Responses of billabong rotifer communities to inundation

Daily plankton collections were taken from a billabong of the River Murray for two weeks prior to inundation in March 1990, and continued for ten days after flooding. Quantitative responses of the plankton community and the component species were analysed against measured environmental variables and between species. Rotifers and copepod nauplii were the predominant net plankton (> 53 µm). Significant negative or positive responses to inundation were detected for most common taxa of 63 rotifer species recorded. A four-fold dilution from intrusion of river water masked rapid population increases. Opportunistic responses to inundation appear to be a survival strategy in the highly unpredictable billabong environment.     

Distribution of rotifers in North Island,New Zealand,and their potential use as bioindicators of lake trophic state

The distribution and ecology of planktonic rotifers was investigated in 33 lakes in the North Island, New Zealand, between 1997 and 1999. A total of 79 species of monogonont rotifer were identified, with an average of 21 species per lake, a diversity which is high in comparison with many previous New Zealand studies. Most species recorded were cosmopolitan taxa, and were widespread in their distribution over the North Island. Multivariate analyses (Multi-Dimensional Scaling and Canonical Correspondence Analysis) did not distinguish distinct lake groupings based on rotifer communities, but rather gradients in assemblages, which were most highly associated with lake trophic state. Based on these responses, the development of potential rotifer bioindicator schemes for lake trophic state is described and discussed.     

Detrital feeding in natural zooplankton communities: Discrimination between live and dead algal foods

Freshwater zooplankton species differ in their consumption of live and dead algal cells when tested in situ. Using isotopically-labeled living and heat-killed Chlamydomonas reinhardti as models for phytoplankton and detrital seston, respectively, we tested differential feeding on these foods by 3 rotifers and 2 microcrustaceans. Keratella cochlearis selectively feeds on detrital materials while 2 sympatric rotifer species, Conochilus dossuarius and Kellicottia bostoniensis show no ability to discriminate between the living and dead foods. Both the copepod Diaptomus spatulocrenatus and a cladoceran, Bosmina sp., differentially consume living cells.     

The role of seed traits in determining the phylogenetic structure of temperate plant communities

Background and Aims

Phylogenetic clustering of species within plant communities can be expected to result from environmental filtering acting on an evolutionary-conserved plant trait. One such a candidate trait is the embryo to seed-size ratio (E:S). A high E:S may allow faster germination immediately after imbibition, and is therefore assumed to be advantageous in dry habitats. In this study the hypothesis was tested that habitat filtering driven by soil moisture conditions and acting on seed germination and seedling establishment is an important ecological mechanism in structuring temperate plant communities.

Methods

Vegetation samplings were performed in three habitats located within 200 km of each other in western Europe: Ellenberg indicator values showed that the habitats selected differed substantially in terms of soil moisture and light availability. E.S ratio and seed mass data for all genera were obtained from literature. Data were analysed using recently developed phylogenetic methods.

Key Results

Genera with a similar E:S tend to co-occur, as low and high E:S genera dominate in moist and dry habitats, respectively. A phylogenetically clustered pattern of community structure was evident, and dispersion of E:S was positively related to phylogenetic dispersion.

Conclusions

The phenotypically and phylogenetically clustered pattern indicates that E:S-mediated habitat filtering is an important assembly process structuring the plant community of the temperate climate habitats studied.     

Distribution of rotifer assemblages in North Island, New Zealand, lakes: relationships to environmental and historical factors

1. The geographical distribution of planktonic rotifer species was investigated in 31 lakes in the North Island of New Zealand.
2. A total of 78 species was recorded. Species richness, previously thought to be low in New Zealand, was found to be comparable with that of northern temperate lakes with an average of 21.1 species found per lake. The large, deep oligotrophic Lake Taupo had the lowest richness, and the artificial reservoirs the highest.
3. The distribution of species, investigated using multivariate techniques [Cluster analysis, canonical correspondence analysis (CCA)], was most strongly associated with trophic state gradients. For example, Conochilus unicornis, C. dossuarius and Ascomorpha ovalis were associated with more oligotrophic conditions, and Brachionus budapestinensis, B. calyciflorus and Keratella tropica with more eutrophic conditions. Inorganic turbidity was also of importance in determining rotifer distributions in some shallower lakes.
4. Some species, for example K. australis and C. exiguus , appear to be limited in distribution by poor dispersal abilities.     

