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Energy Flow and Trophic Structure
Abstract
As Odum (1971a) succinctly put it,
The transfer of food energy from the source in plants through a series of organisms, with repeated eating and being eaten, is referred to as a food chain. At each transfer a large proportion, 80 to 90 percent, of the potential energy is lost as heat. Therefore the number of ‘links’ in a sequence is limited, usually four or five ... The number of consumers that can be supported by a given primary production output very much depends on the length of the food chain; each link in the chain decreases the available energy by about one order of magnitude.
... Early studies focussing on the effect of energy flow on the food web, suggested that organisms at the end of a food web (i.e. top predators) must be limited by their food supplies (Odum 1971;Pimm 1988). In recent years, studies of energy flow in marine ecosystems have increased tremendously showing considerable evidence that food web and trophic structure studies facilitate ecosystem and community understanding (e.g. ...
... The trophic structures are modified and limited by the amount of energy flow (Odum 1971;Pimm 1988). In general, trophic structures are represented by the food web. ...
... Complex relationships associated with highly diverse natural communities can be analyzed by grouping taxonomically or functionally similar organisms (Chase and Leibold 2003;Hughes et al. 2005). By doing so, it helps simplify the ecological analysis of community structure (Pimm 1988). In this way, it has been common to pool organisms in functional groups that share similar functional attributes or into functional guilds, that exploit a common food source (Giller and Gee 1987;Bonsdorff and Pearson 1999;Nordström et al. 2010). ...
The sub-Antarctic Magellan region in southern Chile belongs to the most extensive fjord regions of the world. Coastal and marine environments are exposed to natural and anthropogenic perturbations. Research on the marine ecosystems have received some attention, however, research on the flow of energy is rather limited. To trace energy flow and resource distribution across communities is of considerable concern to current ecological studies for understanding how marine benthic ecosystems are organized, the base of which food sources they are built upon and how benthic organisms utilize resources. Heterogeneous environmental conditions along the Sub-Antarctic Magellan region, however, suggest the possibility of great heterogeneity in community structure and population dynamics. Studies of the trophic structure and energy flow are essential in this context. The aim of this thesis is to increase the knowledge of the ecological role of benthic species to communities living in the sub-Antarctic Magellan region. The main objectives of this research are (i) to investigate the trophic ecology of conspicuous species and their ecological role in the marine benthic communities of the Magellan region, (ii) to describe the trophic structure of two shallow-water benthic community types in the Strait of Magellan in order to establish baseline descriptions of trophic relationships for community structure and function, and (iii) to estimate benthic secondary production in this sub-Antarctic region as a proxy for energy flow along latitudinal gradients. The main results indicate that both local/regional environmental conditions and biological features cause clear differences in the trophic structure and energy flow patterns. This research gives valuable insight into ecological functioning of marine benthic communities present in the sub-Antarctic Magellan region and offers useful information to build food web models.
... While the amount of biomass and production was clearly lower in the litter-excluded stream, the distribution of production along the trophic continuum was little affected. Several different hypotheses have been presented examining potential determinants of food chain length (Oksanen et al. 1981, Pimm 1988, Hairston and Hairston 1993. Energy flow may determine food chain length, because thermodynamic energy losses at each trophic transfer make available energy for a top trophic level vanishingly small (Oksanen et al. 1981). ...
... Energy flow may determine food chain length, because thermodynamic energy losses at each trophic transfer make available energy for a top trophic level vanishingly small (Oksanen et al. 1981). Alternatively, exogenous disturbance can keep food chains short, since top predators have less stable populations than basal species (Pimm 1988), although this idea is disputed on theoretical grounds (Sterner et al. 1997). Hairston and Hairston (1993) suggested that trophic structure is not controlled by the amount of energy at the base of the food web, but rather by the attributes of species within trophic levels. ...
... While the amount of biomass and production was clearly lower in the litter-excluded stream, the distribution of production along the trophic continuum was little affected. Several different hypotheses have been presented examining potential determinants of food chain length (Oksanen et al. 1981, Pimm 1988, Hairston and Hairston 1993. Energy flow may determine food chain length, because thermodynamic energy losses at each trophic transfer make available energy for a top trophic level vanishingly small (Oksanen et al. 1981). ...
