Report of the Annual Conference of the Cryptogamic Section, 1948

Background: Trait-based assembly rules are a powerful tool in community ecology, used to explore the pattern and process of community structure (richness and composition).

Aims: A preliminary test for the utility of trait-based assembly rules in explaining cryptogamic epiphyte communities (lichens and bryophytes).

Methods: We sampled epiphytes from three different tree species (aspen, birch and pine), and from trees of contrasting age. The community composition of epiphyte species (taxon analysis) and functional groups (trait analysis) was summarised using multivariate ordination (nonmetric multidimensional scaling, NMDS).

Results: Ordination documented a widely observed pattern in which different tree species have taxonomically different epiphyte communities. However, NMDS sample scores were correlated to tree age in the trait-based analysis, but not in the taxon analysis.

Conclusions: Our results point to the existence of a common pattern in community traits during succession (on trees of different age) when measured for epiphyte communities with contrasting taxonomic composition. This pattern is evidenced by consistent trends in lichen growth form and reproductive strategy (sexual vs. asexual).     

Environment is more relevant than spatial structure as a driver of regional variation in tropical tree community richness and composition

Background: Understanding how factors related to environment and geographical distance explain community variation allows insights about how ecological niche and neutral processes control tropical community assembly.

Aims: Quantify how variation in regional tree community richness and composition in a humid tropical forest across a mountain chain are related to niche and putative neutral processes.

Methods: We used a variation partitioning routine based on Redundancy Analysis to model tropical tree community richness and composition within three distinct elevation belts, as a function of environment and spatial structure, using data from 32 studies in the Serra do Mar Range, south-eastern Brazil.

Results: Environmental effects were greater than spatial structure effects to explain community variation in the three elevation belts. There was a trend of decreasing spatial structure effects while environmental effects remained constant from lower to higher elevations. Patterns were congruent for species richness and composition.

Conclusions: We suggest that on tropical mountains, niche-related processes are equally relevant for tropical forest community assembly at all elevations, while neutral processes become weaker towards higher elevations. Determining if this trend is a consequence of the greater heterogeneity of environmental conditions associated with higher elevations in tropical mountainous terrain remains an important area of research.     

Patterns of phylogenetic community structure of sand dune plant communities in the Yucatan Peninsula: the role of deterministic and stochastic processes in community assembly

ABSTRACT

Background: Tropical sand dunes are ideal systems for understanding drivers of community assembly as dunes are subject to both deterministic and stochastic processes. However, studies that evaluate the factors that mediate plant community assembly in these ecosystems are few.

Aims: We evaluated phylogenetic community structure to elucidate the role of deterministic and stochastic processes in mediating the assembly of plant communities along the north of the Yucatan Peninsula, Mexico.

Methods: We used plastid genetic markers to evaluate phylogenetic relationships in 16 sand-dune communities. To evaluate the role of climate in shaping plant community structure we carried out linear regressions between climatic variables and mean phylogenetic distance. We estimated the Net Relatedness Index and Nearest Taxon Index to identify ecological processes mediating community assembly.

Results: Observed phylogenetic structure was not different from random, suggesting that stochastic processes are the major determinants of community assembly. Climate was slightly correlated with phylogenetic diversity suggesting that abiotic environment plays a minimal role in community assembly.

Conclusions: Random assembly appears to be the primary factor structuring the studied sand dune plant communities. Environmental filters may represent a secondary factor contributing to the observed phylogenetic structure. Thus, both processes may act simultaneously to mediate the assembly of sand-dune plant communities.     

