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241.
Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parents investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.Communicated by D. Gwynne 相似文献
242.
Low level liquid radioactive waste discharges from the Sellafield nuclear fuel reprocessing plant in north west England had
generated environmental inventories of about 3 × 1016 Bq of137Cs, 6.8 × 1014 Bq of239,240Pu and 8.9 × 1014 Bq of241Am by 1990. Most of the239,240Pu and241Am and about 10% of the137Cs has been retained in a deposit of fine marine sediment close to the discharge point. The quantities of radionuclides discharged
annually from Sellafield decreased by two orders of magnitude from the mid-1970s to 1990 but estimated critical group internal
and external exposure decreased by less than one order of magnitude over this period. This indicates that during the period
of reduced discharges, radionuclides already in the environment from previous releases continued to contribute to the critical
group exposure and highlights the need to understand processes controlling the environmental distribution of the radionuclides.
Redistribution of the contaminated marine sediment is potentially of major significance in this context, in particular if
it results in transport of radionuclides to intertidal areas, where contact with the human population is relatively likely.
A review is presented of published work relating to Sellafield waste radionuclides in Irish Sea sediments. Data on temporal
and spatial trends in radionuclide concentrations and activity ratios are collated from a number of sources to show that the
dominant mechanism of radionuclide supply to intertidal areas is by redistribution of the contaminated marine sediment. The
implications of this mechanism of supply for trends in critical group radiation exposure are considered. 相似文献
243.
Polycyclic aromatic hydrocarbons storage by Fusarium solani in intracellular lipid vesicles 总被引:1,自引:0,他引:1
Verdin A Lounès-Hadj Sahraoui A Newsam R Robinson G Durand R 《Environmental pollution (Barking, Essex : 1987)》2005,133(2):283-291
Accumulation and elimination of polycyclic aromatic hydrocarbons (PAHs) were studied in the fungus Fusarium solani. When the fungus was grown on a synthetic medium containing benzo[a]pyrene, hyphae of F. solani contained numerous lipid vesicles which could be stained by the lipid-specific dyes: Sudan III and Rhodamine B. The fluorescence produced by Rhodamine B and PAH benzo[a]pyrene were at the same locations in the fungal hyphae, indicating that F. solani stored PAH in pre-existing lipid vesicles. A passive temperature-independent process is involved in the benzo[a]pyrene uptake and storage. Sodium azide, a cytochrome c oxidation inhibitor, and the two cytoskeleton inhibitors colchicine and cytochalasin did not prevent the transport and accumulation of PAH in lipid vesicles of F. solani hyphae. F. solani degraded a large range of PAHs at different rates. PAH intracellular storage in lipid vesicles was not necessarily accompanied by degradation and was common to numerous other fungi. 相似文献
244.
The logistics of bulk relief supplies 总被引:3,自引:0,他引:3
Roger Knott 《Disasters》1987,11(2):113-115
245.
246.
Euro Chlor Risk Assessment for the Marine Environment Osparcom Region: North Sea - Trichloroethylene
Jean-Charles Boutonnet Christ De Rooij Veronique Garny Andre Lecloux Roger Papp Roy S Thompson Dolf Van Wijk 《Environmental monitoring and assessment》1998,53(3):467-487
This risk assessment on trichloroethylene (TRI) was carried out specifically for the marine environment, according to the methodology laid down in the EU risk assessment Regulation (1488/94) and the Guidance Document of the EU New and Existing Substances Regulation (TGD, 1997). The study consists of the collection and evaluation of data on effects and environmental concentrations from analytical monitoring programs in large rivers and estuaries in the North Sea area. The risk is indicated by the ratio of the "predicted environmental concentrations" (PEC) and the "predicted no effect concentrations" (PNEC) for the marine aquatic environment. In total, 19 studies for fish, 30 studies for invertebrates and 14 studies for algae have been evaluated. Both acute and chronic toxicity studies have been taken into account and the appropriate assessment factors have been used to define a PNEC value of 150 µg/l. Most of the available monitoring data apply to rivers and estuaries and were used to calculate PECs. The most recent data (1991-1995) support a typical PEC of 0.1 µg TRI/l water and a worst case PEC of 3.5 µg TRI/l water. The calculated PEC/PNEC ratios give a safety margin of 40 to 1,500 between the predicted no effect concentration and the exposure concentration. Additional evaluation of environmental fate and bioaccumulation characteristics showed that no concern for food chain accumulation is expected. 相似文献
247.
