The influence of white seabream (Diplodus sargus) production on macrobenthic colonization patterns

The present work evaluates the influence of fish production on macrobenthic colonization over large areas (approximately 700 m²), where the colonizing populations are not nearby the disturbed area. Sampling was undertaken within newly created aquaculture earthen ponds under two contrasting conditions: white seabream (Diplodus sargus) production and no production (control). Macrobenthic and geochemical samples were collected 7, 23, 54, 93 and 180 days after filling the earthen ponds with seawater pumped from a water reservoir for the first time. The water reservoir was also sampled, and is used as a reference for the colonizing populations. Macrobenthic colonization rate in the ponds was low, probably due to the isolation of the disturbed habitat, to the large size of the defaunated area, and possibly to geochemical constraints. Initial colonization was by insect larvae (mainly chironomids), the bivalves Cerastoderma spp., the polychaetes Pseudopolydora paucibranchiata and Hydrodoides elegans, and nemerteneans. The number of species was similar in control and production ponds, even though under production higher total abundance values were observed. Although well represented in the water reservoir, the amphipod Microdeutopus gryllotalpa was only observed within the new ponds after 6 months. Preliminary results suggest that macrobenthic colonization patterns were influenced by fish production, as assemblages were significantly different among ponds. Higher food availability due to fish production may explain the results obtained, but ecological reasons, such as predation, may also contribute for shaping the macrobenthic communities.     

Estimating plant competition coefficients and predicting community dynamics from non-destructive pin-point data: a case study with Calluna?vulgaris and Deschampsia?flexuosa

A method is proposed for estimating plant competition coefficients and predicting the dynamics of herb and grassland plant communities from non-destructive pin-point measurements. The method is applied to inter-specific competition in a natural heathland community with relatively few interacting species. The study shows that the dynamics of the heathland plant community may be thought of as essentially a two-species system of Calluna vulgaris and Deschampsia flexuosa. There were significant competitive interactions between C. vulgaris and D. flexuosa. D. flexuosa affected both the cover and compactness of C. vulgaris individuals as a function of the compactness the previous year, whereas C. vulgaris significantly affected only the compactness of D. flexuosa. There was a significant negative effect of drought on the compactness of both C. vulgaris and D. flexuosa individuals, whereas night warming had no significant effects on either species. The predicted long-term outcome of the competitive interaction between C. vulgaris and D. flexuosa was that of unstable equilibrium, where the more dominant of the two will outcompete the other. However, when both species are found at relatively high plant covers the two species are predicted to co-exist for a long time period relatively to the time scale of the ageing process of C. vulgaris. Direct analyses of the inter-specific competitive interactions in natural plant communities with non-destructive measurements can provide important new insight into the processes that determine the composition of plant communities.     

Scale- and intensity-dependent disturbance determines the magnitude of opportunistic response

Opportunistic, fugitive or pioneer species are species that posses life-history characteristics that allow them to respond quickly to disturbances. Their abundance during the early stages of succession is central to ecological models of benthic soft-sediment succession and these species can play important roles in affecting subsequent successional trajectories. Nevertheless, numerous studies have demonstrated seemingly random patterns of opportunistic responses following disturbance, questioning the generality of currently accepted successional models. In this paper we provide examples from two case studies and argue that the spatial scale or magnitude of disturbance is key to the development of opportunistic responses, and that the scale of disturbance may be particularly important in determining (a) the levels of resources made available and (b) the magnitude of release from competitive interactions, which permit opportunists to flourish.     

The concept of stcucture in phytosociology with references to classification of plant communities

Summary The concept of structure in phytosociology has been analysed. Three families of structure characteristics have been distinguished: (1) qualitative constituent, (2) quantitative constituent and (3) relational characteristics. Selected structural features are illustrated in some detail and completed by references. The key role of spatial structure has been emphasized and a simple method for the introduction of the parameters of spatial structure in data processing has been proposed. Some remarks to the present syntaxonomy have been added from the spatial structure point of view.Contribution from the Working Group for Data-Processing, International Society for Vegetation Science.Thanks are due to Drs. J. Jenik and J. Kvt for advice and to the Editors for linguistic help.     

Community structure of the Mota Magra forest block (Udaipur)

Summary The community structure of the Mota-Magra forest block (24°35N L and 75 49E L), 14 km east of Udaipur town is described. The area supports forest of mixed dry deciduous nature in which Boswellia serrata, Lannea coromandelica and various species of Acacia are dominant tree species. The protected stand has been found to be richer in respect of tree density and basal cover. In the protected stand the basal cover of tree species has been found to increase from hill base to hill top. The northern and eastern aspects were found to be richer than the southern and western aspects respectively. The possible causes responsible for these differences have been discussed. Observation on the maturity index of the community at each site, constance class and A/F ratio of the perennial species have been presented.Nomenclature follows that in present use at the Herbarium of the Botanical Survey of India, Dehradun.Our sincere thanks are due to Shri A. L. Sankhla, I.F.S., Divisional Forest Officer, Udaipur for the permission to work in the Mota Magra Forest Block. Thanks are also due to Prof. Y. D. Tiagi, Head, Botany Department S.B.S.H., University of Udaipur, Udaipur, for the laboratory facilities.     

