bluuebunny/crossref_metadata_2025 huggingface dataset:
Insularization of Tanzanian Parks and the Local Extinction of Large Mammals
Authors: Newmark William D.
Published: March 2003

Island biogeography theory predicts that species will be lost on habitat “islands” created by the fragmentation of continental regions. Many Tanzanian parks are rapidly becoming habitat islands as a result of human settlement, agricultural development, and the active elimination of wildlife on adjacent lands. The rate of extinction of mammals in six Tanzanian parks over the last 35–83 years is significantly and inversely related to park area, suggesting that increasing insularization of the parks has been an important contributory factor in large mammal extinctions. I compared observed patterns of persistence of mammals in Tanzanian parks to predictions derived from earlier extinction models. The predictions of the S1 models of Soulé et al. (1979) and Burkey (1994) and the S2 and S3 models of Soulé et al. (1979) match very closely the observed pattern of persistence of mammals in Tanzanian parks. The loss of mammal species will probably continue, particularly in the smaller parks. Establishment of wildlife corridors linking the parks in northern Tanzania could help to reduce the potential loss of species in the future.
Changes in Distribution and Abundance of the Loggerhead Shrike
Authors: Cade Tom J. , Woods Christopher P.
Published: March 2003

The Loggerhead Shrike (Lanius ludovicianus) was once widely distributed and common over most of North America, occupying an exclusive breeding range with no other shrikes. Although it occurs in a wide variety of plant associations, this shrike is generally found in landscapes characterized by widely spaced shrubs and low trees interspersed with short grasses, forbs, and bare ground, habitats which include deserts, scrub lands, savannas, and some agricultural settings. The Loggerhead Shrike seems to have been always most abundant in the southern and western portions of its range, with high breeding densities from Florida across the gulf states to Texas and throughout the arid regions of the West. A northeastward expansion in range occurred in the late 1800s in association with deforestation and agriculture. A similar north central expansion occurred in the 1900s with agricultural development of the northern Great Plains and aspen parklands. Contraction and decrease in numbers have been noted in parts of its range since the 1940s, concurrent with the regrowth of forests, loss of pasturelands, and intensive row‐crop agriculture. More recently, Christmas Bird Count data and Breeding Bird Survey data have revealed an overall downward trend across the continent at least since 1966, although numbers are stable or increasing in some locations. Field studies generally implicate alterations in habitat structure and loss of habitat as factors responsible for changes in breeding distribution and overall abundance. Nevertheless, considering its entire distribution in North America and its historical expansions and contractions of range associated with habitat changes, the Loggerhead Shrike does not appear threatened with extinction as a species. We favor a hands‐on approach to management of the critically endangered subspecies, L. l. mearnsi and L. l. migrans, however, and recommend extensive preservation of the natural scrub desert, shrub‐steppe, western oak savanna, and southern savanna vegetation types, which appear to be optimal, core habitats for this species, as well as fostering land‐use practices that favor shrikes in agricultural and suburban landscapes.
Reflections on “What is Ecosystem Management?”
Authors: Grumbine R. Edward
Published: March 2003

I review 10 dominant themes of ecosystem management described in the paper “What is Ecosystem Management?” (Grumbine 1994a) based on feedback received from managers actively implementing ecosystem management projects in the field. My emphasis is on practical advice from working professionals for working professionals. Key points include the importance of managing for ecological integrity, the need for social as well as scientific data, suggestions for implementing cooperation strategies and conservation partnerships, a pragmatic definition of adaptive management, and first steps toward changing the structure of natural resource organizations. As ecosystem management evolves, the pressure for change within traditional resource management agencies appears to be reaching a critical point.
Old‐Growth Mangrove Forests in the United States
Authors: Lugo Ariel E.
Published: March 2003

Criteria used to identify old‐growth forests in the Pacific Northwest have not been proven applicable in other ecological life zones. For example, Pacific Northwest criteria are not suitable for the identification of old‐growth mangrove forests. To identify old‐growth mangroves one has to take into account differences in stand structure and function due to geomorphology, within‐site environmental gradients, and regional disturbance regimes. A flexible and holistic approach is needed. Stand age, defined in terms of Pacific Northwest forests, is not necessarily the best criterion for identifying for conservation mangrove forests or any forest outside the Pacific Northwest. No single stand will have all old‐growth characteristics, and even if they are present in a stand, these characteristics do not necessarily assure that the stand is old growth. Whether a mangrove stand reaches old‐growth stage depends on the dynamics of coastal conditions under which it grows. Moreover, it is necessary to differentiate between the age of trees in a stand and the age of the mangrove system, which includes the substrate. Old‐growth mangrove stands are improbable states for this ecosystem type, and they can revert to younger stages. Mangroves offer a challenge to the concept of the old‐growth forest, and through our analysis of this system we show that when ecosystem functions and states are evaluated it is necessary to avoid geographic biases based on particular ecological conditions.
Low Genetic Variability in the Hawaiian Monk Seal
Authors: Kretzmann Maria B. , Gilmartin William G. , Meyer Axel , Zegers Gerard P. , Fain Steven R. , Taylor Bruce F. , Costa Daniel P.
Published: March 2003

