Towards a trait-based quantification of species niche

Aims Although the niche concept is of prime importance in ecology, the quantification of plant species' niches remains difficult. Here we propose that plant functional traits, as determinants of species performance, may be useful tools for quantifying species niche parameters over environmental gradients.Important findings Under this framework, the mean trait values of a species determine its niche position along gradients, and intraspecific trait variability determines its niche breadth. This trait-based approach can provide an operational assessment of niche for a potentially large number of species, making it possible to understand and predict species niche shifts under environmental changes. We further advocate a promising method that recently appeared in the literature, which partitions trait diversity into among- and within-community components as a way to quantify the species niche in units of traits instead of environmental parameters. This approach allows the switch of the focus from ecological niches to trait niches, facilitating the examination of species coexistence along undefined environmental gradients. Altogether, the trait-based approach provides a promising toolkit for quantifying the species ecological niche and for understanding the evolution of species niche and traits.     

Mowing and fertilizer effects on seedling establishment in a successional old field

Aims We used a 10-year field experiment that consisted of mowing and fertilizer treatments to evaluate the role of niche limitation in seedling establishment of species from different functional groups and of varying local abundance in an old field undergoing succession.Methods Seedlings of nine different species were planted into a successional field subjected to mowing and fertilizer treatments for 10 years that resulted in different plant communities and resource availability. Species representative of the factorial combination of three functional groups (C 4 grasses, C₃ grasses and legumes) and three abundance categories (abundant, present, or absent in the old field) were planted in four treatments resulting from the factorial combination of annual spring mowing (mowed and unmowed) and fertilizer application (annually fertilized and unfertilized). Survivorship, relative growth rate (RGR) and biomass were measured to determine the role of niche limitation on recruitment and growth.Important findings Mowing increased the establishment success of seedlings. Fertilization had little influence on seedling performance and survivorship. C₃ grasses had the highest survivorship, while C₄ grasses and legumes had equivalent RGRs, but higher than C₃ grasses. By contrast, survivorship of legumes was unrelated to mowing or fertilizer, suggesting that establishment of this functional group was dependent on other, unmeasured conditions or processes. Species already present, but at low abundance, performed better than locally abundant or absent species. Propagule limitation may restrict the arrival of a species. However, recruitment and establishment was subject to niche limitation, which varied among species, functional groups and whether a species is already resident at the site and its abundance. Thus, species interactions restrict establishment during old-field succession, supporting the niche limitation hypothesis.     

Niche separation and weak interactions in the high tidal zone of saltmarsh‐mangrove mixing communities

1. Saltmarsh‐mangrove ecotones occur at the boundary of the natural geographic distribution of mangroves and salt marshes. Climate warming and species invasion can also drive the formation of saltmarsh‐mangrove mixing communities. How these coastal species live together in a “new” mixed community is important in predicting the dynamic of saltmarsh‐mangrove ecosystems as affected by ongoing climate change or human activities. To date, the understanding of species interactions has been rare on adult species in these ecotones.
2. Two typical coastal wetlands were selected as cases to understand how mangrove and saltmarsh species living together in the ecotones. The leaves of seven species were sampled from these coastal wetlands based on their distribution patterns (living alone or coexisting) in the high tidal zone, and seven commonly used functional traits of these species were analyzed.
3. We found niche separation between saltmarsh and mangrove species, which is probably due to the different adaptive strategies they adopted to deal with intertidal environments.
4. Weak interactions between coexisting species were dominated in the high tidal zone of the two saltmarsh‐mangrove communities, which could be driven by both niche differentiation and neutral theory.
5. Synthesis. Our field study implies a potential opportunity to establish a multispecies community in the high tidal zone of saltmarsh‐mangrove ecotones, where the sediment was characterized by low salinity and high nitrogen.

     

Patterns of plant functional traits in the biogeography of West African grasses (Poaceae)

Grasses (Poaceae) are the largest family of vascular plants in Burkina Faso with 254 species. In the savannahs they are the most important family in terms of abundance and species richness, in other habitats, such as gallery forests, there are only few species. On the country scale there is a change in growth form: while in the Sahelian north most grasses are small therophytes, the Sudanian south is characterized by tall, often perennial grasses. To analyse these patterns in detail, we compiled a database on grass occurrences and used it in an ecological niche modelling approach with the programme Maxent to obtain country‐wide distribution models. Secondly we used data on photosynthetic type, height, leaf width and growth form to aggregate the species distributions and quantified the relative importance of functional groups per grid cell. Pronounced latitudinal differences could be shown for life forms, photosynthesis and size: the drier north is characterized by smaller, mainly therophytic grasses with a high share of C4 NAD‐ME photosynthesis, while the more humid south is characterized by tall, often hemicryptophytic grasses with C4 NADP‐ME photosynthesis. For leaf width, no clear country‐wide patterns could be observed, but local differences with more broad‐leaved grasses in humid areas.     

