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381.
Sperm allocation in an uncertain world 总被引:3,自引:0,他引:3
Models of optimal sperm allocation are constructed using stochastic dynamic programming techniques, yielding predictions
about sperm allocation when males mate sequentially, breeding time is finite, sperm stores are limited and females vary in
quality. The models suggest that uncertainty of future reproductive opportunities should favour withholding of sperm, so that
males tend to allocate less (for a given level of stored sperm) earlier in the breeding season. This effect is more pronounced
the greater the variance in female quality. We also show that while allocation will be influenced by mate value, it is not
necessarily optimal to allocate preferentially to high-quality females, since the benefits of a higher-quality mate may be
offset by increased risk of rejection of sperm or higher sperm competition. The relationship between mate quality and level
of allocation will depend strongly on the amount of remaining stored sperm, with males whose supplies are depleted being more
likely to favour lower-quality partners.
Received: 12 September 1997 / Accepted after revision: 28 June 1998 相似文献
382.
For intersexual selection to occur, it is necessary that females choose between males. It is now well appreciated that constraints
exist, which preclude females sampling all the available males in a population. These constraints are likely to have caused
the evolution of sampling rules (such as the “best-of-n” rule) by which females sample males. Here we investigate the impact of female subsampling of the male population, not on
the evolution of sampling behaviour, but on the population-level correlation between a male trait and currencies such as reproductive
success. This study is important as it illustrates when population-level correlations can be safely used to infer the presence
and strength of sexual selection in the field. We find that the correlation between a male trait and a mate choice variable
rises steeply as the number of males sampled by each female increases, flattening above seven to ten males sampled. This shape
is found to be remarkably robust, and little affected by, for example, the mate choice variable used, by noise in assessment,
by sampling behaviour depending on female quality, or by population size. The only variable found to have a large impact is
male clumping according to their “quality”. If females are sampling about four males, the maximum correlation that can be
found at the population level is in the range 0.4–0.6, perhaps as little as 0.1 if males are strongly clumped. A recent review
of the literature suggests that four is the average number of males that females sample. Thus, the absence of a strong correlation
cannot by itself be used to infer that sexual selection is weak, as it may be due to females sampling few males.
Received: 18 May 1998 / Accepted after revision: 18 July 1998 相似文献
383.
Changes in male guppy courting distance in response to a fluctuating light environment 总被引:1,自引:0,他引:1
In the guppy (Poecilia reticulata), effective courting by a male requires visual contact with the female. Therefore, environmental light intensity may affect
male display behavior, particularly initial courtship distance. We found that male guppies courted at exact and predictable
distances from the female given a particular light level, both in field and laboratory studies. In lower light levels (<0.1 μmol m−2 s−1), for example at dawn, dusk, or under heavy canopy, males court females at closer and less variable distances (<3 cm). At
higher light levels, which occur during most of the day and with less canopy cover, males often court from twice or three
times further out. Light levels over guppy streams change over relatively short time periods and ranges, correlating with
variation in courtship distances. Laboratory manipulations of irradiance confirmed that courtship distance depends on illumination.
Hence, courtship distances may be set by the effect of lighting on signal efficiency, minimization of energy or time expenditures,
or predation risk.
Received: 16 December 1997 / Accepted after revision: 8 August 1998 相似文献
384.
