Biomass Of Dominant Species Research Articles

Modelling the complete life cycle of an arctic copepod reveals complex trade-offs between concurrent life cycle strategies

Calanus hyperboreus is a large-bodied, biomass dominant species that performs a crucial ecosystem energy transfer by converting the spring phytoplankton bloom into lipid reserves that fuel the higher trophic levels of the Gulf of St. Lawrence (GSL) pelagic ecosystem, including the critically endangered North Atlantic right whale (Eubalena glacialis). Given that the GSL, the southernmost core habitat of C. hyperboreus, is undergoing rapid warming, developing a population model allows us to synthesize existing knowledge of the species, and to examine the species response to environmental conditions. To simulate the multi-year life cycle in the northwest GSL, model equations are implemented for ingestion, assimilation, respiration, egg production, stage development, mortality, and vertical migration behaviors including dormancy entry and exit. The 1-D particle-based model predicts the evolution of individual stage, structural mass, lipid, age, sex, abundance, and egg production, as well as the seasonal evolution of the population structure in the northwest GSL. Individual lipid-based thresholds inform the timing of ontogenetic vertical migration. Life cycle targets defined from a literature review are used to guide model parameterization and assess its performance. The simulated population structure, phenology, and size at stage are generally consistent with observations. Under 10 years of repeat year forcing, the model simulates a quasi-stable overwintering population composed of late stages CIV, CV and CVI. Observations suggest that stage CIV is the first overwintering stage in the GSL, and point to the occurrence of iteroparous females. Using the model, the relative success of diverse dormancy and reproductive phenotypes are explored. Second reproduction females reproduce earlier in winter than first reproduction females, with implications for the ability of the new generation to match the spring bloom and accumulate sufficient lipid to overwinter as stage CIV. Without iteroparity, the time window of reproduction contracts and the population is reduced, underscoring the role of a flexible multi-year life cycle in population success.

Nitrogen niche partitioning between tropical legumes and grasses conditionally weakens under elevated CO2

Abstract Plant community biodiversity can be maintained, at least partially, by shifts in species interactions between facilitation and competition for resources as environmental conditions change. These interactions also drive ecosystem functioning, including productivity, and can promote over‐yielding‐ an ecosystem service prioritized in agro‐ecosystems, such as pastures, that occurs when multiple species together are more productive than the component species alone. Importantly, species interactions that can result in over‐yielding may shift in response to rising CO2 concentrations and changes in resource availability, and the consequences these shifts have on production is uncertain especially in the context of tropical mixed‐species grasslands. We examined the relative performance of two species pairs of tropical pasture grasses and legumes growing in monoculture and mixtures in a glasshouse experiment manipulating CO2. We investigated how over‐yielding can arise from nitrogen (N) niche partitioning and biotic facilitation using stable isotopes to differentiate soil N from biological N fixation (BNF) within N acquisition into above‐ground biomass for these two‐species mixtures. We found that N niche partitioning in species‐level use of soil N versus BNF drove species interactions in mixtures. Importantly partitioning and overyielding were generally reduced under elevated CO2. However, this finding was mixture‐dependent based on biomass of dominant species in mixtures and the strength of selection effects for the dominant species. This study demonstrates that rising atmospheric CO2 may alter niche partitioning between co‐occurring species, with negative implications for the over‐yielding benefits predicted for legume‐grass mixtures in working landscapes with tropical species. Furthermore, these changes in inter‐species interactions may have consequences for grassland composition that are not yet considered in larger‐scale projections for impacts of climate change and species distributions. Read the free Plain Language Summary for this article on the Journal blog.

