Feeding behaviour in Littorina littorea: a study of the effects of ingestive conditioning and previous dietary history on food preference and rates of consumption

Feeding responses of the generalist herbivore, Littorina littorea (L.), to the perceived taste of macroalgae were assessed with respect to the effects of recent dietary intake and to overlapping versus nonoverlapping distributions of winkles and algae. The extent of grazing on artificial substrates impregnated with crude algal extracts was used as a measure of rate of response to the odour of preferred algae, and of feeding preference among less preferred algae, in a variety of designs. Adult L. littorea collected from a site where a range of algae were present showed preference among extracts of fucoids, whereas adults from a nearby site showed no such preference. Juvenile L. littorea of two weight cohorts collected from the former site responded faster to Porphyra umbilicalis extract-containing substrate than similar-sized animals from the latter site. Juveniles, fed either Porphyra, Ulva lactuca, or starved for two weeks in the laboratory, responded similarly to Ulva versus Porphyra extracts in a dose-dependent manner across a range of concentrations, although the Porphyra-maintained group consumed more of each, and the starved group less over seven days. Juveniles maintained on a mixed diet of Ulva and Porphyra consumed more Porphyra extract and less Ulva extract over the same period. These results are discussed in relation to the possible role of ingestive conditioning and previous dietary history in determining the occurrence and extent of chemically-mediated feeding preference in L. littorea.     

Activity and respiration in the anemone, Metridium senile (L.) exposed to salinity fluctuations

Activity and respiration in the anemone, Metridium senile (L.), were monitored under both constant and fluctuating salinity conditions. During constant exposure to 50% sea water it was found that the animals retracted the tentacles and that the rate of oxygen consumption decreased by ≈50%. The same response was elicited from animals in 100% sea water in a contracted state. Animals exposed to continually fluctuating salinities were found to retract the tentacles, contract the body wall, and produce amounts of mucus during periods of decreasing salinities. These reactions were reversed during exposure to increasing salinity. Oxygen consumption never ceased entirely in animals exposed to dilute sea water and it was found that during declining oxygen tension M. senile regulated its oxygen consumption until the environmental oxygen tension fell to ≈30% saturation.     

The life history,diet and migration of a lake-dwelling population of the leech Alboglossiphonia heteroclita (L.)

Alboglossiphonia heteroclita has an annual life cycle in Tabley Mere, England. Egg-carrying leeches occurred from early June to mid-July. Young were released from parents in August, and the old cohort died soon after. The mean weight of recruited young increased in early autumn, declined over winter due to low feeding activity, and increased again from early spring until the leeches reproduced.The disappearance of leeches from the littoral zone in winter was due to their migration into deeper waters.Six species of snails collected from shallow and deep waters did not harbour leeches inside their shells or mantle cavities at any time of the year. Laboratory experiments confirmed that the leech does not use snails as a refuge.A serological technique identified the gut contents of field-collected A. heteroclita. Leeches had fed most extensively on oligochaetes followed by snails and then chironomids, lightly on Asellus and caddisflies, and scarcely on amphiphods and cladocerans. In laboratory experiments, in which four prey taxa were offered simultaneously to leeches, the descending order of utilization was oligochaetes, chironomids, Asellus and snails.     

Vulnerability of newly settled plaice (Pleuronectes platessa L.) to predation: effects of habitat structure and predator functional response

Plaice (Pleuronectes platessa) nursery grounds on the Swedish west coast have been subject to increasing cover of annual green macroalgae during recent years, with growth of algae starting at the time of plaice settlement in April to May. A laboratory experiment was performed to investigate how the vulnerability to predation of metamorphosing plaice was affected by the presence of filamentous algae. Predation by shrimps (Crangon crangon) on settling plaice larvae was higher on sand than among algae, whereas predation by crabs (Carcinus maenas) was unaffected by habitat type, suggesting a lower overall mortality of plaice in the vegetated habitat. When predators and prey were presented with a combination of the two habitats, predation by shrimps was as high as that in the sand treatment alone, whereas predation by crabs was lower than that in the two treatments with one habitat. Based on these results, an additional experiment was performed, investigating the functional response of shrimps to six densities of juvenile plaice in a sand habitat with alternative prey present. The proportional mortality of juvenile plaice (12-16 mm total length (TL)) was density-dependent and was best described by a type III (sigmoid) functional response of the predatory shrimps. The results suggested that the combined predation pressure from shrimps and crabs was lower among algae than on sand, but settling plaice and predatory shrimps chose the sand habitat. Plaice densities in the sigmoid part of the obtained functional response curve represented normal to high field densities of plaice on the Swedish west coast, suggesting that shrimp predation could have a stabilising effect on plaice recruitment. The formation of macroalgae mats could therefore lead to a concentration of plaice juveniles in the remaining sand habitat and increased mortality through density-dependent predation by shrimps.     

