bluuebunny/crossref_metadata_2025 huggingface dataset:
Elucidation of structure–function relationships in the lung: contributions from hyperpolarized 3helium MRI
Authors: Kauczor Hans‐Ulrich , Eberle Balthasar
Published: March 2003

Magnetic resonance imaging (MRI) using hyperpolarized 3helium (He) gas as the source of signal provides new physiological insights into the structure–function relationships of the lung. Traditionally, lung morphology has been visualized by chest radiography and computed tomography, whereas lung function was assessed by using nuclear medicine. As all these techniques rely on ionizing radiation, MRI has some inherent advantages. 3He MRI is based on ‘optical pumping’ of the 3He gas which increases the nuclear spin polarization by four to five orders of magnitude translating into a massive gain in signal. Hyperpolarized 3He gas is administered as an inhaled ‘contrast agent’ and allows for selective visualization of airways and airspaces. Straightforward gas density images demonstrate the homogeneity of ventilation with high spatial resolution. In patients with lung diseases 3He MRI has shown a high sensitivity to depict ventilation defects. As 3He has some more exciting properties, a comprehensive four‐step functional imaging protocol has been established. The dynamic distribution of ventilation during continuous breathing can be visualized after inhalation of a single breath of 3He gas using magnetic resonance (MR) sequences with high temporal resolution. Diffusion weighted 3He MRI provides a new measure for pulmonary microstructure because the degree of restriction of the Brownian motion of the 3He atoms reflects lung structure. Since the decay of 3He hyperpolarization is dependent on the ambient oxygen concentration, regional and temporal analysis of intrapulmonary pO2 becomes feasible. Thus, pulmonary perfusion, ventilation /perfusion ratio and oxygen uptake can be indirectly assessed. Further research will determine the significance of the functional information with regard to physiology and patient management.
Effects of a Ginkgo biloba extract on forearm haemodynamics in healthy volunteers
Authors: Mehlsen J. , Drabæk H. , Wiinberg N. , Winther K.
Published: March 2003

The aim was to validate possible vasodilating effects of a Ginkgo biloba extract with a secondary aim of finding a pharmacodynamic signal relating to the active component of these extracts. We studied the effect of G. biloba extract on forearm haemodynamics in 16 healthy subjects (nine females, seven males) with a median age of 32 years (range: 21–47). The study was conducted as a randomized, double‐blinded cross‐over design using oral treatment with G. biloba extract (Gibidyl Forte® t.i.d. or placebo for 6 weeks. Forearm blood flow and venous capacity were measured by strain‐gauge plethysmography. Blood pressure was measured by standard sphygmomanometry, and forearm vascular resistance (FVR) was derived. Measurements were made at baseline and after 3, 6, 9 and 12 weeks of treatment. Forearm blood flow was significantly higher during active treatment after 3 and 6 weeks as compared with placebo treatment for 3 and 6 weeks (P<0·05). Mean arterial blood pressure was unchanged, making the calculated FVR significantly lower during active treatment (P<0·02). It is concluded that oral treatment with a G. biloba extract (Gibidyl Forte®) is able to dilate forearm blood vessels causing increments in regional blood flow without changing blood pressure levels in healthy subjects. The increments in blood flow may be used as a biological signal for pharmacokinetic studies.
Movement Corridors: Conservation Bargains or Poor Investments?
Authors: Simberloff Daniel , Farr James A. , Cox James , Mehlman David W.
Published: March 2003

Corridors for movement of organisms between refuges are confounded with corridors designed for other functions, obscuring an assessment of cost‐effectiveness. The rationales for movement corridors are (1) to lower extinction rate in the sense of the equilibrium theory, (2) to lessen demographic stochasticity, (3) to stem inbreeding depression, and (4) to fulfill an inherent need for movement. There is a paucity of data showing how corridors are used and whether this use lessens extinction by solving these problems. Small, isolated populations need not be doomed to quick extinction from endogenous forces such as inbreeding depression or demographic stochasticity, if their habitats are protected from humans. In specific instances, corridors could have biological disadvantages. Corridor proposals cannot be adequately judged generically. In spite of weak theoretical and empirical bases, numerous movement corridor projects are planned. In the State of Florida, multi‐million‐dollar corridor proposals are unsupported by data on which species might use the corridors and to what effect. Similarly, plans for massive corridor networks to counter extinction caused by global warming are weakly supported. Alternative approaches not mutually exclusive of corridors might be more effective, but such a judgment cannot be made without a cost‐benefit analysis.
Ecological Impacts of Introduced Animals in Nahuel Huapi National Park, Argentina
Authors: VEBLEN THOMAS T. , MERMOZ MONICA , MARTIN CARLOS , KITZBERGER THOMAS
Published: March 2003

Abstract: In Nahuel Huapi National Park in southwestern Argentina, livestock and exotic deer pose important management problems. Due to the economic and social benefits of sport hunting and production of livestock, it is politically impractical to completely eradicate these animals from the park. Instead, park managers attempt to minimize the effects of these introduced animals by preventing their spread into more pristine parts of the park and by trying to diminish their population densities. Managers are also promoting the relocation of livestock production to appropriate sites in the National Reserve part of the park where livestock raising is permitted. Detailed information on the ecological impacts of introduced herbivores is needed both to guide management of the different vegetation types of the park and to support the park managers' public relations campaign justifying exotic animal control.