Macrofauna community of the cold seep area at Site F, South China Sea

A cold seep is one of the typical deep-sea chemical energy ecosystems and a hotspot for studying unique life processes and biogeochemical cycles in the deep sea. Macrofauna, which is one of the most important components of the cold seep ecosystem, has not been thoroughly studied. We examined the macrofauna community at Site F using images collected in 2016 by an imaging and laser profiling system and biological samples collected in 2020 and 2021 by TV grab and a remotely operated vehicle. In total, 41 species were found. The overall number of macrofauna identified at Site F (20,000 m2) reached 252,943 individuals, and the biomass reached 726.15 kg by dry weight. As the dominant species, Gigantidas platifrons and Shinkaia crosnieri reached their highest densities of 629 and 396 individuals/m2, respectively. The comparisons between different stations revealed that the diversity and density, even the biomass of dominant species, were much higher in the south than in the north at Site F in 2020. Correlation analysis showed that methane had a positive effect on macrofauna density. Compared with S. crosnieri, G. platifrons seems to be more adapted to the harsh cold seep environment. Methane consumption rates of the dominant species show that macrofauna are important in influencing seafloor methane fluxes. Our findings provide valuable insights into the ecology, community structure, and biota-environment interaction in the cold seep at Site F.

Phytoplankton Community Response to Environmental Factors along a Salinity Gradient in a Seagoing River, Tianjin, China.

A river-estuary ecosystem usually features a distinct salinity gradient and a complex water environment, so it is enormously valuable to study the response mechanism of living organisms to multiple abiotic factors under salinity stress. Phytoplankton, as an important part of aquatic microorganisms, has always been of concern for its crucial place in the aquatic ecosystem. In this study, phytoplankton data and 18 abiotic factors collected from 15 stations in Duliujian River, a seagoing river, were investigated in different seasons. The results showed that the river studied was of a Cyanophyta-dominant type. Salinity (SAL) was the key control factor for phytoplankton species richness, while water temperature (WT) was critical not only for species richness, but also community diversity, and the abundance and biomass of dominant species. Apart from WT, the abundance and biomass of dominant species were also driven by total nitrogen (TN), nitrate (NO3-), pH, and water transparency (SD). Moreover, total dissolved phosphorus (TDP), pH, and chemical oxygen demand (COD) were crucial for community diversity and evenness. The bloom of dominant species positively associated with TDP led to lower diversity and evenness in autumn. In addition, when available nitrogen was limited, Pseudoanabaena sp. could obtain a competitive advantage through the N2 fixation function. Increased available nitrogen concentration could favor the abundance of Chlorella vulgaris to resist the negative effect of WT. The results show that Oscillatoria limosa could serve as an indicator of organic contamination, and nutrient-concentration control must be effective to inhibit Microcystis bloom. This could help managers to formulate conservation measures.

Precision of mesoplankton sampling: A case study based on three net series in the South Atlantic and in the Black Sea

Mesoplankton is a key element of pelagic communities representing the largest biome on the planet. Many concepts in marine and freshwater biology are based on quantitative estimates of mesoplankton abundance, whereas precision of mesoplankton sampling remains underexplored and may depend on various factors. We analyzed ten contiguous daytime epipelagic samples in the Black Sea and 13 nighttime mesopelagic samples in the South Atlantic. We used a relative error as a measure of the sampling precision and ran a set of Generalized Linear Mixed Models (GLMMs) to estimate effects of six possible factors: abundance, size, diel migration, movement speed, taxonomic group, and net type. Abundance of taxa was the most powerful factor affecting sampling precision (positive effect) followed by the net type (BR provided better precision than Judey net) and taxonomic group. Conversely, size, movement speed, and diel migrations did not significantly influence sampling precision in all sample sets. We conclude that abundance and biomass of dominant species may be estimated with a satisfactory accuracy (relative error <20% of assessed values), which suggests that recent conceptions based on total mesoplankton abundance and biomass (contributed mainly by dominant taxa) are not greatly biased. Quantitative zooplankton structure and biodiversity assessed on the basis of non-transformed matrices are likely more relevant than those based on the root-transformed or presence/absence data.

