scispace - formally typeset
Search or ask a question

Showing papers in "Conservation Biology in 1996"


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

2,204 citations


Journal ArticleDOI
TL;DR: The pathology of natural resource management, defined as a loss of system resilience when the range of natural variation in the system is reduced encapsulates the unsustain- able environmental, social, and economic outcomes of command-and-control resource management is discussed in this article.
Abstract: As the human population grows and natural resources decline, there is pressure to apply increas- ing levels of topdown, command, and~control management to natural resources. This is manifested in at- tempts to control ecosystems and in socioeconomic institutions that respond to erratic or surprising ecosystem behavior with more control Command and control, however, usually results in unforeseen consequences for both natural ecosystems and human welfare in the form of collapsing resources, social and economic strife, and losses of biological diversity. We describe the "pathology of natural resource management, " defined as a loss of system resilience when the range of natural variation in the system is reduced encapsulates the unsustain- able environmental, social, and economic outcomes of command~and~ontrol resource management. If natu- ral levels of variation in system behavior are reduced through command-and~ontrol, then the system be- comes less resilient to external perturbations, resulting in crises and surprises. We provide several examples of this pathology in management. An ultimate pathology emerges when resource management agencies, through initial success with command and control, lose sight of their original purposes, eliminate research and monitoring, and focus on efficiency of control They then become isolated from the managed systems and inflexible in structure. Simultaneously, through overcapitalization, society becomes dependent upon com- mand and control, demands it in greater intensity, and ignores the underlying ecological change or collapse that is developing. Solutions to this pathology cannot come from further command and control (regulations) but must come from innovative approaches involving incentives leading to more resilient ecosystems, more flexible agencies, more self-reliant industries, and a more knowledgeable citizenry. We discuss several aspects of ecosystem pattern and dynamics at large scales that provide insight into ecosystem resilience, and we pro- pose a "Golden Rule" of natural resource management that we believe is necessary for sustainabllity: man- agement should strive to retain critical types and ranges of natural variation in resource systems in order to maintain their resiliency.

1,871 citations


Journal ArticleDOI
TL;DR: There can be no doubt that genetic variation is related to population size, as Sould proposed, and vertebrates should have less genetic variation than invertebrates or plants.
Abstract: Genetic diversity is one of three levels of biological diversity requiring conservation. Genetic theory predicts that levels of genetic variation should increase with effective population size. Sould (19 76) compiled the first convincing evidence that levels of genetic variation in wildlife were related to population size, but this issue remains controversial. The hypothesis that genetic variation is related to population size leads to the following predictions: (1) genetic variation within species should be related to population size; (2) genetic variation within species should be related to island size; (3) genetic variation should be related to population size within taxonomic groups; (4) widespread species should have more genetic variation than restricted spe- cies; (5) genetic variation in animals should be negatively correlated with body size; (6) genetic variation should be negatively correlated with rate of chromosome evolution; (7) genetic variation across species should be related to population size; (8) vertebrates should have less genetic variation than invertebrates or plants; (9) island populations should have less genetic variation than mainland populations; and (10) en- dangered species should have less genetic variation than nonendangered species. Empirical observations sup- port all these hypotheses. There can be no doubt that genetic variation is related to population size, as Sould proposed. Small population size reduces the evolutionary potential of wildlife species.

1,397 citations


Journal ArticleDOI
TL;DR: It is suggested that a minimum of I and a maximum of 10 migrants per generation would be an appro- priate general rule of thumb for genetic purposes, bearing in mind that fctctors other than genetics influence the ideal level of connectivity.
Abstract: In the face of continuing habitat fragmentation and isolation, the optimal level of connectivity be- tween populations has become a central issue in conservation biology. A common rule of thumb holds that one migrant per generation into a subpopulation is sufficient to minimize the loss of polymorphism and het- erozygosity within subpopulations while allowing for divergence in allele frequencies among subpopulations. The one-migrant-per-generation rule is based on numerous simplifying assumptions that may not hold in nat- ural populations. We examine the conceptual and theoretical basis of the rule and consider both genetic and nongenetic factors that influence the desired level qf connectivity among subpopulations. We conclude that one migrant per generation is a desirable minimum, but it may be inadequaite for many natural popula- tions. We suggest that a minimum of I and a maximum of 10( migrants per generation would be an appro- priate general rule of thumb for genetic purposes, bearing in mind that fctctors other than genetics maly fur- ther influence the ideal level of connectivity.

805 citations


Journal ArticleDOI
TL;DR: Captive breeding should be viewed as a last resort in species recovery and not a prophylactic or long-term solution because of the inexorable genetic and phenotypic changes that occur in captive environments.
Abstract: The use of captive breeding in species recovery has grown enormously in recent years, but without a concurrent growth in appreciation of its limitations. Problems with (1) establishing self-sufficient captive populations, (2) poor success in reintroductions, (3) high costs, (4) domestication, (5) preemption of other re- covery techniques, (6) disease outbreaks, and (7) maintaining administrative continuity have all been signif- icant. The technique has often been invoked prematurely and should not normally be employed before a care- ful field evaluation of costs and benefits of all conservation alternatives has been accomplished and a determination made that captive breeding is essential for species survival. Merely demonstrating that a spe- cies" population is declining or has fallen below what may be a minimum viable size does not constitute enough analysis to justify captive breeding as a recovery measure. Captive breeding should be viewed as a last resort in species recovery and not a prophylactic or long-term solution because of the inexorable genetic and phenotypic changes that occur in captive environments. Captive breeding can play a crucial role in re- covery of some species for which effective alternatives are unavailable in the short term. However, it should not displace habitat and ecosystem protection nor should it be invoked in the absence of comprehensive ef- forts to maintain or restore populations in wild habitats. Zoological institutions with captive breeding pro- grams should operate under carefully defined conditions of disease prevention and genetic~behavioral man- agement. More important, these institutions should help preserve biodiversity through their capacities for public education, professional training, research, and support of in situ conservation efforts.

672 citations


Journal ArticleDOI
TL;DR: It is suggested that morphospecies may be used as surrogates for species in some environmental monitoring and conservation, in particular when decisions are guided by estimates of richness and the assessment of turnover.
Abstract: Environmental monitoring and conservation evaluation in terrestrial habitats may be enhanced by the use of invertebrate inventories, but taxonomic and logistic constraints frequently encountered during conventional taxonomic treatment have greatly restricted their use. To overcome this problem we suggest that nonspecialists may be used to classify invertebrates to morphospecies without compromising scientific accuracy. To test this proposition, large pitfall and litter samples of ants, beetles, and spiders from four forest types were sorted to morphospecies by a nonspecialist and to species by specialists. These data were used to generate morphospecies and species inventories and to estimate richness (α diversity) and turnover (β diversity), information frequently used in the above activities. Our results show that the estimates of richness of ants and spiders varied little between morphospecies and species inventories. Differences between estimates of beetle richness were largely influenced by errors of identification in two families, Curculionidae and Staphylinidae. But morphospecies and species inventories yielded identical ranking of forest type using richness. Turnover was assessed by sample ordination, which revealed similar clusters regardless of the type of inventory. Analysis of similarities of assemblages of ants and beetles showed significant differences between all forest types. Spider assemblages showed a lower level of discrimination. The assessment of turnover was consistent among inventories but different between the major taxa. Our findings suggest that morphospecies may be used as surrogates for species in some environmental monitoring and conservation, in particular when decisions are guided by estimates of richness and the assessment of turnover. El monitoreo ambiental y la evaluacion para la conservacion en los habitats terrestres puede ser mejorado con el uso de inventarios de invertebrados. Sin embargo, las restricciones taxonomicas y logisticas que surgen frecuentemente durante los tratamientos taxonomicos convencionales, han restringido en gran medida su uso. Para poder superar este problema, nosotros sugerimos que podria utilizarse personal no especializado para clasificar invertebrados en morfoespecies sin comprometer la exactitud cientifica. Para probar esta propuesta, muestras de hormigas, escarabajos y aranas provenientes de cuatro tipos de bosques fueron ordenadas en morfoespecies por un noespecialista y en especies por un especialista. Estos datos fueron utilizados para generar inventarios de morfoespecies y especies y para estimar riqueza (diversidad alfa) y tasas de renovacion (diversidad beta), informacion que es utilizada frecuentemente en las actividades mencionadas anteriormente. Nuestros resultados muestran que las estimaciones de la riqueza de hormigas y aranas vario muy poco entre los inventarios de morfoespecies y de especies. Las diferencias entre las estimaciones de la riqueza de escarabajos fue en gran medida influenciada por errores en la identificacion de dos familias, Curculionidae y Staphylinidae. Sin embargo, los inventarios de morfoespecies y especies produjeron un ordenamiento identico de los tipos de bosques utilizando la riqueza como parametro. La tasa de intercambio (“turnover”) fue evaluada por medio de metodos de ordenacion de las muestras que revelaron grupos muy similares independientemente del tipo de inventario. Los analisis de similitud de los agrupamientos de hormigas y escarabajos mostraron diferencias significativas entre todos los tipos de bosques. Los agrupamientos de aranas mostraron un bajo nivel de discriminacion. La evaluacion de la tasa de recambio fue consistente entre los inventarios pero diferente entre los taxones mas importantes. Nuestros resultados sugieren que las morfoespecies podrian ser utilizadas como substitutos de las especies en ciertos casos de monitoreos ambientales y de conservacion, en particular, cuando las decisiones estan guiadas por las estimaciones de riqueza y la evaluacion de la tasa de intercambio.

