红树林恢复初期莱氏锥滨螺分布动态

树栖腹足类动物是红树林底栖动物的重要组成部分,其组成和分布受到红树植被的影响。因此,在红树林生态修复中,腹足类动物的恢复依赖于植被的发育。滨螺科(Littorinidae)锥滨螺属(Mainwaringia)动物是亚洲红树林的广布种,但针对其在红树林中的分布及种群特征的研究较少,对红树林植被恢复过程中锥滨螺属动物的恢复动态更是鲜有研究。调查了厦门下潭尾湿地秋茄(Kandelia obovata)红树林恢复初期,新记录种莱氏锥滨螺(Mainwaringia leithii)种群恢复的时间动态,并分析其与植被参数的关系。研究发现,红树林恢复初期,秋茄植被生长迅速,株高、冠幅、基径和覆盖度分别由0.5年生幼林的41.3 cm、25.0 cm、1.04 cm和25%增长为8年生样地的179.2 cm、76.7 cm、5.96 cm和95%。在秋茄胚轴种植6个月左右开始记录到莱氏锥滨螺的个体,其密度和生物量在1.5 a后达到最大(分别为136个/m²和1.86 g/m²),而后逐渐降低,种植3 a后秋茄林内莱氏锥滨螺仅零星分布。除8年生的样地,莱氏锥滨...     

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.     

The role of litter in an old-field community: impact of litter quantity in different seasons on plant species richness and abundance

Summary We studied the effect of removing and adding plant litter in different seasons on biomass, density, and species richness in a Solidago dominated old-field community in New Jersey, USA. We removed all the naturally accumulated plant litter in November (658 g/m²) and in May (856 g/m²) and doubled the amount of litter in November and May in replicated plots (1 m²). An equal number of plots were left as controls. Litter removal and addition had little impact on total plant biomass or individual species biomass in the growing season following the manipulations. Litter removal, however, significantly increased plant densities but this varied depending upon the season of litter removal, species, and life history type. Specifically, the fall litter removal had a much greater impact than the spring litter removal suggesting that litter has its greatest impact after plant senescence in the fall and prior to major periods of early plant growth in spring. Annual species showed the greatest response, especially early in the growing season. Both spring and fall litter removal significantly increased species richness throughout the study. Litter additions in both spring and fall reduced both plant densities and species richness in June, but these differences disappeared near the end of the growing season in September. We concluded than in productive communities where litter accumulation may be substantial, litter may promote low species richness and plant density. This explanation does not invoke resource competition for the decline in species richness. Finally, we hypothesize that there may be broad thresholds of litter accumulation in different community types that may act to either increase or decrease plant yield and diversity.     

Planting densities and bird and rodent absence affect size distributions of four dicots in synthetic tallgrass communities

Variability in the size distributions of populations is usually studied in monocultures or in mixed plantings of two species. Variability of size distributions of populations in more complex communities has been neglected. The effects of seeding density (35 or 350 seeds/species/m²) and presence of small vertebrates on the variability of size distributions were studied for a total of 1,920 individuals of 4 species in replicated synthetic communities of 18 species in northern Illinois. End-of season height and above-ground biomass were measured for prairie perennials Dalea purpurea (purple prairie clover), Echinacea purpurea (purple coneflower), Desmanthus illinoensis (Illinois bundleflower) and Heliopsis helianthoides (early sunflower). Variability in biomass distribution of the four target species was twice as great at low than at high densities when small vertebrates were excluded. Our results suggest that inter- and intraspecific competition may affect all individuals more under high-density conditions, thereby reducing the variability in their biomass distributions within this community. This result, a consequence of plant-plant interaction, is obscured when small birds or mammals are present, presumably because either or both add variance that overwhelms the pattern.     

