bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Habitat Fragmentation on the Reproductive Ecology of Four Plant Species in Mallee Woodland
Authors: Cunningham Saul A.
Published: March 2003

Abstract: Habitat fragmentation has the potential to affect plant reproduction by changing the community of pollinators and natural enemies, the neighborhood of potential mates, the availability of resources, and microclimate. I examined the effect of habitat fragmentation on reproduction of four species found in mallee woodlands of central New South Wales, Australia: Acacia brachybotrya, Senna artemisioides, Eremophila glabra, and Dianella revoluta. At six sites I surveyed plants in a reserve and in a nearby linear strip of vegetation. Two additional sites were established in a large reserve. Many effects were apparent at the extreme end of fragmentation, revealed by two‐way analysis of covariance comparing reserves and linear strips at each site. The nature of the response differed among species. Flower production was greater in most linear strip fragments for S. artemisioides and E. glabra. Fruit set efficiency was significantly greater in linear strips for S. artemisioides and significantly lower for A. brachybotrya, E. glabra, and D. revoluta. Fruit predation was lower in most linear strips for E. glabra. For A. brachybotrya, fruit predation was significantly lower in linear strips. The net effect of these changes was a significant increase in whole‐plant seed production for S. artemisioides, a significant decrease in whole‐plant seed production for A. brachybotrya and in whole‐plant fruit production for D. revoluta, and no consistent effect on whole‐plant fruit production for E. glabra. In contrast, the only pattern apparent when the effect of fragment size was considered over a range from linear strips <40 m wide to a reserve> 140,000 ha was a positive correlation between the fragment size and fruit‐set efficiency of A. brachybotrya. These results suggest that habitat fragmentation can significantly alter important reproductive functions of species, by changing both the plant's physical environment and its interactions with animals.
Holocene Climate in the Western Great Lakes National Parks and Lakeshores: Implications for Future Climate Change
Authors: Davis Margaret , Douglas Christine , Calcote Randy , Cole Kenneth L. , Winkler Marjorie Green , Flakne Robyn
Published: March 2003

Abstract: We reconstruct Holocene climate history (  last 10,000 years) for each of the U.S. National Park Service units in the western Great Lakes region in order to evaluate their sensitivity to global warming. Annual precipitation, annual temperature, and July and January temperatures were reconstructed by comparing fossil pollen in lake sediment with pollen in surface samples, assuming that ancient climates were similar to modern climate near analogous surface samples. In the early Holocene, most of the parks experienced colder winters, warmer summers, and lower precipitation than today. An exception is Voyageurs National Park in northern Minnesota where, by 8000 years ago, January temperatures were higher than today. The combination of high mean annual temperature and lower precipitation at Voyageurs resulted in a dry period between 8000 and 5000 years ago, similar to the Prairie Period in regions to the south and west. A mid‐Holocene warm‐dry period also occurred at other northern and central parks but was much less strongly developed. In southern parks there was no clear evidence of a mid‐Holocene warm‐dry period. These differences suggest that global model predictions of a warm, dry climate in the northern Great Plains under doubled atmospheric CO2 may be more applicable to Voyageurs than to the other parks. The contrast in reconstructed temperatures at Voyageurs and Isle Royale indicates that the ameliorating effect of the Great Lakes on temperatures has been in effect throughout the Holocene and presumably will continue in the future, thus reducing the potential for species loss caused by future temperature extremes. Increased numbers of mesic trees at all of the parks in the late Holocene reflect increasing annual precipitation. This trend toward more mesic conditions began 6000 years ago in the south and 4000 years ago in the north and increased sharply in recent millennia at parks located today in lake‐effect snow belts. This suggests that lake‐effect snowfall is sensitive to continental‐scale changes in climate and could be affected by future climate change. Plant and animal species sensitive to changes in the moisture regime could thus be endangered within the Great Lakes parks.
Rethinking Tropical Forest Conservation: Perils in Parks
Authors: Schwartzman Stephan , Moreira Adriana , Nepstad Daniel
Published: March 2003

Abstract: According to some conservationists, large, pristine, uninhabited parks are the defining criterion of success in conserving tropical forests. They argue that human residents in tropical forests inevitably deplete populations of large animals through hunting, which triggers a chain reaction of ecological events that greatly diminish the conservation value of these forests. Hence, they believe that removal of people from tropical forests is an essential step in the creation of successful parks and in the conservation of nature in the tropics. This approach can lead to undesirable consequences, however. Forest residents—and rural people generally—are potent political actors in tropical forest regions and an essential component of the environmental political constituencies that are necessary for the long‐term conservation of tropical forests. In Amazonia and elsewhere, rural people are defending far bigger areas of tropical forest from unfettered deforestation and logging than are parks, thereby conserving the ecological services provided by these forests and the majority of their component plant and animal species. Moreover, the data are too sparse to judge the effects of forest peoples on populations of large forest animals. The establishment of pristine, tropical forest parks is an important conservation goal, but the exclusive pursuit of this goal undermines the broader objectives of conservation when it identifies forest residents and other rural people as the enemies of nature.
Variation in Pesticide Tolerance of Tadpoles among and within Species of Ranidae and Patterns of Amphibian Decline
Authors: Bridges Christine M. , Semlitsch Raymond D.
Published: March 2003

