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排序方式: 共有360条查询结果,搜索用时 15 毫秒
31.
CHRISTOPHER FIELD CHRISTOPHER LUND NONA CHIARIELLO & BARBARA MORTIMER 《Global Change Biology》1997,3(3):197-206
Experimental grassland ecosystems, in microcosms 0.2 m in diameter and with a 0.95 m soil column, varied in their responses to elevated partial pressure of CO2 (pCO2 ) and altered moisture inputs. Ecosystems on moderately fertile sandstone soil and with a typical mix of moderately fast-growing sandstone species, responded to elevated pCO2 with decreases in mid-season evapotranspiration of nearly 50%. This pattern reversed at the end of the growing season, and sandstone ecosystems under elevated pCO2 continued active transpiration farther into the summer drought. The sandstone ecosystems appeared to convert mid-season water conservation into increased late-season growth. Effects of increased pCO2 on ecosystem evapotranspiration were much smaller in ecosystems with very infertile serpentine soil and a diverse mixture of slow-growing serpentine species. 相似文献
32.
BARBARA ŁOTOCKA EWA OSIŃSKA 《Botanical journal of the Linnean Society. Linnean Society of London》2010,163(1):70-86
The anatomy and ultrastructure of internodes, leaves and petals were compared in Hypericum elegans, H. inodorum, H. olympicum, H. forrestii and two genotypes of H. perforatum. Internode anatomy was variable between species with respect to the structure of the cortical and pith parenchyma, including the presence of secretory reservoirs. Also, the secondary growth was more extensive in shrubs, i.e. H. inodorum and H. forrestii. In leaves, phloem secretory reservoirs were formed in all species, mesophyll secretory reservoirs were absent only in H. elegans and internal nodules were present only in H. elegans and H. perforatum. The petals differed between species in the mesophyll structure and the occurrence and location of secretory structures. The phloem secretory reservoirs lacked sheaths, whereas these were distinct in the mesophyll reservoirs. Other ultrastructural traits of the reservoirs were similar in all the species studied, with the exception of the leucoplast ultrastructure. In internal nodules, the inner cells vs. sheath cells differed in the number of vesicles and other membranous structures and plastid ultrastructure. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 70–86. 相似文献
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Investigating species incidence over habitat fragments of different areas—a look at error estimation
BARBARA TAYLOR 《Biological journal of the Linnean Society. Linnean Society of London》1991,42(1-2):177-191
The use of incidence functions and their error structure is explored as a means of interpreting patterns present in fragmented systems. Incidence functions describe the probability of a species' presence on a fragment. The only information required for an incidence function is presence/absence data for a number of fragments of known size. Methods are developed for establishing prediction bounds on the incidence function. The example developed uses data from mammals on isolated mountaintops. Distributions of number of species expected on a fragment predicted the actual number of species well, but prediction of identities of species on small fragments was poor. Although the number of species expected on an assembly of small fragments compared to a single large fragment of the same total area was nearly always equal, the identity of species differed. Species with large area requirements were never found on any number of small fragments; species which occurred with a medium probability over most fragments had a higher probability of being present in an assembly of small fragments than on a single large fragment. 相似文献
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BARBARA ZIMMERMANN PETTER WABAKKEN HÅKAN SAND HANS C. PEDERSEN OLOF LIBERG 《The Journal of wildlife management》2007,71(4):1177-1182
Abstract: To estimate wolf (Canis lupus) kill rates from fine-scale movement patterns, we followed adult wolves in 3 territories of the Scandinavian wolf population using Global Positioning Systems (GPS) during the winters of 2001–2003. The resulting 6 datasets of 62–84 study days gave a total of 8,747 hourly GPS positions. We visited clusters of positions in the field on average 8.8 days after positioning and found moose (Alces alces) killed by wolves during the study period on 74 (8%) of the 953 clusters. The number of positions and visits to a cluster, their interaction, and the proportion of afternoon positions were significant fixed effects in mixed logistic-regression models predicting the probability of a cluster containing a wolf-killed moose. The models, however, displayed a poor goodness-of-fit and were not a suitable tool for estimating kill rates from positioning data alone. They might be used to reduce fieldwork by excluding unlikely clusters, although the reduction was not substantial. We discuss proximate factors (i.e., human disturbance and access to prey) as well as ultimate factors (i.e., social organization, intra-guild dominance, and litter size) as potential causes of the observed high temporal and spatial variation in prey-handling. For similar future kill-rate studies, we recommend increasing field efforts and shortening positioning intervals. 相似文献
35.
