不同积水生境对河南黄河湿地植物多样性的影响

湿地作为水陆交替的过渡地带,承担着重要的生态服务功能,湿地植物是生态功能作用发挥的基础。不同积水生境与湿地植物物种组成和分布关系密切。黄河流域是国家的重要生态屏障,湿地面积广阔,河南黄河湿地作为黄河湿地的重要组成部分,其积水生境对植物多样性的影响尚不清晰。为研究河南黄河湿地植物的多样性现状以及积水生境对其植物多样性的影响,采用样方和样线相结合的方法对河南省7个黄河湿地自然保护区中的湿地植物进行调查,共设置样方981个。重点分析了不同积水生境湿地植物的主要群系和物种组成,研究了各生境物种多样性和群落多样性特征（α多样性）,对比了的不同积水生境植物物种组成相似性和群落间相似程度（β多样性）,明确了各生境的植物物种排序和指示种。结果表明：（1）河南黄河湿地植物群系以草本群系为主,共发现188种湿地植物,分属56科,138属;（2）不同积水状况湿地植物物种丰富度大小依次为：季节性积水 > 永久性积水 > 间歇性积水 > 季节性水涝,主要群系总数与物种丰富度趋势表现一致;（3）不同积水生境湿地植物的物种组成存在显著差异,季节性积水和永久性积水生境中植物物种组成相似性和群落间相似程度最高,各积水生境均有明显的优势种和指示种。河南黄河湿地积水生境在不同流段差异显著,不同积水生境下植物多样性和主要植物群系有明显区别,进行湿地生态建设时,建议优先保护季节性积水生境,减少季节性水涝生境的产生,以达到维持物种多样性,发挥湿地最大生态价值的目的。     

草海自然保护区空心莲子草群落植物组成及多样性分析

湿地生态系统极易受外来入侵植物侵害, 为调查草海湿地生态系统空心莲子草不同入侵程度的群落物种组成及多样性的变化, 在夏季对草海自然保护区水陆生境的空心莲子草群落进行调查, 按空心莲子草盖度分为水Ⅰ(0-20%)、水Ⅱ(20%-50%)、水Ⅲ(50%-100%)、陆Ⅰ(0-20%)、陆Ⅲ(50%-100%)五种群落类型。结果表明: 在调查的25 个样方中, 水生生境共有10 科22 种植物, 陆生生境共有13 科29 种植物, 随空心莲子草入侵程度的增加, 禾本科植物在两种生境中比例均上升; 地面芽植物种类减少; 根茎型植物种类增加; 水中丛生型植物种类增加, 陆地分枝型植物种类减少; 水中物种丰富度增加, 陆地物种丰富度降低; 两生境多样性和均匀度均呈一致的下降。     

浙北地区不同土地利用下乡村草本层植物多样性研究

该文以浙江省安吉县两个典型乡村—繅舍村和赋石村为例,选取公园、农耕区、河道、人工林地四种不同土地利用类型,用Shannon-Wiener指数、Simpson指数、Sorensen指数为标识多样性的指标,分析不同生境下草本植物多样性差异。结果表明：乡村生境中共记录物种162种,分属47科123属,其中禾本科与菊科物种数占总数的31.48％;农耕区生境的Shannon-Wiener指数、Simpson指数最高,分别为2.76和0.91,农耕区与河道的Sorensen指数最高为0.57。从农耕区、河道、公园到林地生境,草本物种多样性整体呈减小趋势。另外,发现人工绿化措施会导致草本物种减少,如从种植水稻单一作物到复合作物,草本层植物随之改变。单一稻田与复合种植区比较,草本植物主要的科属组成无明显变化,莎草科、菊科、禾本科植物仍占主体;但草本植物群落主要物种组成发生变化,稻田转变成农耕区后,牛筋草、黑麦草,碎米荠、小飞蓬、喜旱莲子草成为草本层群落主要构成植物,水竹叶覆盖度减少,小飞蓬和喜旱莲子草的覆盖度增加。此外,还发现4种生境中共有喜旱莲子草、加拿大一枝黄花、土荆芥三种入侵物种,但未能对本土物种构成显著影响。这表明不同土地利用方式会严重影响草本群落物种组成及物种多样性;土地利用方式的变化,会引起草本植物主要群落构成发生改变;土地利用类型的多样化有利于本土草本物种多样性生存。该研究结果有助于为城镇化进程中保护乡村植物多样性、加速推进美丽中国建设提供技术支撑。     