Abstract: There is significant variation among and within amphibian species with respect to reports of population decline; declining species are often found in environments that are physiograpically similar to environments where the same species is thriving. Because variability exists among organisms in their sensitivity to environmental stressors, it is important to determine the degree of this variation when undertaking conservation efforts. We conducted both lethal (time‐to‐death) and sublethal (activity change) assays to determine the degree of variation in the sensitivity of tadpoles to a pesticide, carbaryl, at three hierarchical levels: among ranid species, among several populations of a single ranid species (  Rana sphenocephala), and within populations of R. sphenocephala. We observed significant variation in time to death among the nine ranid species and among the 10 R. sphenocephala populations we tested. Four out of eight R. sphenocephala populations exhibited significantly different times to death among families. The magnitude of the activity change in response to exposure to sublethal carbaryl levels was significantly different among species and within R. sphenocephala populations. Chemical contamination, at lethal or sublethal levels, can alter natural regulatory processes such as juvenile recruitment in amphibian populations and should be considered a contributing cause of declines in amphibian populations.
Demographic Forecasting in Koala Conservation
Authors: Penn Angela M. , Sherwin William B. , Gordon Greg , Lunney Daniel , Melzer Alistair , Lacy Robert C.
Published: March 2003

Abstract: The koala currently needs conservation intervention. There is clear evidence of decline in many populations, but the existence of other stable or expanding populations offers the possibility of a variety of creative solutions to their conservation problems. The 1998 National Koala Conservation Strategy emphasizes the need to obtain demographic information and to use this information to assess management options for koalas. We need accurate diagnoses of the status of koala populations and forecasts of their demographic future with and without particular management actions. In a qualitative fashion, this process has been undertaken many times on a local and national scale. Quantitative demographic forecasting tools are increasingly available, and koala management could benefit from their application both at the scale of individual populations and more broadly. There is already a considerable body of suitable data on the dispersal, effects of normal and catastrophic environmental variation on reproduction and survival, and on the effects of habitat change. Demographic forecasting, however, is hampered because the full suite of information is rarely available from a single population. In two Queensland populations, retrospective population viability analyses provided forecasts that were in agreement with observed population trends. Work is needed to determine whether data from one population can be applied to other populations. Models can then be developed to make projections at a multipopulation level on the basis of local population dynamics and dispersal. Certain koala populations, because of their long history of study, offer the opportunity to test demographic models retrospectively. These tests will not only aid in fine‐tuning the models for koala biology and data but will also assist with the more general process of validating the models.
Science, Ethical Arguments, and Management in the Preservation of Land for Grizzly Bear Conservation
Authors: Davradou Maria , Namkoong Gene
Published: March 2003

Abstract: Environmental groups advocate the preservation of an area within British Columbia's coastal temperate rainforest as a sanctuary for grizzly bears (   Ursus arctos horribilis). Debate among government, industry, and environmental spokespersons has provided arguments but no resolution. We have applied to this issue available biological knowledge on grizzly bears and the arguments of a range of ethical theories. The theories of three professionally trained ethicists were included: Tom Regan, Holmes Rolston III, and Arne Naess. Aldo Leopold's prominent position in the conservation movement justifies his “land ethic” as a fourth ethical theory. All four theories agree that the area should be preserved. Contrary to this fundamental agreement, the theories diverge when tested against a “hard” conservation scenario, the conflict between the protection of the last surviving grizzly bears versus the survival of a culturally distinct human tribe. Application of the principles developed by Regan and Naess recommend that human interests should override the preservation of grizzly bears, whereas Leopold's and Rolston's arguments favor the preservation of the area for the bears. Our work can be used as a model of how the gap between biological sciences, ethical theories, and ecosystem management can be bridged successfully.
Increased Herbivory in Forest Isolates: Implications for Plant Community Structure and Composition
Authors: Rao Madhu , Terborgh John , Nuñez Percy
Published: March 2003

