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排序方式: 共有803条查询结果,搜索用时 46 毫秒
741.
We present a robust sampling methodology to estimate population size using line transect and capture-recapture procedures for aerial surveys. Aerial surveys usually underestimate population density due to animals being missed. A combination of capture-recapture and line transect sampling methods with multiple observers allows violation of the assumption that all animals on the centreline are sighted from the air. We illustrate our method with an example of inanimate objects which shows evidence of failure of the assumption that all objects on the centreline have probability 1 of being detected. A simulation study is implemented to evaluate the performance of three variations of the Lincoln-Petersen estimator: the overall estimator, the stratified estimator, and the general stratified estimator based on the combined likelihood proposed in this paper. The stratified Lincoln-Petersen estimator based on the combined likelihood is found to be generally superior to the other estimators. 相似文献
742.
We develop the non-parametric maximum likelihood estimator (MLE) of the full Mbh capture-recapture model which utilizes both initial capture and recapture data and permits both heterogeneity (h) between animals and behavioural (b) response to capture. Our MLE procedure utilizes non-parametric maximum likelihood estimation of mixture distributions (Lindsay, 1983; Lindsay and Roeder, 1992) and the EM algorithm (Dempsteret al., 1977). Our MLE estimate provides the first non-parametric estimate of the bivariate capture-recapture distribution.Since non-parametric maximum likelihood estimation exists for submodels Mh (allowing heterogeneity only), Mb (allowing behavioural response only) and M0 (allowing no changes), we develop maximum likelihood-based model selection, specifically the Akaike information criterion (AIC) (Akaike, 1973). The AIC procedure does well in detecting behavioural response but has difficulty in detecting heterogeneity. 相似文献
743.
Andrew M. Bouwma Kenneth J. Howard Robert L. Jeanne 《Behavioral ecology and sociobiology》2005,59(2):222-233
Behavior in eusocial insects likely reflects a long history of selection imposed by parasites and pathogens because the conditions of group living often favor the transmission of infection among nestmates. Yet, relatively few studies have quantified the effects of parasites on both the level of individual colony members and of colony success, making it difficult to assess the relative importance of different parasites to the behavioral ecology of their social insect hosts. Colonies of Polybia occidentalis, a Neotropical social wasp, are commonly infected by gregarines (Phylum Apicomplexa; Order Eugregarinida) during the wet season in Guanacaste, Costa Rica. To determine the effect of gregarine infection on individual workers in P. occidentalis, we measured foraging rates of marked wasps from colonies comprising both infected and uninfected individuals. To assess the effect of gregarines on colony success, we measured productivity and adult mortality rates in colonies with different levels of infection prevalence (proportion of adults infected). Foraging rates in marked individuals were negatively correlated with the intensity of gregarine infection. Infected colonies with high gregarine prevalence constructed nests with fewer brood cells per capita, produced less brood biomass per capita, and, surprisingly, experienced lower adult mortality rates than did uninfected or lightly infected colonies. These data strongly suggest that gregarine infection lowers foraging rates, thus reducing risk to foragers and, consequently, reducing adult mortality rates, while at the same time lowering per-capita input of materials and colony productivity. In infected colonies, queen populations were infected with a lower prevalence than were workers. Intra-colony infection prevalence decreased dramatically in the P. occidentalis population during the wet season.An erratum to this article can be found at 相似文献
744.
Kenneth R Stollery 《Journal of Environmental Economics and Management》1983,10(2):151-165
This article follows papers by Pindyck and Heal and Barrow in applying a Hotelling-type depletion model to a particular resource industry: in this case that of nickel. By means of the model the resource rent per ton of nickel is calculated as the proper index of extractive resource scarcity. The time path of this resource rent indicates that the model explains industry behavior well and that, as in the two previous studies, depletion has been an important determinant of prices and rents in this industry. 相似文献
745.
Kenneth S. Lyon 《Journal of Environmental Economics and Management》1981,8(4):330-344
The paper analyzes the effect of transportation (site specific) costs and the effect of mining (depletion) of the forest on the time path of the price and of the net price of timber in two forestry models. The models differ in that one has zero costs and the other has positive costs. The analyses yield the standard mining theory results for certain cases. They also yield extentions of these results for cases with growth of the harvested trees and/or regeneration on the harvested land. The paper concludes, as one would expect, that the theory of the mine is useful in analyzing the time path of the price of timber. 相似文献
746.