Factors determining the spatial structure of benthic communities of a shallow bay

The species composition and the spatial structure of benthos were studied along a transect running at a depth of 1–18 m on the soft bottom substrates of Zapadnaya Bight of Furugelm Island (Peter the Great Bay, Sea of Japan). This area has been proposed as a major site for long-term monitoring of the Far Eastern State Marine Reserve. Hydrobiological samples of different sizes (16 cm², 0.025, and 1 m²) were taken by a diving method at 5-m intervals from the shore. Benthic communities were distinguished using principal component analysis (PCA), Sørensen's similarity indices, and similarity dendrograms. The grain size composition of bottom sediment was determined. Three benthic communities at depths of 1–3, 4–8, and 14–18 m and two transitional zones were distinguished in Zapadnaya Bight. The benthic communities are characterized by a relative constancy of species composition within their boundaries, and by stable ratios of quantitative characteristics of other species from different ecological groups. The transitional zones, which are comparable in extension with the communities themselves, are characterized by changes in species composition and the presence of characteristic species; here, the substrate type changes and sediment grain sorting is decreased.     

大气CO2浓度升高对稻田土壤线虫群落的影响

本试验利用无锡稻 麦轮作FACE系统研究平台 ,开展了稻田土壤线虫群落对大气CO2 浓度升高响应的研究。实验中共观测到线虫 2 7科 4 0属 ,其中短腔属 (Brevibucca)、茎属(Ditylenchus)和垫刃属 (Tylenchus)为优势属。拔节期稻田土壤线虫总数、食细菌线虫和捕食 /杂食线虫对大气CO2 浓度升高表现出正响应。食真菌线虫在拔节期和抽穗期对CO2 浓度升高表现出负响应 ,成熟期捕食 /杂食线虫对CO2 浓度升高表现出负响应。在FACE条件下 ,植物寄生线虫的潜根属 (Hirschmanniella)和散香属 (Boleodorus)线虫数量显著增加 ,对CO2 浓度升高敏感     

Rotifer community structure in the south basin of Lake Biwa

Seasonal changes in abundance and species composition of rotifers were surveyed at five locations under different physical and chemical conditions in the south basin of Lake Biwa during July 1987–June 1988. Total density of rotifers showed similar seasonal fluctuation with three peaks, although the maximum density showed north (low)-south (high) gradient. Polyarthra spp. (P. vulgaris and P. dolichoptera with low density) dominated except during July–October 1987 and April–May 1988. In the former period the species of Brachionus, Trichocerca, Filinia and Hexarthra, and in the latter, those of Synchaeta, Keratella and Kellicottia had somewhat different proportions in the communities of north and south stations, respectively. The difference in composition during July–October suggests a difference of trophic state between the northern and southern areas in the south basin of Lake Biwa. However, the dominance of Polyarthra and the difference in the composition during April–May 1988 could not be explained by such a difference in trophic state. No critical difference was observed in the community structure of the eastern area of the south basin, where the seasonal fluctuations in nutrient levels and phytoplankton community structure were different from other areas in the south basin. The present results, therefore, suggest that physical and chemical conditions were not effective in controlling the rotifer community structure in the south basin of Lake Biwa.     

Lake trophic state and the limnological effects of omnivorous fish

Ecologists have hypothesized that planktivorous fish have greater effects on the plankton and water quality of oligotrophic lakes than eutrophic lakes. We tested this hypothesis in a tank-mesocosm experiment of factorial design in which five biomass levels of filter-feeding omnivorous gizzard shad (Dorosoma cepedianum) were cross-classified with two levels of lake trophic state achieved by filling tank-mesocosms with water and plankton transported by truck from two lakes with different trophic states. The presence of gizzard shad significantly increased total phosphorus, primary productivity, chlorophyll, and particulate phosphorus (PP) 2–20 and 20–200 μm and significantly decreased Secchi depth, cladocerans, copepods and PP > 200 μm. The effects of gizzard shad on chlorophyll, Secchi depth, cladocerans, copepods and PP 2–20 and > 200 μm were dependent on lake trophic state and most intense in the eutrophic lake system. This experiment suggests that filter-feeding omnivorous fish interact synergistically with trophic state so that the limnological effects of omnivorous fish become more intense with increased eutrophication.     

