Showing papers in "BioScience in 2002"

Urbanization, Biodiversity, and Conservation

Abstract: A the many human activities that cause habitat loss (Czech et al. 2000), urban development produces some of the greatest local extinction rates and frequently eliminates the large majority of native species (Vale and Vale 1976, Luniak 1994, Kowarik 1995, Marzluff 2001). Also, urbanization is often more lasting than other types of habitat loss. Throughout much of New England, for example, ecological succession is restoring forest habitat lost from farming and logging, whereas most urbanized areas in that region not only persist but continue to expand and threaten other local ecosystems (Stein et al. 2000). Another great conservation challenge of urban growth is that it replaces the native species that are lost with widespread “weedy” nonnative species. This replacement constitutes the process of biotic homogenization that threatens to reduce the biological uniqueness of local ecosystems (Blair 2001). Urban-gradient studies show that, for many taxa, for example, plants (Kowarik 1995) and birds and butterflies (Blair and Launer 1997), the number of nonnative species increases toward centers of urbanization, while the number of native species decreases. The final conservation challenge of sprawl is its current and growing geographical extent (Benfield et al. 1999). A review by Czech and colleagues (2000) finds that urbanization endangers more species and is more geographically ubiquitous in the mainland United States than any other human activity. Species threatened by urbanization also tend to be threatened by agriculture, recreation, roads, and many other human impacts, emphasizing the uniquely far-reaching transformations that accompany urban sprawl. About 50% of the US population lives in the suburbs, with another 30% living in cities (USCB 2001). Over 5% of the total surface area of the United States is covered by urban and other built-up areas (USCB 2001). This is more land than is covered by the combined total of national and state parks and areas preserved by the Nature Conservancy. More ominously, the growth rate of urban land use is accelerating faster than land preserved as parks or conservation areas by the Conservancy (figure 1). Much of this growth is from the spread of suburban housing. It is estimated, for example, that residential yards occupy 135,000 acres in the state of Missouri (MDC 2002). This residential landscape represents nearly 1% of the total area of Missouri and is nearly three times the area occupied by Missouri state parks. Here I review the growing literature that documents how urban (and suburban) expansion harms native ecosystems. This knowledge can aid conservation efforts in two major ways. One is through the use of ecological principles—such as preserving remnant natural habitat and restoring modified habitats to promote native species conservation—to reduce the impacts of urbanization on native ecosystems. Rare and endangered species sometimes occur in urbanized habitats (Kendle and Forbes 1997, Godefroid 2001) and thus could be conserved there. Managing the large amount of residential vegetation (1% of the state area, as noted above) in ways that promote native plants and animals could also make a significant contribution to conservation.

Proximate causes and underlying driving forces of tropical deforestation.

Abstract: Articles O ne of the primary causes of global environmental change is tropical deforestation, but the question of what factors drive deforestation remains largely unanswered (NRC 1999). Various hypotheses have produced rich arguments , but empirical evidence on the causes of deforestation continues to be largely based on cross-national statistical In some cases, these analyses are based on debatable data on rates of forest cover change (Palo 1999). The two major, mutually exclusive—and still unsatisfactory—explanations for tropical deforestation are single-factor causation and irre-ducible complexity. On the one hand, proponents of single-factor causation suggest various primary causes, such as shift-On the other hand, correlations between deforestation and multiple causative factors are many and varied , revealing no distinct pattern In addition to chronicling these attempts to identify general causes of deforestation through global-scale statistical analyses, the literature is rich in local-scale case studies investigating the causes and processes of forest cover change in specific localities. Our aim with this study is to generate from local-scale case studies a general understanding of the prox-imate causes and underlying driving forces of tropical deforestation while preserving the descriptive richness of these studies. Proximate causes are human activities or immediate actions at the local level, such as agricultural expansion, that originate from intended land use and directly impact forest cover. Underlying driving forces are fundamental social processes, such as human population dynamics or agricultural policies, that underpin the proximate causes and either operate at the local level or have an indirect impact from the national or global level. We analyzed the frequency of proximate causes and underlying driving forces of deforestation, including their interactions , as reported in 152 subnational case studies. We show that tropical deforestation is driven by identifiable regional patterns of causal factor synergies, of which the most prominent are economic factors, institutions, national policies, and remote influences (at the underlying level) driving agricultural expansion, wood extraction, and infrastructure extension (at the proximate level). Our findings reveal that prior stud-Helmut Geist (e-mail: geist@geog.ucl.ac.be) is a postdoctoral researcher (geography) in the field of human drivers of global environmental change and executive director of the Land Use and Cover Change (LUCC) core project of the International Geosphere-Biosphere Eric Lambin is a professor of geography with research interests in remote sensing and human ecology applied to studies of deforestation, desertification, and bio-mass burning in tropical regions. He is the chair of the IGBP and IHDP …