Top-down determinants of niche structure and adaptation among African Acacias

The role of top-down factors like herbivory and fire in structuring species' niches, even in disturbance-dependent biomes like savanna, remains poorly understood. Interactions between herbivory and fire may set up a potential tradeoff axis, along which unique adaptations contribute to structuring communities and determining species distributions. We examine the role of herbivory and fire in structuring distributions of Acacia saplings in Hluhluwe iMfolozi Park in South Africa, and the relationship of species' niche structure to traits that help them survive herbivory or fire. Results suggest that (1) fire and herbivory form a single trade-off axis, (2) Acacia sapling distributions are constrained by fire and herbivory, and (3) Acacia saplings have adaptations that are structured by the tradeoff axis. Herbivory-adapted species tend to have 'cage'-like architecture, thicker bark, and less starch storage, while fire-adapted species tend to have 'pole'-like architecture, relatively thinner bark, and more starch storage.     

用功能生态学方法揭示峨眉髭蟾蝌蚪和棘腹蛙蟾蝌蚪共存的原因

采用功能生态学的研究方法,选取了3个指标(功能丰富度、功能定位和功能生态位的重叠程度)对峨眉山清音阁黑龙江中峨眉髭蟾蝌蚪和棘腹蛙蝌蚪共存的原因进行了解析。结果表明,峨眉髭蟾蝌蚪功能丰富度的实测值远远小于棘腹蛙蝌蚪。采用自助法随机抽样15和51个个体时,峨眉髭蟾蝌蚪的功能丰富度值显著小于棘腹蛙蝌蚪。同时,非参数多元方差分析的结果显示二者的功能定位存在显著差异。此外,二者功能生态位重叠程度的实测值与采用自助法计算所得值均极低。以上结果表明二者的功能生态位存在明显分化,表现为峨眉髭蟾蝌蚪个体较大,开口较小,眼间距较大,尾部发达且多采用背腹弯曲的游泳模式;而棘腹蛙蝌蚪开口较大,眼睛间距较小,尾部较为短小且多采用脊椎弯曲的游泳模式。鉴于功能性状可以反映生物体对生长环境的响应,推测两种蝌蚪主要栖息地的微生境也存在分化。     

温州湾春季主要游泳动物生态位与种间联结性

根据2013年春季(5月)与2014年春季(5月)在温州湾海域两次渔业资源调查的数据,运用生态位宽度、聚类分析、生态位重叠值、方差比率法、卡方检验、联结系数及功能群划分和营养级构成等方法相结合对主要游泳动物群落物种间的相互关系进行综合分析。结果表明:主要游泳动物共18种,优势种为六丝钝尾鰕虎鱼(Amblychaeturichthys hexanema)、龙头鱼(Harpodon nehereus)及银鲳(Pampus argenteus),其他15种是重要种;生态位重叠值最大值和最小值分别为0.88和0.01,总体差异性较大,部分种对间对生态利用可能存在一定竞争性;由VR值为9.90大于1,W值为366.39远超出置信区间(8.67,27.59),得知游泳动物群落总体上呈显著正相关;共同出现百分率显示强正联结的种对仅3对,不存在无关联种对,但联结系数值显示110对种对趋向独立,说明种对间具有相对独立分布的特性;按食性类型可把主要游泳动物划分成5个功能群,依次是肉食者(C)、杂食者(O)、植食者(Ph)、浮游生物食者(Pl)和碎屑食者(D),各功能群所含物种种类数百分比由高到低依次是CO=PlDPh,依据功能群间的关系得出主要游泳动物占据二、三、四级营养级,集中分布于三、四营养级。     

甘南高寒草甸退化对植物功能群多样性与物种多度分布的影响

为分析甘南高寒草甸植物功能群多样性及其物种多度分布对退化的响应,探讨其多样性的形成与维持机制,采用样地调查法收集数据,并使用物种多度模型对其进行拟合分析。结果表明:随着退化程度的加深,植被优势种以禾草科和莎草科植物为主,逐渐变为杂草功能群植物为主,杂草功能群在群落多样性分布中起着主导作用;全部物种多度分布随着退化程度的加深发生变化,其中,无退化草甸的最优拟合模型是VOLKOV,轻度退化草甸的最优拟合模型是GEO,中度退化草甸和重度退化草甸的最优拟合模型为BRO,资源分配模式由随机分配转向固定分配的分配模式;禾草功能群的最优拟合模型以生态位模型为主,资源分配方式由固定分配和随机分配共同主导,豆科功能群的最优拟合模型是BRO,资源分配方式以固定分配为主,杂草功能群的最优拟合模型从中性模型向生态位模型转变,与全部物种多度分布的最优模型基本一致,且资源分配由随机分配向固定分配转变,可以认为杂草功能群是影响群落物种多度分布的主要原因,但是禾草和豆科功能群的贡献也不可忽视。     

三江平原典型沼泽湿地植物种群的生态位

采用Levins 公式,对三江平原典型沼泽湿地植物群落的优势种群生态位宽度和生态位重叠值进行了研究.结果表明：各湿地植物种的生态位宽度排序为漂筏苔草(0.907)>毛果苔草(0.864) >狭叶甜茅(0.855) >小叶章＝睡菜＝球尾花＝二歧银莲花(0.500).毛果苔草、漂筏苔草、睡菜与球尾花之间,以及狭叶甜茅、小叶章与二歧银莲花的生态位重叠值均较高,说明几种植物在同一资源位上出现的频率相近,利用资源的能力相似,在对资源利用上具有一定的竞争性.睡菜与小叶章和二歧银莲花,以及球尾花与小叶章和二歧银莲花的生态位重叠值均为0,表明几种植物适应环境的方式不同.水分是导致湿地植物生态适应性差异的主导因子,植物对环境生态位适应的程度是水分和营养状况等因素共同作用的结果.湿地植物的生态位特征能较好地表征各植物的生态适应性和分布幅度.     

