Patterns in the distribution of Arctic freshwater zooplankton related to glaciation history

We analysed circumpolar samples from 68 lakes within the 10°C-July isotherm from Arctic Canada, Nunavut, Greenland, Svalbard, Eastern Siberia, the Beringia region, and Alaska. In total, we found 3 species of Anostraca, 17 of Diplostraca, 1 species of cyclopoid and 14 species of calanoid copepods. Our study identifies a wider distribution for some copepods—e.g. Eurytemora pacifica, Leptodiaptomus sicilis, Arctodiaptomus novosibiricus, Cyclops abyssorum—than previously known. Moreover, one anostracan species, Artemiopsis bungei, was recorded in North America for the first time; and one chydoriid, Chydorus gibbus, is a new species for Greenland. We observed that species richness of crustaceans is lower in lakes that were glaciated during the Quaternary period, compared to those not glaciated (e.g. Chukotski Peninsula, Siberia; Point Barrow, Alaska; and Disko Island, Greenland). This confirms the findings of classic studies: glaciation has strongly affected the biogeography of freshwater crustaceans in circumpolar areas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

披山岛海区浮游动物种类组成及数量分布特点

根据2007年披山岛海区春季和夏季2个季度浮游动物调查资料,分析和研究了浙江省玉环县披山岛海区浮游动物种类组成和数量分布特点.结果表明:浮游动物共有18种,属3门12属,其中桡足类的种类最多,占总种数的72.22%;主要优势种为中华哲水蚤(Calanus sinicus)、瘦拟哲水蚤(Paracalanus gracilis)、针刺拟哲水蚤(Paracalanus aculeatus)和红小毛猛水蚤(Microsetella rosea).浮游动物的平均丰度及生物量均为春季比夏季高,春季的平均丰度为6.55×103个/m3,夏季为6.13×103个/m3;春季的平均生物量为216.49 mg/m3,夏季为98.26 mg/m3.桡足类的生物量占浮游动物总量的75.97%～97.55%,是决定披山岛浮游动物数量分布和变动的主要成分.与历史资料和邻近海域相比较,披山岛海区生物量与其接近或大于东海各海域.春、夏两季生物多样性(H′)有显著性差异(P<0.05),春季具有较高的生物多样性,且远海的生物多样性大于近海.     

A review of systematics,distribution and ecology of tropical freshwater zooplankton

Studies on tropical freshwater zooplankton which commenced in the mid-19th century have been intensified during the past twenty years or so. The whole region, barring a few areas, has been investigated, including very recently tropical Australia. The widely scattered literature is briefly summarized with comments. Some general distributional patterns are emerging. There is a dearth of ecological studies especially on seasonality and production. Systematics lags behind the North Temperate zone in most tropical regions.     

The influence of freshwater discharge on the distribution of zooplankton in the southern Kara Sea

Zooplankton was collected on two cruises to the southern Kara Sea to study the effect of the freshwater outflow of the rivers Ob and Yenisej on plankton distribution. Calanoid copepods dominated the composition with more than 75% of all specimens collected in both years; Drepanopus bungei was the most abundant species. Species composition showed a wide spectrum from freshwater to marine species. The abundance and community composition of the zooplankton communities followed closely the hydrographic pattern along a gradient from the inner to the outer estuaries, as revealed by cluster analysis and Multi-Dimensional Scaling. There were also differences in species composition and abundance between the two rivers. The stable brackish surface layer created a large distribution area for riverine species, while in the underlying marine water masses, oceanic species penetrated far into the estuaries. In 1997 this area was considerably larger, probably due to a higher freshwater discharge. During the 1999 cruise, which took place 3 weeks earlier, salinities were generally higher. Both species composition and overall abundances were higher in 1999 than in 1997, due especially to the enormous increase of Limnocalanus macrurus and Pseudocalanus major.     

Measuring and modeling the motor system with machine learning

The utility of machine learning in understanding the motor system is promising a revolution in how to collect, measure, and analyze data. The field of movement science already elegantly incorporates theory and engineering principles to guide experimental work, and in this review we discuss the growing use of machine learning: from pose estimation, kinematic analyses, dimensionality reduction, and closed-loop feedback, to its use in understanding neural correlates and untangling sensorimotor systems. We also give our perspective on new avenues, where markerless motion capture combined with biomechanical modeling and neural networks could be a new platform for hypothesis-driven research.     