... Energy flow may determine food chain length, because thermodynamic energy losses at each trophic transfer make available energy for a top trophic level vanishingly small (Oksanen et al. 1981). Alternatively, exogenous disturbance can keep food chains short, since top predators have less stable populations than basal species (Pimm 1988), although this idea is disputed on theoretical grounds (Sterner et al. 1997). Hairston and Hairston (1993) suggested that trophic structure is not controlled by the amount of energy at the base of the food web, but rather by the attributes of species within trophic levels. ...
Food webs based on flows of organic matter were developed for two small streams to examine food web response to a large reduction in detrital inputs. At the study site, Coweeta Hydrologic Laboratory in the southern Appalachians, leaf litter inputs and associated microbial assemblages are the main energy source for food webs in headwater streams. We eliminated leaf litter inputs to one stream using a net placed over the first 180 m of stream from its origin. Food webs based on flow of organic matter were developed for a reference stream and the litter-excluded stream for two months, July and December of year 1 of the litter exclusion, to examine effects of leaf litter exclusion on the trophic base of the food web, size distribution of flows, predator-prey interactions, and trophic structure. Flows (mg AFDM· m-2· d-1; AFDM = ash-free dry mass) were estimated using gut content analyses for detritus and prey items, coupled with secondary production estimates. We used a whole-stream 13C tracer method to estimate assimilation of bacteria by invertebrates. The food webs encompassed most (84-91%) of invertebrate secondary production, but
... [ 14 C]-bicarbonate measures the rates of autotrophy in both eukaryotic and prokaryotic systems (e.g., Wetzel & Likens, 1991;Pederson & Ekendahl, 1992). Assessing the rates of heterotrophic activity is also crucial to understanding the energetics of the system, and specifically how much carbon could be cycled through a 'microbial loop' before being utilized by higher trophic levels (e.g., Pimm, 1988;Lampert & Sømmer, 1997;Chesson et al., 2002;Naeem, 2002). [ 14 C]-leucine incorporations are a common technique in aquatic studies of heterotrophic microbial productivity because leucine is incorporated almost exclusively into proteins (e.g., Kirchman et al., 1985;Jørgensen, 1992;Kirchman, 1993;Touminen, 1995;Díaz-Raviña & Bååth, 1996). ...
... Despite widespread recognition of chemolithoautotrophic metabolism in a variety of habitats, from deep-sea hydrothermal vents to caves, it is still unclear how these microbial communities function in situ for most ecosystems, or how much potential there is for chemolithoautotrophy to support higher trophic levels. The rate of primary productivity, in particular, is a crucial driver of ecosystem dynamics that can affect the length and complexity of the food chain (e.g., Pimm, 1988;Lampert & Sømmer, 1997;Naeem, 2002). Ecosystems energetically dependent on chemolithoautotrophic production were first discovered over thirty years ago, but our understanding of energetic dynamics in these communities is still rudimentary. ...
Although ecosystems thriving in the absence of photosynthetic processes are no longer considered unique phenomena, we haveyet to understand how these ecosystems are energetically sustained via chemosynthesis. Ecosystem energetics were measuredin microbial mats from active sulfidic caves (Movile Cave, Romania; Frasassi Caves, Italy; Lower Kane Cave, Wyoming, USA; andCesspool Cave, Virginia, USA) using radiotracer techniques. We also estimated bacterial diversity using 16S rRNA sequences torelate the productivity measurements to the composition of the microbial communities. All of the microbial communities investigatedwere dominated by chemolithoautotrophic productivity, with the highest rates from Movile Cave at 281 g C/m2/yr. Heterotrophicproductivities were at least one order of magnitude less than autotrophy from all of the caves. We generated 414 new 16S rRNAgene sequences that represented 173 operational taxonomic units (OTUs) with 99% sequence similarity. Although 13% of theseOTUs were found in more than one cave, the compositions of each community were significantly different from each other (P≤0.001).Autotrophic productivity was positively correlated with overall species richness and with the number of bacterial OTUs affiliated withthe Epsilonproteobacteria, a group known for sulfur cycling and chemolithoautotrophy. Higher rates of autotrophy were also stronglypositively correlated to available metabolic energy sources, and specifically to dissolved sulfide concentrations. The relationship ofautotrophic productivity and heterotrophic cycling rates to bacterial species richness can significantly impact the diversity of highertrophic levels in chemolithoautotrophically-based cave ecosystems, with the systems possessing the highest productivity supportingabundant and diverse macro-invertebrate communities.
