bluuebunny/crossref_metadata_2025 huggingface dataset:
The Decline of Amphibians in California’s Great Central Valley
Authors: Fisher Robert N. , Shaffer H. Bradley
Published: March 2003

Declines in amphibian populations are rarely reported on the community or ecosystem level. We combined broad‐scale field sampling with historical analyses of museum records to quantify amphibian declines in California’s Great Central Valley. Overall, amphibians showed an unambiguous pattern of decline, although the intensity of decline varied both geographically and taxonomically. The greatest geographical decline was detected in the counties of the Sacramento and San Joaquin Valleys. Two species, Rana aurora and Bufo boreas were identified as the most affected by decline, whereas Pseudacris regilla was the least affected. The Coast Range counties had little or no detectable decline. We provide new evidence implicating introduced predators as a primary threat. Introduced predators occur at lower elevations than native species, and our data indicate that for some native species there has been significant restriction to higher elevation sites from a formerly broader distribution. Our historical approach provides a strategy for identifying declining amphibian communities that complements more detailed, long‐term monitoring programs and provides an assessment of the pattern of change that is a necessary prerequisite for the development of field experiments that test hypothesized mechanisms of change.
Conservation Implications of Patterns of Horn Regeneration in Dehorned White Rhinos
Authors: Rachlow Janet L. , Berger Joel
Published: March 2003

The demand for rhino horn has led to drastic declines in numbers of rhinos in Asia and Africa. Although all trade in rhino products has been illegal since the mid‐1970s, a lucrative illegal market flourishes and poaching continues. Horn removal from African rhinos has been conducted in Zimbabwe, Namibia, and Swaziland to deter poaching. Regeneration of horns following dehorning has created the potential for a sustainable harvest of rhino horn through dehorning programs. Establishment of a regulated legal market for rhino horn has been suggested to help fund rhino conservation programs in African countries. However, evaluation of an economic harvest of rhino horn from dehorning programs has been limited because few data on rates and form of horn regeneration exist. Because rate of horn regeneration will determine the interval at which rhino horns could be harvested profitably, we measured horn regrowth for two white rhino (Ceratotherium simum) populations studied in Zimbabwe between 1991–1995. Measurements of horn sizes were collected before and after dehorning, and mass to volume relationships were calculated. Von Bertalanffy growth curves were used to model horn size and rates of horn regrowth relative to age. Adult males had larger horn bases (p < 0.001) and faster rates of horn regrowth than adult females. Regenerated horn mass for adult males (>1.3 kg/yr) was almost twice the mass of adult females. Based on an economic model for profit maximization, intervals for dehorning range from 1.16 to 1.51 years and vary with both sex and age. We suggest managers use these values as minimum dehorning intervals to balance profits with longer‐term management goals. Rates of horn regeneration are likely to be less important than law enforcement in determining the efficacy of dehorning as a deterrent to rhino poaching.
Effects of Habitat Loss and Fragmentation on the Behavior and Demography of Gray‐Tailed Voles
Authors: Wolff Jerry O. , Schauber Eric M. , Edge W. Daniel
Published: March 2003

We monitored the short term behavioral and demographic responses of gray‐tailed voles (Microtus canicaudus) to the reduction and fragmentation of their habitat. Our objectives were (1) to test whether animals perished or moved into remaining fragments after 70% of their habitat was removed; and (2) to test the null hypothesis that the social structure and demography of animals would not differ between habitats consisting of one large continuous fragment (625 m2), a mosaic of 25 small fragments (each 25 m2) separated by 4 m of bare ground, and control, unmanipulated habitats (1850 m2). We conducted the experiment in 12, 0.2‐ha enclosures planted with alfalfa with four replicates for each of two manipulated treatments and a control. A 70% reduction in habitat did not adversely affect adult survival, reproductive rate, juvenile recruitment, or population size. However, an influx of unrelated females into habitat fragments resulted in decreased juvenile recruitment in those fragments. Voles from cleared habitat moved into the remaining habitat and did not measurably affect the resident population. Similarly, the demography of voles did not differ significantly among the large‐fragment, small‐fragment, and control enclosures. Peak density estimates based on the amount of habitat in each enclosure were 545 animals per hectare in control, 1056 in large‐fragment, and 2880 in small‐fragment enclosures. Reduced movement of animals among the small fragments was the most obvious effect of habitat fragmentation. Six percent of females and 15% of males moved among small fragments within a week compared to approximately 60% moving comparable distances in large‐fragment and control enclosures. Rates of juvenile dispersal and sexual maturation declined throughout the summer on all treatments, were associated with season and density, and were only marginally associated with habitat loss and fragmentation. We conclude that at the time of habitat removal and fragmentation, populations were small enough to accommodate a 70% reduction in habitat and still continue to increase in numbers. The social system of gray‐tailed voles was sufficiently flexible to accommodate an influx of animals to withstand densities> 1000 voles per ha. The behavioral and demographic features of gray‐tailed voles are similar to those reported for other small mammals, thus confirming the use of voles for ecological model systems in habitat fragmentation studies.
The Application of Neutral Landscape Models in Conservation Biology
Authors: With Kimberly A.
Published: March 2003