Vertical migration, hatching rates, and distribution of egg stages in freshwater zooplankton

In shallow, thermally stratifield lakes, the developing eggs carried by pelagic crustacean zooplankton are exposed to regularly alternating higher and lower temperatures during daily vertical migration. Rate summation techniques for determining the duration of egg developiment suggest that (1) the distribution of egg stages in the population will not change because of the alternating temperatures, and (2) the majority of young animals will not be hatched or released in the warmer, upper waters of the lake. This latter result is probably positively adaptive, but it may be brought about entirely mechanistically by the more rapid development in warmer waters.     

Evidence of coprophagy in freshwater zooplankton

1. Vertical transport of nutrients in sedimenting faecal material is greatly reduced by coprophageous organisms. Unfortunately, nearly all work on faecal production, sedimentation and coprophagy has dealt with copepods in marine ecosystems. Here, we report the first evidence of coprophagy in freshwater zooplankton from oligotrophic and eutrophic lakes. We used ¹⁴C‐labelled algae and faecal material to estimate the rates of algal clearance and coprophagy. 2. Measured feeding rates per individual on faecal material were similar (Daphnia pulex, D. rosea, Leptodiaptomus tyrelli) or even higher (D. lumholtzi) than filtering rates on phytoplankton. This finding does not necessarily implicate active selection of faeces over algae because: (i) we did not use the same food concentrations for faeces and algae, and (ii) grazers of slightly different sizes were used in each test. 3. Weight‐specific clearance rates of L. tyrelli and Holopedium gibberum on faecal matter (0.084–0.089 mL μg^?1 h^?1) were higher than in the daphniids (0.026 mL μg^?1 h^?1). 4. The data indicate that coprophagy in freshwater ecosystems is an important mechanism of nutrient recycling, and this process should be taken into account when studying nutrient fluxes within lakes and reservoirs.     

Calcium content of crustacean zooplankton and its potential role in species distribution

SUMMARY 1. The occurrence and species composition of crustacean zooplankton in Norwegian lakes was related to ambient Ca concentrations, pH, total phosphorus and chlorophyll a , and to the presence/absence of other zooplankters and a planktivorous fish (roach: Rutilus rutilus ).
2. Ambient Ca concentrations appeared to influence the distribution of Daphnia species: Daphnia longispina often occurred in Ca-rich lakes with low fish-predation pressure while the smaller Daphnia cristata often occurred in opposite conditions.
3. Body Ca contents were measured in zooplankters from a wide range of localities, to examine Ca requirements and thus the potential for Ca-limitation of common species.
4. All Daphnia species had relatively high specific Ca contents [ranging from 0.8 to 4.4% Ca dry weight (DW)⁻¹] compared with other cladocerans and also copepods (ranging from 0.1 to 0.4% Ca DW⁻¹). Within the Daphnia genus, the specific Ca content increased with increasing body size of the species, and thus the large-bodied species had especially high Ca demands.
5. Because of their high Ca demands, species of Daphnia could be competitively disadvantaged in softwater lakes relative to less Ca-demanding species.     

Species composition and distribution of the freshwater fish fauna of Southern Vietnam

Two hundred and fifty-five fish species occurring in freshwaters in the South of Vietnam are listed. Their geographical distribution is briefly discussed.     

Scale-dependence and mechanisms of dispersal in freshwater zooplankton

Communities of organisms form as a result of both interspecific and abiotic interactions within local habitat patches and dispersal among patches in a region. Local processes are expected to play a dominant role when dispersal occurs much more often than extinction. We performed two field experiments to examine rates and mechanisms of dispersal in freshwater pond zooplankton communities. First, we tested the effect of distance from a source on the rate of colonization of artificial habitat by placing wading pools at 5, 10, 30 and 60 m from two natural fishless ponds and observing the succession of zooplankton. Seventy-eight percent of the species in the source ponds that were capable of living in the pools colonized at least once during the experiment. A new species was found in the pools on average once every four days, suggesting that colonization events occur on the order of days to weeks for many species. Colonization rates declined further from the source at one pond but not the other, and the effect of distance was relatively weak at both ponds. This suggests that many species disperse broadly over short distances. The second experiment tested the role of animal vectors for zooplankton dispersal by restricting access to the pools. Eight treatments were imposed that excluded potential animal vectors along a body size gradient from large mammals to small insects. While the treatments affected zooplankton colonization, many species invaded even when all animals larger than 1 mm were excluded. Animal vectors may therefore be less important for dispersal than wind. Our results suggest that zooplankton are highly effective dispersers over short distances, and can disperse via several mechanisms. Local interactions should therefore play a dominant role in structuring these communities at small regional scales.     

