【作者】 望甜；

【导师】 韩博平； Henri Dumont；

【作者基本信息】 暨南大学 ， 水生生物学， 2010， 博士

【摘要】 捕食和竞争是引起生物种群波动的最主要原因,也是调节生态系统结构的主要动力。流溪河水库是一座亚热带大型深水贫中营养水库,浮游动物种类丰富,生物多样性高,本论文调查了2006～2009流溪河浮游动物(甲壳类、轮虫,以原生动物中的砂壳虫和蜗虫属中扁虫)的种群动态与时空分布,分析了捕食和竞争对浮游动物群落组成、结构和动态变化的影响,以及由捕食和竞争引起的浮游动物的的垂直迁移和垂直分布。流溪河水库是一座贫中营养水体,叶绿素a浓度较低,浮游动物的捕食和竞争活动激烈。甲壳类是流溪河水库浮游动物的绝对优势类群,桡足类站浮游动物比例的61.7%-82.6%,枝角类占浮游动物总生物量的15.7%～29.8%,轮虫的生物量在水库中呈逐年下降的趋势,其组成以小个体轮虫为主。水库的优势种和主要滤食者是舌状叶镖水蚤和奥氏秀体溞,其次是脆弱象鼻溞、颈沟基合溞和中剑水蚤。流溪河浮游动物的演替模式和温带水体的PEG模型比较相似,有一些温带大型滤食者如盔型溞的参与。最大生物量与最小生物量平均比为13.4,有比较明显的季节演替和季节规律,这是流溪河水库区别于其他热带水体的显著特征。同时,流溪河水库也有一些典型的热带浮游动物种类如秀体溞,网纹溞,舌状叶镖水蚤,扁虫等等,它们的演替和季节动态则具有热带水体浮游动物的特征,表现出喜高温、夏季种群数量高、种群发展快、对食物浓度要求较高等特点。舌状叶镖水蚤在整个华南地区分布非常广泛,是敞水浮游区最常见的优势种,也是热带地区最重要的大型滤食者,在流溪河水库中其种群数量中在桡足类所占的比例呈逐年上升趋势。种群丰度波动范围为0～36.5 ind/L,多年丰度均值为6.8 ind／L,生物量波动范围为0-926.3μg／L,生物量上是水库浮游动物的绝对优势种。舌状叶镖水蚤是暖水型滤食者,其生物量与叶绿素a有显著的负相关性(r=0.330(*)；p=0.016,N=42).,而与温度呈极显著正相关性(r=-0.309(*)；p=0.020,N=45).舌状叶镖水蚤是大型K-型选择者,体长大、食物浓度低、食物范围宽、逃避捕食能力强、竞争力强,故而是适应高温、高强度捕食压力的热带优势的滤食者。在贫营养条件下,其种群增长率为的盔型溞种群增长率的5倍。温度和食物浓度上升能够提高舌状叶镖水蚤的发育速度。通过提高防御能力,降低死亡率来抵御捕食压力是舌状叶镖水蚤作为大型K-型选择者适应热带高强度捕食压力的显著特征。奥氏秀体溞世代短,繁殖较快,对食物浓度要求比较高,与温度呈显著正相关性,动态变化随温度的变化比较明显,种群丰度波动范围在0～15.2 ind/L之间,多年均值丰度为2.3 ind/L。在水温较高的情况下,秀体溞能提高发育速度,和每胎怀卵数量,并且寿命不受影响。在热带水体中,水温高而鱼类活跃,捕食作用强烈,对浮游动物来说,最适应这种环境的生存策略是尽量缩短时代时间加快发育速度,增加繁殖率,以弥补捕食带来的种群的损失,特别是随温度升高的这种变化。垂直迁移是指浮游动物在整个水层一天之内进行垂直的迁移活动。流溪河水库是一座北回归线上修建有50年以上的大型深水水库,水温常年较高,水体分层显著,水库有养鱼的历史,鱼类捕食压力较大,浮游动物垂直迁移活动强烈。在流溪河水库中,优势甲壳类的垂直迁移特点随捕食压力、食物浓度、季节差异、发育阶段以及自身生活策略的不同而表现出不同的特点。奥氏秀体溞和无节幼体在所有季节和所有体长的个体均没有明显的垂直迁移活动,种群绝大部分停留在温水层,种群分布和叶绿素a浓度分布呈显著正相关性(r=0.305*；p=0.035；N=36)。脆弱象鼻溞,颈沟基合溞和模糊秀体溞是比较小的枝角类,受到无脊椎捕食者薄皮溞,幽蚊幼虫捕食因素的影响,在流溪河水库中在夏季呈逆向垂直迁移模式,即白天种群停留于水体表层,而晚上种群迁移至水体底层,而冬季则不进行垂直迁移活动。方形网纹溞,微型裸腹溞和盔型溞,所有个体,无论体长大小,在所有季节都进行垂直迁移活动,并且迁移幅度较大。舌状叶镖水蚤和中剑水蚤是流溪河水库中体长最大的浮游动物,但由于发育时间较长,迁移规律随年龄阶段的桡足幼体的不同情况较复杂。总体来说,发育阶段较早的桡足幼体垂直迁移能力微弱,或不进行垂直迁移,分布于水体食物浓度较丰富的水层,而成体和晚期桡足幼体则进行幅度较大的垂直迁移活动。博平近剑水蚤体长最小,其垂直迁移规律是夏季进行小幅度的垂直迁移,冬季则没有垂直迁移行为,种群停留在水体上表层。有壳变形虫是一类分布非常广泛、种类丰富的单细胞原生动物,它们的外形差异很大,并也常见于敞水区。在流溪河水库中,主要有6个种类。这些砂壳虫能够以水体中很多种类的轮虫、多甲藻为食,甚至能够摄食中型浮游生物包括无节幼体等,其摄食种类跟砂壳虫的口径大小有关：其中D. tuberspinifera偏好摄食一种直径为30μm的多甲藻,D. biwae对一种直径为25μm的多甲藻的种群则具有明显的抑制作用,砂壳虫对软体和有坚硬外壳的食物均有良好的处理方式；Asplancha, Stentor, Ploesome和中剑水蚤是砂壳虫的捕食者,其中,砂壳虫是中剑水蚤的重要食物来源,其种群跟中剑水蚤呈正相关性。砂壳虫最显著的特征是进行底栖-浮游的生活周期循环,种群高峰出现于正夏,时空差异分布显著,河流区和过渡区水体扰动较大、食物较为丰富的位置种群丰度最高。砂壳虫集中于食物较为丰富的暖水层0-12m,种群高峰出现于8m。砂壳虫受食物影响比受捕食因素影响更大,其种间种内竞争比较激烈,同类相食在砂壳虫各种类之间比较普遍。伪足对砂壳虫的生命活动具有重要意义,其口径大小决定了伪足的活跃程度与摄食能力以及砂壳虫的食物生态位范围。流溪河水库2004～4005年间进行了人为的高强度捕鱼导致水库鱼类的密度大幅度下降,浮游性的扁虫的种群在2006～2009年出现于每年的初夏。当扁虫一出现时,盔型溞的种群消失(7月),进入休眠状态,这比鱼类对盔型溞带来的捕食压力的种群消失时间(8月)提前了一个月,而方形网纹溞则取代了盔型溞的优势。结合实验室培养、观察、大型围格、以及野外采样数据分析,在无扁虫的情况下,盔型溞由于其滤食能力更强,其竞争优势大于网纹溞,但盔型溞对扁虫毒素非常敏感,因此在有扁虫的情况下,竞争优势被对扁虫毒素耐受性较大的网纹溞取代。扁虫对其自身产生的毒素也非常敏感,因此种群不能维持在很高的浓度,而方形网纹溞虽然也被扁虫捕食,但由于其耐受性种群反而取得与其他动物竞争优势。更多还原

【Abstract】 Predation and competition are the main factors regulating population dynamics in freshwater organisms and also the most important structuring forces in freshwater ecosystems. Liuxihe Reservoir is a large deep oligo-mesotropic sub-tropical reservoir with high diversity of zooplankton species,. The present study investigated structures and dynamics of zooplankton communities in the reservoir from 2006～2009, explored the role of predation and competition in structuring zooplankton communities, vertical distribution patterns and population dyanmics.Liuxihe Reservoir is an oligo-mesotropic water body with low chlorophyll a concentration, the zooplankton suffered from food limitation, and strong competition, consequently, predation can evidently modify competition consequence.Zooplankton biomass composition in Liuxihe Reservoir was predominated by crustaceans, of which copepods accounted for 61.7%～82.6%. Cladocreans contributed a percentage of 15.7%～29.8%. Rotifers