Leptodora kindti: efficient predator and preferred prey item in Neusiedler See,Austria

In the Neusiedler See, Leptodora kindti appeared in the plankton in April/May; the growing season lasted until November. Its optimum conditions prevailed during the summer months, when densities of >500 ind. m^–3 were recorded. First, males appeared by the mid/end of August, while maximum resting egg production occurred in September. At temperatures below 10 °C the population declined.At high population levels, L. kindti caused suppression of its preferred prey item, the juveniles of Diaphanosoma mongolianum. Twenty-five to 45% of juvenile Diaphanosoma can be eliminated by Leptodora. This predation impact is a pronounced but short-term event. During the periods of high Leptodora densities, a significant relationship between Leptodora predation and the death rate of Diaphanosoma is found.The older developmental instars of L. kindti are themselves endangered by the impact of planktivorous fish (i.e. Pelecus cultratus, Alburnus alburnus), which show a preference for Leptodora larger than 6 mm. Frequently, elimination by fish corresponds with high death rates of Leptodora. During the periods when adult Leptodora occurred in numbers >50 ind. m^–3, 55% of the variance connected with its death rate can be attributed to fish predation. The success of this population of L. kindti is discussed within the framework of predator-prey interactions.     

Population dynamics of alien gammarid species in the River Odra estuary

During the period of 1988–2000, three alien gammarid species, i.e. Gammarus tigrinus Sexton, 1939, Pontogammarus robustoides G. O. Sars, 1894, and Dikerogammarus haemobaphes (Eichwald, 1841) were recorded in the Odra estuary. This study, the first record of G. tigrinus and P. robustoides in Poland, focuses on the distribution, abundance, and biomass as well as on population structure of the three new species found in the coastal zone of the estuary. G. tigrinus and P. robustoides were first sampled in the Szczecin Lagoon (mid-part of the estuary) in 1988. The densities of both species were high from the time they were first recorded and exceeded 10 000 ind. m^–2, while the biomass was 25 and 140 g m^–2, respectively. G.tigrinus occurred at higher densities in northern and eastern parts of the Lagoon, while P. robustoides was particularly abundant in the south-eastern part, most heavily affected by River Odra discharge. In 1999, the third gammarid, D. haemobaphes, was recorded in the southern part of the estuary. Both in 1999 and 2000, the species was found in qualitative samples (dredge collections of Dreissena polymorpha) taken from the western branch of the river. As estimated from quantitative samples, densities and biomass in the eastern branch were rather low and did not exceed 150 ind. m^–2 and 2.7 g m^–2, respectively. The Szczecin Lagoon population of G. tigrinus produces at least two generations within a year: a summer one and an overwintering one. The latter is dominated by older and larger specimens. The species may reproduce in the Lagoon from April until November.     

The keystone role of leaf-removing crabs in mangrove forests of North Brazil

Principle factors which influence mangroveleaf litter turnover, in particular therole of leaf-removing crabs, were evaluatedin a riverine mangrove site nearBragança (Pará, North Brazil). Ourspecial interest was focussed on the roleof the leaf-removing crab Ucidescordatus. Leaf litter fluxes between themangrove forest and the adjacent estuarywere investigated by estimating the biomassand fate of leaf litter material and propagules. Vegetation is dominated by Rhizophora mangle, with Avicenniagerminans trees, both up to 25 m high,found intermittently. During 1997, Rhizophora trees produced around 1.40 gDW m^-2 d^-1 of leave fall and0.75 g DW m^-2 d^-1 of propagules.Leaf decomposition rates on the ground wereabout 0.06 g DW m^-2 d^-1,irrespective of species, habitat or siteexposure. This amount accounts for <3%of total leaf fall. Average leaf litterbiomass present on the ground was 0.01 gDW m^-2 d^-1. When the mangroveforest was flooded (on average 10 days permonth) the quantity of leaf litterand propagules washed out with the springtide was 10 and 17 times greater thanduring neap tide. Nevertheless, tidalexport and decomposition together made upless than 39 percent of annual leaf litterfall. The bulk of the remaining amount isapparently removed by Ucides. Eachcrab consumed about 1.30 g DW of leaflitter material and propagules per day.Since the average density of these crabswas 1.38 crabs m^-2, it is proposedthat Ucides is a keystone species inBragantinian mangroves.     

