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1.
The aim of this paper was to study the life cycle, the annual secondary production, and the spatial and temporal variation of the species Campsurus truncatus and C. violaceus in two reservoirs in Minas Gerais, Brazil. Campsurus truncatus was recorded in 11 months and had a multivoltine lifecycle with a secondary production of 4.61 g.m?2.year?1. Campsurus violaceus was collected in eight months and had a bivoltine lifecycle with a secondary productivity of 1.96 g.m?2.year?1.  相似文献   

2.
SUMMARY. 1. The diet of the Eurasian dipper Cinclus cinclus. a riverine bird from a globally widespread genus, was assessed through all stages of its annual cycle using published data and field studies from streams of contrasting chemistry. Time-activity budgets were also compiled throughout the year and used to estimate annual energy requirements from the stream ecosystem. 2. The annual energy requirements for a territorial pair ranged from 148,000 to 158,000 kJ yr?1 depending on whether one or two broods were reared. After allowing for assimilation efficiency, these requirements were estimated to represent 10.5–11.0 kg dry mass of fish and invertebrates. Using representative values for territory size (4680–11,250 m2), annual exploitation of secondary production was estimated at 0.93–2.35 g dry mass m?2. 3. Several features combined to focus the predatory load on certain organisms over different stages of the annual cycle. These included the availability and selection of alternative prey, the need to provision nestlings with large items such as trichopteran larvae, and the use by females of calcium-rich prey such as fish prior to egg formation. 4. Across their range of territory size, annual exploitation (dry mass) by dippers was estimated at 0.06–0.29 g m?2 for Plecoptera. 0.02–0.22 g m?2 for Ephemeroptera. 0.59–1.11 g m?2 for Trichoptera and 0–0.78 g m?2 for fish. Exploitation of Ephemeroptera. I richoptera and fish were all highest in circumneutral streams, but exploitation of Plecoptera was highest in acidic streams because other prey were scarce. 5. Cottids dominated the fish component of the diet. Influences on their density could be substantial according to available data on production in Welsh streams. Hydropsychids and limnephilids dominated the trichopteran component, with exploitation again representing potentially substantial amounts of production. Contemporaneous data are required on benthic production and exploitation by the birds. 6. The ecological role of birds in rivers particularly, and aquatic ecosystems generally, is currently neglected but worthy of considerable research effort.  相似文献   

3.
Quantitative samples were used to investigate density, biomass and annual production of the benthic invertebrate fauna in a small Danish stream. Forty-eight taxa were found and the total invertebrate densities varied from 3 810 m?2 in July to 20 040 m?2 in December. The total mean annual biomass of the invertebrate fauna was 6.1 g ash-free dry wt m?2. The annual production of the invertebrates was estimated from their mean annual biomass and their annual P/B ratio. Production of the primary consumers (herbivores and detritivores) was 21.4 g ash-free dry wt m?2 y?1 and of secondary consumers (carnivores) 1.1 g m?2 y?1. The amount of invertebrate production available to the trout population and the importance of the species as food for trout are discussed.  相似文献   

4.
This study investigates aspects of the life history of the polychaete Thoracophelia furcifera on a sandy beach in southern Brazil. Two fixed transects perpendicular to the shoreline in the intertidal zone were sampled fortnightly from May 2008 to April 2009 at low tide. Five T. furcifera samples were collected along each transect and sediment temperature and the salinity of interstitial water were recorded. The material was washed over 0.5- and 0.088-mm sieves, and the width of setiger 8 of each specimen was measured. A total of 5,870 organisms were examined and the estimated parameters of the von Bertalanffy growth curve were L 3.60?mm (Wd8S), K 0.63?year?1, C 0.3 and WP 0.97 (Rn 0.132). Life span was 2.6?years, instantaneous mortality rate Z was 3.8?year?1 and the growth index φ′ 0.91. Mean density ranged from 644.44?±?191.77 to 2,783.33?±?453.64 ind m?2 and mean biomass ranged from 2.52?±?0.55 to 9.52?±?1.83?g?m?2. Recruitment occurred from April to July and ovigerous females were found from June to November. Annual secondary production was 6.582?g?m?2?year?1, mean biomass was 5.638?g?m?2 and turnover rate was 1.167. The high values for density, secondary production and biomass suggest that T. furcifera constitute an important food source. These features of T. furcifera’ life strategy demonstrate the significant role this species plays in ecosystem dynamics.  相似文献   