Abstract: Understanding processes driving population declines and, ultimately, species loss in forest isolates has significant implications for the long‐term maintenance of species diversity. We investigated a potential mechanism driving loss of plant species in small, medium, and large land‐bridge islands in Lago Guri, a 4300‐km2 hydroelectric impoundment in the State of Bolivar, Venezuela. Our hypothesis was that elevated Atta ( leaf‐cutter ants) herbivory on small Guri islands, attributable to release from predation, could result in reduced sapling densities, with potentially negative effects on preferred plant species. We experimentally established Atta preferences among 43 common tree species. Vegetation plots on small, medium, and large land masses were examined for variation in density, size‐class distribution, and representation of preferred and less preferred species of small stems. Densities of adult trees of preferred and less preferred species were compared between Atta colony foraging zones and control plots without active Atta colonies, and between foraging zones on the small islands and the large island. Small stem densities were significantly reduced on the small islands, especially in the sapling category (≥1 m tall, <1 cm dbh). On medium and large land masses, preferred species were underrepresented in both sapling (≥1 m tall, <1 cm dbh) and juvenile (≥1 cm dbh, <10 cm dbh) size classes. On small islands, however, both preferred and less preferred species showed reduced representation in the sapling size class. Adults of preferred species were significantly reduced within Atta foraging zones compared with control plots without Atta colonies. Small stem densities were independent of adult tree densities for preferred species on small islands and for both preferred and less preferred species on large land masses. High levels of Atta herbivory could be a potentially important cause of reduced plant recruitment on small Guri islands. Our findings contribute to understanding of the role of altered ecological interactions as deterministic mechanisms driving a process of change in the structure and composition of fragmented communities.
Source‐Sink Dynamics of a Declining Eastern Kingbird Population and the Value of Sink Habitats
Authors: Murphy Michael T.
Published: March 2003

Abstract:I developed a demographic model for species inhabiting a mosaic of habitats of varying quality and among which dispersal was limited only by territorial behavior. I used the model to describe an ongoing decline of an Eastern Kingbird( Tyrannus tyrannus)population breeding in the Charlotte Valley of central New York and to explore the possibility that the population utilized a network of source‐sink habitats. Population size declined in upland and floodplain habitats between 1989 and 1999, but remained stable along a riparian zone (the “creek”). Population size after 10 years was predicted accurately when I used the empirically observed, habitat‐specific rates of adult survival, productivity, and adult dispersal among habitats, and assumed a 5% rate of immigration into the upland. Simulation of the effect of density‐dependent variation in reproductive success or a small increase in adult survival in all habitats failed to improve the model's predictive ability. The model indicated that none of the subpopulations was self‐sustaining over 50 years and that population decline was driven by declining adult survival. Further analyses, however, showed that small increases in adult survival along the creek changed the creek habitat into a source and reversed population trends. Simulation of realistic rates of habitat loss as a result of forest maturation did not affect predicted population size at 50 years, but, assuming that the area of pasture and grazed lands continues to decline at current rates, the kingbird population is predicted to become extinct locally within 40 years. Riparian zones appear to be source habitats for kingbirds and should be targeted for protection. Sink habitats were also important because in every year most of the kingbird population bred on the floodplain or in the upland and many floodplain birds later dispersed to the creek. Preservation of open space is thus critical for maintenance of kingbird populations in eastern North America.
Songbird and Medium‐Sized Mammal Communities Associated with Exurban Development in Pitkin County, Colorado
Authors: Odell Eric A. , Knight Richard L.
Published: March 2003

Abstract: Residential development is occurring at unprecedented rates in the Rocky Mountain region of the United States, with unknown ecological consequences. We conducted our research in exurban development in Pitkin County, Colorado, between May and June in 1998 and 1999. Unlike suburban development, exurban development occurs beyond incorporated city limits, and the surrounding matrix remains the original ecosystem type. We surveyed songbirds and medium‐sized mammals at 30, 180, and 330 m away from 40 homes into undeveloped land to examine the effect of houses along a distance gradient, and in developments of two different housing densities as well as undeveloped sites to examine the effect of housing density. We placed bird species into one of two groups for the house‐distance effect: (1) human‐adapted species, birds that occurred in higher densities close to developments and lower densities farther away and (2) human‐sensitive species, birds that occurred in highest densities farthest from homes and in lowest densities close to development. For both groups, densities of individual species were statistically different between the 30‐ and 180‐m sites. Six species were classified as human‐adapted, and six were classified as human‐sensitive for the house‐distance effect. Dogs (Canis familiaris) and house cats (   Felis domesticus) were detected more frequently closer to homes than farther away, and red foxes (   Vulpes vulpes) and coyotes (Canis latrans) were detected more frequently farther away from houses. With respect to the effect of housing density, most avian densities did not differ significantly between high‐ and low‐density development but were statistically different from undeveloped sites. Six species were present in higher densities in developed areas, and eight species were present in higher densities in undeveloped parcels. Similar results were found for mammalian species, with dogs and cats detected more frequently in high‐density developments and red foxes and coyotes detected more frequently in undeveloped parcels of land. From an ecological standpoint, it is preferable to cluster houses and leave the undeveloped areas in open space, as opposed to dispersing houses across the entire landscape.
Using Remote Sensing to Reassess the Mass Mortality of Diadema antillarum 1983–1984
Authors: Phinney Jonathan T. , Muller‐Karger Frank , Dustan Phil , Sobel Jack
Published: March 2003