河北唐山曹妃甸-乐亭海域自然牡蛎礁分布及生态意义

牡蛎礁是生态系统服务价值最高的海洋生境之一,目前我国自然牡蛎礁分布和生态现状的基础信息仍然较缺乏。于2019年3月对河北唐山曹妃甸-乐亭海域自然牡蛎礁的空间分布、生态环境、牡蛎生物学和礁体动物群落开展了调查,并评估了该牡蛎礁的生态系统服务价值。该海域自然牡蛎礁分布于溯河(SR)、溯河口海域(SRE)和捞鱼尖海域(LYJ),总面积约15 km~2,是目前我国面积最大的自然牡蛎礁。基于96个牡蛎样品的16S rDNA检测,共识别出92个长牡蛎Crassostrea gigas、3个侏儒牡蛎Nanostrea fluctigera和1个巨蛎属未知种Crassostrea sp.。自然牡蛎礁中牡蛎平均密度介于104—3912个/m~2之间,不同礁区间牡蛎平均密度的大小排序为：SRE>SR>LYJ (P<0.05),平均生物量的大小排序为：SR>SRE>LYJ (P<0.05),平均壳高的大小排序为：SR>SRE=LYJ (P<0.05)。在该牡蛎礁内记录到49种礁体动物,其中软体动物16种、节肢动物16种、环节动物8种、棘皮动物5种、腔肠动物2种...     

The nematode fauna of a temperate Australian mangrove mudflat; its population density,diversity and distribution

The nematode fauna of an estuarine mangrove Avicennia marina mudflat in Southeastern Australia has been intensively studied. About 85% of the nematodes occur in the top cm of soft mud, but 5–7 species inhabit the deeper anoxic mud down to 10 cm, both at low and high tide. One square metre was intensively sampled from four zones with different nematode faunas. At the low tide zone 58% of the nematodes were epistrate feeders, including many diatom-feeders, but in the mangrove zone selective microbial feeders made up over 60% of the population, while between high water neap and high water spring, above the mangrove zone, omnivore/predators and plant root feeding nematodes increased in relative importance. Random replicate cores reliably sampled species occurrence, but gave a high variance in density estimates. Replicate aliquots from homogenised mud gave lower density variance. Nematode densities (maximum 5 × 10⁶ m^-2) were not as high as have been reported from non-mangrove estuaries in other countries, but were within the range found in mangroves elsewhere in Australia. Margalef Species Richness values ranged from 1.7 to 3.89, which is similar to values found in other mangroves mudflats in Australia. Nematode biomass ranged from 888 mg dry weight m² (383 mg C m^-2) at the low tide zone to 19 mg dry weight m^-2 (8 mg C m^-2) at the upper tide level.     

On the distribution patterns and population dynamics of sublittoral and profundal oligochaeta fauna from Lake Banyoles (Catalonia,NE Spain)

Oligochaeta assemblages from Lake Banyoles were composed of one species of Naididae and eight species of Tubificidae, Potamothrix heuscheri (8–1350 ind. m^–2) being the most abundant and widely distributed species, followed by Limnodrilus hoffmeisteri (25–858 ind. m^–2) and Psammoryctides barbatus (12–792 ind. m^–2). The remaining species were Potamothrix hammoniensis, Potamothrix bavaricus, Limnodrilus claparedeanus, Branchiura sowerbyi, Aulodrilus pigueti and Dero digitata, all of which occurred at lower densities and with restricted distributions.Regardless of sampling depth, maximum densities of oligochaetes were found in winter (up to 5,142 ind. m^–2 in December) and secondarily in June. Immature Tubificidae with hair setae and mature P. heuscheri were present and dominant throughout the year. Cestode parasites were recorded infesting L. hoffmeisteri and P. heuscheri populations.Oligochaeta densities increased with depth, but low oxygen concentrations (less than 1 mg l^–1) during a long period (4 months) in some basins of the lake acted as a key factor in reducing the density of worms and the species richness to one species, Potamothrix heuscheri.     

