The genusPicris (Asteraceae,Lactuceae) in Tropical Africa

Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica Sch. Bip. (Ethiopia),P. xylopoda Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned.     

Comparison of species ordinations resulting from alternative indices of interspecific association and different numbers of included species

Summary Several measures of interspecific association are compared. Dispersion and covariance are limited in value because they respond to the commonness of the species compared. Correlation is not so limited but it responds to discrepancies in commonness among the species. The practical result of these relationships between commonness and association is that only the most common species can occupy periferal positions in a species ordination. Rare species are relegated to positions near the center not on the basis of their phytosociological pattern but simply because of their rarity. Both Cole's index of association and the tetrachoric correlation overcome the problem imposed by the relationship between ordination position and species commonness and they both produce very similar results. The effect of differing numbers of species on the ordination configuration is examined using both Pearson's correlation and Cole's index. The basic pattern of the ordination is set with the first few species when Cole's index is used, however, since rare species are given more weight in the analysis with this index, the addition of several very rare species can change the configuration of the ordination.Nomenclature of species is given in Table 1.Research supported by the Eastern Deciduous Forest Biome Project, US-IBP, funded by the National Science Foundation under Interagency Agreement AG-199, BMS69-01147 A09 with the Energy Research and Development Administration — Oak Ridge National Laboratory. Research also supported by the U.S. Energy Research and Development Administration under contract with the Union Carbide Corporation. Contribution No. 240 from the EDFB, US-IBP. Publication No. 790. Environmental Sciences Division, ORNL.     

Site Variation in Littoral Periphyton Populations: Correlation and Regression with Environmental Factors

Over a six month period, littoral periphyton communities on vertically oriented glass slides were quantitatively sampled from four stations in Elk Lake, British Columbia. Correlation and multiple regression analyses were employed to assess the temporal interrelationships between 15 environmental variables, concurrently measured, and the periphyton populations, expressed as total cell counts and species diversity, for the complete data set of each station. At all stations there was a statistically significant increase in total cell populations with increasing length of slide exposure; positive correlations also occurred with pH, temperature, nitrite, nitrate and copper, while negative ones occurred with oxygen, orthophosphate and hardness (magnesium and total). At all but one station there was a significant decrease in species diversity with increasing slide exposure duration, a decrease attributed to the simultaneous increase in standing crop resulting in intensified competition for diminishing substrate area suitable for cell colonization. Multiple stepwise regression analyses demonstrated that greater than 80% of the variation in periphyton total cells at all four stations could be reliably predicted or described in terms of length of slide exposure, phosphate (ortho and total), and hardness (calcium and total). On the other hand, exposure duration and total cell populations were the most important variables associated with changes in species diversity at three of the four stations. In general, correlations and regressions between standing crop and environmental variables were more statistically reliable and consistent between stations than comparable analyses with species diversity. Use of multiple regression and correlation disclosed the importance of small, non statistically significant variation in ecologically relevant variables and permitted objective comparison of stations.     

Environmental filtering rather than dispersal limitation dominated plant community assembly in the Zoige Plateau

Identifying the mechanisms that underlie the assembly of plant communities is critical to the conservation of terrestrial biodiversity. However, it is seldom measured or quantified how much deterministic versus stochastic processes contribute to community assembly in alpine meadows. Here, we measured the decay in community similarity with spatial and environmental distance in the Zoige Plateau. Furthermore, we used redundancy analysis (RDA) to divide the variations in the relative abundance of plant families into four components to assess the effects of environmental and spatial. Species assemblage similarity liner declined with geographical distance (p < .001, R ² = .6388), and it decreased significantly with increasing distance of total phosphorus (TP), alkali‐hydrolyzable nitrogen (AN), available potassium (AK), nitrate nitrogen (NO₃ ⁺–N), and ammonia nitrogen (NH₄ ⁺–N). Environmental and spatial variables jointly explained a large proportion (55.2%) of the variation in the relative abundance of plant families. Environmental variables accounted for 13.1% of the total variation, whereas spatial variables accounted for 11.4%, perhaps due to the pronounced abiotic gradients in the alpine areas. Our study highlights the mechanism of plant community assembly in the alpine ecosystem, where environmental filtering plays a more important role than dispersal limitation. In addition, a reasonably controlled abundance of Compositae (the family with the highest niche breadth and large niche overlap value with Gramineae and Cyperaceae) was expected to maintain sustainable development in pastoral production. These results suggest that management measures should be developed with the goal of improving or maintaining suitable local environmental conditions.     