Neutral landscape models, derived from percolation theory in the field of landscape ecology, are grid‐based maps in which complex habitat distributions are generated by random or fractal algorithms. This grid‐based representation of landscape structure is compatible with the raster‐based format of geographical information systems (GIS), which facilitates comparisons between theoretical and real landscapes. Neutral landscape models permit the identification of critical thresholds in connectivity, which can be used to predict when landscapes will become fragmented. The coupling of neutral landscape models with generalized population models, such as metapopulation theory, provides a null model for generating predictions about population dynamics in fragmented landscapes. Neutral landscape models can contribute to the following applications in conservation: (1) incorporation of complex spatial patterns in (meta)population models; (2) identification of species’ perceptions of landscape structure; (3) determination of landscape connectivity; (4) evaluation of the consequences of habitat fragmentation for population subdivision; (5) identification of the domain of metapopulation dynamics; (6) prediction of the occurrence of extinction thresholds; ( 7) determination of the genetic consequences of habitat fragmentation; and (8) reserve design and ecosystem management. This generalized, spatially explicit framework bridges the gap between spatially implicit, patch‐based models and spatially realistic GIS applications which are usually parameterized for a single species in a specific landscape. Development of a generalized, spatially explicit framework is essential in conservation biology because we will not be able to develop individual models for every species of management concern.
Alternate Species Concepts as Bases for Determining Priority Conservation Areas
Authors: Peterson A. Townsend , Navarro‐Sigüenza Adolfo G.
Published: March 2003

Abstract:Analysis of geographic concentrations of endemic taxa is often used to determine priorities for conservation action; nevertheless, assumptions inherent in the taxonomic authority list used as the basis for analysis are not always considered. We analyzed foci of avian endemism in Mexico under two alternate species concepts. Under the biological species concept, 101 bird species are endemic to Mexico and are concentrated in the mountains of the western and southern portions of the country. Under the phylogenetic species concept, however, total endemic species rises to 249, which are concentrated in the mountains and lowlands of western Mexico. Twenty‐four narrow endemic biological species are concentrated on offshore islands, but 97 narrow endemic phylogenetic species show a concentration in the Transvolcanic Belt of the mainland and on several offshore islands. Our study demonstrates that conservation priorities based on concentrations of endemic taxa depend critically on the particular taxonomic authority employed and that biodiversity evaluations need to be developed in collaboration or consultation with practicing systematic specialists.
Twenty‐Six Years of Green Turtle Nesting at Tortuguero, Costa Rica: An Encouraging Trend
Authors: Bjorndal Karen A. , Wetherall Jerry A. , Bolten Alan B. , Mortimer Jeanne A.
Published: March 2003

The green turtle (Chelonia mydas) population that nests at Tortuguero, Costa Rica, is the largest in the Atlantic by at least an order of magnitude. Surveys to monitor the nesting activity on the northern 18 km of the 36‐km beach were initiated in 1971 and extended to the entire beach in 1986. From the survey data, we estimated the total number of nesting emergences on the northern 18 km for each year from 1971 through 1996. Evaluation of the trend in nesting emergences indicated a relatively consistent increase from 1971 to the mid‐1980s, constant or perhaps decreasing nesting during the late 1980s, and then resumption of an upward trend in the 1990s. Evaluation of trends in sea turtle nesting populations requires many years of data because of the large degree of annual variation in nesting numbers. The trends reported in this study must be evaluated with caution for several reasons. First, if the mean number of nests deposited by each female each year (clutch frequency) varies significantly among years, changes in the number of nesting emergences among years could reflect changes in the number of nesting females, clutch frequency, or both. Second, we only assessed the trend in one segment of the population (mature females), which may or may not represent the trend of the entire green turtle population and which, because of late maturity, may not reflect changes in juvenile mortality for many years. Third, survey frequency, and thus confidence in annual estimates, varied among years. The upward population trend must be assessed from the perspective of the catastrophic decline that the Caribbean green turtle populations have experienced since the arrival of Europeans. If careful management is continued in Costa Rica and adopted throughout the region, the collapse of the Caribbean green turtle populations—which seemed imminent in the 1950s—can be avoided.
Human Population Density and Prediction of Local Plant Extinction in Britain
Authors: Thompson Ken , Jones Allan
Published: March 2003