Arid community responses to nitrogen and carbon addition depend on dominant species traits and are decoupled between above‐ and below‐ground biomass

AbstractQuestionsArid communities are strongly limited by soil resources including water and nitrogen (N). Plants compete for N with other plants and microorganisms, which are also limited by carbon (C). We propose that above‐ and below‐ground plant responses to soil resources are modulated by community structure (species relative abundances, “mass ratio hypothesis”) and species traits (relative growth rates — RGRs). We evaluated the single and combined effects of soil N and C addition on the above‐ and below‐ground biomass accumulation of perennial grass patches in an arid community, and the mechanisms involved in their responses.LocationPatagonian steppe, Argentina.MethodsWe added N (2 g N m−2; NH4NO3) and C (330 g C m−2; sucrose) to 1‐m2 field plots in a factorial design. After two years, we harvested above‐ground (n = 5 plots) and below‐ground biomass (n = 10 soil cores) and sorted it by species. We measured potential soil respiration as a proxy of microbial activity.ResultsTotal above‐ground biomass increased by 55% as a result of N and decreased by 45% as a result of C addition, in relation to controls. C addition reduced total below‐ground biomass by 42%. The above‐ground differences were associated with changes in the biomass of dominant species according to their RGRs. Poa ligularis (dominant, high RGR) increased by 92% as a result of N addition while Pappostipa speciosa (dominant, low RGR) decreased by 55% as a result of C addition. Intermediate and subordinate grasses did not modify their biomass, independently of their RGR. Potential soil respiration was three times higher in plots with C addition than in control plots.ConclusionsCommunity biomass was explained by a combination of mass ratio hypothesis and specific RGR, as dominant grasses controlled above‐ground community responses to N (high‐RGR species) and C addition (low‐RGR species). Our findings highlight the independence between the above‐ and below‐ground processes and the importance of considering community equitability and species characteristics to predict plant community responses to changes in soil resources.

A pilot study on the application of environmental DNA to the estimation of the biomass of dominant species in the northwestern waters of Jeju Island

A pilot study on the application of environmental DNA to the estimation of the biomass of dominant species in the northwestern waters of Jeju Island

The relationship between diversity and productivity from a three-dimensional space view in a natural mesotrophic lake

The relationship between diversity and productivity (DPR) is a hot topic in ecology, whereas most evidence comes from studies of manipulated terrestrial ecosystems or from two-dimensional space views. In this study, we determined DPR of submerged plants in a natural mesotrophic lake, Lake Erhai, along its water depth in 2013 and 2019. Our results demonstrated that the community productivity was significantly negatively correlated with plant biodiversity from a three-dimensional space view (all of the water depths) in Lake Erhai due to strong competition effects among submerged species. However, DPR patterns at each water depth (from two-dimensional space views) were various, which might be because these DPR patterns were disturbed by many biotic and abiotic factors or their interplays. Both total biomass and biomass of dominant species negatively correlated with species richness. Moreover, total biomass was positively correlated with biomasses of dominant species. Accordingly, we can presume that DPR patterns are largely determined by relationships between biomasses of dominant species and biodiversity in our study. Our results showed that species number in 2019 was generally smaller than that in 2013 and submerged species were migrating from deep water to shallow water with lake eutrophication in such a short time. Accordingly, measurements should be conducted quickly to control the eutrophication process of Lake Erhai to improve its multiple valuable functions and services.

Community Stability Was Maintained by Divergent Mechanisms in Arid Desert Ecosystem

More attention has been paid to the effects of diversity and dominance on community temporal stability rather than spatial stability in the main biome globally. Moreover, the maintenance mechanisms underlying the stability patterns of plant communities dominated by different plants in the Gobi Desert remain unknown. This article addresses the maintenance mechanism of plant community stability dominated by different plants in the Gobi Desert northwest of China. Four communities dominated by Sympegma regelii, Reaumuria songarica, Nitraria sphaerocarpa, and Gymnocarpos przewalskii, respectively, were selected in the national nature reserve, and a total of 240 quadrats, 20 × 20 m each, were established in the four communities. The correlations among species richness, species evenness, species diversity, community stability, and the biomass of dominant species were analyzed by linear regression model and structural equation model. The dominant species determined positively and directly the stability of the N. sphaerocarpa community, while diversity acted negatively in the maintenance of G. przewalskii community stability. However, species richness contributed mainly and positively to the maintenance of stability in the S. regelii community. Direct and negative effect of species richness and positive function of diversity were found in the maintenance of stability in the R. songarica community. Taken together, community stability is maintained by the divergent mechanisms in arid environment, which depends on the dominant species and diversity. The study could provide reference for the management of communities in the arid desert regions.