Population and reproductive biology of the fiddler crab Uca thayeri Rathbun, 1900 (Crustacea: Ocypodidae) in a tropical mangrove from Northeast Brazil

Population and reproductive biology of Uca thayeri Rathbun, 1900 were studied for the first time in a tropical mangrove. Absolute density, sex ratio, population structure, handedness, breeding season and fecundity were investigated. Seven transects were delimited in a mangrove area of the Pacoti River, Northeast of Brazil (3° 43′ 02″ S/38° 32′ 35″ W). On each transect, ten 0.25 m² squares were sampled on a monthly basis during low tide periods from September 2003 to August 2004. A total of 483 crabs were obtained, of which 250 were males, 219 non-ovigerous females, and 14 ovigerous females. The U. thayeri population presented bi-modal size frequency distribution, with males and non-ovigerous females not differing significantly size-wise. Ovigerous females were larger than males and non-ovigerous females. The overall sex ratio (1:1.07) did not differ significantly from the expected 1:1 proportion. The major cheliped was the right one in 50% of the males. The observed density was of 8.5 individuals/m², with the specimens being found mostly in shaded areas. Ovigerous females were found in 5 months of the year, coinciding with the rainy season, suggesting that the population of U. thayeri presents seasonal reproductive events. Juvenile crabs were more abundant during the dry period, while larger crabs were found mainly during the rainy period. The fecundity of the studied population was much smaller than that of subtropical populations of this species. The regression analysis shows that the number of eggs increases linearly with the increase of carapace width.     

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.     

Size structure and distribution of Ovassiminea brevicula (Gastropoda) in a Thai mangrove swamp

Ovassiminea brevicula (Pfeiffer) (Assimineidae: Gastropoda) was oneof the most abundant and representative benthic invertebrates in the SamutSongkhram mangrove swamp, Thailand. It lived mainly in the mangrove forest with high average densities ranging from 44 to 340 snails·m^-2and abundant in the sites where much litter, dead branches and seedlingswere present. Average shell length in the mature forest ranged from 4.73to 5.74 mm (range: 2.26–8.30 mm) and size structures showeddifferent patterns among the stations. In the seaward mudflat, O. breviculaappeared immediately after the saplings of Avicennia alba Blume1826 were planted. Thereafter, its densities increased with the growth of A. alba trees, probably due to provision of favourable microhabitats underthe canopies. In the mudflat with only small saplings and outside the canopyof the young forest 2 years after planting, mean shell lengths were 3.45 and3.19 mm respectively. Under the canopy of the young forest, however,mean shell length was 4.34 mm with a few larger snails. Three cohortswere separated for snail populations in the mature forest and larval recruitmentseemed to occur from February to May.     

The effect of increased nutrient availability on vegetation dynamics in wet heathlands

A three year fertilization experiment was conducted in which nitrogen (N series: 20 g N m^–2 yr^–1), phosphorus (P series: 4 g P m^–2 yr^–1) and potassium (K series: 20 g K m^–2 yr^–1) were added to a mixed vegetation of Erica tetralix and Molinia caerulea. At the end of each growing season the percentage cover of each species was determined. At the end of the experiment percentage cover of each species was found to be positively correlated with the harvested biomass. In the unfertilized control series the cover of Erica and Molinia did not change significantly during the experiment. In all fertilized series however, especially in the P series, cover of Erica decreased significantly. The cover of Molinia increased significantly in the P series only.In the fertilized series the biomass of Erica and total biomass per plot did not change significantly compared with the control series. In the P series the biomass of Molinia increased significantly.It is suggested that with increasing phosphorus or nitrogen availability Molinia outcompetes Erica because the former invests more biomass in leaves which in turn permits more carbon to be allocated to the root system, which thereupon leads to a higher nutrient uptake.     

Crown light environments of saplings of two species of rain forest emergent trees

Summary The crown light environments of saplings of two Costa Rican rain forest tree species were simultaneously compared. The species, Dipteryx panamensis (Pitt.) Record & Mell., a relatively shade-intolerant species, and Lecythis ampla Miers, a shade-tolerant species, have contrasting growth and branching patterns. Quantum sensors were placed throughout the crowns of saplings up to 2.5 m tall and quantum fluxes were recorded with microloggers for seven-day periods. The shade-intolerant species had total quantum flux densities 35% larger than those of the shade-tolerant species, but totals for both species were less than 2% of full sun. More than 90% of the quantum flux densities measured within the crowns of both species were less than 25 mol m^-2s^-1. Lateral light was an important component of daily quantum flux totals; for saplings of both species, the half-hour with the maximum average irradiance for the day frequently occurred in mid-morning or midafternoon. Despite dissimilar crown and leaf display, there was no difference in the overall variability of irradiance within the crowns of the two species. However, quantum fluxes received within the crowns differed substantially in both species. Within-crown locations differed significantly from day to day because of variation in weather conditions. Daily total quantum flux densities and totals expressed as a percent of full sun were significantly correlated with height growth over the previous 12 months.     

