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91.
Fernando G. Brun Elleke van Zetten Eva Cacabelos Tjeerd J. Bouma 《Helgoland Marine Research》2009,63(1):19-25
Seagrasses are well known ecosystem engineers that can significantly influence local hydrodynamics and the abundance and biodiversity
of macrobenthic organisms. This study focuses on the potential role of the seagrass canopy structure in altering the abundance
of filter-feeding organisms by modifying the hydrodynamic driven food supply. We quantified the effect of two ecosystem engineers
with contrasting canopy properties (i.e. Zostera noltii and Cymodocea nodosa) on the food intake rate of a suspension-feeding bivalve Cerastoderma edule living in these seagrass meadows. Field experiments were carried out in two seagrass beds (Z. noltii and C. nodosa) and bare sediment, located on sandflat characterised by a relatively high hydrodynamic energy from waves and currents. Results
demonstrated that the filter-feeding rate was almost twofold increased when C. edule was inhabiting Z. noltii meadows (1.10 ± 0.24 μg Chl g Fresh Weight−1) when compared to cockles living on the bare sediment (0.65 ± 0.14 μg Chl g FW−1). Intermediate values were found within C. nodosa canopy (0.97 ± 0.24 μg Chl g FW−1), but filter feeding rate showed no significant differences with values for Z. noltii meadows. There were no apparent correlations between canopy properties and filter-feeding rates. Our results imply that food
refreshment within the seagrass canopies was enough to avoid food depletion. We therefore expect that the ameliorated environmental
conditions within vegetated areas (i.e. lower hydrodynamic conditions, higher sediment stability, lower predation pressure…)
in combination with sufficient food supply to prevent depletion within both canopies are the main factors underlying our observations. 相似文献
92.
The threat to biodiversity due to invasive alien species is considered second only to that of habitat loss. Given the large
number of species that are currently invading ecosystems all over the world, we need to distinguish invaders with minor effects
from those with large effects in order to prioritize management efforts. Ecological niche models can be used to predict the
potential distribution of an invasive species from occurrence records and environmental data layers. We used the Ecological
Niche Factor Analysis (ENFA), a presence-only predictive modelling approach, to describe the invasive ring-necked parakeets’
realized niche and to identify areas suitable for the parakeet in northern Belgium. ENFA proved to be a robust and reliable
modelling technique, able to gauge the ecological requirements of an invasive species without the need to include historical
information on the starting point of the invasion. ENFA shows that the parakeets tend to occupy relatively rare habitats compared
to the main environmental conditions in northern Belgium, although they show some tolerance for environmental conditions inside
parks and forests. The general distribution of the ring-necked parakeet is governed primarily by the amount of older forest
patches, parks and built-up area in the landscape—reflecting the parakeets’ need for suitable nesting cavities and its reliance
upon urban areas to forage. Our resulting habitat suitability maps show that the parakeets have ample room to further increase
their range in northern Belgium. Our results indicate some concern for increased competition between parakeets and the nuthatches,
native cavity nesters known to suffer from competition with parakeets, as some regions known as nuthatch strongholds are highly
likely to be invaded by the parakeets. 相似文献
93.
The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding
of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order
to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that
shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial
configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides
the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and
spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest
(LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color
photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years
old) were selected within a study area of 28 km2. The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity
(Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch.
Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants.
Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species
richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate
that there is a link between landscape structure and species diversity and composition and that patches that have similar
area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition,
forest patches that were closer together had more similarity in woody plant species composition than patches that were farther
apart, suggesting that seed dispersal for some species is limited at the scale of 10 km. 相似文献
94.
A sound monitoring of appropriate biodiversity indicators is necessary in order to assess the progress towards the internationally agreed target of halting the loss of biodiversity by 2010. However, existing monitoring schemes often do not address species richness as a key component of biodiversity directly or do so with insufficient methods. I provide an overview and assessment of the large variety of different sampling approaches for small-scale plant species richness. Major shortcomings of many of these are (i) non-uniform plot sizes or shapes; (ii) analysis of only one spatial scale despite the scale dependence of nearly all biodiversity parameters; (iii) lack of replication of smaller subplots; and (iv) exclusion of bryophytes and lichens despite their often large contribution to total plant diversity. Based on this review, I propose a new standardised sampling approach for plant diversity patterns at small scales that is applicable for a multitude of purposes and in any biome. In its basic variant, species composition is recorded on nested squares of 0.01 m2, 0.1 m2, 1 m2, 10 m2, and 100 m2, with all smaller subplots being replicated at least 3-fold and evenly spaced within the next larger plot. Not only terricolous vascular plants, but also bryophytes, lichens, macro-algae as well as non-terricolous taxa should be recorded with the any-part system, i.e. those plants are counted within a plot whose superficial parts reach over it. This approach can be used to assess plant diversity patterns (i) of individual plots of interest, (ii) along environmental gradients, (iii) within specific vegetation types, or (iv) for landscape sectors. In the latter case, the series of nested plots must be placed randomly or systematically, but irrespective of plot homogeneity. The proposed approach allows the calculation of many meaningful biodiversity indicators, while being well compatible with a range of other sampling schemes, but avoiding their shortcomings. As this approach is not very time-consuming in its basic variant, but can easily be extended for specific purposes, I suggest its use for any kind of biodiversity studies and particularly for monitoring. 相似文献
95.
