Density Of Feeders Research Articles

Prevalence of nematode infection and faecal egg counts in free-range laying hens: relations to housing and husbandry

1. Faecal samples from 19 commercial, 65 week old free-range egg laying flocks were examined to assess the prevalence and number of parasitic nematode eggs. Data were collected to characterise the housing, husbandry, behaviour and welfare of the flocks to examine possible relationships with the egg counts. 2. Eggs of at least one genus of nematode were present in the faeces of all 19 flocks. Heterakis eggs were detected in 17 (89%) flocks, Ascaridia in 16 (84%), Trichostrongylus in 9 (47%), and Syngamus in 6 (32%). Faecal egg counts (FEC) were greatest for Ascaridia and Heterakis. 3. For each nematode genus, there was no significant difference in FEC between organic (N = 9) and non-organic (N = 10) flocks, or between static (N = 8) and mobile (N = 11) flocks. 4. FEC were correlated with a range of housing, husbandry and management practices which varied between the nematode genus and included depth of the litter, percentage of hens using the range, and number of dead hens. Statistical analysis indicated relationships with FEC that included light intensity above the feeder, indoor and outdoor stocking density, fearfulness in the shed and on the range, distance to the nearest shelter, and swollen toes. 5. None of the FEC for any of the genera was correlated with weekly egg production or cumulative mortality. 6. Although nematode FEC were highly prevalent among the flocks, the overall lack of relation to other welfare and production measures suggests that these infections were not severe.

The Ecological Engineering Mode Design for the Purification of Miniature Landscape Lake

According to the requirement of water quality function of the miniature landscape lake, the ecological engineering mode has been used to search for the purification method of miniature landscape lake through rational design for size and density of filter feeders, plant-eating fish and aquatic higher plants. The predication results show that: The chub and bighead with the dosing density of 300 fix phosphorus 11.767 kg. The mussels with the dosing density of 0.15 fix phosphorus 1.731 kg. The phosphorus fixed by 70 grass carp and lotus is 0.192 kg and 1.5 kg. The removal of phosphorus is total 15.19 kg, which exceeds the annual phosphorus input of the lake. The prediction effect on ecological engineering mode design is ideal and it can be looked as an ideal method to purify miniature landscape lakes.

How are nematode communities affected during a conversion from conventional to organic farming in southern French vineyards?

The rate of conversion from conventional vineyards to organic farming practices is increasing. Organic farming improves some soil properties, although some organic practices have negative effects on soils. The objective of this work was to study the long-term effects of organic farming through the use of soil nematodes as bio-indicators of soil processes. Our experimentation was conducted in a commercial vineyard where plots belonged to two types of viticulture: conventional viticulture and organic viticulture (for 7, 11 and 17 years). The nematode community structure and nematode indices were determined. The main result was that organic practices increased soil nematode density. An increase in the available resources, as measured by a higher enrichment index (EI), led to an increase in the microbial feeder density and mainly opportunistic fungal-feeding nematodes. A greater density of plant-feeding nematodes was attributed to the presence of a grass cover. The functioning of the soil was shifted with the decomposition channel of the soil organic matter becoming more fungal than bacterial. Even though changes were observed in the nematode community structure following the conversion, the maturity index (MI), the plant-parasitic index (PPI) and the structure index (SI) remained constant. Consequently, the organic practices did not improve the soil food web length or complexity even though the biological activity, as measured by microbial biomass and total nematode density, increased.

Hunting management in relation to profitability aims: red-legged partridge hunting in central Spain

Game management is widely implemented in Spain, affecting more than 70 % of land cover. Management intensity may be linked to the financial aims of hunting estates, but no study of these aspects has been developed in Spain, where commercial hunting is common. Through interviews with game managers and field surveys, we quantified physical and economic traits, management techniques, and hunting methods in a sample of 59 small-game hunting estates located in south-central Spain (where red-legged partridge hunting has the highest socioeconomic importance in the country). We compared non-commercial estates (aimed for leisure, managed mainly by local hunting societies) and commercial estates (aimed at financial benefit); among the latter, we also assessed “intensive” estates (a special category of commercial estates licensed to release farm-reared partridges without temporal or numerical limits throughout the hunting season). Commercial estates had more intensive management, including more and larger partridge releases, higher density of supplementary feeders and more intensive predator control. Thus, any positive or negative effects on biodiversity of these management techniques would be higher in commercial than in non-commercial estates. Commercial estates also retained more natural vegetation, which may help to enhance the landscape and biodiversity value of farmland in central Spain. On the other hand, differences in management and hunting styles were most marked between intensive and other type of estates (both commercial and non-commercial); this indicates that intensive estates are qualitatively different from other small-game estates, both ecologically (hunting based on releases and driven shooting) and economically (higher inputs and outputs). It would be desirable to find ways to quantify the environmental or social costs and benefits of different management techniques, and integrate them in the economics of hunting estates.

