Low Food Levels Research Articles

Strategies of phenotypic low‐food adaptation in Daphnia: Filter screens, mesh sizes, and appendage beat rates

Daphnia collects more food at low particle concentrations by increasing its maximum filtering rate either by enlarging the area of its filter screens or by increasing its appendage beat rate (ABR). Various species of Daphnia grown at low levels of food phenotypically enlarge their filter screens. Models of the flow across a filter predict that the energy required to obtain a certain increase in filtering rate is a linear function of the screen area but increases proportionally to the square of ABR. A daphniid should be able to increase its filtering rate without expending more energy if it enlarges the filter and sirnultaneously reduces ABR. To test the model predictions, we measured morphometric parameters (areas, OF en space, intersetular distances) of the filters and ABR for Daphnia adapted to high food and to low food. Daphniids adapted to low food not only have larger filter screens, they also have finer meshes. In Daphnia adapted to low food, mean ABR is slightly reduced and there is a negative relationship between filter-screen area and ABR in the low-food treatment. Gains in filtering rate are higher and reductions in ABR are lower than predicted by the equilibrium model, hence Daphnia optimizes input rather than minimizing energy expenditures for filtering.

Interaction Between Food Availability and Predation Mortality Mediated by Adaptive Behavior

Increased activity rates in larval anurans rates are associated with both higher growth rates and higher predation mortality. Models of adaptive foraging behavior in the face of predation risk predict that at higher resource levels, foraging activity should be reduced. Thus, at higher resource levels predation mortality should also be reduced. We manipulated the resources available to Rana catesbeiana tadpoles and then measured the activity of tadpoles in the presence of caged dragonfly larvae and the mortality rate of the tadpoles when the dragonflies were free to forage. At low food levels the tadpoles moved more often and more quickly. Similarly, at low food levels the tadpoles suffered higher predation mortality. The dependence of predation mortality on resources available to prey underlines the futility of characterizing population regulation as being due to predation or resources. Adaptive variation in behavior responds to both pressures simultaneously. These results suggest the possibility that adaptive variation in behavior may lead to density—dependent population regulation. Density—dependent depletion of resources by prey should lead to increased activity levels, which will result in higher per capita predation rates. The generality of the trade—off between growth rate and mortality rate argues that this mechanism may be widespread. If adaptive variation in behavior is as widespread as it appears, incorporating this variation into population dynamic modelling may improve our ability to predict the outcome of interactions within ecological communities.

Experiments on the effects of food and density on voltinism in a stream‐dwelling water strider (Aquarius remigis)

SUMMARY1. The stream water strider Aquarius remigis shows a latitudinal pattern of variation in voltinism. In general, populations with shorter growing seasons (e.g. in eastern Canada) tend to be univoltine (animals that reach adulthood in the summer overwinter before reproducing in the following spring), whereas populations with somewhat longer growing seasons (e.g. in the north‐eastern United States) tend to be bivoltine.2. This pattern was broken at our study site in the south‐eastern United States (Kentucky) where A. remigis had a long growing season, but was almost always univoltine. In summer 1993, however, adult A. remigis in central Kentucky displayed a bivoltine reproductive cycle; i.e. individuals in some pools began breeding shortly after maturing to the adult stage.3. A field survey documented a negative relationship between local water strider density and reproductive activity in prediapause adults. A laboratory experiment manipulating food availability and density, revealed that animals held at low density with high food levels displayed greater mating activity and egg production than did their counterparts at higher density or lower food levels.4. A laboratory experiment also showed that high water strider density resulted in a greater frequency of very short pair durations (< 10 min).5. Although the observed effects of density and food availability on mating activity of prediapause adults seem intuitively reasonable, they differ from the patterns observed in overwintered adults. The difference in reproduction patterns might be due to differences in selective pressures on prediapause vs. post‐diapause adults.

