首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20篇
  2018年   2篇
  2012年   1篇
  2011年   1篇
  2010年   1篇
  2009年   1篇
  2008年   3篇
  2005年   4篇
  2004年   3篇
  2002年   1篇
  2001年   1篇
  1999年   1篇
  1998年   1篇
排序方式: 共有20条查询结果,搜索用时 78 毫秒
1.
Herrera J 《Annals of botany》2005,95(3):431-437
BACKGROUND AND AIMS: Flowers are relatively invariant organs within species, but quantitative variation often exists among conspecifics. These variations represent the raw material that natural selection can magnify, eventually resulting in morphological divergence and diversification. This paper investigates floral variability in Rosmarinus officinalis, a Mediterranean shrub. METHODS: Nine populations were selected in three major southern Spanish habitats (coast, lowland and mountains) along an elevation gradient. Flower samples from randomly chosen plants were collected from each population, and a total of 641 flowers from 237 shrubs were weighed while still fresh to the nearest 0.1 mg. Leaves from the same plants were also measured. Variations among habitats, sites and plants were explored with general linear model ANOVA. Leaf-flower covariation was also investigated. KEY RESULTS: Most (58%) mass in flowers was accounted for by the corolla, whose linear dimensions correlated directly with flower mass. Averaged over plants, the mass of a flower varied between 12 mg and 38 mg. Habitat, site (within habitat) and shrub identity had significant effects on mass variance. Flowers from the coast were the smallest (17 mg) and those from the mountains the largest (25 mg on average). A pattern of continuously increasing flower size with elevation emerged which was largely uncoupled from the geographical pattern of leaf size variation. CONCLUSIONS: As regards flower size, a great potential to local differentiation exists in Rosmarinus. Observed divergences accord with a regime of large-bodied pollinator selection in the mountains, but also with resource-cost hypotheses on floral evolution that postulate that reduced corollas are advantageous under prevailingly stressful conditions.  相似文献
2.
Climate change can harm many species by disrupting existing interactions or by favouring new ones. This study analyses the foreseeable consequences of climatic warming in the distribution and dynamics of a Mediterranean pest that causes severe defoliation, the pine processionary caterpillar Thaumetopoea pityocampa, and the effects upon the relict Andalusian Scots pine Pinus sylvestris nevadensis in the Sierra Nevada mountains (southeastern Spain). We correlated a set of regional data of infestation by T. pityocampa upon Scots pine, from a broad ecological gradient, with climatic data for the period 1991–2001, characterized by alternating warm and cold winters. Defoliation intensity shows a significant association with previous warm winters, implying that climatic warming will intensify the interaction between the pest and the Scots pine. The homogeneous structure of the afforested pine woodlands favours the outbreak capacity of the newcomer, promoting this new interaction between a Mediterranean caterpillar pest and a boreal tree at its southern distribution limit.  相似文献
3.
4.
5.
6.
Abstract: Gcyc is a developmental gene, present in the Gesneriaceae family, that has both highly conserved and highly variable regions. Ramonda myconi (Gesneriaceae) is a paleoendemic plant restricted to mountainous areas of NE Spain. In this study we examine the population variation in the coding region of Gcyc in R. myconi. The fast-evolving nature of the coding regions of the Gcyc gene plus the ancient history of R. myconi together provide an appropriate background to obtain the first insights into population-level variation in developmental genes of flowering plants. One locus of Gcyc was specifically amplified and sequenced. Four single nucleotide polymorphisms (SNPs) were detected in the 420 sequenced bases of the gene in two R. myconi populations. The Pyrenean population had only one SNP while all four SNPs were present in the southern population. Three out of four SNPs were non-synonymous. Such novel results indicate that the detection of SNPs in R. myconi over its entire distribution area could be used as an aid to reconstructing the population history of the species, as well as to investigate the relationship between developmental genes and morphological traits.  相似文献
7.
