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1.
Freshwater crayfish are key members of aquatic communities due to their large size and abundance. Although most commonly regarded as herbivores and detritivores, they are also selective predators. The crayfish plague fungus Aphanomyces astaci (Schikora) led to the elimination of a stock of white-clawed crayfish, Austropotamobius pallipes (Lereboullet) from Lough Lene, Co. Westmeath, in 1987. Samples taken of the flora and benthic communities of two Irish lakes, one (Lough Bane) formerly containing crayfish and the other (Lough Lene) immediately following a plague outbreak, were compared to similar samples taken a year later and ecological shifts were noted and compared to laboratory feeding results. Over time, Chara strands increased in mean length, and molluscs became more abundant.  相似文献   
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亚高山竹类占据着野生大熊猫(Ailuropoda melanoleuca)食物组分的99%,竹子的生命周期与大熊猫的生活史密切相关,竹子的更新和生长直接影响着大熊猫的生存与保护.为了弄清大熊猫的采食利用和人为砍伐是否促进或制约竹子的繁殖更新,应用样方法、定位观察法,连续研究了卧龙自然保护区大熊猫栖息地内野化培训大熊猫采食、人为砍伐和对照样方中拐棍竹无性系种群的更新动态.结果表明,在相同种群数量和环境条件的基础上(p>0.05),被大熊猫采食竹子的比例为67.07%,致死率29.07%;人为砍伐竹子的比例为65.67%,致死率46.68%,可见与大熊猫采食相比,砍伐更为影响拐棍竹种群的生存.从出笋数量来看,不同处理方式有利于拐棍竹无性系种群的更新(p<0.05),尤其是人为砍伐措施大大提高了竹子的出笋率,但人为砍伐样方的竹笋质量(地径和株高生长)却远低于大熊猫采食和对照样方,未能达到大熊猫觅食的选择利用标准.不同年份之间,各种处理方式下的拐棍竹出笋数量波动较大(p=0.006~0.035),并随着恢复时间的延长,逐渐趋于相似(2007,p=0 825).不同处理方式之间,拐棍竹无性系种群的年补充率,各年份均具有显著性差异(p<0.05,除2007年外),年死亡率仅2003年和2004年有明显的差异(p<0.05),2005~2007年均不显著(p>0.05).拐棍竹无性系种群的年补充率与年死亡率之间表现出年补充率﹥年死亡率的格局(p<0.05),唯有大熊猫采食样方的2004年和2005年、人为砍伐和对照样方的2005年的年死亡率略高于年补充率(p>0.05),这表明拐棍竹无性系种群对大熊猫采食和人为砍伐具有无性系整合的补偿效应.  相似文献   
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An enclosure experiment was conducted to assess the effects of a zooplankton elimination on the structure of a phytoplankton community. Phytoplankton biomass and production were higher in grazer-free enclosures, while the productivity per unit biovolume was lower. Exclusion of zooplankton favoured the majority of algal species, especially chrysophyceans (Dinobryon spp.) and the diatom Rhizosolenia, while mucilagineous green-algae were disfavoured. Middle sized algae (ESD 15–50 µm) and those with the largest Surface Area/Volume ratio were proportionally most favoured by the elimination of grazers.These differences in phytoplankton community structure are discussed in relation to effects of direct selective grazing and nutrient recycling by zooplankton. Some differences, as the immediate positive response of Dinobryon and Rhizosolenia, are probably caused by grazing release, while others, e.g. the response of mucilagineous species, might be caused by changed competitive relationships between the algae.  相似文献   
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Abstract Introduced perennial grasses are one of the greatest constraints to prairie restoration. Herbicides suppress but do not eliminate introduced grasses, so we explored the interaction of herbicide with two additional controls: heavy clipping (to simulate grazing) and competition from native species. A 50‐year‐old stand of the introduced perennial grass Agropyron cristatum (crested wheatgrass) in the northern Great Plains was seeded with native grasses and treated with herbicide annually for 7 years in a factorial experiment. Clipping was applied as a subplot treatment in the final 3 years. Both herbicide and clipping significantly reduced the cover of A. cristatum, but clipping produced an immediate and consistent decrease, whereas herbicide control varied among years. The cover of A. cristatum decreased significantly with increasing cover of a seeded native grass, Bouteloua gracilis (blue grama), suggesting that both top‐down (i.e., grazing) and bottom‐up (i.e., resource competition) strategies can contribute to A. cristatum control. No treatment had any effect on the seed bank of A. cristatum. Even in the most effective control treatments, A. cristatum persisted at low amounts (approximately 5% cover) throughout the experiment. The cover of B. gracilis increased significantly with seed addition and herbicide, and, after 7 years, was similar to that in undisturbed prairie. The total cover of native species increased significantly with clipping and herbicide, and species richness was significantly higher in plots receiving herbicide. Clipping season had no effect on any variable. In summary, no method extirpated A. cristatum, but clipping reduced its cover by 90% and doubled the cover of native species. Extirpation might not be a realistic goal, but relatively simple management allowed coexistence of native species.  相似文献   
