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排序方式: 共有536条查询结果,搜索用时 93 毫秒
21.
Francesco De Bello Wilfried Thuiller Jan Lepš Philippe Choler Jean‐Christophe Clément Petr Macek Maria‐Teresa Sebastià Sandra Lavorel 《植被学杂志》2009,20(3):475-486
Questions: Trait differentiation among species occurs at different spatial scales within a region. How does the partitioning of functional diversity help to identify different community assembly mechanisms? Location: Northeastern Spain. Methods: Functional diversity can be partitioned into within‐community (α) and among‐communities (β) components, in analogy to Whittaker's classical α and β species diversity concept. In light of ecological null models, we test and discuss two algorithms as a framework to measure α and β functional diversity (the Rao quadratic entropy index and the variance of trait values). Species and trait (specific leaf area) data from pastures under different climatic conditions in NE Spain are used as a case study. Results: The proposed indices show different mathematical properties but similarly account for the spatial components of functional diversity. For all vegetation types along the climatic gradient, the observed α functional diversity was lower than expected at random, an observation consistent with the hypothesis of trait convergence resulting from habitat filtering. On the other hand, our data exhibited a remarkably higher functional diversity within communities compared to among communities (α?β). In contrast to the high species turnover, there was a limited functional diversity turnover among communities, and a large part of the trait divergence occurred among coexisting species. Conclusions: Partitioning functional diversity within and among communities revealed that both trait convergence and divergence occur in the formation of assemblages from the local species pool. A considerable trait convergence exists at the regional scale in spite of changes in species composition, suggesting the existence of ecological redundancy among communities. 相似文献
22.
Plant species diversity and environmental heterogeneity: spatial scale and competing hypotheses 总被引:1,自引:0,他引:1
Jeremy T. Lundholm 《植被学杂志》2009,20(3):377-391
Questions: What is the observed relationship between plant species diversity and spatial environmental heterogeneity? Does the relationship scale predictably with sample plot size? What are the relative contributions to diversity patterns of variables linked to productivity or available energy compared to those corresponding to spatial heterogeneity? Methods: Observational and experimental studies that quantified relationships between plant species richness and within‐sample spatial environmental heterogeneity were reviewed. Effect size in experimental studies was quantified as the standardized mean difference between control (homogeneous) and heterogeneous treatments. For observational studies, effect sizes in individual studies were examined graphically across a gradient of plot size (focal scale). Relative contributions of variables representing spatial heterogeneity were compared to those representing available energy using a response ratio. Results: Forty‐one observational and 11 experimental studies quantified plant species diversity and spatial environmental heterogeneity. Observational studies reported positive species diversity‐spatial heterogeneity correlations at all points across a plot size gradient from ~1.0 × 10?1 to ~1.0 × 1011 m2, although many studies reported spatial heterogeneity variables with no significant relationships to species diversity. The cross‐study effect size in experimental studies was not significantly different from zero. Available energy variables explained consistently more of the variance in species richness than spatial heterogeneity variables, especially at the smallest and largest plot sizes. Main conclusions: Species diversity was not related to spatial heterogeneity in a way predictable by plot size. Positive heterogeneity‐diversity relationships were common, confirming the importance of niche differentiation in species diversity patterns, but future studies examining a range of spatial scales in the same system are required to determine the role of dispersal and available energy in these patterns. 相似文献
23.
We investigate the transition between limiting similarity and coexistence of a continuum in the competitive Lotka-Volterra model. It is known that there exist exceptional cases in which, contrary to the limiting similarity expectation, all phenotypes coexist along a trait axis. Earlier studies established that the distance between surviving phenotypes is in the magnitude of the niche width 2σ provided that the carrying capacity curve differs from the exceptional one significantly enough. In this paper we studied the outcome of competition for small perturbations of the exceptional (Gaussian) carrying capacity. We found that the average distance between the surviving phenotypes goes to zero when the perturbation vanishes. The number of coexisting species in equilibrium is proportional to the negative logarithm of the perturbation. Nevertheless, the niche width provides a good order of magnitude for the distance between survivors if the perturbations are larger than 10%. Therefore, we conclude that limiting similarity is a good framework of biological thinking despite the lack of an absolute lower bound of similarity. 相似文献
24.