Salmon farm impacts on muddy-sediment megabenthic assemblages on the west coast of Scotland

We assessed the impact of salmon farms on the megabenthos associated with muddy habitats using a novel drop-and-drift video camera approach. Megabenthic burrowers and sus- pension feeders were adversely affected by farm proximity, as indicated by modelled benthic flux of dry solids (DSFlux, g m �2 yr �1 ). The burrow-count threshold DSflux was 400, beyond which bur- row density declined rapidly. Suspension feeder densities were reduced by a factor of 4 in close proximity (DSFlux > 8000 g m -2 yr -1 ) to the salmon farms, but only where the sediment was rela- tively muddy. In terms of suspension feeders, threshold levels of DSFlux varied between sites, ranging from 12 to 665 g m -2 yr -1 . There was no evidence that vagile predator/scavengers were either attracted to, or repelled by, salmon farms. We conclude that burrowers and suspension feeders were relatively resilient to salmon farms in muddy, sea-loch habitats and that detectable im pacts did not exceed 100 m from the cage boundary.

The interannual variability of megafaunal assemblages in the Arctic deep sea: Preliminary results from the HAUSGARTEN observatory (79°N)

Although megafaunal organisms play an important role in deep benthic ecosystems and contribute significantly to benthic biomass in the Arctic little is known about their temporal dynamics. Here, we assessed the interannual dynamics of megafaunal organisms from the HAUSGARTEN observatory in the Fram Strait, an area where the effects of climatic forcing are particularly evident. We analysed three congruent camera transects taken in 2002, 2004 and 2007. Environmental parameters were measured in order to be able to put our faunal results into an environmental context. Our results indicate that although the densities of megafaunal species show different patterns over time, most exhibit an overall decrease between 2002 and 2007 and total megafaunal densities decreased regularly from 2002 to 2004 to 2007 (12.16±0.96 to 7.41±0.43 ind m −2). This concurs with a steady increase in bottom-water temperatures and a decrease in the total organic content and microbial biomass of surficial sediments at the same time period. Although suspension feeder densities also decreased, predator/scavenger and deposit feeder densities have declined to such an extent that suspension feeders accounted for almost 100% of the megafauna in 2007. It could thus be argued that the trophic diversity at the central HAUSGARTEN station (2500 m) has decreased. Temperature-related changes in the production of the surface layers may lead to changes in the quality and/or quantity of particles exported to the deep seafloor. The densities of deposit feeders (i.e. holothurians) peaked (1.14±0.13 ind m −2) in 2004, the year following the longest ice cover. These results indicate the importance of ice-related export of particles to the deep seafloor and highlight the need for time-series transects, especially in an era when productive marginal ice zones tend to disappear with the receding sea ice. Although there is a general consensus that the Arctic is in a transition towards a warmer state, only continued observation will allow us to assess if the interannual changes observed are a result of decadal cycles related to the Arctic and North Atlantic Oscillation or if they are indicators of long-term change.

Culturing Human Embryonic Stem Cells with Mouse Embryonic Fibroblast Feeder Cells: Figure 1.

INTRODUCTIONThe potential of human embryonic stem cells (hESCs) to differentiate into diverse cell types of all major tissue types has raised hope that hESCs can be used for novel cell-based therapies as well as fundamental studies of cell lineage differentiation. In order to support the growth of hESCs, mouse embryonic fibroblasts (MEFs), typically isolated from E13-E14 mouse embryos and between passages three and seven, are routinely used as feeder cells. Feeder density is a critical determinant of successful hESC culture. In the presence of too few feeder cells, hESCs may not maintain self-renewal and pluripotency properties; they may also fail to attach to feeder cells appropriately. At excessively high density, feeder cells may detach from the plate such that hESC colonies will be lost. Here we describe an efficient method for culturing and passaging hESCs by enzyme (collagenase) for culture on irradiated MEFs. The protocol can be used for routine hESC culture for basic research.