Increases in heat-induced tree mortality could drive reductions of biomass resources in Canada’s managed boreal forest

The Canadian boreal forest provides valuable ecosystem services that are regionally and globally significant. Despite its importance, the future of the Canadian boreal forest is highly uncertain because potential impacts of future climate change on ecosystem processes and biomass stocks are poorly understood. We investigate how anticipated climatic changes in coming decades could trigger abrupt changes in the biomass of dominant species in Canada’s boreal forests. Using the dynamic global vegetation model LPJ-LMfire, which was parameterized for the dominant tree genera in Canada’s boreal forests (Picea, Abies, Pinus, Populus) and driven by a large range of climate scenarios grouped by two forcing scenarios (RCP 4.5/8.5), we simulated forest composition, biomass, and the frequency of disturbance, including wildfire, from Manitoba to Newfoundland. Results suggest that responses of this region to a warmer future climate will be very important, especially in southern boreal areas and under the RCP 8.5 forcing scenario. In these areas, reductions of total aboveground biomass incurred by fire and heat-induced tree mortality events are projected; the fertilizing effect of increasing atmospheric CO2 on forest productivity is unlikely to compensate for these losses. Decreases in total forest stocks would likely be associated with forest cover loss and a shift in composition in particular from needleleaf evergreen (softwood) to broadleaf deciduous (hardwood) taxa. The simulated future reduction in softwood biomass suggests that forest management strategies will have to be adapted to maintain a sustainable level of forest harvest and tree density that meets demands for wood products, while maintaining other ecosystem services.

Biomass-dominant species shape the productivity-diversity relationship in two temperate forests

A negative productivity-diversity relationship was determined for biomass-dominant species at the community level. This study thus supports the hypothesis in which the effects of individual species on the productivity-diversity relationships at the community level are related to their biomass density, an important functional trait. The productivity-diversity relationships have been extensively studied in various forest ecosystems, but key mechanisms underlying the productivity-diversity relationships still remain controversial. The objective of this study is to explore the productivity-diversity relationships at the community level, and to investigate the roles of individual species in shaping the community-level relationships between productivity and diversity under different forest types. The study was conducted in two fully stem-mapped temperate mixed forest plots in Northeastern China: a natural secondary forest plot, and an old-growth forest plot. An individual-based study framework was used to estimate the productivity-diversity relationships at both species and community levels. A homogeneous Thomas point process was used to evaluate the significance of productivity-diversity relationship deviating from the neutral. At the species level, most of the studied species exhibit neutral productivity-diversity relationship in both forest plots. The percentage of species showing negative productivity-diversity relationship approaches linearly a peak value for very close neighborhoods (the secondary forest plot: r = 3 m, 38%; the old-growth forest plot: r = 4 m, 42%), and then decreases gradually with increasing spatial scale. Interestingly, only a few species displayed positive productivity-diversity relationship within their neighborhoods. Dominant species mainly exhibit negative productivity-diversity relationship while tree species with lower importance values exhibit neutral productivity-diversity relationship in both forests. At the community level, a consistent pattern of productivity-diversity relationship was observed in both forests, where tree productivity is significantly negatively associated with local species richness. Four biomass-dominant species (Juglans mandshurica Maxim., Acer mono Maxim.,Ulmus macrocarpa Hance and Acer mandshuricum Maxim.) determined a negative productivity-diversity relationship at the community level in the secondary forest plot, but only one species (Juglans mandshurica) in the old-growth forest plot. The productivity-diversity relationship is closely related to the dominance of individual species at the species level. Moreover, this analysis is the first to report the roles of biomass-dominant species in shaping the productivity-diversity relationship at the community level.