650 citations


Journal ArticleDOI
TL;DR: The results indicate that translocated birds were less successful at establishing self-sustaining populations than translocated mammals, and generally corroborate the results of Grifftth et al. (1989).
Abstract: In 1993 we conducted a follow-up study of the 1987 survey by Griffith et al. (1989) of 421 avian and mammalian translocation programs in North America, Australia, and New Zealand to reassess the programs’ status and the biological and methodological factors associated with success. Our survey response rate was 81%. Approximately 38% of usable programs in 1993 reported a change in outcome from 1987 (e.g., a translocated population was “declining” but now is “self-sustaining”), but the difference between the overall success rates was not statistically significant (66% in 1987 and 67% in 1993). Since 1987, an increase was observed in the median number of animals translocated per program (31.5 to 50.5), median duration of releases (2 to 3 years), and proportion of programs releasing more than 30 animals (46% to 68%). Multiple logistic regression analyses indicated that release into the core of the historical range, good-to-excellent habitat quality, native game species, greater numbers of released animals, and an omnivorous diet were positively associated with translocation success. Moreover, our results indicate that translocated birds were less successful at establishing self-sustaining populations than translocated mammals. Our findings, using comparable logistic analyses, generally corroborate the results of Grifftth et al. (1989). Variables not found to be significantly correlated with translocation success include species’ reproductive potential (number of offspring and first age of reproduction), number and duration of the releases, and source of the translocated animals (wild-caught versus captive-reared). En 1993 realizamos un estudio de seguimiento de la evaluacion de 421 programas de translocacion de aves y mamiferos en Norteamerica, Australia y Nueva Zelandia hecha por Griffith et al. (1989), para reevaluar la situacion del programa y los factores biologicos y metodologicos asociados con se exito. La tasa de respuesta a nuestra encuesta fue de un 81%. Aproximadamente un 38% de los programas vigentes en 1993 reportaron un cambio en los resultados de 1987 (e. g., una poblacion translocada se encontraba “declinando,” pero ahora se encuentra “auto-sopsteniendose”) De cualquier manera, la diferencia entre las tasas de exito no fueron estadisticamente significativas (66% en 1987 y 67% en 1993). Desde 1987 se ha observado un incremento en el numero promedio de animales translocados por programa (31.5 a 50.5), la duracion promedio de las liberaciones (2 a 3 anos) y una proporcion de programas de liberacion de mas de 30 animales (46% al 68%). Un analisis de regresion logistica multiple indica que las liberaciones dentro de un rango historico relacionan positivamente los hatbitats de buena a excelente calidad, las especies deportivas nativas, un mayor numero de animales liberados y una dieta omnivora con una translocacion exitosa. Ademas, nuestros resultados indican que las aves translocadas fueron menos exitosas para establecer poblaciones autosostenibles que los mamiferos translocados. Nuestras observaciones corroboraron los resultados de Griffith (1989) por medio de comparaciones de analisis logistico. Variables encontradas como no significativas con el exito de la translocacion incluyen potencial reproductivo de la especie (numero de crias y edad a la primera reproduccion), numero y duracion de liberaciones y la fuente de animales translocados (salvajes-capturados vs. captivos-liberados).

623 citations


Journal ArticleDOI
TL;DR: It is suggested that hybridization is an increasing threat to rare species because ecological barriers are being disrupted by human activities and the negative consequences of hybridization are unlikely to be compensated for by immigration from conspecific populations.
Abstract: Much has been written about the role of interspecific competition, disease, herbivory, and the loss of key mutualisms in the extinction of rare plant species. Interspecific hybridization rarely is considered among the biotic interactions that promote extinction. We show how hybridization may contribute to the demise of rare plant species through demographic swamping and genetic assimilation by an abundant congener. We contend that the growth of the hybrid subpopulation is the key to rare species assimilation, and we show how the production of hybrid seed, the fitness of hybrids, and pest pressure affect hybrid proliferation. We also discuss how habitat disturbance, unspecialized pollinators, and weak crossing barriers promote hybridization, and how the negative consequences of hybridization are unlikely to be compensated for by immigration from conspecific populations. We also illustrate stages in the demise of species in island floras. We suggest that hybridization is an increasing threat to rare species because ecological barriers are being disrupted by human activities. Se ha escrito bastante sobre el papel que han jugado en la extincion de las especies vegetales raras, factores tales como la competencia interspecifica, las plagas y las enfermedades, la presencia de herbivoros y la perdida de claves de mutualismo. Sin embargo en pocas ocasiones la hibridacion interespecifica se ha incluido entre las interacciones de tipo biotico que promueven la extincion. El objetivo de este trabajo es el de demostrar que la hibridacion puede contribuir a la extincion de una especie determinada, a traves de su eliminacion demografica y su asimilacion por otra especie congenerica que sea mucho mas abundante. Se sugiere que la clave para la asimilacion de la especie rara se encuentra en la formacion de subpoblaciones hibridas y se discuten aquellas variables que afectan a la proliferacion de los hibridos. Se muestra que el grado de abundancia de los hibridos depende en gran medida de la produccion de semilla hibrida, la adaptabilidad de los hibridos y la presion que ejercen las plagas y enfermedades. Asi mismo se discute como la hibridacion se ve favorecida por el grado de alteracion del habitat, la existencia de polinizadores no especializados y de barreras debiles de cruzamiento. Es poco probable que las consecuencias negativas de la hibridizacion se vean compensadas por la inmigracion de individuos desde poblaciones coespecificas. Damos ejemplos de este proceso en la flora de islas. Se sugiere que la hibridizacion es una amenaza creciente para la persistencia de las especies raras debido a que muchas de las barreras ecologicas han sido severamente alteradas por actividades humanas.

606 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared three quantitative methods for choosing 5% of all the 10 × 10 km grid cells in Britain to represent the diversity of breeding birds: hotspots of richness, which selects the areas richest in species; hotspots with range-size rarity (narrow endemism); and sets of complementary areas, which select areas with the greatest combined species richness.
Abstract: Biodiversity conservation requires efficient methods for choosing priority areas for in situ conservation management. We compared three quantitative methods for choosing 5% (an arbitrary figure) of all the 10 × 10 km grid cells in Britain to represent the diversity of breeding birds: (1) hotspots of richness, which selects the areas richest in species; (2) hotspots of range-size rarity (narrow endemism), which selects areas richest in those species with the most restricted ranges; and (3) sets of complementary areas, which selects areas with the greatest combined species richness. Our results show that richness hotspots contained the highest number of species-in-grid-cell records (with many representations of the more widespread species), whereas the method of complementary areas obtained the lowest number. However, whereas richness hotspots included representation of 89% of British species of breeding birds, and rarity hotspots included 98%, the areas chosen using complementarity represented all the species, where possible, at least six times over. The method of complementary areas was also well suited to supplementing the existing conservation network. For example, starting with grid cells with over 50% area cover by existing “Sites of Special Scientific Interest,” we searched for a set of areas that could complete the representation of all the most threatened birds in Britain, the Red Data species. The method of complementary areas distinguishes between irreplaceable and flexible areas, which helps planners by providing alternatives for negotiation. This method can also show which particular species justify the choice of each area. Yet the complementary areas method will not be fully able to select the best areas for conservation management until we achieve integration of some of the more important factors affecting viability, threat, and cost.