Habitat selection of two gobies (Microgobius gulosus, Gobiosoma robustum): influence of structural complexity, competitive interactions, and presence of a predator

Herein I compare the relative importance of preference for structurally complex habitat against avoidance of competitors and predators in two benthic fishes common in the Gulf of Mexico. The code goby Gobiosoma robustum Ginsburg and clown goby Microgobius gulosus (Girard) are common, ecologically similar fishes found throughout the Gulf of Mexico and in the southeastern Atlantic Ocean. In Florida Bay, these fishes exhibit habitat partitioning: G. robustum is most abundant in seagrass-dominated areas while M. gulosus is most abundant in sparsely vegetated habitats. In a small-scale field survey, I documented the microhabitat use of these species where their distributions overlap. In a series of laboratory experiments, I presented each species with structured (artificial seagrass) versus nonstructured (bare sand) habitats and measured their frequency of choosing either habitat type. I then examined the use of structured versus nonstructured habitats when the two species were placed together in a mixed group. Finally, I placed a predator (Opsanus beta) in the experimental aquaria to determine how its presence influenced habitat selection. In the field, G. robustum was more abundant in seagrass and M. gulosus was more abundant in bare mud. In the laboratory, both species selected grass over sand in allopatry. However, in sympatry, M. gulosus occupied sand more often when paired with G. robustum than when alone. G. robustum appears to directly influence the habitat choice of M. gulosus: It seems that M. gulosus is pushed out of the structured habitat that is the preferred habitat of G. robustum. Thus, competition appears to modify the habitat selection of these species when they occur in sympatry. Additionally, the presence of the toadfish was a sufficient stimulus to provoke both M. gulosus and G. robustum to increase their selection for sand (compared to single-species treatments). Distribution patterns of M. gulosus and G. robustum likely result from a synthesis of various biotic and abiotic filters, including physiological tolerances to environmental factors, dispersal ability of larvae, and availability of food. Selection for structural complexity, competition, and presence of predators may further define the resulting pattern of distribution observed in the field.     

The influence of sex,sexual condition and age on the exploratory behaviour of wild wood mice (Apodemus Sylvaticus L.)

From April 1978 to April 1980 the exploratory behaviour of more than 1000 wild wood mice was studied in a modified open field test situation. The influence of sex, sexual condition and age on the exploratory activity was investigated. Sufficient data being available, the exploratory activity of both sexually active and sexually inactive adult males and adult females, of both sexually active and sexually inactive subadult males and subadult females and of both sexually inactive juvenile males and females was compared by means of a one way analysis of variance for each two-month period. In other analyses the influence of age of adult males and adult females on the exploratory behaviour was further examined. No differences could be found in the exploratory activity displayed by males or females and by sexually active or sexually inactive animals. Also a clear influence of age was absent. The interindividual variation was very large.     

Some factors governing prey selection by the 15-spined stickleback, Spinachia spinachia (L.)

Using mysids as prey, the relative importance of four characters governing prey selection by Spinachia spinachia (L.) were examined. Moving prey were taken in preference to stationary prey of equal length and when the fish were hungry they could be induced to take moving non-optimum sized prey in preference to optimum sized stationary ones. A comparison of the frequency of attack on portions of the prey showed that heads were preferred to tails and darkened mysids to light ones. The order of preference was dark colour > head > light colour > tail and there was some indication that the stimuli presented by these characters were additive. It is concluded that the fish attacked the head of the prey because of its shape (greater thickness and presence of appendages) and darker colour. The colour of the prey did not affect the size (length) of prey taken. In general, the stimuli presented by the four characters could be ranked in the order movement ? length > colour > shape.     