... Spiders, being predators, are less abundant than other arthropod taxa (Pimm, 1988), which may explain why very few bat species consume them in great quantities. While such dietary specialization may allow spider eating bats to reduce competition, it is also advantageous when the abundance of other resources, mainly flying insects, is lower due to adverse weather conditions (Burles et al., 2009), or during seasons of lower insect abundance. ...
Myotis emarginatus is one of the few bats known to feed mostly on spiders. In order to study the importance of this type of prey, we analysed the species’ diet in five colonies across the Iberian Peninsula using amplicon metabarcoding in order to describe its composition at the species level, and analyse its geographic variability within the peninsula. We identified 138 prey species, belonging to 11 different arthropod orders. Among them, 45 species of spiders were identified, mostly of the
orb-web building guild, as consumed by 82 out of 106 studied bats, corresponding to every colony and season sampled. Besides, lepidopterans and dipterans were also consumed in every colony.
Among the latter, the stable fly Stomoxys calcitrans was especially important in two of the colonies, showing that M. emarginatus can also opportunistically exploit different resources or foraging grounds, such as cattle sheds, which affects the composition of its diet also at ordinal level of prey.
... As such, high primary production supports higher abundances (and often diversity) of biota. How much productivity one trophic level passes on to the next ('trophic transfer efficiency') depends on the proportion consumed, assimilated during digestion, respired (that is, used as energy to move around, etc.) and converted into new growth -this is rarely more than a few percent for most food webs (Slobodkin 1960;Pimm 1988). As food chains in aquatic ecosystems tend to be relatively long (more than three trophic levels), small changes in transfer efficiency from one level to the next can result in significant variations in productivity at the top levels. ...
... As such, high primary production supports higher abundances (and often diversity) of biota. How much productivity one trophic level passes on to the next ('trophic transfer efficiency') depends on the proportion consumed, assimilated during digestion, respired (that is, used as energy to move around, etc.) and converted into new growth -this is rarely more than a few percent for most food webs (Slobodkin 1960;Pimm 1988). As food chains in aquatic ecosystems tend to be relatively long (more than three trophic levels), small changes in transfer efficiency from one level to the next can result in significant variations in productivity at the top levels. ...
... As such, high primary production supports higher abundances (and often diversity) of biota. How much productivity one trophic level passes on to the next ('trophic transfer efficiency') depends on the proportion consumed, assimilated during digestion, respired (that is, used as energy to move around, etc.) and converted into new growth -this is rarely more than a few percent for most food webs (Slobodkin 1960;Pimm 1988). As food chains in aquatic ecosystems tend to be relatively long (more than three trophic levels), small changes in transfer efficiency from one level to the next can result in significant variations in productivity at the top levels. . ...
... Tropical phytotelmata may also contain all stages in the life history of several copepods, crabs, and frogs. I set a steady input of 3 mg C d -1 of litter into a 40 ml phytotelm, based on literature data [24]. Assuming that bacteria must process the litter, and that mosquito larvae eat only protozoans, 7-15% of litter carbon is converted to mosquitoes, depending on assumptions about food web connections. ...
Multivorous food webs potentially connect secondary production of microorganisms to metazoan consumers. The actual amount of carbon flux from microorganisms to metazoans is dependent on assimilation efficiency, the length of food chains, the chemical and physical nature of available organic matter, connectivity, and retentiveness. Ruminant nutrition appears to be the most efficient in transferring organic carbon from a microbial food web to metazoans. Phytotelmata (small water bodies contained by plants) contain little-studied microbial food webs that support a metazoan community. Salt marshes, though productive, have major losses of carbon to microbial loops in sediments and additional losses in the detritus food web. In the more productive of the ocean systems, there may be a tradeoff for metazoan consumers between direct consumption of large phytoplankton and consumption of larger protozoans that are feeding on picophytoplankton. Low-productivity central ocean systems may be dominated by this latter food web structure in which the microbial food web is an inefficient intermediary between most of the primary production and metazoan consumers.