592 citations


Journal ArticleDOI
TL;DR: The role of large carnivores as keystone species is discussed in this article, where a plan for recovery of grizzly bears (Ursus arctos) proposed by Shaffer (1992) covers, in part, 34% of the state of Idaho (compared to 8% covered by a U.S. Fish and Wildlife Service proposal).
Abstract: Large carnivores need large areas of relatively wild habitat, which makes their conservation challenging. These species play important ecological roles and in some cases may qualify as keystone species. Although the ability of carnivores to control prey numbers varies according to many factors and often is effective only in the short term, the indirect effects of carnivores on community structure and diversity can be great. Perhaps just as important is the role of carnivores as umbrella species (i.e., species whose habitat area requirements encompass the habitats of many other species). Conservation areas large enough to support populations of large carnivores are likely to include many other species and natural communities, especially in regions such as the Rocky Mountains of Canada and the United States that have relatively low endemism. For example, a plan for recovery of grizzly bears (Ursus arctos) proposed by Shaffer (1992) covers, in part, 34% of the state of Idaho (compared to 8% covered by a U.S. Fish and Wildlife Service proposal) and would capture 10% or more of the statewide ranges of 71% of the mammal species, 67% of the birds, 61% of the amphibians but only 27% of the reptiles native to Idaho. Two-thirds (67%) of the vegetation types in Idaho would have 10% or more of their statewide area included in the Shaffer plan. The U.S. Fish and Wildlife Service recovery zones provide a much poorer umbrella. The umbrella functions of large carnivores are expected to be poorer in regions with high endemism. The application of metapopulation concepts to large carnivore conservation has led to proposals for regional reserve networks composed of wilderness core areas, multiple-use buffer zones, and some form of connectivity. The exceptional vagility of most large carnivores makes such networks feasible in a region with low human population density, such as the Rocky Mountains, but mortality risks still need to be addressed. Roads are a major threat to carnivore recovery because of barrier effects, vehicle collisions, and increased accessibility of wild areas to poachers. Development, especially for tourism, is also becoming a threat in many parts ofthe region. Los carnivoros mayores requieren de extensas areas de habitat relativamente natural, lo cual hace de su conservacion un reto. Estas especies juegan un papel ecologico importante y pueden, en algunos casos, ser consideradas como especies clave. Aunque la capacidad de los carnivoros para controlar la abundancia de sus presas varia en funcion de numerosos factores y a menudo solo es a corto plazo, los efectos indirectos de los carnivoros sobre la estructura y diversidad de la comunidad pueden ser grandes. Posiblemente igual importancia tiene el papel de los carniivoros como especies sombrilla (i.e., especies cuyos requerimientos de extension del habitat comprenden los habitats de muchas otras especies). Es probable que areas de conservacion suficientemente grandes para mantener poblaciones de carnivoros mayores incluyan muchas otras especies y comunidades naturales, especialmente en regiones con endemismo relativamente bajo, tal como las Montanas Rocallosas. Por ejemplo, un plan de recuperacion de osos pardos (Ursus arctos) propuesto por Schaffer (1992) abarca, en parte, el 34% del estado de Idaho (comparado con el 8% del Servicio de Pesca y Vida Silvestre de los E.U.) abarcaria el 10% o mas de los rangos estatales de distribucion del 71% de las especies de mamiferos, 67% de aves y 61% de anfibios, pero solo el 21% de reptiles nativos de Idaho. Dos tercios (67%) de los tipos de vegetacion de Idaho tendrian 10% o mas de su extension en el estado incluida en la propuesta de Schaffer. Las zonas de recuperacion propuestas por el Servicio de Pesca y Vida Silvestre constituyen una sombrilla Mas pequena. Se espera que en regiones de alto endemismo la funcion cobertora de los carnivoros mayores es mas pobre. La aplicacion del concepto de metapoblacion en la conservacion de carnivoros mayores ha llevado a propuestas de redes regionales de reservas interconectadas de alguna manera y compuestas por zonas nucleo y zonas de amortiguamiento de usos multiples. La vagilidad excepcional de la mayoria de los carnivoros permite dichas redes en una region con baja densidad poblacional humana, tal como las Montanas Rocallosas, aunque los riesgos de mortalidad deberan ser considerados. Los caminos son una amenaza mayor para la recuperacion de carnivoros por fungir como barreras, propiciar colisiones con vehiculos y facilitar el acceso a cazadores furtivos. El desarrollo especialmente para el turismo tambien se esta convirtiendo en una amenaza en muchas partes de la region.

582 citations


Journal ArticleDOI
TL;DR: In this article, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.).
Abstract: Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested. Se estimo la propension de las comunidades de plantas riberenas a la invasion a partir del porcentaje de especies invasoras encontradas a lo largo del Rio Adaour (Sudoeste de Francia) y a lo largo del arroyo Lookout/Rio McKenzie/Rio Willamette (Cascadas Centrales, Oregon, EUA). A escala de porche una la propension de la comunidad de plantas riberenas a las invasiones fue comparda, entre un sitio excepcionalmente rico en el Rio Adour y parches seleccionados en las cuencas de Hoh y Dungeness (Peninsula Olimpica, Washington, EUA). Las especies invasoras representaron un 24% de las 1396 especies de Adour y un 30% de las 851 especies de McKenzie. Estas tambien representaron un 24% de las 148 especies de la cuenca de Hoh y un 28% de las 200 especies de la cuenca de Dungeness. Tendencias similares fueron encontradas a lo largo del Rio Adour y del McKenzie, para los cambios en el numero total de especies y en el porcentaje de especies invasoras por sitio. Estas tendencias podrian estar relacionadas a los regimenes intermedios de perturbacion y a la estructura fisica de los corredores riberenos. Los factores climaticos y humanos tambien se encuentran involucrados en estos cambios longitudinales. Se encontro una relacion lineal positiva entre el numero total de especies y el porcentaje de especies invasoras observado en cada sitio. A una escala de parche, la mayoria de las muestras de la comunidad contenian especies invasoras. Sin bien, los parches vegetativos maduros parecieron ser propensos a la invasion, las comunidades mas jovenes presentaron mas especies invasoras que las comunidades mas antiguas. En cuanto a los corredores en su totalidad, se encontro una relacion lineal positiva entre la riqueza total de especies y el porcentaje de especies invasoras en cada tipo de parche para el sito mas rico del Rio Adour. Esta relacion puede ser explicada parcialmente por las caracteristicas del paisaje, consideradas dentro de un contexto sucesional. Se sugiere el uso de reglas empiricas y la importancia de los sistemas riberenos para el monitoreo de la conservacion de grupos de especies locales y regionales.

Journal ArticleDOI
TL;DR: In this paper, the authors reviewed European and North American and Japanese literature on ungulate traffic collisions and found no strong evidence of the effects of permanent warning signs, 90° light mirrors, scent, or acoustic fencing on the number of kills per crossing.
Abstract: The expansion of highways and roads can fragment natural habitats and thus decrease the viability of ungulate subpopulations. It can also increase the number of vehicle collisions with wildlife. Although collisions apparently contribute to only a minor part of the annual mortality for most ungulate populations, they have become a serious road-safety problem in Europe, the United States, and Japan. To better understand this threat to biodiversity and road safety, we reviewed European and, secondarily, North-American and Japanese literature on ungulate traffic collisions. In contrast to the results of some long-term studies, we argue that the relationship suggested between the number of road kills and traffic volume is confounded by population dynamics, changes in traffic volume, and sampling intensity. Although sexes may run distinct seasonal risks of collision, the age and sex composition of road kills reflect population structure in the field. We also argue that observed seasonal and daily patterns in the number of road kills, related to life-history features of the species involved, should form the template for solutions to the problem. We found no strong evidence of the effects of permanent warning signs, 90° light mirrors, scent, or acoustic fencing on the number of kills per crossing. To reduce the risk of ungulate traffic collisions, we recommend a combination of fencing and wildlife passages for roads and railroads that combine high traffic volume with high speed. For secondary roads we recommend seasonal application of intermittently lighted warning signs, triggered if possible by the ungulates. We emphasize the need for educational programs.

