our presentation will focus on ANPP and we will deal with belowground net primary production (BNPP) as a separate topic. Furthermore, our treatment of NPP in this chapter will ignore the effects of herbivory, which will be covered in detail in chapter 16. Our approach will be to start with a regional-scale view of ANPP in shortgrass ecosystems and work toward a site-scale view. We will begin by briefly placing ANPP in the shortgrass steppe in its larger context of the central North American grassland region. We will then describe the regional-scale patterns and controls on ANPP, and then move to the site-scale patterns and controls on ANPP. At the site scale, we will describe both temporal and spatial dynamics, and controls on ANPP as well as BNPP. We will then discuss relationships between spatial and temporal patterns in ANPP and end the chapter with a short, speculative section on how future global change may influence NPP in the shortgrass steppe. Temperate grasslands in central North America are found over a range of mean annual precipitation from 200 to 1200 mm.y–1 and mean annual temperatures from 0 to 20 oC (Lauenroth et al., 1999). The widely cited relationship between mean annual precipitation and average annual ANPP allows us to convert the precipitation gradient into a production gradient (Lauenroth, 1979; Lauenroth et al., 1999; Noy-Meir, 1973; Rutherford, 1980; Sala et al., 1988b).