Background and AimsHorizontal gene transfer (HGT) is an important evolutionary mechanism because it transfers genetic material that may code for traits or functions between species or genomes. It is frequent in mitochondrial and nuclear genomes but has not been demonstrated between plastid genomes of different green land plant species.MethodsWe Sanger-sequenced the nuclear internal transcribed spacers (ITS1 and 2) and the plastid rpl16 G2 intron (rpl16). In five individuals with foreign rpl16 we also sequenced atpB-rbcL and trnLUAA-trnFGAA.Key ResultsWe discovered 14 individuals of a moss species with typical nuclear ITSs but foreign plastid rpl16 from a species of a distant lineage. None of the individuals with three plastid markers sequenced contained all foreign markers, demonstrating the transfer of plastid fragments rather than the entire plastid genome, i.e. entire plastids were not transferred. The two lineages diverged 165–185 Myr BP. The extended time interval since lineage divergence suggests that the foreign rpl16 is more likely explained by HGT than by hybridization or incomplete lineage sorting.ConclusionsWe provide the first conclusive evidence of interspecific plastid-to-plastid HGT among land plants. Two aspects are critical: it occurred at several localities during the massive colonization of recently disturbed open habitats that were created by large-scale liming as a freshwater biodiversity conservation measure; and it involved mosses whose unique life cycle includes spores that first develop a filamentous protonema phase. We hypothesize that gene transfer is facilitated when protonema filaments of different species intermix intimately when colonizing disturbed early succession habitats. 相似文献
96.
中国陆地生态系统碳源/汇整合分析 总被引:4,自引:0,他引:4
国家尺度陆地生态系统碳收支及其循环过程的研究对于提升地球系统科学与全球变化科学的科技创新能力、提高我国参与应对全球气候变化国际行动和维护国家利益的话语权、保障国家生态安全和改进生态系统管理都具有重要意义。近年来,我国已经在气候变化与陆地生态系统碳循环领域开展了大量的研究工作,主要包括国家清查、生态系统模型模拟、大气反演等手段。然而,由于大尺度陆地生态系统碳源/汇的估算存在很大的不确定性,目前尚未形成国家尺度的陆地生态系统碳源/汇的整合分析。通过搜集已发表的关于中国陆地生态系统及其组分碳源/汇的59篇文献,整合国家清查、生态系统模型模拟、大气反演3种研究手段,分析中国陆地生态系统碳源/汇大小以及时间尺度上的动态变化。结果表明,在1960s-2010s期间中国陆地生态系统碳汇整体呈上升趋势,平均为(0.213±0.030)Pg C/a,其中森林、草地、农田和灌木生态系统碳汇分别为(0.101±0.023)Pg C/a、(0.032±0.007)Pg C/a、(0.043±0.010)Pg C/a和(0.028±0.010)Pg C/a。森林生态系统中的植被碳汇远大于土壤碳汇,然而这种格局在草地和农田生态系统却相反,而且1960s-2010s期间中国主要植被类型的生态系统碳汇总体上随时间呈增加趋势。融合多源数据(地面观测、激光雷达、卫星遥感等)、多尺度数据(样地尺度、站点尺度、区域尺度)以及多手段数据(联网观测、森林清查、模型模拟),有助于全面准确地评估中国陆地生态系统碳源/汇及其对气候变化的响应。 相似文献
97.
The general tendency for species number (S) to increase with sampled area (A) constitutes one of the most robust empirical laws of ecology, quantified by species–area relationships (SAR). In many ecosystems, SAR curves display a power-law dependence, S∝Az. The exponent z is always less than one but shows significant variation in different ecosystems. We study the multitype voter model as one of the simplest models able to reproduce SAR similar to those observed in real ecosystems in terms of basic ecological processes such as birth, dispersal and speciation. Within the model, the species–area exponent z depends on the dimensionless speciation rate ν, even though the detailed dependence is still matter of controversy. We present extensive numerical simulations in a broad range of speciation rates from ν=10-3 down to ν=10-11, where the model reproduces values of the exponent observed in nature. In particular, we show that the inverse of the species–area exponent linearly depends on the logarithm of ν. Further, we compare the model outcomes with field data collected from previous studies, for which we separate the effect of the speciation rate from that of the different species lifespans. We find a good linear relationship between inverse exponents and logarithm of species lifespans. However, the slope sets bounds on the speciation rates that can hardly be justified on evolutionary basis, suggesting that additional effects should be taken into account to consistently interpret the observed exponents. 相似文献
98.
Habitat destruction, often caused by anthropogenic disturbance, can lead to the extinction of species at an unprecedented rate. It is important, therefore, to consider habitat destruction when assessing population viability. Another factor often ignored in population viability analysis, is the Allee effect that adds to the risk of populations already on the verge of extinction. Understanding the Allee effect on species dynamics and response to habitat destruction has intrinsic value in conservation prioritization. Here, the Allee effect was considered in a multi-species hierarchical competition model. Results showed that species persistence declines dramatically due to the Allee effect, and certain species become more susceptible to habitat destruction than others. Two extinction orders emerged under habitat destruction: either the best competitor becomes extinct first or the best colonizer first. The extinction debt and order, as well as the time lag between habitat destruction and species extinction, were found to be determined by species abundance and the intensity of the Allee effect. 相似文献
99.
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
100.
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