恢复初期红树林树栖滨螺科动物的组成与分布

滨螺科动物是红树林中常见的底栖动物,它们的形态、行为和分布等与红树林植被密切相关。本文调查了植被恢复初期(3年生)红树林树栖滨螺科动物的组成和分布情况,并探讨滩涂高程和树种对滨螺科动物分布的影响。结果表明:植被恢复初期滨螺科物种已成为优势类群,密度达到32.67 ind·m~(-2);黑口滨螺在不同滩涂高程下均为优势种,其密度和生物量在黄零1.8 m高程的秋茄林内较其他林地(黄零2.2和2.6 m)高;粗糙滨螺仅出现在黄零1.8 m的秋茄林内;种植于黄零1.6 m高程的桐花树林内黑口滨螺的生物量和密度均大于同样高程下的秋茄林,但桐花树林内的个体小于秋茄林内的个体;粗糙滨螺在不同树种间的分布没有明显差异;滨螺科物种的分布在红树林恢复初期随生境的异质性表现出差异,这种差异可能与植被形态导致的物理环境差异以及滨螺科物种活动习性、繁殖扩散模式等生物学特性有关。     

人工红树林中黑口滨螺和黑线蜒螺分布的差异性

研究了福建九龙江河口不同林龄、不同红树种类的人工林中黑口滨螺（Littoraia elanostoma）和黑线蜒螺（Nerita lineata）的分布情况.结果表明,黑线蜒螺主要分布于秋茄林内,且其生物量随林龄增加而增加;桐花树林内黑口滨螺的生物量和密度均大于林龄相近的秋茄林,但个体大小则小于秋茄林.黑口滨螺的生物量在桐花树林内随林龄增加呈现先增加后减少的趋势,而在秋茄林内则随林龄增加而减少.这种差异性反映了人工红树林植物种类及其演替过程对腹足类动物分布的影响.     

广西北部湾典型海岛红树林的结构特征、空间格局及种间种内关联性

为研究广西北部湾茅尾海自然保护区海岛红树林群落的空间点格局和演替规律,在典型红树林海岛设置调查样地,以样地内的桐花树(Aegiceras corniculatum)、秋茄(Kandelia obovata)、白骨壤(Avicennia marina)等红树植物为研究对象,构建单变量函数的完全空间随机模型、异质泊松模型与双变量函数的环形转变模型,分析3种红树林种群的结构特征、空间格局及种内种间关联性。结果发现：(1)桐花树种群的小树和中树的个体数目较多,种群年龄结构呈金字塔型,种群处于增长状态;秋茄种群的中树个体数目较多,种群结构呈钟型,种群数量处于稳定状态;白骨壤个体数相对较少,且幼树较少老树较多,种群更新受阻,种群结构呈纺锤型,属于衰退型种群。(2)红树林群落整体上呈现出空间集聚的分布特征,从不同种群的集聚程度来看：桐花树>白骨壤>秋茄。(3)随着空间尺度的增大,红树林群落在空间分布上依次表现出聚集、随机和均匀3种特征。(4)桐花树与秋茄、白骨壤的种间关系随着尺度增加均表现为空间无关联性-空间负关联性-空间无关联性的演变特征,秋茄与白骨壤的种间关系则为全尺度的空间无关联性。(5)桐花树种内不同龄级之间存在空间正关联性、空间无关联性和空间负关联性,秋茄种内不同龄级之间均表现出空间无联性,白骨壤种群则在不同龄级之间均出现空间正关联性。(6)红树植物种群的空间格局受到自身繁殖特性、生境异质性、种内和种间竞争、病虫害等多种因素的影响。红树林人工种植和恢复需要结合沿海地区的自然生态条件,按照红树林种群的适应形态学特点、群落类型和自然演替规律,种植乡土红树植物,适当引进外来物种,研制出近似天然的人工红树林林分结构,提高群落的生物多样性和群落稳定性,发挥红树林湿地生态系统的生态环境效应。     