We examined the ecological effects of introduced animals along the vegetation gradient from Andean rain forests through xeric woodlands to the Patagonian steppe. We sampled 30 stands for floristic composition and structure, assessed browse intensity, and compared stands of similar abiotic habitat but of different browsing regimes. Deer and livestock have significantly altered floristic composition and stand structure along this gradient. They impair tree regeneration and pose a long‐term threat to the continued existence of a forest cover.
Rates of Deforestation in Los Tuxtlas, a Neotropical Area in Southeast Mexico
Authors: DIRZO RODOLFO , GARCIA MARIA C.
Published: March 2003

Abstract: On the basis of ground surveys, aerial photographs (for 1967 and 1976), and satellite imagery (for 1986), maps of rain forest distribution were developed for the northern part of the Sierra de Los Tuxtlas (Veracruz, southeast Mexico).

Forest coverage maps for 1967, 1976, and 1986 show dramatic deforestation proceeding up from the lowlands, with the remaining natural vegetation now increasingly restricted to the high, steep, and less accessible parts of the Sierra. From the digitizing of the maps it was estimated that (1) during the nearly 20 years of this analysis the vegetation was reduced by 56%, and (2) by early 1986, approximately 84% of the original forest area had been lost.

The derived annual deforestation rates (expressed as the percentage of remaining forest that is cleared per year) were 4.2% for the interval 1967–1976 and 4.3% for 1976–1986. Were these trends and rates to continue, only 8.7% of the original vegetation would persist by the year 2000, and then only in the form of an archipelago of very small forest fragments of which the largest would be the now‐protected areas (e.g, the Los Tuxtlas Biological Station with only 640 ha), and the most inaccessible tracts.

Immediate action is urgently needed to protect these small but rich remnants and preserve them as foci of potential biological inocula for future ecorestoration of these, the northernmost tropical forests on the continent.
The Ginkgos of Tian Mu Shan
Authors: TREDICI PETER DEL , LING HSIEH , YANG GUANG
Published: March 2003

Abstract: The question of whether or not Ginkgo biloba still exists in the wild has been debated by botanists, without resolution, for almost a hundred years. Most of the controversy has focused on a single population of trees located on Tian Mu Shan (Tian Mu Mountain) in Zhejiang Province, China, a site of human activities for approximately 1500 years. Regardless of its origin, the Tian Mu Shan Ginkgo population is biologically significant by virtue of its long survival in a semi‐natural state under conditions of intense interspecific competition. A total of 167 Ginkgos were counted and measured in the 1018 ha Tian Mu Shan Reserve. Many of the trees were growing on disturbance‐generated microsites, such as stream banks, steep rocky slopes, and the edges of exposed cliffs. Forty percent of the censused individuals were multitrunked, consisting of at least two trunks greater than 10 cm in diameter at breast height. Most of these secondary trunks originated from root‐like “basal chichi,” that are produced at the base of trees that have experienced damage from soil erosion or other factors. No Ginkgos less than 5 cm in basal diameter were found in the mature forests of Tian Mu Shan. This lack of seedling reproduction is caused by several factors: (1) the lack of sunny microsites suitable for seedling growth, (2) seed collection by people, and (3) seed predation by animals. In the absence of successful seedling establishment, secondary trunk formation from basal chichi is the single most important factor in explaining the long term persistence of Ginkgo on Tian Mu Shan.
Post‐Perturbation Genetic Changes in Populations of Endangered Virgin River Chubs
Authors: Demarais Bruce D. , Dowling Thomas E. , Minckley W.L.
Published: March 2003

A 34‐kilometer reach of the Virgin River, Utah‐Arizona‐Nevada, was poisoned with rotenone in an attempt to eradicate non‐native red shiners (Cyprinella lutrensis), a species implicated in the decline of native fish populations in the American West. An error in detoxification resulted in lethal concentrations of piscicide passing through an additional 50 kilometers of stream. We used allozyme electrophoresis to analyze genetic variation among pre‐ and post‐poison samples of endangered Virgin River chubs (Gila seminuda). Pre‐poison samples indicated a single panmictic population in the river. In contrast, fish subsequently produced through natural recruitment in poisoned reaches exhibited deviations from the original pattern of genetic variation. A genetic bottleneck caused by severe reduction in the number of spawning adults was indicated. The altered pattern persisted 2.5 years post‐poisoning, indicating unexpectedly slow recolonization from the unpoisoned reach upstream. Genetic variation among hatchery‐produced young was similarly unrepresentative of the original pattern because of the small number of brood fish used in propagation. Because of their small numbers and/or restricted distribution, endangered species are particularly vulnerable to natural or anthropogenic catastrophes. Assessment of the genetic impact of such events is essential but requires that baseline data are available.
Topology of Extinction and Endangerment of Native Fishes in the Pacific Northwest and California (U.S.A.)
Authors: Frissell Christopher A.
Published: March 2003