MONIKA SCHIESS-MEIER SANDRA RAMSAUER TEFO GABANAPELO BARBARA KÖNIG 《The Journal of wildlife management》2007,71(4):1267-1274
Abstract: Problem Animal Control Registers, where farmers report livestock losses due to predators as a prerequisite for financial compensation, allow quantifying the human-predator conflict. We analyzed such registers from the Kweneng District of Botswana to assess the impact of native predators on livestock over 3 years. Leopards (Panthera pardus), lions (Panthera leo), wild dogs (Lycaon pictus), brown hyenas (Hyaena brunnea), and cheetahs (Acinonyx jubatus) altogether claimed 2,272 head of livestock. During 2002, the year with the highest impact, the number of animals reported depredated (954) represented 0.34% of the livestock in the district. Leopards and lions caused 64% of the losses. Leopard livestock predation mainly affected calves and was consistent over the district and over time. In contrast, lion predation concentrated on adult cattle, was characterized by local hot spots close to reserve borders, decreased with increasing distance to a reserve, and increased during 2002, an unusually dry year. Interviews with 60 farmers and herders within 30 km of Khutse and Central Kalahari Game Reserves revealed an annual loss of 2.2% of their livestock to predators. Here, small farms (max. 100 domestic animals) suffered relatively higher losses than large, commercial farms, not only due to predation (small farms: 11.7%; large farms: 1.0%) but also from other causes (small: 12.6%; large: 2.8%), even though herders on large farms guarded 5 times more livestock per person than those on small farms. To reduce livestock predation in most of the district where lions are absent, we recommend maternity corrals for pregnant females and calves to better protect vulnerable calves during day and night. In areas close to a reserve where lions roam, herders' incentives to keep all livestock protected in a corral at night have to be enhanced because, according to the registers, only 3 predation cases were reported to have happened inside a corral. 相似文献
36.
PETTER WABAKKEN HÅKAN SAND ILPO KOJOLA BARBARA ZIMMERMANN JON M. ARNEMO HANS C. PEDERSEN OLOF LIBERG 《The Journal of wildlife management》2007,71(5):1631-1634
Abstract: We document a new record dispersal for wolves worldwide. The natal straight-line dispersal distance of a Global Positioning System-collared female wolf from the Scandinavian population was 1,092 km from southeast Norway to northeast Finland, with a multistage actual travel distance of >10,000 km. Natural gene flow to the isolated, inbred Scandinavian wolf population may occur if survival of dispersers is improved. 相似文献
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39.
Reclaiming Applied Anthropology: Its Past, Present, and Future 总被引:1,自引:0,他引:1
Growing concerns about anthropology's impact in both academia and the broader social arena have led to calls for more "public" and more relevant anthropology. In this article, we expand on these exhortations, by calling for systematic joining of critical social theory with application and pragmatic engagement with contemporary problems. We argue for the repositioning of applied anthropology as a vital component of the broader discipline and suggest that it should serve as a framework for constructing a more engaged anthropology. In revisiting disciplinary history and critiques of applied anthropology, we demonstrate the central role that application has played throughout anthropology's evolution, address common misconceptions that serve as barriers to disciplinary integration, examine the role of advocacy in relation to greater engagement as well as the relationship of theory to practice, and conclude with an assessment of the diverse work that is subsumed under the inclusive rubric of "anthropology in use." 相似文献
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