... The quantification of trophic transferences by size categories is, therefore, fundamental to establish the particular energy pathways and community efficiency in any system. Theoretically, it is assumed that when producers are too small to be effectively grazed by the most common zooplankton crustacea, small-sized herbivores such as protozoans and larval microcrustaceans are required to transfer energy toward higher trophic levels via carnivorous zooplankton (Capriulo and Ninivaggi, 1982;Pimm, 1988). Smaller consumers, moreover, seem able to utilize relatively larger food particles. ...
The grazing activity of nanozooplankton natural assemblages on phytoplankton was analysed in the polyhaline and euhaline zones of the estuary of Mundaka throughout the spring–summer–autumn period. Grazing experiments were conducted in situ using the dilution method. Incubations occurred within a relatively wide range of initial chlorophyll concentration (1–10 μg chl l−1), but saturated feeding kinetics were not observed in most experiments. The heterotrophic nanoplankton grazed on average between 43 and 51% (mean values from all dilutions data and the 3 more diluted data, respectively) of the phytoplankton stock in the polyhaline zone, and between 36 and 43% in the euhaline. The grazing impact on primary production averaged around 65% in both zones, but showed higher variability in the euhaline (0–223%) than in the polyhaline (15–117%). Herbivore pressure was found to be higher in polyhaline waters on average, but between-zone differences were not significant. The nanozooplankton herbivory was not clearly related to water temperature, nor to phytoplankton biomass (expresed as chlorophyll concentration), and the coupling between production and consumption was weak, being more unbalanced in the euhaline zone. Nanozooplankton grazing was sometimes found to cause phytoplankton decline, while at other times its impact was negligible. In addition, indirect evidence suggests that nanozooplankton grazing activity may be affected by predation pressure from mesozooplankton in the polyhaline zone. Seasonal patterns of phytoplankton exploitation by heterotrophic nanoplankton differed among saline zones, suggesting that the fate of phytogenic carbon in the estuary of Mundaka may be highly variable both spatially and seasonally.
... Food chains are short, with most of the routes in the web defining two level chains (Figs 2 and 3). Short food-webs are characteristic of resilient and benthic systems (Pimm & Lawton, 1977;Briand, 1983;May, 1986;Pimm, 1988;Pimm et al., 1991;Hairston & Hairston, 1993). ...
Energetic and dynamic constraints have been proposed as rival factors in determining food-web structure. Food-web length might be controlled either by the amount of energy entering the web (energetic constraints) or by time span between consecutive disturbances relative to time needed to build up a population (dynamic constraints). Dynamic constraints are identified with processes functioning at a regional scale such as climate, lithology and hydrogeology. Energetic constraints are related with processes operating both at a regional and a local scale. We studied the contribution of energetic constraints to food-web organization in two temporary saline lakes with similar dynamic constraints. Lakes were sampled fortnightly during two hydroperiods (1994/1995 and 1995/1996). Differences in energetic constraints between lakes result in divergent assemblages of primary producers. Consumer assemblages in both lakes, however, are similar in species composition although differ in total biomass and species abundances. Food-webs are short with a high proportion of omnivores. To simulate an increase in the energy input entering to these systems, an addition of nutrients (to a final concentration of 100 gl–1 P-PO4
3-) was done in mesocosms placed within the lakes in order to obtain an increase in the phytoplankton biomass. No significant response to nutrient enrichment was found in food-web structure (composition, density or biomass).
... The high redundancy in the Kromme Estuary suggests that this estuary would be better able to cope with perturbations, since it has the most parallel pathways at hand. Pimm (1988) pointed out that the time a unit of energy stays in the system can be related to its recovery from disturbance and the longer the transit time, the longer the recovery time. ...