Throughout the world, and particularly in densely populated countries like Britain, human activities exert a dominant influence on the abundance of both plants and animals. The commonness and rarity of plants in Britain has been plausibly linked to human land use. In Western Europe the identity of increasing and decreasing plants appears to depend on human population density, which is itself a crude measure of human impact on the landscape. The publication of new data on the changing distributions of scarce British plants allowed us to investigate the relationship between loss of scarce plants and human population density in Britain. Our results confirm that a direct effect of human population density on local plant extinctions can be detected at the regional scale in Britain. Although intensive agriculture is conventionally regarded as the greatest threat to British wildlife, our analysis suggests that urbanization may be at least as significant a danger.
War Zones and Game Sinks in Lewis and Clark’s West
Authors: Martin Paul S. , Szuter Christine R.
Published: March 2003

The journals of Lewis and Clark reveal a major difference in the taxa, numbers, and behavior of megafauna on either side of the Rocky Mountains in western North America. Two prior events set the stage for what Lewis and Clark would find. The first was the extinction around 13,000 years ago of two‐thirds of the native megafauna of the American West. The second was the effects on Indians of deadly new diseases and new technologies brought by Europeans in the post‐Columbian era. Populations of large animals, which were preferred prey for native people, were not immune to European influence. Along the Columbia River corridor west of the Rockies, tens of thousands of people lived in a game sink. Here Lewis and Clark’s party found too few animals to live off the land by hunting. They adapted poorly to the local diet of fish and roots offered by the Nez Perce and bought dogs and horses to sustain themselves. To the east, uninhabited lands along the Upper Missouri and the Yellowstone rivers supported an abundance of wild game, especially bison, elk, deer, pronghorn, and wolves. This game source occupied part of a buffer zone of 120,000 km2 probed by various Indian war parties, some of them armed with muskets. William Clark recognized the relationship and near the end of their journey he wrote that they found large numbers of large animals in the land between nations that were at war. Both the abundance of game in buffer or war zones and scarcity of big game in sinks have been misinterpreted as a natural or typical condition. Although efforts to restore ecosystems to what is described in early journals may have merit, they are aimed at a flickering target. Long before these journals were written, the land had been stripped of most of its native megafauna through human influence. In the absence of humans, we predict that much larger populations of bison, elk, deer, and wolves would have ranged the West than were reported in historic documents.
The Gaps between Theory and Practice in Selecting Nature Reserves
Authors: Prendergast John R. , Quinn Rachel M. , Lawton John H.
Published: March 2003

Abstract:Over the last three decades a great deal of research, money, and effort have been put into the development of theory and techniques designed to make conservation more efficient. Much of the recent emphasis has been on methods to identify areas of high conservation interest and to design efficient networks of nature reserves. Reserve selection algorithms, gap analysis, and other computerized approaches have much potential to transform conservation planning, yet these methods are used only infrequently by those charged with managing landscapes. We briefly describe different approaches to identifying potentially valuable areas and methods for reserve selection and then discuss the reasons they remain largely unused by conservationists and land‐use planners. Our informal discussions with ecologists, conservationists, and land managers from Europe and the United States suggested that the main reason for the low level of adoption of these sophisticated tools is simply that land managers have been unaware of them. Where this has not been the case, low levels of funding, lack of understanding about the purpose of these tools, and general antipathy toward what is seen as a prescriptive approach to conservation all play a part. We recognize there is no simple solution but call for a closer dialogue between theoreticians and practitioners in conservation biology. The two communities might be brought into closer contact in numerous ways, including carefully targeted publication of research and Internet communication. However it is done, we feel that the needs of land managers need to be catered to by those engaged in conservation research and that managers need to be more aware of what science can contribute to practical conservation.
Effects of Introduced Mosquitofish and Bullfrogs on the Threatened California Red‐Legged Frog
Authors: Lawler Sharon P. , Dritz Deborah , Strange Terry , Holyoak Marcel
Published: March 2003