The Human Footprint and the Last of the Wild

Abstract: I Genesis, God blesses human beings and bids us to take dominion over the fish in the sea, the birds in the air, and every other living thing. We are entreated to be fruitful and multiply, to fill the earth, and subdue it (Gen. 1:28). The bad news, and the good news, is that we have almost succeeded. There is little debate in scientific circles about the importance of human influence on ecosystems. According to scientists’ reports, we appropriate over 40% of the net primary productivity (the green material) produced on Earth each year (Vitousek et al. 1986, Rojstaczer et al. 2001). We consume 35% of the productivity of the oceanic shelf (Pauly and Christensen 1995), and we use 60% of freshwater run-off (Postel et al. 1996). The unprecedented escalation in both human population and consumption in the 20th century has resulted in environmental crises never before encountered in the history of humankind and the world (McNeill 2000). E. O. Wilson (2002) claims it would now take four Earths to meet the consumption demands of the current human population, if every human consumed at the level of the average US inhabitant. The influence of human beings on the planet has become so pervasive that it is hard to find adults in any country who have not seen the environment around them reduced in natural values during their lifetimes—woodlots converted to agriculture, agricultural lands converted to suburban development, suburban development converted to urban areas. The cumulative effect of these many local changes is the global phenomenon of human influence on nature, a new geological epoch some call the “anthropocene” (Steffen and Tyson 2001). Human influence is arguably the most important factor affecting life of all kinds in today’s world (Lande 1998, Terborgh 1999, Pimm 2001, UNEP 2001). Yet despite the broad consensus among biologists about the importance of human influence on nature, this phenomenon and its implications are not fully appreciated by the larger human community, which does not recognize them in its economic systems (Hall et al. 2001) or in most of its political decisions (Soulé and Terborgh 1999, Chapin et al. 2000). In part, this lack of appreciation may be due to scientists’ propensity to express themselves in terms like “appropriation of net primary productivity” or “exponential population growth,” abstractions that require some training to understand. It may be due to historical assumptions about and habits inherited from times when human beings, as a group, had dramatically less influence on the biosphere. Now the individual deci-

Lidar Remote Sensing for Ecosystem Studies

Abstract: Articles R emote sensing has facilitated extraordinary advances in the modeling, mapping, and understanding of ecosystems. Typical applications of remote sensing involve either images from passive optical systems, such as aerial photography and Landsat Thematic Mapper (Goward and Williams 1997), or to a lesser degree, active radar sensors such as RADARSAT (Waring et al. 1995). These types of sensors have proven to be satisfactory for many ecological applications , such as mapping land cover into broad classes and, in some biomes, estimating aboveground biomass and leaf area index (LAI). Moreover, they enable researchers to analyze the spatial pattern of these images. However, conventional sensors have significant limitations for ecological applications. The sensitivity and accuracy of these devices have repeatedly been shown to fall with increasing aboveground biomass and leaf area index (Waring et al. 1995, Carlson and Ripley 1997, Turner et al. 1999). They are also limited in their ability to represent spatial patterns: They produce only two-dimensional (x and y) images, which cannot fully represent the three-dimensional structure of, for instance, an old-growth forest canopy.Yet ecologists have long understood that the presence of specific organisms, and the overall richness of wildlife communities, can be highly dependent on the three-dimensional spatial pattern of vegetation (MacArthur and MacArthur 1961), especially in systems where biomass accumulation is significant (Hansen and Rotella 2000). Individual bird species, in particular, are often associated with specific three-dimensional features in forests (Carey et al. 1991). In addition, other functional aspects of forests, such as productivity, may be related to forest canopy structure. Laser altimetry, or lidar (light detection and ranging), is an alternative remote sensing technology that promises to both increase the accuracy of biophysical measurements and extend spatial analysis into the third (z) dimension. Lidar sensors directly measure the three-dimensional distribution of plant canopies as well as subcanopy topography, thus providing high-resolution topographic maps and highly accurate estimates of vegetation height, cover, and canopy structure. In addition , lidar has been shown to accurately estimate LAI and aboveground biomass even in those high-biomass ecosystems where passive optical and active radar sensors typically fail to do so. The basic measurement made by a lidar device is the distance between the sensor and a target surface, obtained by determining the elapsed time between the emission of a short-duration laser pulse and the arrival of the reflection of that pulse (the return signal) at the sensor's receiver. Multiplying this …

Landscapes to Riverscapes: Bridging the Gap between Research and Conservation of Stream Fishes

Abstract: R and streams, by their very nature long ribbons of aquatic habitat, are inherently difficult to study. Approaching the banks of a flowing-water (lotic) system, one can see only a short fragment of the entire stream, from one bend to another, and can gain little appreciation for important features that lie beyond view. Moreover, materials transported downstream by the flow, and organisms traveling up or down the hydraulic highway, are soon gone from the reach and the opportunity to study them is often lost. Lakes present their own challenges for study, but by contrast to streams, one can usually see large expanses from shore that encompass all major habitats needed for aquatic organisms to complete their life history, such as gravel shoals, beds of aquatic vegetation, and open water habitats. Much of our knowledge of the ecology of rivers and streams is based on observations and experiments on organisms and habitat in the short fragments we can view or quickly traverse on foot, and this limited understanding underpins our efforts at conservation of stream fishes. Here, we argue that this understanding is incomplete, like viewing only disjunct parts of a landscape painting through small holes in a curtain draping it. We propose that a continuous view of rivers is essential for effective research and conservation of their fishes and other aquatic biota—a view not just of disjunct reaches but of the entire spatially heterogeneous scene of the river environment, the riverscape, unfolding through time. One symptom of our incomplete understanding is the alarming rate of decline over the last 50 years of fishes that inhabit rivers and streams of North America. The public is aware that salmon are disappearing from the Pacific Northwest, with about a quarter of the 214 stocks of anadromous salmon and trout imperiled a decade ago (Nehlsen et al. 1991). Even little-known small fishes native to Great Plains and southwestern desert streams have suffered drastic declines (Minckley and Douglas 1991, Fausch and Bestgen 1997), and many are now either protected by federal or state listing as endangered or threatened species or are being considered for such protection. North America harbored the greatest diversity worldwide of temperate freshwater fishes (Warren and Burr 1994), crayfishes (Taylor et al. 1996), and mussels (Williams et al. 1993), but about 30% to 75% of the taxa in each group are at increased risk of extinction (i.e., categorized as rare, threatened, or endangered species). Fishes are also the most imperiled vertebrates worldwide (Allan and Flecker 1993, Leidy and Moyle 1998) and a large proportion spend at least part of their lives in streams.