新疆天山峡谷不同坡向野核桃种群分布格局

在天山峡谷野核桃分布的4条沟谷的阳坡和阴坡设置8个4000 m²样地,应用相邻格子法对野核桃每木调查,在不同尺度(面积)上采用方差/均值比率法和偏离指数(C_x)、负二项参数(K)、丛生指数(I)、平均拥挤度(m^*)、聚块性指数(PAI)、聚集指数(C_a)等聚集强度指数对野核桃种群分布格局进行分析.结果表明: 随尺度增大,野核桃种群由集群分布向随机分布过渡;在25 m²尺度上,种群整体呈集群分布,但不同样地种群聚集强度存在较大差异,西沟阴坡种群聚集程度最大,南沟阴坡种群聚集程度最小;在50～400 m²尺度上,种群整体呈随机分布.在25 m²尺度上,幼树、小树和壮年树均呈集群分布,壮年树聚集强度最大,小树聚集强度最小;当取样尺度达到200～400 m²时,幼树、小树、壮年树和大树均呈随机分布.野核桃种群格局规模为25 m²,格局强度为2.49～9.38 m²;种群组分中小树格局强度最大,壮年树格局强度最小.取样尺度与种群斑块大小接近,采用适合的测定方法并应用多指数综合判定,一般可获得可靠的结论.     

淇澳岛两种红树林区大型底栖动物群落比较

对珠海淇澳岛天然秋茄(Kandelia candel)与人工恢复无瓣海桑(Sonneratia apetala)两种红树林林地间大型底栖动物群落结构进行了比较研究.结果显示,天然秋茄林与人工无瓣海桑林林地大型底栖动物种类组成及数量分布都存在差异,秋茄林大型底栖动物平均生物量、栖息密度分别为668.64g·m^-2和8370个·m^-2,无瓣海桑林分别为511.64g·m^-2和4748个·m^-2.两个红树林剖面不同潮位带大型底栖动物结构存在差异,秋茄林生物量和栖息密度的最高值都在中潮带,主要是由节肢动物和软体动物所主导:无瓣海桑林栖息密度的最高值也是在中潮带,生物量变化比较不规则.两个红树林剖面大型底栖动物群落特征的季节变化较明显,生物量都是秋季处于最高水平:栖息密度都是冬季处于最高水平,秋季最低:生物多样性都是夏季处于最低,但最高值秋茄林剖面是在春季,而无瓣海桑林剖面则是秋季.研究结果表明,林地底质和盐度等生境条件以及红树林群落的高度、郁闭度和林下通风透光等生态特征的差异是造成红树林底栖动物群落差异的重要原因.     

红树林植被对大型底栖动物群落的影响

大型底栖动物是红树林生态系统的重要组成部分,从红树林大型底栖动物种类、红树林与其周边生境大型底栖动物群落的比较,以及生境变化对动物群落的影响等方面阐述了红树林植被与大型底栖动物群落的关系.从物种数量上看,软体动物和甲壳类动物构成了红树林大型底栖动物的主要部分.影响大型底栖动物分布的环境因素包括海水盐度、潮位和土壤特性等,但在小范围区域,林内动物的分布更多地与红树林植被特性和潮位有关.因此,由于红树林植被破坏或者恢复引起的生境变化,将导致大型底栖动物群落和常见物种种群的变化,尤其对底上动物影响明显;随着人工恢复红树林的发育,林内底栖动物的多样性相应增加,优势种也发生变化.相比位于相同潮位的无植被滩涂,红树林可促进潮间带生物多样性.     

深圳福田红树林植被碳储量和净初级生产力

红树林是滨海湿地“蓝碳”的主要类型之一.准确和定位评估不同植物群落的固碳能力,对于红树林保育管理和恢复造林具有指导作用.本研究对深圳福田红树林4种代表性群落(白骨壤群落、秋茄群落、海桑群落、无瓣海桑群落)的各个植被碳库组分(乔木植物生物量碳库、林下灌丛碳库、呼吸根碳库、枯立木碳库、枯倒木碳库和枯枝落叶层碳库等)进行调查,计算各群落的植被碳储量,并通过生长增量-凋落物产量法计算得到各群落的净初级生产力.结果表明: 白骨壤群落、秋茄群落、海桑群落和无瓣海桑群落的植被碳储量分别为28.7、127.6、100.1、73.6 t C·hm^-2,各群落的净初级生产力分别为8.75、7.67、9.60、11.87 t C·hm^-2·a^-1.位于深圳市中心的福田红树林,每年固定大气CO₂高达4000 t.本研究结果将为红树林“蓝碳”碳汇功能的评估提供理论指导,并为我国红树林碳汇林建设提供依据.     

