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1.
New aspects of sex change among reef fishes: recent studies in Japan   总被引:7,自引:0,他引:7  
New aspects of sex change in reef fishes are reviewed with special emphasis on recent studies in Japan. For protogyny, studies on both monandric and diandric species have been conducted, but the distinction of primary males from prematurational secondary males seems to need further examination. For protandry, detailed field studies on anemonefishes have revealed alternative life-history styles associated with movements between hosts before or after maturation. The most interesting new aspect has been the discovery of 2-way sex change within a species. Conditions for evolution of 2-way sex change are examined in relation to the size-advantage model and social control mechanisms. A fish may change sex when it becomes dominant in a mating group, but a dominant fish may also change sex in the reverse direction when its social status changes to subordinate through inter-group movement. Two-way sex change has hitherto been reported only from basically protogynous fishes (e.g., Gobiidae, Pomacanthidae, Cirrhitidae, Epinephelinae). Possibilities of the reverse sex change in the protandrous anemonefishes are discussed with data from some unpublished studies.  相似文献
2.
We assessed the importance of three behavioral processes on the fitness of individual females as mediated via maternal care in matrilineally organized social groups of spotted hyenas Crocuta crocuta. These were maternal choice of foraging tactic, the maintenance of individual dominance rank (social status) within the adult female hierarchy, and the behavioral support provided by mothers to their daughters when daughters acquired their position in the adult female hierarchy. The effects of all behavioral processes were closely linked. Maternal care was dependent on maternal social status because high ranking females had priority of access to food, and individual maternal choice of foraging tactic was frequency – and social status-dependent when medium prey abundance provided an opportunity for such a choice. At medium prey abundance, low ranking females went on costly long distance commuting trips to forage on migratory herds outside the group territory, whereas high ranking females fed on kills within the group territory. As a consequence, offspring of high ranking females grew faster, had a higher chance of survival to adulthood, and thus high ranking females had a higher lifetime reproductive success. Daughters of high ranking females usually acquired a social status immediately below that of their mother provided they enjoyed the effective support from their mothers as coalition partners, and they gave birth to their first litter at an earlier age than daughters of low ranking mothers. Spotted hyenas are therefore an example of the silver-spoon effect. This study shows that the frequency-dependent outcome of behavioral processes can be a key determinant of maternal reproductive success in social carnivores and have a profound influence on the reproductive career prospects of offspring.  相似文献
3.
种群内部因素对动物免疫功能的影响   总被引:4,自引:0,他引:4       下载免费PDF全文
李凤华  王德华  钟文勤 《生态学报》2002,22(12):2208-2216
动物的免疫状况与种群动态的关系是近年来动物生态学研究的热点之一。总结了种群内部因素对动物免疫功能的影响,并介绍了几种免疫调节假说,对于不同的研究对象,种群密度的高低对其可产生不同的影响。在一个种群中,优势个体往往具有较高的免疫水平;雌性个体的免疫水平高于雄性个体,这可部分归因于性激素的作用,动物处于繁殖期时免疫水平有所下降。婚配制度的作用效果是复杂的,为了能够成功进行繁殖而面临更大选择压力的性别可能具有更强的免疫水平有所下降,婚配制度的作用效果是复杂的,为了能够成功进行繁殖而面临更大选择压力的性别可能具有更强的免疫功能,许多研究者根据野外研究结果探讨了种群调节的免疫机制问题,认为个体的免疫能力受到遗传和环境因素的影响,其变化状况将关系到整个种群的数量波动,还介绍了生态学研究中采用的免疫学指标。评价了这些指标对实验结果的影响,并对今后的研究方向提出了几点建议。  相似文献
4.
On the evolution of delayed recruitment to food bonanzas   总被引:2,自引:2,他引:0  
Whereas food sharing by immediate recruitment to food bonanzasis relatively common, especially among birds, delayed recruitmentfrom overnight roosts is comparatively rare, although it hasbeen studied extensively in the common raven (Corvus corax).Two hypotheses have been advanced to explain the evolution ofdelayed recruitment. Under the status-enhancement hypothesis,delayed recruiting is favored because the recruiter's social statusincreases with the number of followers it leads to a food source.The posse hypothesis also focuses on the number of individualsrecruited to a site, but in this case aggregation is favoredbecause larger groups are more likely to usurp a carcass defendedby a pair of territorial adult ravens. We used a game-theoreticmodel to explore the logic of immediate versus delayed recruitmentin the light of these hypotheses. In particular, we identified threecritical values of the probability of immediate recruitment:that below which delayed recruitment is a cooperative strategy,that below which delayed recruitment is an evolutionarily stablestrategy, and that below which a mutant strategy of delayedrecruitment will invade a population of immediate recruitersto reach fixation. The model demonstrates that either status enhancementor the posse effect may alone suffice for the evolution of delayed recruitmentto food bonanzas via mutualistic information sharing at communal roosts.  相似文献
5.