Journal ArticleDOI
TL;DR: The authors examined and compared human attitudes toward wolves (Canis lupus), grizzly bears (Ursus arctos horribilis), and mountain lions (Puma concolor) in North America, with an emphasis on the Rocky Mountains of the United States and Canada.
Abstract: We examined and compared human attitudes toward wolves (Canis lupus), grizzly bears (Ursus arctos horribilis), and mountain lions (Puma concolor) in North America, with an emphasis on the Rocky Mountains of the United States and Canada. Primary research, literature review, and secondary data were in- cluded in the analysis. Wolves were historically persecuted by Euro-American settlers, but they have been the focus of a significant attitudinal transformation during the latter half of this century. Many now view the wolf in positive and protective ways. Considerable variation remains, however, in contemporary attitudes. At- titudes toward mountain lions have been highly ambivalent, never assuming the prominence or clarity of views on wolves. The behavior and physiology of the species, along with human psychological factors, are im- portant reasons for the difference in human perceptions of wolves and mountain lions. We also examined at- titudes toward grizzly bears. Many indigenous cultures revered grizzly bears, although European settlers were interested in exploiting and eliminating them. Today, perceptions of grizzly bears range from positive to negative. Our recommendations include targeting key groups with education programs, building support through the use of spokespeople within the target groups, integrating human and ecological concerns, and de- signing species-specific education initiatives in some cases.

Journal ArticleDOI
TL;DR: In this article, the authors propose guidelines for hygiene and quarantine procedures and for monitoring the parasite status of both captive and free-living animals to reduce potential disease risks presented by wildlife translocations.
Abstract: Threats posed to conservation programs by the translocation of pathogens along with the translocation of host species are being increasingly recognized However, publications on this subject have appeared primarily in veterinary literature which often is not read widely by those who fund, plan, or carry out the majority of wildlife translocations The problem of wildlife disease and translocations has been written about in detail recently, but in almost all cases has been limited to exploring the immediate effects of pathogens on the target species I discuss the possible adverse effects of wildlife translocations that result from disease transmission In addition to examining the effects on target species, I discuss the possible direct and indirect effects of parasite translocations on sympatric species and on the evolution of ecosystems in the long-term To reduce potential disease risks presented by wildlife translocations, I propose some guidelines for hygiene and quarantine procedures and for monitoring the parasite status of both captive and free-living animals En forma creciente, estan siendo reconocidas las amenazas a las que se encuentran expuestos los programas de conservacion debido a la translocacion de patogenos junto con la translocacion de especies de animales objeto Sin embargo, las publicaciones sobre este tema han aparecido principalmente en la literatura veterinaria especializada, la cual frecuentemente no es leida por aquellos que proveen los fondos, planean o llevan a cabo la mayoria de las translocaciones de especies silvestres El tema de las enfermedades de las especies silvestres y las translocaciones ha sido considerado en detalle recientemente, pero en casi todos los casos ha sido limitado a explorar los efectos immediatos del patogeno sobre la especie objeto En el presente trabajo, discuta los posibles efectos adversos de la translocacion de especies silvestres que son causados por la transmision de enfermedades Ademas de examinar los efectos sobre las especies objeto de la translocacion, discuto los posibles efectos directos e indirectos de la translocacion del parasito sobre las especies simpatricas, asi como tambien sobre la evolucion a largo plazo del ecosistema Para finalizar, propongo algunos lineamientos basicos sobre los procedimientos de higiene y cuarentena y sobre el monitoreo del status del parasita de los animales en cautiverio y en libertad Estos lineamientos tienen la finalidad de reducir los riesgos potenciales de la transmision de enfermedades debido a la translocacion de especies silvestres

Journal ArticleDOI
TL;DR: Data suggest that competition with spotted hyaenas may limit or exclude wild dogs when hyaena density is high, and competition with lions appears less intense, but direct predation by lions on wild dogs is important.
Abstract: African wild dogs (Lycaon pictus) are endangered largely because their population-density is low under all conditions. Interspecific competition with larger carnivores may be a factor limiting wild dog density. The density of wild dogs on a 2600-km2 area of the Selous Game Reserve (Tanzania) was 0.04 adults/km2. Spotted hyaena (Crocuta crocuta) density for the same area was estimated by audio playbacks as 0.32 hyaenas/km2. Lion (Panthera leo) density, determined from the ratio of hyaenas to lions, was 0.11 lions/km2. Across six ecosystems including Selous, there were strong negative correlations between wild dog and hyaena densities (r = −0.92; p = 0.01) and between wild dog and lion densities (r = −0.91; p = 0.03). Hyaenas out-numbered wild dogs by ratios ranging from 8:1 to 122:1. Ratios of lions to wild dogs ranged from 3:1 to 21:1. The diets of hyaenas and wild dogs overlap extensively; those of wild dogs and lions show less overlap. Where hyaenas are common and visibility is good, interference competition from hyaenas at wild dog kills is common and reduces wild dogs’ feeding time. Where hyaena density is lower and visibility is poor, interference competition at wild dog kills is rare. Wild dogs are commonly killed by lions and occasionally by hyaenas. These data suggest that competition with spotted hyaenas may limit or exclude wild dogs when hyaena density is high. Competition with lions appears less intense, but direct predation by lions on wild dogs is important. Competition and predation by larger carnivores may be of broad importance to the conservation of wild dogs and other medium-sized carnivores. Los perros salvajes Africanos (Lycaon pictus), se encuentran en peligro debido principalmente a que su densidad poblacional es baja. La competencia interespecifica con carnivoros mayores, podria ser un factor que limita la densidad de los perros salvajes. La densidad de los perros salvajes en un area de 2600 km2 de la Reserva de Caza de Selous (Tanzania) fue de 0.04 adultos/km2. La densidad de la hiena moteada (Crocuta crocuta) en la misma zona, fue estimada en 0.32 hienas/km2. La densidad de los leones (Panthera leo) fue estimada a partir de la proporcion entre hienas y leones y fue de 0.11 leones/km2. Existieron fuertes correlaciones negativas entre la densidad de perros salvajes y la de las hienas (r = −0.92, P = 0.01) y entre aquella de los perros salvajes y la de los leones (r = −0.91, P = 0.03) a traves de seis ecosistemas, incluyendo al de Selous. Las hienas fueron mas numerosas que los perros salvajes con proporciones que variaron entre 8: 1 y 122:1. La proporcion entre leones y perros salvajes vario entre 3:1 y 21:1. Las dietas de las hienas y de los perros salvajes se superponen en forma extenso, mientras que las dietas de los perros salvajes y de los leones muestran una menor superposicion. En las areas donde las hienas son comunes y la visibilidad es buena, la competencia de interferencia de las hienas con las presas cazadas por los perros salvajes, es comun y reduce la longitud del periodo de alimentacion de los perros salvajes. En las areas donde la densidad de las hienas es baja y la visibilidad es pobre, la competencia por interferencia con las presas cazadas por los perros salvajes es baja. Los perros salvajes son comunmente cazados por los leones y ocasionalmente por las hienas. Estos datos sugieren que la competencia con las hienas moteadas podria limitar o excluir a los perros salvajes cuando la densidad de las hienas es alta. La competencia con los leones parece ser menos intensa, pero la de predacion directa de los leones sobre los perros salvajes es importante. La competencia y la de predacion por parte de carnivoros mayores podria ser de gran importancia para la conservacion de los perros salvajes y otros carnivoros de tamano intermedio.

Journal ArticleDOI
TL;DR: The authors of as discussed by the authors proposed that exotic pathogens may be responsible for some recent declines of amphibian populations on other continents and that the intercontinental spread of such pathogens is greatly facilitated by human activities such as the thriving international trade in aquarium fish.
Abstract: In the montane rain forests of eastern Australia at least 14 species of endemic, stream-dwelling frogs have disappeared or declined sharply (by more than 90%) during the past 15 years. We review available information on these declines and present eight lines of evidence that collectively suggest that a rapidly spreading, epidemic disease is the most likely responsible agent. The extreme virulence of the putative frog patbogen suggests it is likely exotic to Australian rain forests. We propose that exotic pathogens may be responsible for some recent declines of amphibian populations on other continents and that the intercontinental spread of such pathogens is greatly facilitated by human activities such as the thriving international trade in aquarium fish. Our hypothesis may help explain why some amphibian populations in seemingly pristine environments have mysteriously declined. En las selvas tropicales montanosas del este de Australia, al menos 14 especies endemicas de ranas que habitan en arroyos, han desaparecido o declinado en forma marcada (en mas de un 90%) durante los ultimos 15 anos. Revisamos la informacion disponible sobre esta declinacion y presentamos ocho lineas de evidencia que en conjunto sugieren que el agente responsable mas probable es la rapida dispersion de una enfermedad epidemica. La extrema virulencia del patogeno putativo de la rana sugiere un probable origen exotico de la selva tropical Australiana. Proponemos que los patogenos exoticos pueden ser responsables de algunas de las recientes declinaciones de las poblaciones de anfibios en ostros continentes. Mantenemos asi mismo que la dispersion intercontinental de tales patogenos esta siendo facilitada en gran medida por actividades humanas, tales como el prospero comercio internacional de los peces para acuarios. Nuestra hipotesis podria ayudar a explicar porque algunas poblaciones de anfibios en ambientes aparentemente pristinos ha declinado misteriosamente.