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保护区内放牧活动对野生动物保护存在负面影响,明确不同物种对放牧干扰的行为响应对制定更有针对性的保护管理政策具有重要意义。使用红外相机研究卧龙自然保护区放牧活动对多种珍稀野生动物的影响,分析放牧激励政策实施前后大熊猫(Ailuropoda melanoleuca)及其同域分布的小熊猫(Ailurus fulgens)、川金丝猴(Rhinopithecus roxellana)、水鹿(Rusa unicolor) 4种珍稀野生动物的照片数、空间分布以及活动模式的变化,探讨这4种动物对放牧的行为响应策略。结果表明:(1)一期(2012—2013),2012年10月实施了禁马政策,同年12月实施放牧(牛羊)激励政策)家畜照片数量很少,4种野生动物照片数相对较多。二期(2014—2015)家畜的照片数显著增加(P0.01),小熊猫(P0.05)与川金丝猴(P0.01)的照片数均显著减少,大熊猫、水鹿的照片数也呈减少趋势;到三期(2016—2017),大熊猫、小熊猫及水鹿3种关注野生动物的照片数基本回升到激励政策实施前的水平,无川金丝猴照片记录。(2)一期,4种野生动物在研究区域有较广的分布;二期,大熊猫、小熊猫的空间分布范围均缩小,无川金丝猴空间分布信息,而家畜、水鹿的空间分布范围有所增加;到三期,大熊猫、小熊猫的空间分布基本恢复到放牧激励政策实施前的区域,无川金丝猴的空间分布信息。(3)放牧激励政策实施前后,大熊猫、小熊猫及川金丝猴活动模式无明显变化,但水鹿的活动更加集中于傍晚,以避开人类与家畜的活动高峰。同域分布的不同的野生动物对人类活动(如放牧)的行为响应策略不同,各保护区在制定相关保护政策时应综合考虑人类干扰对多个物种的影响,增加决策的科学性与合理性。  相似文献   
7.
Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small‐scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta‐analysis of the outcomes of plant–herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between‐taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore–plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed‐nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed‐nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore–plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant–herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top‐down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants.  相似文献   
8.
Understanding how historical processes modulate the response of ecosystems to perturbations is becoming increasingly important. In contrast to the growing interest in projecting biodiversity and ecosystem functioning under future climate scenarios, how legacy effects originating from historical conditions drive change in ecosystems remains largely unexplored. Using experiments in combination with stochastic antecedent modelling, we evaluated how extreme warming, sediment deposition and grazing events modulated the ecological memory of rocky intertidal epilithic microphytobenthos (EMPB). We found memory effects in the non‐clustered scenario of disturbance (60 days apart), where EMPB biomass fluctuated in time, but not under clustered disturbances (15 days apart), where EMPB biomass was consistently low. A massive grazing event impacted on EMPB biomass in a second run of the experiment, also muting ecological memory. Our results provide empirical support to the theoretical expectation that stochastic fluctuations promote ecological memory, but also show that contingencies may lead to memory loss.  相似文献   
9.
The complex intermixing morphology is critical for the performance of the nanostructured polymer:fullerene bulk heterojunction (BHJ) solar cells. Here, time resolved in situ grazing incidence X‐ray diffraction and grazing incidence small angle X‐ray scattering are used to track the structure formation of BHJ thin films formed from the donor polymer poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) with different fullerene derivative acceptors. The formation of stable bimolecular crystals through the intercalation of fullerene molecules between the side chains of polymer crystallites is investigated. Such systems exhibit more efficient exciton dissociation but lower photo‐conductance and faster decay of charges. On the basis of the experimental observations, intercalation obviously takes place before or with the formation of the crystalline polymer domains. It results in more stable structures whose volume remains constant upon further drying. Three distinct periods of drying are observed and the formation of unidimensional fullerene channels along the π‐stacking direction of polymer crystallites is confirmed.  相似文献   
10.
半干旱草地长期封育进程中针茅植物根系格局变化特征   总被引:6,自引:3,他引:3  
苏纪帅  赵洁  井光花  魏琳  刘建  程积民  张金娥 《生态学报》2017,37(19):6571-6580
以云雾山不同封育年限草地针茅植物根系和土壤为研究对象,对其根系特征、土壤特性及两者关系进行研究,以探讨分析封育对针茅根系格局的影响。结果表明:(1)针茅植物根系生物量、根长密度、根表面积和根体积在封育初期轻微下降,之后缓慢上升,并在封育30 a草地得到显著增加。(2)随封育年限增加,各根系指标在3种针茅物种间的组成格局具有类似变化规律,具体表现为:长芒草在放牧草地所占比例最高,之后逐渐降低,并在封育30 a草地消失;大针茅所占比例呈先升后降变化规律,并在封育22 a草地达到最大值;甘青针茅仅出现于封育30 a草地,且占据优势地位。(3)大针茅和甘青针茅0—0.6 mm径级根系比例高于大针茅,使其根系直径显著低于大针茅,比根长和比根面积显著高于大针茅;此外,长芒草根组织密度显著高于长芒草和甘青针茅。(4)长期封育在显著提高土壤水分、养分含量和土壤氮磷比的同时显著降低土壤碳氮比,但对微生物生物量碳、氮无明显影响。(5)针茅根系特征与土壤指标的关联性分析显示针茅根系受土壤氮资源的显著影响。  相似文献   
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