Garden bird feeding predicts the structure of urban avian assemblages

ABSTRACTHouseholds across the developed world cumulatively spend many millions of dollars annually on feeding garden birds. While beneficial effects on avian assemblages are frequently claimed, the relationships between levels of garden bird feeding and local avian populations are unknown. Using data from a large UK city, we show that both avian species richness and abundance vary across different socioeconomic neighbourhood types. We examined whether patterns in bird feeding could explain this variation. The density of bird feeding stations across the urban environment was strongly positively related to avian abundance, after controlling for differences in habitat availability. This effect was almost exclusively driven by the abundance of those species known to utilize garden feeding stations frequently. In contrast, the density of feeding stations had no effect on avian species richness. We also examined variation in the proportion of households in different communities that provide food for birds, a factor that is not correlated with feeder density. The prevalence of bird feeding across different neighbourhoods declined as socioeconomic deprivation increased, and increased with avian species richness and abundance. Our results suggest that the provision of supplementary food for birds by multiple landowners across a city can impact the status of urban bird populations. The potential for harnessing these actions for conservation needs to be explored.

Trophic structure and functioning in a eutrophic and poorly flushed lagoon in southwestern Taiwan

Tapong Bay, a eutrophic and poorly flushed tropical lagoon, supports intensive oyster culture. Using the Ecopath approach and network analysis, a mass-balanced trophic model was constructed to analyze the structure and matter flows within the food web. The lagoon model is comprised of 18 compartments with the highest trophic level of 3.2 for piscivorous fish. The high pedigree index (0.82) reveals the model to be of high quality. The most-prominent living compartment in terms of matter flow and biomass in the lagoon is cultured oysters and bivalves, respectively. The mixed trophic impacts indicate that phytoplankton and periphyton are the most-influential living compartments in the lagoon. Comparative analyses with the eutrophic and well-flushed Chiku Lagoon and non-eutrophic tropical lagoons show that high nutrient loadings might stimulate the growth and accumulation of phytoplankton and periphyton and therefore support high fishery yields. However, net primary production, total biomass, fishery yields per unit area, and mean transfer efficiency of Tapong Bay were remarkably lower than those of Chiku Lagoon. The lower transfer efficiency likely results from the low mortality of cultured oysters and invasive bivalves from predation or the lower density of benthic feeders constrained by the hypoxic bottom water as a result of poor flushing. This might therefore result in a great proportion of flows to detritus. However, the hypoxic bottom water might further reduce the recycling of the entering detritus back into the food web. In contrast to many estuaries and tropical lagoons, poor flushing of this eutrophic tropical lagoon might induce a shift from detritivory to herbivory in the food web.

Culture and Expansion of the Human Embryonic Stem Cell Line HS181, Evaluated in a Double-Color System

An approach of using RFP-transfected human foreskin fibroblasts (hFS-RFP) to support the growth of GFP expressing human embryonic stem cells (hES; HS181-GFP) is reported. The two-color system was applied to detect interactions between hFS and human embryonic stem cells (hES). After overnight culture, the hES cell colonies showed a behavior of "pushing away" the underlying feeder cells. This phenomenon occurred with both a low and high density of feeders. The density of the feeder cell layer, however, influenced the growth pattern of hES cell colonies. At a high feeder cell density, the hES colonies were more pointed and aligned with the direction of the fibroblasts, whereas less dense feeder layers allowed a more rounded and flat hES colony formation. Not surprisingly, a small fraction of mitotically inactivated feeder cells reattached after passage and remained viable in the cultures for up to four subsequent passages. The prospect of using the two-color system for detection of possible fusion events between hES cells and feeder cells was assessed by screening a large number of cell cultures for double RFP/EGFP expressing cells. The results indicate that fusion events are extremely rare (<10-6), or alternatively that after fusion the dual expression of both EGFP and RFP is not easily detected for other reasons. In summary, a two-color system allows analysis of colony formation and also helps to identify and follow the differentiation of cells.