According to the immunocompetence hypothesis, testosterone stimulatesthe expression of male sexually selected traits while decreasingimmunocompetence. This proposed trade-off was studied by experimentalsupplementation of testosterone to small, subordinate, dull-coloredmale lizards, Psammodromus algirus. Experimental males showeda tendency to overlap their home range with fewer small malesthan did control males and tended to be more aggressive. However,control males were observed more frequently attending femalesthan experimental males. The area of patches of breeding coloration,the number of ticks, and the frequency of recoveries of testosterone-supplementedand control males did not differ significantly. The resultssuggest that small adult males with high levels of testosteronebehave more aggressively, which may be advantageous to securinga breeding territory in the next season. However, the hormonedid not apparently affect ornamentation or parasite load. Weargue that, whatever the mechanisms involved, blocking effectsof testosterone may be adaptive because being cryptic facilitatesa sneaking strategy, and low ectoparasite load may improve survival  相似文献
6.
Synopsis Juvenile Atlantic salmon emigrate from the river in a given year as a consequence of a physiological decision influencing appetite and growth during the previous summer. The direction of the decision depends on developmental performance exceeding a genetically determined threshold at that time, and that performance is governed by environmental opportunity. The animal's foraging efficiency (ability to avoid predators, and to compete) determines how well that opportunity is used. Those fish which maintained relatively high growth after July preferred higher stream flows, and were more likely to hide than to flee from a predator. Predator vigilance reduced intake, and ability to discriminate edible particles. Early competitive ability depended on fierceness rather than size, and ultimate large size was a consequence of dominant status. Initial status among high ranking individuals (but not among low ones) predicted the likelihood of maintaining growth in late summer. Size by July was the better predictor for low ranked fish. The influence of high status on life-history variation depends on how much it suppresses the growth of those lower in the hierarchy. Invited review  相似文献
7.
This article is an ethnographic study of Persian-language weblogs (blogs), focusing on a divisive argument among Iranian bloggers that came to be known as the "vulgarity debate." Sparked by a controversial blogger who ridiculed assertions that Islam was compatible with human rights, the debate revolved around the claim that blogging had a "vulgar spirit" that made it easy for everything from standards of writing to principles of logical reasoning to be undermined. My study focuses primarily on the linguistic side of the controversy: I analyze blogging as an emergent speech genre and identify the structural features and social interactions that make this genre seem "vulgar." I also examine the controversy as a confrontation between bloggers with unequal access to cultural capital and a struggle over "intellectualist" hegemony. In the conclusion, I use the construct of "deep play" to weave together multiple layers of structure, explanation, and meaning in the debate.  相似文献
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Trade-offs between reproduction and survival are important determinants of life-history characteristics of lizards. Organisms cannot increase the allocation of limited resources to reproduction without diverting a proportional amount of energy from another trait. Locomotor performance is an ecologically relevant trait that potentially influences survival by affecting the ability to escape from predators. Most studies have used female lizards as subjects because pregnancy is known to reduce their locomotor abilities, whereas little is known on costs of reproduction in males. In this study we suggest that in males of the lizard Lacerta monticola reproductive investment in morphological traits that confer dominance (i.e. head size) might lead to a low probability of survival by decreasing investment in other traits that affect locomotor performance (i.e. limb symmetry). We staged laboratory agonistic encounters between males and measured their morphology and burst speed on a race track to examine possible relationships between morphology, social dominance and locomotor capacity. Our results indicate that social dominance was positively related to relative head height, and that escape speed was negatively related to levels of fluctuating asymmetry in femur length, but also negatively related to relative head height. Males with greater relative head height also had more asymmetrical femurs, thus dominant males suffered a decrease in locomotor performance. Males with higher heads tend to dominate male–male interactions and hence may gain access to reproductive females, thus increasing their current reproduction success. However, this might occur at the expense of future survivorship mediated by a decrease in escape speed. Therefore, in male L. monticola there might be a trade-off between current reproductive success and survival.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002; 77 , 201–209.  相似文献
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