大青沟森林植物群落主要木本植物生态位研究

探讨了大青沟森林植物群落主要木本植物的生态位宽度、生态位重叠等生态位测度问题。结果表明 :在乔木种群中大果榆、蒙古栎、色木槭、叶底珠的生态位宽度较大。朝鲜柳、水曲柳、茶条槭、春榆、黄菠萝、小叶朴的生态位宽度较小。     

棉花根际固氮菌、解磷菌及解钾菌的相互作用

目的通过对棉花根际促生细菌N2126、P1108和K2116菌株单独接种和混合接种,根据这些菌株的固氮、解磷、解钾能力和细胞数量的变化,了解它们之间的相互作用。方法将这3株菌株设置4个不同的组合:N2126+P1108、P1108+K2116、N2126+K2116及N2126+P1108+K2116,分别测定培养液中全氮含量,水溶性磷、钾含量和细胞数量。结果P1108对N2126的生长有促进作用但抑制K2116的生长,N2126和K2116之间存在拮抗作用。N2126、P1108和K2116混合培养后,三者细胞数量分别占培养液中细胞总数的6.4%、89.2%和4.4%;培养液中的全氮含量比不接种时下降了0.7%;水溶性磷、钾含量比不接种时分别增加了19.0%和12.2%。结论P1108为3株菌株混合培养时的优势菌株,3株菌株混合培养有助于磷、钾释放。     

高寒草甸地区小哺乳动物群落与植物群落演替关系的研究

本文阐述了小哺乳动物群落和植物群落的演替关系;验证了动物群落对植物群落结构的非独立性假设。小哺乳动物群落种的多样性与植物群落的盖度和高度呈显著负相关,植物群落的演替引起小哺乳动物群落的相应演替。并通过加速次生植被演替进程的试验,调控了有害小哺乳动物群落,提出从生态演替规律出发,在退化严重的草地上,通过人的合理参与,协调动植物群落间的结构关系,以达到人类获取畜牧业最大持续生产量,最终使生物生产量得到永续利用的目的。     

Secondary plant succession: how is it modified by insect herbivory?

The effects of foliar- and root-feeding insects on the dynamics of an early successional plant community, representing the first four years of colonisation, were examined. Subterranean insect herbivores were found to increase in density with increasing successional age of the plant community. In early succession, chewing insects mainly Coleoptera (Scarabaeidae) and Diptera (Tipulidae) were dominant. This was in direct contrast to the foliar-feeding insects, which were dominated by sap-feeders (mainly Auchenorrhynchan Hemiptera).Reduction of both foliar- and root-feeding insects with appropriate insecticides had different, but dramatic, consequences for the plant community. Reducing foliar herbivory resulted in large increases in perennial grass growth, with plant species richness being reduced as the grasses outcompeted the forbs. Reducing subterranean herbivory prolonged the persistence of annual forbs, greatly increased perennial forb colonisation and, as a consequence, plant species richness. Foliar-feeding insects thus act to delay succession by slowing grass colonisation. In contrast, root-feeding insects accelerate succession by reducing forb persistence and colonisation. The structure of early successional plant communities is therefore modified by the two modes of herbivory.This paper was presented at the Vth International Congress of Ecology (INTECOL), Japan, 1990, entitled Successional Communities of Plants and Insects.     

In situ survival of forest bryophytes in small‐scale refugia after an intense forest fire

Question: Species can persist in landscapes with recurring disturbances either by migrating to places suitable for the moment or by enduring the threatening conditions. We investigated to what extent boreal forest bryophytes survived an intense forest fire in situ and whether bryophytes had started to recolonize the area 7‐8 years later. Location: Tyresta National Park, eastern Sweden. Methods: We recorded bryophytes in 14 burnt and 12 forest reference plots (50 × 50 m). In each plot we investigated 15 random 1‐m² micro‐plots. In plots in the burnt area we also examined micro‐plots at locations of all fire refugia, and in case of the forest references, of 10 potential refugia. Results: We found on average three small refugia per 50 × 50‐m plot; each containing on average 4.8 forest bryophytes, a level similar to that of micro‐plots in the references, but significantly higher than in random micro‐plots in the burnt plots (1.5 species). Many refugia were located in rocky areas, but few were in wet sites. The burnt area remained dominated by a few fire‐favoured species, even if recolonization of forest bryophytes had begun. There was, however, no significant correlation between number of refugia and number of forest species in random micro‐plots, leaving open the question of the importance of refugia as regulators of early succession. Conclusion: We conclude that small‐scale refugia can also occur for sensitive species such as forest bryophytes, and that the refugia in our case were frequently found on rocky or mesic rather than wet sites. The role of such refugia in recolonization, however, warrants further investigation.     