The development of the retinomotor reactions in larval plaice (Pleuronectes platessa, L.) and turbot (Scophthalmus maximus, L.)

The development of the retinomotor reaction was examined histologically in the larvae of plaice (Pleuronectes platessa, L.) and turbot (Scophthalmus maximus, L.). In plaice retinal pigment migration is present from hatching, but, in turbot, does not occur until just before metamorphosis. In both species rods first develop at metamorphosis. Plaice show cone migration, but this does not occur in turbot. During dark-adaptation retinal pigment contraction started at ≈ 100 lux in all stages of plaice. Before metamorphosis pigment was fully contractedimmediately below 1000 lux, but after metamorphosis full contraction did not occur until the light intensity had fallen to < 1.0 lux. The thresholds for cone migration in plaice showed similar changes, although the actual light intensities were about an order of magnitude lower. In turbot there was always an abrupt transition between light- and dark-adaptation; the thresholds for this fell from ≈ 10 lux at the start of metamorphosis to between 1.0 and 10 lux at the end. The lower threshold light intensities in turbot compared to plaice may indicate that vision is of greater importance in the feeding of the former species.     

Health food versus fast food: the effects of prey quality and mobility on prey selection by a generalist predator and indirect interactions among prey species

1. In order to understand the relative importance of prey quality and mobility in indirect interactions among alternative prey that are mediated by a shared natural enemy, the nutritional quality of two common prey for a generalist insect predator along with the predator's relative preference for these prey was determined. 2. Eggs of the corn earworm Helicoverpa zea (Lepidoptera: Noctuidae) were nutritionally superior to pea aphids Acyrthosiphum pisum (Homoptera: Aphididae) as prey for big‐eyed bugs Geocoris punctipes (Heteroptera: Geocoridae). Big‐eyed bugs survived four times as long when fed corn earworm eggs than when fed pea aphids. Furthermore, only big‐eyed bugs fed corn earworm eggs completed development and reached adulthood. 3. In two separate choice experiments, however, big‐eyed bugs consistently attacked the nutritionally inferior prey, pea aphids, more frequently than the nutritionally superior prey, corn earworm eggs. 4. Prey mobility, not prey nutritional quality, seems to be the most important criterion used by big‐eyed bugs to select prey. Big‐eyed bugs attacked mobile aphids preferentially when given a choice between mobile and immobilised aphids. 5. Prey behaviour also mediated indirect interactions between these two prey species. The presence of mobile pea aphids as alternative prey benefited corn earworms indirectly by reducing the consumption of corn earworm eggs by big‐eyed bugs. The presence of immobilised pea aphids, however, did not benefit corn earworms indirectly because the consumption of corn earworm eggs by big‐eyed bugs was not reduced when they were present. 6. These results suggest that the prey preferences of generalist insect predators mediate indirect interactions among prey species and ultimately affect the population dynamics of the predator and prey species. Understanding the prey preferences of generalist insect predators is essential to predict accurately the efficacy of these insects as biological control agents.     

Effects of prey density,prey size and predator size on rates of feeding by an intertidal predatory gastropod Morula marginalba Blainville (Muricidae), on several species of prey

As a prerequisite for models of foraging behaviour of the whelk, Morula marginalba Blainville (Muricidae), the effects of variation in density of prey on the rate of feeding of the predator were examined in field conditions for three coexisting species of prey. Densities of prey used were those at which the prey, two limpets and a barnacle, occurred naturally in the rocky intertidal habitat.Large limpets, Cellana tramoserica (Sowerby) can resist attacks by predatory gastropods by raising the mantle over the outside of the shell. These experiments showed that no C. tramoserica were killed by Morula marginalba even at very great densities and with no alternative prey present. For the small limpet Patelloida latistrigata (Angas), one of the whelk's most highly preferred prey, juveniles were eaten 1.4 times as fast as adults. Fitting the random predator equation gave greater attack coefficients and shorter handling times for juvenile than adult limpets.Sizes of both predator and prey affected rates of eating barnacles, Tesseropora rosea (Krauss), but not in a simple way. Whelks of 15-mm aperture length ate adult barnacles 4.2 times faster than did 12-mm whelks, but there was no significant difference in the rates at which the two sizes of snail ate juvenile barnacles.Rates of feeding on T. rosea and Patelloida latistrigata increased significantly with prey density. These results form a basis for including the density of prey in models of spatial dispersion of the predatory gastropod Morula marginalba.     

