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991.
Nested distribution of amphibians in the Zhoushan archipelago, China: can selective extinction cause nested subsets of species? 总被引:8,自引:0,他引:8
Because of their poor dispersal ability, amphibians are well suited for testing the selective extinction theory on islands.
Amphibian fauna in the Zhoushan archipelago, China, exhibit a high level of nestedness (C = 0.893), and the species number is lower on islands than on similar sized areas on the mainland. No correlation was found
between island-specific species richness and the nearest distance from a larger island, distance from the mainland or density
of human population. These results suggest that no amphibian colonisation has occurred in the archipelago since island isolation
7000–9000 years ago. Furthermore, the results imply that selective extinction contributes to the nestedness of amphibians
in the Zhoushan archipelago. The incidence of a species on the islands is significantly correlated with log area of the smallest
island occupied by the species and the number of provinces on the Chinese mainland in which the species occur. However, there
is no correlation with average body length of adults and island occurrence. It is concluded that (1) the area of the smallest
island occupied by a species is a good estimate of the minimum area for a viable population of the species and a good predictor
of species incidence on islands, (2) species with a restricted distribution range are more vulnerable to extinction from islands
than those with a wide distribution range and (3) the effect of body size on occurrence on the islands is uncertain, and may
be specific to the archipelago and taxa studied. The observed nestedness of amphibian assemblages has two implications for
conservation: (1) not only can all the species found in several small reserves be found on a large reserve of the same total
size, but additional species can be found on the single large reserve; (2) for a reserve to maintain viable populations of
all species in a region it should be at least as large as the smallest island occupied by the most vulnerable species.
Received: 16 December 1996 / Accepted: 22 September 1997 相似文献
992.
Hajime Iwamura Shigeru Murakami Jun-Ichi Koga Satoshi Matsubara Koichi Koshimizu 《Phytochemistry》1979,18(8):1265-1268
Ten 4-substituted-2-methylthiopyrido[2,3-d]pyrimidines were synthesized and tested for their cytokinin-antagonistic activity by the tobacco callus bioassay. This series of compounds constitutes the first example of anti-cytokinins which possess a fused 6-6 membered ring system. The treatment of Lineweaver and Burk, the method of classical enzyme kinetics, revealed competitive inhibition of cytokinin-induced tobacco callus growth. The variation of activity with the systematic transformation of 4-substituents was analysed quantitatively with physicochemical substituent parameters and regression analysis. The results indicated the predominant importance of substituent width for binding of the antagonists at the receptor site of cytokinins. 相似文献
993.
994.
Thomas Hovestadt H. Joachim Poethke K. Eduard Linsenmair 《Journal of Biogeography》2005,32(4):677-684
Aim To investigate the relationship between the slope z of the species–area relationship (SAR) and the intensity of spatial patterns in species number and dissimilarity for woody plants with different modes of seed dispersal. According to island theory we expect, for any given archipelago, steeper slopes and more pronounced spatial patterns for groups of less dispersive species. Location Ivory Coast, West Africa. Methods In a West African forest–savanna mosaic we collected presence–absence data for woody plant species in 49 forest islands. The parameters of the SARs were fitted by nonlinear regressions and then compared for plant species aggregated according to their mode of seed dispersal. We used the Mantel test to calculate the intensity of spatial patterns in species number, i.e. residual deviation from SAR, and species dissimilarity. Results The z‐value for bird‐dispersed species was lower (0.11) than that for wind‐dispersed species (0.27), with mammal‐dispersed species taking an intermediate value (0.16). This result suggests that, as a group, bird‐dispersed species are better colonizers. The spatial pattern in species number as well as species similarity was more pronounced for bird‐ compared with wind‐dispersed species. Main conclusions The standard interpretation of the theory of island biogeography claims that shallow slopes in the SAR imply low isolation of islands, i.e. good dispersal abilities of species. The results of our study appear to contradict this statement. The contradiction can eventually be resolved by a more detailed account of the colonization process, i.e. by distinguishing between dispersal and consecutive establishment of populations. 相似文献
995.
H P SINGH DAIZY R BATISH S KAUR H RAMEZANI R K KOHLI 《The Annals of applied biology》2002,141(2):111-116
The effect of four monoterpenes ‐ citronellol, citronellal, cineole and linalool ‐ on the germination, growth and physiology of Cassia occidentalis was investigated. All four monoterpenes reduced germination of C. occidentalis seeds but to varying extents. Citronellal and linalool completely inhibited germination beyond the concentrations of 55 and 110 μM, respectively, whereas in response to treatment of citronellol no germination was observed beyond 330 μM. Further, the growth of seedlings, measured in terms of seedling length and biomass, was also adversely affected. A reduction in chlorophyll content of the cotyledonary leaves of C. occidentalis was also noticed, indicating an adverse effect on photosynthesis. Likewise, respiratory ability of growing seeds was also impaired in response to all four monoterpenes, clearly indicating that monoterpenes affect energy metabolism. On the basis of overall phytotoxicity, potency of monoterpenes was in the order of citronellal > linalool > citronellol > cineole. The results from this study suggest that both citronellal and linalool possess strong phytotoxic potential and can thus serve as lead molecules for the synthesis of bioherbicides. 相似文献
996.
997.
Summary The number and frequencies of subfamilies in a honey bee colony were determined by DNA fingerprinting. Queen and brood samples were taken from three colonies with artificially inseminated queens and from one colony with a naturally mated queen. UsingHae III restriction enzyme and (GATA)4 oligonucleotide, the number of subfamilies in the colonies with artificially inseminated queens corresponded with the number of drones used for insemination. In the colony with the naturally mated queen, 12 subfamilies were found in a random sample of 104 workers. Considering that subfamily frequencies range from 1 to 26%, introcolonial worker relationship was estimated to be 0.328, corresponding to a genetical effective number of 6.4 matings. 相似文献
998.
间接性害虫为害与作物产量损失的关系:Ⅱ.取食繁殖器官害虫 总被引:1,自引:0,他引:1
本文试从分散的材料中概括出主要大田作物繁殖器官被害与产量损失之间的一般关系。不同作物对繁殖器官被害的产量反应有某些共同性。在生殖生长初期损失全部或部分繁殖器官经常引起增产,在后期损失幼嫩的繁殖器官对产量无不利影响,但在中期损失繁殖器官一般导致明显减产,表现了受害时的生长阶段的普遍重要意义。在繁殖器官损失量过大,作物品种晚熟或有限生长习性强,水、肥条件及温度与光照条件不良,补偿期过短,植株密度过小或过大,中部繁殖器官受害以及遭受连续为害情况下,减产的可能性增大。这与叶片损失后的产量反应有类似之处。本文归纳出的这一认识可供在作物产量损失测定等工作时参考。 相似文献
999.
笔者用收获法对浙江建德山区的天然次生青冈常绿阔叶林群落的第一性生产力进行了研究。本文报道了林木层样木的生物量优化回归模型,并对模型进行了分析、检验和估算。结果表明,立木各器官变量之间存在着很好的相对生长关系;进行分层次、种类(组分)和自变量的模型选优是十分必要的;各种模型都有较高的精度,可以对该群落的生物量作出有效的估计;种间模型的有效组合适用于亚乔木层的种类和乔木层的伴生种类;种类(组分)间的模型差异与它们在群落中所处的地位或所起作用密切相关;净第一性生产力在各器宫中的分配比例是植物群落结构与功能在种间关系、生态位分化和种群动态特征上的综合反映。 相似文献
1000.