南中国海地区湿地植物多样性研究

对南中国海地区湿地的植物多样性进行了深入研究,调查范围包括浅水海域、潮间带滩涂、河口地带和三角洲冲积平原、三角洲基塘等湿地类型。基本弄清了南中国海湿地植物的生境多样性、物种多样性以及生态系统多样性,为有效保护和合理利用南中国海湿地资源提供科学的依据。调查表明,南中国海近海近岸湿地生境多样性复杂,物种丰富。主要生境类型有浅海水域湿地等13类;湿地高等植物的生态系统主要有红树林湿地生态系统等6种;南中国海地区湿地共有高等植物179科,593属,829种。国家Ⅰ级保护植物3种,Ⅱ级保护植物9种。     

杭州西溪和绍兴镜湖国家湿地公园内的维管植物多样性

调查显示,杭州西溪湿地共有维管植物511种,其中蕨类和裸子植物各11种、被子植物489种,隶属于111科352属;绍兴镜湖湿地维管植物384种,其中蕨类12种、裸子植物11种、被子植物361种,隶属于101科285属.两地物种较为丰富.区系成分、生态类型和生长型比较以及β多样性分析均显示,两地有较高的物种相似度,这与两地同处于亚热带东部地区以及相似的人类影响有关.西溪和镜湖的湿地植物分别为280种(54.8%)和200种(52.1%),占据总物种数量的比例较低,是一定程度退化湿地的表现.建议在今后的修复和建设中,多培育湿地环境和湿地植物;同时需保留一定的管理强度,使多样化的生境、丰富有益的动植物物种得以维持,两湿地的生态和社会服务功能得到更好的体现.     

基于植物多样性特征的武汉市城市湖泊湿地植被分类保护和恢复

湿地植被多样性特征及其影响因素的调查分析是湿地植被保护与恢复策略制定的基础。借鉴生物多样性热点分析原理,在武汉市城市湖泊湿地植物多样性调查的基础上,研究了湖泊湿地的植被多样性特征,探讨了城市湖泊湿地植被分类保护与恢复对策。结果表明,武汉市湿地维管束植物的物种丰富度、植物多样性、优势度和均匀度指数在各湖泊间的变化趋势较为一致,但在空间变化幅度上存在一定差异。按照物种丰富度、多样性、优势度、均匀度、湿地植被群丛数目,以及典型湿地植物的物种所占比例、丰富度和优势度的差异,可将调查涉及的26个典型湖泊湿地分为原生植被湖泊、次生植被湖泊、人工植被湖泊和退化植被湖泊4类。原生植被湖泊应建立相对严格的湿地保护区,优先保护原有湿地植被。次生植被湖泊最多,城市发展区内的次生植被湖泊应建立30-100m的植被缓冲带,促进植被自然恢复和发育;而农业区的次生植被湖泊应引导和规范湖泊周围的农业生产模式,以减少人类活动干扰。人工植被湖泊应通过建立城市湿地公园,人工促进植被的近自然恢复。而退化植被湖泊则应尽快采用生态工程法促进湿地植被生境改善,并积极开展近自然湿地植被重建与恢复。     