Recent studies have provided a broad data base on extinction and endangerment of species, subspecies, and distinct populations of inland fishes in western North America. Development of a synoptic, regional‐scale image of extinction and risk of extinction is complicated by the small size and linear distribution of fluvial aquatic habitats and by interspecific variation in areal extent of populations. I developed a regional map of extinction‐risk isopleths based on the number of extinct and persistently declining species in drainage basins of the Pacific Northwest and California. This topological synthesis is useful for delineating and monitoring areas of historic and ongoing loss of aquatic biodiversity, and for relating losses to patterns of land use and habitat modification, climate hydrology, and geomorphology. From an ecological perspective, endangerment of numerous indigenous populations of seven widely distributed species of anadromous salmonids in this region is as important as the more local, diffuse effects of declines in more than 60 endemic, nonanadromous species and subspecies. The simultaneous decline of numerous taxa in basins not afflicted with dams or diversions suggests that cumulative damage to aquatic habitats caused by logging, grazing, urbanization, and other land uses plays a major role in icthyofaunal impoverishment.
The Use of Species Accumulation Functions for the Prediction of Species Richness
Authors: SoberónM. Jorge , LlorenteB Jorge
Published: March 2003

We develop a stochastic theory of the accumulation of new species in faunistic or floristic inventories. Differential equations for the expected list size and its variance as a function of the time spent collecting are presented and solved for particular cases. These particular cases correspond to different models of how the probability of adding a new species changes with time, the size of the list, the complexity of the area sampled, and other parameters. Examples using field data from butterflies and mammals are discussed, and it is argued that the equations relating sampling effort with size of the list may be useful for conservation purposes because they should lend formality to comparisons among lists and because they may have predictive power by extrapolating the asymptotic size of the lists. The suitability of different models to a variety of field situations is also discussed.
Predation on Blackbuck by Wolves in Velavadar National Park, Gujarat, India
Authors: JHALA YADVENDRADEV V.
Published: March 2003

Abstract: The role of predation on the endangered blackbuck antelope (Antelope cervicapra) by the endangered Indian wolf (Canis lupus pallipes) in Velavadar National Park, Gujarat, India, was evaluated in terms of ratios of predator to prey. Food habits of wolves were determined from scat analysis and by direct observation. Consumption was estimated from unutilized portions of blackbuck kills. Wolves preyed primarily on blackbuck (88% biomass consumption), rodents, and hares (Lepus nigricollis). Wolves consumed 4.62 (S.E. 0.11) kg/wolf/kill and made kills at an interval of 3.5 (S.E. 0.5) days. Daily consumption by wolves was estimated at 1.33 kg/wolf. The number of blackbuck killed annually per wolf was estimated between 35 and 39. Between 142 to 158 blackbuck per wolf were considered essential to maintain a stable blackbuck population. Managing the grassland habitat by annual removal of the exotic shrub Prosopis juliflora, minimizing human disturbance to wolves at kills, and reducing predation on blackbuck by feral dogs were some ways to ensure continued viability of this wolf‐blackbuck system.
The Effect of Edge on Avian Nest Success: How Strong Is the Evidence?
Authors: Paton Peter W.C.
Published: March 2003

Wildlife biologists historically considered the edge between adjacent habitat types highly productive and beneficial to wildlife. A current dogma is that edges adversely affect a wide range of avian species by increasing depredation and parasitism rates of nests. I critically evaluated existing empirical evidence to test whether there was a gradation in nest success as a function of distance from an edge. Researchers investigating this question have been inconsistent in their experimental designs, making generalizations about edge‐effect patterns difficult. The majority of studies I examined found nest success varied near edges, with both depredation rates (10 of 14 artificial nest studies, and 4 of 7 natural nest studies) and parasitism rates (3 of 5 studies) increasing near edges. In addition, there was apositive relationship between nest success and patch size (8 of 8 studies). The most conclusive studies suggest that edge effects usually occur within 50 m of an edge, whereas studies proposing that increased depredation rates extend farther than 50 m from an edge are less convincing. Prior research has probably focused on distances too far from an edge to detect threshold values, and future research should emphasize smaller scales. 100–200 m from an edge at 20–25 m increments. Researchers often use relatively arbitrary habitat characteristics to define an edge. Therefore, I propose that only openings in the forest canopy with a diameter three times or more the height of the adjacent trees should be included in edge analyses. This review suggests that fragmentation of eastern North American temperate forests could lead to increased nest predation and parasitism, and there is need to determine if similar processes occur in other forested regions of North America.
Predicting Extinction Times from Environmental Stochasticity and Carrying Capacity
Authors: Foley Patrick
Published: March 2003