Carbon flow networks of the Kromme, Swartkops and Sundays estuaries, situated on the south coast of South Africa, were analysed using ecological network analysis. A major difference between the three estuaries is the freshwater inflow regimes: The Kromme Estuary receives very little freshwater (annual mean 0.07 m−3 s−1), the Swartkops Estuary receives annually about 0.82 m−3 s−1 while the Sundays Estuary receives on average about 2.74 m−3 s−1 annually. Ecological network analysis revealed differences between most ecosystem attributes such as the cycling of carbon, trophic structure, the organisational and developmental status in terms of ascendency and redundancy, and regarding the contribution to and dependencies of compartments to and on one another in the network. Due to the lack of frequent freshwater inflow and consequently the renewal of the nutrient pool, the Kromme Estuary recycles most of its material and showed the highest detritivory/herbivory ratio (57:1), whereas the Sundays recycles the least proportion and had the lowest detritivory/herbivory ratio at 10:1. The Sundays Estuary, hitherto believed to be dominated by pelagic production, was found to rely more on the benthic biota in terms of carbon throughput as inferred from the contribution and dependency coefficients, than on pelagic communities. Due to the low rate of fresh water inflow into the Kromme Estuary, the absence of an axial salinity gradient, a comparatively high Finn Cycling Index of 40%, and the long water exchange time, this system appears to have developed into an “arm” of the sea. System level properties such as the A/C ratio, the Average Mutual Information index, and the food web connectance index, increase from the lowest values calculated for the Kromme Estuary, intermediate for the Swartkops Estuary, and highest for the Sundays Estuary, while the FCI followed an inverse trend between the three systems.
... First, the productivity of terrestrial and aquatic ecosystems is very low due to cold temperatures and nutrient limitation in these glaciated, granitic watersheds (Knapp et al. 2001a). Resource exploitation by nonnative predators is expected to be most severe under these conditions, a situation where the effects of competition are expected to be greatest (Pimm 1988, Holt et al. 1994. ...
Trophic linkages between terrestrial and aquatic ecosystems are increasingly recognized as important yet poorly known features of food webs. Here we describe research to understand the dynamics of lake food webs in relation to a native riparian amphibian and its interaction with introduced trout. The mountain yellow-legged frog Rana muscosa is endemic to alpine watersheds of the Sierra Nevada Mountains and the Transverse Ranges of California, but it has declined to a small fraction of its historical distribution and abundance. Although remaining frogs and introduced trout feed in different habitats of alpine lakes, our stable-isotope analyses clearly show that the same resource base of benthic invertebrates sustains their growth. During one period, insect emergence from naturally fishless lakes was nearly 20-fold higher compared to adjacent lakes with trout, showing that fish reduce availability of aquatic prey to amphibious and terrestrial consumers. Although trout cannot prey on adult frogs due to gape limitation, foraging post-metamorphic frogs are 10 times more abundant in the absence of trout, suggesting an important role for competition for prey by trout in highly unproductive alpine watersheds. Most Sierran lakes contain fish, and those that do not are usually small isolated ponds; in our study, these two lake types supported the lowest densities of post-metamorphic frogs, and these frogs were less reliant on local, benthic sources of productivity. Since Rana muscosa was formerly the most abundant vertebrate in the Sierra Nevada, the reduction in energy flow from lake benthos to this consumer due to fish introductions may have had negative consequences for its numerous terrestrial predators, many of which have also declined. We suggest that disruptions of trophic connections between aquatic and terrestrial food webs are an important but poorly understood consequence of fish introduction to many thousands of montane lakes and streams worldwide and may contribute to declines of native consumers in riparian habitats.
Floristic composition in Pinus cembroides Zucc. forest was studied under the approach of system elasticity and resilience, to evaluate the changes trend and to suggest better utilization practices. An analysis of six floristic inventories realized at different times was carried out. Two at a regional level which includes the meridional mountain ranges pinyon pine forest of San Luis Potosí, México and four at a local level, from La Amapola, San Luis Potosí, México. It was assumed that the floristic composition had been irreversible changed by the utilization practices. Proportion of species by life forms and rate of change in botanical composition were evaluated. The latter, transformed to rate of return, allowed to estimate the resilience of the forest. It was confirmed the stability of the pinyon pine forest within the observed interval, six years at the regional level and twelve at the local level. There was less than 10% variation among inventories in the number of species by life forms. Trees, at the local level, and forbs at the regional one, even within the stability of the pinyon pine forest, are moving towards other alternative state, while the opposite is happening for shrubs at both scales.