The Hawaiian monk seal (   Monachus schauinslandi) is a critically endangered species that has failed to recover from human exploitation despite decades of protection and ongoing management efforts designed to increase population growth. The seals breed at five principal locations in the northwestern Hawaiian islands, and inter‐island migration is limited. Genetic variation in this species is expected to be low due to a recent population bottleneck and probable inbreeding within small subpopulations. To test the hypothesis that small population size and strong site fidelity has led to low within‐island genetic variability and significant between‐island differentiation, we used two independent approaches to quantify genetic variation both within and among the principal subpopulations. Mitochondrial control region and tRNA gene sequences (359 base pairs) were obtained from 50 seals and revealed very low genetic diversity (0.6% variable sites), with no evidence of subpopulation differentiation. Multilocus DNA fingerprints from 22 individuals also indicated low genetic variation in at least some subpopulations (band‐sharing values for “unrelated” seals from the same island ranged from 49 to 73%). This method also provided preliminary evidence of population subdivision (  F′st estimates of 0.20 and 0.13 for two adjacent island pairs). Translocations of seals among islands may therefore have the potential to relieve local inbreeding and possibly to reduce the total amount of variation preserved in the population. Genetic variation is only one of many factors that determine the ability of an endangered species to recover. Maintenance of existing genetic diversity, however, remains an important priority for conservation programs because of the possibility of increased disease resistance in more variable populations and the chance that inbreeding depression may only be manifest under adverse environmental conditions.
Effects of Motorized Tourboats on the Behavior of Nonbreeding American Flamingos in Yucatan, Mexico
Authors: Galicia Eduardo , Baldassarre Guy A.
Published: March 2003

We assessed the effect of motorized tourboats on the behavior of nonbreeding American flamingos (  Phoenicopterus ruber ruber) in the Celestún Estuary, a Special Biosphere Reserve in Yucatán, Mexico, from November 1994 through February 1995. We measured these effects by comparing activity budgets between flocks of flamingos disturbed and undisturbed by tourboats. Disturbance reduced feeding time from 40% before disturbance to 24% after, a 40% loss. Boat disturbance increased alert behavior by 400%. Tourboats averaged 13 per day and caused a disturbance 75% of the time or 3.3 hours per day. Potential loss of feeding time for individuals was estimated at 13% but is likely much higher on days with excessive numbers of tourboats. Flamingos returned to normal feeding rates (40%) within 20 minutes after disturbance. Most tourists (52%) were from Mexico, followed by Germany (14%), and 88% of Mexican visitors were willing to pay an entrance fee to the Celestún Reserve. Conservation efforts should focus on education of tourboat operators to reduce disturbance to flamingos, education of tourists through a visitor’s center and brochures produced in Spanish and English, and expanded involvement of local people.
Developmental Instability in Fragmented Populations of Prairie Phlox: A Cautionary Tale
Authors: Heard Stephen B. , Campbell Michael A. , Bonine Mary L. , Hendrix Stephen D.
Published: March 2003

Abstract:Considerable attention has recently been focused on using levels of developmental instability among members of a population to detect environmental or genetic stresses on animals or plants. It is not yet clear, however, that high developmental instability in a sample of individuals always indicates environmental stress or poor genetic quality. We studied 13 fragmented populations of prairie phlox (  Phlox pilosaL.) to test the hypothesis that developmental instability should decrease with increasing population size—as expected if small populations suffer genetic problems associated with inbreeding or are exposed to more environmental stress than larger populations. We used two different measures of developmental instability, each calculated for two different traits: radial asymmetry of flowers (for petal width and petal length) and modular fluctuating asymmetry of leaves (  for leaf widths at two points along the leaf  ). There were weak but significant correlations among individuals for four of six pairwise combinations of these measures. Surprisingly, three of our four measures of developmental instability showed strong population size effects that were opposite to those expected: developmental instability increased with population size. We conclude that measures of developmental instability cannot be applied uncritically for biomonitoring without considerable knowledge of developmental mechanisms, natural history, and population biology of the species in question.
Extinction Thresholds for Species in Fractal Landscapes
Authors: With Kimberly A. , King Anthony W.
Published: March 2003