Managers of small populations often need to estimate the expected time to extinction Te of their charges. Useful models for extinction times must be ecologically realistic and depend on measurable parameters. Many populations become extinct due to environmental stochasticity, even when the carrying capacity K is stable and the expected growth rate is positive. A model is proposed that gives Te by diffusion analysis of the log population size nt (= loge Nt). The model population grows according to the equation Nt+1 = RtNt, with K as a ceiling. Application of the model requires estimation of the parameters k = logK, rd = the expected change in n, vr = Variance(log R), and ϱ the autocorrelation of the rt. These are readily calculable from annual census data (rd is trickiest to estimate). General formulas for Te are derived. As a special case, when environmental fluctuations overwhelm expected growth (that is rd 0), Te = 2no(k ‐ no/2)/vr. If the rt are autocorrelated, then the effective variance is vre vr (1 + ϱ)/(1 ‐ ϱ). The theory is applied to populations of checkerspot butterfly, grizzly bear, wolf, and mountain lion.
A Comparison of Direct and Environmental Domain Approaches to Planning Reservation of Forest Higher Plant Communities and Species in Tasmania
Authors: Kirkpatrick J.B. , Brown M.J.
Published: March 2003

The planning of representative systems of nature conservation reserves can be based on a wide variety of criteria. The ready availability of data on the physical attributes of the environment, and the patchiness of biological data, have made reservation planning based on environmental classifications an attractive option for decision makers. We developed an environmental classification based on ecologically relevant variables and used it to plan a forest reserve system for Tasmania. We then used biological distributional data and the same targets and procedures to choose a forest reserve system. The analyses based on the environmental classification selected the same areas as equivalent analyses based on biological distributional data to a greater degree than could be expected by chance. Many rare species and communities missed selection by environmental classificatory units (environmental domains), however, and the proportions of ranges of selected taxa varied widely. Conversely, environmental domains were missed by a reservation strategy based only on biological data. These domains might reflect some gaps in the biological data. A reservation planning approach based on both biological data and domains may produce better results than either used in isolation.
Nurse Plant and Floral Biology of a Rare Night‐Blooming Cereus, Peniocereus striatus (Brandegee) F. Buxbaum
Authors: Suzán Humberto , Nabhan Gary P. , Patten Duncan T.
Published: March 2003

The Sonoran night‐blooming cereus (Peniocereus striatus) is a rare cactus found in the Sonoran Desert. Its survival is dependent on maintenance of its habitat and its ability to recruit. This study evaluates the role of nurse plants in P. striatus survival and the floral and pollination ecology controlling recruitment. A strong association was detected between P. striatus and its nurse plants, which include Olneya tesota and Larrea tridentata. Because of the harvesting of Olneya tesota and Prosopis velutina for charcoal over a 20,000 square km area of its range, this night‐blooming cereus is vulnerable to rapid habitat degradation in both Sonora (Mexico) and adjacent Arizona (U.S.A.). The temporal and local scarcity of sphingid moths available for pollination caused by pesticides and small flower numbers, appear to produce low recruitment rates. These two important threats to the biotic associates of this cactus have increased its natural rarity. This can only be alleviated through international cooperation.
Predicting Richness of Native, Rare, and Exotic Plants in Response to Habitat and Disturbance Variables across a Variegated Landscape
Authors: McIntyre S. , Lavorel S.
Published: March 2003

Species richness of native, rare native, and exotic understorey plants was recorded at 120 sites in temperate grassy vegetation in New South Wales. Linear models were used to predict the effects of environment and disturbance on the richness of each of these groups. Total native species and rare native species showed similar responses, with richness declining on sites of increasing natural fertility of parent material as well as declining under conditions of water enrichment (resulting from human‐induced changes in drainage characteristics, leading to increased run‐off), severe livestock grazing, and soil disturbance. The response of rare native species to water enrichment, however, was significantly greater than that of all native species. Exotic species richness varied in reverse to that of native species with positive responses to water enrichment and soil disturbance. The contrasting behaviors are attributed to differences in the evolutionary history of native and exotic assemblages and their resulting preadaptations to a landscape recently subjected to agricultural settlement. It would appear that for exogenous disturbances, the intermediate disturbance hypothesis is not supported by our data. In the sampled region, pastures represent the major land‐use in terms of area, but have relatively low densities of native and rare species compared with more lightly grazed areas. However, their management is considered to be essential to the maintenance of diversity on a regional scale.
Threatened Plant, Animal, and Fungus Species in Swedish Forests: Distribution and Habitat Associations
Authors: Berg Åke , Ehnström Beng , Gustafsson Lena , Hallingbäck Tomas , Jonsell Mats , Weslien Jan
Published: March 2003