How dams vary and why it matters for the emerging science of dam removal

Abstract: D are structures designed by humans to capture water and modify the magnitude and timing of its movement downstream. The damming of streams and rivers has been integral to human population growth and technological innovation. Among other things, dams have reduced flood hazard and allowed humans to settle and farm productive alluvial soils on river floodplains; they have harnessed the power of moving water for commerce and industry; and they have created reservoirs to augment the supply of water during periods of drought. In the 5000 or so years that humans have been building dams, millions have been constructed globally, especially in the last 100 years (Smith 1971, WCD 2000). If dams have successfully met so many human needs, why is there a growing call for their removal? The answers to this question require an appreciation of society’s changing needs for, and concerns about, dams, including the emerging recognition that dams can impair river ecosystems (Babbit 2002). But decisions about dam removal are complex, in no small part because great scientific uncertainty exists over the potential environmental benefits of dam removal. Certainly, the scarcity of empirical knowledge on environmental responses to dam removal contributes to this uncertainty (Hart et al. 2002). More fundamentally, however, a scientific framework is lacking for considering how the tremendous variation in dam and river attributes determines the ecological impacts of dams and the restoration potential following removal. Such an ecological classification of dams is ultimately needed to support the emerging science of dam removal. In this article, we develop a conceptual foundation for the emerging science of dam removal by (a) reviewing the ways that dams impair river ecosystems, (b) examining criteria used to classify dams and describing how these criteria are of limited value in evaluating the environmental effects of dams, (c) quantifying patterns of variation in some environmentally relevant dam characteristics using governmental databases, (d) specifying a framework that can guide the development of an ecological classification of dams, and (e) evaluating the ways that dam characteristics affect removal decisions and the future of dam removals. We restrict our analysis to the United States, where dam removals are currently hotly debated; however, the ecological framework we advocate could also be generalized to other parts of the world.

Biogeographic Patterns and Conservation in the South American Cerrado: A Tropical Savanna Hotspot

Abstract: )ofthe land surface in SouthAmerica,Africa,and Asia.Most people know these savannasbecause oftheir unique assemblages ofabundant and exquisitewildlife;however,they have only recently begun to receive thekind ofattention from a conservation viewpoint that hasbeen given to tropical rain forests (Myers et al.2000).Thelargest,richest,and possibly most threatened tropical sa-vanna in the world is the Cerrado,a large region that occu-pies the center ofSouth America.In an effort to identify theworld’s most important biodiversity hotspots,Myers andcolleagues (2000) ranked the Cerrado among the 25 most im-portant terrestrial hotspots.It is the only region on their listdominated by tropical savannas.The biodiversity ofthe Cer-rado is impressive;in an area of1.86 million km

Pacific Salmon in Aquatic and Terrestrial Ecosystems

Abstract: S runs in the Pacific Northwest have been declining for decades, so much so that many runs are threatened or endangered; others have been completely extirpated (Nehlsen et al. 1991). This “salmon crisis” looms large in the public eye, because it has serious and wideranging economic, cultural, and ecological repercussions. Billions of dollars have gone into industrial and agricultural projects that alter regional rivers in ways that, often unintentionally, make them inaccessible or unsuitable for salmon. Recently, billions more have been spent in largely unsuccessful attempts to restore the languishing salmon runs (Lichatowich 1999). Moreover, enormous nonmonetary resources have been expended in assigning and denying responsibility for failed runs and debating the possible efficacy of various remedies. As resources that are devoted to reversing declining runs of salmon have increased, scientists and resource managers have been expanding our understanding of the ecological role of salmon and other anadromous fishes, which return from the sea to spawn in fresh water. We have known for years that spawning salmon serve as a food resource for wildlife species (e.g., Shuman 1950) and, when they die after spawning (as most Pacific salmon do), their carcasses provide nutrients (e.g., carbon [C], nitrogen [N], phosphorus [P]) to freshwater systems (e.g., Juday et al. 1932). More recently, scientists have documented that these “salmon-derived nutrient” subsidies may have significant impacts on both freshwater and riparian communities and on the life histories of organisms that live there (Willson et al. 1998, Cederholm et al. 1999). Because of the burgeoning interest in salmon, growing indications of their ecological importance, and recent calls for management to consider the role of salmon in aquatic and terrestrial ecosystems (e.g., Larkin and Slaney 1997), we take this opportunity to review what is understood about the function of salmon as key elements of ecological systems. Our objectives are twofold. First, we expand on previous reviews of salmon (Willson et al. 1998, Cederholm et al. 1999) to include recent research that has amplified and modified earlier ideas about the contribution of salmon to ecosystem processes. In doing so, we describe the composition, magnitude, and distribution of marine inputs to freshwater and terrestrial systems via salmon. We use an expanding group of studies pertaining to stream nutrient budgets and salmon physiology to construct a schematic that illustrates salmon-derived products and the pathways by which they enter and are retained in aquatic and terrestrial food webs. We then consider the ecological variation associated with salmonid ecosystems and how this may influence the ecological response to the salmon input. Second, we consider how this variation in ecosystem response may influence management and conservation efforts.