Abstract:
Predicting species’ responses to habitat loss and fragmentation is one of the greatest challenges facing conservation biologists, particularly if extinction is a threshold phenomenon. Extinction thresholds are abrupt declines in the patch occupancy of a metapopulation across a narrow range of habitat loss. Metapopulation‐type models have been used to predict extinction thresholds for endangered populations. These models often make simplifying assumptions about the distribution of habitat (random) and the search for suitable habitat sites (random dispersal). We relaxed these two assumptions in a modeling approach that combines a metapopulation model with neutral landscape models of fractal habitat distributions. Dispersal success for suitable, unoccupied sites was higher on fractal landscapes for nearest‐neighbor dispersers (moving through adjacent cells of the landscape) than for dispersers searching at random (random distance and direction between steps) on random landscapes. Consequently, species either did not suffer extinction thresholds or extinction thresholds occurred later, at lower levels of habitat abundance, than predicted previously. The exception is for species with limited demographic potential, owing to low reproductive output , in which extinction thresholds occurred sooner than on random landscapes in all but the most clumped fractal landscapes . Furthermore, the threshold was more precipitous for these species. Many species of conservation concern have limited demographic potential, and these species may be at greater risk from habitat loss and fragmentation than previously suspected.
Impact of Village Hunting on Wildlife Populations in the Western Dja Reserve, Cameroon
Authors: Muchaal Pia K. , Ngandjui Germain
Published: March 2003

Abstract:
The Dja Biosphere Reserve, a lowland rainforest in southern Cameroon, supports extensive biotic communities with a high proportion of endemic fauna and flora. A growing human population afflicted by an economic crisis and a predilection for game meat has augmented pressures on the faunal resources. We conducted a 2‐year study to assess the spatial distribution and intensity of hunting in the western Dja Reserve and the implications for the management of these activities. We mapped the area where the villagers hunt, determined snare densities, and collected biological data on species killed. Surveys using standard line‐transect methodology were conducted on mammalian game species in the various hunting zones across strata of human‐disturbed and less‐disturbed areas. In the three hunting zones of the village of Mekas, snare density decreased as distance from the village increased. Despite a 64% lower snare density, the monthly overall capture rate was four times higher there than in the zone closest to the village. The number of animals that rotted on snares was three times higher in the farthest hunting region from the village. Except for the four common arboreal primates, encounter rates and densities of game species tended to decrease with proximity to human activity and with an increase in snare densities. Duikers (Cephalophus spp.) comprised 63.5% of animals killed. We used
Robinson and Redford’s (1991) production model to determine the sustainability of the present harvest rates. Harvest rates of C. monticola, C. dorsalis, and C. callipygus in two of the hunting zones were between one and three times higher than the populations can theoretically sustain. As species are depleted, hunters will journey even further into the forest to hunt. To reduce waste, subsistence hunting should be limited to within 15 km of the village. Ecological studies to determine stochastic and deterministic influences on the duiker populations are required to ensure their conservation within the Dja Reserve.
Viability and Conservation of an Exploited Sage Grouse Population
Authors: Johnson Kris Harold , Braun Clait E.
Published: March 2003

We analyzed the viability of the Sage Grouse (Centrocercus urophasianus) population of North Park, Colorado, to evaluate its supposed decline due to hunting pressure and habitat degradation. Demographic data from 23 years of surveys were used to parameterize a post‐breeding, female‐based projection matrix with three life stages: juveniles, yearlings, and adults. The population was found to be approximately stable or in decline only if immigration and apparent surveying errors were factored from the data set. Adult and juvenile survival and adult and juvenile reproduction, respectively, were identified as the most limiting demographic factors. Empirical evidence from designed experiments with Sage Grouse has shown that these demographic factors respond markedly to habitat manipulations, especially brush manipulation. Several plausible management scenarios were evaluated with 100‐year population projections generated through Monte Carlo simulation (1000 iterations), sampling from a normal probability distribution entraining the observed variability in each demographic parameter (95% confidence limits). Habitat manipulations to achieve moderate levels (~15% canopy cover) of sagebrush (Artemisia tridentata) are recommended. Regression analyses with power tests showed correspondence between hunting mortality and total mortality for juveniles and adults. Provided that habitat manipulations improve the survival of juveniles and adults, population viability may be conserved without reducing harvest by hunters.
In Situ Conservation of Wild Chiles and Their Biotic Associates
Authors: Tewksbury Joshua Jordan , Nabhan Gary Paul , Norman Donald , Suzán Humberto , Tuxill John , Donovan Jim
Published: March 2003

