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251.
Ultrasonic examination in a thirty-eight year old woman about to undergo midtrimester amniocentesis suggested an intra-abdominal fetal mass confirmed by amniography. The mass was a grossly distended urinary bladder. The patient aborted spontaneously before chromosome analysis demonstrated a 47,XY, + 18 karyotype. 相似文献
252.
Parks as Shibboleths 总被引:1,自引:0,他引:1
253.
The Importance of Site-Specific Information in the Design of Policies to Control Pollution 总被引:2,自引:0,他引:2
The presence and concentration of pollutants in groundwater are influenced by geophysical processes and the behavior of economic agents. The purpose of this paper is to assess the importance of spatial variability in physical parameters in the design of efficient pollution regulations. Alternative tax policies are evaluated in terms of effects on farm profit utilizing a spatially distributed, dynamic simulation model which links economic behavior with the geophysical processes that determine groundwater quality. The empirical focus is the control of groundwater nitrates arising from irrigated agriculture in Malheur County, Oregon. Results indicate that a detailed accounting of spatial variance in physical parameters had little effect on selection of a cost-minimizing tax policy to control groundwater nitrate concentration. This result implies that relatively simple tax schemes and models to evaluate these tax schemes may be adequate in some settings. 相似文献
254.
Genetic Analyses to Establish Captive Breeding Priorities for Endangered Snake River Sockeye Salmon 总被引:3,自引:0,他引:3
Shawn A. Cummings Ernest L. Brannon Karen J. Adams & Gary H. Thorgaard 《Conservation biology》1997,11(3):662-669
The plight of the Snake River sockeye salmon presents a challenging genetic puzzle for conservation biologists. Although the Snake River sockeye has been declared endangered, assessment of captive breeding strategies are complicated because a healthy non-migratory strain of O. nerka (kokanee) resides in Redfish Lake, Idaho—the same lake the anadromous fish return to for spawning. The migration of 1-year-old fish (outmigrants) from the lake each year and the observation of non-migratory fish spawning in areas previously used by the sockeye further complicate the issue. We estimated the relatedness of these strains by direct examination of their genetic similarity. Mixed DNA fingerprint analyses suggested that the outmigrants were more closely related to the anadromous sockeye than to the kokanee. Closer analysis using a probe, One-HO.8, to examine allele frequencies at a single locus revealed polymorphism in a number of O. nerka populations. Within the Redfish Lake populations this probe detected an allele present at 0.21 frequency in the kokanee (n = 43), 0.01 (n = 324) in the outmigrants, and absent among 13 anadromous fish. These results support a close genetic relationship of the outmigrants to the anadromous sockeye and the probable utility of the outmigrants in a captive breeding program to restore the anadromous strain. 相似文献
255.
Fungi cultivated by fungus-growing ants (Attini: Formicidae) are passed on between generations by transfer from maternal
to offspring nest (vertical transmission within ant species). However, recent phylogenetic analyses revealed that cultivars
are occasionally also transferred between attine species. The reasons for such lateral cultivar transfers are unknown. To
investigate whether garden loss may induce ants to obtain a replacement cultivar from a neighboring colony (lateral cultivar
transfer), pairs of queenright colonies of two Cyphomyrmex species were set up in two conjoined chambers; the garden of one colony was then removed to simulate the total crop loss
that occurs naturally when pathogens devastate gardens. Garden-deprived colonies regained cultivars through one of three mechanisms:
joining of a neighboring colony and cooperation in a common garden; stealing of a neighbor's garden; or aggressive usurpation
of a neighbor's garden. Because pathogens frequently devastate attine gardens under natural conditions, garden joining, stealing
and usurpation emerge as critical behavioral adaptations to survive garden catastrophes.
Received: 16 June 2000 / Accepted in revised form: 14 September 2000 相似文献
256.
257.
UVR-absorbing mycosporine-like amino acids (MAAs) were detected in tissues of Strongylocentrotus purpuratus and in ten species of Rhodophyte macroalgae (eight previously untested) collected from intertidal microhabitats in November and January 2006?C2007 in Central California (35°09??N, 120°45??W). In sea urchins, MAA concentrations were higher in ovaries than testes, while epidermal concentrations were similar between sexes. Ovaries and epidermal tissues had similar MAA signatures and broadband UVA/UVB absorbance, while testes had a narrower absorption ranges shifted toward higher energy wavelengths. Sea urchins occupying pits in the substrate exhibited lower MAA concentrations than those outside pits, suggesting adult microhabitat may impact UV protection. Light levels did not influence gonadal MAA concentrations, but correlated with elevated epidermal MAA concentrations for males in the sunniest microhabitat. This study suggests sex and habitat strongly influence MAA concentrations among individual S. purpuratus and that allocation of MAA sunscreens to tissues in response to UVR is sex-dependent. 相似文献
258.
259.
This paper reviews a workshop discussion postulated on the notion that social, economic and behavioural factors are responsible
for the creation of environmental hazards and benefits that, in turn, can affect human health, with concomitant effects on
future social well-being. The workshop case study centred on environmental health investigations, public engagement and partnership
work undertaken following the death of two neighbouring children in Cheshire. Discussion included questions of causality and
generalisability. It revealed how the attribution of responsibility for environmental damage to health is fraught with difficulties.
It may often militate against an informed and open debate among interested parties, with concomitant implications for reducing
the danger from environmental hazards. To improve communication, vocabulary needs to be free from jargon and acronyms, and
differences in conceptual approach between different disciplines need to be better understood. The definition of the ‘community’
is itself far from clear-cut, yet questions of how to involve this community in intervention processes are important ones.
The workshop identified a clear need for better, more considered forms of communication with communities and the public if
fears are to be allayed, but recognised the additional costs that this would incur. 相似文献
260.
Perspectives of the Scientific Community on the Status of Ecological Risk Assessment 总被引:1,自引:0,他引:1
/ Views from a wide variety of practicing environmental professionals on the current status of ecological risk assessment (ERA) indicate consensus and divergence of opinion on the utility and practice of risk assessment. Central to the debate were the issues of whether ERA appropriately incorporates ecological and scientific principle into its conceptual paradigm. Advocates argue that ERA effectively does both, noting that much of the fault detractors find with the process has more to do with its practice than its purpose. Critics argue that failure to validate ERA predictions and the tendency to over-simplify ecological principles compromise the integrity of ERA and may lead to misleading advice on the appropriate responses to environmental problems. All authors felt that many improvements could be made, including validation, better definition of the ecological questions and boundaries of ERA, improved harmonization of selected methods, and improvements in the knowledge base. Despite identified deficiencies, most authors felt that ERA was a useful process undergoing evolutionary changes that will inevitably determine the range of environmental problems to which it can be appropriately applied. The views expressed give ERA a cautious vote of approval and highlight many of the critical strengths and weaknesses in one of our most important environmental assessment tools.KEY WORDS: Ecological risk assessment; Ecology; Probability 相似文献