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751.
In this paper we address the problem of estimation of the variance of a normal population based on a balanced as well as an unbalanced ranked set sample (RSS), which is a modification of the original RSS of McIntyre (1952).We have proposed several methods of estimation of variance by combining different unbiased between and within estimators, and compared their performances 相似文献
752.
Eduardo Soto-Galera Joel Paulo-Maya Eugenia López-López José Angel Serna-Hernández John Lyons 《Environmental management》1999,24(1):133-140
Chirostoma charari and C. compressum, and they are presumed extinct. Twelve (63%) of the remaining species had declines in distribution. Sixteen (80%) of the 20
localities sampled had lost species. The greatest declines occurred in Lago de Cuitzeo proper and in the lower portion of
the Río Grande de Morelia watershed. Species losses from the lake were attributable to drying and hypereutrophication of the
lake because of substantial reductions in the amount and quality of tributary inputs, whereas losses from the Río Grande de
Morelia watershed were the result of pollution from agricultural, municipal, and industrial sources, especially in the region
around the city of Morelia. Three localities in the upper portion of the Río Grande de Morelia watershed—Cointzio reservoir,
La Mintzita spring, and Insurgente Morelos stream—contained most of the remaining fish species diversity in the basin and
deserve additional protection. Fish faunal changes indicated major declines in the health of aquatic ecosystems in the Morelia–Cuitzeo
basin. 相似文献
753.
本文报告了川江上游核排污水环境中90 Sr 的监测结果。表明:90 Sr 在河水和底泥中的含量与排污距离密切相关,在不同水生物种之间的蓄积分布有显著性差异,其中底泥和含钙高的生物对90 Sr 有较强的浓集作用。所以,选用指示性物种能提高90 Sr 监测灵敏度,是核污染监测的较好方法。 相似文献
754.
755.
珠江三角洲地区酸雨污染简析 总被引:15,自引:0,他引:15
以珠江三角洲地区主要城市的降水常规监测数据资料为依据,简要分析了该地区降水酸度和酸雨频率年度变化情况,并对酸雨的危害进行了初步的探讨。研究结果表明:该地区酸雨污染依然严重,降水酸度与二氧化硫污染等因素有关,酸雨类型以硫酸型为主。 相似文献
756.
José A. Donázar Alejandro Travaini Olga Ceballos Alejandro Rodríguez Miguel Delibes Fernando Hiraldo 《Behavioral ecology and sociobiology》1999,45(1):55-65
Phenotype-limited interference models assume competitive asymmetries among conspecifics and unequal sharing of resources.
Their main prediction is a correlation between dominance status and patch quality: dominant individuals should preferentially
exploit better-quality habitats. We tested assumptions and predictions of the phenotype-limited interference model in Andean
condors (Vultur gryphus), a New World vulture with strong sexual size dimorphism (males are 30–40% heavier than females). We recorded searching birds
in habitats differing in quality: mountains and plains. We also observed scavenging behaviour at 20 sheep carcasses, and videotaped
5 of them. Intraspecific hierarchy at carcasses was based on size: males dominated females and, within each sex, older birds
dominated younger ones. Adult males and juvenile females occupied extreme positions in the feeding hierarchy. Aggression was
directed at those individuals belonging to lower hierarchical levels. In high-quality areas (mountains), more condors arrived
at carcasses. Juvenile females were more often observed searching in low-quality areas (plains), far from breeding areas and
main roost sites. GLM analyses of individual behaviour showed that the hierarchy did not influence time of arrival, but low-ranking
individuals spent more time at carcasses, especially if the number of condors at arrival was high. Additionally, low-ranking
condors spent less time feeding at carcasses when individuals of higher hierarchical levels were present. On the other hand,
the number of condors present had a positive effect on feeding rates of dominant individuals, probably because of a reduction
in individual vigilance. These results support most of the assumptions and predictions of the phenotype-limited distribution
model, although a spatial truncated distribution between phenotypes was not observed. Asymmetric feeding pay-off, unequal
parental roles and sexual selection constraints could favour sexual divergence in body size in Andean condors.
Received: 6 April 1998 / Accepted after revision: 11 July 1998 相似文献
757.
Testis size variation in the greenfinch Carduelis chloris : relevance for some recent models of sexual selection 总被引:3,自引:0,他引:3
Interspecific evidence that testis size responds to selection caused by sperm competition has been obtained from many taxa. However, little is known about the sources of intraspecific variation in testis size, although such variation may have functional significance. Variation in testis size and asymmetry was studied within and between eight geographically separated (and genetically differentiated) populations of greenfinches Carduelis chloris. The relationships between testis size and plumage brightness (degree of yellowness) and the prevalence of haematozoan infections were also investigated in three of these populations, as they related to the predictions of the immunocompetence handicap hypothesis, and Møller's hypothesis relating directional testis asymmetry to phenotypic quality. There were large differences between populations in testis size, with males from northern populations having larger testes than those from southern populations. Within populations, large testes were associated with larger body size and greater age. When the influence of these factors was removed statistically, males with large testes were more likely to be infected with haematozoan parasites, and had brighter yellow plumage. No evidence was found that directional asymmetry in testis size was related to either of these measures of phenotypic quality. These results are consistent with the hypothesis that males with large testes, while signalling higher phenotypic quality as revealed by increased plumage brightness, also pay a cost in terms of reduced immunocompetence, revealed by the increased probability of infection in these males. That these patterns were similar in three different populations adds further strength to these conclusions. Our results suggest that studying the sources of variation in testis size among individuals can reveal interesting processes in sexual selection. 相似文献
758.
The host size model, an adaptive model for maternal manipulation of offspring sex ratio, was examined for the parasitoid
wasp Spalangia endius. In a Florida strain, as the model predicts, daughters emerged from larger hosts than sons, but only when mothers received
both small and large hosts simultaneously. The pattern appeared to result from the mother's ovipositional choice and not from
differential mortality of the sexes during development. If sex ratio manipulation is adaptive in the Florida strain, it appears
to be through a benefit to daughters of developing on large hosts rather than through a benefit to sons of developing on small
hosts. Both female and male parasitoids were larger when they developed on larger hosts. For females, developing on a larger
host (1) increased offspring production, except for the largest hosts, (2) increased longevity, (3) lengthened development,
and (4) had no effect on wing loading. For males, development on a larger host had no effect on any measure of male fitness
– mating success, longevity, development duration, or wing loading. In contrast, a strain from India showed no difference
in the size of hosts from which daughters versus sons emerged, although both female and male parasitoids were larger when
they developed on larger hosts. These results together with previous studies of Spalangia reveal no consistent connection between host-size-dependent sex ratio and host-size-dependent parasitoid size among strains
of S. endius or among species of Spalangia.
Received: 28 October 1998 / Received in revised form: 20 May 1999 / Accepted: 30 May 1999 相似文献
759.
760.
街谷地区CO污染现状分析 总被引:1,自引:0,他引:1
本文分析了典型街谷地区CO污染的现状及其浓度的垂直分布和水平分布的变化情景。由监测结果可知,街谷地区CO浓度是较高的,而且峰值出现在采暖期。 相似文献