Ant association facilitates the evolution of diet breadth in a lycaenid butterfly

The role of mutualistic interactions in adaptive diversification has not been thoroughly examined. Lycaenid butterflies provide excellent systems for exploring mutualistic interactions, as more than half of this family is known to use ants as a resource in interactions that range from parasitism to mutualism. We investigate the hypothesis that protection from predators offered to caterpillars by ants might facilitate host-range evolution. Specifically, experiments with the butterfly Lycaeides melissa investigated the role of ant association in the use of a novel host, alfalfa, Medicago sativa, which is a sub-optimal host for larval development. Survival on alfalfa is increased by the presence of ants, thus supporting the hypothesis that interaction with ants might be important for host-range evolution. Using a demographic model to explore ecological conditions associated with host-range expansion in L. melissa, we conclude that the presence of ants might be an essential component for populations persisting on the novel, sub-optimal host.     

三峡库区消落带现存草本植物组成与生态位

为揭示经历长期水位变动后,三峡水库消落带优势植物对可利用资源的分享状况、不同资源环境下植物种群生态位特征以及植物种间竞争和共存机制,对三峡库区秭归段典型消落带现存优势草本物种的种群空间格局及生态位特征进行研究.结果表明: 该区共有草本植物39种,隶属18科32属,以禾本科、菊科、蓼科和大戟科植物为主;狗牙根、狗尾草、狼把草和毛马唐具有较大的重要值和生态位宽度,为主要优势种;海拔145～155 m段植物生态位宽度前3位依次为狗牙根＞酸模叶蓼＞狗尾草;海拔155～165 m段植物生态位宽度前3位依次为狗尾草＞毛马唐＞狗牙根;海拔165～175 m段植物生态位宽度前3位依次为狗尾草＞狼把草＞红蓼;不同海拔物种间生态位重叠均保持较高状态,生态位宽度较小物种也可与生态位宽度较大物种有较大的生态位重叠值,仅凭生态位宽度不能判定生态位重叠值.消落带经历7次水位涨落周年后,大多数优势物种为一年生草本植物,生态位分化程度较低,在资源匮乏且不稳定的生境中种间竞争强烈,消落带植被仍处于群落演替的初级阶段.     

植物群落功能多样性计算方法

以性状为基础的功能多样性指数在预测生态系统功能中起到越来越重要的作用.本文对近年来陆续出现的植物群落功能多样性指数进行综述.依据物种多样性指数的组成,功能多样性指数分为功能丰富度、功能均匀度和功能离散度指数.介绍了这3类指数的计算方法,有助于更好、更准确地理解“生物多样性-环境-生态系统功能”的关系.     

Tree species diversity promotes aboveground carbon storage through functional diversity and functional dominance

The relationship between biodiversity and ecosystem function has increasingly been debated as the cornerstone of the processes behind ecosystem services delivery. Experimental and natural field‐based studies have come up with nonconsistent patterns of biodiversity–ecosystem function, supporting either niche complementarity or selection effects hypothesis. Here, we used aboveground carbon (AGC) storage as proxy for ecosystem function in a South African mistbelt forest, and analyzed its relationship with species diversity, through functional diversity and functional dominance. We hypothesized that (1) diversity influences AGC through functional diversity and functional dominance effects; and (2) effects of diversity on AGC would be greater for functional dominance than for functional diversity. Community weight mean (CWM) of functional traits (wood density, specific leaf area, and maximum plant height) were calculated to assess functional dominance (selection effects). As for functional diversity (complementarity effects), multitrait functional diversity indices were computed. The first hypothesis was tested using structural equation modeling. For the second hypothesis, effects of environmental variables such as slope and altitude were tested first, and separate linear mixed‐effects models were fitted afterward for functional diversity, functional dominance, and both. Results showed that AGC varied significantly along the slope gradient, with lower values at steeper sites. Species diversity (richness) had positive relationship with AGC, even when slope effects were considered. As predicted, diversity effects on AGC were mediated through functional diversity and functional dominance, suggesting that both the niche complementarity and the selection effects are not exclusively affecting carbon storage. However, the effects were greater for functional diversity than for functional dominance. Furthermore, functional dominance effects were strongly transmitted by CWM of maximum plant height, reflecting the importance of forest vertical stratification for diversity–carbon relationship. We therefore argue for stronger complementary effects that would be induced also by complementary light‐use efficiency of tree and species growing in the understory layer.