IntroductionFood Chains and Food WebsInteraction Strength in Food WebsImplications of Food webs and trophodynamics for Fish and Fisheries ScienceConclusions
AcknowledgementsReferences
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[formerly EXPERIENTIA:] The goal of this article is twofold: 1) It aims at providing an overview on some major results obtained from energy flow studies in individuals, populations, and communities, and 2) it will also focus on major mechanisms explaining community structures. The basis for any biological community to survive and establish a certain population density is on the one hand energy fixation by primary producers together with adequate nutrient supply and the transfer of energy between trophic levels (bottom-up effect). On the other hand, predator pressures may strongly control prey population densities one or more trophic levels below (top-down effect). Other interpopulation effects include competition, chemical interactions and evolutionary genetic processes, which further interact and result in the specific structuring of any community with respect to species composition and population sizes.
In the tropho-dynamic analysis of ecosystems the heuristic, discrete concept of trophic level has been replaced by the more realistic, continuous definition of trophic position. In ecological network analysis (ENA) the suite of matrix manipulations called canonical trophic aggregation (CTA) apportions each species’ feeding activity to a series of discrete trophic levels sensu Lindeman. The effective trophic position is computed as the sum of the fractions of trophic activity that each species performs at different trophic levels. In this paper we present an extension of the CTA that combines matrix manipulation and sensitivity analysis. Applying this “extended” CTA to an hypothetical network and to real ecosystems we show how trophic position can be computed taking into account the contribution of external inflows, making it scale-insensitive. Moreover “extended” CTA solves ambiguities related to trophic position in the presence of multiple non-living nodes, considering them as imports.
1. The importance of the recycling of organic matter for the overall carbon and nutrient flow in a food web, e.g., by the microbial loop has been recognized for pelagic and other ecosystems during the last decade. In contrast, analyses of the trophic food web structure conducted, e.g., by network analysis based on mass-balanced flow diagrams (i.e., computation of, e.g., trophic positions and transfer efficiencies, organismal composition of trophic levels) which greatly contribute to our understanding of the flow and cycling of matter in food webs, have not yet responded adequately to this fact by developing coherent techniques with which dead organic matter and its consumers could be considered in the models. 2. At present, dead organic matter (measured in units of carbon or nutrients) is either allocated to a fixed trophic position (between zero and one), or the trophic position of dead autochthonous material depends on the trophic position of the organisms which released it. This causes partially ambiguous and incon- sistent interpretations of key measures like trophic transfer efficiences and trophic positions and greatly hampers cross-system comparisons. 3. The present paper describes and compares four different definitions of the trophic position of dead autochthonous organic material which have either been newly invented or already used. Their impact on the resulting trophic positions of individual groups is illustrated using a food web model from the pelagic zone of Lake Constance. The present analysis evaluates the partially far reaching consequences of the definition chosen, and suggests to allocate all dead organic material to the 'zeroth' trophic level irrespectively of its origin (alloch- thonous or autochthonous), chemical composition and the commodity used to quantify the food web model (e.g., units of carbon or nutrients). By this means trophic positions and trophic transfer efficiencies get a clear and consistent ecological interpretation, while inconsistencies between analyses conducted in units of carbon or nutrients and some operational problems can be overcome and cross-system comparisons and empirical verification are facilitated.
Although the impact of acidification on planktonic grazer food webs has been extensively studied, little is known about microbial food webs either in the water column or in the sediments. Protozoon-bacterium interactions were investigated in a chronically acidified (acid mine drainage) portion of a lake in Virginia. We determined the distribution, abundance, apparent specific grazing rate, and growth rate of protozoa over a pH range of 3.6 to 6.5. Protozoan abundance was lower at the most acidified site, while abundance, in general, was high compared with other systems. Specific grazing rates were uncorrelated with pH and ranged between 0.02 and 0.23 h, values similar to those in unacidified systems. The protozoan community from an acidified station was not better adapted (P = 0.95) to low-pH conditions than a community from an unacidified site (multivariate analysis of variance on growth rates for each community incubated at pHs 4, 5, and 6). Both communities had significantly lower (P < 0.05) growth rates at pHs 4 and 5 than at pH 6. Reduced protozoan growth rates coupled with high grazing rates and relatively higher bacterial yields (ratio of bacterial-protozoan standing stock) at low pH indicate reduced net protozoan growth efficiency and a metabolic cost of acidification to the protozoan community. However, the presence of an abundant, neutrophilic protozoan community and high bacterial grazing rates indicates that acidification of Lake Anna has not inhibited the bacterium-protozoon link of the sediment microbial food web.
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