Function Of Food Concentration Research Articles

Warmer temperature increases toxicokinetic elimination of PCBs and PBDEs in Northern leopard frog larvae (Lithobates pipiens).

We studied the temperature dependence of accumulation and elimination of two polychlorinated biphenyls (PCBs; PCB-70 and PCB-126) and a commercial mixture of congeners of polybrominated diphenyl ethers (PBDEs; DE-71™)) in Northern leopard frog (Lithobates pipiens) tadpoles. We reared tadpoles at 18, 23, or 27 °C for 5.3 or up to 13.6 weeks (longer at cooler temperature where development is slower) on diets containing the toxicants, each at several different toxicant concentrations, and compared tissue concentrations as a function of food concentration and rearing temperature. Following > 1 month of accumulation, tissue concentrations of all three toxicants in exposed tadpoles were linearly related to dietary concentrations as expected for first order kinetics, with no significant effect of rearing temperature.We also raised free-swimming L. pipiens tadpoles for 14 days on foods containing either toxicant at 18 or 27 °C during an accumulation phase, and then during depuration (declining toxicant) phase of 14 days we provided food without toxicants and measured the decline of toxicants in tadpole tissue. All the congeners were eliminated faster at warmer rearing temperature, as expected. Using Arrhenius' equation, we calculated that the apparent activation energy for elimination of both PCB congeners by tadpoles was 1.21eV (95% confidence interval 0.6-1.8eV). We discuss how this value was within the range of estimates for metabolic reactions generally (range 0.2 - 1.2eV), which might include metabolic pathways for biotransformation and elimination of PCBs. Furthermore, we discuss how the lack of an effect of rearing temperature on tadpole near-steady-state tissue residue levels suggests that faster elimination at the warmer temperature was balanced by faster uptake, which is plausible considering the similar temperature sensitivities (i.e., activation energies) of all these processes. Although interactions between toxicants and temperature can be complex and likely toxicant-dependent, it is plausible that patterns observed in tadpoles might apply to other aquatic organisms. Published data on depuration in 11 fish species eliminating 8 other organic toxicants indicated that they also had similar apparent activation energy for elimination (0.82±0.12eV; 95% confidence interval 0.56 - 1.08eV), even though none of those studied toxicants were PCBs or PBDEs. Additional research on toxicant-temperature interactions can help improve our ability to predict toxicant bioaccumulation in warming climate scenarios.

Modeling of egg production by Temora longicornis from the southern Baltic Sea including salinity

Abstract The paper presents modeling of egg production (Egg — no. of eggs female−1 d−1) by Temora longicornis in the changing environmental conditions of the southern Baltic Sea (Gdańsk Deep). It is hypothesized that the food-saturated rate of egg matter production is equivalent to the specific growth rate of copepods. Based on the findings from the south-western Baltic Sea, Egg of T. longicornis is evaluated as a function of food concentration, temperature and salinity over a wide range of these parameters. Subsequently, the rate of reproduction during the seasons in the Gulf of Gdańsk is determined. According to our calculations, values of Egg reach ca 11 eggs per day in April and decline strongly in June-July, while the second smaller peak in reproduction occurs in September, ca 8 eggs per day. Our results suggest that egg production rates of T. longicornis depend not only on food concentration and temperature, but also on salinity, which is a masking factor in the Baltic Sea.

Diet restriction and life history trade‐offs in short‐ and long‐lived species of Daphnia

The life-extending effects of diet restriction are well documented. One evolutionary model that accounts for this widespread conservation is the resource allocation model, where the selected individuals are those that can delay reproduction during periods of resource limitation. In this study, we use closely related species of a model organism, Daphnia, with widely divergent lifespans to address the relationship between diet restriction and longevity and assess whether the relationships are owing to trade-offs between reproductive and somatic investment. Specifically, we conducted a common garden experiment and constructed reaction norms for lifespan, fecundity, and body size as a function of food concentration. Our study provides evidence that the short-lived species in our study, D. pulex, shows the classically observed relationship of enhanced lifespan in response to reduced diet intake, but does not divert resources to somatic maintenance at the expense of reproduction during chronic diet restriction. In contrast, we find no evidence that the long-lived species in our study, D. pulicaria, gains any life-extending effects through diet restriction. Combined, our results provide evidence that the resource allocation model is not sufficient to explain the evolution of diet-mediated lifespan plasticity.