Wild congeners of domesticated crops increasingly serve as sources of genes for improving crop cultivars. Although wild congeners have been included in seed collections for ex situ storage, there has been little work to protect populations of these wild species in their natural habitats for in situ conservation. We assessed the distribution of chile plants (Capsicum annuum L. var. aviculare[Dierbach] D’Arcy and Eshbaugh) relative to the dominant woody vegetation of one subpopulation in a single drainage in southern Arizona, U.S.A. Wild chiles were not found in direct sun, and the distribution of chiles under different nurse plants could be a function of random chance, microenvironmental differences under different nurse‐plant species, or nonrandom dispersal by chile consumers. To examine chile distribution, we measured the association of wild chiles with nurse‐plant species and compared these associations with the available cover provided by each nurse plant. We also measured the buffering capacity of each nurse‐plant species, conducted mammalian and avian food‐preference experiments to determine the taxa dispersing chiles, and conducted time‐budget studies of potential chile dispersal agents. Wild chiles were not randomly distributed: over 75% were under the canopies of fleshy‐fruited shrubs that collectively made up less than 25% of the cover. We found limited evidence that differences in buffering capacity affected chile distribution. Food‐preference experiments suggested that birds are the only effective dispersal agents, and the time budgets of three common bird species were strongly correlated with chile plant distribution. These results lend support for directed dispersal by avian consumers. The distribution of chiles appears to be a function of interactions between consumers, nurse plants, and the secondary chemicals in the chiles themselves. Only through studies of in situ populations can we understand the interactions that sustain both wild‐crop relatives and the genetic variability essential to future crop management.
Conservation of Biodiversity in a World of Use
Authors: Redford Kent H. , Richter Brian D.
Published: March 2003

Abstract: Biodiversity conservation has become the stated objective of national governments, state agencies, local communities, and scientific organizations. Yet despite this attention the term biodiversity remains poorly defined. One of the unfortunate consequences of this lack of definition is a proliferation of claims that biodiversity can be both used and conserved. This claim is difficult to assess without a more precise way of defining biodiversity. We offer a heuristic framework for measuring the consequences of human use for biodiversity. Our definition of biodiversity includes three components: genetic, population/species, and community/ecosystem. Each component has its own three attributes: composition, structure, and function. Using this definition, we assessed the effects of different types of human use on the different components and attributes of biodiversity. We show that (1) different degrees of human use or alteration result in differential conservation of biodiversity components; (2) some components and attributes of biodiversity are more sensitive to human use than others; and (3) only extremely limited use or virtually no alteration will protect all components.
Extirpation and Recolonization in a Metapopulation of an Endangered Fish, the Tidewater Goby
Authors: Lafferty Kevin D. , Swift Cam C. , Ambrose Richard F.
Published: March 2003

Abstract: The tidewater goby ( Eucyclogobius newberryi ), an endangered species in the United States, occurs in a series of isolated coastal wetlands in California. Using historical presence‐absence data and our own surveys, we estimated annual rates of extirpation and recolonization for several populations of the goby in southern California. As predicted, large wetlands had lower rates of extirpation than small wetlands. There was a negative but statistically nonsignificant correlation between recolonization rate and distance to the nearest northerly source population. Populations at small sites were sensitive to drought, presumably because droughts can eliminate suitable habitat at small wetlands. Populations in small wetlands have declined over time, even after accounting for variation in stream flow, supporting the species' endangered status. Our study emphasizes the need to understand metapopulation dynamics for conserving species where the unit of conservation is a local population. It is also emphasizes the importance of not treating metapopulations as identical units. Finally, our results provide a means for describing the decline of a species that is complex in time and space and provide insight into how to target protection measures among metapopulations.
The Importance of Systematic Biology in Defining Units of Conservation
Authors: Dimmick Walter Wheaton , Ghedotti Michael J. , Grose Michael J. , Maglia Anne M. , Meinhardt Daniel J. , Pennock David S.
Published: March 2003

Abstract:
Conservation biology is linked inextricably with systematic biology. The principles of systematic biology, however, have not been integrated completely into the practice and principles of conservation biology. Systematists have recognized for some time that a number of evolutionary processes lead to the diversification of lineages. Yet some present units of conservation, such as the evolutionarily significant unit (Waples 1991), primarily emphasize only one of these processes, adaptation. Allopatric speciation produces biodiversity without requiring any adaptive shift (and consequent adaptive differences between daughter species), so definitions of conservation units that emphasize adaptation may underestimate biodiversity. We estimated the frequency of different modes of speciation for three groups of vertebrates. The frequency of allopatric speciation varies among these groups, but is an important type of speciation in two of the three groups studied. Our results, and the results of other published studies of the frequency of modes of speciation, demonstrate that any unit of conservation defined solely in terms of adaptation is likely to underestimate biological diversity.
Conservation Implications of Dietary Dilution from Debris Ingestion: Sublethal Effects in Post‐Hatchling Loggerhead Sea Turtles
Authors: McCauley Shannon J. , Bjorndal Karen A.
Published: March 2003