Abstract: The 1983–1984 mass mortality of the sea urchin Diadema antillarum remains one of the most severe die‐offs ever recorded in the Caribbean. Before 1983, the herbivore D. antillarum was pervasive on coral reefs in the region. Nine months after first detection of the mass mortality, 95% of the urchins had perished, and algal cover of coral increased between 100% and 250%. A water‐borne pathogen was hypothesized as the causative agent, but it was never isolated. To date, surface current patterns have been used exclusively to explain both the cause and the distribution patterns of the mortality event. Using archived satellite images, we re‐examined the water‐borne pathogen hypothesis and investigated whether other mechanisms could also account for the dissemination pattern in some areas. In addition, archived satellite images were utilized to detect changes in coral reef reflectance. For infections in the Gulf of Mexico and Bermuda, satellite images confirm that surface currents are likely responsible for the distribution of the pathogen. For infections in the eastern Caribbean (Curacao, U.S. Virgin Islands, Barbados), however, another mechanism, possibly ballast water exchange, must be considered because the surface current and infection patterns do not coincide. Changes in coral reflectance were detectable from Landsat thermatic mapping data before and after the mass mortality and correspond to the change in algal cover. Results from our study demonstrate the potential of satellite images for use in determining connectivity between regions of the Caribbean and in detecting changes in coral reef cover.
Importance of Roadless Areas in Biodiversity Conservation in Forested Ecosystems: Case Study of the Klamath‐Siskiyou Ecoregion of the United States
Authors: Strittholt James R. , Dellasala Dominick A.
Published: March 2003

Abstract: Although many roadless areas on federal lands have been mapped in the United States since the 1970s, there has been little specific research on how and to what degree roadless areas contribute to biodiversity conservation. We examined the ecological attributes of mapped roadless areas for the Klamath‐Siskiyou ecoregion of northwestern California and southwestern Oregon (U.S.A.). Attributes examined include special elements (such as natural heritage, serpentine geology, late‐seral forests, Port Orford cedar [ Chamaecyparis lawsoniana ]), and key watersheds; elevation and habitat representation; and overall landscape connectivity. We compared designated wilderness to roadless areas, giving special attention to the relative importance of small roadless areas (405–2024 ha). We mapped nearly 500 roadless areas of ≥405 ha. Roadless areas occupied more than twice the land area of wilderness (approximately 27% of the entire ecoregion) and contained approximately 36% of the known occurrences of heritage elements, 37% of the mapped serpentine habitats, 36% of the remaining late‐seral forests, 60% of Port Orford cedar strongholds, and 42% of key watersheds for aquatic biodiversity. In addition, roadless areas were composed of significant amounts of low‐ and mid‐elevation sites and a substantial number of the 214 mapped physical‐biological habitat types with strong complementarity with designated wilderness. Fragmentation analyses showed that roadless areas contributed to regional connectivity in important ways. Also, small roadless areas were an important component of the roadless‐areas conservation assessment. For the Klamath‐Siskiyou ecoregion, roadless areas and designated wilderness provide an important foundation upon which to develop a comprehensive regional conservation strategy.
Status Review of the Protected‐Area System in Myanmar, with Recommendations for Conservation Planning
Authors: Rao Madhu , Rabinowitz Alan , Khaing Saw Tun
Published: March 2003

Abstract: Myanmar is among the most biologically diverse countries in mainland Southeast Asia. In contrast to its neighbors, large areas of Myanmar's forest cover remain intact, providing a unique opportunity to conserve biodiversity within protected areas. High levels of deforestation, unrestricted hunting, and destructive agricultural practices have resulted in significant wildlife declines and rapid loss of natural habitats. We analyzed the status of 20 of the 31 officially gazetted protected areas in Myanmar within a framework that classified activities incompatible with protected‐area status into two broad categories, small and large scale. Small‐scale incompatibilities driven by economic necessity and lack of alternatives for local populations within and adjacent to protected areas occurred more frequently than large‐scale incompatibilities driven by larger economic interests. Extraction of nontimber forest products was reported in 85% of the protected areas and ranked highest among the 15 identified incompatibilities. Grazing, hunting, fuelwood extraction, and permanent settlements occurred in more than 50% of the parks surveyed. Forty percent of the protected areas had some infrastructure for reserve management (with significant gaps) but insufficient on‐site personnel to adequately perform management activities. Thirty‐five percent had approximately half their staff trained in basic field techniques, and 60% had a planning document that was yet to be implemented. Older protected areas were affected by a greater number of incompatibilities than recently established protected areas. Major recommendations include the critical need to address the issue of hunting; involving local communities in the management of protected areas and buffer zones; building the technical capacity of protected‐area staff; implementing a comprehensive land‐use plan focused on stabilizing land use; and amending existing wildlife laws to fulfill international treaty obligations.
Effects of War and Civil Strife on Wildlife and Wildlife Habitats
Authors: Dudley Joseph P. , Ginsberg Joshua R. , Plumptre Andrew J. , Hart John A. , Campos Liliana C.
Published: March 2003