Subterranean Ecosystems: A Truncated Functional Biodiversity

Abstract: T biodiversity varies among habitats is a basic tenet of ecology. Many hypotheses have been advanced to explain these variations: ecosystem stability and complexity (e.g., Pimm 1984), ecosystem predictability, habitat heterogeneity (e.g., Tilman 1982), and disturbance (the intermediate disturbance hypothesis; Grime 1973). Whatever the cause of its fluctuations, there is evidence that, at a certain threshold, biodiversity is critical to the maintenance of ecosystems. The link between biodiversity and ecosystem function depends on the dissipation of energy, and productivity might be the ultimate factor that controls species richness at local and, to some degree, at regional scales (Ricklefs and Schluter 1993). Ecosystem function accounts for the relative stability of biodiversity ratios between similar habitats of different continents (Caley and Schluter 1997). In contrast, absolute measures of biodiversity in similar habitats of different regions may differ greatly, which has been interpreted as a result of historical processes (Ricklefs and Schluter 1993). Biodiversity patterns of subterranean terrestrial and aquatic ecosystems are in line with these general observations. However, the features of this environment (absence of light, limited variations in temperature, paucity of food, high physical fragmentation) (Ginet and Decou 1977, Camacho 1992) provide unique opportunities to explore biodiversity issues and to test some of the general hypotheses listed above. Subterranean habitats predominate on the continental and ocean margins. Considering the continental earth, 97% of all unfrozen freshwater is subsurface, whereas lakes and rivers represent less than 2%. Terrestrial subterranean habitats encompass the whole unsaturated zone (vadose zone) of underground, most evident in karstic areas (caves, fissures, cracks, etc.), which represent nearly 4% of the rock outcrops of the world. Because they develop in rocks or sediments that protect them against surface environmental changes, these subterranean ecosystems, in contrast to most surface ecosystems which are short-lived (rivers, wetlands, or forests), may persist relatively unchanged for millions of years. In the last two decades groundwater ecology has developed rapidly, forming an important branch of limnology (Stanford and Simon 1992, Gibert et al. 1994, Stanford and Valett 1994, Danielopol et al. 1999). Recent literature has focused on general characteristics of subterranean ecosystems and interac-

Dam Removal: Challenges and Opportunities for Ecological Research and River Restoration

Abstract: W flow is a “master variable” (sensu Power et al. 1995) that governs the fundamental nature of streams and rivers (Poff et al. 1997, Hart and Finelli 1999), so it should come as no surprise that the modification of flow caused by dams alters the structure and function of river ecosystems. Much has been learned during the last several decades about the adverse effects of dams on the physical, chemical, and biological characteristics of rivers (Ward and Stanford 1979, Petts 1984, Poff et al. 1997, Poff and Hart 2002). Increasing concerns about these impacts, together with related social and economic forces, have led to a growing call for the restoration of rivers by removing dams (AR/FE/TU 1999, Pejchar and Warner 2001). For the purposes of this paper, we define restoration broadly as an effort to compensate for the negative effects of human activities on ecological systems by facilitating the establishment of natural components and regenerative processes, although we acknowledge that these efforts rarely eliminate all human impacts (see Williams et al. 1997 for alternative definitions). Interest in dam removal as a means of river restoration has focused attention on important new challenges for watershed management and simultaneously created opportunities for advancing the science of ecology. One challenge lies in determining the magnitude, timing, and range of physical, chemical, and biological responses that can be expected following dam removal. This information is needed to decide whether and how dam removals should be performed to achieve specific restoration objectives (Babbitt 2002). Opportunities for advancing ecological research also exist because dam removal represents a major, but partially controllable, perturbation that can help scientists test and refine models of complex ecosystems. In contrast to the small-scale experiments that traditionally have been employed in stream and river ecology, the unusually large magnitude and spatial extent of dam removal WE DEVELOP A RISK ASSESSMENT FRAME-

The Ecology and Evolutionary History of an Emergent Disease: Hantavirus Pulmonary Syndrome

Abstract: I the spring of 1993, a previously undescribed disease emerged in the Southwest, killing 10 people during an 8-week period in May and June. Early during an infection, victims experienced flu-like symptoms for several days, but their condition suddenly and rapidly deteriorated as their lungs filled with fluids; death usually occurred within hours of the onset of this crisis period. There was no cure, no successful medication or treatment, and the disease agent (virus, bacterium, or toxin) was completely unknown. For the first few weeks, the mortality rate was 70%. Researchers from many disciplines immediately focused on the outbreak, attempting to identify the agent and understand the causes and dynamics of the disease. Within weeks, scientists at the Centers for Disease Control and Prevention (CDC) identified the agent as a previously unknown hantavirus (Bunyaviridae), subsequently named Sin Nombre virus, or SNV (Nichol et al. 1993). Because hantaviruses were known to be transmitted by rodents, investigators undertook an intensive small mammal field sampling campaign in the Four Corners region of New Mexico and Arizona. Shortly thereafter, CDC identified the viral reservoir host as a common and widely distributed rodent, the deer mouse, Peromyscus maniculatus (figure 1; Childs et al. 1994). During the identification period, on the medical side, physicians and medical staff made rapid progress in developing treatment methods to stabilize and sustain patients through the crisis period, thereby substantially improving patient survivorship; nonetheless, the mortality rate fell only to about 40%, where it remains today. The emergence of this new disease prompted many questions about its history, causes, and dynamics. Was this a newly Terry L. Yates (e-mail: tyates@unm.edu) is a professor in the Departments of Biology and Pathology at the University of New Mexico, Albuquerque, NM 87131. Cheryl A. Parmenter, Robert R. Parmenter, John R. Vande Castle, Jorge Salazar-Bravo, and Jonathan L. Dunnum are with the Department of Biology and the Museum of Southwestern Biology, University of New Mexico. James N. Mills, Thomas G. Ksiazek, Stuart T. Nichol, and Joni C. Young are with the Centers for Disease Control and Prevention, Atlanta, GA 30333. Charles H. Calisher and Barry J. Beaty are with the Arthropod-borne and Infectious Diseases Laboratory, Foothills Campus, Colorado State University, Fort Collins, CO 80523. Kenneth D. Abbott is with the Department of Biology, Yavapai College, Prescott, AZ 86301. Michael L. Morrison is with the Department of Wildlife and Fisheries Sciences, University of Arizona, Tuscon, AZ 85721. Robert J. Baker is with the Department of Biology and The Museum, Texas Tech University, Lubbock, TX 79409. Clarence J. Peters is with the Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555. © 2002 American Institute of Biological Sciences. The Ecology and Evolutionary History of an Emergent Disease: Hantavirus Pulmonary Syndrome