Abstract: Ingestion of anthropogenic debris by marine species has been documented extensively; fewer studies have attempted to quantify the sublethal effects caused by debris ingestion. One potential sublethal effect is reduced nutrient gains from diets diluted by consumption of debris. Post‐hatchling and juvenile loggerhead sea turtles (Caretta caretta) consume substantial quantities of debris. We evaluated the effects of dietary dilution on voluntary intake in post‐hatchling loggerheads to assess their ability to compensate for the presence of inert diluents in their diet by increasing dry mass intakes to maintain nutrient gains. Mean daily intakes of dry mass did not increase significantly with dietary dilution, so intakes of energy and nitrogen on a 50% dilution diet were significantly lower than on a 10% dilution diet. Therefore, post‐hatchling loggerheads have an extremely limited ability to compensate for dietary dilution and would experience sublethal effects from decreased energy and nitrogen gains on dilute diets. Decreased nutrient intakes have serious conservation implications because of possible decreased growth rates, longer developmental periods at sizes most vulnerable to predation, depleted energy reserves, reduced reproductive output, and decreased survivorship.
Demography of Two Mexican Spotted Owl Populations
Authors: Seamans Mark E. , Gutiérrez R. J. , May Christopher A. , Peery M. Zachariah
Published: March 2003

Abstract: The Mexican Spotted Owl (Strix occidentalis lucida) is a threatened subspecies of the southwestern United States and northern Mexico. Although threatened, little is known about its population status. We studied the demography of the Mexican Spotted Owl in one study area in Arizona and one in New Mexico from 1991 to 1997. We estimated annual survival rates (φ), fecundity rates (  b), and abundance (  N) to test the hypothesis that population trends were stationary. Although annual fecundity rates (   for Arizona and 0.380 for New Mexico) and annual juvenile survival rates ( for Arizona and 0.109 for New Mexico) differed in magnitude between the study areas, they exhibited similar temporal patterns. Annual survival for territorial owls varied randomly in Arizona but declined linearly in New Mexico. Mean annual survival for territorial owls was 0.814 in Arizona and 0.832 for owls ≥3 years old and 0.644 for owls 1–2 years old in New Mexico. Based on survival and fecundity estimates, the annual rates of change (λ^) indicated that both populations were declining at ≥10% a year. These estimates were corroborated by observed declines in abundance. Some regional factor may have been affecting fecundity, whereas a combination of factors may have been affecting survival. Two possible reasons for the population declines are declines in habitat quality and regional trends in climate.
Predicting the Vulnerability of Tropical Reef Fishes to Exploitation with Phylogenies and Life Histories
Authors: Jennings Simon , Reynolds John D. , Polunin Nicholas V. C.
Published: March 2003

Abstract:Fishing has led to local extirpations of reef fishes. For conservation and management purposes, it is important to identify all those species that are vulnerable to fishing, but this cannot be done using a priori assessments or by describing trends in abundance because the necessary scientific resources are not available. Thus the predictions of vulnerability that provide the basis for conservation action will have to be made with existing data or data that can be acquired rapidly before further extirpations occur. The life histories of species may determine their responses to exploitation, and we describe how an easily measured parameter, maximum observed size, is related to population trends of exploited fishes on coral reefs. Using a phylogenetic comparative approach, we demonstrated that species of grouper (Epinephelinae), snapper (Lutjanidae), and parrotfish (Scaridae) that decreased in abundance more than their nearest phylogenetic relative had greater maximum size. Our results suggest that one can predict the vulnerability of reef fishes to exploitation based on responses of their relatives. The quality of the prediction was good for the intensively fished groupers and snappers but poor for the lightly fished parrotfishes. Our approach may help proactive conservationists and fishery managers identify and conserve vulnerable species in new, developing, or lightly exploited fisheries, thereby reducing their reliance on reactive management methods.
A Framework for Evaluating the Effects of Human Factors on Wildlife Habitat: the Case of Giant Pandas
Authors: Liu Jianguo , Ouyang Zhiyun , Taylor William W. , Groop Richard , Tan Yingchun , Zhang Heming
Published: March 2003

Abstract:To address the complex interactions between humans and wildlife habitat, we developed a conceptual framework that links human factors with forested landscapes and wildlife habitat. All the components in the framework are integrated into systems models that analyze the effects of human factors and project how wildlife habitat would change under different policy scenarios. As a case study, we applied this framework to the Wolong Nature Reserve in Sichuan Province (southwestern China), the largest home of the giant panda (Ailuropoda melanoleuca). We collected ecological and socioeconomic data with a combination of various methods ( field observations, aerial photographs, government documents and statistics, interviews, and household surveys) and employed geographic information systems and systems modeling to analyze and integrate the data sources. Human population size has increased by 66% and the number of households in the reserve has increased by 115% since 1975, when the reserve was established. During the same period, the quality and quantity of the giant panda habitat dramatically decreased because of increasing human activities such as fuelwood collection. Systems modeling predicted that under the status quo, human population in the reserve would continue to grow and cause more destruction of the remaining panda habitat, whereas reducing human birth rates and increasing human emigration rates would lower human population size and alleviate human impacts on the panda habitat. Furthermore, our simulations and surveys suggested that policies encouraging the emigration of young people would be more effective and feasible than relocating older people in reducing human population size and conserving giant panda habitat in the reserve.
Factors Influencing the Effectiveness of Wildlife Underpasses in Banff National Park, Alberta, Canada
Authors: Clevenger Anthony P. , Waltho Nigel
Published: March 2003