Abstract:Historically, the no‐man's land created by human warfare often protected wildlife and habitats by limiting human incursions and human population densities within disputed territories. Relatively few examples of this phenomenon have been identified in conjunction with recent and ongoing wars in developing countries, however. Modern wars and civil strife are typically associated with detrimental effects on wildlife and wildlife habitats. Most cited instances of contemporary war‐zone refuges refer to military security areas that are functionally and geographically distinct from actual battlefields or areas subject to armed civil conflicts. The disappearance of the war‐zone refuge effect is attributable to modern trends in the scale, intensity, or technologies associated with military conflicts and violent civil strife. Munitions and chemical agents exert both immediate and residual effects, direct and indirect, on wildlife and habitats. Overharvesting of wildlife and vegetation in conflict zones exacerbates existing constraints on the access to natural resources, threatening both the resource base and the livelihoods of local communities dependent on these resources. Socioeconomic studies have identified causative linkages between environmental degradation and violent civil strife, with the scarcity of natural resources fostering the emergence of war and civil conflicts in developing countries. Wars and civil strife create positive feedback that reinforces and amplifies interactions between and among ecosystem vulnerability, resource availability, and violent conflict. Strong and flexible partnerships between local communities, nongovernmental organizations, and international institutions may be a critical factor in mitigating the effects of war on wildlife by helping to maintain continuity in conservation efforts during periods of political instability.
Nest Predators and Fragmentation: a Review and Meta‐Analysis
Authors: Chalfoun Anna D. , Thompson Frank R. , Ratnaswamy Mary J.
Published: March 2003

Abstract:Population declines of many avian species are often attributed to increased rates of nest predation in fragmented landscapes, yet mechanisms underlying these effects have rarely been examined. We reviewed the literature to determine the extent to which hypotheses about nest predators and fragmentation have been invoked and compared this to the number of direct tests of predators with respect to habitat edge, patch size, or landscape type. We also conducted a meta‐analysis of tested predator effects to evaluate whether predator responses—numerical, functional, or species richness—to fragmentation depend on spatial scale (edge, patch, or landscape), landscape type, geographic region, or predator taxa. We found 120 papers containing hypotheses about nest predators and fragmentation, but only 31 with hypothesis tests. Most tests were of a single predator species or guild, whereas most cited hypotheses generalized across broader taxonomic groups. Results of predator tests were variable, but some general patterns were evident. Predator effects, including increased abundance, activity, or species richness in edges, small patches, or certain landscapes, were more prevalent (1) in tests conducted at the landscape scale than at the local scale, ( 2) in agricultural landscapes than in predominantly forested landscapes, (3) in certain biogeographic regions, and (4) for avian predators than for mammalian predators. Local‐scale (edge and patch) effects were most common when the land surrounding patches was agricultural and when tests were conducted within agricultural landscapes. The response of nest predators to fragmentation is complex, taxon‐specific, and context‐dependent. Conservation efforts for declining avian species may therefore need to be customized according to the nest‐predator species primarily responsible for local nest mortality and the nature of the landscape mosaic.
Adaptive Management in Habitat Conservation Plans
Authors: Wilhere George F.
Published: March 2003

Abstract: Habitat conservation plans ( HCPs) allow incidental take of threatened or endangered species in exchange for conservation measures that minimize and mitigate such taking. Habitat conservation plans entail a compromise between regulatory certainty and scientific uncertainty. This compromise is controversial because many HCPs are thought to inadequately address scientific uncertainty. Adaptive management is the systematic acquisition and application of reliable information to improve natural resource management over time. Ideally, under adaptive management, conservation strategies are implemented as a deliberate experiment. This approach can establish cause‐and‐effect relationships and point the way toward optimal strategies. Adaptive management has been promoted as essential to management under uncertainty, but few HCPs incorporate genuine adaptive management. Habitat conservation plans will continue to lack adaptive management until certain conditions are met, such as acknowledgment that an HCP is a management hypothesis, landowner interest in improving biological outcomes, and sufficient financial resources. Economic incentives would encourage adaptive management in HCPs. Habitat conservation plan permittees might receive direct payments or tax deductions for reliable information that benefits a species. “Mitigation credits” could be awarded for information produced through adaptive management. In effect, habitat would be exchanged for information that benefits a species. Successful use of mitigation credits would depend on correctly valuing information and enforcement of the U.S. Endangered Species Act. Under a “precautionary polluter pays principle,” an HCP permittee would put up an environmental assurance bond. Portions of the bond are returned with interest as adaptive management demonstrates that environmental damages are unlikely to occur. Funds spent on adaptive management are funds unavailable for habitat protection, so limited financial resources may force a compromise between protecting habitat and acquiring knowledge.
Predicting Extinction Vulnerability in Skates
Authors: Dulvy Nicholas K. , Reynolds John D.
Published: March 2003