Assessing the scale-specific importance of niches and other spatial processes on beta diversity: a case study from a temperate forest 总被引:1,自引:0,他引:1
Niche processes and other spatial processes, such as dispersal, may simultaneously control beta diversity, yet their relative
importance may shift across spatial and temporal scales. Although disentangling the relative importance of these processes
has been a continuing methodological challenge, recent developments in multi-scale spatial and temporal modeling can now help
ecologists estimate their scale-specific contributions. Here we present a statistical approach to (1) detect the presence
of a space–time interaction on community composition and (2) estimate the scale-specific importance of environmental and spatial
factors on beta diversity. To illustrate the applicability of this approach, we use a case study from a temperate forest understory
where tree seedling abundances were monitored during a 9-year period at 40 permanent plots. We found no significant space–time
interaction on tree seedling composition, which means that the spatial abundance patterns did not vary over the study period.
However, for a given year the relative importance of niche processes and other spatial processes was found to be scale-specific.
Tree seedling abundances were primarily controlled by a broad-scale environmental gradient, but within the confines of this
gradient the finer scale patchiness was largely due to other spatial processes. This case study illustrates that these two
sets of processes are not mutually exclusive and can affect abundance patterns in a scale-dependent manner. More importantly,
the use of our methodology for future empirical studies should help in the merging of niche and neutral perspectives on beta
diversity, an obvious next step for community ecology.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
25.
Biodiversity effects on ecosystem functioning in forests have only recently attracted increasing attention. The vast majority
of studies in forests have focused on above-ground responses to differences in tree species diversity, while systematic analyses
of the effects of biodiversity on root systems are virtually non-existent. By investigating the fine root systems in 12 temperate
deciduous forest stands in Central Europe, we tested the hypotheses that (1) stand fine root biomass increases with tree diversity,
and (2) ‘below-ground overyielding’ of species-rich stands in terms of fine root biomass is the consequence of spatial niche
segregation of the roots of different species. The selected stands represent a gradient in tree species diversity on similar
bedrock from almost pure beech forests to medium-diverse forests built by beech, ash, and lime, and highly-diverse stands
dominated by beech, ash, lime, maple, and hornbeam. We investigated fine root biomass and necromass at 24 profiles per stand
and analyzed species differences in fine root morphology by microscopic analysis. Fine root biomass ranged from 440 to 480 g m−2 in the species-poor to species-rich stands, with 63–77% being concentrated in the upper 20 cm of the soil. In contradiction
to our two hypotheses, the differences in tree species diversity affected neither stand fine root biomass nor vertical root
distribution patterns. Fine root morphology showed marked distinctions between species, but these root morphological differences
did not lead to significant differences in fine root surface area or root tip number on a stand area basis. Moreover, differences
in species composition of the stands did not alter fine root morphology of the species. We conclude that ‘below-ground overyielding’
in terms of fine root biomass does not occur in the species-rich stands, which is most likely caused by the absence of significant
spatial segregation of the root systems of these late-successional species. 相似文献
26.
Intraspecific variation in habitat-forming species can have important ecological consequences at the population, community,
and ecosystem level. However, the contribution of genetic variation among individuals to these effects is seldom documented.
We quantified morphological and physiological variation among genotypes of a marine foundation species, the seagrass Zostera marina. We grew replicate shoots of eight genetically distinct Zostera individuals collected from Bodega Bay, California, in a common garden environment and then quantified shoot production and
morphology, nutrient uptake, and key photosynthetic parameters. We found that genotypes differed in shoot production, biomass,
and both root and shoot nutrient uptake rates, even when corrected for genotype-specific biomass differences. In addition,
the rank order of uptake ability differed for ammonium and nitrate, indicating that genotypes may exhibit resource partitioning
of different forms of nutrients. Our results suggest that both niche complementarity among genotypes and the sampling/selection
effect could contribute to previously observed positive effects of seagrass clonal diversity on resource utilization and biomass
production. Further, they highlight that genotypic variation in key traits of habitat-forming species could have measurable
effects on community structure and function. 相似文献
27.
Mary Jane West-Eberhard has suggested that plasticity may be of primary importance in promoting evolutionary innovation and
diversification. Here, we explore the possibility that the diversification of phytophagous insects may have occurred through
such a process, using examples from nymphalid butterflies. We discuss the ways in which host plant range is connected to plasticity
and present our interpretation of how West-Eberhard’s scenario may result in speciation driven by plasticity in host utilization.
We then review some of the evidence that diversity of plant utilization has driven the diversification of phytophagous insects
and finally discuss whether this suggests a role for plasticity-driven speciation. We find a close conceptual connection between
our theory that the diversification of phytophagous insects has been driven by oscillations in host range, and our personal
interpretation of the most efficient way in which West-Eberhard’s theory could account for plasticity-driven speciation. A
major unresolved issue is the extent to which a wide host plant range is due to adaptive plasticity with dedicated modules
of genetic machinery for utilizing different plants. 相似文献
28.