Abstract: Wildlife crossing structures are intended to increase permeability and habitat connectivity across roads. Few studies, however, have assessed the effectiveness of these mitigation measures in a multispecies or community level context. We used a null model to test whether wildlife crossing structures serve large mammal species equally or whether such structures limit habitat connectivity across roads in species‐specific ways. We also modeled species responses to 14 variables related to underpass structure, landscape features, and human activity. Species performance ratios (observed crossing frequency to expected crossing frequency) were evaluated for four large carnivore and three ungulate species in 11 underpass structures in Banff National Park, Alberta, Canada. Observed crossing frequencies were collected in 35 months of underpass monitoring. Expected frequencies were developed from three independent models: radio telemetry, pellet counts, and habitat‐suitability indices. The null model showed that species responded to underpasses differently. In the presence of human activity carnivores were less likely to use underpasses than were ungulates. Apart from human activity, carnivore performance ratios were better correlated to landscape variables, and ungulate performance ratios were better correlated to structural variables. We suggest that future underpasses designed around topography, habitat quality, and location will be minimally successful if human activity is not managed.
Genetic Variability in Swayne's Hartebeest, an Endangered Antelope of Ethiopia
Authors: Flagstad Øystein , Syvertsen Per Ole , Stenseth Nils ChR. , Stacy John E. , Olsaker Ingrid , Røed Knut H. , Jakobsen Kjetill S.
Published: March 2003

Abstract:Swayne's hartebeest (Alcelaphus buselaphus swaynei) is an endangered antelope that survives in four or five relict populations in Ethiopia. We examined the two main populations (Senkele and Nechisar) for mitochondrial (D‐loop) and nuclear (microsatellite) variability in order to measure levels of genetic variation within the subspecies and degree of differentiation between populations. For comparison, we examined samples from a large population of red hartebeest (Alcelaphus buselaphus caama). Bothswayneiandcaamaexhibited high levels of variation. There was significant differentiation between the populations ofswayneiat Senkele and Nechisar, and gene diversity in Nechisar, the smaller of the two populations, was significantly lower than that in Senkele. Many mitochondrial haplotypes and microsatellite alleles present at high frequencies among the Senkele individuals were missing in Nechisar, suggesting that the translocation of animals from Senkele undertaken in 1974 did not contribute notably to the gene pool in Nechisar. Subsamples taken from Senkele in 1988 and 1995 showed a significant change in allele frequencies, a change that probably can be attributed to a massive population decline during this period. We recommend that both populations be protected in situ to maintain as much as possible of the diversity that exists within the taxon and that a breeding program be established. In spite of the earlier unsuccessful attempt, we argue that translocation of animals for enhancement of population size as well as genetic variation in Nechisar should be considered.
The Natural Imperative for Biological Conservation
Authors: Angermeier Paul L.
Published: March 2003

Abstract: To contribute significantly to environmental policy of the next century, conservationists will need to reach a consensus on their fundamental values and goals and to persuade society to adopt them. Resolution of the debate over the continued role of naturalness as a guiding concept has important implications for how conservation is practiced and the future of the discipline. I examine five aspects of naturalness in the context of biological conservation: (1) its utility, (2) its assessment, (3) its relation to values and ethics, (4) alternative imperatives, and (5) implications of adopting it as a guiding concept. Naturalness can be viewed as a continuous gradient with completely natural and completely artificial extremes. Human actions are unnatural to the extent that they rely on technology to transform natural ecosystems. The ecological consequences of technological transformation often overwhelm the capacity of other biota to adapt and are a root cause of biodiversity loss. The naturalness of most ecosystems or ecosystem alterations can be assessed objectively despite imperfect knowledge if evolutionary limits and natural ranges of variability are carefully considered. Most conservationists value naturally evolved biotic elements such as genomes and communities over artificial elements. This judgment, which is not shared by society at large, is based on intrinsic and instrumental values, including respect for nature and recognition that many ecosystem amenities stem from natural processes. Given the wide accessibility of ecologically destructive technology, fundamental shifts in societal values and approaches to ecosystem alteration are needed to achieve conservation. Respect for nature must supplant the prevailing world view of human superiority. Although sometimes difficult to assess, naturalness is a more reasonable guide for conservation than are other ecosystem features such as diversity, productivity, or evolution, and naturalness is the foundation for several current conservation concepts such as ecological integrity and ecological restoration. Conservation biologists can help develop conservation practices and ethics that emphasize the importance of natural ecosystems. Key roles include refining distinctions between natural and anthropogenic conditions, devising ways to use ecosystems without losing biotic diversity, and facilitating shifts in societal values toward more respect for nature.
Raptors and Red Grouse: Conservation Conflicts and Management Solutions
Authors: Thirgood Simon , Redpath Steve , Newton Ian , Hudson Peter
Published: March 2003