干旱荒漠区植物生态位对水盐的响应

全球气候变化对生态系统功能的影响决定着种群地位和群落演替,由于干旱区的特殊性成为研究生物响应环境变化的热点地区。为探索艾比湖流域荒漠区植物生态位对土壤水盐梯度的响应,在研究水、盐含量和植物生态位特征的基础上,应用变系数模型,分析了土壤水盐梯度下的群落组成和生态位响应趋势。结果显示:(1)随土壤水盐梯度的降低,艾比湖流域群落的物种组成呈倒"V"型分布,说明土壤水盐交互作用影响着植被分布和群落类型。(2)高水盐环境下,胡杨(Populus euphratica)、琵琶柴(Reaumuria soongorica)和梭梭(Haloxylon ammodendron)等生态位宽度值(B_i)较大,柽柳(Tamarix ramosissima)、骆驼刺(Alhagi sparsifolia)和甘草(Glycyrrhiza uralensis)等B_i较小;中水盐环境下,白刺(Nitraria schoberi)和琵琶柴的B_i较大,铃铛刺(Halimodendron halodendron)、甘草和盐节木(Halocnemum strobilaceum)的B_i较小;低水盐环境下,梭梭、花花柴(Karelinia caspica)和琵琶柴等B_i较大,盐节木的B_i较小;说明土壤水盐环境和物种生态学特性是影响B_i的重要因素。(3)物种水平上,B_i较大的种群与其他物种的生态位重叠(O_(ij))一般较大,但B_i较小的物种间的O_(ij)不一定小(例如:高水盐土壤环境下柽柳和骆驼刺的O_(ij)为1);群落水平上,B_i与O_(ij)具有一定的正相关性;说明由于资源纬度的相似性增大了低B_i物种间的O_(ij),并且B_i和O_(ij)由物种向群落尺度转换时,两者之间的关系存在冗余。(4)土壤水盐梯度与群落生态幅呈现一种非线性相关特征,高水盐格局对群落B_i有一定的促进效应,而低水盐模式对B_i具有一定的限制作用,表明土壤水盐的协同效应影响着物种在群落的地位,并在一定程度上决定了群落向正负两极演替的方向。     

Abundance,richness and composition of lianas in forest communities along an elevation gradient in New Caledonia

Background: Lianas are an abundantand dynamic component of tropical forests, and their abundance ispredicted to increase with global change. A better understandingof factors that explain their distribution is required, especially onoceanic islands for which few data are available.

Aims: Identifythe environmental factors that shape liana communities in NewCaledonian forests

Methods: We studied liana abundance,basal area, richness and climbing modes in 27 forest plots (20m × 20 m) along an elevation gradient (sea level to ca. 1000 ma.s.l.) that covers different forest types and precipitation regimes.

Results: We inventoried 992 lianas belonging to 71 species. The abundance and basal area decreased logarithmically withincreasing elevation while species richness tended to peak at midelevations.Twining lianas were the most abundant and species-richfunctional group. We found no clear relationship between climbingmodes and forest structure.

Conclusions: Our results show thatliana abundance decreases with increasing elevation in responseto lower precipitation in seasonal dry forest. At high elevation (600–1000 m a.s.l.), climbing secondary hemi-epiphytes replace lianasprobably as a result of climate-based niche differentiation. Variationof species richness along the gradient could not be explained byprecipitation or by forest structural parameters.     

烟台近海浮游动物优势种空间生态位研究

根据2018年春、夏季烟台近海海域的调查资料,以浮游动物优势种(类)为研究对象,运用Levins公式和Pianka指数分析了浮游动物优势种(类)的生态位宽度和生态位重叠程度,采用冗余分析(RDA)研究了影响浮游动物优势种(类)空间生态位分化的主要因素。研究结果表明,浮游幼虫和桡足类是烟台近海浮游动物群落结构的主要组成群体,春、夏季浮游动物优势种(类)更替率为73.33%。依据烟台近海浮游动物优势种(类)的生态位宽度值,可将其划分为广生态位、中生态位和窄生态位三大类群,广生态位种类为浮游动物优势种(类)的主要构成群体,春季代表种类有短角长腹剑水蚤(Oithona brevicornis)、拟长腹剑水蚤(Oithona similis)等,夏季代表种类有小拟哲水蚤(Paracalanus parvus)、克式纺锤水蚤(Acartia clausi)等。生态位重叠指数与物种分布的环境位点的重合情况密切相关,广生态位种类之间的生态位重叠程度要高于窄生态位种类与其他种类之间的生态位重叠程度。RDA分析表明,春季影响浮游动物优势种(类)空间生态位分化的主要因素为海水温度、盐度和无机氮(DIN),夏季为海水盐度、叶绿素a(Chl a)、无机氮(DIN)和活性磷酸盐(PO_4-P)。     