北方典型沼泽湿地高低土壤水分下植物群落特征

北方沼泽湿地在水源供给、缓解水土流失、遏制草地沙化等方面具有重要作用,明确其植物群落物种组成和多样性特征对提升其生态系统服务功能具有重要意义。目前,在北方地区开展大尺度湿地植被调查的研究仍相对较少。土壤水分是驱动植物群落发展的主导环境因素之一,为了解高低土壤水分背景下湿地植物群落特征差异及关键驱动要素,对我国7个北方典型沼泽湿地的植物群落物种组成及多样性特征进行了调查,分析了植物群落物种组成及多样性特征与环境因子的关系,以及沼泽湿地植物群落内克隆植物的分布特征。研究结果发现不同沼泽湿地的植物群落物种组成和多样性差异显著,但无明显的地带性分布规律,物种分布呈现区域性。群落物种多样性受降水、温度、土壤养分等多种环境因素的共同影响。沼泽湿地高低土壤水分背景下植物群落的物种组成和多样性差异显著,低土壤水分下植物群落物种多样性指数显著高于高土壤水分下植物群落。低土壤水分下物种多样性主要受降水和总氮影响,而高土壤水分下物种多样性主要受温度和总磷的影响。高土壤水分下克隆植物物种数和盖度在沼泽湿地植物中占有较高的比例,表明克隆植物比非克隆植物更适应高土壤水分环境。研究结果表明了7个沼泽湿地植被的区域性...     

天然林和人工林外来入侵和本地植物对比研究: 以弄岗国家级自然保护区为例

外来植物的入侵严重威胁了自然保护区的生物多样性。为探讨自然保护区内天然林和人工林林下外来植物入侵状况及其与本地优势植物的种间关系, 本研究以弄岗国家级自然保护区为研究区域, 结合保护区内4种生境72个样方的野外调查数据, 利用生态位宽度、生态位重叠和种间联结指数比较了不同生境中外来入侵草本植物的多样性和生态位宽度以及外来入侵草本植物与本土优势草本植物的生态位重叠和种间联结。结果表明: 弄岗国家级自然保护区4种生境共记录6种外来入侵草本植物, 隶属于3科6属, 其中菊科物种数量最多。外来入侵植物多样性呈现出秋枫(Bischofia javanica)人工林 > 麻竹(Dendrocalamus latiflorus)次生林 > 人面子(Dracontomelon duperreanum)人工林 > 广西澄广花(Orophea polycarpa)次生林的特征。除广西澄广花次生林生境的外来入侵草本植物丰富度与本土草本植物丰富度呈显著正相关外, 其余生境均无显著的相关关系。三叶鬼针草(Bidens pilosa)的生态位宽度最大, 为4种生境均有分布的外来入侵植物。4种生境的外来入侵植物与本土优势植物生态位重叠和种间联结程度均较低, 种间竞争较弱。本研究明确了弄岗国家级自然保护区天然林和人工林中外来入侵草本植物的分布及其与本土草本植物的种间关系。     

四川攀西地区云南松群落物种多样性和谱系多样性对紫茎泽兰入侵的影响

外来植物入侵严重威胁着入侵地本土植物多样性和生态系统功能, 认识外来物种的入侵机制有助于提高对入侵植物的防控能力。本文以攀西地区云南松(Pinus yunnanensis)林下外来入侵植物紫茎泽兰(Ageratina adenophora)为研究对象, 基于大量野外群落调查, 从群落可入侵性入手, 分析了环境因子和群落物种多样性、谱系多样性等群落生态学特征对紫茎泽兰入侵的影响。结果表明: 海拔、坡向和火烧强度等环境因子和冠层郁闭度、灌木层盖度等生物因子对研究区紫茎泽兰入侵强度没有显著影响(P > 0.05); 但群落灌木层物种多样性和草本层组分种与紫茎泽兰的亲缘关系显著影响紫茎泽兰的入侵强度(P < 0.05), 说明灌木层对光照等环境资源的占用和草本层(同层)物种对相似资源的竞争能够在很大程度上抑制紫茎泽兰的入侵。     