Abstract: Recovering predator populations may present problems for conservationists if their prey are of economic or conservation value. We address this issue by examining the conflict between raptor conservation and management of Red Grouse (  Lagopus l. scoticus) in Britain. Heather moorland is a distinctive habitat that supports an important assemblage of breeding birds. Large areas of moorland are managed by private landowners for shooting grouse. Although grouse shooting benefits conservation by retaining heather moorland, it is currently unclear whether grouse management directly benefits other upland birds. Human persecution has greatly restricted the range and abundance of most raptor species in Britain. Following the introduction of bird protection laws, the decline in gamekeeping, and the restriction of organochlorine pesticides, raptor populations have started to recover. Persecution of raptors on grouse moors is widespread and limits the range and abundance of Hen Harriers ( Circus cyaneus), Peregrine Falcons (  Falco peregrinus), and Golden Eagles (Aquila chrysaetos). In some circumstances, raptor predation can reduce both the breeding density and productivity of Red Grouse. Limitation of grouse populations through raptor predation is most likely to occur where raptors are at high density because of the abundance of alternative prey, and grouse are at low density either because of poor management or the cyclic nature of some grouse populations. In the long term, habitat management may reduce densities of alternative prey, leading to reductions in raptor densities and their predation on grouse. More active intervention may be required, however, if grouse moors are to remain viable in the short‐term. Current research is focused on manipulating harrier diet through diversionary feeding. Complementary research is needed to investigate methods to reduce raptor numbers locally while ensuring their national status.
Biodiversity and Disease Risk: the Case of Lyme Disease
Authors: Ostfeld Richard S. , Keesing Felicia
Published: March 2003

Abstract:Utilitarian arguments concerning the value of biodiversity often include the benefits of animals, plants, and microbes as sources of medicines and as laboratory models of disease. The concept that species diversity per se may influence risk of exposure to disease has not been well developed, however. We present a conceptual model of how high species richness and evenness in communities of terrestrial vertebrates may reduce risk of exposure to Lyme disease, a spirochetal (  Borrelia burgdorferi) disease transmitted by ixodid tick vectors. Many ticks never become infected because some hosts are highly inefficient at transmitting spirochete infections to feeding ticks. In North America, the most competent reservoir host for the Lyme disease agent is the white‐footed mouse (  Peromyscus leucopus), a species that is widespread and locally abundant. We suggest that increases in species diversity within host communities may dilute the power of white‐footed mice to infect ticks by causing more ticks to feed on inefficient disease reservoirs. High species diversity therefore is expected to result in lower prevalence of infection in ticks and consequently in lower risk of human exposure to Lyme disease. Analyses of states and multistate regions along the east coast of the United States demonstrated significant negative correlations between species richness of terrestrial small mammals (orders Rodentia, Insectivora, and Lagomorpha), a key group of hosts for ticks, and per capita numbers of reported Lyme disease cases, which supports our “dilution effect” hypothesis. We contrasted these findings to what might be expected when vectors acquire disease agents efficiently from many hosts, in which case infection prevalence of ticks may increase with increasing diversity hosts. A positive correlation between per capita Lyme disease cases and species richness of ground‐dwelling birds supported this hypothesis, which we call the “rescue effect.” The reservoir competence of hosts within vertebrate communities and the degree of specialization by ticks on particular hosts will strongly influence the relationship between species diversity and the risk of exposure to the many vector‐borne diseases that plague humans.
Effects of Roads on Hydrology, Geomorphology, and Disturbance Patches in Stream Networks
Authors: Jones Julia A. , Swanson Frederick J. , Wemple Beverley C. , Snyder Kai U.
Published: March 2003

Abstract:We outline a view of how road networks interact with stream networks at the landscape scale and, based on examples from recent and current research, illustrate how these interactions might affect biological and ecological processes in stream and riparian systems. At the landscape scale, certain definable geometric interactions involving peak flows (  floods) and debris flows (rapid movements of soil, sediment, and large wood down steep stream channels) are influenced by the arrangement of the road network relative to the stream network. Although disturbance patches are created by peak‐flow and debris‐flow disturbances in mountain landscapes without roads, roads can alter the landscape distributions of the starting and stopping points of debris flows, and they can alter the balance between the intensity of flood peaks and the stream network's resistance to change. We examined this conceptual model of interactions between road networks and stream networks based on observations from a number of studies in the H. J. Andrews Experimental Forest, Oregon (U.S.A.). Road networks appear to affect floods and debris flows and thus modify disturbance patch dynamics in stream and riparian networks in mountain landscapes. We speculate that these changes may influence the rates and patterns of survival and recovery of disturbed patches in stream networks, affecting ecosystem resilience, and we outline an approach for detecting such effects based on a patch dynamics perspective. A field sampling scheme for detecting the magnitude of various road effects on stream and riparian ecology could involve (1) landscape stratification of inherent stream network susceptibility to floods or debris flows, (2) overlay of road and stream networks and creation of areas with various densities of road‐stream crossings, emphasizing midslope road‐stream crossings, and (3) designations of expected high‐ and low‐impact stream segments based on numbers of upstream road‐stream crossings where sampling of selected biological variables would be conducted.
Role of Light Availability and Dispersal in Exotic Plant Invasion along Roads and Streams in the H. J. Andrews Experimental Forest, Oregon
Authors: Parendes Laurie A. , Jones Julia A.
Published: March 2003