Ecological Causes and Consequences of Demographic Change in the New West

Abstract: R areas in the American West are undergoing a dra m a tic tra n s i ti on in dem ogra phy, econ om i c s ,a n d eco s ys tem s . Long known as the “Wi l d ” We s t , the regi on has been ch a racteri zed by low human pop u l a ti on den s i ties and vast tracts of u n s et t l ed or undevel oped land (Wi l k i n s on 1993, Power 1998). For most of the 1900s, the pop u l a ti on of m a ny ru ral areas in the West grew very slowly or even dec re a s ed . Because local econ omies were based on natu ral re s o u rce indu s tries su ch as mining, l oggi n g, f a rm i n g, and ra n ch i n g, m a ny re s i dents of the regi on con s i dered con s erva ti on stra tegies on public lands detri m ental to local econ omic devel opm en t . E f forts to establish natu re re s erves and to pre s erve p u blic lands from com m ercial devel opm ent were seen as res tri cting the use of vital natu ral re s o u rce s . In recent dec ade s ,p a rts of that Wild West have given way to the “ New ” West (Ri ebsame et al. 1 9 9 7 ) . People from t h ro u gh o ut the Un i ted States have been migra ting to the Rocky Mountains and the inland We s t . With a pop u l a ti on growth ra te of 2 5 . 4 % , the mountain West was the faste s t growing regi on of the co u n try du ring the 1990s. Su rpri si n gly, rapid pop u l a ti on increases are occ u rring not on ly in urban areas su ch as Denver and Salt Lake Ci ty but also in ru ra l co u n ti e s ,m a ny of wh i ch are gaining pop u l a ti on even faster than urban areas (Th eobald 2000). Some 67% of the co u nties in the Rocky Mountains grew faster than the nati onal avera ge du ring the 1990s (Beyers and Nel s on 2000). Con s equ en t ly, s m a ll cities su ch as Bozem a n , Mon t a n a , and Moa b, Ut a h , a re beginning to ex peri en ce traffic con ge s ti on and s prawl . Some of the ru ral pop u l a ti on growth in the New We s t repre s ents an intra regi onal red i s tri buti on of people from the h i gh plains, wh i ch con ti nue to lose pop u l a ti on (Jo h n s on 1 9 9 8 ) , to more mountainous are a s . Ma ny of the new re s i den t s , h owever, a re in-migrants from other regi ons thro u gh o ut the Un i ted States (Ri ebsame et al. 1 9 9 7 ) . The re s i dents of a ru ra l su b d ivi s i on in a boom co u n ty in Montana might inclu de recent arrivals from big East Coast citi e s ,m i dwe s tern farm s ,a n d the nearest small town . Am ong the in-migrants are reti ree s , we a l t hy young adu l t s , and profe s s i onals in com p uter techn o l ogy, real estate , and other servi ce indu s tries (Nel s on 1999).

Insect Defoliation and Nitrogen Cycling in Forests

Abstract: O of defoliating insects can have dramatic effects on forest ecosystems. Studies have shown that defoliation can decrease transpiration and tree growth and increase tree mortality, light penetration to the forest floor, and water drainage (Stephens et al. 1972, Campbell and Sloan 1977, Houston 1981). The allocation of carbon to various parts of the tree may be altered, production of defensive compounds in foliage may increase (Schultz and Baldwin 1982), and seed production may decline for many years after defoliation (McConnell 1988, Gottschalk 1990). Shifts in tree species composition (Doane and McManus 1981, Glitzenstein et al. 1990) and changes in the population size of insectivorous birds and other wildlife may also occur (Holmes et al. 1986, USDA Forest Service 1994). Several studies of insect outbreaks have also indicated an increased loss of nitrogen (N) from forest ecosystems in drainage water following defoliation, suggesting an increase in soil-available nitrogen that is subject to leaching (Swank et al. 1981, McDonald et al. 1992, Webb et al. 1995, Eshleman et al. 1998, Reynolds et al. 2000). Large losses of nitrogen via leaching would reduce long-term forest production in Nlimited ecosystems. In addition, the export of nitrate (NO3 –) to stream water can acidify downstream waters (Webb et al. 1995) and contribute to eutrophication of coastal waters and estuaries (Fisher and Oppenheimer 1991). At first glance, the view held by many investigators that forest ecosystems leak N in large quantities after defoliation fits the general notion of nitrogen behavior in disturbed ecosystems. Significant nitrogen losses have been observed in response to disturbances such as intensive harvesting (Likens et al. 1970), fire (Bayley and Schindler 1991), and severe windstorms (Schaefer et al. 1996). However, defoliation differs qualitatively from these other disturbances in three ways. First, most of the trees usually remain alive with their woody structure intact after defoliation by insects. (Exceptions are the high mortality rates caused by repeated severe defoliations of hardwood trees or by severe defoliation of conifers.) Second, physical disturbance of the soil is minimal and significant erosion is therefore unlikely to occur. And third, if the trees are not killed, the time for substantial canopy recovery is often measured in weeks rather than years. In this article we examine the mechanisms and magnitudes of N-cycle perturbations by defoliation, drawing heavily on the considerable body of research on the gypsy moth (Lymantria dispar L.), an introduced lepidopteran that has been the major defoliator of hardwood forests in the northeastern United States during the last 5 or 6 decades (Doane and McManus 1981). We attempt to establish a more coherent view of the likely consequences of defoliation for N cycling, and we make the case that, contrary to the commonly held view, the response of forest ecosystems to defoliation is primarily one of redistribution, rather than loss, of nitrogen.