The freshwater zooplankton of Central America and the Caribbean

So far mainly sporadic studies have been made on the freshwater zooplankton of this region. We studied material from Costa Rica, Cuba, Bahamas, El Salvador, Haiti and Trinidad and listed unpublished species data from Jamaica. In all 183 species of Rotifera; 104 of Cladocera; 64 Calanoida and Cyclopoida and a few Ostracoda are known from the region which includes Central America, the Caribbean Islands from the Bahamas to Trinidad and the islands off South America and Central America. Records from individual countries are generally low except for Cuban Cladocera and Copepoda. The total number of Copepoda and Cladocera recorded for the whole regions appears to be reasonably comprehensive. Daphnia is rare or absent from the equatorial regions and it is likely that the low species diversity may be due partly to the lack of a range of habitat types.     

Predation risk and the structure of freshwater zooplankton communities

Summary Many predators inflict substantial mortality on their prey. The prey respond to these selective pressures with changes in their spatial and temporal overlap with the predator (density risk responses), or with changes in their vulnerability to the predator (prey vulnerability responses). Here we develop a simple predation model that permits quantification of the basic response types of the prey in nature. We then test the hypothesis that prey response will be proportional to the intensity of the predation mortality relative to all other sources of mortality and decreased natality acting on the prey. A significant regression relationship is obtained for the prey vulnerability response but not for any of the density risk responses. The individual response values and regression statistics are used to interpret the relative importance of the different response types and to assess the predator's influence on prey community structure.Supported by Lehigh University Environmental Studies Center     

Species composition and distribution of the freshwater fish fauna of the North of Vietnam

Two hundred and three fish species and subspecies occurring in fresh water in the North of Vietnam are listed. The geographical and ecological problems connected with these fishes are discussed.     

The rarity concept and the commonness of rarity in freshwater zooplankton

1. Regional distribution, frequency of occurrence and relative abundance were scored in 2467 Norwegian lakes for all the recorded 130 species of crustacean zooplankton. The majority of species were rare in the sense that 65% of species were recorded in fewer than 10% of localities. Only six species were recorded in more than 50% of localities, and the median number of species in a given locality was 14 (i.e. 10% of the total species pool). 2. Abundances of all species were scored according to the fraction of lakes in which they were recorded, their geographical range of distribution, and their numerical abundance. Typically the most rare species were rare by all three criteria, and vice versa for the common species, pointing to rarity as an inherent property of some species. For some species this rarity reflects being on the edge of their distributional range, while for others rarity seems to be a consequence of their life cycle strategies. 3. Some of the truly rare species have high dispersal rates and high colonization abilities, but are rapidly replaced by other species. Others are confined to specific habitats, often highly eutrophic, pointing to highly specialized niche adaptations. 4. A major cause for the few truly common species seems to be the limited number of species that are able to coexist within a given locality, reflecting ‘the ghost of competition past’ and predation pressure. 5. While species composition and species richness may reflect colonization abilities and stochastic events, the presence or absence of species is not only a random lottery but also a consequence of species‐specific attributes.     

