Competition and niche partitioning in a floodplain ecosystem: a cladoceran community squeezed between fish and invertebrate predation

Seasonal floodplains occasionally comprise highly productive zooplankton communities which are exposed to rapid shifts in predator regimes, also between vertebrate and invertebrate predators.We recorded the impact of two co-occurring zooplankton predators, the notonectid Anisops sardea and 0+ fish fry of Tilapia rendalli (max gape size 1 mm), on a cladoceran community dominated by Ceriodaphnia reticulata (0.25–0.78 mm), Daphnia laevis (0.6– 1.8 mm) and Scapholeberis kingi (0.27–0.8 mm). Both predators strongly reduced abundance of all prey species, yet with a striking size-selective effect for Daphnia prey only, where fish showed a strong preference for small individuals, while Anisops preferred large Daphnia individuals. This contrasts with the general view of size selection in invertebrate versus vertebrate predators, but is logically caused by the feeding mode of the notonectid, and the gape size limitation of the fish fry. The two predators also showed a dietary niche differentiation in terms of both prey selection and habitat choice. T. rendalli fed preferably on small species and size classes, whereas predation from A. sardea concentrated on large prey. Competitive interference was indicated when feeding on Ceriodaphnia, and niche partitioning when feeding on the two other species. The predatory pattern suggests long-lasting coexistence in the system.     

补播禾草对玛曲高寒沙化草地植物生态位特征的影响

研究了玛曲高寒沙化草地植物群落特征,探讨补播禾草对物种多样性和植物量的影响。结果表明,补播第2年各处理的重要值均以异针茅为最大,说明补播没有使异针茅的优势地位受到太大影响,异针茅为玛曲当前高寒沙化草地的优势种,乳浆大戟生态位宽度最大,为0．992,生态位重叠最大发生在紫羊茅和异针茅,以及紫羊茅和乳浆大戟之间,为0．997。补播后随着禾草种类数量的增加,能提高高寒草地的质量,是提高退化高寒草地生产力的有效手段。     

山西五台县草地啮齿类动物空间生态位宽度及重叠度研究

研究了山西五台县草地啮齿动物生态位宽度及重叠度。结果表明:啮齿动物区系含2目、5科、11属、14种,平均捕获率为6.05%,除山地草原类草地与山地草甸类草地之间啮齿动物数量差异不显著外,其余各类之间均达差异显著水平(︱t︱t0.05);研究区域14种啮齿动物的空间生态位宽度指数在0.000 2~0.826 4,其中,生态位宽度指数0.5的种数占总种数的35.71%,0.1~0.5的占42.86%,0.1的占21.43%;生态位重叠度指数在0.837 7~0.000 2,没有生态位完全重叠的种,却有一定数量生态位完全不重叠的种;重叠度较高的占28.89%,重叠度较低的占51.11%,重叠度最低的占20.00%。生态位宽度及重叠度指数较低表明研究区域内啮齿类动物种的生态位分化程度较大。     

Stable isotope analysis of diet confirms niche separation of two sympatric species of Namib Desert lizard

We used stable isotopes of carbon and nitrogen to study the trophic niche of two species of insectivorous lizards, the Husab sand lizard Pedioplanis husabensis and Bradfield's Namib day gecko living sympatrically in the Namib Desert. We measured the δ¹³C and δ¹⁵N ratios in lizard blood tissues with different turnover times (whole blood, red blood cells and plasma) to investigate lizard diet in different seasons. We also measured the δ¹³C and δ¹⁵N ratios in available arthropod prey and plant tissues on the site, to identify the avenues of nutrient movement between lizards and their prey. Through the use of stable isotope mixing models, we found that the two lizard species relied on a largely non‐overlapping but seasonally variable array of arthropods: P. husabensis primarily fed on termites, beetles and wasps, while R. bradfieldi fed mainly on ants, wasps and hemipterans. Nutrients originating from C₃ plants were proportionally higher for R. bradfieldi than for P. husabensis during autumn and late autumn/early winter, although not summer. Contrary to the few available data estimating the trophic transfer of nutrients in ectotherms in mixed C₃ and C₄/crassulacean acid metabolism (CAM) plant landscapes, we found that our lizard species primarily acquired nutrients that originated from C₄/CAM plants. This work adds an important dimension to the general lack of studies using stable isotope analyses to estimate lizard niche partitioning and resource use.     

陕北黄土丘陵区撂荒演替生态位研究

利用陕北黄土丘陵区17个不同撂荒年限的群落样方数据,分析了撂荒演替中20个主要种的演替生态位宽度和生态位重叠指数,3种生态位宽度指数以Levin和Shannon-Wiener指数适用性较好,2种指数表明演替前期主要种的生态位宽度较窄,后期较宽;演替各阶段优势种生态位较宽,伴生种较窄。根据演替生态位重叠指数,利用种的极点排序和系统聚类法分析了种的演替生态学特性,结果表明,4种生态位重叠指数以Morisita和Pianka指数在演替生态位的研究中适用性较好,种的极点排序与种极点分析和实际观察结果基本一致,指示了种的生态对策连续统,说明种的演替方向和相对竞争能力;系统聚类中类内种的生态学特性基本一致,3类的划分结果表明第1类为定居优势种,位于演替序列前期;第2类为竞争优势种,位于演替后期;第3类为定居-竞争相对平衡种,位于演替中期。     