A. Peters L. B. Astheimer C. R. J. Boland A. Cockburn 《Behavioral ecology and sociobiology》2000,47(6):438-445
Testosterone has been proposed as a physiological link between the level of sexual signalling and male condition. Bright plumage
is one of the most noticeable sexual signals and is often used by females as a basis for mate choice. Yet bright male plumage
is not necessarily testosterone dependent. We investigated the role of testosterone in the moult into seasonal nuptial plumage
in male superb fairy-wrens. Early pre-nuptial moult is under intense intersexual selection and males can acquire the bright
plumage any time between autumn and the next spring. Testosterone was always undetectable or very low in males in dull eclipse
plumage. During the pre-nuptial moult, both the number of males with detectable testosterone and average testosterone levels
increased sharply. High testosterone was more correlated with nuptial plumage than with presence of the cloacal protuberance
(indicative of sperm storage). Subcutaneous testosterone implants always induced the pre-nuptial moult within 2–3 weeks after
implantation, even well outside the natural time range of moulting. Moreover, removal of the implants before the nuptial plumage
was completed, arrested the moult process. The evidence suggests that development of the nuptial plumage is testosterone dependent,
although we cannot exclude that testosterone exerts its action after conversion to a metabolite such as oestrogen. Once the
nuptial plumage was completed, all males maintained substantially elevated testosterone, sometimes months before the onset
of breeding. These high levels could be necessary to maintain the plumage, and/or are involved in courtship displays. The
results are discussed with respect to potential costs involved in acquiring and maintaining the nuptial plumage.
Received: 17 January 2000 / Received in revised form: 24 February 2000 / Accepted: 25 February 2000 相似文献
385.
386.
为研究多因素影响下系统遭遇危险事件前预防方案的选优,在集对分析和空间故障树基础上提出比选方法。首先,论述集对分析与空间故障树理论结合的可行性;其次,研究系统故障预防的多因素多方案比选方法和步骤;最后,通过实例进行分析。研究结果表明:停运方案没有因素分量系数影响,其损失是停运带来的经济损失;无措施方案的系统常分量系数最小,因素分量系数最大;采取措施方案中,当常分量系数相差不大时,因素分量系数积最小者为最优方案。使用赵森烽-克勤概率表示危险事件的发生特征是可行的;常分量系数代表方案对系统故障预防效用的可靠性,因素分量系数代表该可靠性的稳定性;结合常分量系数和因素分量系数即可确定最优方案。该方法适合于故障发生对因素变化敏感的系统。 相似文献
387.
非点源污染负荷模型的比较与选择 总被引:3,自引:0,他引:3
随着点源污染治理的深入,非点源污染的严重性日益凸显。对非点源污染进行定量化和有效控制的方法是通过非点源污染负荷模型对各类非点源的形成、迁移转化以及负荷量进行模拟。然而,非点源污染模型大都由发达国家开发,而且结构和参数各不相同,如何在实际应用中选择适合的模型成为非点源污染模拟的重要问题。文章选择国内常用的SWAT、HSPF、AnnAGNPS和GWLF 4个非点源污染模型,从结构、输入输出以及所应用的流域来对模型进行比较,最后给出非点源污染模型在国内使用时,模型选择的原则和建议。 相似文献
388.
煤矸石是我国排放是量最大的工业固体废弃物之一,弃之为害、用之为宝。本文主要论述了煤矸石的综合利用途径的有效性。 相似文献
389.
以汉江中游襄阳市为研究对象,在分析襄阳市自然地理和社会经济条件的基础上,构建反映区域水资源承载力水平的评价指标体系,由17项指标组成,利用向量模法对襄阳市2000—2012年的水资源承载力进行现实评价。结果显示,期间襄阳市水资源承载力评价值维持在0.2939~0.4114,属于较弱承载力,但有不断改善的趋势。随着2014年中线工程首次实现调水,汉江下泄水量减少,其水资源供需矛盾将更加突出。研究结果对于襄阳市科学合理地开发利用水资源、加强生态环境建设,以减小调水带来的不利影响,具有一定的理论参考价值和实践指导意义。 相似文献
390.
目前我国水土重金属污染的形势严重.现行执法的依据《污水综合排放标准》体现了对持久蓄积性污染物实行封闭零排放的原则精神.但目前从水质的监测评价到污染物的削减控制过程中,存在着一系列背离和混淆二类污染物排放标准和控制要求的问题.为扭转当前我国水土重金属严重污染,首要的应从端正环境保护系统的技术路线开始,并阐述了其技术要点;同时还提出对5种重点重金属实施独立的环境保护立法,才能保证源头严控超量排放技术路线的实施. 相似文献