Evidence for community assembly constraints during succession in dune slack plant communities

Community assembly during succession can be constrained by both local and regional factors. Despite an increasing regional species pool size during succession, we found a limit on the number of species in 1 × 1 m plots in dune slacks. Three alternative hypotheses (habitat heterogeneity, dispersal limitation and niche limitation) explaining this community saturation were tested. A null model analysis showed that species richness in the plots had an unusually low variance suggesting that beta habitat diversity was not likely to explain the limitation on species richness. Because we did not find a correlation between the distribution of species over the slack and their dispersal capacity, we also excluded the dispersal limitation hypothesis. Finally, a guild proportionality analysis revealed that the abundances of forb, graminoid and ruderal species showed low an unusually low variance over all age classes involved. This provides evidence for nonrandom community assembly during succession, likely to be determined by competitive exclusion among species of the same guild.     

Linking small-scale topography with microclimate,plant species diversity and intra-specific trait variation in an alpine landscape

Background: Small-scale topographic complexity is a characteristic feature of alpine landscapes, with important effects on alpine plant distribution.

Aims: We investigated the links between small-scale topographic complexity and resultant microclimatic heterogeneity, vascular-plant species richness and beta diversity, and realised niche width and trait variation of some target species.

Methods: We recorded temperature and soil moisture within 10 sites (40 m × 40 m) of differing topographic complexity in alpine terrain at Finse, Norway (N 60° 36?, E 7° 33?). Plant species occurrence and traits of target species were recorded in 16 sample plots at each site.

Results: Sites differed significantly in microclimatic heterogeneity, and topographically rough sites were always more heterogeneous than flatter ones. Greater species richness and turnover was associated with greater microclimatic heterogeneity, and rough sites contained 15–55% more species than flatter ones. Plant species had on average wider realised niches when growing at rough sites. Individuals of Bistorta vivipara, but not those of Luzula spicata, tended to exhibit greater phenotypic variation at rough sites.

Conclusions: Rough alpine terrains create small-scale variation in microclimate, promoting species richness and beta diversity. In the event of climate change, small-scale microclimatic heterogeneity might allow plant species to escape from regional climate change by short-distance migration to local micro-refugia. This study suggests that the opportunity for such responses would be greater in topographically complex terrains.     

Changes in the Structure of Bryophytic Communities with the Progress of Succession on Sand-dunes

Abstract

Reference is made to a previous paper discussing relationships between habitat conditions and the structure of bryophytic communities, as expressed by the application of a classification of growth-form in British terrestrial bryophytes. The effects of a changing habitat upon community structure are now considered by investigating the representation of certain growth-form types as succession proceeds on a sand-dune. The sequence of vegetation zones passing inland across the dunes is regarded as indicative of the stages in succession.

The relative prevalence of the chief growth-form types is expressed semi-quantitatively by (a) a logarithmic transformation of frequency data for component species, and (b) a comparison of shoot-weights from a series of samples, with the following results:

(1) Pioneer colonization of the mobile dunes is carried out mainly by species of a Short turf growth-form; to a lesser extent by representatives of the Mat form.

(2) The latter reach their maximum in the fixed dune community, when Wefts enter and become prominent.

(3) Wefts are predominant in the bryophytic community of the dune pasture.

The growth-form of the chief species in each group is described in some detail, including reference to a degree of plasticity in the form adopted by Brachythecium albicans(a Mat-former). The relationships between the structure characteristic of the communities at each stage in succession and the prevailing environmental conditions are examined.

Grateful acknowledgement is made to Mrs. E. T. Robertson for her help in the field and in the planning of this work.     