Feeding and growth kinetics of the planktotrophic larvae of the spionid polychaete Polydora ciliata (Johnston)

We studied the effect of food concentration on the feeding and growth rates of different larval developmental stages of the spionid polychaete Polydora ciliata. We estimated larval feeding rates as a function of food abundance by incubation experiments with two different preys, presented separately, the cryptophyte Rhodomonas salina (ESD = 9.7 µm) and the diatom T. weissflogii (ESD = 12.9 µm). Additionally, we determined larval growth rates and gross growth efficiencies (GGE) as a function of R. salina concentration. P. ciliata larvae exhibited a type II functional response. Clearance rates decreased continuously with increasing food concentration, and ingestion rates increased up to a food saturation concentration above which ingestion remained fairly constant. The food concentration at which feeding became saturated varied depending on the food type, from ca. 2 µg C mL − 1 when feeding on T. weissflogii to ca. 5 µg C mL − 1 when feeding on R . salina. The maximum carbon specific ingestion rates were very similar for both prey types and decreased with increasing larval size/age, from 0.67 d − 1 for early larvae to 0.45 d − 1 for late stage larvae. Growth rates as a function of food concentration ( R. salina) followed a saturation curve; the maximum specific growth rate decreased slightly during larval development from 0.22 to 0.17 d − 1 . Maximum growth rates were reached at food concentrations ranging from 2.5 to 1.4 µg C mL − 1 depending on larval size. The GGE, estimated as the slope of the regression equations relating specific growth rates versus specific ingestion rates, were 0.29 and 0.16 for early and intermediate larvae, respectively. The GGE, calculated specifically for each food level, decreased as the food concentration increased, from 0.53 to 0.33 for early larvae and from 0.27 to 0.20 for intermediate larval stages. From an ecological perspective, we suggest that there is a trade-off between larval feeding/growth kinetics and larval dispersal. Natural selection may favor that some meroplanktonic larvae, such as P. ciliata, present low filtration efficiency and low growth rates despite inhabiting environments with high food availability. This larval performance allows a planktonic development sufficiently long to ensure efficient larval dispersion.

Appendicularian ecophysiology. II. Modeling nutrition, metabolism, growth and reproduction of the appendicularian Oikopleura dioica

A model has been developed to simulate the growth of an individual appendicularian ( Oikopleura dioica) from egg to spawning. This model uses a new set of experimental data presented in a companion paper in this volume and estimates growth rates and generation times as well as clearance rates, house and fecal pellet production and reproductive capacity at different temperatures and food concentrations. According to the model outputs, the weight of a single house represents 11.5% of the individual's total weight, a lower value than previously estimated. The relative weight of one fecal pellet varies as a function of food concentration. The model also confirms that the minimum food concentration for growth is about 20–30 µg C l − 1 and that growth is maximal for a 100 µg C l − 1 feeding concentration. The limits of the growth optimum in relation to food concentration and temperature can be considered as a first description of the fundamental ecological niche of appendicularians. This model can be used both for predicting (1) the impact of in situ observed populations on the pico- and nanoseston and (2) the production of large aggregates. These two pieces of information are often needed for large-scale biogeochemical models.

Prorocentrum minimum(clone Exuv) is nutritionally insufficient, but not toxic to the copepod Acartia tonsa

This study tested whether the dinoflagellate Prorocentrum minimum is nutritionally insufficient or toxic to the copepod Acartia tonsa. Experiments were carried out with adult female A. tonsa and the P. minimum clone Exuv, both isolated from Long Island Sound. Initially, the functional and numerical responses of A. tonsa feeding on exponentially growing P. minimum cells were characterized. These experiments revealed that A. tonsa readily ingested P. minimum cells, up to the equivalent of 200% of body carbon day −1, but egg production was relatively low, with a maximum egg production rate of 22% of body carbon day −1. Hence, the egg production efficiency (egg carbon produced versus cell carbon ingested) was low (10%). In a separate experiment, ingestion and egg production rates were measured as a function of food concentration with cells in different growth stages (early-exponential, late-exponential/early-stationary, and late-stationary growth phase) to simulate conditions during a bloom. There was no indication that cells in the stationary phase resulted in lower ingestion or egg production rates relative to actively growing cells. Egg hatching success remained high (>80%) and independent of the cell growth phase. In a third experiment specifically designed to test the hypothesis that P. minimum is toxic, ingestion, egg production and egg hatching success were measured when females were fed mixtures of P. minimum and the diatom Thalassiosira weissflogii, but in which total food concentration was held constant and the proportion of P. minimum in the mixed diet varied. A. tonsa readily ingested P. minimum when it was offered in the mixed diet, with no detrimental effects on egg production or egg hatching observed. Supplementing P. minimum with T. weissflogii increased both the egg production rate and the egg production efficiency. It is concluded that P. minimum is nutritionally insufficient, but not toxic to A. tonsa. Finally, it is estimated that in the field grazing by A. tonsa is approximately equivalent to 30% of the maximum daily growth rate of P. minimum. Hence, copepod grazing cannot be ignored in field and modeling studies of the population dynamics of P. minimum.