三峡水库蓄水对消涨带植被的初步影响

三峡库区消涨带植被一直受到广泛关注。为了研究水库蓄水对175 m以下消涨带原有植被的潜在影响,2008年8月在三峡大坝上游长江干流从巴南到秭归12个监测点,设立68个5 m×5 m永久监测样方,比较被水淹过的156 m以下与当时尚未水淹的156～175 m地段植被物种组分、物种多样性和草本层生物量的差异。结果表明：被水淹过与尚未水淹的植被物种组分存在显著差异,DCA可以将二者明显分开,156 m以上尚未水淹的植被以灌丛为主;156 m以下被水淹过的植被以草丛为主,优势种包括多年生草本：狗牙根（Cynodon dactylon）、牛鞭草（Hemarthria altissima）和硬秆子草（Capillipedium assimile）;一年生草本：狗尾草（Setaria viridis）、毛马唐（Digitaria ciliaris）和千金子（Leptochloa chinensis）。木本植物基本死亡,只有枫杨（Pterocarya stenoptera）、牡荆（Vitex negundo）和地瓜（Ficus tikoua）存活。此外,被水淹过的植被中灌木物种数比例显著降低,而一年生草本物种数比例显著增加。被水淹过和尚未水淹植被的物种多样性也存在显著差异,被水淹过植被物种总数、灌木和多年生草本物种数显著低于尚未被水淹过的植被,但一年生草本物种数没有显著差异。被水淹过的植被草本层生物量与尚未水淹的植被没有显著差异。可见,水淹显著改变了消涨带原有植被物种组分和物种多样性,但一年生草本物种数和草本层生物量没有显著差异。未来175 m以下的植被中,草本尤其是一年生草本将占据优势。在消涨带植被恢复选择适应水淹生境物种过程中,应分别从植物的生活史、生理学和形态学等角度进行筛选,尤其应重视生活史适应策略植物的应用。被水淹过的156 m以下现有优势草本和存活的灌木可以作为三峡库区未来消涨带植被恢复的备选物种。     

Impacts of Myriophyllum aquaticum invasion in a Mediterranean wetland on plant and macro-arthropod communities

The invasion by alien macrophytes in aquatic ecosystems may produce a strong alteration of the native aquatic vegetation leading to heavy impacts for both plant and faunal native diversity. Myriophyllum aquaticum is an aquatic plant native of Southern America, invasive in several part of the world. We studied the effects of M. aquaticum invasion on plant and macro-arthropod communities in the canals around a protected wetland in the Mediterranean basin. We sampled plant and macro-arthropod communities in 10 transects in invaded and non-invaded tracts of the canals. We assessed the differences in plant and macro-arthropod species richness, diversity, taxonomic diversity and species composition between invaded and non-invaded habitats by means of univariate and multivariate analyses. Our study shows a significant loss of plant diversity between non-invaded to invaded sites, leading to communities numerically and taxonomically impoverished and highly divergent in the species composition. We also detected significant differences in arthropod species composition between invaded and non-invaded transects. Some taxa such as mosquitoes and malacostraca were more frequent in the M. aquaticum-dominated stands. Furthermore, the study shows a positive relation between invaded habitats and juvenile individuals of the invasive alien crayfish Procambarus clarkii.     

Grazing, Environmental Heterogeneity, and Alien Plant Invasions in Temperate Pampa Grasslands

Temperate humid grasslands are known to be particularly vulnerable to invasion by alien plant species when grazed by domestic livestock. The Flooding Pampa grasslands in eastern Argentina represent a well-documented case of a regional flora that has been extensively modified by anthropogenic disturbances and massive invasions over recent centuries. Here, we synthesise evidence from region-wide vegetation surveys and long-term exclosure experiments in the Flooding Pampa to examine the response of exotic and native plant richness to environmental heterogeneity, and to evaluate grazing effects on species composition and diversity at landscape and local community scales. Total plant richness showed a unimodal distribution along a composite stress/fertility gradient ranging several plant community types. On average, more exotic species occurred in intermediate fertility habitats that also contained the highest richness of resident native plants. Exotic plant richness was thus positively correlated with native species richness across a broad range of flood-prone grasslands. The notion that native plant diversity decreases invasibility was supported only for a limited range of species-rich communities in habitats where soil salinity stress and flooding were unimportant. We found that grazing promoted exotic plant invasions and generally enhanced community richness, whereas it reduced the compositional and functional heterogeneity of vegetation at the landscape scale. Hence, grazing effects on plant heterogeneity were scale-dependent. In addition, our results show that environmental fluctuations and physical disturbances such as large floods in the pampas may constrain, rather than encourage, exotic species in grazed grasslands.     