Abstract:
Exotic species have frequently caused declines of native fauna and may contribute to some cases of amphibian decline. Introductions of mosquitofish ( Gambusia affinis) and bullfrogs ( Rana catesbeiana) are suspected to have caused the decline of California red‐legged frogs ( Rana aurora draytonii). We tested the effects of mosquitofish and bullfrog tadpoles on red‐legged frog tadpoles in spatially complex, speciose communities. We added 720 hatchling red‐legged frog tadpoles to each of 12 earthen ponds. Three ponds were controls, 3 were stocked with 50 bullfrog tadpoles, 3 with 8 adult mosquitofish, and 3 with 50 bullfrogs plus 8 mosquitofish. We performed tests in aquaria to determine whether red‐legged frog tadpoles are preferred prey of mosquitofish. Mosquitofish fed on a mixture of equal numbers of tadpoles and either mosquitoes, Daphnia, or corixids until < 50% of prey were eaten; then we calculated whether there was disproportionate predation on tadpoles. We also recorded the activity of tadpoles in the presence and absence of mosquitofish to test whether mosquitofish interfere with tadpole foraging. Survival of red‐legged frogs in the presence of bullfrog tadpoles was less than 5%; survival was 34% in control ponds. Mosquitofish did not affect red‐legged frog survival, even though fish became abundant (approximately 1011 per pond). Two mechanisms may have blocked the effects of mosquitofish on tadpole survival: (1) fish ponds contained fewer predatory invertebrates, and (2) mosquitofish preferred other prey to red‐legged frogs in laboratory trials. Red‐legged frog tadpoles suffered more injuries in ponds with fish, however, and weighed 34% less at metamorphosis. The growth decrease could have been caused by injuries or by lower foraging levels in the presence of fish. Laboratory results showed that young tadpoles were less active in the presence of mosquitofish. Although both mosquitofish and bullfrogs affected red‐legged frogs, the impact of bullfrogs on the survival of red‐legged frogs may contribute more strongly to their decline.
Evaluation of the Contribution of Genetic Research to the Management of the Endangered PlantZieria prostrata
Authors: Hogbin Patricia M. , Peakall Rod
Published: March 2003

Abstract:Zieria prostrata(Rutaceae) is known from only four headlands within a 3‐km stretch of coastline in New South Wales, Australia. The species was presumed to have occurred at a headland 24 km south of its present range. We used random amplified polymorphic DNA analysis to assess patterns of genetic variation within and among the extant populations. The analysis also included an individual reputedly rescued from the now extinct population. A high level of population divergence was revealed by principal coordinate analysis and an analysis of molecular variance (AMOVA; 37% among populations). Our genetic findings provide implications for the conservation management of the species. First, the loss of any one population would lead to a severe loss of genetic variation. Second, an adequate ex situ collection must sample the full range of genetic diversity from all populations. Third, the consequences of mixing populations may be an important conservation consideration if further translocations proceed. Fourth, the individual apparently sampled prior to its population extinction is genetically similar to individuals from one of the extant sites. This degree of similarity was unexpected and, after further investigation, led to the conclusion that prior existence of the species at the site is doubtful. Subsequently, a planned reintroduction program was abandoned. So far, of these four management implications, only the last has had a direct management outcome. Those implications that failed to lead to practical management outcomes did so because the same management recommendations could be obtained without genetic research. Clearly, the challenge for more effective conservation is to identify those cases in which genetic studies are likely to produce practical outcomes for conservation managers. This may be best achieved by assessing the outcomes of genetic studies already conducted.
Community Conservation and the Future of Africa's Wildlife
Authors: Hackel Jeffrey D.
Published: March 2003

Abstract: The term community‐based conservation (CBC) refers to wildlife conservation efforts that involve rural people as an integral part of a wildlife conservation policy. The key elements of such programs are that local communities participate in resource planning and management and that they gain economically from wildlife utilization. In part, CBC is seen as an alternative to the more exclusionary protectionist policies of the past, which often alienated rural people from conservation efforts. The new approach acts to make rural people a constituency for wildlife and therefore active backers of wildlife protection. Africans, however, are struggling with severe social and economic problems such as poverty, long‐standing economic stagnation, rapid population growth, and environmental deterioration. Because of the pressures that Africans face in making a living, the application of CBC may not occur as readily or as successfully as its advocates would hope. It may also be that the approach is being oversold. I use brief case studies from Madagascar, Ethiopia, Zimbabwe, and Swaziland to highlight the possible conflicts between rural people's economic needs and the implementation of community conservation. In addition, the CBC literature treats the role of protection vaguely, as it does the question of what might happen if CBC fails to achieve wildlife conservation goals. Community‐based conservation is an obvious advance over past practices because of its inclusive philosophy, but if rural people accept CBC because of its economic benefits, they may reject it at some point in the future if a better economic alternative is presented. Thus, CBC programs can work to produce a better relationship between wildlife and people, but only a vast improvement in the lives of rural Africans will ultimately produce a more secure future for the continent's wildlife.
Bird Communities and Habitat as Ecological Indicators of Forest Condition in Regional Monitoring
Authors: Canterbury Grant E. , Martin Thomas E. , Petit Daniel R. , Petit Lisa J. , Bradford David F.
Published: March 2003