Competitor densities,habitat, and weather: effects on interspecific interactions between wild deer species

There is a growing interest on the potential interplay between weather, habitat, and interspecific competition on population dynamics of wild herbivores. Favorable environmental conditions may buffer the negative effects of competition; conversely, competition may be expected to be stronger under harsh environmental conditions. We investigated relationships between competitor abundance, weather, and habitat cover on density and local distribution of a medium-sized herbivore, the roe deer Capreolus capreolus, as well as its spatial overlap with fallow deer Dama dama in a Mediterranean protected area. Over 11 years (2007–2017), roe deer density was not affected by spring–summer rainfall in the previous year and decreased with increasing density of fallow deer in the previous year. Hence, over the considered temporal scale, results supported a major role of competition over weather in influencing population trends of roe deer. At a finer spatial scale, roe deer occupancy was negatively affected by local abundance of fallow deer, especially in “poorer” habitats. We found a slight support for a positive effect of fallow deer density on interspecific spatial overlap. Moreover, fine-scale spatial overlap between deer species increased with decreasing rainfall in spring–summer. Fallow deer were introduced to our study area in historical times and their role as superior competitors over roe deer has been found also in other study areas. We suggest a potential role of harsh weather conditions during the growing season of vegetation (i.e. scarce rainfall) in triggering the potential for ecological overlap, emphasizing the negative effects of interspecific competition.     

苜蓿套种与单种对昆虫种群动态及群落结构的影响

从单种、套种两种种植模式出发,初步探讨天敌、害虫在单种、套种两种基本模式下的发生规律,解决苜蓿种植模式调整后对苜蓿害虫影响情况不清造成苜蓿受害情况不明的问题,为指导宁夏地区牧草种植模式调整,促进苜蓿增产提供理论依据。采用网捕、诱集等方法搜集整理田间害虫、天敌种类和数量,通过典型性相关分析法对数据进行分析。结果表明：不同栽培模式下苜蓿草地中昆虫种类与个体数的差异很大,单种的苜蓿草地中害虫发生量普遍高于套种的苜蓿草地;单种的苜蓿草地中主要害虫的个体数普遍高于套种的害虫,优势天敌也同样表现出这种分布规律;单种的苜蓿草地生境中昆虫的总个体数、植食性昆虫的个体数以及捕食性昆虫的个体数都明显高于套种的苜蓿草地。套种苜蓿虫害、天敌变动规律较为复杂,除了种植模式之外,还需要采取多种手段防范因外部虫源引入造成的集中暴发。     

低铜饲粮添加枯草芽孢杆菌对5～16周龄五龙鹅肠道发育、微生物菌群结构及血清酶活性的影响

本试验旨在研究低铜饲粮添加枯草芽孢杆菌对5~16周龄五龙鹅肠道发育、微生物菌群结构及血清酶活性的影响。试验选用29日龄五龙鹅360只,随机分为6组,每组6个重复,每个重复10只(公母各占1/2)。Ⅰ组为最适铜添加组(铜添加水平为16 mg/kg,未添加枯草芽孢杆菌);Ⅱ~Ⅵ组为枯草芽孢杆菌添加组,铜添加水平分别为0、4、8、12、16 mg/kg,枯草芽孢杆菌添加水平均为250mg/kg。试验期12周。结果表明:1)Ⅱ~Ⅵ组的空肠绒毛高度和绒腺比极显著高于Ⅰ组(P0.01),空肠隐窝深度显著或极显著低于Ⅰ组(P0.05或P0.01);Ⅲ、Ⅴ、Ⅵ组的空肠肠壁厚度显著高于Ⅰ组(P0.05)。Ⅱ~Ⅵ组之间的空肠绒毛高度、肠壁厚度和绒腺比无显著差异(P0.05);Ⅱ组的空肠隐窝深度显著低于Ⅴ和Ⅵ组(P0.05)。2)Ⅱ~Ⅵ组的盲肠大肠杆菌数量极显著低于Ⅰ组(P0.01),盲肠双歧杆菌和乳酸杆菌数量显著或极显著高于Ⅰ组(P0.05或P0.01)。Ⅱ~Ⅵ组之间的盲肠大肠杆菌、双歧杆菌和乳酸杆菌数量差异不显著(P0.05)。3)Ⅳ组的血清谷丙转氨酶(ALT)活性显著低于Ⅰ组(P0.05),Ⅴ组血清谷草转氨酶(AST)和乳酸脱氢酶(LDH)活性显著低于Ⅰ组(P0.05);Ⅱ组血清ALT、AST、LDH活性与Ⅰ组差异不显著(P0.05)。Ⅳ组血清碱性磷酸酶(AKP)活性显著高于Ⅰ组(P0.05);Ⅱ组血清AKP活性显著低于Ⅰ组(P0.05)。由此可见,低铜饲粮添加枯草芽孢杆菌能够促进五龙鹅肠道发育,优化微生物菌群结构;铜对鹅肠道发育及微生物菌群结构影响较小。适宜的枯草芽孢杆菌和铜添加水平能够维护机体健康,相互间具有协同作用。