Syn-anti conformational switching: Synthesis and X-ray structures of tweezer and anti form in a zinc porphyrin dimer induced by axial ligands

Stepwise addition of 1,2-diaminobenzene to a Zn-1,2-bis(meso-octaethylporphyrinyl)ethane produces both tweezer and anti-form of the complex depending on the concentration of the axial ligand which exhibit two major equilibrium steps (with two step-wise binding constants): first, guest ligation leading to the formation of 1:1 host-guest tweezer structure (K₁) and, second, guest molecule ligation (K₂) forming 1:2 host-guest anti species and the corresponding binding constants are 1.82 × 10³ M⁻¹ and 1.34 × 10² M⁻¹, respectively. However, when guest like 1,4-diaminobenzene and 4-CN-pyridine are used, the ligand geometry prevents its entry into interporphyrin cavity to form a tweezer structure, thus producing only the 1:2 anti complex. Single crystal X-ray structures of both tweezer and anti form produced in a single Zn-bisporphyrin are reported here for the first time. The nonbonding Zn···Zn distance within a molecule is 5.55 and 10.01 Å in tweezer and anti form, respectively. Although the average Zn-N (por) distances are comparable for both the forms, the Zn-N (1,2-diaminobenzene/4-CN-pyridine) distances and the displacement of Zn from the mean porphyrin planes are larger in tweezer compared to anti conformation.     

Hypoxic avoidance behaviour in cod (Gadus morhua L.): The effect of temperature and haemoglobin genotype

Hypoxia can influence fish growth, survival and on larger scales, population structure. These effects may be influenced by water temperature, and may vary intra-specifically with genotype. In Atlantic cod (Gadus morhua L.), the two haemoglobin homozygotes (Hb-I?11 and Hb-I?22) vary in oxygen affinity at different temperatures, which is thought to correspond to variation in hypoxia tolerance. We therefore tested if hypoxic avoidance behaviour in cod 1) depends on ambient temperature and 2) is modified by haemoglobin genotype. In a laminar flow choice box, we subjected juvenile cod to an initial phase of non-escapable hypoxia, and a subsequent recovery phase, where one habitat was kept at 20% O₂ saturation while the other was raised in steps to full saturation. The experiment was performed at 5 and 15 °C with Hb-I?11 and Hb-I?22 cod. Cod responded to inescapable hypoxia by reducing their overall swimming speed and then, at the initial levels of the recovery phase, avoiding the most hypoxic habitat, irrespective of temperature or genotype. Fish recovered quickly as O₂ levels increased, as evidenced by increased swimming speed and time spent in the most hypoxic habitat. The avoidance response depended strongly on temperature: the relative reduction in speed and avoidance of the most hypoxic habitat was more pronounced at 15 than at 5 °C. During the recovery phase, stressed fish initially maintained a higher swimming speed in the most hypoxic habitat. However, as O₂ increased, swimming speed in both habitats converged. This point of convergence occurred at a lower O₂ saturation at 5 °C. Fish ventilation rate in inescapable hypoxia was also higher at 15 °C. Haemoglobin genotype did not influence either ventilation rates or the nature of the hypoxic avoidance response at either temperature, but Hb-I?11 cod swam faster than Hb-I?22 cod in normoxia at 15 °C. Our results indicate that increased temperature limits the ability of cod of both haemoglobin genotypes to exploit hypoxic habitats. This may have negative future consequences for coastal cod stocks in light of increasing global temperatures and eutrophication in coastal waters.     

Optimal foraging by the swallow (Hirundo rustica, L): Prey size selection

The foraging ecology of the swallow (Hirundo rustica) was investigated in the field and compared with predictions of optimal foraging theory. Prey items were selected primarily by size. The inclusion of an item in the diet depended on the absolute abundance of the high-ranking prey and not of the low-ranking ones. Small items of low profitability were, however, included when food was abundant and more small items were taken when they were relatively abundant. Energetics data are used to show that it is profitable in terms of net energy gain for the swallow to take a mixture of large and small items, whereas optimal foraging theory would predict exclusive specialization on large, high-ranking items. Other possible explanations for the inclusion of small items in the diet are discussed.     