Coexistence of Banksia species in southwestern Australia: the role of regional and local processes

Abstract. 60 of the 75 Banksia species are confined to southwestern Australia where five or six species often coexist. We explored the role of regional species richness, niche differentiation, and habitat specialization in structuring banksia assemblages. The diversity of growth forms and categories of seed production and response to fire were assessed in actual assemblages at 40 sites throughout southwestern Australia. Diversity indices at each site were compared with those from null communities assembled on the basis of the abundance and sociability of taxa in regional species pools. The relationship between local and regional species richness suggests that processes at the scale of 100-m² quadrats limit local richness and therefore coexistence. However, there was no consistent evidence that taxa are differentiated by growth form or regeneration strategy. No particular biological profile makes a banksia adept at coexisting with a wide range of other taxa. Habitat specialization is an important factor contributing to lower local richness than would be predicted from niche differentiation of taxa in regional pools. There is recent empirical evidence of several mechanisms whereby the number of coexisting banksias is increased beyond the limits suggested by simple niche theories. Variability in the fire regime also provides a mechanism for maintaining local species richness because different fires favour recruitment of different taxa.     

缙云山大头茶(Gordonia acuminata)生态位研究

基于四川缙云山森林群落演替系列群落取样, 采用Ｌｅｖｉｎｓ 生态位宽度、Ｆｅｉｎｓｉｎｇ 和Ｓｐｅａｒｓ相似性比例生态位宽度及Ｌｅｖｉｎｓ 生态位重叠、Ｐｅｔｒａｉｔｉｓ 生态位重叠等计测公式, 对大头茶（ Ｇｏｒ ｄｏｎｉａ ａｃｕｍｉｎａｔａ） 种群的生态位特征及动态进行了研究。结果表明, 大头茶种群生态位宽度在演替系列群落中由小到大再减小, 它与缙云山森林群落其它优势乔木种群的生态位特定重叠主要表现在同针叶林中的川灰木（ Ｓｙｍｐｌｏｃｏｓ ｓｅｔｃｈｕｎｅｎｓｉｓ） 、杉木（ Ｃｕｎｎｉｎｇｈａｍｉａ ｌａｎｃｅｏｌａｔａ） 、马尾松（Ｐｉｎｕｓ ｍａｓｓｏｎｉａｎａ） 种群上; 反之, 其它优势乔木种群在大头茶种群上的生态位特定重叠在大头茶纯林中表现较显著; 从总体上, 所选１５ 个优势种群在各类群落中均不表现出显著的生态位普遍重叠。反映了大头茶种群在缙云山森林群落演替中的先锋拓殖作用, 亦为其常绿阔叶林的重要种群之一, 但它更重要的是一森林群落演替过渡类型的优势种群。     

乌鲁木齐达坂城山区地衣生态位特征的研究

为揭示达坂城山区地衣对生境资源的利用状况及竞争程度,该研究在野外设置30个样方并调查其物种盖度数据,利用生态位宽度、生态位重叠指数及排序分析,探讨达坂城山区地衣的生态位特征及环境影响因子。结果表明:(1)达坂城山区生态位最宽的为丽黄鳞衣(Rusavskia elegans)和内卷野粮衣(Circinaria contorta),对不同环境具有较强的适应性,其他地衣物种生态位宽度较窄,对环境资源利用程度低。(2)物种间生态位重叠值整体偏低,生态位重叠值较高的物种对极少,地衣物种生态位分化程度高,物种间竞争不激烈。(3)生态位较宽的物种与多数物种之间都存在生态位重叠,但重叠值较低; 一些生态位较窄的物种与其他物种之间的生态位重叠值较高; 生态位重叠和生态位宽度之间并无直接的线性关系。(4)地衣物种沿海拔梯度分布具有差异,海拔、光照强度、湿度、风速和人为干扰是本地区地衣群落物种生态位特征差异的主导环境因子。综上所述,达坂城山区地衣物种由于生境资源的竞争占据各自独特的生态位,形成了生态位的分化,群落较为稳定,沿海拔梯度的生境条件差异是物种差异分布的重要原因。该研究可为地衣群落构建研究提供理论依据,并对该地区地衣物种的多样性和生境保护具有重要意义。     

Environmental Productivity and Biodiversity Effects on Invertebrate Community Invasibility