Vertical distribution and population dynamics of copepods by dynamic optimization

Vertical distribution and population dynamics of copepods are viewed as a consequence of individual maximization of reproductive value (RV). RV for all individuals of all size classes (stages) and conditions (physiological states) is found by dynamic programming, and specifies a trajectory of optimal habitats in time and space. The optimal habitat is found by balancing the risk of predation and growth. Predation risk from visually searching planktivores is included as a mechanistic submodel, and growth is a function of individual size, food concentration, temperature, and energetic costs of migratory behaviour. The optimal policy followed by single individuals eventually gives rise to the population dynamics, based on individual mortality and reproduction rates. The model focuses on the role of temperature, predators, and food resources on dynamics and distribution, and shows that food can affect predation risk through both physiological and physical mechanisms. In fact, increased food concentration may influence dynamics more through reduced predation than through increased growth, because the planktivores’ searching efficiency is very sensitive to increased turbidity. This effect is suggested as a potentially important factor in the survival of planktonic organisms susceptible to visually searching predators, and may be most beneficial to macrozooplankton and fish larvae. The optimal copepod response (vertical migration) to increased density of planktivores is to seek less risky habitats, and therefore the predation risk of copepods is a non-linear function of planktivore density. The model suggests that optimal die1 migration intensity is changed with food density from no migration at low food levels, reaches a maximum at intermediate levels, but is reduced again at high algal concentrations.

The Allocation of Resources to Reproduction in Daphnia Galeata: Against the Odds?

Variation in offspring is a size common phenomenon in many organism. In cladoceran zooplankton large offspring are known to have a high starvation resistance. One could, therefore, expect offspring to be large at low food levels, whereas at higher food levels the production of more, but smaller, offspring would yield the highest parental fitness. However, in Daphnia galeata I found that individual offspring were smallest at a low food level and largest at intermediate food levels. Moreover, in contrast to the predictions made by several theoretical models, I found that larger mothers produce larger offspring. The first discrepancy between data and theory could be explained by the existence of a maximum offspring size, combined with the difficulty of Daphnia to produce one egg less than was done in reality. The dependence of offspring size on maternal size could be explained by the higher likelihood of intraspecific competition when large (=old) females are present, and hence higher starvation risks for the offspring. It was found that embryonic respiration was lowest at the lower food levels and hence the smaller individual egg size seemed to be compensated by lower carbon losses during development.

Effects of crowding and different food levels on growth and reproductive investment of Daphnia.

The effects of daphniid crowding on juvenile growth rate, length at first reproduction, clutch size and egg size of four species of Daphnia were compared with the effects of food level. Juvenile Daphnia were grown to primipary in a flow-through system in water conditioned by different densities of the same, or another, species. At high ambient food levels, water from Daphnia that had been crowded at densities ≥150 l-1 depressed growth rate and lowered body size and clutch size of D. hyalina and D. galeata; effects on the same traits of D. magna and D. pulicaria were variable (stimulation, depression, or no effect). D. hyalina and D. galeata responded to gradients of increasing daphniid density (0-300 l-1) by altering egg mass, somatic mass and clutch size to maintain a relatively constant reproductive investment; egg mass increased with crowding and then decreased in a pattern consistent with Glazier's (1992) hypothetical model of changes in offspring size in relation to food quantity and maternal demand. Effects of crowding by conspecifics were indistinguishable from those of other species. This study, which uncouples the effect of crowding per se from ambient resource depletion, shows that chemical substances released by high densities of Daphnia can cause changes in life-history traits comparable to those that occur in response to low food levels.