5.
Net production of theEcklonia cava community was monitored on a monthly basis for a year, and annual net production was estimated. Growth rate of blades reached a maximum of about 13 g dry wt·m?2·day?1 in spring and a minimum of about 2 g dry wt·m?2·day?1 in late summer. Annual production of blades was calculated to be 2.84 kg dry wt·m?2·year?1. If the growth of stipes is taken into account, annual net production is estimated to be about 2.9 kg dry wt·m?2·year?1. Standing crop was monitored monthly for two and a half years, and a close negative correlation was found between seasonal change in standing crop and net production. Standing crop reached a maximum of about 3 kg dry wt·m?2 in summer and a minimum of about 1 kg dry wt·m?2 in winter. Low productivity in summer at a period of maximum biomass may be explained by the dense canopy and the large area of reproductive portion occupying a blade, which diminish net assimilation.  相似文献   

6.
An ecological study of dry matter production was made in a dwarf forest dominated byAlnus maximowiczii at the timberline of Mt. Fuji. Annual gross production was estimated by two methods, namely the summation method using stem analysis and total photosynthesis calculated from leaf area and photosynthetic rate per leaf area. Seasonal changes in relative light intensity and in leaf area were measured in a quadrat. Photosynthesis and respiration rates of samples were measured in temperature-regulated assimilation chambers. The phytomass was 2,989 g d.w.m?2, and those of stems and branches, leaves, and roots were 1,672 g, 293 g, and 1,024 g respectively. The growing period of this plant was about four months and this plant expanded leaves quickly. The maximum gross photosynthetic rate was 21 mg CO2dm?2 h?1 on September 1. Annual net production estimated by examining the annual rings was 922 g d.w.m?2 year?1 and annual respiration was 735 g. Annual gross production estimated from photosynthetic rates was 1,747 g d.w.m?2 year?1. The sum of annual net production by stem analysis and respiration agree closely with gross production estimated from photosynthetic rate. Gross production of this dwarf forest is comparable to the beech forest of the upper cool temperate zone owing to the high photosynthetic rate ofAlnus maximowiczii.  相似文献   

7.
Open-pit mining of lignite in East Germany has created landscapes with extreme environmental conditions. Post-mining aquatic habitats are characterized by low biodiversity and simple food webs due to the impact of acid mine drainage. In this study, the ecology of the filter-feeding caddisfly Neureclipsis bimaculata (L.) was examined, which is abundant in the acidic Floßgraben stream (pH 2.5–3.6) in Lower Lusatia, Germany. From benthic samples, we measured larval size and biomass and estimated population dynamics. The seston drift was sampled and retention efficiency of the larvae’s nets was assessed in a field tracer experiment to evaluate diet availability. Mean annual abundance was 1,380 ind m?2 with a biomass of 1,010 mg m?2. Annual secondary production of N. bimaculata was 8,450 mg m?2. The larval microdistribution reflected the preference for in-stream wood and a limitation by low flow velocity. Morphometric factors of the larvae in the acidic stream were in the range of morphometric factors found in circumneutral streams that covered a range of trophic levels. Although coverage by iron particles reduced flow, the nets account for 63% of the mean particle retention. It is suggested that the retention efficiency and the availability of drifting organisms allowed the larvae to feed on 8.4 mg m?2 per day, which revealed a ratio of biomass production to ingested food of 60%.  相似文献   