Swedish forestry is among the most technically developed in the world; a large part of all forest is used for commercial forestry, which has had a large impact on the structure and function of forest ecosystems. We have compiled present knowledge on the distribution and habitat associations of 1487 threatened forest species in Sweden, made an attempt to identify structures and elements that are critical for their occurrence and suggest guidelines for the maintenance of threatened forest species. Habitat associations and distribution patterns of the threatened species were roughly the same for all organism groups. A significantly higher proportion of the 1487 species in all organism groups (cryptogams, vascular plants, invertebrates, and vertebrates) were found in the south (temperate/hemiboreal region) than in the north (hemiarctic/boreal region) of Sweden. For each organism group, the southern deciduous forest contained the most threatened species. Coniferous forests and other deciduous forests were also relatively species‐rich, while deforested areas and scrub areas were the least species‐rich habitats for the studied species. Most groups were dependent on specific elements in the habitat, which all were characteristic of old forests. Old living trees (especially deciduous trees) were critical for vertebrates, invertebrates, and cryptogams. Logs were critical for invertebrates and cryptogams. Snags were especially important for invertebrates and to some extent for vertebrates and cryptogams. Vascular plants were more dependent on abiotic factors and stand/site‐related factors, such as forest density and forest age, than were the other groups. All groups, however, were largely dependent on old forests or habitat elements associated with old forests. The threatened populations of forest species of international importance (supposed endemics to Scandinavia or with more than 10% of the European population in Sweden) were found to a relatively large extent in coniferous forests in the north of Sweden, while the other threatened species were more restricted to deciduous forests in the south.
Genetic Variation and Outcrossing Rate in Relation to Population Size in Gentiana pneumonanthe L
Authors: Raijmann Léon E.L. , Van Leeuwen Nico C. , Kersten Ralph , Oostermeijer J. Gerard B. , Den Nijs Hans C.M. , Menken Steph B.J.
Published: March 2003

The amount of genetic variation in the rare perennial herb Gentiana pneumonanthe L. was determined to explore its relation to population size. Differences in isozyme variation between maternal plants and their offspring were used to investigate the relationship between population size and outcrossing rate. In 25 populations in The Netherlands, differing in size from 1 to more than 50,000 flowering individuals, 16 allozyme loci were analyzed on leaves of maternal plants and offspring grown in a greenhouse. Population size was significantly positively correlated with the proportion of polymorphic loci, but only marginally with heterozygosity and the mean effective number of alleles. Most of the studied populations were characterized by a complete absence of rare alleles, and F‐statistics suggest relatively high levels of genetic differentiation among populations and thus a low level of gene flow. Leaf samples (maternal) were mostly in Hardy‐Weinberg equilibrium, while several offspring samples showed an excess of homozygotes, which suggests selection favoring heterozygotes. Because most small populations consist only of adult survivors from formerly larger populations, this may partly explain the absence of a clear relationship between genetic variation of the maternal plants and population size. A significant positive correlation was found between the level of cross‐fertilization and population size. From these results, we conclude that, to some degree, small populations have a reduced level of genetic variation, while their present isolation in nature reserves has resulted in a very limited interpopulational gene flow level. At present a higher level of inbreeding in small populations contributes to a further loss of genetic variation and may also result in reduced offspring fitness.
Biodiversity and Ecosystem Function
Authors: Risser Paul G.
Published: March 2003

In at least some circumstances, biodiversity affects various ecosystem functions and the ways in which ecosystems respond to disturbance. Because these interactions occur at many spatial and temporal scales and throughout all levels of biological organization, it is difficult to decide where to focus attention on interactions between biodiversity and ecosystem function. The loci for initial attention is important for setting research priorities to understand these interactions further, for organizing known information to instruct the development of natural resource policies, and for identifying biodiversity conservation priorities. Holling (1992) argues that ecosystem behavior can be understood from a few dominating ecological processes that structure the ecosystem. In the temporal dimension, these key structuring processes dictate a few dominant temporal frequencies that drive other processes. Thus, the most effective strategy for studying interactions between biodiversity and ecosystem function is to focus on the key structuring processes at intermediate scales of space and time. Thereafter, other ecological conditions signify situations in which the interactions between biodiversity and ecosystem function are particularly strong: early to midsuccessional status, low soil fertility, intermediate levels of disturbance, biotic interactions only where there is collaborative indication of importance, invading species that differ significantly from native species in resource acquisition or utilization, and ecotones.
Effects of Ecotourism on Distribution of Waterbirds in a Wildlife Refuge
Authors: Klein Mary L. , Humphrey Stephen R. , Percival H. Franklin
Published: March 2003