模拟N沉降对太岳山油松人工林和天然林草本群落的影响

由于人类活动氮沉降呈逐年增加的趋势,进而增加了陆地生态系统氮的输入,从而影响陆地生态系统多样性、物种组成和功能。为揭示氮沉降增加对油松林草本群落的影响,于2009年7月在太岳山油松人工林和天然林,设计4个施氮水平:对照(CK,0 kg N hm-2a-1),低氮(LN,50 kg N hm-2a-1),中氮(MN,100 kg N hm-2a-1)和高氮(HN,150 kg N hm-2a-1),研究草本群落的生物多样性、生物量以及草本元素含量对模拟N沉降的响应。研究结果表明:模拟N沉降未能显著影响人工林草本群落的生物多样性(P0.05),而中氮、高氮显著降低了天然林草本群落的生物多样性(P0.05);从Jaccard指数和Sorensen指数分析得出人工林不同氮水平之间草本群落差异性较小,而天然林不同氮水平之间草本群落差异性较大。模拟N沉降没有显著改变人工林草本群落生物量(P0.05),而高氮明显促进天然林草本群落生物量的增加(P0.05)。与对照相比,模拟N沉降提高了人工林和天然林羊胡子苔草叶根中的全N含量(P0.05),而降低了全Mg的含量(P0.05),并且根部元素含量变化与土壤养分含量变化较为一致。施氮提高了N/K、N/Ca、N/Mg(P0.05)的比值。说明油松林下草本群落对氮沉降的响应因林分土壤N饱和程度以及林地利用历史的不同而产生差异,其中天然林响应最为敏感。     

Spatial variation in density of stream benthic fishes in northern Hokkaido, Japan: does riparian vegetation affect fish density via food availability?

The densities of two benthic fishes, the Siberian stone loach (Noemacheilus barbatulus) and the wrinklehead sculpin (Cottus nozawae), and the biomass of their food resources (i.e., periphyton and benthic invertebrates) were compared between forest and grassland streams in northern Hokkaido, Japan, to examine whether riparian deforestation had positive effects on the benthic fishes via enhancement of food availability. The comparisons indicated that riparian vegetation had little influence on periphyton, invertebrates, or fishes. Regression analysis indicated that spatial variations in loach and sculpin densities were explained more by substrate heterogeneity, competitor abundance, or both, rather than by food abundance. However, when the two species were combined as benthic insectivores, a strong correlation was found between total benthic fish density and invertebrate biomass. Our results suggest that, although total benthic fish abundance was food limited, riparian vegetation had no positive effects via food availability on the benthic fishes in our streams.     

Macrobenthos of a tidal impoundment at the Mai Po Marshes Nature Reserve,Hong Kong

The composition and spatial distribution patterns of the macrobenthic faunal assemblages of an 8-ha tidal impoundment operated as a traditional shrimp pond at the Mai Po Marshes Nature Reserve, Hong Kong, were studied in relation to temporal changes in local environmental conditions. Species richness, abundance and biomass of macrobenthos across 5 different sub-habitats (seaward, middle, and landward parts of open water unvegetated areas, and Phragmites- and Kandelia-dominated, vegetated areas) within the pond were examined bimonthly between January 1997 and January 1998. Grab samples were collected randomly within the sub-habitats. Key physical environmental parameters of the sampling sites were also measured. A total of 46 species of macrobenthos was recorded: 11 polychaetes, 11 molluscs, 13 crustaceans and 11 insects. Mean species density in the five sub-habitats ranged from 0 to 3907 indm^–2, with mean biomass ranging from 0 to 96.9 gm^–2. The macrobenthos showed spatial and temporal differences among the sub-habitats and across sampling times. Species abundances of Polychaeta, Mollusca and Crustacea were significantly higher in the three open water areas than in the two vegetated (Phragmites- and Kandelia-dominated) areas, with an inverse pattern for Insecta. There were no clear temporal patterns although abundance and biomass generally increased in the cooler months. Results of a canonical correspondence analysis suggest that macrobenthic species richness, abundance and biomass in the open areas were positively correlated with salinity, while water depth, dissolved oxygen and sediment organic matter content had little relationship with the macrobenthic assemblage parameters. Ordination by multi-dimensional scaling suggests that different habitats supported distinct macrobenthic assemblages. The macrobenthic assemblage in the tidal pond was less species rich but denser than those in the neighboring tidal mangrove and mudflat, suggesting that conversion of these areas into extensively managed tidal aquaculture ponds results in reduced species richness in tropical mangrove habitats.     