Rotifer occurrence in relation to age,depth and trophic state of quarry lakes

An effect of age of quarry lakes on rotifer abundance and species composition has been evaluated. Rotifers occurred in all lakes under study. They were even found in the youngest (2 years of age) one, Rogonica 4, but both rotifer density and species richness were low there. Rotifer communities of much higher density and species diversity were noted in lakes only 4–6 years older. Lakes of over 30 years of age were strongly differentiated in rotifer numbers and species structure. In general, age of quarry lakes has an impact on rotifer communities only at the very beginning of the process of colonization. Several years later other factors become more important, e.g., depth or trophic state of the lakes.     

Development of an Index of Trophic Completeness for benthic macroinvertebrate communities in flowing waters

The analysis of the trophic structure of benthic macroinvertebrate communities can be used in biological assessments of the condition of river ecosystems. Using the trophic, or functional approach, the Index of Trophic Completeness (ITC) was developed. The goal was to overcome the problems and drawbacks of using conventional diversity or biotic indices in biological assessments of rivers, such as limitation to distinct geographical regions or focus on species richness without regard for ecosystem functioning. Following an extensive review of the literature on the trophic characteristics of benthic macroinvertebrates, a large number of species (±300) were characterized according to a number of trophic criteria: plant:animal ratio in the diet, feeding mechanism, food size, food acquisition behaviour, and energy and substance transfers. On the basis of their trophic characteristics, the species could be divided into 12 trophic groups. After examination of data from geographically diverse rivers, it was concluded that any undisturbed riverine benthic macroinvertebrate community should be represented by members of each of these 12 trophic groups, with each group fulfilling a function in the benthic community. Being a community which plays a central role in the functioning of the aquatic ecosystem, the benthic invertebrates are expected to respond to disturbances to the hydrobiocoenose. The outcome of an ITC assessment is clearly presentable in the form of a pie graph with 12 wedges, each representing one of the 12 defined trophic groups. Functionally complete communities are represented by 12 wedges; a blank wedge indicates that a trophic group is not represented. This paper describes the preliminary developments in the ITC method, its potential as a biological assessment method in rivers in different geographical zones, and presents examples of trial mappings of Russian and European rivers. The application of the ITC to these rivers demonstrated the absence of ITC trophic groups at sites under the influence of anthropogenic activity.     

Reproductive success of the rotifer Brachionus calyciflorus feeding on ciliates and flagellates of different trophic modes

SUMMARY 1. The nutritional value of the bacterivorous ciliate Tetrahymena pyriformis and the algivorous ciliate Coleps sp., as well as the heterotrophic flagellate Chilomonas paramecium and the autotrophic flagellate Cryptomonas ovata , were investigated in population growth experiments using the rotifer B. calyciflorus . The two ciliates, both flagellates, which were of similar size, shape and mobility, were each offered as a sole diet and as a supplement to the alga Monoraphidium minutum , known to support reproduction of B. calyciflorus .
2. To further test nutritional differences between the prey organisms, prey selection experiments were conducted in which B. calyciflorus was able to select between the bacterivorous and algivorous ciliate, and between the heterotrophic and autotrophic flagellate.
3. The results demonstrated that both ciliates and the heterotrophic flagellate were not sufficient to support reproduction of B. calyciflorus when offered as a sole diet. They were, however, a good supplement to algal prey (except for the bacterivorous ciliate T. pyriformis ). In the prey selection experiments, B. calyciflorus positively selected for the algivorous Coleps sp. and the autotrophic C. ovata.
4. Overall, ciliates and heterotrophic flagellates may enhance survival of B. calyciflorus , but reproduction of the rotifer is likely to rely on algal prey. Both higher population growth of B. calyciflorus when fed the algivorous Coleps and the autotrophic Cryptomonas, along with their positive selection, give evidence for prey specific differences in nutrition, with algivorous or autotrophic prey species tending to be of higher nutritional value.     