Humans visiting natural areas often disturb wildlife, possibly displacing animals from desirable habitat. To hold ecotourism at acceptable levels refuge managers need to know which species are likely to be affected and which response occurs at different levels of disturbance. Displacement of waterbirds at J. N. “Ding” Darling National Wildlife Refuge, Florida (U.S.A.), by specific human activities was demonstrated experimentally by Klein in 1993. We assessed the extent of this effect of ecotourism on the distribution of 38 species of waterbirds by surveying birds in plots of known distance from a dike along which wildlife tours occurred. Most resident species were less sensitive to disturbance than were migrants. Migrant ducks were most sensitive when they first arrived, mid‐October to mid‐December, usually remaining more than 80 m from the drive, even at low levels of human visitation. Herons, egrets. Brown Pelicans (Pelecanus occidentalis), and Anhingas (Anhinga anhinga) were most likely to remain close to areas of high human activity. Shorebirds were displaced at intermediate distance and visitation levels. Mottled Ducks (Anas fulvigula) and several of the ardeids seemed to include two groups differing in behavior, one habituated to humans and one sensitive to disturbance. Public education and changes in management practices are needed to reduce disturbance. Guided tours and low‐disturbance zones where people stay in their cars could reduce the negative effects of tourists, especially in the fall when migrants arrive. The number of human visitors may have to be reduced or the wildlife drive closed on certain days during the tourist season.
Effects of Human Activity on Global Extinction Risk
Authors: Kerr Jeremy T. , Currie David J.
Published: March 2003

Both natural and anthropogenic factors are important in determining a species’ risk of extinction. Little work has been done, however, to quantify the magnitude of current anthropogenic influences on the extinction process. The purpose of this study is to determine the extent to which measures of the intensity of human activity are related to the global variability of two measures of species’ susceptibility to extinction. We observed six indices of human activities in 90 countries, and we tested their relationships to the proportion of threatened bird and mammal species in each country, as well as to mammalian population density. After correcting for area effects, latitudinal diversity gradients, and body size (for population density), 28 to 50% of the remaining variation was statistically attributable to anthropogenic variables. Different measures of anthropogenic influence were most closely related to extinction risk in birds and mammals. Human population density was the variable most closely related to the proportion of threatened bird species per country, whereas per capita GNP was more important for mammal species. Mammalian population density strongly correlates with the extent of protected area per country. Contrary to suggestions in earlier literature, our work does not support the hypothesis that habitat loss is a prime contributor to species loss because frequencies of threatened birds and mammals are not closely related to patterns of land use.
Plant Species Lost in an Isolated Conservation Area in Metropolitan Boston from 1894 to 1993
Authors: Drayton Brian , Primack Richard B.
Published: March 2003

A recensus was undertaken of the Middlesex Fells (West), a 400‐ha woodland park in Metropolitan Boston, to determine how species composition changed between 1894 (the time of first census) and 1993. This park is isolated by an 0.5‐km‐wide barrier of roads and development from the eastern half of the Fells preserve, is at least 5 km from other protected areas, and is strongly affected by human activity. Out of 422 original plant species, 155 species were no longer present in 1993. Sixty‐four new species were recorded on the site in 1993, the majority of them exotic species. The proportion of native species in the flora went from 83% in 1894 to 74% in 1993. Overall, the number of native species is declining at a rate of O.36% per year, whereas the exotic species are increasing at a rate of 0.18% per year. Many of the native species lost were attractive and well‐known components of the native flora, such as orchids and lobeliads. Many remaining native plant species have been reduced to one or a few small populations. Species of moist woods were disproportionately lost from the Fells. The loss of species has coincided with an increase in human activity, including ground fires, a greater number of trails and roads, thinning of the forest, and trampling of the vegetation, all of which may have contributed to species loss. A policy to stop and reverse this progressive loss of species might include preventing new trails from being developed, closing off some existing trails, excluding people from sensitive areas, and reintroducing some of the lost species.
Sustainability and the Scientist’s Burden
Authors: Lélé Sharachchandra , Norgaard Richard B.
Published: March 2003

Natural scientists are being encouraged by environmental and developmental agencies to define and operationalize the concept of sustainability in a “scientific” manner. Such an approach is fraught with dangers because values, opinions, and social influences are an inextricable part of science, especially applied science. Natural scientists’ attempts to define sustainability, particularly to decide what should be sustained, cannot therefore be value‐neutral. They simply end up shifting value judgments to different levels by choosing either a single obvious objective, an arbitrary range of objectives, or an arbitrary method of aggregating different preferences. This lack of self‐reflectiveness on the part of scientists has important consequences for the direction of research and its political implications. Natural scientists should heed lessons from earlier cases of scientists’ involvement in policy and redefine the terms of reference before shouldering their social burden. The dilemma of pursuing objective science in a value‐loaded and socially charged discourse can be resolved by properly understanding the role of analysis and by pursuing a socially grounded pluralistic approach to problem definition and research methodology.
Limitation of African Wild Dogs by Competition with Larger Carnivores
Authors: Creel Scott , Creel Nancy Marusha
Published: March 2003