Species diversity and distribution of aquatic macrophytes in the Northern Quark, Baltic Sea

The occurrence of aquatic macrophytes was studied in a northern transition area of the Baltic Sea; the Northern Quark, Gulf of Bothnia. In the area there is a gradual, marked change in environmental conditions, the most prominent of which is a decrease in salinity from 5.0% in the Bothnian Sea to 3.5% in the Bothnian Bay. In all, 40 species of macrophytes were observed; 10 fucophyceans, 10 bangiophyceans, 8 chlorophyceans, 3 charophyceans, 1 tribophycean, 1 nostocophycean, 6 phanerogams and 1 water moss. 26 of the observed species were of marine and 14 of lacustrine origin. There was a clear change in species composition and community structure from south to north over the area. The vegetation at the southernmost localities had a marine character, with belt-forming Fucus vesiculosus and a comparatively diverse flora of macroalgae. Further north, an ephemeral, lacustrine vegetation dominated by benthic diatoms and Cladophora aegagropila prevailed. The ratio marine: lacustrine species decreased from 4.2 to 1 when comparing a southern and a northern sub-area of the Northern Quark. The species observed include 57 % of the marine macrophytes noted in the Aland and Archipelago Seas (N Baltic Proper) during the past two decades. Two marine species, Aglaothamnion roseum and Ahnfeltia plicata , are reported for the first time from the Northern Quark. This comprises a northern extension of their distribution limit with approximately 300 km.     

Root Strength and Root Area Ratio of Forest Species in Lombardy (Northern Italy)

Forest vegetation is known to increase hillslope stability by reinforcing soil shear resistance and by influencing hydrologic conditions of soil. Although the importance of plant root systems for hillslope stability has received considerable attention in recent years, the quantification of such an effect needs more investigation. In this paper, we present a synthesis of the data gathered in the last 5 years for some species in different locations of the Alps and Prealps of Lombardy (Northern Italy) with the aim to increase our knowledge on root tensile strength and on Root Area Ratio distribution within the soil. Concerning root tensile strength we developed tensile strength–diameter relationships for eight species: green alder (Alnus viridis(Chaix) D.C.), beech (Fagus sylvatica L.), red willow (Salix purpurea L.), goat willow (Salix caprea L.), hazel (Corylus avellana L.), European ash (Fraxinus excelsior L.), Norway spruce (Picea abies (L.) Karst.) and European larch (Larix decidua Mill.). Results show a great variability among the different species and also for the same species. In general, however, root strength (in terms of tension) tends to decrease with diameter according to a power law, as observed by other Authors. Comparing the power law fitting curves for the considered species, it can be observed that they fall in a relatively narrow band, with the exception of hazel, which appears the most resistant. Concerning the evaluation of root distribution within the soil we estimated the Root Area Ratio (the ratio between the area occupied by roots in a unit area of soil) according to its depth for five species (beech, Norway spruce, European larch, mixed hazel and ash) in three locations of Lombardy. Results show that there is a great variability of root density for the same species well as for different points at the same locality. The general behaviour of root density, in any case, is to decrease with depth according to a gamma function for all the studied species. The results presented in this paper contribute to expanding the knowledge on root resistance behaviour and on root density distribution within the soil. The studied location have allowed the implementation of soil–root reinforcement models and the evaluation of the vegetation contribution to soil stability.     

Species diversity, spatial distribution, and assemblages of zooplankton within the Strait of Magellan in austral summer

The main aim of this work was to identify zooplankton assemblages by means of statistical testing and associate them with hydrographic properties of the Strait of Magellan and its microbasins. Zooplankton samples were collected by the R/V Cariboo in late austral summer 1991. Nineteen stations were sampled by BIONESS from the surface layer to 900 m depth, along the main longitudinal axis of the Strait of Magellan. There was a marked regional-scale pattern in zooplankton species diversity and richness, related to the hydrographical features of the Strait and its sub-basins. Six groups of samples were identified by cluster analysis in terms of zooplankton structure, and related to sea-water properties of temperature, salinity, and Chl a (Sperman’s correlation coefficient). Plankton assemblages of the Strait of Magellan seem closely linked to the remote sub-Antarctic and adjacent ocean biota, but populations may have independent evolutionary lines and population dynamics.     

An unsupervised machine learning method for assessing quality of tandem mass spectra

Background

In a single proteomic project, tandem mass spectrometers can produce hundreds of millions of tandem mass spectra. However, majority of tandem mass spectra are of poor quality, it wastes time to search them for peptides. Therefore, the quality assessment (before database search) is very useful in the pipeline of protein identification via tandem mass spectra, especially on the reduction of searching time and the decrease of false identifications. Most existing methods for quality assessment are supervised machine learning methods based on a number of features which describe the quality of tandem mass spectra. These methods need the training datasets with knowing the quality of all spectra, which are usually unavailable for the new datasets.