Culture and expansion of the human embryonic stem cell line HS181, evaluated in a double-color system.

An approach of using RFP-transfected human foreskin fibroblasts (hFS-RFP) to support the growth of GFP expressing human embryonic stem cells (hES; HS181-GFP) is reported. The two-color system was applied to detect interactions between hFS and human embryonic stem cells (hES). After overnight culture, the hES cell colonies showed a behavior of "pushing away" the underlying feeder cells. This phenomenon occurred with both a low and high density of feeders. The density of the feeder cell layer, however, influenced the growth pattern of hES cell colonies. At a high feeder cell density, the hES colonies were more pointed and aligned with the direction of the fibroblasts, whereas less dense feeder layers allowed a more rounded and flat hES colony formation. Not surprisingly, a small fraction of mitotically inactivated feeder cells reattached after passage and remained viable in the cultures for up to four subsequent passages. The prospect of using the two-color system for detection of possible fusion events between hES cells and feeder cells was assessed by screening a large number of cell cultures for double RFP/EGFP expressing cells. The results indicate that fusion events are extremely rare (<10(-6)), or alternatively that after fusion the dual expression of both EGFP and RFP is not easily detected for other reasons. In summary, a two-color system allows analysis of colony formation and also helps to identify and follow the differentiation of cells.

Assessing Landowner Activities Related to Birds Across Rural-to-Urban Landscapes

Fluctuations of bird abundances in the Midwest region of the United States have been attributed to such factors as landscape change, habitat fragmentation, depredation, and supplemental feeding. However, no attempt has been made to estimate the collective role of landowner activities that may influence birds across a landscape. To investigate how landowners might influence birds when the majority (> 90%) of land is privately owned, we surveyed all 1694 private domestic landowners living on three breeding bird survey routes (approximately 120 km) that represent a continuum of rural-to-urban landscapes in Southeastern Michigan from October through December 2000. Our survey was designed to investigate (1) the proportion of landowners involved in bird feeding, providing bird houses, planting or maintaining vegetation for birds, gardening, landscaping, applying fertilizer, and applying pesticides or herbicides; (2) whether differences existed between urban, suburban, and rural landowner activities; and (3) whether landowners that carried out a given activity were sociodemographically different from those who did not. Of the 968 respondents (58.5% response rate), 912 (94%) carried out at least one of the activities on their land and the average landowner carried out 3.7 activities. A total of 65.6% fed birds, 45.7% provided bird houses, 54.6% planted or maintained vegetation for birds, 72.7% gardened, 72.3% landscaped, 49.3% applied fertilizer, and 25.2% applied pesticides or herbicides. Significant differences existed between the landscapes, with rural landowners having more bird houses and applying pesticides or herbicides in greater frequency. Similarly, urban landowners had a greater density of bird feeders and houses, but planted or maintained vegetation in the lowest frequency. Participation in activities varied by demographic factors, such as age, gender, and occupation. Scaling each activity to all landowners, including nonrespondents, across all landscapes indicates that between 14% and 82% of landowners may be engaged in a particular activity, with application of pesticides or herbicides having the least potential involvement (13.9%-55.4%) and gardening having the greatest potential involvement (40.1%-81.6%). Taken collectively, our results indicate that landowners are both intentionally and unintentionally engaged in a wide range of activities that are likely to influence bird populations.

FEEDER CELL DENSITY—A KEY PARAMETER IN HUMAN EMBRYONIC STEM CELL CULTURE

A key issue in human embryonic stem (ES) cell culture that has largely been ignored is the high degree of variability in the murine embryonic fibroblast (MEF) feeder cell density, which has been reported by different studies and protocols. Presumably, too low a feeder cell density would result in insufficient levels of secreted factors, extracellular matrix, and cellular contacts provided by the feeder cells for the maintenance of human ES cells in the undifferentiated state. Too high a feeder cell density, on the other hand, may result in a more rapid depletion of nutrients and oxygen within the in vitro culture milieu, as well as physically hinder the attachment and growth of ES colonies during serial passaging. Preliminary investigations by our group revealed that an elevated MEF cell density of 32,000 cells/cm2, above the recommended value of 20,000 cells/cm2, appeared to be highly detrimental to the attachment and growth of serially passaged ES colonies of the H9 line (WiCell Research Institute Inc., Wilmington, MA, USA). At the edge of ES colonies that have attached to the higher density feeder layer (32,000 cells/cm2), the ES cells appear to stack up to form a "bulge." This was not observed under the recommended feeder cell density of 20,000 cells/cm2. By contrast, other established ES cell lines are routinely propagated at much higher feeder densities of 60,000 to 70,000 cells/cm2. This report briefly discusses the issue of MEF feeder cell density in relation to our preliminary observations, and the results of other studies.