Journal ArticleDOI
TL;DR: In this paper, the authors synthesize empirical information for each large carnivore species in the Rocky Mountains regarding three basic mechanisms of resilience at different hierarchical levels: behavioral plasticity in foraging behavior that ameliorates flux in food availability, demographic compensation that mitigates increased exploitation, and dispersal that provides functional connectivity among fragmented populations.
Abstract: Large carnivores evolved behaviors and life-history traits that conferred resilience to environmental disturbances at various temporal and spatial scales. We synthesize empirical information for each large carnivore species in the Rocky Mountains regarding three basic mechanisms of resilience at different hierarchical levels: (1) behavioral plasticity in foraging behavior that ameliorates flux in food availability, (2) demographic compensation that mitigates increased exploitation, and (3) dispersal that provides functional connectivity among fragmented populations. With their high annual productivity and dispersal capabilities, wolves (Canis lupus) possess resiliency to modest levels of human disturbance of habitat and populations. Cougars (Puma concolor) appear to have slightly less resiliency because of more specific requirements for stalking habitat and lower biennial productivity. Grizzly bears (Ursus arctos horribilis) possess much less resiliency because of their need for quality forage in spring and fall, their low triennial productivity, and the strong philopatry of female offspring to maternal home ranges. Based upon limited information, wolverines (Gulo gulo) appear more susceptible to natural fluctuations in scavenging opportunities and may have lower lifetime productivity than even grizzly bears. By accelerating the rate and expanding the scope of disturbance, humans have undermined the resiliency mechanisms of large carnivores and have caused widespread declines. Both the resiliency profiles and the historical record attest to the need for some form of refugia for large carnivores. With their productivity and dispersal capability, wolves and cougars might respond adequately to refugia that are well distributed in several units across the landscape at distances scaled to successful dispersal (e.g., less than five home range diameters). With their lower productivity and dispersal capability, grizzly bears and wolverines might fare better in a landscape dominated by larger or more contiguous refugia. Refugia must encompass the full array of seasonal habitats needed by large carnivores and should be connected to other refugia through landscape linkages. La evolucion del comportamiento y de caracteristicas de la historia natural de los carnivoros mayores les ha conferido resistencia a perturbaciones ambientales en varias escalas temporales y espaciales. En este trabajo sintetizamos informacion empirica sobre cada especie de carnivoro mayor en las Montanas Rocallosas en relacion con tres mecanismos basicos de resistencia en distintos niveles jerarquicos: (1) plasticidad conductual en la conducta del forrajeo que mejora el flujo de disponibilidad de alimento, (2) compensacion demografica que atenua el incremento de la explotacion y (3) dispersion que proporciona conectividad funcional a las poblaciones fragmentadas. Los lobos (Canis lupus) son resistentes a niveles moderados de perturbacion humana de su habitat y poblaciones debido a su elevada productividad anual y sus capacidades de dispersion Los pumas (Puma concolor) aparentan ser ligeramente menos resistentes debido a que tienen requerimientos de habitat para acechar y una productividad bianual menor. Los osos pardos (Ursus arctos horribilis) son mucho menos resistentes debido a su necesidad de forraje de calidad en la primavera y el otono, su baja productividad trianual y la marcada filopatria de las hembras de la progenie por los rangos de hogar materno. Con base en informacion limitada, los carcayus (Gulo gulo) son aparentemente mas susceptible a las fluctuaciones naturales en las oportunidades de busqueda de alimento y podrian tener una productividad a lo largo de su vida aun menor a la de los osos pardos (Ursus arctos horribilis). Los humanos han minado los mecanismos de resistencia de los carnivoros mayores y provocado su declinacion al acelerar y expandir el alcance de las perturbaciones. Tanto los perfiles de resistencia, como el registro historico dan testimonio de la necesidad de establecer algun tipo de refugios para carnivoros mayores. Por su productividad y capacidad de dispersion, los lobos y pumas pueden responder adecuadamente en refugios bien distribuidos en varias unidades a lo largo del paisaje, espaciados para una dispersion exitosa (e.g. 5 diametros del rango de hogar). Debido a su menor productividad y capacidad de dispersion, los osos pardos y los carcayus podrian estar mejor en un paisaje dominado por refugios mas grandes o contiguos. Los refugios deben abarcar toda la serie de habitats estacionales que requieran los carnivoros mayores y deben estar conectados con otros refugios mediante corredores en el paisaje.

Journal ArticleDOI
TL;DR: In the Mombasa Marine National Park, a heavily fished area was converted into a marine reserve and the number of fishers allowed was slowly decreased between 1991 and 1992.
Abstract: Numbers offish and their wet weights were estimated in Kenyan coral-reef lagoons on seven reefs over 6 years. Two sites were protected from fishing for over 20 years, whereas the other five sites were heavily fished in recent years. A heavily fished site was converted into a marine park (Mombasa Marine National Park, approximately 10 km2 no fishing allowed), and the number of fishers allowed was slowly decreased between August 1991 and August 1992. The area adjacent to the park was converted into a marine reserve (only fishing traps, lines, and gill nets allowed) that provided fishing grounds for fishers excluded from the park. Data from a fish-landing site adjacent to the newly created marine park were collected for 3 years and analyzed to determine the effect of the park’s creation on fish catches. Results suggest that fishing in the reserve reduced fish wet weight by about a factor of 10 and reduced fish numbers and species richness by a factor of two. Both field studies and landing data suggest harvesting at a bionomic equilibrium. For example, approximately 65% of the landing site’s fishing grounds were protected with the creation of the park, and 65% of the fishers quit the studied landing, leaving nearly the same density of fishers in the remaining area (∼ 12 fishers/km2). Further, fishers using pull seines were excluded from the reserve, and their numbers were replaced by fishers using other gear (mostly basket traps). Although the overall catch per unit effort increased by about 110% after the park’s creation, the total fish landed decreased by 35% and the catch per unit effort decreased toward the end of the study period despite increasing fish abundance in the park. Although establishment of small parks elsewhere have increased the total catch, the large park we studied did not; one reason may have been the lower ratio of edge to park area of the large park. Alternatively, the park’s edge may have provided a good fishing area, so fishing effort may have been highest along the park’s edge. Consequently, a barrier may have been created that restricted fish dispersal to most of the reserve. Therefore, the area that had an increased catch was small (< 1 to 2 km from the edge) and could not compensate for the lost fishing area. Most fish species within the park showed recovery after fisher exclusion. Total fish wet weights 3 years after the fishers’ exclusion were 25% below the older marine parks. Poor recovery of the herbivoroas parrot and surgeonfish can account for much of this shortfall. Competition for resources with sea urchins appear to be slowing recovery of these two groups. A study site 2.5 km from the park’s southern boundary, in the reserve section of the protected area, showed no changes in fish abundance over the study period, despite changing gear regulations.