防洪改善计划对鸟类的生态影响

香港特别行政区新界内有23 hm^2的鱼塘和22 hm^2的耕地,在“元朗-锦田-牛潭尾主要防洪改善计划”中被改变成两条防洪渠（防洪渠60号和43号）.于该防洪改善计划中的生态监察调查中发现这两条防洪渠的鸟类数量均较原先的生境大大减少.在耕地改变成防洪渠43号的过程中,鸟类密度由33.9 只/hm^2减少至2.2只/hm^2.在鱼塘改变成防洪渠60号的过程中,鸟类密度由5.2 只/hm^2 减少至0.4只/hm^2.研究亦发现一些原本在鱼塘和耕地很常见的鸟类物种因为生境被改变而消失.这些转变可能和食物,植被及生境复杂程度的减少有关.另一方面,为纾缓因这防洪改善计划中损失的耕地生境,渠务署在防洪渠43号的河岸铺上混凝土草格,促进植物繁衍,为鸟类提供生境.但研究发现以混凝土草格建造的草坡并未能提供有效的纾缓措施,取代耕地生境以减少生态影响.     

兰州滨河公园自生植物物种组成及多样性分析

调查研究兰州4处滨河公园自生植物的物种组成和多样性特征,为低成本、低养护和野趣自然的园林景观规划提供参考。在黄河兰州主城区段自西向东选取银滩湿地公园、马滩湿地公园、马拉松主题公园、雁滩公园,通过网格系统取样法共设置344个样方,调查研究滨河公园自生植物物种组成和分布特征。结果表明,4处滨河公园共有44科118属163种;在物种来源中,乡土物种79种（48.46%）、国内外来物种53种（32.51%）、国外外来物种14种（8.58%）、入侵植物有17种（10.42%）;4处滨河公园间α多样性存在显著差异（P<0.05）;银滩湿地公园、马滩湿地公园、马拉松主题公园、雁滩公园的多样性指数H''分别为4.76、4.36、4.064、3.99;均匀度指数J''分别为0.53、0.586、0.56、0.54;丰富度指数R''分别为30.68、29.47、22.80、20.27;平均多度分别为55.43、44.82、50.16、39.40。兰州滨河公园自生植物资源较为丰富,在未来的城市园林绿地建设中可合理规划,提高自生植物的应用比例,并根据不同环境营造具有地域特色的自生植物景观。     

北京永定河-海河干流河岸带植物的区系分析

探讨了北京永定河-海河干流河岸带植物区系特征。结果表明,河岸带植被中共有维管束植物37科100属134种,其中包括种子植物36科100属133种,蕨类植物1科1种。北京永定河-海河干流河岸带植物种类比较丰富,其中,在科的组成结构上,植物种类主要集中于少数几个大科如为禾本科和菊科,而多数科只有少数种或单种。在属的组成结构上,主要以单种属和小属为主。对其中种子植物的植物区系分布类型在种级水平上进行了分析,结果表明:河岸带共有4大类区系性质成分和16个地理成分类型,总体呈温带特性,各类温带分布类型67种,占河岸带植物总种数的50%。各河段河岸带植物区系结构存在差异:永定河山峡段与海河干流段区系结构比较相近,各结构在植物种所占比例上的排序为温带类世界类热带类亚洲类;而大部分长期干涸的永定河平原段,则温带类热带类世界类亚洲类。     

