鳜鱼的耗氧率及其池塘养殖

本文较详细地报道了鳜鱼的耗氧率和窒息点,并对鳜鱼和作其饲料的鱼同池饲养的可能性进行了探讨。结果表明,鳜鱼耗氧量和体重正相关（ｒ＝０．９９）,耗氧率与体重反相关（ｒ＝－０．９７）;在水温２０℃,鱼种耗氧率约为０．１４ｍｇ／ｇ．ｈ．,成鱼约为０．１２ｍｇ／ｇ．ｈ．;耗氧量和耗氧率均与水温正相关（ｒ＝０．９０,ｒ＝０．９４）,水温１３—３０℃时,体重２３０±１１．７ｇ的鳜鱼。耗氧量为１４．３１—４２．１３ｍｇ／尾。ｈ．,耗氧率为０．０５９—０．１７５ｍｇ／ｇ．ｈ．;鳜鱼耗氧率昼夜变化与家鱼相反,黄昏至凌晨是高峰期,为０．１２—０．１５ｍｇ／ｇ．ｈ．（Ｔ＝２０℃）,白天是低谷期,为０．０７—０．１０ｍｇ／ｇ．ｈ;;鳜鱼的窒息点与家鱼类较接近,变化范围为０．４５—０．７６ｍｇ／Ｌ;鳜鱼和作其饲料的鱼在同一池塘中饲养,既可持续不断地提供鳜鱼充足的适口饵料,又简单易行,成本低,效益高,有较大的价值。     

The influence of the diel climatic cycle on the depth-time distribution of phytoplankton and photosynthesis in a shallow equatorial lake (Lake Baringo,Kenya)

Lake Baringo is a shallow equatorial lake. This paper reports a diel study of the depth-time distribution of phytoplankton and photosynthesis at one location in Lake Baringo on 10 March 1989. The water column shows a pattern of diurnal stratification probably accentuated by the high turbidity of the water and therefore rapid attenuation of solar energy. This stratified pattern breaks down at night due to atmospheric cooling and the regular onset of winds in the early evening. The phytoplankton is dominated byMicrocystis aeruginosa with some associated epiphytes. It concentrates in the narrow euphotic zone during the diurnal period of stratification due to buoyancy of theMicrocystis; evening breakdown of the thermocline results in the phytoplankton being mixed throughout the water column. A series of measurements of photosynthesis throughout the diurnal period gives an areal rate of 3.8 g O₂ m⁻² d⁻¹. The relationship between this value and the level of fish exploitation in Lake Baringo is discussed. The diel cycle in Lake Baringo is interpreted as dominating over any seasonal limnological cycle in the lake.     

Animal community structure as a function of stream size

The species-area relationship of the island biogeography theory was calculated for macroinvertebrates in 22 coastal, adjacent streams. A z-value of 0.19 was obtained. The low z-value was probably a consequence of the short distances between streams as well as high dispersal rates. In addition, a cluster analysis based on the dissimilarity of species assemblages showed that stream size was of prime importance in categorizing the streams. To a smaller extent water quality affected the community structure in the streams.     

Field observations on the lepidophagous teleost Terapon jarbua (Forsk»l)

Synopsis Foraging behaviour of the lepidophagous Indo-Pacific teleost Terapon jarbua in the Bulolo and Mtumbane estuaries of southern Africa is described. These observations suggest that scale removal from large fish and the complete ingestion of fish fry represents a modified form of predation. Prey reaction to T. jarbua shoals is also discussed.     