Journal ArticleDOI
TL;DR: Evidence is presented that predation by mosquitofish and crayfish may cause localized decline of newts in mountain streams of southern California.
Abstract: One goal of conservation biology is to explain population declines. We present field survey data and experimental evidence that implicate introduced predators as a possible cause of decline in the California newt (Taricha torosa). In 1994 and 1995 we surveyed 10 streams in the Santa Monica Mountains of southern California for amphibians. These streams contained California newts when surveyed between 1981 and 1986. Of the 10 streams surveyed in 1994, three contained introduced mosquitofish (Gambusia affinis) and/or crayfish (Procambarus clarkii). These three streams contained no California newt eggs, larvae, or adults. The seven streams without introduced predators contained California newts. We conducted laboratory and field experiments to determine if California newt larvae and egg masses are susceptible to predation by mosquitofish and crayfish. Results from these experiments indicate that crayfish consume California newt egg masses and that both mosquitofish and crayfish consume larval newts. In 24-hour field experiments, no newt larvae survived in crayfish enclosures, and only 13% of the larvae survived with mosquitofish. Newt larvae are known to have antipredator adaptations for native predators. Apparently, these adaptations are not adequate for coexistence with introduced crayfish or mosquitofish. Heavy rains in 1995 removed introduced crayfish from one stream. We found newt egg masses, larvae, and adults in that stream the following spring. This same stream showed no evidence of California newts when crayfish were present in matched-date surveys in 1994. These experiments and surveys present evidence that predation by mosquitofish and crayfish may cause localized decline of newts in mountain streams of southern California. Understanding the effects of nonnative species is an important step in preventing detrimental introductions in the future.

Journal ArticleDOI
TL;DR: In a comparison of elasticity matrices for 84 species of plants, the authors showed that the importance of recruitment from seed, stasis, and growth varies systematically between the groups se- melparous herbs, iteroparoas herbs of open habitats, forest herbs, shrubs, and trees.
Abstract: Population projection (Lefleovitch) matrices are now a standard method for quantifying and ana- lyzing the demography and population dynamics of plants. Elasticity analysis of such a matrix indicates the relative effect on the population growth rate (A) of small changes to matrix elements representing different transitions in the life cycle. In a comparison of elasticity matrices for 84 species of plants we show that the rel- ative importance of recruitment from seed (measured by composite elasticity F), stasis (measured by compos- ite elasticity L), and growth (measured by composite elasticity G) varies systematically between the groups se- melparous herbs, iteroparoas herbs of open habitats, forest herbs, shrubs, and trees. We discuss how this result might be used to construct rules of thumb useful in plant conservation. By looking in detaa at how A covarles with the composite elasticities F, I, and G among 16populations of the semelparoas herb Cirsium vulgare and among 15 populations of the rare iteroparoas herb Pedicularis furbishiae, we show that a naive interpretation of elasticities can give a misleading prescription for management. Instead, we show that elasticity analysis supports management prescriptions based upon the successional status of a species or upon its response to disturbance.

Journal ArticleDOI
TL;DR: In this article, the authors observed inter-habitat movements of fruit-eating birds in the eastern Amazonia using towers constructed at the interface between second-growth forest and an active and an abandoned pasture.
Abstract: From towers constructed at the interface between second-growth forest and an active and an abandoned pasture, we observed inter-habitat movements of fruit-eating birds in eastern Amazonia. The abandoned pasture was composed of grasses and forbs with a scattering of shrubs and small trees. The active pasture contained a low, uniform bed of grass. A total of 47 frugivorous bird species was recorded in the second-growth forest. We observed that 18 of these species frequented the adjacent abandoned pasture but only 3 were found in the adjacent active pasture. Fruit-eating birds flying from second-growth forest typically spent only a few minutes in the abandoned pasture, and their movements were generally restricted to a pasture belt of 1–80 m along the border with the second-growth forest. Most inter-habitat movement occurred during the rainy season, which coincided with a peak in fruit availability in the abandoned pasture. Just three bird species, Ramphocelus carbo, Tachyphonus rufus, and Thraupis episcopus, accounted for an estimated 70% of the total movement of frugivores between the second-growth forest and the abandoned pasture. All three species spent most of their time in the abandoned pasture foraging on shrubs and trees but exhibited differences in their preference for specific habitat elements and in their seed-defecation habits. An understanding of bird behaviors in altered landscapes provides important information to planners and policy makers concerned with protecting regional biodiversity and maintaining landscape integrity. This research provides a rationale for placing limits on the size of clearings in the Brazilian Amazon. Desde torres construidas en la interface, entre un bosque de crecimiento secundario y una pastura abandonada, observamos movimientos entre habitats de las aves frugivoras en la Amazonia oriental. La pastura abandonada se encontraba compuesta de pastos y forbias, con arbustos y arboles pequenos esparcidos. La pastura activa contenia una cubierta de pasto baja y uniforme. Un total de 47 especies de aves frugivoras fue registrado en el bosque de crecimiento secundario. Observamos que 18 de estas especies frecuentaron la pastura adyacente abandonada, pero solo 3 se encontraron en la pastura adyacente activa. Las aves frugivoras que volaban del bosque secundario, se quedaban, en la mayoria de los casos, por solo unos pocos minutos en la pastura abandonada y sus movimientos se encontraron generalmente restringidos a un cinturon de pasturas de 1–80 m de ancho a lo largo del borde con el bosque secundario. La mayoria del movimiento entre habitats ocurrio durante la estacion lluviosa, que coincidio con el pico de disponibilidad de frutas en la pastura abandonada. Solo tres especies de aves, Ramphocelus carbo, Tachyphonus rufus y Thraupis episcopus, fueron responsables del 70% del total de los movimientos de frugivoros entre el bosque de crecimiento secundario y la pastura abandonanda. Las tres especies ocuparon la mayor parte de su tiempo en la pastura abandonada alimentandose en arbustos y arboles, pero exhibieron diferencias en su preferencia por los elementos especificos del habitat y en sus habitos de defecacion de semillas. Una comprension del comportamiento de las aves en paisajes alterados provee importante informacion para los planificadores y aquellas personas involucradas en la toma de decisiones en relacion con la proteccion de la biodiversidad regional y el mantenimiento de la integridad del paisaje. Esta investigacion provee una justificacion para la imposicion de limites en el tamano de los clareos de la Amazonia brasilena.

Journal ArticleDOI
TL;DR: In this paper, a 3-year field experiment was conducted in the boreal mixed wood forest of Alberta to determine empirically whether songbirds use buffer strips connecting forest reserves as corridors and if they move along these buffer strips more frequently than they cross adjacent clearcuts.
Abstract: We conducted a 3-year field experiment to measure the frequency of bird movements through riparian buffer strips before and after harvesting of adjacent forest. Our study was conducted in the boreal mixed wood forest of Alberta and was designed to determine empirically whether songbirds use riparian buffer strips of forest connecting forest reserves as corridors and if they move along these buffer strips more frequently than they cross adjacent clearcuts. We used mist nets to obtain an index of the frequency of bird movement in the forest, and we observed bird movements across adjacent clearcuts for comparison. We predicted that the frequency of movement would be greater (1) in buffer strips after harvesting of adjacent forest than before harvesting, (2) in buffer strips than across clearcuts and, (3) in buffer strips than at control sites (lakeshore forest with no adjacent clearcuts). After adjusting for year-to-year variation in abundance, we found that capture rates increased significantly from pre- to post-harvest, but only for juveniles. Capture rates of adults decreased immediately after harvesting, probably because of the removal of an adjacent source of birds that previously moved through the lakeside forest. Movement rates of forest species in clearcuts were significantly lower than capture rates in the forest. The number of adults captured was positively correlated with the number of territories in the buffer strips, indicating that most birds captured were probably residents. The number of local territories was a poor predictor of juvenile captures, supporting the notion that juveniles were likely dispersing individuals. Our results indicate that buffer strips enhanced movements of juveniles (i.e., acted as corridors) and maintained movement rates of adults. Furthermore, there appeared to be a threshold distance between reserves below which birds may be less reluctant to fly across openings, making corridor use less important. Durante 3 anos realizamos un experimento de campo para medir la frecuencia de movimiento de aves a traves de franjas riparaias amortiguadoras antes y despues de talado en el bosque adyacente. Nuestro estudio se llevo a cabo en el bosque boreal mixto de Alberta y fue disenado para empiricamente determinar si las paserinas utilizan como corredores alas franjas riparias amortiguadoras de bosque que conectan reservas y si se mueven a lo largo de estas franjas amortiguadoras mas frecuentemente que a traves de campos abiertos adyacentes. Utilizamos redes de niebla para obtener un indice de la frecuencia de movimiento de aves en el bosque y para comparar observamos los movimientos de aves e a traves de los campos abiertos adyacentes. Predijimos que la frecuencia de movimiento seria mayor (1) en franjas amortiguadoras despues de la tala del bosque adyacente que antes, (2) en franjas amortiguadoras que en campos abiertos y (3) en franjas amortiguadoras que en los sitios control (bosque a orilla de laguna sin campos abiertos adyacentes). Despues de ajustar la variacion anual de abundancia, encontramos que las tasas de captura incrementaron significativamente de pre- a post- tala, pero solo para juveniles. Las tasas de captura de adultos decrecieron inmediatamente despues de la tala, probablemente por la remoscion de una fuente adyacente de aves que previamente se movian a traves del bosque a orilla de laguna. Las tasas de movimiento de especies de bosque a traves de campos abiertos fueron significativamente menores que las tasas de captura en el bosque. El numero de adultos capturados se correlaciono positivamente con el numero de territorios en las franjas amortiguadoras, lo cual indica que la mayoria de las aves capturadas probablemente eran residentes. El numero de territorios locales fue un pronosticador pobre de captura de juveniles, lo cual soporta la idea de que los juveniles posiblemente eran individuos dispersantes. Nuestros resultados indican que las franjas amortiguadoras favorecieron los movimientos de juveniles (i.e. funcionaron como corredores) y mantuvieron las tasas de movimiento de adultos. Mas aun, aparentemente hubo un umbral de distancia entre reservas debajo del cual las aves son menos renuentes a volar a traves de campos abiertos, lo que reduce la importancia del uso de corredores.