8.
Twenty-one monthly collections of the Antarctic limpet Nacella (Patinigera) concinna (Strebel, 1908) were obtained by divers at Signy Island, South Orkney Islands. A mean monthly population density of 123.7 ± 21.2 · m?2, mean biomass of 13.7 ± 2.7 g dry tissue wt · m?2, and annual production of 2.9 g · m?2 were recorded in the depth range 2–12 m below mean low water.Shell growth was slow with a maximum growth rate, in the first 3–5 yr of life, of 3 4 mm per year. Maturity was attained at 7–8 yr (21 mm length), and maximum size (41 mm length) at about 21 yr. Unique spawning behaviour was observed in two Austral springs, and data relating spawning to the spring increase in sea temperature were obtained.  相似文献   

9.
Pomacea flagellata is a gastropod conspicuous in freshwater environments, and represents a fishing resource. To assess their abundance, distribution, and secondary production, monthly samplings were carried out in Bacalar Lake from June 2012 to May 2013 at 12 sampling sites. In each site, three random transects were marked parallel to the shore. All snails on transect were collected and shell length and wet weight measured. The highest density occurred in September (1.27 ind.m?2), lowest in October (0.47 ind.m?2). Shell lengths ranged from 2 to 56 mm, with recruitment in January–March. Growth parameters were L 59.50 mm, K 0.65.year?1; the lifetime span was 3 years. Average biomass reached 5.57 wet g.m?2 and secondary production was 6.025 wet g.m?2.year-1; annual renewal rate P/B 1.08. Highest abundance and secondary production was contributed by individuals between 31 and 41 mm in length. A potential biomass of 25.06 tons of snails was estimated in the lake. Snail densities, secondary production, and turnover were very low during the year, indicating that it is not viable to consider a commercial catch without affecting the population. A ban of 10 years is proposed, and aquaculture practices of snails are recommended to recover the resource.  相似文献   

10.
The regular sea urchin, Strongylocentrotus pallidus (G.O. Sars, 1871), is a widespread epibenthic species in high-Arctic waters. However, little is known about its distribution, standing stock, population dynamics and production. In the northern Barents Sea, S. pallidus was recorded on seabed still photographs at 10 out of 11 stations in water depths of 80–360?m. Mean abundances along photographic transects of 150–300 m length ranged between <0.1 and 14.7?ind. m?2 yielding a grand average of 3.6?ind.?m?2. The small-scale distribution along the transects was patchy, with densities varying from nil to an overall maximum of 25.5 ind. m?2, and exhibited a significant relation to the number of stones present. Sea urchin test diameters, measured on scaled photographs, extended from 7 to 90?mm. Median values at single stations varied from 14 to 46?mm, showing a significant inverse relationship to water depth. Biomass, estimated by combining photographic abundances, size frequencies and a size-mass function established with trawled specimens, ranged between <0.1 and 3.0?g ash-free dry mass m?2, averaging about 1.0?g ash free dry mass m?2. An analysis of skeletal growth bands in genital plates was carried out with 143 trawled individuals ranging in test diameter (D) from 4 to 48?mm. Assuming these bands to represent annual growth marks, the ages of the specimens analysed ranged between 3 and 42 years. A von Bertalanffy function was fitted to size-at-age data to model individual growth pattern (D?=?102.3?mm, k?=?0.011 year?1, t0?=?0.633?year). The annual mortality rate Z of the population in the northern Barents Sea was estimated from a size-converted catch curve to be 0.08 year?1. Applying the weight-specific growth rate method, the average P/B ratio and the mean annual production of this population were estimated as 0.07 year?1 and 0.076?g AFDM m?2 year?1, respectively. In conclusion, S. pallidus is characterized by slow growth, low mortality, high longevity and low productivity. Because of its relatively high biomass, it is considered to contribute significantly to total benthic standing stock and carbon flux in the study area.  相似文献   