Abstract:Ecological indicators for long‐term monitoring programs are needed to detect and assess changing environmental conditions. We developed and tested community‐level environmental indicators for monitoring forest bird populations and associated habitat. We surveyed 197 sampling plots in loblolly–shortleaf pine forests, spanning an area from Georgia to Virginia ( U.S.A.) and representing a gradient in levels of anthropogenic disturbance. Ninety of these plots were randomly selected from a sampling grid, permitting quantitative assessment of cumulative distribution functions for bird community and habitat parameters. Species were independently classified into habitat assemblages indicating birds typical of disturbed habitat (e.g., shrubland, forest edge) and undisturbed habitat (mature forest). Relative abundances of these assemblages were used to form a bird community index—similar to the index of biotic integrity applied to aquatic systems—showing the effects of habitat disturbance on forest bird communities. Bird communities on the majority of the sample area (52–75%, 90% confidence interval) were dominated by disturbance‐tolerant species. Sites dominated by mature‐forest species were comparatively uncommon. Habitat assemblages appeared to be particularly useful tools for environmental monitoring; individual species abundance was positively correlated with assemblage species richness, and assemblage members showed consistent responses to variations in disturbance level. To a lesser extent, component species of nesting guilds showed this pattern of cohesive responses, but those of foraging guilds did not. We also developed a habitat index based on habitat variables that predicted bird community index values. Habitat and bird community indices were strongly correlated in an independent validation dataset, suggesting that the habitat index can provide a reliable predictor of bird community status. The two indices may be used in combination, with the bird community index providing a direct measure of the status of the bird community and the habitat index providing a basis on which to separate changes in the bird community into local habitat effects versus other factors (e.g., landscape level effects, changes on wintering grounds).
Coral Bleaching and Global Climate Change: Scientific Findings and Policy Recommendations
Authors: Reaser Jamie K. , Pomerance Rafe , Thomas Peter O.
Published: March 2003

Abstract: In 1998, tropical sea surface temperatures were the highest on record, topping off a 50‐year trend for some tropical oceans. In the same year, coral reefs around the world suffered the most extensive and severe bleaching ( loss of symbiotic algae) and subsequent mortality on record. These events may not be attributable to local stressors or natural variability alone but were likely induced by an underlying global phenomenon. It is probable that anthropogenic global warming has contributed to the extensive coral bleaching that has occurred simultaneously throughout the reef regions of the world. The geographic extent, increasing frequency, and regional severity of mass bleaching events are an apparent result of a steadily rising baseline of marine temperatures, combined with regionally specific El Niño and La Niña events. The repercussions of the 1998 mass bleaching and mortality events will be far‐reaching. Human populations dependent on reef services face losses of marine biodiversity, fisheries, and shoreline protection. Coral bleaching events may become more frequent and severe as the climate continues to warm, exposing coral reefs to an increasingly hostile environment. This global threat to corals compounds the effects of more localized anthropogenic factors that already place reefs at risk. Significant attention needs to be given to the monitoring of coral reef ecosystems, research on the projected and realized effects of global climate change, and measures to curtail greenhouse gas emissions. Even those reefs with well‐enforced legal protection as marine sanctuaries, or those managed for sustainable use, are threatened by global climate change.
Protected Area Planning in the Tropics: Uganda's National System of Forest Nature Reserves
Authors: Howard P. C. , Davenport T. R. B. , Kigenyi F. W. , Viskanic P. , Baltzer M. C. , Dickinson C. J. , Lwanga J. , Matthews R. A. , Mupada E.
Published: March 2003

Abstract:Uganda is one of the most biologically diverse countries in Africa, with much of its biodiversity represented in a system of 10 national parks, 10 wildlife reserves, and 710 forest reserves, covering 33,000 km2(14%) of the country's area. We focus on the role of the forest reserves in biodiversity conservation and describe a procedure we developed to design a national system of forest nature reserves. In the late 1980s a policy was instituted to dedicate half the area of forest reserves to sustainable timber production and the other half to environmental protection (with 20% as nature reserves). To select suitable sites, a 5‐year, US$1‐million program of biodiversity and resource assessment was undertaken, focusing on five biological indicator species groups and covering all the major forest reserves. Based on data generated by the field studies, we ranked each forest in terms of various criteria—(species richness, rarity, value for nonconsumptive uses, timber production, and importance to local communities)—and used an iterative site selection procedure to choose the most suitable combination of forests for nature reserve establishment. Our procedure maximized complementarity in representing species and habitats in reserves across the whole protected‐area system. We initially selected sites using purely biological criteria but later modified our procedure to ensure that opportunity costs and potential land‐use conflicts were minimized. Our preferred network of sites included 14 forests that, in combination with the existing national parks, would account for 96% of species represented in the country's protected areas. These 14 forests were classified as “prime” and “core” sites and were selected for the establishment of large nature reserves (averaging 100 km2). The addition of 25 smaller “secondary” forest nature reserves (averaging 32 km2) would protect more than 99% of the indicator species.
The Magnitude of Local Host Specif icity for Phytophagous Insects and its Implications for Estimates of Global Species Richness
Authors: Ødegaard Frode , Diserud Ola H. , Engen Steinar , Aagaard Kaare
Published: March 2003