怒江河谷入侵植物与乡土植物丰富度的分布格局与影响因子

外来物种入侵严重威胁着乡土植物多样性并削弱了生态系统服务功能。本文基于滇西北怒江河谷植被调查的样方数据, 从群落水平研究了乡土和入侵植物多样性的空间分布格局, 以及地形、气候、人类干扰等因子对两种格局的影响。本研究共记录到外来入侵植物26种, 隶属于13科21属; 乡土植物1,145种, 分属于158科628属。沿着怒江河谷, 入侵植物物种丰富度随纬度与海拔的增加而减少; 乡土物种丰富度则随纬度增加而增加, 并在海拔梯度上呈单峰格局。运用广义线性模型分析公路边缘效应(反映生境干扰)、气候、地形和土壤等环境因素对物种丰富度分布格局的影响。等级方差分离的结果显示, 公路两侧的生境干扰对入侵种和乡土种的丰富度格局均具有首要影响。在自然环境因子中, 降水量是入侵植物丰富度的主要限制因子, 而乡土物种丰富度则主要受到地形因子尤其是坡向的影响。结构方程模型的分析结果也表明, 乡土植物和入侵植物丰富度之间的负相关关系反映了二者对环境响应的差异。本文结果支持物种入侵的资源可利用性限制假说, 并强调了人类活动对生物多样性的负面影响; 乡土植物或已较好地适应了干旱河谷气候, 但并没有显示出对外来物种入侵的抵抗作用。     

生物入侵对鸟类的生态影响

生物入侵是全球生物多样性面临的最主要威胁之一, 入侵种在改变入侵地环境的同时也使当地的生物受到极大影响。鸟类在生态系统中处于较高的营养级, 生态系统中任何一个环节的变化都可能对鸟类造成一定的影响。本文回顾了哺乳动物、鸟类、无脊椎动物和植物等不同生物类群的入侵对本地鸟类生态影响方面的研究进展。外来生物对鸟类的影响主要表现在以下几方面: (1)外来哺乳动物对成鸟、幼鸟或鸟卵的捕食作用; (2)外来鸟类与本地鸟类竞争栖息地和食物资源, 与当地的近缘种杂交而造成基因流失; (3)外来无脊椎动物改变本地鸟类的栖息环境和食物状况, 甚至直接捕食本地鸟类; (4)外来植物入侵改变入侵地的植物群落组成和结构, 造成本地鸟类的栖息地丧失或破碎化, 并通过改变入侵地生态系统的食物链结构而对高营养级的鸟类产生影响。最后, 作者还提出了该领域有待解决的问题和今后可能的研究方向。     

BIODIVERSITY RESEARCH: Native‐exotic species richness relationships across spatial scales and biotic homogenization in wetland plant communities of Illinois,USA

Aim To examine native‐exotic species richness relationships across spatial scales and corresponding biotic homogenization in wetland plant communities. Location Illinois, USA. Methods We analysed the native‐exotic species richness relationship for vascular plants at three spatial scales (small, 0.25 m² of sample area; medium, 1 m² of sample area; large, 5 m² of sample area) in 103 wetlands across Illinois. At each scale, Spearman’s correlation coefficient between native and exotic richness was calculated. We also investigated the potential for biotic homogenization by comparing all species surveyed in a wetland community (from the large sample area) with the species composition in all other wetlands using paired comparisons of their Jaccard’s and Simpson’s similarity indices. Results At large and medium scales, native richness was positively correlated with exotic richness, with the strength of the correlation decreasing from the large to the medium scale; at the smallest scale, the native‐exotic richness correlation was negative. The average value for homogenization indices was 0.096 and 0.168, using Jaccard’s and Simpson’s indices, respectively, indicating that these wetland plant communities have been homogenized because of invasion by exotic species. Main Conclusions Our study demonstrated a clear shift from a positive to a negative native‐exotic species richness relationship from larger to smaller spatial scales. The negative native‐exotic richness relationship that we found is suggested to result from direct biotic interactions (competitive exclusion) between native and exotic species, whereas positive correlations likely reflect the more prominent influence of habitat heterogeneity on richness at larger scales. Our finding of homogenization at the community level extends conclusions from previous studies having found this pattern at much larger spatial scales. Furthermore, these results suggest that even while exhibiting a positive native‐exotic richness relationship, community level biotas can/are still being homogenized because of exotic species invasion.     