African wild dogs (Lycaon pictus) are endangered largely because their population‐density is low under all conditions. Interspecific competition with larger carnivores may be a factor limiting wild dog density. The density of wild dogs on a 2600‐km2 area of the Selous Game Reserve (Tanzania) was 0.04 adults/km2. Spotted hyaena (Crocuta crocuta) density for the same area was estimated by audio playbacks as 0.32 hyaenas/km2. Lion (Panthera leo) density, determined from the ratio of hyaenas to lions, was 0.11 lions/km2. Across six ecosystems including Selous, there were strong negative correlations between wild dog and hyaena densities (r = −0.92; p = 0.01) and between wild dog and lion densities (r = −0.91; p = 0.03). Hyaenas out‐numbered wild dogs by ratios ranging from 8:1 to 122:1. Ratios of lions to wild dogs ranged from 3:1 to 21:1. The diets of hyaenas and wild dogs overlap extensively; those of wild dogs and lions show less overlap. Where hyaenas are common and visibility is good, interference competition from hyaenas at wild dog kills is common and reduces wild dogs’ feeding time. Where hyaena density is lower and visibility is poor, interference competition at wild dog kills is rare. Wild dogs are commonly killed by lions and occasionally by hyaenas. These data suggest that competition with spotted hyaenas may limit or exclude wild dogs when hyaena density is high. Competition with lions appears less intense, but direct predation by lions on wild dogs is important. Competition and predation by larger carnivores may be of broad importance to the conservation of wild dogs and other medium‐sized carnivores.
Prevalence and Intensity of Intestinal Parasites in Mantled Howling Monkeys (Alouatta palliata) in Northeastern Costa Rica: Implications for Conservation Biology
Authors: Stoner Kathryn E.
Published: March 2003

I examined the prevalence and intensity of intestinal parasitic infections in a population of mantled howling monkeys (Alouatta palliata) at La Selva Biological Reserve, a rainforest in northeastern Costa Rica. I collected fresh fecal samples from individual bowler monkeys from two focal troops from October 1991 through October 1992. The presence of parasite ova and larvae in samples was determined by using a formalin‐ethyl acetate sedimentation technique. Three types of endoparasites were found: (1) a roundworm, Parabronema sp., (2) a physalopterid roundworm, species undetermined, and (3) a fluke, species undetermined. No differences were found in the prevalence of parasitic infections between sexes or troops. No statistical differences were found between the sexes for the intensity of infection. The troop that lived along the river showed a statistically significant higher intensity of nematode infection than the troop that lived mostly in primary forest. Parabronema sp. was found only from individuals in the river group. The prevalence of parasitic infection observed in howlers at La Selva (100%) is higher than has been reported for bowlers in a dry deciduous forest at La Pacifica, Costa Rica (47%). Microclimatic factors, ranging patterns, and home‐range size are identified as important variables that may affect parasitic infections of howler populations. Data from this study suggest that narrow corridor designs may be inappropriate for conservation of primates and possibly other species of arboreal animals.
Simulation of the Effect of Spatial and Temporal Variation in Fire Regimes on the Population Viability of a Banksia Species
Authors: Bradstock R.A. , Bedward M. , Scott J. , Keith D.A.
Published: March 2003

Populations of plants that rely on seeds for recovery from disturbance by fire (obligate seeders) are sensitive to regimes of frequent fire. Obligate seeders are prominent in fire‐prone heathlands of southern Australia and South Africa. Population extinction may occur if there are successive fires during a plant’s juvenile period. Research on the population biology of obligate seeders has influenced the management of fire in these heath and shrublands, but work on the effects of the spatial variability of fires is lacking. We hypothesize that extinction maybe avoided under an adverse fire frequency if fires are patchy. We present a model that simulates the effects of spatial and temporal variations in fire regimes on the viability of a plant population in a grid landscape. Seedling establishment, maturation, senescence, and seed dispersal determine the presence or absence of plants in each cell. We used values typical of serotinous Banksia species to estimate probability of extinction in relation to fire frequency and size. We examined the sensitivity of predictions to dispersal, senescence, fire frequency, spatial burning pattern and size variance, and the size of the grid. Simulations 200 years in length indicated that extinction probability was lowest when mean fire frequency was intermediate and mean fire size was large. When fire frequency was high, extinction probability was high irrespective of fire size. Senescence was more important than high‐frequency fire as a cause of extinction in cells. Interactions between dispersal, fire frequency, and size were complex, indicating that extinction is governed by intercell connectivity. The model indicates that fire patchiness cannot be assumed to ensure avoidance of extinction of populations. Conservation of populations is most likely when fire patchiness is relatively low—when the size of fires is moderate to large and when burned patches are contiguous.
A Method for Assessing Hydrologic Alteration within Ecosystems
Authors: Richter Brian D. , Baumgartner Jeffrey V. , Powell Jennifer , Braun David P.
Published: March 2003