11.
After a brief account of both past and present fishpond management and of its impact on the fishpond vegetation of higher plants, a survey is given of the biomass and total net production in various types of communities constituting this vegetation. Relatively stable and unstable communities are distinguished and further differentiated by the dominant plant life-forms. The biomass and production data are highly variable, depending on actual conditions in the fishpond habitats, but the maximum recorded values of annual net production (in terms of dry matter produced per year) appear to decrease in the following order: the communities dominated by ochthohydrophytes (over 3kg.m?2)-hydroochthophytes and euochthophytes (about 2kg.m?2)-pleustophytes and aerohydatophytes (upto 1kg.m?2)-euhydatophytes (upto 0.5kg.m?2). The original data were gathered in Czechoslovakia and the conclusions apply to fishponds in Central Europe.  相似文献   

12.
1. Freshwater shrimps often dominate the biomass of tropical island streams and are known to have strong effects on stream ecosystem structure and function, but little effort has been dedicated toward quantifying basic energetic and life history attributes such as growth, production and longevity. Such information is critical for understanding both the role of shrimps in ecosystem dynamics and the gravity of threats to shrimp populations posed by human activities such as shrimp harvesting, dam construction and water withdrawal. 2. We quantified growth rates and secondary production of dominant freshwater shrimps for 3 years in two Puerto Rican headwater streams that differ in food web structure because of the presence or absence of predatory fishes that are excluded from reaches above waterfalls. Using growth data, we constructed a minimum longevity model to explore the likely minimum life spans of the two dominant taxa (Atya spp. and Xiphocaris elongata). Finally, we used a bioenergetics model to quantify annual consumption rates of major basal resources by the two taxa. 3. Daily growth rates ranged from ?0.001 to 0.011 day?1, were inversely related to body size, and were higher for small individuals of X. elongata than Atya spp. Mean annual shrimp biomass and secondary production were an order of magnitude higher in the stream that lacked predatory fishes (biomass: 4.34 g AFDM m?2; production: 0.89 g AFDM m?2 year?1) than in the stream with predatory fishes (biomass: 0.12 g AFDM m?2; production: 0.02 g AFDM m?2 year?1). Production : biomass ratios ranged from 0.01 to 0.38. 4. Our longevity model predicted a minimum life span of 8 years for Atya spp. and 5 years for X. elongata in the stream lacking predatory fishes. In contrast, due to a larger average size of X. elongata in the stream with predatory fishes, our model predicted a minimum life span of 11 years. Actual life spans of these taxa are likely to be much longer based on long‐term observations of marked individuals. 5. Estimated consumption rates from the bioenergetics model indicated that Atya spp. and X. elongata are important processors of organic matter resources in streams where they occur at high densities. Atya spp. and X. elongata appeared capable of consuming a large proportion of algal and insect production and the proportion of direct leaf litter inputs consumed was also appreciable (c. 40–60%). However, the consumption of suspended fine particulate organic matter (SFPOM) by Atya spp. is probably only a minor proportion of total SFPOM flux in these streams. 6. Our study suggests that geomorphic features such as waterfalls may play an important role in controlling the distribution and production of freshwater shrimps through their effects on predatory fish movement. Spatial differences in shrimp densities result in landscape‐scale variation in the significance to ecosystem processes of these long‐lived organisms, particularly as processors of major organic matter resources.  相似文献   

13.
Predation by eiders, oystercatchers and herring gulls on natural mussel bedsMytilus edulis was studied in the Königshafen, a sheltered bay in the Wadden Sea. About 15 ha (2.5%) of the Königshafen were covered with mussel patches of a biomass of about 1300 g AFDW m?2. The biomass on the mussel beds was dominated by old mussels and found to be constant over several years. Birds annually removed 30% of the standing stock. Eiders were by far the most important predators and consumed 346 g AFDW m?2, followed by oystercatchers with 28 g AFDW m?2 and herring gulls with 3.6 g AFDW m?2. Birds consumed a substantial part of the annual production of the mussel beds which was estimated from literature data to be approx. 500 to 600 g AFDW m?2. As other predators were absent, the production of the mussels was sufficient to sustain the high predation rate by birds. Stable mussel beds form a short and efficient link between primary production and bird predation which is unusual for the Wadden Sea, where the main part of primary food supply is thought to be unavailable for higher trophic levels.  相似文献   