Altitudinal distribution of native and alien plant species in roadside communities from central Argentina

Roadsides may homogenize the distribution of native species and act as corridors for the spread of alien taxa. We examined the variation in native and alien plant species richness and composition at two spatial scales defined by altitude and habitat type (edges and fill slopes), as well as the relationship between native and exotic species richness in roadside plant communities in mountains from central Argentina. Following a gradient from 1100 to 2200 m a.s.l. along a mountain road, plant species cover was recorded within sample plots of 30 m × 10 m systematically located at 100‐m altitude intervals on both roadside habitats. Although native species richness decreased with altitude and composition changed accordingly, the number of alien species peaked at both extremes of the elevation gradient and did not reflect an altitudinal replacement of chorological groups. The number of both native and alien species was higher in roadside edges, but a negative association between the richness of native and alien species occurred only on fill slopes, suggesting that roadside habitats differ in their susceptibility to plant species colonization and in the mechanisms driving native and alien species richness. Our results highlight the importance of altitude and roadside habitat as factors controlling plant species richness and composition along roadside communities in central Argentina. Although altitude acts as a filter for native plants, it apparently did not constrain the establishment of alien species along the studied roadsides, indicating that the influence of this road as a plant species corridor may increase with time, promoting the opportunities for aliens to expand their current distribution.     

Patterns of Plant Invasions: A Case Example in Native Species Hotspots and Rare Habitats

Land managers require landscape-scale information on where exotic plant species have successfully established, to better guide research, control, and restoration efforts. We evaluated the vulnerability of various habitats to invasion by exotic plant species in a 100,000 ha area in the southeast corner of Grand Staircase-Escalante National Monument, Utah. For the 97 0.1-ha plots in 11 vegetation types, exotic species richness (log₁₀) was strongly negatively correlated to the cover of cryptobiotic soil crusts (r = −0.47, P < 0.001), and positively correlated to native species richness (r = 0.22, P < 0.03), native species cover (r = 0.23, P < 0.05), and total nitrogen in the soil (r = 0.40, P < 0.001). Exotic species cover was strongly positively correlated to exotic species richness (r = 0.68, P < 0.001). Only 6 of 97 plots did not contain at least one exotic species. Exotic species richness was particularly high in locally rare, mesic vegetation types and nitrogen rich soils. Dry, upland plots (n = 51) had less than half of the exotic species richness and cover compared to plots (n = 45) in washes and lowland depressions that collect water intermittently. Plots dominated by trees had significantly greater native and exotic species richness compared to plots dominated by shrubs. For the 97 plots combined, 33% of the variance in exotic species richness could be explained by a positive relationship with total plant cover, and negative relationships with the cover of cryptobiotic crusts and bare ground. There are several reasons for concern: (1) Exotic plant species are invading hot spots of native plant diversity and rare/unique habitats. (2) The foliar cover of exotic species was greatest in habitats that had been invaded by several exotic species.(3) Continued disturbance of fragile cryptobiotic crusts by livestock, people, and vehicles may facilitate the further invasion of exotic plant species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Grazing in remnant woodland vegetation: changes in species composition and life form groups