Growth and development of copepodite stages of Pseudocalanus spp.

Quantitative expressions are presented describing the effects of temperature and food concentration on the growth and development of the copepodite stages of Pseudocalanus spp. The calculations were made on the basis of experimental data from the literature for two geographically separate populations of Pseudocalanus from Puget Sound (Washington, USA) and from the southern North Sea. Relationships were obtained between the growth parameters for Pseudocalanus sp. from Puget Sound and temperature in the 8–15.5 � C range and food concentrations from 10 mg Cm � 3 to excess, as well as for Pseudocalanus elongatus from the southern North Sea at high food concentrations and in the 4–15 � C temperature range. Also computed was the total development time of P. elongatus for the final four copepodid stages as a function of food concentration from 50 mg Cm � 3 to excess and temperature from 5 to 20 � C. Empirical models computed here may be used

Response thresholds to recruitment signals and the regulation of foraging intensity in the ant Myrmica sabuleti (Hymenoptera, Formicidae)

The optimal foraging theory predicts that colonies of social insects must be able to adjust the intensity of their foraging behaviour as a function of the quality of the food discovered. Here, the mechanisms allowing the regulation of recruitment as a function of food concentration in the ant Myrmica sabuleti were analyzed. Although the total number of foragers engaged in food collection during recruitments increased with increasing concentration of sucrose solutions (0.1 vs. 1 M), neither the proportion of recruiting scouts nor the invitation behaviour performed by the scouts in the nest can explain this relationship. Foragers trail more when coming back from a 1 M than from a 0.1 M sucrose solution. However, this alone cannot explain the collective patterns observed since the mean numbers of workers leaving the nest after the entry of a scout coming back from either 0.1 or 1 M sources were not significantly different. We suggest that a spatial distribution of the foragers in the nest as a function of their motivational state could be part of the regulation process. The ants located near the nest entrance would respond to both low and high trail pheromone signals, but those located deeper in the nest would respond only to high level signals, resulting in higher recruitment rate towards richer sources.

Growth and grazing by the thecate heterotrophic dinoflagellate Diplopsalis lenticula (Diplopsalidaceae, Dinophyceae)

The thecate heterotrophic dinoflagellate Diplopsalis lenticula Bergh was shown to feed on a wide range of phytoplankton of different size and taxonomic groups. Growth and ingestion rates of D. lenricula feeding on the diatom Ditylum brightwellii (West) Grunow were measured as a function of food concentration. Growth rate increased with food concentration until it reached saturation at c. 300 D. brightwellii cells ml−1. Maximum specific growth rate was 0.25 d−1 at a food concentration of 500 cells ml−1. A prey concentration as low as 30 cells ml−1 supported growth. Ingestion and clearance rates were estimated by two different methods based on estimates of prey loss rate and on counts of digested food particles. Ingestion rate increased with increasing food concentration up to a maximum rate of 1 or 0.2 prey dinoflagellate−1 h−1, depending on which of the two methods of estimation was used. Clearance rate decreased with increasing prey concentration. Maximum clearance rates at low food concentration were 2.7 and 1.2 μl dinoflagellate−1 h−1, corresponding to volume-specific clearance rates of 1.5 × 105 and 6.4 × 104 h−1, respectively.