Development of Pseudocalanus elongatus (Copepoda, Calanoida) cultured at different temperature and food conditions

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 119:99-110 (1995) - doi:10.3354/meps119099 Development of Pseudocalanus elongatus (Copepoda, Calanoida) cultured at different temperature and food conditions Klein Breteler, W. C. M., Gonzalez, S. R., Schogt, N. The pelagic copepod Pseudocalanus elongatus Boeck was bred 3 times from nauplius stages I and II to maturity at 5, 10, 15 and 20*C and at 4 different rations of autotrophic and heterotrophic food. The rate of development of the copepods increased with increasing temperature and food supply. The shortest generation times (from egg to adult) were 59 d at 5*C and 19 d at 15*C. The generation time nearly doubled when food concentration was very low. At 20*C mortality rates were high and development did not proceed faster than at 15*C. At all food levels the stage duration was generally constant (nearly isochronal), but the last 1 or 2 developmental stages took longer. The relationship between development time and temperature is described by Belehrádek's functions at different food levels. This relationship predicts a generation time of approximately 45 d during spring bloom conditions in the North Sea and about 30 d during summer due to food limitation. Field estimates from the literature are too scarce to evaluate the presumption of food limitation during summer conditions. Some evidence of a low critical food level was found compared to other North Sea copepod species. Together with a fast development rate at low temperatures, this may explain the numerical dominance of P. elongatus in the North Sea and the northeast Atlantic Ocean. Pseudocalanus . Copepods . Cultivation . Development . Temperature . Food Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 119. Publication date: March 23, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Variation and Plasticity of Biomass Allocation in Daphnia

1. For organisms with indeterminate growth a trade-off between growth and reproduction is expected. The detection of this trade-off depends not only on the covariance between these two traits, but also on the variation of their sum, the total production (TP = growth + reproduction). The smaller the relative variation in TP, the more likely it is to detect the trade-off. To investigate this trade-off, we studied biomass allocation and variation of 56 clones of Daphnia magna from two populations under two food conditions. 2. Broad-sense heritabilities of clutch mass, growth, TP and the allocation ratio (R = clutch mass/TP) were higher in rich than in poor food conditions. Growth and R showed no genetic variation at the low food level

Phenotypic plasticity of the filter screens in Daphnia: Adaptation to a low‐food environment

Daphnia can enlarge the area of the screens on its filtering limbs in response to low concentrations of food. Seven species of Daphnia had larger filter screens when grown at low levels of food compared to animals of the same size raised at high levels of food. The increase in screen area varied between 19 and 83% among species. Larger filter screens resulted in higher filtering and feeding rates. Threshold food concentrations for growth, calculated from the carbon budget for different Daphnia species, were biased when adaptation of the filter screens was ignored. Daphnids used for measuring assimilation rates are usually cultured at high levels of food and thus have small filter screens. If filter‐screen enlargement is taken into consideration in estimating assimilation rates, thresholds come close to the realistic values measured in long‐term growth experiments. Filter‐screen adaptability is considered a response to varying nutritional conditions in the pelagic zone.

Response of Mesocyclops (Cyclopoida: Copepoda) to Biological and Physicochemical Attributes of Rainwater Tanks

The population growth and survival of Mesocyclops aspericornis (Daday) and Mesocyclops darwini (Dussart & Fernando) were compared in rainwater tanks at Amity Point, Stradbroke Island, and natural breeding habitats in other Queensland localities. The biological and physicochemical attributes of these biotopes were measured and it was found that pH, protozoan numbers, and chlorophyll level all significantly affected Mesocyclops persistence and population growth. While these three factors accounted for 82% of the variation, low food levels were considered to be the major factor limiting growth and survival. Protozoan and algal levels in tanks were one-fifth that of natural breeding sites. In a series of laboratory trials, Mesocyclops population growth was maximal in the pH range of 6.0–8.0 and in salinities below 1.66 parts per thousand. Greatest growth also occurred in media with both protozoans and algae at levels greater than 32,000 per ml and 3.9 μ g/liter, respectively. The variability of and low food levels in rainwater tanks will limit broad scale use of copepods for biocontrol of Aedes larvae in these sites.