Weaving Traditional Ecological Knowledge into Biological Education: A Call to Action

Abstract: A s scientists and educators, we train our students to thoroughly examine all the available evidence and to consider alternative explanations for biological phenomena. In peer review, we critically assess whether the author has carefully cited the appropriate primary sources. And yet, in our biology curricula, we are perhaps unknowingly ignoring an entire body of knowledge that has potential significance to contemporary science and policy: traditional ecological knowledge (TEK). Indigenous peoples are the stewards of fully 4 percent of the land area of the United States and represent some 700 distinct communities possessing detailed knowledge of the biota of their homelands. Native American land holdings in North America collectively contain more wildlands than all of the national parks and nature conservancy areas in North Amer-ica (Nabhan 2000). Globally, indigenous peoples inhabit areas with some of the highest remaining biodiversity on the planet (Durning 1992) and are actively engaged as partners in biodiversity conservation (Weber et al. 2000). Issues of sustainable development, resource management, and ecological restoration all include Native American stakeholders. Federal agencies are required to consult with tribes on a government to government basis on a host of scientific and natural resource policies. Thus, college biology graduates have a high probability of encountering issues involving indigenous cultures and TEK. However, the majority of scientific professionals and educators have little understanding of the value of TEK or its cultural context. Traditional ecological knowledge is increasingly being sought by academics, agency scientists, and policymakers as a potential source of ideas for emerging models of ecosystem management, conservation biology, and ecological restoration. It has been recognized as complementary and equivalent to on Biodiversity calls for recognition, protection, and utilization of TEK. Researchers in pharmaceutical laboratories and in agricultural experiment stations worldwide are beginning to recognize the knowledge of indigenous peoples in scientific research. New directions in applied biology that have direct parallels and precedents in traditional knowledge include ecosystem management, medicine, pharmacology, agroecology, wildlife, fisheries, and animal behavior. Biological research is moving to explore these approaches, yet acknowledgment or understanding of traditional ecological knowledge is rare in the scientific community. Most college ecology courses begin a history of the discipline with 19th-century Europe, neglecting the highly sophisticated precedents in indigenous knowledge systems. My goal in this article is to present the case that exposure to TEK has a legitimate role in the education of the next generation of biologists, environmental scientists, and …

Top Carnivores in the Suburbs? Ecological and Conservation Issues Raised by Colonization of North eastern North America by Coyotes

Abstract: J a handful of individual members of a population of top predators—wolves and tigers, orcas, and great white sharks, for example—hold the potential to disproportionately influence animal and plant communities. The importance of this phenomenon, known as a “top-down”effect, has been demonstrated in several recent studies. For example, as few as four killer whales may be responsible for a shift in 800 kilometers of Alaskan near-shore community structure, from a structure dominated by kelp forests with few herbivores to one with high numbers of sea urchins and low kelp densities (Estes et al. 1998). Similarly, just two or three wolf packs indirectly control tree community organization by regulating moose numbers in 544-km2 Isle Royale, Michigan (Post et al. 1999). In coastal southern California, the presence or absence of coyotes in patches of sage–scrub habitat directly controls the distribution and abundance of smaller carnivores, which in turn alter scrub-breeding bird communities (Crooks and Soule 1999). Today in northeastern North America, the top terrestrial predator is the coyote, Canis latrans, an immigrant to the region that is anything but rare. Historically, the species was unknown to European settlers of eastern North America, who were more concerned with the presence of wolves and cougars. Coyotes were a predator of the Great Plains. Lewis and Clark didn’t catch their first glimpse of a coyote until 1804, when they reached the eastern edge of present-day Nebraska (Ambrose 1996). Times have changed. Over the past two centuries the coyote has dramatically expanded its geographical range and is now ubiquitous throughout northeastern North America (Figure 1; Parker 1995, Gompper 2002). It has even colonized seemingly isolated geographical regions such as Cape Cod and the Elizabeth Islands of Massachusetts, Cape Breton Island, Prince Edward Island, and Newfoundland of Atlantic Canada, as well as urban habitats such as parts of New York City. The culmination of this range expansion may arguably be the capture of a wild coyote in Central Park in the heart of Manhattan in 1999 (Martin 1999).

Workshop Biology: Demonstrating the Effectiveness of Active Learning in an Introductory Biology Course

Abstract: T University of Oregon’s Workshop Biology curriculum is one of many experimental approaches to teaching introductory college-level science that emerged during the last decade (Lawson et al. 1990, Ebert-May et al. 1997, Laws 1997, McNeal and D’Avanzo 1997, Wyckoff 2001). Our motivation for developing Workshop Biology came partly from a concern that, despite generally favorable student course evaluations, our traditional approaches (for example, teacherdirected, “cookbook” activities and demonstrations) did not provide students with valuable skills or even with a body of knowledge that lasted much beyond the end of the term. The Workshop Biology project aimed at improving science literacy among nonscience majors in the context of a major research university. The curriculum was developed, implemented, and evaluated during the period 1991–1994. The project included both the development of the Workshop Biology course (a three-term, lab-based introductory sequence for nonscience majors) and a thorough evaluation of its effectiveness as compared with a traditional lecture-based course. The Workshop Biology curriculum incorporated three leading approaches in science education reform: (1) directly confronting students’ misconceptions through concrete experiences, or what we refer to as “conceptual change”; (2) integrating “science as inquiry” into the underlying philosophy of the course; and (3) introducing science in context. The idea of “conceptual change”was drawn from the very successful Workshop Physics approach (Thornton and Sokoloff 1990, Laws 1997), which focuses on identifying common misconceptions and then confronting them through concrete experiences. We drew the name for our course, Workshop Biology, from this approach. Programs that teach “science as inquiry” focus on the need for students to experience the process of science in order to view science as a way of knowing, rather than as a body of knowledge. For example, the BioQUEST curriculum consortium’s “3 P’s” model, problem posing, problem solving, and peer persuasion (Peterson and Jungck 1988), helps students gain skills in the full range of scientific practice. Similarly, case studies can motivate students to search out information and develop analytical skills needed to solve a problem presented by a realistic, interesting case (Herreid 1994a, 1994b). Finally, programs addressing “science in context”focus on the personal and social