Preliminary studies on the role of protozoa in the food web of Donghu Lake

Plankton from Station I of Donghu Lake, an eutrophic lake, was divided into three groups (2–32 μm, 32–112 μm and >112 μm) by filtering the water sample through 2, 32, 112 μm pores. It was supposed that the 2–32 μm Protozoa (group 1) was fed on by the 32–112 μm Protozoa and small rotifers (group 2) and >112 μm large rotifers, cladocerans and copepods (group 3). The feeding rate of zooplankton in situ was estimated by counting the protozoan individuals and also by the14C-NaHCO3 method. The P/B ratio of the small Protozoa (group 1) was 2.9 for 6 h and 1.2 for 24 h. The feeding rate of the 32–112 μm zooplankton on small Protozoa (2–32 μm) was about 2/3 the total feeding rate of zooplankton, and that of >112 μm zooplankton on the 2–32 μm Protozoa was 1/3 of the total feeding rate. The lower the density of feeders, the higher were the feeding rates. The daily production of the 2–32 μm protozoans was 1.559 mg/L, which equaled to 25% of the daily food consumption of other zooplankton. Isotope experiments showed result similar to that from the above direct counting method.

Cavity-dwelling suspension feeders in coral reefs - a new link in reef trophodynamics

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 188:105-116 (1999) - doi:10.3354/meps188105 Cavity-dwelling suspension feeders in coral reefs--a new link in reef trophodynamics Claudio Richter*, Mark Wunsch Zentrum für Marine Tropenökologie, Fahrenheitstr. 1, 28359 Bremen, Germany *E-mail: crichter@uni-bremen.de ABSTRACT: The small-scale distributions of chlorophyll a (chl a), pheopigments, oxygen and currents were determined in horizontal sections between coral reef cavities and benthic boundary layer waters (BBL) to estimate rates of grazing and respiration by cryptic cavity-dwelling (coelobite) suspension feeders. We investigated 0.5 to 5 m long and 0.1 to 1 m wide cavities in fringing reefs on the western coast of the Gulf of Aqaba (Red Sea), between 2 and 16 m depth. Within cavities net currents averaged 0.9 cm s-1, or 22% of the current speed measured in BBL ~2 m away from the reef. In spite of rapid flushing of cavity waters within a few minutes, we encountered significant chl a and oxygen depletions relative to BBL, particularly under oligotrophic conditions. Chl a depletions amounted, on average, to 0.10 ± 0.03 mg m-3 (median ± median absolute deviation [MAD]) or 54% (max. 86%) of BBL values and showed a positive relation to coelobite suspension feeder densities. Pheopigments, by contrast, remained remarkably constant, indicating selective grazing of the mainly picoplankton-sized food. Oxygen depletions were weak and mainly related to flushing. In sack-shaped cavities they amounted to 13.6 ± 6.1 mmol m-3 or 3 to 9% of BBL concentrations. Analyses of water flow and chl a distributions show that under oligotrophic summer conditions 0.7 g C m-2 d-1 of phytoplankton disappears within the upper 1 m of cavernous reef framework. This conservative estimate is about 1 order of magnitude higher than grazing rates of coral-dominated communities on the exposed reef, rendering cryptofauna suspension feeding an important and new pathway of extrinsic organic matter into coral reefs. KEY WORDS: Cavities · Crevices · Cryptofauna · Coelobites · Phytoplankton · Grazing · Respiration · Coral reefs Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 188. Publication date: November 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