Abstract: We examined the roles of dispersal mechanism, a biological barrier; light availability, an environmental barrier; and level of disturbance, a physical barrier, in explaining the spatial patterns of exotic plant species along road and stream segments in a forest landscape in the western Cascade Range of Oregon (U.S.A). The presence or absence of 21 selected exotic plant species and light levels were observed along 0.3‐ to 1.0‐km transects within four habitat types. Each habitat represented a different level of disturbance: high‐use roads, low‐use roads, abandoned roads, and streams in the H. J. Andrews Experimental Forest. Nearly 300 50 × 2–m sampling units were surveyed along five transects in each habitat type. We used ordination (nonmetric multidimensional scaling) and logistic regression to analyze data. All of the nearly 200 sampling units along roads with high and low levels of vehicle traffic contained at least one exotic plant species, and some contained as many as 14. Streams that were most recently disturbed by floods 20–30 years ago and abandoned spur roads with no traffic for 20–40 years also had numerous exotic species. Roads and streams apparently serve multiple functions that enhance exotic species invasion in this landscape: they act as corridors or agents for dispersal, provide suitable habitat, and contain reservoirs of propagules for future episodes of invasion. Species‐specific dispersal mechanisms, habitat characteristics, and disturbance history each explain some, but not all, of the patterns of exotic species invasion observed in this study.
Population Persistence and Offspring Fitness in the Rare BellflowerCampanula cervicariain Relation to Population Size and Habitat Quality
Authors: Eisto Anna‐Kaija , Kuitunen Markku , Lammi Antti , Saari Veli , Suhonen Jukka , Syrjäsuo Susanna , Tikka Päivi M.
Published: March 2003

Abstract:Data from several animal species and a few plant species indicate that small populations face an elevated risk of extinction. Plants are still underrepresented in these studies concerning the relation between population size and persistence. We studied the effect of population size on persistence among natural populations of the rare bellflowerCampanula cervicariain Finland. We monitored 52 bellflower populations for 8 years and found that the mean population size decreased from 24 to 14 during this period. Small populations with ≤5 individuals were more prone to losing all fertile plants than were larger ones. Reduction in population size was nevertheless unrelated to the degree of population isolation, measured as the distance to the nearest known population. To test the hypothesis that offspring fitness is lower in small populations, we germinated bellflower seeds from different‐sized populations in a laboratory and found that seed germination ability was independent of population size. The seedlings raised from seeds of small populations grew faster than those taken from larger populations. Population size was negatively related to the amount of shade in the habitats. In conclusion, decreasing population sizes ofC. cervicariaseemed not to be caused by lowered germination ability or growth rate in small populations; rather, population size reductions appeared to be due to closing of vegetation in the habitats.
Environmental Models of Cetacean Abundance: Reducing Uncertainty in Population Trends
Authors: Forney Karin A.
Published: March 2003

Abstract: Trends in population abundance are often used to monitor species affected by human activities. For highly mobile species in dynamic environments, however, such as cetaceans in the marine realm, natural variability can confound attempts to detect and interpret trends in abundance. Environmental variability can cause dramatic shifts in the distribution of cetaceans, and thus abundance estimates for a fixed region may be based on a different proportion of the population each time. This adds variability, decreasing statistical power to detect trends and introducing uncertainty whether apparent trends represent true changes in population size or merely reflect natural changes in the distribution of cetaceans. To minimize these problems, surveys ideally would be based on species‐specific design criteria that optimize sampling within all relevant habitat throughout a species' range. Our knowledge of cetacean habitats is limited, however, and financial and logistic constraints generally force those surveying cetacean abundance to include all species within a limited geographic region. Alternately, it may be possible to account for environmental variability analytically by including models of species‐environment patterns in trend analyses, but this will be successful only if such models have interannual predictive power. I developed and evaluated generalized additive models of cetacean sighting rates in relation to environmental variables. I used data from shipboard surveys of Dall's porpoise (  Phocoenoides dalli) and short‐beaked common dolphins (   Delphinus delphis) conducted in 1991, 1993, and 1996 off California. Sighting rates for these two species are variable and can be partially accounted for by environmental models, but additional surveys are needed to model species‐environment relationships adequately. If patterns are consistent across years, generalized additive models may represent an effective tool for reducing uncertainty caused by environmental variability and for improving our ability to detect and interpret trends in abundance.