Assessment of factors influencing the composition,body size and turnover rate of zooplankton in Parakrama Samudra,an irrigation reservoir in Sri Lanka

This paper considers which of the following factors influenced the taxonomic composition, body size, fecundity and birth rates of the zooplankton inhabiting a tropical irrigation reservoir: (a) wash-out and/or dilution of the population which arose from the water regime to which the reservoir was subjected by management; (b) the size-selective or species-selective predation; (c) the effect of food limitation upon the body size, egg size, post-embryonic duration and fecundities of the planktonic species and (d) the metabolic consequences of high tropical temperatures. Many of these impinge upon the characteristics of tropical zooplankton and it is appropriate that this synthesis of published results on the zooplankton of Parakrama Samudra, Sri Lanka, was prepared for the Symposium on Tropical Zooplankton held at Sao Carlos, Brazil, in December 1982.Daily losses of planktonic rotifers due to wash-out or by dilution were low and not significant compared with their capacity for recruitment but this may be a serious source of loss for the planktonic crustaceans which were virtually absent from this reservoir. Daily death rates (estimated by subtraction) were much higher and were mainly due to predation by a planktonic fish, Ehirava fluviatilis, and by Asplanchnella brightwelli. The main loss occurred during the day and on larger individuals of the brachionid species, Trichocerca spp. and Filinia longiseta, thus resulting in a small-sized rotifer community. This appeared to be due mainly to predation by the fish which was responsible also for the further reduction of rotifer body size in 1980 compared with 1979. Small rotifer body size was not caused by conditions of food deficiency because fecundity and birth rates were relatively high though not optimal. High tropical temperatures aggravate the cost of cumulative respiration resulting from food-limited prolongation of the juvenile phase and will raise the food threshold levels for growth and for reproduction above those adequate for temperate situations.     

Zoobenthos of the Cheshskaya Bay (southeastern Barents Sea): spatial distribution and community structure in relation to environmental factors

Structural and functional characteristics of zoobenthos of the Cheshskaya Bay (SE Barents Sea) were studied at 21 stations in June/July 1995. Strong prevailing cyclonic and tidal currents result in relatively uniform temperature and salinity in the area. Sediments consist mainly of sand and pebbles, while the flux of suspended matter from rivers locally increases the share of finer fractions. Analysis of species composition (419 taxa), abundance (up to 4,200 ind m⁻² and up to 29,000 ind m⁻² with juveniles) and biomass (up to >6,000 g wet wt m⁻²) indicates high species richness in most parts of the bay, especially in the northeast. Analysis of community structure using production characteristics of species revealed a general predominance of suspension feeders partitioned into seven communities. The dominant species of these communities were Mytilus edulis and Balanus crenatus (Type 1), B. crenatus (Type 2), Modiolus modiolus and Verruca stroemia (Type 3), Flustra foliacea and V. stroemia (Type 4), Hydrallmania falcata (Type 5), V. stroemia and Chirona hameri (Type 6), and Ophelia limacina (Type 7). The structure of the communities is mainly regulated by sediment type, water depth and, to some extent, by riverine input. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Differences in predation among morphotypes of the rotifer Asplanchna silvestrii

