81 resultados para niche partitioning
em Chinese Academy of Sciences Institutional Repositories Grid Portal
Resumo:
物种共存机制一直是群落生态学研究的核心内容。解释物种共存的假说很多,近年来最引人注目的是生态位分化假说和群落中性理论。这两种理论对群落内物种共存的相对重要性是目前群落生态学研究的热点。国际上这方面的研究基本集中在热带森林大样地内,而针对亚热带森林大样地的相关研究却非常少见。本文以浙江古田山24公顷常绿阔叶林永久固定监测样地第一次调查数据为基础,研究样地内木本植物与生境关联和与地形因子梯度相关,目的在于探讨物种生境生态位分化在亚热带常绿阔叶林内物种多样性维持中的作用,也为了解决当前物种生境关联相关研究中的一些不足之处。 本研究首先采用Torus转换检验分析古田山样地内90种常见木本植物与5类生境关联,结果表明有75种(83.3%)至少与一类生境类型显著相关,说明大部分亚热带森林群落内物种具有生境特化的特性。与CTFS全球大样地类似研究结果相比,古田山样地内生境特化的物种比例更高,这与古田山样地复杂的地形条件密切相关。通过本研究,证明地形条件越复杂,物种特化比例越高的趋势确实存在。在古田山样地,虽然83.3%的物种有生境特化的特性,但生境特化没有排他性,即并不完全排斥其他生境,在非最适生境也能稳定与其他物种共存。根据本研究与生境负相关的平均物种数与被检测的物种比例估算,古田山样地内生境异质性对物种多样性维持的贡献率约为19.6%,说明物种生境特化对于物种共存有一定的作用,但贡献并不大,除了生境异质性,仍有其他因素决定物种共存。 目前有关物种生境关联的研究都假设同一物种的个体对于生境偏好一致,不管胸径大小是否相同,很少有人研究不同生长阶段生境偏好的变化。本研究利用Torus转换检验比较样地内60种常见木本植物在3个生活史阶段(幼苗阶段、小树阶段和成熟阶段)与5类生境关联的变化,结果表明大部分物种在其幼苗和小树阶段的生境偏好比较一致,但成熟阶段与前两个阶段差别比较大,说明物种在生活史不同阶段的生境偏好可能发生改变。 由于生境划分没有统一的标准,不同学者用不同的方法划分生境类型和数量,主观性很大,造成不同研究地点、不同研究者之间的研究结果可比性差。本研究尝试利用直接梯度分析方法重新分析物种空间分布与地形梯度相关,用以代替生境关联分析。利用CCA分析检验样地内90种常见木本植物与4种地形因子梯度(海拔、凹凸度、坡度和坡向)的相关情况,发现有76个(84%)物种的空间分布与地形梯度相关,说明大部分物种具有沿地形因子梯度分布的特性。4种地形因子梯度变化对90个物种空间分布的解释量约为20%,说明地形异质性对于物种共存有一定作用,但贡献并不大。对生境关联分析和直接梯度法分析结果进行比较,两种方法分析结果一致,得到的结论也一致。直接梯度分析方法可以避免生境划分对研究结果的影响,是今后类似研究中值得采纳的方法。 本研究的结果表明地形异质性引起的生态位分化在古田山样地群落内物种多样性维持中起一定的作用,但贡献不大,因此需要更深入地研究其他环境因素引起的生态位分化在物种多样性维持中的作用,同时也需要进一步研究中性过程在物种多样性维持中的作用,以更全面地探讨生态位分化假说和中性理论在亚热带常绿阔叶林内物种共存的相对重要性。
Resumo:
In reciprocal mutualism systems, the exploitation events by exploiters might disrupt the reciprocal mutualism, wherein one exploiter species might even exclude other coexisting exploiter species over an evolutionary time frame. What remains unclear is how such a community is maintained. Niche partitioning, or spatial heterogeneity among the mutualists and exploiters, is generally believed to enable stability within a mutualistic system. However, our examination of a reciprocal mutualism between a fig species (Ficus racemosa) and its pollinator wasp (Ceratosolen fusciceps) shows that spatial niche partitioning does not sufficiently prevent exploiters from overexploiting the common resource (i.e., the female flowers), because of the considerable niche overlap between the mutualists and exploiters. In response to an exploiter, our experiment shows that the fig can (1) abort syconia-containing flowers that have been galled by the exploiter, Apocryptophagus testacea, which oviposits before the pollinators do; and (2) retain syconia-containing flowers galled by Apocryptophagus mayri, which oviposit later than pollinators. However, as a result of (2), there is decreased development of adult non-pollinators or pollinator species in syconia that have not been sufficiently pollinated, but not aborted. Such discriminative abortion of figs or reduction in offspring development of exploiters while rewarding cooperative individuals with higher offspring development by the fig will increase the fitness of cooperative pollinating wasps, but decrease the fitness of exploiters. The fig fig wasp interactions are diffusively coevolved, a case in which fig wasps diversify their genotype, phenotype, or behavior as a result of competition between wasps, while figs diverge their strategies to facilitate the evolution of cooperative fig waps or lessen the detrimental behavior by associated fig wasps. In habitats or syconia that suffer overexploitation, discriminative abortion of figs or reduction in the offspring development of exploiters in syconia that are not or not sufficiently pollinated will decrease exploiter fitness and perhaps even drive the population of exploiters to local extinction, enabling the evolution and maintenance of cooperative pollinators through the movement between habitats or syconia (i.e., the metapopulations).
Resumo:
Sequences of the mitochondrial cytochrome b (1140 bp) and nuclear IRBP (1152 bp) genes were used to assess the evolutionary history of Apodemus, using the complete set of Asian species. Our results indicate that speciation in Asia involved three radiations, which supports an earlier study. The initial radiation yielded A. argenteus (Japanese endemic), A. gurkha (Nepalese endemic), and the ancestral lineage of the remaining Asian species. This lineage subsequently diverged into four groups: agrarius-chevrieri (agrarius group), draco-latronum-semotus (draco group), A. peninsulae, and A. speciosus (Japanese endemic). The final step consisted of divergence within two species groups as a consequence of the geography of the Yunnan-Guizhou plateau and Taiwan. The ecological ability of two Apodemus-species to inhabit one locality via niche partitioning likely drove the second radiation and shaped the basic geographical pattern seen today: A. argenteus and A. speciosus in Japan, A. agrarius and A. peninsulae in northern China, and the A. agrarius and A. draco groups in southern China. The three radiations are estimated to have occurred 7.5, 6.6, and 1.8-0.8 Mya respectively, using the IRBP clock, based on rat-mouse divergence 12 Mya. (C) 2003 The Linnean Society of London.
Resumo:
Based on some fundamental quantum chemical descriptors computed by PM3 Hamiltonian, by the use of partial least-squares (PLS) analysis, a significant quantitative structure-property relationship (QSPR) model for logK(ow) of polychlorinated dibenzo-p-dioxins and dibenzo-p-furans (PCDD/Fs) was obtained. The QSPR can be used for prediction. The intermolecular dispersive interactions and thus the bulkness of the PCDD/Fs are the main factors affecting the logK(ow). The more chlorines in the PCDD/F molecule, the greater the logK(ow) values. (C) 2001 Elsevier Science Ltd. All rights reserved.