胜利河连续系统中蜉蝣优势种的生产量动态和营养基础

大型底栖动物在河流生态系统中发挥着重要作用, 2009 年3月至2010 年3月间对长江中游支流巴河流域的胜利河大型底栖动物群落优势种类的生产力进行为期1 周年的调查研究, 结果表明, 主要蜉蝣优势种扁蜉、等蜉和红斑蜉的生活史为3代/年、3代/年和 2代/年。现存量呈现出1-3级河流增加,而4级又较3级有所下降的趋势。采用龄期频率法( instar-frequency method) 测算的平均周年生产量分别为扁蜉, 200.13 g/(m².a) , P/B 为23.69; 等蜉, 82.06 g/(m².a), P/B 为18.12;红斑蜉, 12.30 g/(m².a), P/B 为8.78。三种蜉蝣的生产量动态在时间上与现存量动态较一致,但彼此各不相同。扁蜉的日均产量于2009年3月在二级河流中达到最大(363.56 mg/m².d),等蜉于2010年3月在三级河流中到达最大(282.76 mg/m².d),而红斑蜉于2009年3月在一级河流中到达最大(33.36 mg/m².d)。生产量的营养基础分析结果表明,扁蜉前肠内含物中无形态碎屑、动物组织、植物纤维、丝状藻类、硅藻所占平均比例为74.37%,4.19%,17.11%,4.29%,0.04%,对生产量的贡献率分别为77.15%,11.27%,6.57%,4.95% ,0.04%;等蜉前肠内含物中无形态碎屑、动物组织、植物纤维、真菌、丝状藻类和硅藻所占平均比例为65.64%,6.17%,23.04%,0.54%,4.53%,对生产量的贡献率分别为: 68.16%,16.61%,8.86%,1.03%,5.23%,0.09%,0.10%;红斑蜉前肠内含物中,无形态碎屑、动物组织、植物纤维、真菌、丝状藻类和硅藻所占平均比例为41.14%,5.96%,38.04%,1.34%,11.21%,2.31%,对生产量的贡献率分别为46.67%,17.52%,15.98%,2.81%,14.13%,2.91%。这与我们在黑竹冲和叹气沟的研究结果存在一定差异,可能与这些溪流自身环境和地区分布有关。     

Predictors of Introduction Success in the South Florida Avifauna

Biological invasions are an increasing global challenge, for which single-species studies and analyses focused on testing single hypotheses of causation in isolation are unlikely to provide much additional insight. Species interact with other species to create communities, which derive from species interactions and from the interactions of species with the scale specific elements of the landscape that provide suitable habitat and exploitable resources. I used logistic regression analysis to sort among potential intrinsic, community and landscape variables that theoretically influence introduction success. I utilized the avian fauna of the Everglades of South Florida, and the variables body mass, distance to nearest neighbor (in terms of body mass), year of introduction, presence of congeners, guild membership, continent of origin, distribution in a body mass aggregation or gap, and distance to body-mass aggregation edge (in terms of body mass). Two variables were significant predictors of introduction success. Introduced avian species whose body mass placed them nearer to a body-mass aggregation edge and further from their neighbor were more likely to become successfully established. This suggests that community interactions, and community level phenomena, may be better understood by explicitly incorporating scale.     

Detecting Invasions of Marine Organisms: Kamptozoan Case Histories

Detecting marine invasions can be challenging, especially for lesser-known taxa, and requires (a) thorough field surveys of the region of interest for members of the taxon, (b) systematic analyses to identify all species found, (c) literature searches for the worldwide distribution of these species and for previous records of the taxon in this region, and (d) application of rigorous criteria to assess whether each species found is native or introduced. We carried out these steps in order to detect and document kamptozoan (entoproct) invasions on the American mid-Atlantic coast. We report on the occurrence of two colonial kamptozoans (Barentsia benedeni, Loxosomatoides laevis) in Chesapeake Bay (Maryland and Virginia, USA). On the American Atlantic coast, B. benedeni had previously only been reported from Massachusetts, although this species has a worldwide distribution in bays and harbors. The genus Loxosomatoides had not previously been reported from North America and L. laevis was known only from India. Since the genus Loxosomatoides was very poorly characterized, we briefly review all four of its species, which differ only slightly from each other. We have also synonymized L. japonicum with L. laevis. We did not find any of the kamptozoan species previously recorded in surveys of Chesapeake Bay and the American Atlantic coast. This is the first detailed consideration of anthropogenic influences on kamptozoan distributions, and we emphasize that most kamptozoan species are cryptogenic pending further investigation.