Abstract: Estimates of the global number of arthropod species range from 2 million to more than 30 million species. One of the most critical assumptions affecting the higher of these estimates is the assumed magnitude of host specificity of phytophagous insects, which varies considerably. Difficulties in estimating this value are caused by both lack of satisfactory data sets and lack of methods for its objective calculation. We provide a new method for predicting host specificity for phytophagous insects at a local scale based on the concept of effective specialization. When the insect‐plant host associations of a restricted number of plant species are known, we can predict the magnitude of host specificity when more plant species are included. Based on 2561 host observations of 697 beetle species on 50 plant species in the canopies of a tropical dry forest in Panama, we predict that host specificity for adult phytophagous beetles in this forest range from 7% to 10%. These values suggest that the higher estimates of global species richness are not tenable.
Evaluating Dispersal Estimates Using mtDNA Data: Comparing Analytical and Simulation Approaches
Authors: Taylor Barbara L. , Chivers Susan J. , Sexton Stephanie , Dizon Andrew E.
Published: March 2003

Abstract: Using genetic data to estimate dispersal is attractive because direct estimation is often infeasible. Unfortunately, analytical tools remain rudimentary. Various standard population genetic formulae estimate dispersal rates between populations but require unrealistic assumptions, such as equal population size. Recent increases in computer speed enable simulations of genetic processes in populations. We designed simulation models to evaluate the adequacy of using analytical formulae to estimate dispersal rates needed for conservation decisions. Our models incorporated genetic stochasticity. They adhered closely to the assumptions of the standard formulae except that we relaxed the assumption that all populations were equal in size. We found that measures of population differentiation, such as the statistic ΦS T  , varied greatly over time, reflecting the stochastic nature of genetic systems. In some cases, however, even large amounts of variation over time made no difference in defining population structure for management purposes, whereas in other cases the opposite was true. Statistics of genetic differentiation were so variable that management decisions based on analytical formulae would often be incorrect. Adjoining populations with little dispersal between them that should be managed separately were by chance alone so genetically similar that they appear panmictic, incorrectly implying that they should be managed as a single unit. The form of distributions of these statistics was complex and did not conform to standard statistical distributions. Furthermore, differences between these distributions for equal and unequal abundance cases indicated that pursuits of simple adjustments to analytical formulae are unlikely to be fruitful. In contrast, our simulation technique can be used in a decision analysis framework because it incorporates uncertainties into a probability distribution. We conclude with a case in which a manager wants to know whether current human‐caused mortality levels can be sustained while maintaining the local population at healthy levels. The example demonstrates how decision analysis for population structure can use the probability distributions generated from simulations to incorporate uncertainty and estimate over‐ and underprotection errors.
Factors Influencing Movement Patterns of Keel‐Billed Toucans in a Fragmented Tropical Landscape in Southern Mexico
Authors: Graham Catherine H.
Published: March 2003

Abstract:Various factors influence animal movements in fragmented landscapes, and determining these factors is key to understanding ecological processes at a landscape scale. My goals were (1) to determine what factors influence movements of Keel‐billed Toucans (   Ramphastos sulfuratus ) in a fragmented landscape in southern Mexico and (2) to use this information to predict how movement patterns might change if the landscape was altered. I developed a cost‐distance geographic information system model that adjusts Euclidean distances by a cost of moving through a certain habitat type. Cost was based on habitat preferences exhibited by toucans. I then used this model to predict how movements might be affected by removal of isolated trees and living fences from the pasture matrix and by removal of forest remnants. Toucans moved more frequently between remnants separated by a low cost‐distance value. There was a cost‐distance threshold beyond which movements between remnants were rare. Below this threshold, fruit abundance influenced toucan movements but remnant area was not influential in that toucans did not preferentially move to large patches. Remnants close to various other remnants were more frequently visited by toucans, indicating that landscape connectivity influences toucan movements. Toucans incurred a 10–30% cost increase when moving in computer‐simulated landscapes, indicating that changes in forest cover or configuration of habitats may negatively affect toucan populations, assuming that increased cost has a fitness consequence. Cost‐distance modeling has been relatively unexplored and may be a valuable tool for determining how the configuration of a landscape impedes or facilitates animal movements.
Centaurea Species: the Forb That Won the West
Authors: Lejeune Katherine D. , Seastedt Timothy R.
Published: March 2003

Abstract: Grasslands of the western United States and Canada are being converted to ecosystems that resemble “old fields,” dominated in terms of percent cover or biomass by forb species. In particular, five species of the genus Centaurea (star thistle, diffuse, spotted, squarrose, and Russian knapweed ) have invaded millions of hectares of western United States and Canadian grasslands. Centaurea species are fundamentally different from the preexisting dominant species and may exploit changes in resource availability to become established. We suspect that they then maintain dominance by preventing resources from returning to levels that favor the native species. Increased atmospheric nitrogen deposition, reduced fire frequency, and, possibly, direct and indirect fertilization resulting from cattle grazing appear to have reduced the historically strong nitrogen limitation to which native species of western grasslands are adapted. We suggest that the success of Centaurea species in dominating grasslands is explained by their ability to compete successfully for the new limiting resource or resources. Our preliminary evidence suggests that phosphorus limitation or a colimitation of phosphorus and water best explains the current dominance patterns.
Evaluation of Museum Collection Data for Use in Biodiversity Assessment
Authors: Ponder W. F. , Carter G. A. , Flemons P. , Chapman R. R.
Published: March 2003