Abstract:Relatively few marine fishes have been assessed under World Conservation Union criteria, yet it is believed that marine fish extinction rates have been underestimated by one order of magnitude (McKinney 1999). Given the paucity of data required for traditional assessment methods, we explored the use of potential correlates of extinction vulnerability to prioritize species for conservation assessment. We focused on the world's 230 species of skates and rays (Rajidae) because they have been identified as one of the most vulnerable groups of marine fishes. We searched for all documented cases of local extinction and compiled a database of body size and latitudinal and depth ranges for all species for which data were available. We found that species that have disappeared from substantial parts of their ranges ( “locally extinct” ) have large body sizes compared with all other skates, but that latitudinal and depth ranges were similar to those of other species. The body size correlate may be due to higher mortality rates and correlations with life‐history parameters such as late age at maturity. We used the locally extinct species that had the smallest size or ranges as benchmarks to generate lists of other species that may be vulnerable. Body size generated the smallest species list (7), excluding the known local extinctions, compared with lists generated by size of latitudinal (150) or depth range (63). Body size was the only trait that correctly identified the known local extinctions, suggesting that it is more useful than range sizes for identifying potentially vulnerable fishes. This provides a simple, objective method of prioritizing species for further assessment, which complements direct methods that are more data‐intensive and time‐consuming.
What Is Missing in Amphibian Decline Research: Insights from Ecological Sensitivity Analysis
Authors: Biek Roman , Funk W. Chris , Maxell Bryce A. , Mills L. Scott
Published: March 2003

Abstract: Inventory, monitoring, and experimental studies have been the primary approaches for documenting and understanding the problem of amphibian declines. However, little attention has been given to placing human‐caused perturbations affecting one or more life‐history stages in the context of the overall population dynamics of particular species. We used two types of ecological sensitivity analysis to determine which vital rates have the strongest influence on the population dynamics of western toads (   Bufo boreas), red‐legged frogs (  Rana aurora), and common frogs (  Rana temporaria), pond‐breeding amphibians that have declined in all or portions of their ranges. Our results suggest that post‐metamorphic vital rates and highly variable vital rates both have a strong influence on the population dynamics of these species and therefore deserve more research and management attention. Ecological sensitivity analysis should be more widely applied to the issue of amphibian declines in order to identify the most plausible mechanisms of decline and prioritize which life‐history stages should be the focus of research and management efforts. Future experimental studies of perturbations in one or more life‐history stage should attempt to link the magnitude of the perturbation measured with the overall population‐level consequences. Finally, current research, inventory, and monitoring efforts should be supplemented with demographic studies so that quantitative analyses can be applied to a wider range of species and life‐history groups.
Philopatry and Homing Behavior of Sea Snakes (Laticauda colubrina) from Two Adjacent Islands in Fiji
Authors: Shetty Sohan , Shine Richard
Published: March 2003

Abstract: The spatial scale at which anthropogenic disturbance affects an animal population depends on the degree of philopatry and homing of individual organisms within that population. Even in highly vagile species, local populations may comprise ecologically separate entities if most animals display strong and consistent site attachment. We conducted a mark‐recapture study on yellow‐lipped sea kraits (  Laticauda colubrina) on two small Fijian islands separated by 5.3 km. These snakes forage over many kilometers in the ocean, but return to land to reproduce, slough, and digest their food. Recovery of marked snakes showed that the populations on these two islands were essentially separate. Relocated snakes returned “home” almost immediately after they were released. Growth rates and mean adult body sizes of male sea snakes also differed between the two islands. This high site fidelity means that activities such as resort development or commercial harvesting for the skin trade are likely to have intense localized effects rather than diffuse broad‐scale effects on sea snake populations. Our results also call into question the feasibility of plans to reintroduce snake populations to areas where a species has been eliminated by overexploitation.
An Experimental Investigation of Landscape Resistance of Forest versus Old‐Field Habitats to Emigrating Juvenile Amphibians
Authors: Rothermel Betsie B. , Semlitsch Raymond D.
Published: March 2003