Phytoplankton light absorption in the deep chlorophyll maximum layer of the Black Sea

ABSTRACT Bio-optical data, obtained during six cruises in the Black Sea carried out during periods of seasonal stratification in years between 1996 and 2016, have been used to parametrize phytoplankton light absorption ( ) in the deep chlorophyll maximum (DCM) layer located near the bottom of euphotic zone. Relationships between and the sum of chlorophyll-a and phaeopigment concentrations (Chl-a) differed from those for the summertime upper mixed layer (UML). Notably, chlorophyll a specific absorption coefficients ( ) were lower in the DCM and more comparable with values typical for winter phytoplankton in the Black Sea. The spectral shapes in the DCM differed markedly from those in winter and in the summer UML, due to a shoulder at ~490 nm and a local maximum at ~550 nm corresponding to the absorption bands of phycourobilin and phycoerythrobilin. Light absorbing properties of phytoplankton in the DCM (amplitude and spectral shape of ) reflected physiological acclimation to local conditions on the cellular level and population shifts leading to changes in the biomass-dominant species, with Synechococcus spp. domination in the DCM. The parameterization of phytoplankton absorption in the DCM will enable refined spectral models of the downwelling radiance and primary production in the Black Sea.

Southern Ocean Mesopelagic Fish Comply with Bergmann’s Rule

AbstractThe applicability of macroecological rules to patterns in body size varies between taxa. One of the most examined is Bergmann’s rule, which states that body size increases with decreasing temperature and increasing latitude, although the rule is not universal and the proposed mechanisms underpinning it are multifarious and lack congruence. This study considers the degree to which Bergmann’s rule applies to the Southern Ocean mesopelagic fish community. We studied patterns in body size, temperature, and latitude across a 12° latitudinal gradient within the Scotia-Weddell sector. Intraspecific Bergmann’s rule was found to apply to 8 of the 11 biomass-dominant species in the family Myctophidae. The rule was also apparent at an interspecific level. Our study suggests that greater attainable body size in this community is a necessary attribute to reach colder regions further south. The adherence of these taxa to Bergmann’s rule enables such species to act as sentinels for identifying the drivers and co...

서해 군산 연안에서 새우조망으로 어획된 저서생물의 종조성 및 군집구조

Abstract Species composition of aquatic organism in the marine ranching area of Gunsan, Korea were investigated using shrimp beam trawl from May to December in 2010. A total of 91 species, 98,127 ind./ ㎢ and 877.6 ㎏/㎢ of aquatic organism were collected. Among them, species were included 60 species in Pisces, 21 in Crustacea and 10 in Mollusca. The individual dominant species, occupying over 10% of total individuals, were Latreutes anoplonyx(47,327 ind/㎢, 48.23%), Crangon hakodatei(11,578 ind./㎢, 11.80%) and Trachysalambria curvirostris(10,237 ind./㎢, 10.40%). And the biomass dominant species, occupying over 9% of total biomass, were Paralichthys olivaceus(135 ㎏/㎢, 15.4%), Okamejei kenojei(98.2 ㎏/㎢, 11.2%) and Portunus tribuberculatus(84.8 ㎏/㎢, 9.6%). From the cluster and MDS analysis based on Bray-Curtis similarity matrix of fourth root transformed data of number of species and individuals per unit area collected more than two times during this survey by each month and station was divided into three different groups. Group A showed seasonal similarity of characteristic of distribution in August and November, Group B in December and Group C in May. Key words : Species composition, Community structure, Dermersal organisms, Gunsan, Shrimp beam trawlCorresponding author : 051-626-9895, bluejuve@gmail.com 2016 (R2016051) .