Abstract:Natural‐history collections in museums contain data critical to decisions in biodiversity conservation. Collectively, these specimen‐based data describe the distributions of known taxa in time and space. As the most comprehensive, reliable source of knowledge for most described species, these records are potentially available to answer a wide range of conservation and research questions. Nevertheless, these data have shortcomings, notably geographic gaps, resulting mainly from the ad hoc nature of collecting effort. This problem has been frequently cited but rarely addressed in a systematic manner. We have developed a methodology to evaluate museum collection data, in particular the reliability of distributional data for narrow‐range taxa. We included only those taxa for which there were an appropriate number of records, expert verification of identifications, and acceptable locality accuracy. First, we compared the available data for the taxon of interest to the “background data,” comprised of records for those organisms likely to be captured by the same methods or by the same collectors as the taxon of interest. The “adequacy”of background sampling effort was assessed through calculation of statistics describing the separation, density, and clustering of points, and through generation of a sampling density contour surface. Geographical information systems (GIS) technology was then used to model predicted distributions of species based on abiotic (e.g., climatic and geological) data. The robustness of these predicted distributions can be tested iteratively or by bootstrapping. Together, these methods provide an objective means to assess the likelihood of the distributions obtained from museum collection records representing true distributions. Potentially, they could be used to evaluate any point data to be collated in species maps, biodiversity assessment, or similar applications requiring distributional information.
Application of Extinction and Conservation Theories for Forest Birds in Nicaragua
Authors: Gillespie Thomas W.
Published: March 2003

Abstract: An increasing number of empirical studies have been done on the effects of tropical forest fragmentation on avian communities, but few researchers have applied these theories to assess the vulnerability of birds in poorly researched countries such as Nicaragua. I used a logistic regression to determine which natural‐history characteristics were most important in predicting a list of threatened birds known to occur in Nicaragua. The best model included five macroecological variables ( body weight, habitat specificity, trophic group, forest preference, and biogeography within Nicaragua). I used this model to generate predicted probabilities of extinction for all forest birds in Nicaragua. The predicted probability of extinction from the best model ranked 63% of the extinction‐prone birds from La Selva, Costa Rica, and 59% of the extinction‐prone birds from Barro Colorado, Panama, in the first quartile of all forest birds recorded in Nicaragua. This method provides a first‐order approximation of which species deserve global and national priorities for conservation. The central and Atlantic regions of Nicaragua deserve high priority for conservation at a global scale, whereas the Atlantic region deserves the highest priority for conservation at a national scale. The Nicaraguan Ministry of Natural Resources and the Environment has done an adequate job of identifying areas for conservation based on the proportion of decreed nature reserves in each biogeographic region and the distribution of forest birds with a high predicted probability of extinction. Forest birds in central Nicaragua, however, may currently be the most vulnerable to local extinction because of low forest cover within decreed reserves.
Clearance and Fragmentation of Tropical Deciduous Forest in the Tierras Bajas, Santa Cruz, Bolivia
Authors: Steininger M. K. , Tucker C. J. , Ersts P. , Killeen T. J. , Villegas Z. , Hecht S. B.
Published: March 2003

Abstract: The Tierras Bajas is an area of 20,000 km 2 of lowland deciduous forest in eastern Santa Cruz, Bolivia, that has undergone rapid change during the past two decades. As part of the largest remaining area of intact deciduous tropical forest in the world, it has been nominated a priority area for conservation by several environmental organizations. We quantified the spatial and temporal patterns of deforestation in the area by digital processing of high‐resolution satellite imagery from 1975 through 1998. The estimated rate of deforestation was among the highest in the world for such a limited area, ranging from 160 km 2/year in the early1980s to almost 1200 km 2/year in the late 1990s. Although most deforestation up to 1984 was in Bolivian peasant and Mennonite colonies, most deforestation after 1984 was in non‐Mennonite industrial soybean farms. The level of fragmentation of uncut forest, caused by the spatial patterns of deforestation, also differed among these broad land‐use types. Deforestation in planned and spontaneous peasant colonies was complex in shape, forming relatively large areas of edge‐affected forest, whereas that in Mennonite and other industrial farms was in large, rectangular increments, creating relatively less edge. But the distribution of these farms and the practice of initially clearing around the peripheries of properties resulted in the isolation of large areas of forest. In 1998 four‐fifths of the remaining forest were either within 1 km of a clearance edge or in isolated fragments of <50 km2. Compared with deforested areas, the areas of isolated and edge‐affected forest were disproportionately large during the early stages of frontier colonization. These results imply that if the fragmentation effects of deforestation are to be minimized, conservation planning must occur at the earliest stages of frontier development.
Anthropogenic Disturbance and Patch Dynamics in Circumpolar Arctic Ecosystems
Authors: Forbes Bruce C. , Ebersole James J. , Strandberg Beate
Published: March 2003