Productivity influences the availability of resources for colonizing species. Biodiversity may also influence invasibility of communities because of more complete use of resource types with increasing species richness. We hypothesized that communities with higher environmental productivity and lower species richness should be more invasible by a competitor than those where productivity is low or where richness is high. We experimentally examined the invasion resistance of herbivorous meiofauna of Jamaican rock pools by a competitor crustacean (Ostracoda: Potamocypris sp. (Brady)) by contrasting three levels of nutrient input and four levels of species richness. Although relative abundance (dominance) of the invasive was largely unaffected by resource availability, increasing resources did increase the success rate of establishment. Effects of species richness on dominance were more pronounced with a trend towards the lowest species richness treatment of 2 resident species being more invasible than those with 4, 6, or 7 species. These results can be attributed to a ‘sampling effect associated with the introduction of Alona davidii (Richard) into the higher biodiversity treatments. Alona dominated the communities where it established and precluded dominance by the introduced ostracod. Our experimental study supports the idea that niche availability and community interactions define community invasibility and does not support the application of a neutral community model for local food web management where predictions of exotic species impacts are needed.     

A trait-based approach predicting community assembly and dominance of microbial invasive species

Understanding the mechanisms underlying community assembly helps to define success and susceptibility to biological invasions. Here, we explored phytoplankton community assembly following niche and neutral paradigms and using a trait-based approach. Under the hypothesis that the morphology-based functional groups (MBFG) clusters species with similar niche, we analysed how trait-related differences in fitness influence dominance of an invasive species. This was based on literature review, field data and model simulations. We predict that invading species can be dominant if: 1) do not belong to the local MBFG but use unexploited areas of the niche, or 2) belong to the resident MBFG but exhibit a higher fitness due to a particular combination of traits. The invasive dinoflagellate Ceratium furcoides was used as the model species to evaluate these hypotheses, its morphological (e.g. volume) and physiological (e.g. growth rates) traits were compared with species from the same (V: photosynthetic flagellates) and different (VII: colonial cyanobacteria) MBFG. Fitness was estimated using models parametrized with MBFG rates (R*, ability to draw down phosphate) under different environmental conditions (i.e. flushing). Results contributed to support both hypotheses. First, the alternation of C. furcoides and cyanobacteria dominance was explained by the use of different niches. Secondly, species from MBFG V were dominant under similar environments. Within this group V C. furcoides showed higher fitness under low flushing and high predation, advantage provided by a distinctive combination of traits. The application of trait-based approaches to represent the niche and estimate fitness along environmental gradients was useful to evaluate community assembly and can be used to predict the dominance of microbial species invasions.     

Distinguishing the importance between habitat specialization and dispersal limitation on species turnover

Understanding what governs community assembly and the maintenance of biodiversity is a central issue in ecology, but has been a continuing debate. A key question is the relative importance of habitat specialization (niche assembly) and dispersal limitation (dispersal assembly). In the middle of the Loess Plateau, northwestern China, we examined how species turnover in Liaodong oak (Quercus wutaishanica) forests differed between observed and randomized assemblies, and how this difference was affected by habitat specialization and dispersal limitation using variation partitioning. Results showed that expected species turnover based on individual randomization was significantly lower than the observed value (P < 0.01). The turnover deviation significantly depended on the environmental and geographical distances (P < 0.05). Environmental and spatial variables significantly explained approximately 40% of the species composition variation at all the three layers (P < 0.05). However, their contributions varied among forest layers; the herb and shrub layers were dominated by environmental factors, whereas the canopy layer was dominated by spatial factors. Our results underscore the importance of synthetic models that integrate effects of both dispersal and niche assembly for understanding the community assembly. However, habitat specialization (niche assembly) may not always be the dominant process in community assembly, even under harsh environments. Community assembly may be in a trait‐dependent manner (e.g., forest layers in this study). Thus, taking more species traits into account would strengthen our confidence in the inferred assembly mechanisms.     