海南橡胶林植物多样性特征

为探讨人工林物种多样性维持机制及人为干扰后人工林群落的多样性恢复机制, 作者依据自然林的核心理论建立了一个1 ha的橡胶(Hevea brasiliensis)林固定样地, 通过研究近自然管理后样地内植物物种组成与分布来探讨近自然管理后橡胶林生物多样性的特征。结果表明: 近自然管理后橡胶林群落物种多样性较高, 1 ha样地内共有植物69科155属183种。在面积为4,000 m²、3,000 m²和2,000 m²时分别包含了样地内大约90%的种、属和科; 逻辑斯蒂模型拟合拟合种-面积曲线效果较好(R²=0.997), 证明了1 ha取样尺度可以满足橡胶林群落物种多样性研究的需要。多度-面积曲线和丰富度-面积曲线与随机分布模型有明显的差异, 表明橡胶林群落内个体数及物种分布呈非随机性。(4)对数级数模型和对数正态模型拟合橡胶林群落的种-多度分布都不理想, 相比而言后者拟合效果稍好。     

广西珍珠湾三种红树林林分土壤碳氮储量的研究

为了探讨不同红树林林分土壤有机碳(soil organic carbon,SOC)和全氮(total nitrogen,TN)储量空间的分布特征以及与C/N的相关性,该研究以广西防城珍珠湾红树林湿地为对象,通过样地调查取样和实验室分析,测定了SOC和TN的含量以及土壤碳储量的计量,揭示了广西北仑河珍珠湾秋茄、木榄和混交林三种红树林林分SOC和TN储量空间的分布特征以及C/N与SOC和TN的相关性。结果表明:(1)秋茄、木榄和混交林的SOC储量分别为140.73、124.94、144.71 t·hm~(-2),三者无显著性差异(P0.05);木榄和混交林垂直分布特征表现为20～40 cm0～20 cm40～60 cm,秋茄表现为随着土层深度的增加而递减。(2)秋茄、木榄和混交林的TN储量分别为6.49、5.01、5.87 t·hm~(-2),表现为随着土层深度的增加而减少的趋势。(3)秋茄、木榄和混交林的SOC与TN储量之间的相关性极显著(P0.01),相关系数分别为0.924、0.971和0.844,说明SOC与TN之间存在一定的耦合效应。(4)三种林分的C/N比值范围为16.77～24.39,表明有机质主要来源于陆地,木榄和混交林土壤的C/N值与SOC储量有显著的相关性(P0.05),三种林分的C/N比值与TN储量相关性均不显著。(5)三种红树林林分的土壤碳储量均高于我国森林土壤碳储量的平均值,且SOC与TN储量之间的相关性极显著。     

黄山亚热带常绿阔叶林的群落特征

黄山是我国东部高山之一, 处于亚热带季风气候区, 属南北植物区系交替的过渡带, 是第四纪冰期动植物的避难所。其地带性植被为常绿阔叶林, 植被垂直分布明显, 是中国生物多样性保护优先区域, 也是世界文化与自然遗产地以及享誉全球的风景名胜区。2014年, 我们在黄山建立了10.24 ha的森林动态监测样地, 并完成了首次调查。本文从物种组成、区系特征、径级结构和空间分布格局等方面分析了样地中植物的群落特征。结果表明: 样地内有维管植物59科129属191种, 其中乔木层内胸径≥ 1 cm的木本植物46科97属153种; 热带性质的科、属分别占总科、属数的65.79%和45.36%, 温带性质的科、属分别占34.21%和51.55%。样地内珍稀濒危物种较多, 其中国家II级重点保护野生植物6种、《中国生物多样性红色名录——高等植物卷》中的近危物种7种、《濒危野生动植物种国际贸易公约》(CITES)附录II物种1种以及64种中国特有种, 这些物种具有较高的保护和研究价值。当取样面积小于2,150 m²时, 物种数随着面积的增加而急剧增加; 其后增加速率明显降低; 但大于57,950 m²时, 增加速率又略变大。稀有种69种, 占总树种数的45.10%。壳斗科和杜鹃花科的重要值占一半以上。建群种甜槠(Castanopsis eyrei)的重要值达26.25%, 其次分别为细齿叶柃(Eurya nitida) (7.63%)、马银花(Rhododendron ovatum) (7.60%)、马尾松(Pinus massoniana) (6.29%)和檵木(Loropetalum chinense) (4.83%)。样地平均胸径为4.10 cm, 小径木的数量占较大优势。乔木层可分为两个亚层, 甜槠在两个亚层的个体数量均最多, 马尾松数量也比较多。甜槠、细齿叶柃、马银花、马尾松等均呈较显著的聚集分布。     