Hydrologic regimes play a major role in determining the biotic composition, structure, and function of aquatic, wetland, and riparian ecosystems. But human land and water uses are substantially altering hydrologic regimes around the world. Improved quantitative evaluations of human‐induced hydrologic changes are needed to advance research on the biotic implications of hydrologic alteration and to support ecosystem management and restoration plans. We propose a method for assessing the degree of hydrologic alteration attributable to human influence within an ecosystem. This method, referred to as the “Indicators of Hydrologic Alteration,” is based upon an analysis of hydrologic data available either from existing measurement points within an ecosystem (such as at stream gauges or wells) or model‐generated data. We use 32 parameters, organized into five groups, to statistically characterize hydrologic variation within each year. These 32 parameters provide information on ecologically significant features of surface and ground water regimes influencing aquatic, wetland, and riparian ecosystems. We then assess the hydrologic perturbations associated with activities such as dam operations, flow diversion, groundwater pumping, or intensive land‐use conversion by comparing measures of central tendency and dispersion for each parameter between user‐defined “pre‐impact” and “post‐impact” time frames, generating 64 Indicators of Hydrologic Alteration. This method is intended for use with other ecosystem metrics in inventories of ecosystem integrity, in planning ecosystem management activities, and in setting and measuring progress toward conservation or restoration goals.
Modeling Human Factors That Affect the Loss of Biodiversity
Authors: Forester Deborah J. , Machlist Gary E.
Published: March 2003

Within conservation biology human factors are treated as driving forces of biodiversity loss, yet there are few empirical studies on how human actions affect biodiversity. We developed and tested an interdisciplinary model of biodiversity loss using socioeconomic and ecological data from 107 countries and structural equation modeling techniques. Some portions of the model fit the data well, other parts were less predictive. Counterintuitive results may be a result of the quality and availability of cross‐national data and statistical limitations in testing a model of such complex processes. This model test provides insight into future research needs for examining human impacts on biodiversity. Issues including data quality, temporal and spatial scale, and model refinement are outlined. The results highlight the importance of relations between human social systems and biodiversity and the potential of interdisciplinary research.
Implications of Phylogenetic Studies for Conservation of Genetic Diversity in Shiitake Mushrooms
Authors: Hibbett David S. , Donoghue Michael J.
Published: March 2003

We consider the impact of recent molecular phylogenetic analyses on conservation issues for shiitake mushrooms. Bused on mating compatibility, shiitake has been considered a single species, Lentinula edodes sensu lato. Phylogenetic analyses of ribosomal RNA internal transcribed spacers (Hibbett et al. 1995), however, suggest that shiitake is composed of four distinct lineages. Thus, under a phylogenetic species concept, four species of shiitake should be recognized. A classification of shiitake based on a phylogenetic species concept would convey information about evolutionary relationships and distribution of genetic variation, whereas a classification based on a biological species concept would lack such information. This is a clear case in which new insights into phylogenetic relationships can be used to target areas for conservation action and formulate international agricultural policies. At the heart of our argument is the belief that the basic units of both taxonomy and conservation should be unique evolutionary lineages of organisms identified through phylogenetic studies.
The Genetic Diversity of Native, Stocked, and Hybrid Populations of Brook Trout in the Southern Appalachians
Authors: Hayes John P. , Guffey Stanley Z. , Kriegler Frank J. , McCracken Gary F. , Parker Charles R.
Published: March 2003

Using mitochondrial DNA (mtDNA) restriction analysis and starch‐gel electrophoresis of the CK‐A2 locus product, we examined genetic variation in 311 brook trout (Salvelinus fontinalis) from 11 native, 5 hatchery‐derived, and 8 hybrid populations in the southern Appalachian Mountains. Native southern Appalachian fish were genetically distinct from hatchery‐derived fish. Southern and hatchery‐derived fish were reliably distinguished based on three mtDNA restriction sites. Native southern haplotypes differed from hatchery‐derived haplotypes by an average of 0.84%. Northern hatchery‐derived haplotypes varied little in mtDNA compared to native southern haplotypes. Introgression of mtDNA haplotypes and the CK‐A2 locus varied among populations, and introgression of allozyme and mtDNA markers was positively correlated. Continued introductions of nonnative strains of brook trout in the southern Appalachians could simplify the genetic structure of native brook trout populations and eliminate unique genotypes.
The One‐Migrant‐per‐Generation Rule in Conservation and Management
Authors: Mills L. Scott , Allendorf Fred W.
Published: March 2003

In the face of continuing habitat fragmentation and isolation, the optimal level of connectivity between populations has become a central issue in conservation biology. A common rule of thumb holds that one migrant per generation into a subpopulation is sufficient to minimize the loss of polymorphism and heterozygosity within subpopulations while allowing for divergence in allele frequencies among subpopulations. The one‐migrant‐per‐generation rule is based on numerous simplifying assumptions that may not hold in natural populations. We examine the conceptual and theoretical basis of the rule and consider both genetic and nongenetic factors that influence the desired level of connectivity among subpopulations. We conclude that one migrant per generation is a desirable minimum, but it may be inadequate for many natural populations. We suggest that a minimum of 1 and a maximum of 10 migrants per generation would be an appropriate general rule of thumb for genetic purposes, bearing in mind that factors other than genetics may further influence the ideal level of connectivity.