Many studies have highlighted the relationship between nutrient fluctuations and enrichment in the process of plant invasion. However, invasion may be also associated with conditions of plant stress, either nutrient depletion or toxicity, in the environment. In this study, we investigate the possible role of nutrient stress in the invasion of Hieracium lepidulum (Stenstroem) Omang, in South Island, New Zealand. We do this by comparing several performance attributes, and their plasticity, for H. lepidulum and a number of co-occurring species, across a series of nutrient depletion and toxicity tests. H. lepidulum had intermediate yields, high root:shoot ratios and high tissue nutrient contents at control nutrient concentrations. H. lepidulum differed in edaphic tolerance from all but Chionochloa flavescens var. brevis, in being insensitive to nutrient dilutions other than nitrogen. The significance of performance in terms of edaphic tolerance and adaptations are discussed. Intermediate yields at control nutrient levels suggest that H. lepidulum should not be competitive compared to high yielding species including Agrostis stolonifera and Poa cita, but should be competitive with lower yielding Coprosma rugosa and C. flavescens var. brevis. Conversely, significant yield decreases under nitrogen limitation stress suggests that H. lepidulum will not likely occupy very nutrient poor sites. H. lepidulum, along with C. flavescens var. brevis, were found to be tolerant of ammonium as an alternative source of nitrogen, while other species were not. These data suggest that H. lepidulum and C. flavescens var. brevis would be relatively tolerant of the stresses associated with acidic soils compared to the other species, but not to stresses associated with absolute shortage of nitrogen. Combined results point to the likely occurrence of H. lepidulum at sites of intermediate fertility. The possible roles of ammonium stress and disturbance reliance in further defining H. lepidulum ecology is discussed. 相似文献
29.
枣麦间作枣园主要蚧虫复合种群结构及生态位 总被引:3,自引:0,他引:3
为了有效地控制枣树蚧害,2002年在太谷地区对枣麦间作枣园的康氏粉蚧(Pseudococcus comstock Kuwane)、日本蜡蚧(Ceroplastes japonicus Green)和梨园蚧(Quadraspidiotus perniciosus Comstock)的复合种群结构及其生态位进行了系统研究.结果表明,在枣树发育早期,3种蚧虫分布范围主要在下、中部的东、南方位,康氏粉蚧的时空二维生态位的宽度较大,是该时期的优势种.到中期3种蚧虫复合种群的分布聚集在树冠上部的西、北方位,时 空二维生态位的宽度以日本蜡蚧较大,种间相似程度和竞争不明显.后期3种蚧虫的复合种群结构在各部位的各个方位的分布无明显差异,但梨园蚧的虫口密度较大,日本蜡蚧在生态位上占据较大的空间.与枣树发育的中期相比,3种蚧虫复合种群结构的相似性与种间竞争系数的平均值要小.蚧害预防应早期控制康氏粉蚧,中期调治3种蚧虫的危害,后期应采取措施压低越冬虫源. 相似文献
30.
The primordial germ cells (PGCs) in the colonial urochordate Botryllus schlosseri are sequestered in late embryonic stage. PGC-like populations, located at any blastogenic stage in specific niches, inside modules with curtailed lifespan, survive throughout the life of the colony by repeated weekly migration to newly formed buds. This cyclical migration and the lack of specific markers for PGC-like populations are obstacles to the study on PGCs. For that purpose, we isolated the Botryllus DDX1 (BS-DDX1) and characterized it by normal expression patterns and by specific siRNA knockdown experiments. Expression of BS-DDX1 concurrent with BS-Vasa, γ-H2AX, BS-cadherin and phospho-Smad1/5/8, demarcate PGC cells from soma cells and from more differentiated germ cells lineages, which enabled the detection of additional putative transient niches in zooids. Employing BS-cadherin siRNA knockdown, retinoic acid (RA) administration or β-estradiol administration affirmed the BS-Vasa+BS-DDX1+BS-cadherin+γ-H2AX+phospho-Smad1/5/8+ population as the B. schlosseri PGC-like cells. By striving to understand the PGC-like cells trafficking between transient niches along blastogenic cycles, CM-DiI-stained PGC-like enriched populations from late blastogenic stage D zooids were injected into genetically matched colonial ramets at blastogenic stages A or C and their fates were observed for 9 days. Based on the accumulated data, we conceived a novel network of several transient and short lived ‘germ line niches’ that preserve PGCs homeostasis, protecting these cells from the weekly astogenic senescence processes, thus enabling the survival of the PGCs throughout the organism's life. 相似文献