Journal ArticleDOI
TL;DR: In this paper, a transect of the Sierra Nevada mountains in western North America that was carefully studied in the early 1900s was revisited, and it was shown that at least five of the seven frog and toad species in the area have suffered serious declines.
Abstract: There has been much concern about widespread declines among amphibians, but efforts to determine the extent and magnitude of these declines have been hampered by scarcity of comparative inventory data. We resurveyed a transect of the Sierra Nevada mountains in western North America that was carefully studied in the early 1900s. Our comparisons show that at least five of the seven frog and toad species in the area have suffered serious declines. One species has disappeared from the area entirely and a second species, formerly the most abundant amphibian in the area, has dwindled to a few small remnant populations. These declines have occurred in a relatively undisturbed, protected area and show some of the same patterns noted in other reports of amphibian declines. Introduced predatory fish, possibly interacting with drought-induced loss of refuge habitats, have contributed to the decline of some species. However, the overall cause of these dramatic losses remains unknown. Ha existido mucha preoccupacion acerca de las declinaciones generalizadas entre anfibios, pero los esfuerzos para determinar el alcance y magnitud de estas declinaciones han sido limitados por la escasez de registros de datos comparativos. En el presente estudio reevaluamos una transecta de las montanas de la Sierra Nevada, en el oeste de Norte America, que fue estudiada cuidadosamente a principios del 1900. Nuestras comparaciones muestran que por to menos cinco de las siete especies de ranas y sapos en el area han sufrido serias declinaciones. Una especie ha desaparecido totalmente del area y una segunda especie, que era el anfibio mas abundante en el area, se ha reducido a unas pocas poblaciones remanentes. Estas declinaciones han ocurrido en areas relativamente protegidas y poco perturbadas, y muestran algunos de los mismos patrones evidenciados en otros reportes sobre la declinacion de anfibios. Los pecos predadores introducidos, que posiblemente interactuen con la perdida de habitat para refugio debido a las sequias, han contribuido a la declinacion de algunas especies. Sin embargo, las causas generales de estas dramaticas perdidas continuan siendo ignoradas.

Journal ArticleDOI
TL;DR: In this paper, the authors combined broad-scale field sampling with historical anialyses of museum records to quantify anmphibian de- clines in California's Great Central Valley.
Abstract: Declines in amphibian populations are rarely reported on the community or ecosystem level. We combined broad-scale field sampling with historical anialyses of museum records to quantify anmphibian de- clines in California's Great Central Valley. Overall, amphibians showed an unambiguous patterna of decline, although the intensity of decline varied both geographically and taxonomically. The greatest geograiphicail de- cline was detected in the counties of the Sacramento and Sana Joaquin Valleys. Two species, Rana aurora and Bufo boreas were identified as the most affected by decline, whereas Pseudacris regilla was the least affected. The Coast Range counties had little or no detectable decline. We provide new evidence implicating introduced predators as a primary threat. Introduced predators occur at lower elevations than native species, and our data indicate that for some native species there has been signaificanat restriction to higher elevation sites from a formerly broader distribution. Our historical approach provides a strategy for identifying declining anm- phibian communities that complements more detailed, long-term mnonitoring programs and provides an as- sessment of the pattern of change that is a necessary prerequisite for the development offield experiments that test hypothesized mechanisms of change.

Journal ArticleDOI
TL;DR: In this article, the authors quantified fragmentation due to roads in a 30,213-ha section of the Medicine Bow-Routt National Forest in sout heastern Wyoming with several indices of landscape structure using a geographic information system.
Abstract: The contribution of roads to forest fragmentation has not been adequately analyzed. We quantified fragmentation due to roads in a 30,213-ha section of the Medicine Bow-Routt National Forest in sout heastern Wyoming with several indices of landscape structure using a geographic information system. The number of patches, mean patch area, mean interior area, mean area of edge influence, mean patch perimeter, total perimeter, and mean patch shape identified patch- and edge-related landscape changes. Shannon-Wiener diversity, dominance, contagion, contrast, and angular second moment indicated effects on landscape diversity and texture. Roads added to forest fragmentation more than clearcuts by dissecting large patches into smaller pieces and by converting forest interior habitat into edge habitat. Edge habitat created by roads was 1.54–1.98 times the edge habitat created by clearcuts. The total landscape area affected by clearcuts and roads was 2.5–3.5 times the actual area occupied by these disturbances. Fragmentation due to roads could be minimized if road construction is minimized or rerouted so that its fragmentation effects are reduced. Geographic information system technology can be used to quantify the potential fragmentation effects of individual roads and the cumulative effects of a road network on landscape structure.

Journal ArticleDOI
TL;DR: In this paper, the authors compared observed patterns of persistence of mamiferos in Tanzanian parks to predictions derived from earlier extinction models and found that the predictions of the S1 models of Soule et al. (1979) and Burkey (1994) match very closely the observed pattern of persistence in Tanzania's parks.
Abstract: 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 Soule et al. (1979) and Burkey (1994) and the S2 and S3 models of Soule 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. La teoria de la biogeografia de islas predice que se perderan especies en “islas” creadas por la fragmentacion de regiones continentales. Varios parques de Tanzania se estan convirtiendo rapidamente en habitats “islas” como resultado de asentamientos humanos, desarrollo agricultural y al activa eliminacion de vida silvestre en tierras adyacentes. La tasa de extincion de mamiferos de en seis parques de Tanzania durante los ultimos 35–83 anos es significativa e inversamente se relaciona con el area del parque, sugiriendo que el creciente aislamiento de los parques ha sido un factor que contribuye a la extincion de mamiferos grandes. Patrones observados de persistencia de mamiferos en parques de Tanzania son comparados con predicciones derivadas de modelos de extincion elaborados tiempo atras. Las predicciones de los modelos S1 de Soule et al. (1979) se aproximan a los patrones observados de persistencia de mamiferos en los parques de Tanzania. La Perdida de especies de mamiferos probablemente continuara, particularmente en los parques pequenos. El establecimiento de corredores que interconecten los parques del Norte de Tanzania podrian ayudar a reducir la perdida potencial de especies en el futuro.

Journal ArticleDOI
TL;DR: In this paper, an incidence function model is derived from a linear first-order Markov chain of the presence or absence of a species in a habitat patch, which can be parameterized with "snapshot" presence/absence data from a patch network.
Abstract: The incidence function model is derived from a linear first-order Markov chain of the presence or absence of a species in a habitat patch. The model can be parameterized with “snapshot” presence/absence data from a patch network. Using the estimated parameter values the Markov chain can be iterated in the same or in some other patch network to generate quantitative predictions about transient metapopulation dynamics and the stochastic steady state. We tested the ability of the incidence function model to predict patch occupancy using extensive data on an endangered butterfly, the Glanville fritillary (Melitaea cinxia) Parameter values were estimated with data collected from a 50-patch network in 1991. In 1993 we surveyed the entire geographic range of the species in Finland, within an area of 50 × 70 km2, with 1502 habitat patches (dry meadows) of which 536 were occupied. Model predictions were generated for the 1502 patches and were compared with the observed pattern of occupancy in 1993. The model predicted patch occupancy well in more than half of the study area, but prediction was poor for one quarter of the area, probably because of regional variation in habitat quality and because metapopulations may have been perturbed away from the steady state. The incidence function model provides a practical tool for making quantitative predictions about metapopulation dynamics of species living in fragmented landscapes.