纹沼螺对苦草生长的影响

在室外受控实验条件下,研究了不同密度(0,150,450个/m2)纹沼螺(Parafossarulus striatulus)对沉水植物苦草(Vallisneria spiralis)生长的影响。结果表明,螺类牧食活动促进了苦草生长,与无螺对照组相比,低密度螺处理组中苦草的相对生长率、株高均增加了20%;高密度组中苦草的相对生长率、叶片数和株高分别增加了28%、15%和27%。分析表明,纹沼螺通过牧食活动降低植物叶片上附着生物干重,从而促进了苦草生长。丰富了螺-草互利关系的研究内容,有助于加深理解水生态系统中生物之间的生态关系。     

Structure of a unique inland mangrove forest assemblage in fossil lagoons on the Caribbean Coast of Mexico

Scrub mangrove wetlands colonize the intertidal zone of fossil lagoons located in carbonate continental margins along the Yucatan Peninsula of Mexico. These unique ecological types were investigated in October, 1994, by locating transects in several mangrove forests along the Caribbean coast of the peninsula. Four species of mangrove occurred at these sites including Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta. This is one of the first examples of a species rich scrub forest. The mangroves fell into three height categories: short scrub less than 1.5 m, tall scrub to 3.0 m, and basin forests between 4.5 and 6 m. Average height, diameter (dbh), basal area, and complexity index generally increased from short scrub to basin forests. Basal area, ranged from 0.16 m² ha^–1 in a short scrub forest intermixed with Cladium jamaicense to 12.9 m² ha^–1 in a basin forest. Density ranged from 1520 trees ha^–1 to over 25,000 trees ha^–1 in a short scrub forest dominated by R. mangle. The complexity index ranged from 0.01 to 8.3. Height, dbh, basal area, and complexity index were positively related. A number of trees were growing as sprouts from larger downed trunks, suggesting that hurricanes, such as Gilbert that occurred in 1988, are important in controlling the structure of these forests. These forests appear isolated from the sea, but are influenced by groundwater exchange occurring at the land-margin zone.     

Long-Term Growth and Succession in Restored and Natural Mangrove Forests in Southwestern Florida

We compared colonization, growth and succession from 1989 to 2000 in a restored mangrove site and in gap and closed canopy sites in a natural mangrove forest. The restored site was created in 1982 and planted with Rhizophora mangle (≈2 m⁻²) propagules. By 1989, Laguncularia racemosa, with densities up to 12.9 tree m⁻², was a dominant in all plots, although densities were greater at edge plots relative to inner plots, and near open water (west plots) relative to further inland (east plots), and in tall mangrove plots relative to scrub plots. Rhizophora mangle (1989 tree densities about 2 m⁻²) was a codominant in inner and scrub plots, while Avicennia germinans had the lowest densities (<1 tree m⁻²) in all plots. From 1989 to 2000 L. racemosa experienced reduced recruitment and apparent density-dependent mortality of canopy individuals in plots with high initial densities. Scrub plots experienced high rates of colonization by R. mangle and L. racemosa, rapid growth in height of all species (1989–1996), followed by a dieoff of L. racemosa in later years (1997–2000) as the canopy came to resemble that of tall mangrove plots. Colonization and growth rates were lower in gap and closed canopy regions of the natural forest relative to rates in the restored site. After 11 years, densities of L. racemosa were 10–20× lower and R. mangle slightly less in the gap relative to densities in tall mangrove plots in the restored site at the same age. Although the restored stand had converged with the natural forest by 2000 in terms of some factors such as species richness, vegetation cover, litterfall, and light penetration, trees were still much smaller and stem densities much higher. Full development of mature structure and ecological function will likely require decades more development.     

Shell Morphological Variation of Littoraria angulifera among and within Mangroves in NE Brazil

The shell morphological variation of the periwinkle Littoraria angulifera (Lamarck, 1822) was studied in tropical northeast Brazilian mangroves. This area was selected because mangroves in different stages of regeneration, and thus different tree heights can be found. We evaluated whether differences in solar radiation due to differences in tree height influenced the distribution and shell morphology of L. angulifera, and carried out an experiment to test if individuals collected from mangroves with different tree heights differed in their resistance to desiccation. We also analysed if there were differences in L. angulifera shell length and shape between tidal levels within a mangrove. Finally, we tested if increased habitat complexity due to the presence of oysters could influence L. angulifera shell length and shape in different-statured mangroves. We predicted that the oysters could reduce desiccation stress on periwinkles in small-statured mangroves but have no effect in taller ones. Shell length and shape varied among mangroves, although a large variation within mangroves was also recorded. Shell proportionality (shell length:width ratio) increased with shell length, and this relationship differed among mangroves; however, no differences were found in a subsequent year. Individuals from small-statured mangroves survived longer than those from taller mangroves in the desiccation experiment, with a weak correlation between shell proportionality and loss of mass. The presence of oysters had no apparent influence on shell morphology that could be correlated with reduced desiccation stress. The patterns found varied greatly both at small and large spatial scales, suggesting that future studies should evaluate phenotypic and genetic variation at the same time to properly understand variation in L. angulifera shell morphology.     