1. Interactions were observed between three morphotypes of the predatory rotifer Asplanchna silvestrii and six different prey (Brachionus plicatilis, B. rotundiformis, B. pterodinoides, B. satanicus, Hexarthra jenkinae and copepod nauplii) to understand the differences in feeding abilities among morphotypes that may have led to the evolution of this predator polymorphism. The outcome of predation events was affected significantly, both by predator morphotype and prey type. Predator morphotypes also interacted differently with different prey types. 2. The two smaller morphotypes, the saccate and the cruciform, responded similarly to prey overall, except that the smallest morphotype (saccate) was unable to ingest the most mobile prey (nauplii) and less able to ingest relatively large prey (B. plicatilis). The largest morphotype, the campanulate, had the highest encounter rate with prey, but the lowest probability of attack after encounter, so that it consumed far fewer prey per feeding bout than did the smaller morphotypes. This may have been because campanulates prefer larger prey than used in this study. 3. Highly mobile prey (H. jenkinae and copepod nauplii) were much less susceptible to predation than the less mobile Brachionus species. While evasiveness reduced attacks by saccates and cruciforms, campanulates did not have a significantly lower attack rate on H. jenkinae and copepod nauplii than on less evasive prey. Large body size moderately defended B. plicatilis against ingestion by saccates only. The short-spined B. satanicus was the only prey that was rejected after capture, resulting in lower ingestion probabilities for B. satanicus than other brachionid prey.     

Seasonal dynamics of rotifer and crustacean zooplankton populations in a eutrophic,monomictic lake with a note on rotifer sampling techniques

The abundances, biomass, and seasonal succession of rotifer and crustacean zooplankton were examined in a man-made, eutrophic lake, Lake Oglethorpe, over a 13 month period. There was an inverse correlation between the abundance of rotifers and crustaceans. Rotifers were most abundant and dominated (>69%) the rotifer-crustacean biomass during summer months (June–September) while crustacean zooplankton dominated during the remainder of the year (>89%). Peak biomasses of crustaceans were observed in the fall (151 µg dry wt l^–1 in October) and spring (89.66 µg dry wt l^–1 in May). Mean annual biomass levels were 46.99 µg dry wt l^–1 for crustaceans and 19.26 µg dry wt l^–1 for rotifers. Trichocerca rousseleti, Polyarthra sp., Keratella cochlearis and Kellicottia bostoniensis were the most abundant rotifers in the lake. Diaptomus siciloides and Daphnia parvula were the most abundant crustaceans. Lake Oglethorpe is distinct in having an unusually high abundance of rotifers (range 217–7980 l^–1). These high densities can be attributed not only to the eutrophic conditions of the lake but also to the detailed sampling methods employed in this study.The research was supported by National Science Foundation grants DEB 7725354 and DEB 8005582 to Dr. K. G. Porter. It is lake Oglethorpe Limnological Association Contribution No. 25 and Contribution No. 371 of the Harbor Branch Foundation, Inc.     

幕阜山森林群落结构与物种多样性研究

幕阜山地处中亚热带-北亚热带过渡地带,物种资源丰富.通过对其典型样地的调查,分别采用Shannon-Wiener指数、Simpson指数和Pielou均匀度指数作为测度指标,研究了幕阜山地区森林群落结构及其物种多样性特征.结果表明,该地区主要有21个森林群落类型.其中常绿阔叶林中,物种丰富度指数与多样性指数在群落梯度上的总体趋势均为灌木层相对高于乔木层,乔木层相对高于草本层;在落叶阔叶林中,其丰富度指数的趋势为灌木层＞草本层和乔木层,而在草本层与乔木层间是波动的,多样性指数的趋势为灌木层＞草本层＞乔木层;在针叶林中,物种丰富度、多样性指数表现的总趋势基本一致,即灌木层的丰富度相对较高,其次为草本层,乔木层的相对较小.在其他群落类型中,多样性指数、均匀度指数在乔木层、灌木层和草本层则表现出多样化的趋势;另外,从总体上看,各种指数在海拔梯度上并未表现出明显的规律性.     

The structure of phytoplankton assemblages in Sicilian reservoirs: some hyphoteses on the driving factors

Abstract

From the analysis of the results of several researches carried out into Sicilian reservoirs to investigate their phytoplankton assemblages, it was highlighted that there is not any clear relationship between the trophic spectrum and the structure and composition of phytoplankton. Only a general increase of total biomass is detectable as the trophic state rises up. Anyway, such increase may cause several secondary modifications in the physical and chemical environment that may act as multidimensional segregating factors for phytoplankton organisms. In these secondary modifications, coupled with the peculiar morphology and hydrology of the water bodies, have to be sought the mechanisms governing the structure of phytoplankton assemblages.