Energetic Bottle-Necks During Breeding and the Reproductive Cost of Being Too Early

Experimental provision of extra food before egg-laying resulted in blue tit females starting to breed significantly earlier than unmanipulated females. When the females had laid their first egg, the experimental food source was withdrawn and females were thus manipulated to lay, incubate and feed nestlings at lower food levels than unmanipulated females. Although tricked into breeding earlier, the experimental females laid the same number of eggs, had no more laying gaps and produced eggs of equal size as the unmanipulated females. Females manipulated to start breeding early started to incubate significantly later in relation to clutch completion than did controls

Resource depression in Daphnia galeata, Daphnia cucullata and their interspecific hybrid: life history consequences

In this study, the effect of the food concentration on several life history parameters of Daphnia galeata, Daphnia cucullata and the hybrid between these two species was examined. The food concentration had a significant effect on both growth and reproduction of all three taxa. Mortality was highly species specific, and to a lesser extent dependent on the food concentration. Changes in life history parameters resulted in changes in the intrinsic rate of population increase (r). The food dependence of the different species was found to be different. Daphnia cucullata had a relatively constant and low r. The r values for the hybrid varied most, with low values compared with the parental species when grown at low food levels and relatively high values at higher food concentrations. Our results suggest that when food concentrations are high the hybrid will have a selective advantage over both parental species, but that at lower food levels D.galeata will have an advantage over both D.cucullata and the hybrid.

Determination of low silicon concentrations in food and coral soil by inductively coupled plasma atomic emission spectrometry

To avoid a positive systematic error in the inductively coupled plasma atomic emission spectrometric determination of silicon, a new microwave dissolution procedure incorporating tertiary amine addition was developed. The determination of low silicon concentration levels in food and coral soils was significantly improved by adding water-soluble tertiary amines to the solution after dissolution with HF. Better accuracy and precision, and an improved detection limit (75 ng ml–1 of Si) were obtained with amine addition than without.

Long-term effects of food allowance and housing on development of stereotypies in pigs

In a previous study (Terlouw et al., 1991, Anim. Behav., 42: 981–991) on the effects of physical restraint and food allowance on the development of stereotypies in pigs ( Sus scrofa), it was found that in both restrained and loose-housed pigs low food levels were accompanied by increased levels of total activity, and of chain manipulation and drinking. We have suggested that these activities may have been the expression of high levels of motivation to feed or forage, which in both housing systems were directed to the chain and to the drinker. The present results confirm the effects of food restriction on the development of stereotypies, as also in the second and third parity individuals receiving a low food allowance (2.5 kg of food per day) spent more time being active, performing higher levels of most activities, in particular chain manipulation and drinking, than individuals receiving a high food allowance (4.0 kg day −1). The effects of physical restraint were mostly limited to the low-fed group: low-fed restrained sows were slightly more active, and they performed more drinking and inactive standing than low-fed loose-housed sows. These effects were restricted to certain times of day. The present study was also the first to investigate the behaviour of the same sows over several parities, and it found that overall levels of total activity and of chain manipulation did not increase over parities. Low-fed sows showed, however, a small increase in sham oral activity and drinking-related activity. High-fed sows showed an increase in feeding rate over parities and low levels of chain manipulation. Positive correlations between individual levels across parities indicated that, in contrast to previous suggestions, sows were relatively consistent in their behaviour. In the fourth parity, increasing the food allowance to 4.0 kg day −1 did not reduce stereotypies in previously low-fed sows; reducing food allowance in previously high-fed sows was accompanied by an increase in activity in the longer term. Stereotypies occurred mainly after the meal with post-feeding activities occurring in a specific sequence. High-fed sows performed a short period of nosing and rooting the trough, then drank and lay down. Low-fed sows, in contrast, persisted in their drinking and in addition performed chain manipulation. The behavioural processes that may underlie these effects are discussed.