Abstract: We used an experimental approach to investigate the effects of landscape composition on the initial dispersal success of juvenile amphibians. Larval amphibians—spotted salamander (Ambystoma maculatum), small‐mouthed salamander (A. texanum), and American toad (  Bufo americanus )—were added to artificial pools in four dispersal arrays on forest edges. Each array consisted of a pool surrounded by a circular drift fence with pitfall traps and two 2.5 × 50 m enclosures (runs) extending into forest and old‐field habitat. Juveniles captured at the circular fences were individually marked and released into either field or forest runs. We determined initial distance, initial rate, total distance, and net distance moved by juveniles in the field versus forest from recaptures in the runs. We also conducted 24‐hour dehydration trials to compare the rates of evaporative water loss by spotted and small‐mouthed salamanders in field and forest. Initial orientation of spotted salamanders and toads was significantly biased toward forest. Orientation of small‐mouthed salamanders did not differ significantly from random expectations. The avoidance of open‐canopy habitat by juvenile American toads in particular indicates that predictions of dispersal behavior based on adult habitat use may be misleading. Spotted salamanders moved almost four times farther and toads more than three times farther into the forest than into the field, and recapture rates of both species were much lower in the field. We attribute the lower recapture rates and shorter distances moved in the field to higher mortality due to desiccation or an abundance of predators. Juvenile spotted and small‐mouthed salamanders experienced greater evaporative water loss in the field. Our data on movement behavior and dehydration rates suggest that old‐field habitats offer greater landscape resistance to dispersing juveniles of some species. Thus, forest fragmentation is likely to reduce dispersal rates between local populations of these three species, with potentially negative consequences for population persistence in altered landscapes.
Grazing Intensity and the Diversity of Grasshoppers, Butterflies, and Trap‐Nesting Bees and Wasps
Authors: Kruess Andreas , Tscharntke Teja
Published: March 2003

Abstract: The maintenance of grasslands as distinct habitats depends on regular management, usually through grazing or mowing, but their species diversity is known to decline with increasing management intensity. The reduction of management intensity can be a useful tool for the long‐term conservation of the biological diversity of grasslands. We analyzed floral and faunal diversity on intensively and extensively (unintensively) grazed pastures and on 5‐ to 10‐year‐old ungrazed grasslands in northern Germany. Each of the three grassland habitats differing in grazing intensity was replicated six times. We related diverse taxa such as grasshoppers, butterfly adults and lepidopteran larvae, and trap‐nesting solitary bees and wasps to vegetation structure. There was an increase of species richness and abundance from pastures to ungrazed grasslands. The percentage of parasitism of the most abundant trap‐nesting species, the digger‐wasp (   Trypoxylon figulus), was also higher on ungrazed grasslands. Decreased grazing on pastures enhanced species richness for adult butterflies only, whereas the abundance of adult butterflies, solitary bees and wasps, and their natural enemies increased. Although the differences in insect diversity between pastures and ungrazed grassland could be attributed to a greater vegetation height and heterogeneity ( bottom‐up effects) on ungrazed areas, the differences between intensively and extensively grazed pastures could not be explained by changes in vegetation characteristics. Hence, intensive grazing appeared to affect the insect communities through the disruption of plant‐insect interactions. A mosaic of extensively grazed grassland and grassland left ungrazed for a few years may be a good means by which to maintain biodiversity and the strength of trophic interactions.
A Multicriteria Assessment of the Irreplaceability and Vulnerability of Sites in the Greater Yellowstone Ecosystem
Authors: Noss Reed F. , Carroll Carlos , Vance‐Borland Ken , Wuerthner George
Published: March 2003

Abstract: We conducted a systematic conservation assessment of the 10.8‐million‐ha Greater Yellowstone Ecosystem (GYE), integrating three basic approaches to conservation planning: protecting special elements, representing environmental variation, and securing habitat for focal species (grizzly bear [   Ursus arctos], wolf [Canis lupus], and wolverine [Gulo gulo]). Existing protected areas encompass 27% of the GYE but fail to capture many biological hotspots of the region or to represent all natural communities. Using a simulated annealing site‐selection algorithm, combined with biological and environmental data based on a geographic information system and static ( habitat suitability) and dynamic (  population viability) modeling of focal species, we identified unprotected sites within the GYE that are biologically irreplaceable and vulnerable to degradation. Irreplaceability scores were assigned to 43 megasites (aggregations of planning units) on the basis of nine criteria corresponding to quantitative conservation goals. Expert opinion supplemented quantitative data in determining vulnerability scores. If all megasites were protected, the reserved area of the GYE would expand by 43% (to 70%) and increase protection of known occurrences of highly imperiled species by 71% (to 100%) and of all special elements by 62% (to 92%). These new reserves would also significantly increase representation of environmental variation and capture critical areas for focal species. The greatest gains would be achieved by protecting megasites scoring highest in irreplaceability and vulnerability. Protection of 15 high‐priority megasites would expand reserved area by 22% and increase the overall achievement of goals by 30%. Protection of highly imperiled species and representation of geoclimatic classes would increase by 46% and 49%, respectively. Although conservation action must be somewhat opportunistic, our method aids decision‐making by identifying areas that will contribute the most to explicit conservation goals.
Fire and Vegetation in a Temperate Peat Bog: Implications for the Management of Threatened Species
Authors: Norton David A. , De Lange Peter J.
Published: March 2003