Alpine vegetation, restricted to the top of high mountains, is among the vegetation types most endangered by global warming, currently predicted to raise temperatures from 1.1 to 6.4 °C, by the end of the century. Nevertheless, background information allowing evaluation of impacts is rather scarce for some geographic zones. Our study of an alpine community on the Plateau of Muses (2600–2750 m a.s.l.) of Mt Olympos, the highest mountain of Greece, conducted in 1993–1994, can provide such background information for the Mediterranean region. We studied features relating to phenology of flowering, floral morphology, distribution and abundance, and flower visitors of plant species that exhibit a biotic pollination syndrome. We identified dominant patterns and we further (i) explored the relative contribution of the plant features and abiotic factors studied in explaining the activity patterns of flower visitors, (ii) examined if flower and visitor traits of the alpine community match each other according to the classical pollination syndromes, and (iii) investigated whether the responses of individual plant species to the yearly climatic variability result into phenological patterns that characterize the whole community. The common strategy of the alpine community was for early flowering and long flower life span; consistently early flowering species were twice as many as late flowering ones, whereas floral longevity (estimated for 36 species) averaged 5.2 days. Duration of flowering (estimated for 57 species) averaged 18.2 days. Climatic variability affected onset of flowering; all late flowering species delayed their flowering during the year characterized by a humid and cold summer. Duration of flowering and floral longevity did not change in a consistent way. Hymenoptera (Aculeates) were the dominant flower visitors. They accounted for 43.3% of the visits recorded, with bumblebees making a little less than half. Diptera followed making 37.5% of the visits (most made by syrphid flies). There was a mismatch between flower-morphology and flower visitor traits; the alpine community had predominantly non-specialized, pale-colour flowers, which are traits assumed to correspond to Diptera dominance and absence of social bees. Visitation was influenced by flower abundance and duration of flowering; proportionately more Diptera, and proportionately less Hymenoptera visited species with short flowering periods and few flowers present in the field. In a number of cases, the phenological and flower visitor patterns of the community of Mt Olympos deviated from those observed in other alpine environments suggesting a mediterranean influence even at high altitudes.  相似文献
8.
A study of the flowering and fruiting phenology was undertaken for twenty species of the xerochamaephytic communities that characterize the mountain-crest areas of the island of Majorca (Balearic Islands, Spain). The flowering period of the species considered extends from March to November, with the majority flowering during the spring and early summer, and a peak in June. The flowering duration at the species level is longest for Rosmarinus officinalis var. palaui (which flowered in spring and autumn) and was shortest for Genista majorica and Rubia balearica. In this community, three strategies were observed that may serve to reduce interspecific competition between pollinators: 1) pollination specialization of white-pink flowers; 2) high diversification of yellow flower pollinators; and 3) the divergence in flowering time of less common flower colours. The flowering duration of individual plants and whole populations are positively correlated, which may indicate that individuals of each population optimize the time which is phenologically useful. The flowering of the spiny cushion species of the community is characterized by a smaller intraspecific overlap in comparison to the other species examined. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献
9.
An opportunity to test Coffman's (1989) proposal that ecological heterogeneity is one of the main factors for chironomid species richness occurred when prolonged drought in southern Spain was broken by heavy rain. Chironomid assemblage composition was studied in two Mediterranean mountain first-order streams, one permanent and the other temporary. Samples were collected in the permanent stream over extreme hydrological conditions: 1991–95 with relatively low and stable flow, and 1996–97 with relatively high and unstable flow. The temporary stream flowed, and therefore was sampled, only during the second period. In the permanent stream, spate events resulted in a notable increase in species richness due to the arrival of 32 species and to the permanence of 81% of the species resident over the prespate period. This relatively high percentage suggests that chironomids, as a group, have important resilience properties. However, some species disappeared from the permanent stream after the spates and the considerable decrease in abundance of other species, shows that, at the species level, resilience may vary greatly within the Chironomidae. Most of the species that appeared in the temporary stream were the same as those of the permanent stream during the fast flow period despite the great ecological differences between the two streams under study, suggesting the key role of discharge in structuring chironomid assemblages. The outstanding exception was the fugitive species Orthocladius calvus, the most abundant species in the temporary stream during the initial successional stages but never collected in the permanent stream. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号