had a decreasing trend within the years, and they were mainly composed of small-bodied species. Among crustaceans, Phyllodiaptomus tunguidus and Diaphanosoma orhidani were the most dominant species and filter feeders, followed by Bosmina fatalis, Bosminiopsis deitorsi, and Mesocyclops sp.As the large fitler feeder Daphnia geleata occurred, the seasonal succession pattern of zooplankton in Liuxihe Reservoir was similar to PEG model in temporal water-bodies. The annual average ratio of the maximum biomass to minimum biomass of zooplankton was about 13.4, indicating a distinct seasonal succession pattern which is the main different characteristics different to other tropical water-bodies. On other hand, the zooplankton mainly consisted of typical tropical zooplankton species such as Phyllodiaptomus tunguidus, Diaphanosoma orhidani, Ceriodaphnia and flatworms. Their succession and dynamics were also typical tropical zooplankton species, with peak populations at high temperatures in summer, short development time, and high food concentration requirements.Phyllodiaptomus tunguidus distributed widely in all South China as the most dominant pelagic species and filter feeders in tropical and sub-tropical water-bodies. It had an increasing trend in the investigation years. Its abundance ranged from 0 to 36.5 ind/L, with an annual average value of 6.8 ind/L; the coorepsonding biomass range was from 0 to 926.3μg/L.. It existed a significant positive correlation to water temperature(r=0.330(*), p=0.016, N=42), and a significant negative correlations with chlorophyll a concentration (r=-0.309(*); p=0.020, N=45). P. tunguidus is a K-strategist and strong competitor with large body size, low threshold food concentration, wide food niches, and strong escaping ability. It well adapted to high water temperatures and strong fish predation pressure. The intrinsic increase rate (r) of population was 5 times of Daphnia geleata at low food concentrations. The intrinsic increase rate of Phyllodiaptomus tunguidus increased with higher temperature and food concentration. The ability to avoid predation is a characteristic feature for Phyllodiaptomus tunguidus to adapt to the tropical water with high predation.Diaphanosoma orhidani has a short life generation time, high reproductive rate and high requirements for food concentration, and its abundance showed a significant correlation to water temperatures. The abundance of Diaphanosoma orhidani was from 0 to 15.2 ind/L with an annual mean value of 2.3 ind/L. Diaphanosoma orhidani can speed development rate and enlarge clutch size without shortening life span under high water temperature. Because predation is comparatively stronge in tropical waterbodies, that the most effective adaptive strategies for zooplankton to survive is to shorten life generation time, increase development time and increase reproduction rate to make up for the predation loss, especially when temperature is higher.Many zooplankton species undergo diel vertical migration (DVM) in which they move up and down the water column within a day. The DVM activity patterns for crustaceans were distinct in Liuxuhe Reservoir. The amplitude for DVM of crustaceans in Liuxihe Reservoir were mainly induced by predation pressure, modified by species-specific life strategies, development stages, and food concentration, radiation and seasonal variations.Diaphanosoma orhidani and naupliar has no diel vertical migration in all seasons, regardless of their development stages. The population stayed mainly in the epilimnion, and their distributions were significantly correlated to chlorophyll a concentration Bosmina fatalis and Bosminopsis deitorsi are small body size cladocerans which are most