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51.
Heterospecific matings are generally assumed to be unconditionally disadvantageous due to reduced viability or fertility of
hybrid offspring. For female collared flycatchers (Ficedula albicollis) mated to male pied flycatchers (Ficedula hypoleuca), the cost of heterospecific pair formation is reduced due to high levels of conspecific extra-pair paternity and a male-biased
offspring sex ratio. In order to investigate whether these cost-reducing mechanisms are the result of female mating strategies,
rather than being a by-product of species incompatibilities, we manipulated the plumage of male collared flycatchers before
pair formation to make them resemble male pied flycatchers. Since species incompatibilities are absent in this design, any
systematic effect of manipulation on sex ratio or paternity would indicate a role of female mating strategy. Paternity was
determined by means of a likelihood approach that controls the errors made in assigning a chick to be ‘within-pair’ or ‘extra-pair’.
Neither the sex ratio nor the male share of paternity was affected by the manipulation in a systematic manner. We therefore
conclude that our experimental data provide no support for the suggestion that female behavioural strategies are markedly
adjusted in response to formation of mixed-species pairs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
52.
We examined the dynamics and avoidance of mate guarding, by males and females, in the blue-footed booby, in which the two social mates are usually simultaneously present on the territory but each of them is unmonitored by the other for one-quarter of its time. Both sexes were promiscuous and liable to switch mates. Cuckolded individuals did not increase their overall presence on the territory, but in response to the extra-pair (EP) courtships of their mates, both sexes doubled their rate of intra-pair (IP) courtship and sometimes showed aggression. The male or female's presence depressed the social mate's EP activity, but intra-pair courtship had no such effect, tending even to propitiate that EP activity. Similarly, when females responded to their social mates' EP courtship with approach or aggression, disruption of EP activity was short-lived. Promiscuous females modified their diurnal pattern of attendance, as if attempting to sidestep monitoring by their mates, but cuckolded males matched the modification. Both sexes tended to perform their EP activities at a distance when their mates were present, possibly to evade monitoring or disruption by their mates. Male and female boobies cannot monitor their mates continuously, they do little to facultatively adjust their presence on territory to the risk of infidelity, and their immediate responses to overt infidelity have only the briefest impact; but the information they acquire while monitoring their mates may be critical to constraining their mates' infidelity and also to calibrating their own reproductive investment. 相似文献
53.
DANIEL R. MAYHEW HERBERT M. SIMPSON MANON DES GROSEILLIERS ALLAN F. WILLIAMS 《Traffic injury prevention》2013,14(3):179-192
A comprehensive evaluation of the Nova Scotia graduated licensing program was conducted. This program was implemented on October 1, 1994 and applies to all novice drivers, regardless of age. It spans 2 1/2 years in two stages: a 6-month learner phase, followed by a 24-month newly licensed driver phase. During both phases several driving restrictions apply, most notably a requirement for adult supervision at all times in the learner phase and a night driving restriction from midnight to 5 a.m. in the newly licensed driver phase. The evaluation of this program used a series of increasingly refined analyses that controlled for the influence of other explanatory variables. All the analyses showed that the graduated licensing program in Nova Scotia was associated with a significant reduction in crashes. For drivers age 16, there was a 24 percent decrease in total crashes during the first full year of the program and a 37 percent reduction during the first 3 years of the program. Comparable decreases occurred in injury crashes. Improvements also were observed for all novice drivers, not just those who are young - there was a 19 percent decrease in the crash rate for all novice drivers. Comparisons with results from other graduated licensing programs indicate the Nova Scotia program has been more effective than others in reducing crashes. 相似文献
54.
55.
Corey R. Freeman-Gallant 《Behavioral ecology and sociobiology》1997,40(6):395-400
Empirical relationships between parentage and male parental care are commonly interpreted in the context of life-history
models that consider increased offspring survivorship as the only benefit of paternal effort. However, indirect benefits associated
with male care can also influence a male's response to cuckoldry: if females allocate paternity according to their prior experience
with male parental care, it may pay for males to provision extra-pair young in early broods. Here, I assess the relationship
between first-brood parentage and paternal care in a population of Savannah sparrows (Passerculussandwichensis) where a male's fertilization success in the second brood appears to be influenced by his prior parental performance. Based
on the multi-locus DNA fingerprinting of 17 first broods, male feeding effort was influenced by parentage (percent of brood
resulting from within-pair fertilizations) but not by brood size, male mating status (monogamous versus polygynous), timing
of breeding (hatching date), structural size (wing length) or condition (mass). Males provided more care to broods that contained
few within-pair young. This result supports the idea that males provision young to increase their future mating success, but
alternative hypotheses involving male quality and timing of breeding cannot be excluded.