James N. Macri Kevin Spencer Kenneth Garver Philip D. Buchanan Burhan Say Nancy J. Carpenter Francoise Muller Andre Boué 《黑龙江环境通报》1994,14(2):97-103
The median maternal serum free beta human chorionic gonadotropin (hCG) multiple of the median (MOM) of 480 Down syndrome cases in the second trimester was 2·64, significantly greater than the reported median MOM of intact hCG (p<0·0001). In 234 of these cases from retrospective and prospective studies, the effectiveness of maternal serum free beta hCG was evaluated in combination with alpha-fetoprotein (AFP) and maternal age in second-trimester Down syndrome screening. Down syndrome detection in the gestational age range of 14–16 weeks was 82 per cent. In all gestational weeks (14–22), a 77·7 per cent Down syndrome detection rate was achieved. In prospective screening of 44 272 patients under the age of 35 years, 69 per cent of Down syndrome cases were detected (73 per cent in gestational weeks 14–16). The false-positive rate for the prospective study was 3·8 per cent. The use of free beta hCG combined with maternal serum AFP and maternal age-related risk for Down syndrome in a screening population (i.e., women under 35 years) yields an improved detection efficiency over other protocols. 相似文献
747.
One reach of a northern California stream, burned by intense wildfire in 1979, was studied to monitor changes and recovery
from the fire. Benthic macroinvertebrates collected three weeks and one to four, six, eight, and 11 years following the wildfire
were used to assess stream condition and compared to samples from a reach of a nearby unburned stream. Transportable sediment
was measured 11 years following the fire. The fire was also used as a worst case example to compare results with a standard
cumulative watershed effects assessment methodology.
Benthic invertebrate density and taxa richness of the burned reach were both low compared to the unburned reach three weeks
after the fire. Mean density was significantly higher in the burned reach in the three years following the fire, while taxa
richness was significantly lower in the burned reach over the same time period. Higher density and lower richness in the burned
reaches persisted throughout the study period but were not significant after three years. Mean Shannon diversity of the burned
reach was significantly lower than that of the unburned reach for each year of the study, although absolute differences diminished
throughout the 11-year study period.
Transportable sediment was significantly higher in the burned reach than the unburned comparison. Pearson correlations between
sediment and biological metrics were weak. Although the correlation between invertebrate diversity and a measure of watershed
disturbance (equivalent roaded acres) was high (r=0.95) for the burned watershed, the measure appeared to be a poor indicator of cumulative effects on stream condition. The
measure (ERA) was poorly correlated with invertebrate diversity in the unburned reach and, while the ERA calculations indicated
substantial recovery, biological and physical measures indicated recovery of the burned stream reach was incomplete. 相似文献
748.
ABSTRACT: Annual evapotranspiration from a watershed (ETws) is a function of annual precipitation (P) and fraction of the watershed covered by shrubs and trees (C). Other characteristics are not significant in explaining variance of ETws. A rational equation, ETws = (1-C) ETg + CETst, wherein ETg is the ET of herbaceous cover and ETst is the ET of shrubs and trees, is proposed. The equation has been calibrated for ET and P in inches for the watershed of Lake Cachuma on the Santa Ynez River. This equation, ETmax = 2.14(1-C)P0.647+ 4.53 C1.76 P0.68, is recommended for estimating maximum annual ET demand for conceptual models. Where C is not known, the upper limit of ET = f (P) may be approximated by use of 0.65 for C. The equation has been derived for large unmanaged watersheds. Applicability for evaluation of contemporary multiple purpose vegetation management should be determined by studies of the hydrology of small openings in shrub and tree cover. 相似文献
749.
750.
Kenneth H. Reckhow 《Journal of the American Water Resources Association》1996,32(5):929-935
ABSTRACT: The US Environmental Protection Agency is currently developing guidance for assessing environmental impact using biocriteria within a regulatory framework. Of particular interest are statistical methods of design and analysis to test for impairment of biological assemblages in stream ecosystems associated with water pollution. Current recommendations emphasize frequentist statistical methods with the problem expressed as one of classical hypothesis testing. An empirical Bayes approach is proposed here as an alternative and applied for multi-site inference. The advantages of an empirical Bayes approach, in particular the substantive contribution of collateral information from nearby sites, are discussed in contrast to traditional methods that employ site-specific information only. The approach is illustrated in an application concerning trends in the Index of Biotic Integrity (IHI) for the Scioto River in Ohio. 相似文献