Abstract. Grazing by domestic livestock in native woodlands can have major effects on ecosystem functioning by the removal of plant species that form important functional groups. This paper documents the changes in floristics in a large group of remnants of native woodland left after agricultural clearing in southwestern Australia. Species richness and diversity were significantly reduced in remnants and the proportion of exotic species increased. Detrended Correspondence Analysis (DCA) was used to identify floristic and environmental patterns among plots and identified two distinct groups based on grazing intensity. This indicated that the significance of the relationship between grazing effects and DCA floristic axes was greater than edaphic characteristics that normally influence floristic patterns. Floristic characteristics of sites that were influencing the position of plots on the ordination diagram included proportion of exotic species and proportion of native perennial shrubs and herbs. Numbers of species of native shrubs and perennial herbs were significantly reduced in grazed plots and numbers of exotic annual grasses and herbs were significantly higher. Other life form groups such as native perennial grasses and geophytes were not significantly affected by grazing. Reproductive strategies of perennial species showed a significant decrease in numbers of resprouters and a significant increase in numbers of facultative seeder/sprouters. Exclosure plots showed increases in number and cover of perennial shrubs and herbs after three years whereas number and cover of exotic species did not change. Time series DCA showed that the floristic composition of exclosure plots in grazed sites became closer to that of the ungrazed sites.     

Land‐use and isolation interact to affect wetland plant assemblages

Different management regimes imposed on similar habitat types provide opportunities to investigate mechanisms driving community assembly and changes in species composition. We investigated the effect of pasture management on vegetation composition in wetlands with varying spatial isolation on a Florida cattle ranch. We hypothesized that increased pasture management intensity would dampen the expected negative effect of wetland isolation on native species richness due to a change from dispersal‐driven community assembly to niche‐driven assembly by accentuated environmental tolerance. We used native plant richness, exotic plant richness and mean coefficient of conservatism (CC) to assess wetland plant assemblage composition. Sixty wetlands were sampled, stratified by three levels of isolation across two pasture management intensities; semi‐native (less intensely managed; mostly native grasses, never fertilized) and agronomically improved (intensely managed, planted with exotic grasses, and fertilized). Improved pasture wetlands had lower native richness and CC scores, and greater total soil phosphorus and exotic species coverage compared to semi‐native pasture wetlands. Increased wetland isolation was significantly associated with decreases in native species richness in semi‐native pasture wetlands but not in improved pasture wetlands. Additionally, the species–area relationship was stronger in wetlands in improved pastures than semi‐native pastures. Our results indicate that a) native species switch from dispersal‐based community assembly in semi‐native pastures to a species‐sorting process in improved pastures, and b) recently‐introduced exotic species already sorted for more intensive management conditions are primarily undergoing dispersal‐based community assembly. That land‐use may alter the relative importance of assembly processes and that different processes drive native and exotic richness has implications for both ecosystem management and restoration planning.     

Scale-dependent relationships between native richness, resource stability and exotic cover in dock fouling communities of Washington, USA

Aim In terrestrial plant communities, the relationship between native species diversity and exotic success is typically scale‐dependent. It is often proposed that within local neighbourhoods, high native diversity limits resources, thereby inhibiting exotic success. However, environmental variation that manifests over space or time can create positive correlations between native diversity and exotic success at larger scales. In marine habitats, there have been few multi‐scale surveys of this pattern, so it is unclear how diversity, resource limitation and the environment influence the success of exotic species in these systems. Location Washington, USA. Methods I analysed nested spatial and temporal surveys of fouling communities, which are assemblages of sessile marine invertebrates, to test whether the relationships between native richness, resource availability and exotic cover supported the diversity‐stability and diversity‐resistance theories, to test whether these relationships changed with spatio‐temporal scale, and to explore the temperature preferences of native and exotic fouling species. Results Survey data failed to support diversity‐stability theory: space availability actually increased with native richness at the local neighbourhood scale, and neither space availability nor variability decreased with native richness across larger spatio‐temporal scales. I did find support for diversity‐resistance theory, as richness negatively correlated with exotic cover in local neighbourhoods. Unexpectedly, this negative correlation disappeared at intermediate scales, but emerged again at the regional scale. This scale‐dependent pattern could be partially explained by contrasting water temperature preferences of native and exotic species. Main conclusions Within local neighbourhoods, native diversity may inhibit exotic abundance, but the mechanism is unlikely related to resource limitation. At the largest scale, correlations suggest that native richness is higher in cooler environments, whereas exotic richness is higher in warmer environments. This large‐scale pattern contrasts with the typical plant community pattern, and has important implications for coastal management in the face of global climate change.