Abstract:It has been 30 years since environmental concern was first expressed over the prospect of large‐scale resource development in the Arctic. Human effects are more extensive within the tundra biome now than at any time in the past. With or without predicted climatic changes, interaction among different natural and contemporary anthropogenic disturbance regimes are bound to have a significant effect on local and regional vegetation patterns and plant migration. We summarize the results of recent studies of patchy anthropogenic disturbance. We pay particular attention to the natural regeneration of plant communities, emphasize patch dynamics over the medium term (20–75 years), and discuss the data in the context of popular models of vegetation change following disturbance. Disturbance is important because it produces patches of partially or totally denuded ground that permit propagule establishment but may also open affected areas to erosion. Even relatively low‐intensity, small‐scale disturbances have immediate and persistent effects on arctic vegetation and soils. On all but the wettest sites, the patches support new, relatively stable vegetation states. Where slope is minimal, such disturbances are capable of expanding over large areas in as short a time as 4 years. The effects result in an artificial mosaic of patches of highly variable quality and quantity that comprise feeding and nesting habitats for terrestrial herbivores.
Species‐Richness Correlations of Six Different Taxa in Swedish Seminatural Grasslands
Authors: Vessby Karolina , Söderström Bo , Glimskär Anders , Svensson Birgitta
Published: March 2003

Abstract: An important question in conservation biology is whether the biodiversity of different taxa is correlated. We studied the extent to which the number of species of six different taxa—plants, birds, butterflies, bumblebees, ground beetles, and dung beetles—in 31 Swedish seminatural grasslands covary, and whether species diversity can be related to habitat variables. During 1996 and 1997, we surveyed plants and animals with appropriate techniques for each taxa and mapped the grassland habitat. In general, correlations between taxa were few. Grassland plant diversity (currently used as an indicator for conservation value) was only significantly positively correlated to total bird diversity. Bumblebee diversity was significantly positively related to both total and grassland butterflies, whereas there was a significant negative relationship between grassland birds and dung beetles. Plants, birds, bumblebees, and butterflies showed significant similarities in patterns of species composition, as did birds, butterflies, grassland butterflies, and ground beetles. The total number of plants and both subsets of birds (total and grassland) were significantly positively related to area, whereas there was a significant negative association between area and dung‐beetle diversity. The diversity of both butterflies and bumblebees was significantly negatively related to the proportion of short‐grazed field layer. Bumblebees showed a positive relationship with junipers, whereas ground beetles and grassland birds were negatively associated with trees. The total number of bird species was positively influenced by the occurrence of shrubs. Our results suggest that neither the species richness of grassland plants nor that of any other of the surveyed taxa can be used as an indicator for total biodiversity in seminatural grasslands. The lack of similar patterns of species composition among taxa also makes it difficult to define functional groups with similar habitat demands. Until we have more detailed knowledge of the demands of species and taxa, it is important that we direct management efforts so that we provide a wide spectrum of grassland characteristics.
Method for Selection of Old‐Forest Reserves
Authors: Siitonen Paula , Tanskanen Antti , Lehtinen Antti
Published: March 2003

Abstract:We used a multi‐objective greedy heuristic algorithm in a landscape area of 96,000 ha in northern Finland to select old‐forest stands that would best complement existing reserves in terms of achievement of conservation objectives while minimizing costs. Several quantitative nonspatial and spatial objectives for quality, proportion of area, and spatial distribution of old forests were specified in cooperation with foresters and conservation planners. The cost of each stand was calculated on the basis of the economic value of forest land. The algorithm calculated cost‐benefit ratios for the stands on the basis of how well each stand satisfied the objectives and at what cost. In every cycle, the algorithm selected the stand with the best cost‐benefit ratio. The algorithm included three spatial functions—continuous area, connectivity, and isolation—that were used to determine the spatial distribution of the stands. In addition, an option for preselection of stands (e.g., existing reserves) was included. A comparison between two solutions, one with and one without spatial objectives, showed that the network of selected old‐forest stands was less fragmented and more evenly distributed with use of the spatial objectives. The use of spatial objectives did not increase costs or the area needed, and the nonspatial objectives were met in both solutions. The nonspatial and spatial objectives are defined by the user, so the algorithm can be applied to other multi‐objective problems.