DISTURBANCE OF THE MARINE BENTHIC HABITAT BY COMMERCIAL FISHING: IMPACTS AT THE SCALE OF THE FISHERY

Commercial fishing is one of the most important human impacts on the marine benthic environment. One such impact is through disturbance to benthic habitats as fishing gear (trawls and dredges) are dragged across the seafloor. While the direct effects of such an impact on benthic communities appear obvious, the magnitude of the effects has been very difficult to evaluate. Experimental fishing-disturbance studies have demonstrated changes in small areas; however, the broader scale implications attributing these changes to fishing impacts are based on long-term data and have been considered equivocal. By testing a series of a priori predictions derived from the literature (mainly results of small-scale experiments), we attempted to identify changes in benthic communities at the regional scale that could be attributed to commercial fishing. Samples along a putative gradient of fishing pressure were collected from 18 sites in the Hauraki Gulf, New Zealand. These sites varied in water depth from ∼17 to 35 m and in sediment characteristics from ∼1 to 48% mud and from 3 to 8.5 μg chlorophyll a/cm3. Video transects were used for counting large epifauna and grab/suction dredge and core sampling were used for collecting macrofauna. After accounting for the effects of location and sediment characteristics, 15–20% of the variability in the macrofauna community composition sampled in the cores and grab/suction dredge samples was attributed to fishing. With decreasing fishing pressure we observed increases in the density of echinoderms, long-lived surface dwellers, total number of species and individuals, and the Shannon-Weiner diversity index. In addition, there were decreases in the density of deposit feeders, small opportunists, and the ratio of small to large individuals of the infaunal heart urchin, Echinocardium australe. The effects of fishing on the larger macrofauna collected from the grab/suction dredge samples were not as clear. However, changes in the predicted direction in epifaunal density and the total number of individuals were demonstrated. As predicted, decreased fishing pressure significantly increased the density of large epifauna observed in video transects. Our data provide evidence of broad-scale changes in benthic communities that can be directly related to fishing. As these changes were identifiable over broad spatial scales they are likely to have important ramifications for ecosystem management and the development of sustainable fisheries.

Aquatic arthropod communities in Nepenthes pitchers: the role of niche differentiation, aggregation, predation and competition in community organization.

The structure and organization of aquatic arthropod communities in Nepenthes ampullaria pitchers were studied at two sites (M in Malacca and K in Kuching) in Malaysia. The communities consisted mainly of aquatic dipteran larvae. Community M was dominated by a filter feeder, Tripteroides tenax, which reached a high density despite a strongly aggregated distribution. Community K had five trophic groups: carrion feeders, filter feeders, detritus feeders, nipping predators and hooking predators, each including multiple species. The summed density of filter feeders in Community K remained much below the level attained by filter feeders in Community M. Niche differentiation within each trophic group with regard to pitcher age and feeding behaviour was not sufficient to allow species coexistence through niche separation alone. Aggregated distributions directly reduced interspecific encounters. Nevertheless, species belonging to the same trophic group commonly shared the same pitcher, because of high occurrence probabilities of dominant species and positive associations between some taxa (due mainly to similar occupancies by pitcher age). Predator coexistence in Community K may have been facilitated by self-limitation of the large predators through intraspecific cannibalism strengthened by aggregation. Prey coexistence, on the other hand, may have relied more on population suppression by predation, especially the selective removal of old instar Tripteroides.

Effect of Water and Nitrogen, and Grazing on Nematodes in a Shortgrass Prairie

Effect of Water and Nitrogen, and Grazing on Nematodes in a Shortgrass Prairie

Production of filter-feeding Trichoptera in an impounded and a free-flowing river

Production was estimated (size frequency method) for five species of Hydropsychidae and two species of Philopotamidae at two sites on the impounded North Anna River and two sites on the free-flowing South Anna River. Total production was highest (3250.0 g dry weight (DW)∙ha−1∙year−1 at the site immediately below the dam. At the other sites total production ranged from 94.0 to 515.1 g DW∙ha−1∙year−1. An attempt was made to determine the influence of various factors on production. From an analysis of the trophic dynamics of production, seston energetics, and rates of consumption we conclude that the zooplankton released from the reservoir greatly enriches the seston in a narrow size range (105–864 μm) that corresponds to the size of the zooplankton released from the reservoir and the capture net mesh size of the hydropsychids. The extremely high density of filter feeders below the dam reduces the food quality of the seston and limits production downstream. Ecological interactions also were found to influence production, requiring detailed knowledge of the biology of individual species to understand the dynamics of a system.