环境筛选和扩散限制在地表和地下螨群落物种共存中的调控作用

识别扩散限制和环境筛选在群落物种共存中的相对作用,是土壤动物群落物种共存机制研究的重要内容,然而少有针对地表和地下土壤动物群落的探讨。在三江平原农田生态系统,设置一个50 m×50 m的空间尺度,探讨环境筛选和扩散限制对地表和地下土壤螨群落物种共存的调控作用。基于Moran特征向量图(MEMs)和变差分解的方法来区分环境筛选和扩散限制的调控作用;采用偏Mantel检验进一步分析环境距离和空间距离的相对贡献;使用RDA分析环境因子对螨群落物种组成的解释能力。变差分解结果表明,空间变量对地表、地下和地表-地下土壤螨群落具有较大的显著方差解释量,而环境变量和空间环境结构的解释量相对较小且不显著;偏Mantel检验没有发现环境距离或空间距离的显著贡献;RDA分析表明土壤p H值、大豆株高和土壤含水量对土壤螨群落具有显著的解释能力,说明环境变量对螨群落物种组成的重要作用。研究表明,在三江平原农田生态系统,地表和地下土壤螨群落物种共存主要受到扩散限制的调控作用,同时环境筛选的调控作用也不容忽视。     

近30年来白洋淀湿地景观格局变化及其驱动机制

湿地是水陆相互作用形成的独特生态系统,其景观格局极易受到气候变化和人类活动的影响。利用1984—2014年的11期遥感影像数据,综合运用GIS技术和景观格局指数方法,对白洋淀湿地景观格局变化特征及其驱动力机制进行了分析。结果表明,1984—2014年期间,挺水植物和沉水植物呈减少趋势,农田和居民点持续快速增长,纯水体为"增加—减少—再增加"的趋势,林地和裸土地变化幅度不大。其中挺水植物一直是白洋淀最主要的景观类型,占研究区总面积比例达到37%—61%。农田的平均斑块面积最大,挺水植物的最大斑块指数和分维度指数最高,挺水植物和农田的聚集度指数最大,居民点、林地和裸土地空间分布离散,破碎化程度高,连通性差。1989—2004年白洋淀景观多样性指数呈减少趋势,景观格局趋于不稳定,同期聚集度指数上升,湿地连通性增加;1984—1989年和2004—2014年期间白洋淀多样性指数上涨,聚集度指数逐年下降,景观异质性增加。人口和社会经济发展是影响白洋淀景观格局变化的主要因素。     

Strong invaders are strong defenders – implications for the resistance of invaded communities

Many ecosystems receive a steady stream of non‐native species. How biotic resistance develops over time in these ecosystems will depend on how established invaders contribute to subsequent resistance. If invasion success and defence capacity (i.e. contribution to resistance) are correlated, then community resistance should increase as species accumulate. If successful invaders also cause most impact (through replacing native species with low defence capacity) then the effect will be even stronger. If successful invaders instead have weak defence capacity or even facilitative attributes, then resistance should decrease with time, as proposed by the invasional meltdown hypothesis. We analysed 1157 introductions of freshwater fish in Swedish lakes and found that species’ invasion success was positively correlated with their defence capacity and impact, suggesting that these communities will develop stronger resistance over time. These insights can be used to identify scenarios where invading species are expected to cause large impact.     

Dieback of riparian alder caused by the Phytophthora alni complex: projected consequences for stream ecosystems

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Ecological features affect patterns of plant communities in Mediterranean temporary rock pools

In this paper, the results of a study on the ecology, floristic composition and spatial assemblages of temporary limestone rock pool plant communities of a central Mediterranean area (S Sicily, the Maltese Islands and Lampedusa) are presented. A total of 76 temporary pools were studied, distributed between the infra-mediterranean and thermo-mediterranean bioclimatic belt. For each temporary rock pools, the floristic composition and cover of the species were determined using standard relevé methods. Moreover, for 50 of these pools, pH, conductivity, soil depth, water-level, altitude and floristic richness and diversity index were assessed. The plant communities were analysed using unweighted pair group method using arithmetic averages and Euclidean distance classification and ordination methods such as canonical correspondence analysis (CCA). A total of four plant communities with specific floristic composition were established, each one with a different dominant species: Callitriche truncata; Elatine gussonei; Tillaea vaillantii and Lythrum hyssopifolia. According to the CCA, the spatial patterns of plant communities follow an ecological gradient related to water level and depth/size of the rock pools: these are the main ecological features affecting the distribution of the plant communities of rock pools. In addition, floristic richness and diversity index showed a slight increase in trend from temporary pools submerged for long periods towards pools submerged for short periods.