Sublethal Consequences of Stream‐Dwelling Predatory Stoneflies on Mayfly Growth and Fecundity

Predators can have consequences on prey populations and communities that extend well beyond direct predator—induced mortality. Predator—prey interactions often affect prey feeding rates, growth rates, or fecundities, thereby significantly affecting reproductive success of prey adults. Thus, investigation of the sublethal fitness consequences of behavioral responses of prey to predators is essential to our understanding of the total impact of predators on prey populations and communities. Feeding (algal grazing) rates, growth rates, and fecundities of Baetis bicaudatus (Baetidae) larvae were measured in replicated circular flow—through stream channels to determine the sublethal consequences on fitness correlates of the presence of predatory stoneflies (Perlodidae). Gut fullness of 24—h starved Baetis larvae was measured using fluorometry after 24 h (short—term experiments) in four treatments: (1) ambient resource rocks and no predators, (2) low resource rocks and no predators, (3) ambient resource rocks and one female perlodid stonefly (Megarcys signata), or (4) Kogotus modestus whose mouthparts were glued to prevent lethal effects of predation. Mid—instar male and female Baetis larvae were reared for 3 wk until wing pad maturation (long—term experiments) and subjected to all but the Kogotus treatment. Predator avoidance significantly reduced levels of Baetis gut fullness, over the short term, to levels intermediate between the high and low resource treatments. Longer term residence with predatory stoneflies caused larvae of both male and female Baetis to mature at significantly smaller sizes than in the treatment with ambient food but no predators. Mayflies with predators matured at sizes similar to those held with low food levels over the long term. Interestingly, both starved larvae and those avoiding predators did not grow during the experimental period in contrast to about a 50% growth rate of larvae experiencing ambient food levels, but no predators. Similarly, egg biomass per mature female larva was significantly reduced in both starved and predator treatments. The proportion of total body mass allocated to eggs was only reduced in starved mayflies indicating that the females avoiding predators accrued less total mass, but allocated a similar proportion to eggs as did well—fed Baetis. These data convincingly demonstrate that predator avoidance can have dramatic consequences on mayfly fitness. The mechanism explaining those fitness consequences is probably a disruptive drift/swim response by Baetis to encounters with stoneflies, which reduces Baetis' feeding rates. If we accept the assumption that natural selection has shaped the foraging behavior of organisms to maximize fitness, foragers need to make decisions that maximize both survivorship (minimizing risk of predation) and fecundity. In mayflies fecundity is entirely a function of resource acquisition by the larvae, which makes them particularly vulnerable to such sublethal effects of predation. Nonetheless, we suspect that the types of sublethal costs of predator avoidance documented by this and other recent studies are nearly universal consequences or organisms foraging under predation risk.

Analysis of naturally occurring mycotoxins in feedstuffs and food.

Aflatoxins, zearalenone, deoxynivalenol, fumonisins, and their respective metabolites require specific procedures for their determination because of their diverse chemistry and occurrence in complex matrices of feedstuffs and foods. Major sources of error in the analysis of these mycotoxins arise from inadequate sampling and inefficient extraction and cleanup procedures. The determinative step in the assay for each of these toxins is sensitive to levels below those that are considered detrimental to humans and animals. Aflatoxins can be determined in grains and animal fluids and tissues by TLC, HPLC, gas chromatography-mass spectrometry (GC-MS), and ELISA procedures. Zearalenone, an estrogenic mycotoxin, can readily be determined in cereal grains and foods by HPLC (50 ng/g) and by TLC (300 ng/g). No incurred levels of zearalenone or its metabolites have been detected in animal tissues destined for human consumption. Deoxynivalenol can be determined in wheat and corn at 300 ng/g by a rapid TLC procedure and at 325 ng/g by a GC method. Although not tested collaboratively, an HPLC procedure and an ELISA screening procedure are capable of detecting deoxynivalenol at low (nanograms/gram) levels in feedstuffs and foods. The recently characterized fumonisins can be detected by TLC, HPLC, and GC-MS at levels below those now considered harmful. Thin-layer chromatography and HPLC (with fluorescence detection of derivatives) procedures can detect fumonisins at approximately 100 ng/g; GC-MS is required for detection at lower levels.