敦煌西湖荒漠-湿地生态系统优势物种生态位研究

水文情势改变会引起土壤盐分变化,直接影响到荒漠-湿地生态系统植被的分布与演替。基于对57个样地、171个样方植物物种分布影响较大的土壤pH值和土壤电导率两个环境因子,将其划分为6个梯度等级,测度分析了敦煌西湖植被群落中15个主要优势种的生态位特征,了解不同物种利用资源和占据生态空间的能力,对维持和科学保育植物群落的多样性具有重要意义。结果表明：（1）在土壤pH值和电导率梯度两个资源维上,多枝柽柳和芦苇的重要值和生态位宽度均较大,说明这两个物种适应能力强能够较好地利用环境资源,分布范围大且均匀。它们作为敦煌西湖植被群落中的广域种,具有重要的生态地位和作用。其次生态位较宽的疏叶骆驼刺、胡杨和苏枸杞对环境因子也具有较强的适应能力。（2）两个土壤因子梯度下植物种群生态位宽度相似,但也存在差异。如泡泡刺、蒙古沙枣在土壤pH值梯度资源维上的生态位宽度值远大于在土壤电导率梯度资源维上,但尖叶盐爪爪和甘蒙柽柳在土壤电导率梯度资源维上生态位宽度较大,表现出较强的耐盐能力,从而说明这些物种对不同土壤因子的利用能力和适应性不完全相同。（3）在两个资源维上优势物种间的生态位重叠值小于0.5的种对均为61对,占总种对的58.10%,因此生态位重叠值整体保持在较低水平,说明物种在土壤pH值和土壤电导率两个环境梯度上生态位分化明显。（4）敦煌西湖优势物种间总体表现为不显著的负关联,表明物种之间处于竞争关系,但竞争强度不大且群落结构稳定性较弱。     

Time and space in the community structure of a species-rich limestone grassland

Abstract. The community structure of a species-rich grassland was investigated at a small spatial scale (0.001 m²), to determine whether evidence suggesting assembly rules could be found in temporal or spatial variation in either species richness or guild proportions. The community was alvar limestone grassland on the island of Öland, Sweden. Three sites were sampled: two lightly grazed, the other recently ungrazed. Plots with and without fertilizer were compared. Evidence was sought for restriction on the ability of species to co-occur within a limited spatial area. Restriction due to a limited number of niches available,‘niche limitation’, could be manifest as lower variance in quadrat richness than expected under a null model (i.e. RV_r, the ratio of observed: expected variance in richness, would be < 1.0). In several cases, RV_r values were significantly < 1.0, even using a patch model to allow for possible spatial variation in the environment. Low RV_r values were found only at the smallest square quadrat size, 10 cm². On Fertilized plots in the years immediately after application of fertilizer, low RV_r could not be demonstrated. Explanations of low RV_r other than niche limitation are considered, such as environmental heterogeneity (present and/or historical) and limitations to the co-occurrence of individual plant modules. Assembly rules based on guild membership were sought by looking at the variance across quadrats in the proportions of species from morphological guilds. An assembly rule would be seen as relatively constant proportion, estimated via RV_gp, the ratio of observed: expected variances in guild proportions. Significant guild proportionality was found in some cases. There was no evidence of guild proportionality in the years after the application of fertilizer. The significant effects in RV_r were more numerous than expected on a random basis, though not observed in every site in every year. Similar trends were seen in RV_gp. At the space/time scales examined, the species in a plant community may be constrained by assembly rules only intermittently, e.g. when resources are more limiting (Wiens 1977). Under this concept, when competition is relaxed, such as following fertilizer application, there is a temporary microhabitat ‘waterhole’ in which more species can coexist, and the assembly rules break down, at least temporarily whilst the species composition adjusts. There was some indication of a return to more deterministic community structure four years after fertilization commenced. Variants of van der Maarel's Carousel model were tested. A Niche-limited Carousel Model (i.e. a model in which there is some limitation in the number of species that can occupy a microsite) would imply restricted variation in richness through time for a single quadrat (temporal RV_r). Overall differences between years in species richness were demonstrated, and their effect removed; after this adjustment there was support for the Niche-limited Carousel Model. The extent of this limitation varied between sites. There were also consistent differences between quadrats in species richness. There was little evidence for constancy of guild proportions through time. The site that showed the strongest community structure in time and space, least year-to-year variation in mean species richness, and least response to fertilizer perturbation, is that on the shallowest soil. Possibly the thin soil results in greater resource limitation, supporting suggestions that assembly rules are stronger when resources are more limited.     