Growth rate of the marine planktonic ciliate Strombidinopsis cheshiri Snyder and Ohman as a function of food concentration and interclonal variability

A clonal culture of the ciliate Strombidinopsis cheshiri Snyder and Ohman was established from British Columbian coastal waters. Using the solitary 4 μm diatom Thalassiosim pseudonana (Hustedt) Hasle and Heimdal as food, a numerical response was obtained by keeping the ciliates in semi-continuous culture, measuring specific growth rates at different prey concentrations, and fitting the data to a rectangular hyperbolic function; this provided growth and mortality rates. From the experiments four pieces of information were obtained for S. cheshiri: 1) the threshold concentration (i.e., the prey concentration where ciliate growth = 0) was ~ 10 3· ml −1 (~6 ng C · ml −1); 2) the major increase in growth rate occurred between 10 3–10 4 prey · ml −1 (~ 6–60 ng C · ml −1); 3) the maximum growth rate was μ = 0.985 (~ 1.4 divisions · day −1); and 4) the ciliate was capable of selfing conjugation. The growth rate data were, however, variable due to sub-clonal differences (i.e., clones secondarily isolated from the original clone). Data obtained from examining cell isolates suggested that the sub-clonal differences were caused by clonal ageing and selfing conjugation. Consequently, abnormally low growth rates were assumed to be due to ciliates with a high mutational load; outliers were removed and not included in the final numerical response. This is the first observation of selfing conjugation in oligotrichs and one of only a few observations of clonal ageing for these ciliates. The results suggest that 1) this genus may be useful for future work on oligotrich mating and 2) older cultures of these ciliates should be used with caution when estimating ecological parameters.

A biochemical index of duration of the molt cycle for planktonic Crustacea based on the chitin‐degrading enzyme, chitobiase

The activity of chitobiase over an entire molt cycle was measured in Daphnia magna; it increased by 5‐fold from intermolt to premolt (when animals are in apolysis). Duration of the entire molt cycle increased about 3‐fold with a decrease in temperature from 25 to 6°C, but increased by <2‐fold over an 80‐fold difference in food concentration. There was a strong (r2 = 0.95) linear relationship between chitobiase activity and duration of the molt cycle, as modulated by food concentration, in asynchronous populations of D. magna. The relationship between chitobiase activity and duration of the molt cycle, as modulated by temperature, was also highly significant (r2 = 0.77) but nonlinear. The relationship between chitobiase activity and temperature is also nonlinear (r2 = 0.67). Asignificant linear relationship between chitobiase activity and duration of the molt cycle was also found for a natural population of Daphnia rosea (r2 = 0.88). Regressions of enzyme activity with body size and glucosamine content for three species of Daphnia indicate that differences exist between species. Chitobiase activity is an index of the proportion of animals in apolysis in a population. Because this proportion changes as a function of food concentration, but apparently not as a function of temperature, chitobiase activity is a measure of the duration of the molt cycle as limited by food concentration.

Observations of the free‐swimming behavior of Acartia tonsa: Effects of food concentration and turbulent water motion

The free‐swimming behavior of the calanoid copepod Acartia tonsa is described as a function of food concentration and quantified turbulence.In still water, Acartia spent most of its time feeding. Time allocated to feeding bouts did not change much as a function of food concentration (from 98% to 81%). Functional response to food was mainly determined by the duration of feeding bouts and the proportion of time spent in them. Lengthy feeding bouts might be involved with the actual capture and ingestion of food, while brief feeding bouts might be involved in the search for an optimum food density and the discrimination of food quality.Turbulence did not affect the amount of time allocated to feeding bouts but induced a significant shift to bouts of shorter duration at low food concentration. Computed encounter rates were 2.5 times higher in the presence of turbulence and indicated that turbulence intensity might have been enough to increase realized food concentrations to levels comparable to satiation at some of the low food concentrations tested.

Aspects of feeding, growth and stage development by trochophora larvae of the boreal polychaete Mediomastus fragile (Rasmussen) (Capitellidae)

Planktotrophic larvae of the boreal capitellid polychaete Mediomastus fragile (Rasmussen) were hatched and reared to metamorphosis. Larvae were fed Isochrysis galbana and grazing rate, growth and developmental stage were recorded as a function of food concentration, 0–1350 μgC·1 −1. The larvae exhibited delayed stage shifts and reduced growth rates at low food concentrations, <150 μgC·1 −1. Maximum specific growth rate and the maintenance energy requirement were notably low, indicating adaptation to low in situ food concentrations. Larvae were able to capture and ingest particles in the size spectrum between 2 and 10 μm. The optimal particle size was 7 μm. The larvae enter the plankton in the early spring, when the phytoplankton size spectrum is typically dominated by large algal cells, exceeding the size for efficient uptake. The physical limitations for particle capture are therefore a potential limit for grazing. The ability to delay larval development is an advantage for a planktotrophic larva functioning as a growing dispersive organism.