Forest Fragmentation of the Conterminous United States: Assessing Forest Intactness through Road Density and Spatial Characteristics

Abstract: O the past few centuries,widespread disturbance of native forests of the conterminous United States has dramatically altered the composition, structure, extent, and spatial pattern of forestlands (Curtis 1956, Whitney 1994). These forests have been either permanently replaced by other land uses or degraded to varying degrees by unsustainable forestry practices, forest fragmentation, exotic species introduction, or alteration of natural disturbance regimes. Habitat fragmentation is generally defined as the process of subdividing a continuous habitat type into smaller patches, which results in the loss of original habitat, reduction in patch size, and increasing isolation of patches (Andrén 1994). Habitat fragmentation is considered to be one of the single most important factors leading to loss of native species (especially in forested landscapes) and one of the primary causes of the present extinction crisis (Wilcox and Murphy 1985). Although it is true that natural disturbances such as fire and disease fragment native forests, human activities are by far the most extensive agents of forest fragmentation (Burgess and Sharpe 1981). For example, during a 20-year period in the Klamath–Siskiyou ecoregion, fire was responsible for 6% of forest loss, while clear-cut logging was responsible for 94% (Staus et al. 2001). Depending on the severity of the fragmentation process and sensitivity of the ecosystems affected, native plants, animals, and many natural ecosystem processes (e.g., nutrient cycling, pollination, predator–prey interactions, and natural disturbance regimes) are compromised or fundamentally altered. For many species, migration between suitable habitat patches becomes more difficult, leading to smaller population sizes, decreased gene flow, and possible local extinctions (Wilcove 1987, Vermeulen 1993). As native forests become increasingly fragmented, ecosystem dynamics switch from being predominantly internally driven to being predominantly externally driven (Saunders et al. 1991). Simultaneously, remnant patches become altered by changes within the patches themselves (Chen et al. 1995, Woodroffe and Ginsberg 1998) as the remnants become more and more isolated, thereby resulting in further ecological degradation across the landscape. Declines in forest species as a result of fragmentation have been documented for numerous taxa, including neotropical migrant songbirds

Rain and Rodents: Complex Dynamics of Desert Consumers

Abstract: W is the lifeblood of the desert. It comes in rains that are typically scant and sporadic, but can be so intense as to cause flooding. Because water is the resource in shortest supply, the amount and timing of precipitation directly limits plant growth and primary production. Seasons of exceptionally heavy and frequent rains produce the spectacular desert blooms shown in nature films and magazines. Seasons of exceptionally high rainfall are also thought to cause increases in rodent populations and outbreaks of rodentborne diseases such as hantavirus and plague. El Niño is supposed to cause exceptionally heavy winter rainfall in the deserts of southwestern North America, leading in turn to plant growth, abundant seeds and insects, high populations of small mammals, density-dependent increases in parasites and diseases, and increased contact between rodents, their pathogens, and humans, resulting in disease epidemics. Thus, the outbreak of the Sin Nombre strain of hantavirus that killed 27 people in the Four Corners region of the southwestern United States in the summer of 1993 was attributed to the rains, plant production, and rodent increases triggered by the El Niño events of 1991–1992 and 1992–1993 (Harper and Meyer 1999). Ecologists have long been interested in these kinds of complicated pathways of interactions and particularly in how relationships between resources and consumers affect the structure and dynamics of ecosystems. The “bottom-up” pattern of regulation described above occurs when pulsatile resource inputs are transmitted up food chains, causing increases first in plants and then in successively higher trophic levels. This contrasts with “top-down” regulation, in which the feeding activities of top carnivores cascade down food chains to affect successively lower trophic levels (e.g., Hairston et al. 1960, Oksanen et al. 1981, Carpenter and Kitchell 1988). But ecological systems are complex, and there is reason to believe that resource–consumer relationships can exhibit chaotic or other forms of complicated nonlinear dynamics (e.g., Schaffer and Kot 1985, Hanski et al. 1993, Hastings et al. 1993, Lima et al. 1999). Long-term ecological studies provide unique opportunities to study resource–consumer relationships in realistically complex natural settings. Since 1977 we have been monitoring the weather, plants, and rodents in the Chihuahuan Desert near Portal, Arizona (figure 1; Brown 1998, Ernest et al. 2000). The resulting data allow us to evaluate the relationship between El Niño events and rainfall, the dependence of plants on precipitation, and the ways in which episodic rains affect desert rodent populations. After 23 years of study, we are far from understanding the dynamics of this ecosystem. One thing that is clear, however, is that simple bottom-up regulation does not occur. The responses of desert consumers to precipitation are complex and nonlinear.