Journal ArticleDOI
TL;DR: The problem of value-loaded and socially charged discourse can be resolved by properly understanding the role of analysis and by pursuing a socially grounded pluralistic approach to problem definition and research methodology as mentioned in this paper.
Abstract: Natural scientists are being encouraged by environmental and developmental agencies to define and operationalize the concept of sustainability in a "scientific" manner Such an approach is fraught with dangers because values, opinions, and social influences are an inextricablepart of science, especially applied science Natural scientists' attempts to define sustainability, particularly to decide what should be sustained, cannot therefore be value-neutral They simply end up shifting value judgments to different levels by choosing either a single obvious objective, an arbitra y range of objectives, or an arbitra y method of aggregating dif- ferentpreferences This lack of self-reflectiveness on the part of scientists has important consequences for the direction of research and its political implications Natural scientists should heed lessons from earlier cases of scientists' involvefnent in policy and redefine the terms of reference before shouldering their social burden The dilemma of pursuing objective science in a value-loaded and socially charged discourse can be resolved by properly understanding the role of analysis and by pursuing a socially grounded pluralistic approach to problem definition and research methodology La sostenibilidad y la carga que soportan 10s cientificos Resumen: Los cientqico naturalistas son incitados por Ins agencias ambientales y de desarrollo para que definan y operacionalicen de una manera '%ientfica" el concept0 de sostenibilidad Tal enfoque estu lleno de peligros, ya que 10s valores, las opiniones y las influencias sociales son una parte intrinseca de b ciencia, es- pecialmente de la ciencia aplicada Los intentos de 10s cientzjCicos naturalistaspor definir la sostenibilidad, 1) en particular para decidir que es lo que se debe sostener, no pueden por lo tanto ser neutrales Los juicios de valor son simplefnente cambiados al escoger un objetivo unico "obvio," una serie arbitraria de objetizjos o bien un me'todo arbitrario de agregacidn de diferentes preferencias Esta falta de auto-reflexidn por parte de los cientvicos tiene consecuencias importantes en la direccidn de b investigacidn y para sus implicaciones politicas Los cientficos naturalistas harian bien en prestar atencidn u las lecciones de los casos anteriores de implicacidn de cientqicos en la politica y en redefinir 10s terminos i'e referencia, antes de eclnarse sobre la es- palda la "carga" social El dilema de buscar una ciencia objetiua en un discurso cargado de valores sociales puede resolverse mediante una apropiada comprensidn del rol del "andlisis"~) mediante la busqueda de zdn enfoque socialplumlista en la definicidn de losproblenzas y en la ~netodologia de la investigacidn

Journal ArticleDOI
TL;DR: In this article, a model of forest fragmentation effects on densities of forest-breeding birds was developed and data from an active industrial forest landscape was provided to test the model and empirical data indicate that densities increased within a forest stand soon after the onset of fragmentation as a result of displaced individuals packing into remaining habitat.
Abstract: The early development of forest fragmentation effects on forest organisms is poorly understood partly because most fragmentation studies have been done in agricultural or suburban landscapes, long after the onset of fragmentation. We develop a temporal model of forest fragmentation effects on densities of forest-breeding birds and provide data from an active industrial forest landscape to test the model. The model and our empirical data indicate that densities of several forest-dwelling bird species can increase within a forest stand soon after the onset of fragmentation as a result of displaced individuals packing into remaining habitat. Along with higher densities in the newly formed fragments, pairing success in one species, the Ovenbird (Seiurus aurocapillus), was lower in fragments than nonfragments, possibly due to behavioral dysfunction resulting from high densities. Thus, density was inversely related to productivity. The duration and extent of increased densities following onset of fragmentation depends on many factors, including the sensitivity of a species to edge and area effects, the duration and rate of habitat loss and fragmentation, and the proximity of a forest stand to the disturbance. Incipient forest fragmentation may affect populations differently from later stages of fragmentation when the geometry of the landscape has reached a more stable configuration. Our model and data indicate, for reasons unrelated to traditional edge effects, that large tracts of forest can be important because they are relatively free from the variety of plant and animal population dynamics that might take place near new edges, including the encroachment of individuals displaced by habitat loss. Los efectos del desarrollo temprano de la fragmentacion del bosque sobre los organismos es poco conocido, en parte, porque la mayoria de los estudios de fragmentacion han sido llevados a cabo en paisajes agricolas o suburbanos mucho despues de iniciado el proceso de fragmentacion. En el presente trabajo desarrollamos un modelo temporal de la fragmentacion del bosque y sus efectos sobre las densidades de las aves que se crian en bosques y proveemos datos de un paisaje forestal industrial activo para probar el modelo. El modelo y nuestros datos empiricos indican que las densidades de varias especies de aves que habitan el bosque pueden incrementarse immediatamente despues del comienzo de la fragmentacion como resultado de la acumulacion de los individuos desplazados en el habitat remanente. Junto con las altas densidades en los nuevos fragmentos formados, el exito en el apareamiento en Seiurus aurocapillus fue mas bajo en los fragmentos que en el paisaje no fragmentado debido, posiblemente, a una disfuncion del comportamiento como resultado de las altas densidades. Por lo tanto, la densidad estuvo inversamente relacionada con la productividad. La duracion y la extension de las densidades incrementadas que siguen el inicio de la fragmentacion dependen de varios factores, incluyendo la sensbilidad de las especies a los bordes y n efectos del area, la duracion y la tasa de la perdida del habitat y la fragmentacion y la proximidad del bosque a la perturbacion. La fragmentacion incipiente del bosque puede afectar a las poblaciones en forma distinta que los estadios mas avanzados de fragmentacion, cuando la geometria el paisaje ha alcanzado una configuracion mas estable. Nuestro modelo y datos indican, por razones no relacionadas a los tradicionales efectos de los bordes, que las grandes areas continuas de bosque pueden ser importantes por que estas se encuentran relativamente libres de la dinamica poblacional de una gran variedad de plantas y animales que ocurren en la cercania de los nuevos bordes, incluyendo la intrusion de los individuos desplazados por la perdida del habitat.

Journal ArticleDOI
TL;DR: The recent reintroduction of the gray wolf (Canis lupus) to Yellowstone signifies a constructive change, but the overall record in the United States on large carnivore conservation remains poor as discussed by the authors.
Abstract: The recent reintroduction of the gray wolf (Canis lupus) to Yellowstone signifies a constructive change, but the overall record in the United States on large carnivore conservation remains poor. Many developing countries are determined to do a better job of conserving predators, including their critical habitat and prey populations. We describe current efforts to protect tigers (Panther tigris), jaguars (Panthera onca), and large-scale forest habitat in Asia, Central America, and Africa. These initiatives take a comprehensive approach that includes biological field research, the identification of local human interests, and a growing recognition of the need for cooperation across political lines. Though often supported by U.S. technical assistance, this international experience could be used better to inform and improve carnivore conservation efforts in North America. Failure to improve our domestic performance or to fully appreciate the contributions of far less developed countries could weaken global efforts to maintain and restore populations of large carnivores. La reciente reintroduccion del lobo en el Parque Nacional Yellowstone marca un cambio constructivo; sin embargo, el patron general de los Estados Unidos en conservacion de los grandes carnivores es pobre. La determinacion de muchos de Ios paises en desarrollo en la conservacion de los depredadores es mucho mas fuerte, incluyendo esfuerzos para la conservacion de habitat critico y poblaciones de presas. Se describen los esfuerzos que actualmente se estan haciendo para proteger tigres, jaguares y habitats boscosos de gran escala en Asia, America Central y Africa. Estas iniciativas tienen un enfoque amplio, que incluye investigaciones biologicas de campo, identificacion de intereses humanos locales, y el reconocimiento creciente de que se necesita cooperacion por encima de las lineas politicas. Aunque muchas veces apoyada por ayuda tecnica de los Estados Unidos, esta experiencia internacional puede ayudar a informar y mejorar la conservacion de los carnivoros en los Estados Unidos. Asi mismo, el no mejorar neustra situacion local, o el no apreciar las contribuciones de aquellas naciones menos desarrolladas, puede debilitar los esfuerzos globales para mantener y restaurar las poblaciones de grandes carnivoros.