14.
We present 9 years of eddy covariance measurements made over an evergreen Mediterranean forest in southern France. The goal of this study was to quantify the different components of the carbon (C) cycle, gross primary production (GPP) and ecosystem respiration (Reco), and to assess the effects of climatic variables on these fluxes and on the net ecosystem exchange of carbon dioxide. The Puéchabon forest acted as a net C sink of ?254 g C m?2 yr?1, with a GPP of 1275 g C m?2 yr?1 and a Reco of 1021 g C m?2 yr?1. On average, 83% of the net annual C sink occurred between March and June. The effects of exceptional events such the insect‐induced partial canopy defoliation that occurred in spring 2005, and the spring droughts of 2005 and 2006 are discussed. A high interannual variability of ecosystem C fluxes during summer and autumn was observed but the resulting effect on the annual net C budget was moderate. Increased severity and/or duration of summer drought under climate change do not appear to have the potential to negatively impact the average C budget of this ecosystem. On the contrary, factors affecting ecosystem functioning (drought and/or defoliation) during March–June period may reduce dramatically the annual C balance of evergreen Mediterranean forests.  相似文献   

15.
The annual dynamics of live and dead fine roots for trees and the field layer species and live/dead ratios were investigated at a coniferous fern forest (Picea abies L. Karts) in Sweden. Our methods of estimating the average amount of fine roots involved the periodic sampling of fine roots in sequential cores on four sampling occasions. The highest live/dead ratio was found in the upper part of the humus layer for both tree and field-layer species and decreased with depth. Most tree fine roots on the four sampling occasions were found in the mineral soil horizon, where 86, 81, 85 and 89% of <1 mm and 89, 88, 89 and 92% of <2 mm diameter of the total amounts of live fine roots in the soil profile were found. The mean amounts of live fine roots of tree species for the total soil profile on the four sampling occasions was 317, 150, 139 and 248 g m?2 for <1 mm and 410, 225, 224 and 351 g m?2 for <2 mm diameter fine roots. The related amount of dead fine roots was 226, 321, 176 and 299 g m?2 and 294, 424, 282 and 381 g m?2, respectively. Average amounts of live and dead fine-roots and live/dead ratios from other Picea abies forest ecosystems were within the range of our estimates. The production of fine roots, <1 and <2 mm in diameter, estimated from the annual increments in live fine roots, was 207 and 303 g m?2. The related accumulation of dead fine roots was 257 and 345 g m?2, The turnover rate of tree fine roots <1 mm in diameter in the total soil profile amounted to 0.7 yr?1 for live and 0.8 yr?1 for dead fine roots. The related turnover rates for tree fine roots <2 mm were 0.4 yr?1 and 0.7 yr?1. Our data, although based on minimum estimates of the annual fluxes of live and dead fine roots, suggests a carbon flow to the forest soil from dead fine-roots even more substantial than from the needle litter fall. Fine-root data from several Picea abies forest ecosystems, suggest high turnover rates of both live and dead tree fine-roots.  相似文献   

16.
A multi-compartment model was developed to summarize existing data and predict soil carbon sequestration beneath switchgrass (Panicum virgatum) in the southeastern USA. Soil carbon sequestration is an important part of sustainable switchgrass production for bioenergy because soil organic matter promotes water retention, nutrient supply, and soil properties that minimize erosion. A literature review was undertaken for the purpose of model parameterization. A sensitivity analysis of the model indicated that predictions of soil carbon sequestration were affected most by changes in aboveground biomass production, the ratio of belowground-to-aboveground biomass production, and mean annual temperature. Simulations indicated that the annual rate of soil carbon sequestration approached steady state after a decade of switchgrass growth while predicted mineral soil carbon stocks were still increasing. A model-based experiment was performed to predict rates of soil carbon sequestration at different levels of nitrogen fertilization and initial soil carbon stocks (to a 30-cm depth). At a mean annual temperature of 13°C, the predicted rate of soil carbon sequestration varied from ?28 to 114?g?C?m?2?year?1 (after 30?years) and was greater than zero in 11 of 12 simulations that varied initial surface soil carbon stocks from 1 to 5?kg?C?m?2 and nitrogen fertilization from 0 to 18?g?N?m?2?year?1. The modeling indicated that more research is needed on the process of biomass allocation and on nitrogen loss from mature plantations, respectively, to improve our understanding of carbon and nitrogen dynamics in switchgrass agriculture.  相似文献   

