排序方式: 共有17条查询结果,搜索用时 31 毫秒
1.
TERRA R. KELLY JESSE GRANTHAM DANIEL GEORGE ALACIA WELCH JOSEPH BRANDT L. JOSEPH BURNETT KELLY J. SORENSON MATTHEW JOHNSON ROBERT POPPENGA DAVID MOEN JAMES RASICO JAMES W. RIVERS CARIE BATTISTONE CHRISTINE K. JOHNSON 《Conservation biology》2014,28(6):1721-1730
Large‐scale poisoning events are common to scavenging bird species that forage communally, many of which are in decline. To reduce the threat of poisoning and compensate for other persistent threats, management, including supplemental feeding, is ongoing for many reintroduced and endangered vulture populations. Through a longitudinal study of lead exposure in California condors (Gymnogyps californianus), we illustrate the conservation challenges inherent in reintroduction of an endangered species to the wild when pervasive threats have not been eliminated. We evaluated population‐wide patterns in blood lead levels from 1997 to 2011 and assessed a broad range of putative demographic, behavioral, and environmental risk factors for elevated lead exposure among reintroduced California condors in California (United States). We also assessed the effectiveness of lead ammunition regulations within the condor's range in California by comparing condor blood lead levels before and after implementation of the regulations. Lead exposure was a pervasive threat to California condors despite recent regulations limiting lead ammunition use. In addition, condor lead levels significantly increased as age and independence from intensive management increased, including increasing time spent away from managed release sites, and decreasing reliance on food provisions. Greater independence among an increasing number of reintroduced condors has therefore elevated the population's risk of lead exposure and limited the effectiveness of lead reduction efforts to date. Our findings highlight the challenges of restoring endangered vulture populations as they mature and become less reliant on management actions necessary to compensate for persistent threats. Patrones Espaciotemporales y Factores de Riesgo por Exposición a Plomo en Cóndores de California Durante 15 Años de Reintroducción 相似文献
2.
Abstract: Many mammalian carnivores are in local or global decline. To slow this process, continued planning to protect these species is warranted, Still, the data bases that we have at our disposal do not adequately document population requirements for space at scales appropriate for conservation planning. To illustrate this problem, we have collected published data for 214 population censuses of carnivores. We tested for a relationship between the number of individuals censused and the size of study site for our entire data set. We conducted the same test for each family, for which we obtained sufficient and qualifying census data With areas ranging from less than 10 km2 to over 40,000 km2 , we obtained a significant regression (p < .001; r2 = 76%) for the sample as a whole. We examined the distribution of densities with increasing area and found that the relationship was not constant but decreased We noticed that numbers per census-area size increased with a slope (m < 1). We also noticed that the sizes of study areas were unevenly distributed Only 7% of the studies in our sample censused regions larger than 10,000 km2 . It remains unclear to what extent and how the density decreases with increasing scale We expect that extrapolations from small scales to larger ones are likely to underestimate space requirements for carnivores. 相似文献
3.
BENJAMIN S. RAMAGE DOUGLAS SHEIL HANNAH M.W. SALIM CHRISTINE FLETCHER NUR‐ZATI A. MUSTAFA JOANN C. LURUTHUSAMAY RHETT D. HARRISON ELIZABETH BUTOD AHMAD DZAMIR DZULKIPLY ABD RAHMAN KASSIM MATTHEW D. POTTS 《Conservation biology》2013,27(2):364-372
Tropical forest ecosystems are threatened by habitat conversion and other anthropogenic actions. Timber production forests can augment the conservation value of primary forest reserves, but studies of logging effects often yield contradictory findings and thus inhibit efforts to develop clear conservation strategies. We hypothesized that much of this variability reflects a common methodological flaw, simple pseudoreplication, that confounds logging effects with preexisting spatial variation. We reviewed recent studies of the effects of logging on biodiversity in tropical forests (n = 77) and found that 68% were definitively pseudoreplicated while only 7% were definitively free of pseudoreplication. The remaining proportion could not be clearly categorized. In addition, we collected compositional data on 7 taxa in 24 primary forest research plots and systematically analyzed subsets of these plots to calculate the probability that a pseudoreplicated comparison would incorrectly identify a treatment effect. Rates of false inference (i.e., the spurious detection of a treatment effect) were >0.5 for 2 taxa, 0.3–0.5 for 2 taxa, and <0.3 for 3 taxa. Our findings demonstrate that tropical conservation strategies are being informed by a body of literature that is rife with unwarranted inferences. Addressing pseudoreplication is essential for accurately assessing biodiversity in logged forests, identifying the relative merits of specific management practices and landscape configurations, and effectively balancing conservation with timber production in tropical forests. Pseudoreplicación en Bosques Tropicales y Efectos Resultantes Sobre la Conservación de Biodiversidad 相似文献
4.
Abstract: Die-offs of cordgrass are pervasive throughout western Atlantic salt marshes, yet understanding of the mechanisms precipitating these events is limited. We tested whether herbivory by the native crab , Sesarma reticulatum , is generating die-offs of cordgrass that are currently occurring on Cape Cod, Massachusetts (U.S.A.), by manipulating crab access to cordgrass transplanted into die-off areas and healthy vegetation. We surveyed 12 Cape Cod marshes to investigate whether the extent of cordgrass die-off on creek banks, where die-offs are concentrated, was related to local Sesarma grazing intensity and crab density. We then used archived aerial images to examine whether creek bank die-off areas have expanded over the past 2 decades and tested the hypothesis that release from predation, leading to elevated Sesarma densities, is triggering cordgrass die-offs by tethering crabs where die-offs are pervasive and where die-offs have not yet been reported. Intensity of crab grazing on transplanted cordgrass was an order of magnitude higher in die-off areas than in adjacent vegetation. Surveys revealed that Sesarma herbivory has denuded nearly half the creek banks in Cape Cod marshes, and differences in crab-grazing intensity among marshes explained >80% of variation in the extent of the die-offs. Moreover, the rate of die-off expansion and area of marsh affected have more than doubled since 2000. Crab-tethering experiments suggest that release from predation has triggered elevated crab densities that are driving these die-offs, indicating that disruption of predator–prey interactions may be generating the collapse of marsh ecosystems previously thought to be exclusively under bottom-up control . 相似文献
5.