Abstract: Fire plays an important role in structuring wetland ecosystems, but previous studies of New Zealand wetlands have lacked adequate experimental controls. We investigated the effects of fire on the vegetation of a New Zealand peat bog through analysis of microclimate patterns, vegetation change, and peat stratigraphy. We focused on the role of fire in sustaining threatened plant species such as the critically endangered orchid Corybas carsei. Experimental fire significantly increased the surface radiation and daytime soil temperature, and these elevated levels of radiation and temperature persisted 53 months after burning. Immediately after fire no living plant material remained in the burn plots, but within 2 months many of the rhizomatous species were resprouting and 50 months later had returned to prefire abundance. Obligate‐seeding species did not recover their former abundance, but several species not observed in the plots prior to the burns established after fire. Species richness, diversity, and evenness increased following fire but declined in the control plots. Species dominance decreased after fire but increased in the control plots. C. carsei, which was killed during the fire, reappeared in the burn plots 1 year later at a higher density than prior to burning and was still present 4 years after fire. C. carsei flowering was also enhanced following the fire. We found evidence of historical fires, which was supported by radiocarbon dates from a much older adjacent wetland. Our results suggest that disturbances such as fire are important for maintaining a diversity of plant communities, including the presence of nationally threatened and declining plant species in peat bogs. Without such disturbances species such as C. carsei are likely to become locally extinct.
Effects of Local Habitat Characteristics and Landscape Context on Grassland Butterfly Diversity
Authors: Collinge Sharon K. , Prudic Kathleen L. , Oliver Jeffrey C.
Published: March 2003

Abstract: Recent ecological studies suggest that the landscape context of native habitat remnants may significantly influence plant and animal abundance and distribution within those remnants. Other research has revealed a weak link between landscape context and native community composition. To understand the relative importance of local and regional habitat characteristics for grassland butterflies, we assessed butterfly community diversity in four types of grassland habitats surrounded by varying amounts of urban development near Boulder, Colorado ( U.S.A.). We recorded butterfly species abundance and composition in 66 grassland study plots on five sampling dates in 1999 and 2000. Grasslands were of four types: native shortgrass, native mixed grass, native tallgrass, and planted hayfields. Grasslands also varied in quality, determined by the abundance of native versus exotic plant species. We observed highly significant effects of grassland type on butterfly species richness and composition. For example, tallgrass plots supported significantly higher butterfly species richness than shortgrass plots ( p < 0.01). Habitat quality also affected butterfly species richness and composition. Low‐quality plots generally supported fewer species than moderate‐ or high‐quality plots (  p < 0.05). Landscape context—the percentage of urbanization in the surrounding landscape—did not significantly predict butterfly species richness or composition. Our observations suggest that for the grassland butterfly communities in our study, (1) grassland type was the primary determinant of species richness and composition, (2) habitat quality secondarily affected butterfly community diversity, and (3) landscape context did not significantly predict butterfly species composition. Our findings emphasize the importance of maintaining high‐quality grassland habitat to protect native butterfly diversity.
Effectiveness of Conservation Targets in Capturing Genetic Diversity
Authors: Neel Maile C. , Cummings Michael P.
Published: March 2003

Abstract:Any conservation actions that preserve some populations and not others will have genetic consequences. We used empirical data from four rare plant taxa to assess these consequences in terms of how well allele numbers ( all alleles and alleles occurring at a frequency openface>0.05 in any population ) and expected heterozygosity are represented when different numbers of populations are conserved. We determined sampling distributions for these three measures of genetic diversity using Monte Carlo methods. We assessed the proportion of alleles included in the number of populations considered adequate for conservation, needed to capture all alleles, and needed to meet an accepted standard of genetic‐diversity conservation of having a 90–95% probability of including all common alleles. We also assessed the number of populations necessary to obtain values of heterozygosity within ±10% of the value obtained from all populations. Numbers of alleles were strongly affected by the number of populations sampled. Heterozygosity was only slightly less sensitive to numbers of populations than were alleles. On average, currently advocated conservation intensities represented 67–83% of all alleles and 85–93% of common alleles. The smallest number of populations to include all alleles ranged from 6 to 17 ( 42–57% ), but <0.2% of 1000 samples of these numbers of populations included them all. It was necessary to conserve 16–29 ( 53–93% ) of the sampled populations to meet the standard for common alleles. Between 20% and 64% of populations were needed to reliably represent species‐level heterozygosity. Thus, higher percentages of populations are needed than are currently considered adequate to conserve genetic diversity if populations are selected without genetic data.