Received: 13 August 1996 / Accepted after revision: 22 February 1997 相似文献
56.
A recent turn towards a more contextually sensitive apprehension of the challenge of making everyday life less resource hungry has been partly underwritten by widespread evidence that the environmental values people commonly profess to hold do not often translate into correspondingly low impact actions. Yet sometimes the contexts of everyday life can also conspire to make people limit their consumption without ever explicitly connecting this to the environmental agenda. This paper considers this phenomenon with reference to UK studies from both ends of the generational spectrum. The first questioned how older people keep warm at home during winter and the second examined how young people get rid of no longer wanted possessions. Both found that, though the respondents involved were acting in certain ways that may be deemed comparatively low impact, they were hitherto relatively indifferent to the idea of characterising these actions as such. We outline three ways in which sustainability advocates might respond to the existence of such “inadvertent environmentalists” and consider how they might inspire studies that generate fresh intervention ideas instead of lingering on the dispiriting recognition that people do not often feel able to act for the environment. 相似文献
57.
Patterns of courtship behavior and ejaculate characteristics in male red-winged blackbirds 总被引:1,自引:0,他引:1
David F. Westneat Lisa A. McGraw Jennifer M. Fraterrigo Tim R. Birkhead F. Fletcher 《Behavioral ecology and sociobiology》1998,43(3):161-171
Sperm competition in birds is likely to have important effects on the behavior and physiology of reproduction in both sexes.
For males, such competition should select for large sperm reserves and behavioral adjustment of copulation when reserves are
low. We investigated both these possibilities in free-living red-winged blackbirds (Agelaius phoeniceus), a highly polygynous species with apparently strong sperm competition. We found that the recent copulatory behavior of males
did not affect the propensity to copulate with a model female. Ejaculates collected from individual males at 1-h intervals
showed no evidence of sperm depletion, yet repeated ejaculates collected less than 10 min apart did. Male ejaculate size was
significantly larger if it was the first one of the day (i.e., after an overnight rest). The average ejaculate size was 12.5
(±12.5 SD) million sperm. Males captured during the breeding season had an average of 111.7 (±52.8) million sperm stored in
their seminal glomera. Because males average a peak copulation rate of six per female per day, in one day a male might utilize
all the sperm in his seminal glomera if more than two females on his territory are fertilizable. We hypothesize that polygyny
and sperm competition in this species have combined to select for rapid replenishment of the seminal glomera throughout the
day, in contrast to other species that have been studied. Testis size and sperm reserves of male red-winged blackbirds are
intermediate between monogamous species and species with intense sperm competition. Several possible explanations for this
are discussed.
Received: 21 October 1997 / Accepted after revision: 15 February 1998 相似文献
58.
59.
土壤210Pb放射性活度变化可以用来指示土壤侵蚀速率变化、计算水土流失速率,但是在其他方面的应用,特别是岩溶环境的应用相对较少。在进行洞穴年轻沉积石笋年代测试过程中,发现目前应用的CIC(恒定初始放射性活度模式)初始活度恒定的假设需要进行验证。通过对广西桂林茅茅头大岩上覆土壤层进行季节采样和210Pb放射性活度、土壤有机质、粒径等分析,发现土壤剖面表层20~30cm内的210Pb放射性活度季节变化明显,可能响应了大气环境、土壤生态环境的变化。但是土壤剖面基底210Pb放射性活度基本保持恒定,说明土壤层厚度大于20~30cm时,土壤层中210 Pb变化对洞穴年轻沉积物表层210Pb活度变化影响不大,洞穴上覆层对洞穴沉积物210Pb放射性活度的影响主要在于土壤有机质和粘粒向下迁移。因此,影响洞穴石笋210Pb放射性活度的关键因素在土壤厚度、土壤中随有机质和粘粒迁移的210 Pb量的变化,进而推广到洞穴年轻沉积物210Pb定年,在土壤层厚度大于20~30cm时,洞穴相对封闭环境下,可以应用CIC模式对洞穴沉积物进行年龄计算。 相似文献
60.
浅析我国青少年犯罪的原因及对策 总被引:1,自引:1,他引:0
陈媛 《湖南环境生物职业技术学院学报》2006,12(1):77-81
进入新世纪后,我国青少年犯罪出现许多新情况,表现出许多新的特点,究其原因不外乎两个方面:一是客观原因,二是主观原因,因此为了减少和遏止青少年犯罪,必须采取对策进行有效的预防和治理. 相似文献