Seed dispersal spectra of plant communities in the Iberian Peninsula

We studied the seed dispersal spectra of 46 Iberian plant communities of five types: potential woodland, forest fringe, substitutional scrubland, nitrophile communities and montane communities. There were no significant differences between the spectra of communities of the same type from Mediterranean and Eurosiberian regions. Biotic dispersal is most common at mature stages of succession, and abiotic dispersal at immature stages.     

黑石顶自然保护区森林次生演替中优势种群与生态因子的关联度分析

用灰色关联度分析对黑石顶森林次生演替过程中优势种群的重要值与环境因子的关联性进行分析。结果表明先锋种马尾松、杉木和荷术与环境因子的关联度受群落透光度的影响最大,阳生性种鸭脚木、泡花树、罗浮柿和腺叶山矾与各环境因子的关联度差别不大,中生性种小叶胭脂、硬叶稠、短花序桶、陈氏钓樟和黄果厚壳桂与环境因子的关联度受物种丰富度和群落密度的影响最大,而中生性种粘木和阿丁枫与群落透光度的关联度最大。环境因子对演替各阶段优势种群的影响由强到弱的顺序为群落透光度＞物种丰富度、群落密度＞土壤条件,在各优势种群受环境因子的综合影响中,中生性种受影响相对较大。     

煤炭开采对野生植物物种丰富度和物种组成的影响

煤炭开采引发的生态环境破坏早已引起关注,对其破坏机理和修复方法进行研究显得非常重要。本文探讨了煤炭开采对野生植物物种丰富度和物种组成成分的影响。从分布在晋西北地区的338个煤矿中,随机选择16个煤矿作为研究对象,调查了煤炭采空区和非采空区地面的野生植物物种,用Gleason丰富度指数分析了煤矿采空区和非采空区的野生植物物种丰富度差异,同时用Srensen指数分析了煤炭采空区野生植物物种组成成分和非采空区植物物种组成成分的相似性。结果表明:煤炭开采造成了野生植物物种数的减少,采空区的野生物种丰富度明显少于非采空区;煤炭开采也造成了野生植物物种组成成分的变化,采空区和非采空区的野生植物物种组成成分出现明显差异。     

西双版纳不同演替状态热带次生林土壤节肢动物群落特征

采用样地调查法,对西双版纳4种不同演替状况热带次生林：中平树(Macavanga denticulate)、崖豆藤(Millettia laptobotrya)、野芭蕉(Musa acuminata)与黄竹(Dendrocalamus membranaceae)林的土壤节肢动物群落结构与季节变化进行了研究．结果表明,4类不同演替状况次生林土壤节肢动物群落在数量优势类群组成上无较大差异,蜱螨目为所有4类林地的突出优势类群,膜翅目、弹尾目和鞘翅目在不同林地中分别为不同数量等级的次优势类群,而在常见和稀有类群的组成上,各林地表现出较大的差异．土壤节肢动物类群数、个体数和DG多样性指数以正向演替的崖豆藤林最高,偏途演替的黄竹林最低,但中平树、崖豆藤和野芭蕉林的差异不大．4类林地土壤节肢动物类群数和个体数的垂直分布分别以凋落物层和土壤表层(0～5cm)最高,其它各层分布因林地不同各异,并存在明显的季节差异．各林地土壤节肢动物个体数和类群数的季节消长总体表现出干季和雨季初期与末期高于雨量最大的雨季中期,由于不同林地植被结构、凋落物数量和质量以及土壤水热状况不同,其季节变化显现样地差异,除了受林地降水量和温度变化影响外,食物的丰欠和栖息场所的干扰状况也有重要的影响作用．     

Some floristic and ecological characteristics of association Bromo-Plantaginetum mediae Ht. (31)49 on permanent plot No. 82 (National Park Plitvice Lakes — Croatia)

Plot 82 is one of a hundred permanent plots that have been set up in Croatia for the purpose of long-term and continual investigations of ecosystems and their successions. It is located in the area of Karleuine Plase within the Plitvice Lakes National Park. Vegetation on the plot belongs to association Bromo-Plantaginetum mediae. The association develops in mountainous regions of continental Croatia within a wide altitude range, from 180–1300 m a.s.l. on shallow soil over pervious carbonate rocks. The floristic composition and phytocoenological characteristics of the association have been analyzed using the common methods of the phytocoenological school Zürich-Montpellier, on the basis of 17 phytocoenological records. In addition to floristic composition, some site characteristics have been analysed: soil moisture, calcium carbonate, phosphates, pH value, humus, cation exchange capacity and nitrogen mineralization on the site and in the laboratory. The results obtained are comparable with the data presented in the available phytocoenological and ecological literature.