17.
The paper sums up the first knowledge obtained from the study of seasonal changes in the growth and decomposition rate of underground plant biomass in a grassland community (Polygalo-Nardetum) in the highland ?eskomoravská vrchovina. The maximum increment of underground organs per day was recorded in late summer (14.04 g. m?2.d?1). The period of May to July was characterized by the highest rate of decomposition of underground parts per day (up to 27 g.m?2.d?1). The estimated annual net production of underground plant organs was 0.81 kg.m?2.  相似文献   

18.
19.
Estuaries are well known for their role as nutrient and detrital sinks that stimulate high levels of both primary and secondary production which, in turn, support a large biomass of fishes per unit area. This study reviews available information on coastal fish biomasses (g m?2 wet mass) and productivity (g m?2 wet mass year?1) in order to place South African data on these topics into a global perspective. Using biogeographic fish productivity estimates, together with estuarine water area, the approximate annual teleost production in South African estuaries was calculated at 585, 1706 and 13 904 t in the cool temperate, warm temperate and subtropical regions, respectively. Total annual fish production in estuaries on the subcontinent is conservatively estimated at 16 195 t, but this figure is likely to fluctuate widely, depending on recruitment success and annual environmental conditions pertaining to these systems. Approximately 2000 t of fish are estimated to be harvested by fishing activities in South African estuaries each year, which represents c. 12% of annual fish production. Although this figure may appear sustainable, the reality is that there are a few heavily targeted estuary‐associated marine species at the top of the food chain that are being overexploited by both anglers and subsistence fishermen. Natural mortalities due to piscivorous fish and bird predation has been estimated at c. 3% of total fish biomass per month in the East Kleinemonde Estuary, but this figure will vary considerably depending on bird abundance and foraging patterns along the coast. In contrast to catches made by the fishermen, piscivorous fishes and birds are targeting mainly juvenile marine fish and small estuarine resident species that are very abundant and generally low down in the food web.  相似文献   

20.
Energy derived from second generation perennial energy crops is projected to play an increasingly important role in the decarbonization of the energy sector. Such energy crops are expected to deliver net greenhouse gas emissions reductions through fossil fuel displacement and have potential for increasing soil carbon (C) storage. Despite this, few empirical studies have quantified the ecosystem‐level C balance of energy crops and the evidence base to inform energy policy remains limited. Here, the temporal dynamics and magnitude of net ecosystem carbon dioxide (CO2) exchange (NEE) were quantified at a mature short rotation coppice (SRC) willow plantation in Lincolnshire, United Kingdom, under commercial growing conditions. Eddy covariance flux observations of NEE were performed over a four‐year production cycle and combined with biomass yield data to estimate the net ecosystem carbon balance (NECB) of the SRC. The magnitude of annual NEE ranged from ?147 ± 70 to ?502 ± 84 g CO2‐C m?2 year?1 with the magnitude of annual CO2 capture increasing over the production cycle. Defoliation during an unexpected outbreak of willow leaf beetle impacted gross ecosystem production, ecosystem respiration, and net ecosystem exchange during the second growth season. The NECB was ?87 ± 303 g CO2‐C m?2 for the complete production cycle after accounting for C export at harvest (1,183 g C m?2), and was approximately CO2‐C neutral (?21 g CO2‐C m?2 year?1) when annualized. The results of this study are consistent with studies of soil organic C which have shown limited changes following conversion to SRC willow. In the context of global decarbonization, the study indicates that the primary benefit of SRC willow production at the site is through displacement of fossil fuel emissions.  相似文献   

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