Mangrove litter dynamics in La Mancha Lagoon,Veracruz, Mexico

In the mangrove surrounding the coastal lagoon of La Mancha, Veracruz, Mexico, we studied litter fall, litter standing crop, and turnover rates in four different mangrove settings, based on the ecological classification of Lugo and Snedaker (1974). We studied those three prominent ecological processes at the basin, fringe and riverine mangrove settings, being the last one a relict riverine stand. The aim was to describe and compare litter dynamics among mangrove types in a lagoon with an ephemeral inlet, as a way of understanding functional heterogeneity within this coastal ecosystem. The daily average values of litter fall were different (P < 0.01) among mangrove site basin I, formed by Avicennia germinans and Rhizophora mangle (2.35 g/m²/day); basin II, formed by Laguncularia racemosa, Avicennia germinans, and Rhizophora mangle (2.93 g/m²/day); fringe with Rhizophora mangle (2.13 g/m²/day); and relic riverine, also with R. mangle (4.70 g/m²/day). The amount of litter standing crop was different among sites (P < 0.001), and also between the dry and rainy season, for each mangrove type (P < 0.001). Turnover ratios were higher in basin I and basin II sites (6.34 and 7.44 times per year) than in relic riverine and fringe mangroves (1.49 and 2.39 times per year). Interstitial salinity and sediment nutrients varied among mangrove types and could influence litter production. Since this lagoon has an ephemeral inlet, continuous inundation throughout 7–8 months per year has an important effect on litter dynamics.     

Mollusk collecting and environmental change during the Prehistoric Period in the Mariana Islands

Archaeological research in the Mariana Islands has revealed changes in mollusk collecting during the Prehistoric Period (approximately 1500 BC to AD 1521). The earliest people at Tumon Bay, Guam and Chalan Piao, Saipan collected mostly bivalves, especially the arc clam Anadara antiquata. After several hundred years, they no longer collected A. antiquata, but collected smaller bivalves instead. By AD 1000, they collected mostly gastropods, primarily the coral reef species Strombus gibberulus gibbosus. One possible explanation is that the people preferred the large arc clam but overharvested it until they were forced to eat the smaller bivalves and then the snails. However, recent evidence in the form of mangrove wood and mangrove pollen supports another explanation, one of non-anthropogenic environmental change. In this case, the relative sea-level decline, which took place in the Marianas within the last 4,000 years, caused the demise of mangrove habitats and of the arc clam at Tumon Bay, Guam and Chalan Piao, Saipan. As mangrove habitats were diminished by sea-level decline, collecting effort shifted to coral reefs, and S. gibberulus gibbosus was harvested throughout the remainder of the Prehistoric Period and into the Historic Period. Southern Guam is the only area in the Marianas in which A. antiquata increased in abundance during the Prehistoric Period. The same types of evidence, mangrove wood and mangrove pollen, indicate that, in contrast to the situation at Tumon Bay and Chalan Piao, mangroves increased in abundance in southern Guam.     

Spatial and temporal distribution of Myrophis punctatus (Ophichthidae) and associated fish fauna in a northern Brazilian intertidal mangrove forest

The mangrove forest along the northern Brazilian coast is not inundated during low tide. However, many fish species stay in the mangrove forest during this time. Tidal behaviour strategies are described for fish species that linger in the mangrove forest during low tide. The samples were taken at the end of the dry season (December 1996) and at the end of the rainy season (July 1997). Fish were captured using an ichthyotoxic plant extract (Ichthyotere cunabi). Spatial and temporal fish density and biomass were analyzed statistically. Thirty-six samples were taken with a total density of 2.8 ind m^-2 and a total biomass of 17.4 g m^-2 distributed among seven families and 14 species. Myrophis punctatus was the most important species in number (1.66 ind m^-2) and weight (12.68 g m^-2) of all catches. The total fish densities were not significantly different among areas and between months, although, total biomass differed significantly in time and space. The densities and biomass for the three most dominant species (M. punctatus, Poecilia spp. and Gobionellus smaragdus) differed significantly among species. Only the biomass of these species showed significant monthly differences. The only significant main effect on variance in the densities and biomass of M. punctatus were encountered between months. In addition, the factor area was significantly different for the variable number of species.     