Results

This study proposes an unsupervised machine learning method for quality assessment of tandem mass spectra without any training dataset. This proposed method estimates the conditional probabilities of spectra being high quality from the quality assessments based on individual features. The probabilities are estimated through a constraint optimization problem. An efficient algorithm is developed to solve the constraint optimization problem and is proved to be convergent. Experimental results on two datasets illustrate that if we search only tandem spectra with the high quality determined by the proposed method, we can save about 56 % and 62% of database searching time while losing only a small amount of high-quality spectra.

Conclusions

Results indicate that the proposed method has a good performance for the quality assessment of tandem mass spectra and the way we estimate the conditional probabilities is effective.

     

Quantitative comparison of food niches in some freshwater zooplankton

Summary The abilities of some zooplankton (rotifers, cladocerans, copepods) to ingest different sizes and kinds of food cells were quantified by determining the relative efficiencies with which they ingested nine tracer-cell types, ranging from a coccoid bacterium (0.45 m³) to the alga Cryptomonas erosa (800–920 m³). These efficiencies were obtained by dividing the clearance rate of each zooplankton group (species population, developmental stage or size class of a species population) on each ³²P-labeled cell type by that of a simultaneously-offered, ³³P-labeled, standard cell type — Chlamydomonas reinhardtii. Similarities of efficiency patterns on these cell types (food niches) between all possible pairs of the 17 zooplankton groups from 4 ecosystems were determined by calculating correlation coefficients. Although the utilization of the tested cell types may vary greatly within a species, three feeding guilds could be distinguished — based primarily on the efficiencies with which the smallest cell types were ingested. Guild I (Poyarthra vulgaris, Keratella crassa, Diaptomus minutus nauplii) ate the smallest cells (<4 m diameter) (bacterium, Synechococcus, Nannochloris) and Ankistrodesmus very ineffifently but the three Cryptomonas species very efficiently. Guild II (Bosmina longirostris, D. minutus copepodites and Adults) had higher efficiencies on Synechococcus, Nannochloris, Ankistrodesmus, Stichococcus, and Stephanodiscus than guild I but similarly low ones on the bacterium and high ones on the Cryptomonas species. Guild III (Conochilus inicornis, Keratella cochlearis, Ceriodaphnia quadrangula, Diaphanosoma leuchtembergianum) differed from guilds I and II in having uniformly high efficiencies on all the small cells as well ad the larger ones. Principal component analysis of the matrix of correlation coefficients provided objective confirmation of the three guilds and provided a visual representation of the food niches of the 17 zooplankton groups in 3-dimensional space.     

Measuring and modeling dispersal of adult zooplankton

Habitat fragmentation poses an inherent problem for metacommunity dynamics, as dispersal among communities is hindered by increasing isolation and the loss of patches. Wetlands are one such system that have undergone excessive destruction and fragmentation in recent years. Zooplankton within these communities have historically been considered frequent and widespread dispersers, but direct, quantitative measures of zooplankton dispersal are rare. In this study, I performed two experiments to quantify zooplankton dispersal and to identify the primary dispersal vectors. I first set up an array of traps at 10, 30, 60, 120 and 180 m around an isolated pond to collect dispersing individuals. Nearly 1,500 adult zooplankton were captured in traps up to 180 m from the pond, with approximately 60% of dispersers being captured in traps at 10 m from the pond. A second experiment using open and animal-excluded traps suggested that large animals were the primary dispersal vector for these zooplankton. Using a subset of these data, I fit four models to describe the shape and magnitude of adult cladoceran dispersal at this site. All models showed the majority of cladocerans were deposited very close to the source pond, with three models suggesting that the trapping area encompassed 67% or more of the dispersal distances. These results suggest that adult zooplankton movement among ponds may be significant in areas where aquatic habitats are plentiful. Yet, in recent years climate change and anthropogenic disturbances have reduced the number and size of aquatic habitats in many regions of the world, likely curtailing effective transport of individuals in many cases. As a result, fragmented zooplankton metacommunities may experience increased dispersal limitation, stronger priority effects, higher levels of inbreeding and selection against traits engendering high dispersability. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.