Type-3 functional response in limnetic suspension-feeders, as demonstrated by in situ grazing rates

Field-measured grazing rates (ml/animal/d) of cladocerans (mostly daphniids) and diaptomids were assembled from various published studies and plotted as a function of corresponding phytoplankton concentration (µg l−1 f.w.). Filtering rates of both zooplankton groups initially increased with seston concentration until maximal grazing rates were observed at approximately 4 × 102 and 1 × 102 µg l−1 for cladocerans and copepods, respectively; at higher algal concentrations, filtering rates of both declined as a function of food concentration. The shape of these curves are most consistent with Holling's (1966) Type 3 functional response.

Feeding, assimilation, and growth of mud snail larvae, Nassarius obsoleyus (Say), on three different algal diets

Nassarius obsoletus (Say) veliger larvae were fed three different phytoplankton diets in the laboratory: Isochrysis galbana Parke, Thalassiosira pseudonana (Hust.) Hasle & Heimdal, and Dunaliella tertiolecta Butcher. The relationship between growth rate and ability of the larvae to ingest and assimilate the different algae was investigated. To properly design the assimilation experiments, certain basic aspects of the feeding biology of the gastropod larvae were studied: the relationship between container size and feeding rate, light level and feeding rate, rate of gut evacuation in the presence and absence of food, and filtration and ingestion rates as a function of food concentration. Growth rates, ingestion rates, and efficiencies of carbon retention varied with the algal species provided, although relative growth could not be predicted from measurements of relative rates of carbon uptake from the different phytoplankton species. Larval growth rates are probably determined primarily by the abilities of the different algal species used in our experiments to provide necessary micro-nutrients. Retention efficiencies (carbon retained/carbon ingested) were low, ranging between ≈9 and 17%. Estimates of maximum assimilation efficiencies for young Nassarius obsoletus veligers are also much lower than most values reported for other Zooplankton.

Kinetics of Food Utilization by Oysters

ABSTRACT OYSTERS were grown in raceways for 121 days. Each raceway received water at a different combination of flow rate and food concentration. The weight growth data indicate that, for a given set of physical parameters, food concentration controls the growth rate. Using a chemical reaction model the rate of food uptake and the rate of growth were determined as a function of food concentration. These rates were used to predict conversion (ratio of growth to food) as a function space time (ratio of number of animals to flow rate).

Experimental studies on the transfer of 65Zn in high concentration by euphausiids

The uptake and elimination of 65Zn by Euphausia pacifica, in ‘clean’ sea water and in several concentrations of radioactive phytoplankton food, have been measured at 10 °C. Measurement was done on time schedules to simulate those which vertically-migrating euphausiids would spend in and out of a hypothetical 65Zn pool at the sea surface at different seasons of the year in temperate latitudes. From a knowledge of the total 65Zn body burdens reached at any time t, and of the mechanisms and rates of loss of 65Zn in radioactive and non-radioactive water, transfer of 65Zn via euphausiids from the ‘hot’ surface pool to non-radioactive water below may be assessed. With inital concentrations of 25μ Ci 65Zn/l, equilibrium body burdens were achieved in ‘clean’ sea water in about four days under all time schedules. The level of equilibrium body burden was a function of time schedule (time spent in the radioactive solution). In radioactive food, equilibrium body burdens were not reached in five days. Below about 10 5 cells/ml, uptake through food was a function of food concentration, but was not apparently affected by food concentrations above 10 5 cells/ml. When uptake was from ‘clean’ sea water, elimination was by molting of the animal's chitinous exoskeleton and by exchange with non-radioactive water. When uptake was from labelled food, elimination was from fecal pellet deposition as well as molting and exchange. Molting, exchange, and fecal pellet deposition represented different percentage losses from total body burden, depending largely upon the time the animal spent in and out of 65Zn and the source of 65Zn (water or food). Summations of these losses have been used to estimate transfer of 65Zn by euphausiids from a ‘hot’ surface pool to waters below the pool.