How to increase juvenile shrimps in mangrove waters?

The distribution, density and species composition of juvenile shrimps were studied in three mangrove zones of Pichavaram, situated on the southeast coast of India. Nine species of shrimps dominated with Metapenaeus monoceros, M. brevicornis and Penaeus indicus were recorded. This shrimp resource was higher in mangrove-lined waters than that in neritic waters. This field observation was experimentally proved using litter bags. The average catch around the litter bags was 0.80 individuals day^–1 for Rhizophora leaves, 1.6 ind. day^–1 for Avicennia leaves and 0.16 ind. day^–1 in control. In general, abundance of juvenile shrimps was the highest around the leaves that were decomposed for 40 days and colonized with high counts of nitrogen-fixing azotobacters. Finally, a vegetation trap technique using mangrove leaves has been proposed for efficient schooling of juvenile shrimps. There was about 3-fold increase in number of shrimp juveniles around the trap than at control waters.     

Factors affecting the distribution and abundance of the commensal <Emphasis Type="Italic">Temnocephala iheringi</Emphasis> (Platyhelminthes: Temnocephalidae) among the southernmost populations of the apple snail <Emphasis Type="Italic">Pomacea canaliculata </Emphasis>(Mollusca: Ampullariidae)

Temnocephala iheringi is the most common temnocephalan inhabiting the mantle cavity of the apple snail Pomacea canaliculata, a freshwater neotropical gastropod that has become a serious rice pest in Southeastern Asia. T. iheringi has been recorded from Mato Grosso (Brazil) to water bodies associated with the Río de la Plata river (Argentina). During an extensive survey in the southern limit of the native area of P.␣canaliculata the presence of T. iheringi eggs was recorded in several apple snail populations, extending the known distribution of the commensal more than 400 km southwards. The aim of this study was to understand the factors affecting the distribution and abundance of T. iheringi among populations of P.␣canaliculata. Only 23% of the apple snail populations inhabiting streams harboured temnocephalans while the occurrence among lentic ones was 71%. T. iheringi was found mostly in populations of apple snails living in non-alkaline sites and where snails attaining sizes larger than 4 cm were very common. The prevalence of the temnocephalans in lentic populations was higher than 90%. The number of eggs on the shell (not including the umbilicus) ranged between 0 and 470 and was different among populations of P.␣canaliculata. The prevalence and number of eggs were lower in the lotic populations, except for a stream population immediately downstream of a lake with commensals. There was no difference between males and females of P. canaliculata neither in the prevalence nor in the number of eggs on the shell. The southernmost population of the world of P. canaliculata harbours commensals that tolerate cold winter water temperatures (4–5 °C) as well as its host. On the other hand, T. iheringi was found only in sites with bicarbonate concentrations lower than 6.6 meq l⁻¹, suggesting that the tolerance of the commensal is very much lower than that of the apple snail (up to 9.95 meq l⁻¹). The number of worms inside each snail or the life history variation of P. canaliculata could explain the influence of the size of the snails on the occurrence of T. iheringi. In the big-sized snails, where the number of commensals is higher, the probability of survival of at least one worm is also higher, specially during the hibernation period, when crawling and feeding are null and snails remain buried. On the other hand, P. canaliculata snails from lentic populations are generally bigger and mostly iteroparous, while those inhabiting streams are smaller and semelparous. In these populations the snails have access to mate only with snails of their same cohort, while in iteroparous populations they can copulate with individuals of other cohorts, allowing the inter-generation transmission of worms and the long term persistence of the population of commensals.     

皂荚提取物的杀螺活性

[目的]研究皂荚生物农药活性,开发利用皂荚资源,发展环境友好的绿色植物源农药。[方法]采用室内生测和田间试验研究皂荚壳乙醇提取物的杀螺活性。[结果]皂荚提取物对福寿螺有显著的毒杀活性,对幼螺和成螺72 h的LC₅₀分别为40.56、109.83 mg·L^-1。田间试验表明,皂荚提取物对福寿螺有较好的防效,施用40 g·m^-2的皂荚提取物处理7 d后卵块减少率为100.00%（成螺失去产卵的能力）,防效为（99.12±1.26）%。[结论]皂荚提取物对福寿螺较好的生物防治效果,是一种潜在的生物杀螺剂。