Two field studies were undertaken to investigate the nature of the relationships between job security, job satisfaction, organizational commitment, and withdrawal cognitions. Study 1 was conducted in an organization immediately following its acquisition by another company (N=137). Study 2 was conducted in an organization that had experienced a number of layoffs and expected more in the future (N=188). Covariance structure analysis was used to test for direct, complete mediating, and partial mediating effects. Study 2 was used to cross-validate the findings from study 1. Results from both studies provide strong support for the proposition that job satisfaction and organizational commitment mediate the effects of job security on withdrawal cognitions. The two studies diverge when explicating the nature of the relations between job security, satisfaction, and commitment. Study 1 suggests job satisfaction completely mediates the effects of job security on commitment. Study 2 suggests that both satisfaction and commitment mediate the relationship between job security and withdrawal cognitions. Contextual differences that may have contributed to these findings are discussed. © 1997 by John Wiley & Sons, Ltd. 相似文献
6.
E. C. M. PARSONS A. ALONSO AGUIRRE AMY L. BAUER LOUISE K. BLIGHT JOHN A. CIGLIANO MELINDA A. COLEMAN ISABELLE M. CÔTÉ MEGAN DRAHEIM STEPHEN FLETCHER MELISSA M. FOLEY REBECCA JEFFERSON MIRANDA C. JONES BRENDAN P. KELAHER CAROLYN J. LUNDQUIST JULIE‐BETH MCCARTHY ANNE NELSON KATHERYN PATTERSON LESLIE WALSH ANDREW J. WRIGHT WILLIAM J. SUTHERLAND 《Conservation biology》2014,28(5):1206-1214
The ocean provides food, economic activity, and cultural value for a large proportion of humanity. Our knowledge of marine ecosystems lags behind that of terrestrial ecosystems, limiting effective protection of marine resources. We describe the outcome of 2 workshops in 2011 and 2012 to establish a list of important questions, which, if answered, would substantially improve our ability to conserve and manage the world's marine resources. Participants included individuals from academia, government, and nongovernment organizations with broad experience across disciplines, marine ecosystems, and countries that vary in levels of development. Contributors from the fields of science, conservation, industry, and government submitted questions to our workshops, which we distilled into a list of priority research questions. Through this process, we identified 71 key questions. We grouped these into 8 subject categories, each pertaining to a broad component of marine conservation: fisheries, climate change, other anthropogenic threats, ecosystems, marine citizenship, policy, societal and cultural considerations, and scientific enterprise. Our questions address many issues that are specific to marine conservation, and will serve as a road map to funders and researchers to develop programs that can greatly benefit marine conservation. Setenta y Un Preguntas Importantes para la Conservación de la Biodiversidad Marina 相似文献
7.
How Many Plants Feed the World? 总被引:9,自引:0,他引:9
Abstract: FAO food supply data for 146 countries were analyzed to identify the plant commodities that account for the top 90% of each country's per capita supply of food plants by weighs calories, protein, and fat. The plant commodities were divided into two groups: species commodities, such as "cabbages," that can be attributed to particular species; and general commodities, such as "hydrogenated oils," whose species composition is not known. A total of 82 species commodities and 28 general commodities contribute 90% of national per capita supplies of food plants. The 82 species commodities consist of 103 species. Fifty-six of these commodities, comprising 75 species, individually account for 5% or more of at least one county's supply of a nutritional category (plant weight, plant calories, plant protein, plant fag. These figures are several times higher than previous findings that very few (7–30) plant species feed the world. The new figures are considered more accurate because they derive from national supply rather than global production data and from several separate measures of the importance of a food commodity rather than one. The results suggest that (1) plant species diversity remains a significant factor for world food supply; and (2) a conservation priority is to maintain both this wider away of species and the diversity of genetic variants that comprise each species. 相似文献
8.
9.
10.
MARK D. BERTNESS† CAITLIN CRAIN‡ CHRISTINE HOLDREDGE NICHOLAS SALA 《Conservation biology》2008,22(1):131-139
Abstract: Although primary productivity in salt marshes is thought to be controlled by physical forces, recent evidence suggests that human disturbances can drive a switch to consumer control in these ecologically valuable ecosystems. We tested the hypothesis that nitrogen enrichment can trigger consumer control in salt marshes in Narragansett Bay, Rhode Island, with (1) a field experiment in which we manipulated nutrient availability (with nutrient additions) and insect herbivory (with insecticide application), (2) a survey of 20 salt marshes that examined the relationship between marsh nutrient status and herbivore pressure, and (3) insect herbivore removal at high and low nutrient input sites to directly test the hypothesis that nutrient enrichment is increasing insect herbivory in these marshes. Experimental nitrogen eutrophication initially increased plant productivity but eventually led to reduced plant biomass due to insect herbivory, and our surveys revealed that marsh nitrogen supply was a good predictor of herbivore damage to plants. Insects had minimal impacts on primary productivity in pristine marshes, but suppressed primary productivity in eutrophic salt marshes by 50–75%. Thus, eutrophication is currently triggering consumer suppression of primary productivity in New England salt marshes and may ultimately jeopardize the ecological and societal services these systems provide. 相似文献