Distribution patterns and predation risk of the coexisting cladocerans Bythotrephes longimanus and Leptodora kindtii in a large lake – Lake Constance

The distributions of the coexisting, planktonic, predatory cladocerans Bythotrephes longimanus and Leptodora kindtii were studied at four different stations (Langenargen-Arbon, Fischbach-Uttwil, Bregenzer Bucht and Zeller See) of a great lake, Lake Constance. The stations Langenargen-Arbon and Fischbach-Uttwil are deep (>200 m) with a high density of the coregonid fish Coregonus lavaretus, the stations Bregenzer Bucht and Zeller See are shallow (<60 m) with lower densities of coregonid fish. B. longimanus was present in the pelagic zone from mid May to November at all stations. L. kindtii generally appeared slightly later in the year than B. longimanus. Peak abundances of B. longimanus with more than 5000 ind. m^–2 (Langenargen-Arbon) appeared in late spring. During summer, when predation pressure by fish is high, abundance of B. longimanus decreased gradually. In contrast, L. kindtii displayed maximum abundances with more than 18 000 ind. m^–2 (Zeller See) in summer. During the summer months, B. longimanus lived in greater depths than L. kindtii. Differences of vertical distribution between both species were most pronounced at the deep stations (Langenargen-Arbon, Fischbach-Uttwil). Analysis of stomachs of the planktivorous fish Coregonus lavaretus showed that B. longimanus was preferred by C. lavaretus over all other prey; Ivlev's selectivity index was 0.97–0.99. Due to this high positive selection for B. longimanus by coregonids, it is surprising that the cladoceran could maintain its existence since the first recordings in 1877. Spatial refuge or indigestible resting eggs may be the underlying mechanism for this phenomenon.     

Effects of dwarf bamboo (Fargesia denudata) density on biomass, carbon and nutrient distribution pattern

Dense dwarf bamboo population is a structurally and functionally important component in many subalpine forest systems. To characterize the effects of stem density on biomass, carbon and majority nutrients (N, P, K, Ca and Mg) distribution pattern, three dwarf bamboo (Fargesia denudata) populations with different stem densities (Dh with 220 ± 11 stems m^?2, Dm with 140 ± 7 stems m^?2, and Dl with 80 ± 4 stems m^?2, respectively) were selected beneath a bamboo-fir (Picea purpurea) forest in Wanglang National Nature Reserve, Sichuan, China. Leaf, branch, rhizome, root and total biomass of dwarf bamboo increased with the increase of stem density, while carbon and nutrient concentrations in bamboo components decreased. Percentages of below-ground biomass and element stocks to total biomass and stocks decreased with the increase of stem density, whereas above-ground biomass and element stocks exhibited the opposite tendency. Moreover, more above-ground biomass and elements were allocated to higher part in the higher density population. In addition, percentages of culm biomass, above-ground biomass and element stocks below 100 cm culm height (H₁₀₀) increased with the increase of stem density, while percentages of branch and leaf biomass below H₁₀₀ decreased. Pearson’s correlation analyses revealed that root biomass, above-ground biomass, below-ground biomass and total biomass significantly correlated to leaf biomass in H_100?200 and total leaf biomass within high density population, while they significantly correlated to leaf biomass in H_50?150 within low density population. The results suggested that dwarf bamboo performed an efficient adaptive strategy to favor limited resources by altering biomass, carbon and nutrients distribution pattern in the dense population.