Human influence on California fire regimes. 总被引:6,自引:0,他引:6
Alexandra D Syphard Volker C Radeloff Jon E Keeley Todd J Hawbaker Murray K Clayton Susan I Stewart Roger B Hammer 《Ecological applications》2007,17(5):1388-1402
Periodic wildfire maintains the integrity and species composition of many ecosystems, including the mediterranean-climate shrublands of California. However, human activities alter natural fire regimes, which can lead to cascading ecological effects. Increased human ignitions at the wildland-urban interface (WUI) have recently gained attention, but fire activity and risk are typically estimated using only biophysical variables. Our goal was to determine how humans influence fire in California and to examine whether this influence was linear, by relating contemporary (2000) and historic (1960-2000) fire data to both human and biophysical variables. Data for the human variables included fine-resolution maps of the WUI produced using housing density and land cover data. Interface WUI, where development abuts wildland vegetation, was differentiated from intermix WUI, where development intermingles with wildland vegetation. Additional explanatory variables included distance to WUI, population density, road density, vegetation type, and ecoregion. All data were summarized at the county level and analyzed using bivariate and multiple regression methods. We found highly significant relationships between humans and fire on the contemporary landscape, and our models explained fire frequency (R2 = 0.72) better than area burned (R2 = 0.50). Population density, intermix WUI, and distance to WUI explained the most variability in fire frequency, suggesting that the spatial pattern of development may be an important variable to consider when estimating fire risk. We found nonlinear effects such that fire frequency and area burned were highest at intermediate levels of human activity, but declined beyond certain thresholds. Human activities also explained change in fire frequency and area burned (1960-2000), but our models had greater explanatory power during the years 1960-1980, when there was more dramatic change in fire frequency. Understanding wildfire as a function of the spatial arrangement of ignitions and fuels on the landscape, in addition to nonlinear relationships, will be important to fire managers and conservation planners because fire risk may be related to specific levels of housing density that can be accounted for in land use planning. With more fires occurring in close proximity to human infrastructure, there may also be devastating ecological impacts if development continues to grow farther into wildland vegetation. 相似文献
248.
Roger H. von Haefen Daniel J. Phaneuf 《Journal of Environmental Economics and Management》2003,45(3):612-630
Continuous and count data demand system models have emerged as attractive alternatives to the discrete choice random utility maximization models (RUMs) that currently dominate the seasonal, multi-site recreation demand literature. This paper compares the frameworks conceptually and investigates their empirical performance with a common data set. Although the two modeling approaches employ substantially different behavioral and econometric assumptions, results from a recreation application based on the 1997 Iowa Wetlands Survey suggest that qualitatively similar policy inferences arise from the competing structures. 相似文献
249.
Summary Seasonal variation in mean hind tibia length and mean testes length is investigated in the yellow dung fly, Scathophaga stercoraria (L.). There is a cycle in mean hind tibia length and mean testes length over a season. The body size curve peaks later than the testes length curve, showing that there is no fixed relationship between the two variables. The causes of variation in testes size and its influence on copula duration are experimentally examined. Increasing the number of Drosophila eaten per day leads to increased mature testes length. Males with larger testes copulate for longer than males with smaller ones, and smaller males copulate for longer than do larger males. While testes shrivel with successive copulas, copula duration remains constant. The more females a male is prepared to copulate with in a day (up to five), the longer he copulates with each. The shrinkage of the testes of males collected throughout a day suggests that males copulate with an average of 4 females per day. The costs of sperm production are thus shown to have a significant influence on the copula duration.Offprint requests to: P.I. Ward at the second address 相似文献
250.
Jenkins RA Ilgner RH Tomkins BA Peters DW 《Journal of the Air & Waste Management Association (1995)》2004,54(2):229-241
Protocols have been developed and applied for the generation of aerosols that are likely to be comparable to those encountered in field settings for the calibration of easily transportable/portable real-time particle monitors. Aerosols generated were simulated environmental tobacco smoke, cedar wood smoke, cooking oil fumes, and propane stove particles. The time-integrated responses of three nephelometers and a monitor for particle-bound polynuclear aromatic hydrocarbons (PAH) were compared with gravimetric respirable suspended particulate matter (RSP) in a controlled-atmosphere chamber. In general, the monitor responses increased linearly with increasing mass concentration. However, the two monitors that reported mass per volume concentrations tended to overreport the actual RSP concentrations by factors up to 4.4. The real-time PAH monitor did not respond to cooking oil fumes, indicative of little PAH being present in the aerosol. One of the monitors that has been used in a variety of studies reported in the literature (DustTrak) was collocated with gravimetric RSP samplers in several hospitality venues in the Louisville, KY, area. Field studies indicated that the units overreported actual RSP concentrations by factors of 2.6-3.1, depending on whether the sampling was conducted in the nonsmoking or smoking sections of the facilities. 相似文献