The Evolution of the Major Histocompatibility Complex in Birds

Abstract: T genetic region that scientists today call the major histocompatibility complex (MHC) was discovered in the 1930s by Peter Gorer in his pioneering studies of antigenic responses to transplanted sera by inbred mouse strains (Gorer 1936). The MHC was genetically defined more precisely by George Snell (1948), who first used the term. Contrary to what many believe, the discovery of cellular antigens in chickens (Gallus gallus), which have functions similar to those in mice, occurred before comparable discoveries in humans (Briles and McGibbon 1948). Thus, studies of the MHC in birds have more than a 50-year history. The immunological and molecular biological revolutions of the 1970s and 1980s, culminating most recently in the complete sequencing of (a) the human leukocyte antigen (HLA; Beck et al. 1999) and (b) the B complex in chickens (Kaufman et al. 1999), revealed that the vertebrate MHC is a complex, multigene family comprising loci encoding receptors on the surfaces of a variety of immune and nonimmune cells. These receptors bind amino acid fragments (or peptides) from foreign pathogens, upon which a cascade of immunological events known as the adaptive immune response is initiated (figure 1). The fundamental position of MHC molecules for initiation and maintenance of both the T cell–mediated and humoral (antibody) arms of the adaptive immune responses has led some immunologists to conclude that the MHC is “the center of the immune universe” (Trowsdale 1995). Those aspects of MHC genes that intrigue immunologists—their function in disease resistance, their unusually high polymorphism and tight linkage into a single “supergene complex”—also intrigue evolutionary biologists and may provide keys to understanding adaptive polymorphism in general and the genetic basis of pathogen resistance in particular. The hypothesis that genetic diversity of MHC genes underlies resistance to the diversity of infectious pathogens arose out of Zuckerkandl and Pauling’s pioneering experiments in mice and population genetics theory, both of which revealed the immunological advantages of heterozygosity, sexual reproduction, and outbreeding (Clarke and O’Donald 1964, Zuckerkandl and Pauling 1965). However, despite the elegant theory that parasitism should drive genetic diversity, empirical examples of the advantages of MHC heterozygosity for rapid parasite clearance have been few, with only a handful of recent but convincing case studies in mammals, for example, HIV (Carrington et al. 1999) and hepatitis (Thursz et al. 1997). Other examples in humans implicate specific MHC haplotypes (multilocus alleles) in resistance to infectious disease, but not heterozygosity per se (e.g., malaria; Hill 1991). Happily for ornithologists, the most striking associations between specific MHC haplotypes and disease resistance are known from chickens—specifically, resistance to a virus causing Marek’s disease. In this case, having the beneficial B-21 haplotype makes an individual 95% resistant, whereas individuals with the B-19 haplotype suffer 100% mortality (Cole 1968). It has been suggested that the tighter linkage of MHC

Potential Responses of Riparian Vegetation to Dam Removal

Abstract: 7hroughout the world, riparian habitats have been • dramatically modified from their natural condition. Dams are one of the principal causes of these changes, because of their alteration of water and sediment regimes (Nilsson and Berggren 2000). Because of the array of ecological goods and services provided by natural riparian ecosystems (Naiman and Decamps 1997), their conservation and restoration have be­ come the focus of many land and water managers. Efforts to restore riparian habitats and other riverine ecosystems have included the management of flow releases downstream of dams to more closely mimic natural flows (Poff et al. 1997), but dam removal has received little attention as a possible ap­ proach to riparian restoration. The riparian vegetation that grows in post-dam removal environments interacts strongly with other factors that are gen­ erally given more direct consideration in dam removal efforts. For example, riparian vegetation can stabilize sediments in for­ mer reservoir pools, perhaps reducing downstream sediment transport that can harm aquatic ecosystems (Bednarek 2001). Vegetation that occupies new surfaces downstream and within the former reservoir pool will influence use by wildlife and for human recreation (ARJFE/TU 1999). Vegetation response to dam removal is highly dependent on changes to the physical environment. Vegetation at the in­ terface between a water body and the surrounding uplands is dominantly structured by the hydrologic gradient. Sites along this gradient differ in the duration, frequency, and tim­ ing of inundation (generally referred to as hydroperiod). Species differences in hydroperiod tolerances and requirements produce zonation and pattern in species composition and gen­ eral cover types along the hydrologic gradient (figure 1). Dam removal may change aspects of the hydrological regime that structure riparian vegetation, including flood and low­ flow regimes and associated water table dynamics. Further, dam removal will generally result in the creation of two classes of bare sediment that can be colonized by riparian . -\"',' ,,,' > ... -.', ' .

How to Avoid Train Wrecks When Using Science in Environmental Problem Solving

Abstract: I collaborations are increasingly common in many areas of science, but particularly in fields involved with environmental problems. This is because problems related to human interactions with the environment typically contain numerous parameters, reflect extensive human alterations of ecosystems, require understanding of physical–biological interactions at multiple spatial and temporal scales, and involve economic and social capital. Distilling useful scientific information in collaborative interactions is a challenge, as is the transfer of this information to others, including scientists, stakeholders, resource managers, policymakers, and the public. While this problem has been recognized by historians and philosophers of science, it has rarely been recognized and openly discussed by scientists themselves (but see NAS 1986). The participation of individuals from a diverse set of scientific disciplines has the potential to enhance the success of problem solving (USGS/ESA 1998). However, obstacles often arise in collaborative efforts for several well-known reasons. First, it is often difficult to find a common language because of disciplinary specialization (Wear 1999, Sarewitz et al. 2000). Second, existing scientific knowledge (theories, models, etc.) may reflect a historical scientific and sociopolitical context that may make it ill suited to address current environmental problems and questions (see, for example, Ford 2000, NSB 2000). Third, collaborations involving multiple disciplines may create difficulties owing to mismatches in space and time scales, in forms of knowledge (e.g., qualitative versus quantitative), and in levels of precision and accuracy (see, for example, Herrick 2000). Fourth, scientists are partly conditioned by nonscientific values. A social fabric may dictate scientists’ worldviews, lead them to favor certain assumptions over others, and underlie the way they study ecosystems (Boyd et al. 1991). In this article, we argue that the success of interdisciplinary collaborations among scientists can be increased by adopting a formal methodology that considers the structure of knowledge in cooperating disciplines. For our purposes, the structure of knowledge comprises five categories of information: (1) disciplinary history and attendant forms of available scientific knowledge; (2) spatial and temporal scales at which that knowledge applies; (3) precision (i.e., qualitative versus quantitative nature of understanding across different scales); (4) accuracy of predictions; and (5) availability of data to construct, calibrate, and test predictive models. By definition, therefore, evaluating a structure of knowledge reveals limitations in scientific understanding, such as what knowledge is lacking or what temporal or spatial scale mismatches exist among disciplines. The epistemological exercise of defining knowledge structures at the onset of a collaborative exercise can be used to construct solvable problems: that is, questions that can be an-