울진바다목장에서 형망으로 어획된 수산자원의 군집구조

To elucidate the variation of species composition, biomass and size distribution of fishery resource in the Uljin marine ranching area was investigated at the 4 stations from 2009 to 2010 based on the dredge sampling. During the survey period, a total of 41 fishery resource species were sampled with a mean density of <TEX>$2,554,633\;ind./km^2$</TEX> and mean biomass was <TEX>$32,946kg/km^2$</TEX>. A total 36 fishery resource species were sampled with a mean density of <TEX>$3,198,793\;ind./km^2$</TEX> and mean biomass <TEX>$41,177kg/km^2$</TEX> in 2009 and it were sampled a total 31 species, mean <TEX>$1,910,473kg/km^2$</TEX> and <TEX>$24,716kg/km^2$</TEX> in 2010. The major individual-dominant species, occupying over 1% of total individuals, were Gomphina veneriformis (2,491,818 ind., 82.2%), Umbonium costatum (221,973 ind., 8.7%), Mactra chinensis (49,879 ind., 2.0%), Glossaulax didyma hayashii (49,879 ind., 1.9%), Blepharipoda liberate (37,714 ind., 1.5%) and Paguridae spp. (27,266 ind., 1.1%). The major biomass-dominant species, occupying over 1% of total biomass, were G. veneriformis (25,124 kg, 76.3%), G. didyma hayashii (2,596 kg, 7.9%), M. chinensis (2,024 kg, 6.1%), Ovalipes punctatus (921 kg, 2.8%) and Glossaulax didyma didyma (567 kg, 1.7%). From the cluster analysis based on Bray-Curtis similarity matrix of fourth root transformed data of species number and individuals was divided into 2 different groups of the fishery resource community (Group A-St.1, Group B-Sts. 2, 3, 4). The 2009 and 2010 mean Shell length (mm) of G. veneriformis was 37.73 mm, 29.76 mm and M. chinensis was 62.03 mm, 44.94 mm, respectively.

A metagenetic approach for revealing community structure of marine planktonic copepods.

Marine planktonic copepods are an ecologically important group with high species richness and abundance. Here, we propose a new metagenetic approach for revealing the community structure of marine planktonic copepods using 454 pyrosequencing of nuclear large subunit ribosomal DNA. We determined an appropriate similarity threshold for clustering pyrosequencing data into molecular operational taxonomic units (MOTUs) using an artificial community containing 33 morphologically identified species. The 99% similarity threshold had high species-level resolution for MOTU clustering but overestimated species richness. The artificial community was appropriately clustered into MOTUs at 97% similarity, with little inflation in MOTU numbers and with relatively high species-level resolution. The number of sequence reads of each MOTU was correlated with dry weight of that taxon, suggesting that sequence reads could be used as a proxy for biomass. Next, we applied the method to field-collected samples, and the results corresponded reasonably well with morphological analysis of these communities. Numbers of MOTUs were well correlated with species richness at 97% similarity, and large numbers of sequence reads were generally observed in MOTUs derived from species with large biomass. Further, MOTUs were successfully classified into taxonomic groups at the family level at 97% similarity; similar patterns of species richness and biomass were revealed within families with metagenetic and morphological analyses. At the 99% similarity threshold, MOTUs with high proportions of sequence reads were identified as biomass-dominant species in each field-collected sample. The metagenetic approach reported here can be an effective tool for rapid and comprehensive assessment of copepod community structure.

울진바다목장에서 어획된 가자미목(Pleuronectiformes) 어류의 군집구조 및 공간분포

To elucidate the variation of species composition, biomass and length distribution of flatfishes by the period and region in the Uljin marine ranching area, bottom trawl survey was investigated at the six stations from Feb. 2008 to Dec. 2010. During the survey period, a total 4 families 17 species in the Pleuronectiformes, average 69,158 <TEX>$ind./km^2$</TEX> and 5,625 <TEX>$kg/km^2$</TEX> were identified, in 2008 appeared in 14 species, average 25,798 <TEX>$ind./km^2$</TEX> and 2,333 <TEX>$kg/km^2$</TEX> and in 2009 appeared in 13 species, average 102,360 <TEX>$ind./km^2$</TEX> and 5,634 <TEX>$kg/km^2$</TEX> and in 2010 appeared in 14 species, average 75,704 <TEX>$ind./km^2$</TEX> and 8,632 <TEX>$kg/km^2$</TEX>. The individual dominant species, occupying over 10% of total individuals, was Pleuronectes herzensteini (20,811 ind., 30.0%), Hippoglossoides pinetorum (18,666 ind., 26.9%) and Glyptocephalus stelleri (13,499 ind., 19.4%) also the biomass dominant species, occuping over 10% of total biomass, was P. herzensteini (2,207 kg, 39.3%), Pleuronectes yokohamae (857 kg, 15.3%), H. pinetorum (761 kg, 13.5%), Kareius bicoloratus (677 kg, 12.1%). From the cluster and MDS analysis based on Bray-Curtis similarity matrix of fourth root transformed data of species number and individuals in the Uljin marine ranching area from Feb. 2008 to Dec. 2010 was divided into two different groups of the flatfishes community in 2008 and from Jan. to Apr. in 2009 and 2010 (Group A) and the pleuronectiform community in from May to Dec. in 2009 and 2010 (Group B). From the cluster and MDS analysis using the similarity of demersal organisms community among six stations, the Uljin marine ranching area was divided into two different groups of Group 1 (St. 1 and St. 3) and Group 2 (St. 2, St. 4, St. 5 and St. 6).