sensitive to invertebrate predation. They showed a reverse diel vertical migration mode in the reservoir, which stayed in the surface water layer during the daytime and descend to deep layers during the night. However, they didn’t show any diel vertical migration in winter. Ceriodaphnia, Daphnia geleata and Moina micrura showed strong diel vertical migration in all seasons, independent of their body size.Phyllodiaptomus tunguidus and Mesocyclops are the largest zooplankton in the reservoir. Their diel vertical migration behavior varied in their development stage. In general, the younger stages of Phyllodiaptomus tunguidus and Mesocyclops showed little or no diel vertical migration, and they stayed mostly in the epilimnion where food is abundant. The later stages and adults showed extended vertical migration. Tropocyclops bopingi, however, due to its small size, showed a short-range vertical migration in summer and no vertical migration in winter, with the main population stayed in the surface layers.Testate amoebae are an abundant and diverse polyhyletic group of shelled protozoa which are quite common and distributed widely in tropical and sub-tropical water bodies In the Liuxihe Reservoir, Difflugia are carnivorous or omnivorous which feed on a large range of food like rotifers, Peridinium or even mesozoans, the food selection mainly depended on the aperture diameter of the prey, for example, D. tuberspinifera preyed mainly on a Peridinium species with a diameter of 30μm, while D. biwae preferred the one of 25μm, and it can suppress the population of this Peridinuim. Asplancha, Stentor, Ploesome, and Mesocyclops are the predators of Difflugia, and the positive correlations between Difflugia and Mesocyclops indicated that Difflugia is an important food source for Mesocyclops when they are abundant in the water column. The characteristic of Difflugia is the bentho-planktonic cycle, with peak population in summer. They have distinct temporal and spatial distribution patterns, and they have much higher abundance in the uprivers and transition region with high water turbulence and food source. They produce gas bubble to be suspended in the pelagic and to move and prey. The vertical sample profiles showed that they don’t have DVM and they distributed mostly in the epilimnion with peak population at a depth of 8m. Competition has more important effect than predation for Difflugia. There were fierce competition between species and within species, and cannibalism was common to be found in Difflugia. Pseudopodia played an important role for Difflugia. Aperture size decided the pseudopodia activity and the food niche range of Difflugia.In Liuxihe, a freshwater reservoir in South China with artificially reduced fish predation pressure since 2004-2005, the zooplankton showed a single yearly pulse of pelagic flatworms in the early summer periods of 2006-2009. As soon as they appear, Daphnia galeata retreats in dormancy, one month earlier (July) under a flatworm than under a fish predation regime (August), but the related Ceriodaphnia quadrangula does not and has a tendency to replace it. We show, using in situ lake sampling, by experiments in large enclosures and by laboratory observations, that Ceriodaphnia is competitively inferior to Daphnia, presumably in its ability to acquire algal food, but has a much higher tolerance to flatworm toxins. As a result, Ceriodaphnia manages to coexist with the flatworm and the balance of the competition is tipped. Observations in the laboratory suggest that flatworm populations autoregulate by being sensitive to their own toxins and that Ceriodaphnia, even though a prey to the worms, may incur less cost than benefit from their presence.更多还原