喀斯特石漠化锑矿区植物群落主要物种生态位特征及其种间联结

锑矿的开采等活动剥离了喀斯特石漠化区的地上植被,导致该区群落物种组成与结构被破坏、生态系统受损或功能丧失。为了解锑矿开采后生态破坏区优势物种亮叶桦(Betula luminifera)群落特征及演替状态,并为复层植被重建的物种选择提供理论依据。基于贵州晴隆大厂镇锑矿生态破坏区调查数据,分析了该区优势物种的Levins生态位宽度和Pianka生态位重叠度,并运用卡方检验(χ²)、Ochiai指数(OI)和Pearson相关性计算了群落优势物种种间联结性。结果表明：(1)石漠化锑矿生态破坏区物种组成远低于未破坏区(30科53属68种),仅为14科18属22种,乔木层物种仅为亮叶桦,灌木层物种重要值由高到低依次为密蒙花(Buddleja officinalis)、茅莓(Rubus parvifolius)和水麻(Boehmeria penduliflora)等,草本层物种重要值由高到低依次为芒(Miscanthus sinensis)、头花蓼(Polygonum capitatum)、破坏草(Ageratina adenophora)、艾草(Artemisia argy...     

Competitive displacement or biotic resistance? Disentangling relationships between community diversity and invasion success of tall herbs and shrubs

Questions: Are negative invasion–diversity relationships due to biotic resistance of the invaded plant community or to post‐invasion displacement of less competitive species? Do invasion–diversity relationships change with habitat type or resident traits? Location/species: Lowlands and uplands of western and southern Germany, Heracleum mantegazzianum; mountain range in central Germany, Lupinus polyphyllus; and coastal dunes of northwest Germany, Rosa rugosa. Methods: We tested the significance and estimated regression slopes of invasion–diversity relationships using generalized linear (mixed effects) models relating invader cover and habitat type to species richness in different plant groups, stratified based on size, life cycle and community association. Results: We found negative, positive and neutral relationships between invader cover and species richness. There were negative linear correlations of invader cover with small plant species throughout, but no negative linear correlation with tall species. Invasion–diversity relationships tended to be more negative in early‐successional habitats, such as dunes or abandoned grasslands, than in late‐successional habitats. Conclusions: Invasion diversity–relationships are complex; they vary among habitat types and among different groups of resident species. Negative invasion–diversity relationships are due to asymmetric competitive displacement of inferior species and not due to biotic resistance. Small species are displaced in early‐successional habitats, while there is little effect on persistence of tall species.     

扎龙湿地藻类优势种生态位及其种间联结性动态分析

为了解扎龙湿地藻类群落结构的季节特征和演替规律,对扎龙湿地藻类群落进行了分析,主要涉及藻类优势度、生态位、MFG功能群划分、生态位重叠值及联结系数分析。结果表明：(1)在检出的8门311种藻类中,夏季种类丰富度最高,全年优势种为狭形纤维藻和啮蚀隐藻。(2)优势种种类和密度季节性差异较大,春季以金藻-绿藻种类为主,夏季以绿藻-隐藻种类为主,秋季以隐藻-绿藻种类为主。(3)生态位宽度值与MFG功能群划分结合分析表明,优势种可分为3个大类别,不同种类对资源利用情况的差异较大,各季节广生态位种能较好的反映扎龙湿地水体环境的季节变化趋势。(4)生态位重叠值在不同季节上有较大差异,O_ik>0.6的占比分别为42.86%(春)、28.57%(夏)和25.00%(秋),表明春季优势种种间资源的竞争最为突出,种间竞争强于夏、秋两季。(5)种间联结性检验结果显示,扎龙湿地藻类优势种间总体联结上呈正关联关系,但是种间联结较为松散,种与种之间相对独立。研究表明,扎龙湿地藻类群落结构生态位测度均存在明显的季节波动,较好反映出水环境季节变化特征,可用来指示湿地水体环境的变化。