Aggression and territoriality among sympatric western plethodontid salamanders

Territoriality has been documented among plethodontid salamanders in eastern North America, but aggressive interactions among western plethodontids are largely unknown. I examined the responses of three sympatric western Plethodon species (P. vehiculum, P. dunni, and P. vandykei) toward conspecific and congeneric salamanders in two laboratory experiments. In experiment 1, I investigated intra- and inter-specific aggression by the three species, and in experiment 2, I examined aggression and dispersion of the salamanders when fed either a high or a low level of food. In experiment 1, P. dunni were more aggressive than P. vehiculum and P. vandykei, which rarely bit their opponents. In experiment 2, two different food levels had no detectable effect on the aggressiveness of residents. Resident P. dunni (males, females, and juveniles) were equally likely to bite conspecific and congeneric salamanders introduced into their cages. However, their dispersion under cover objects was uniform (suggesting territoriality) only in pairings between conspecific individuals. In contrast, P. vehiculum showed little aggression and were randomly dispersed under cover objects. The variety of responses exhibited by the three sympatric species toward conspecific and congeneric salamanders suggests that their populations are only superficially similar in ecology and may be subjected to different intensities of intraspecific competition.

Long-term influence of feeding regime and housing on development of stereotypies in sows

Previous work has shown that feeding regime and not physical restraint is a major cause in the development of stereotypies in closely confined sows, (Teriouw et al, 1991). However, this and a previous report on the relationship between feeding regime and stereotypies in sows (Appleby and Lawrence, 1987) have only studied gilts in their first pregnancy. The objective of this present work was to examine longer-term effects of feeding regime and housing on the development of stereotypies in sows.Thirty-two sows (Cotswold Pig Development Co. Ltd, UK) were allocated to either loose (Lo) or tether (Te) housing and to Low (L; 2.5 kg/day) or high (H; 4.0 kg/day) food levels in a balanced design. Apart from social contact and freedom of movement the housing systems were similar including the provision of chains to the loose housed animals. The behavioural response to these treatments was observed over parities 2,3 and 4 using a time sampling technique, and the data analysed by analysis of variance and linear correlation.

Comparison of five cladoceran species in short- and long-term copper exposure

The study was carried out to assess the effect of both short-and long-term copper exposure on five cladoceran species differing in body size and habitat, i.e. Daphnia magna, D. pulex, D. galeata, Bosmina longirostris, and Chydorus sphaericus. The species-specific 48 h EC50 values for fed neonates were used to determine the chronic exposure levels (52% and 65% of the EC50 values). The experiment was run at two food levels. Long-term copper exposure retarded growth in each of the species studied. However, the copper treatments did not affect the clutch sizes of the experimental animals. At a low food level, copper exposure increased mortality in every species studied. The intrinsic rate of increase, r, was reduced in the copper-exposed populations. The sensitivity to copper was higher in the small lake species, compared to D. magna and D. pulex that are commonly used in standard toxicity tests. Of the species studied, B. longirostris had the highest sensitivity to both acute and chronic copper stress. The different sensitivities of the species studied are discussed in an ecological context.

Family planning inDaphnia: resistance to starvation in offspring born to mothers grown at different food levels

We observed a shift in maternal investment per offspring in clonal cultures of twoDaphnia species. Mothers grown at high food levels produced large clutches of smaller eggs but their offspring could not survive long under starvation conditions. Genetically identical mothers grown at low food levels produced small cultches of larger eggs, and their offspring, albeit low in numbers, were able to survive long periods of starvation. Our data show thatDaphnia mothers are capable of assessing food level and use this information in adjusting their fractional peroffspring allocation of reproductive resources.