Declining diversity in abandoned grasslands of the carpathian mountains: do dominant species matter?

Traditional haymaking has created exceptionally high levels of plant species diversity in semi-natural grasslands of the Carpathian Mountains (Romania), the maintenance of which is jeopardized by recent abandonment and subsequent vegetation succession. We tested the hypothesis that the different life history strategies of dominant grasses cause different patterns of diversity loss after abandonment of traditional haymaking in two types of meadow. Although diversity loss rate was not significantly different, the mechanism of loss depended on the life history of dominant species. In meadows co-dominated by competitive stress-tolerant ruderals, diversity loss occurred following the suppression of dominant grasses by tall forbs, whereas in meadows dominated by a stress-tolerant competitor, diversity loss resulted from increased abundance and biomass of the dominant grass. We conclude that management for species conservation in abandoned grasslands should manipulate the functional turnover in communities where the dominant species is a weaker competitor, and abundance and biomass of dominant species in communities where the dominant species is the stronger competitor.

High-resolution survey indicates high heterogeneity in copepod distribution in the hydrologically active Drake Passage

A mesoscale grid survey of the epipelagic mesozooplankton of Drake Passage during Antarctic spring, 2008, is evaluated. The station grid comprised six parallel frontal transects between 57° and 60° S in the vicinity of the Polar Front, the distance between transects being 18 km. Several parameters were analysed: total zooplankton biomass, biomass of dominant species and the contribution made by each species to the overall plankton biomass. Mesoscale variability was found in all studied parameters and was comparable in magnitude to the macroscale variability of the same parameters. Because of the high variability in zooplankton distribution in the vicinity of active fronts, hydrobiological studies provide more meaningful results if they are made on the basis of a mesoscale grid survey, not on the basis of a single transect.

Effects of Grazing Intensity and Environmental Factors on Species Composition and Diversity in Typical Steppe of Inner Mongolia, China

In the present study, we aim to analyze the effect of grazing, precipitation and temperature on plant species dynamics in the typical steppe of Inner Mongolia, P.R. China. By uncoupling biotic and abiotic factors, we provide essential information on the main drivers determining species composition and species diversity. Effects of grazing by sheep were studied in a controlled experiment along a gradient of seven grazing intensities (from ungrazed to very heavily grazed) during six consecutive years (2005–2010). The results show that plant species composition and diversity varied among years but were little affected by grazing intensity, since the experimental years were much dryer than the long term average, the abiotic constraints may have overridden any grazing effect. Among-year differences were predominantly determined by the abiotic factors of precipitation and temperature. Most of the variation in species dynamics and coexistence between C3 and C4 species was explained by seasonal weather conditions, i.e. precipitation and temperature regime during the early-season (March-June) were most important in determining vegetation dynamics. The dominant C3 species Stipa grandis was highly competitive in March-June, when the temperature levels were low and rainfall level was high. In contrast, the most common C4 species Cleistogenes squarrosa benefited from high early-season temperature levels and low early-season rainfall. However, biomass of Stipa grandis was positively correlated with temperature in March, when effective mean temperature ranges from 0 to 5°C and thus promotes vernalization and vegetative sprouting. Our results suggest that, over a six-year term, it is temporal variability in precipitation and temperature rather than grazing that determines vegetation dynamics and species co-existence of grazed steppe ecosystems. Furthermore, our data support that the variability in the biomass of dominant species, rather than diversity, determine ecosystem functioning. The present study provides fundamental knowledge on the complex interaction of grazing – vegetation – climate.