Male reproductive success in the domestic cat (Felis catus L.): A case history

The domestic cat shows a great variability in different life history traits like its social organization, ranging from a solitary life to living in large social groups depending on environmental conditions. Until now, the mating system has not been shown to vary between populations and was described as promiscuous. Here we present data on the reproductive success of a male, which clearly show that monopolization of females by males is possible in this species.     

Ontogenetic- and condition-related effects of starvation on responsiveness in herring larvae (Clupea harengus L.) during repeated attacks by a model predator

The escape behaviour of fed and food-deprived herring larvae (20-30 mm SL) was studied during repeated attacks with a glass probe in order to investigate the causal mechanisms of starvation-induced changes in reaction to predators. Two experiments were set up: one where the fed and starved larvae were of the same age but of different sizes and one with groups of similar size but different ages. Biochemical and morphological condition measures described the condition of individual larvae. Starved larvae showed a lower responsiveness than fed larger larvae of the same age, and the responsiveness in this experiment decreased with decreasing nutritional status of the larvae. However, starved larvae that were of the same size but older than fed larvae showed a higher responsiveness, which could be explained by differences in development of sensory systems. A combination of condition and developmental factors thus explained the differences between starved and fed larvae. Both starved and fed larvae showed decreasing responsiveness over time with repeated attacks with no difference between starved and fed larvae in the relative change over time. The results emphasise the importance of taking into account individual age and/or development when the nutritional condition of wild-caught larvae is incorporated in survival models.     

Effects of near-bed current speeds on the distribution and behaviour of the lobster, Homarus gammarus (L.)

The distribution of the lobster, Homarus gammarus (L.) appears to be limited to areas of the sea bed with rocky outcrops. It seems likely that this limitation operates because lobsters need to be able to avoid currents created by tidal and wave action and that it is size selective. A series of experiments was made with lobsters in a flume tank, to observe the effects of a range of current speeds and substratum types on lobster behaviour. In addition, depth profiles of flow rates were made by Pitot tube measurements to estimate flow rates within the boundary layer immediately above the sea bed. Predictions of the influence of natural water currents on lobster behaviour have been made using available data on near-bed current speeds. The implications of these predictions to fisheries management and reef construction plans are discussed.     

Prey selection by a spider wasp,Batozonellus lacerticida (Hymenoptera: Pompilidae): Effects of seasonal variation in prey species,size and density

Prey selection by a spider wasp,Batozonellus lacerticida, was investigated at the riverside of the Toyohira River in Misumai, Sapporo, Hokkaido over 7 years from 1981 to 1987. Seventeen species of araneid spiders were found in the study area and six of them were hunted by the wasps. Most (97.3%) of the 223 prey records obtained were of three species,Araneus macacus, A. marmoreus andA. pinguis. Nesting activity of the wasps continued until mid-August in 1981, 1982 and 1986, but stopped in July in 1984, 1985 and 1987. The length of nesting period was related to whether the wasps successfully switched prey species fromA. macacus toA. marmoreus andA. pinguis andA. pinguis or not Switching seemed to occur at the phase when density ofA. macacus remained high, depending on the density of largerA. marmorus andA. pinguis. This switching had large effects on species composition and size distribution of actual prey. Chesson's index α calculated at every 10 day period revealed that the wasps preferredA. macacus to the two other species and large prey to medium and small ones. The effect of prey density on preference depended on whetherA. macacus was present or absent. In the presence of it there were only slight differences in preference among various conditions of prey density. However, whenA. macacus was absent, densities of bothA. marmoreus andA. pinguis had some complementary effects on preference. The importance of prey size selection by pompilid wasps, and implications of density effects on preference are discussed.     

The reproductive response of the sea urchins Paracentrotus lividus (G.) and Psammechinus miliaris (L.) to a hyperproteinated macrophytic diet

The sea urchins Paracentrotus lividus and Psammechinus miliaris are submitted to the same environmental conditions in the Bay of Brest. The relationship between seasonal changes in food source quality and their gonad production was investigated in reproducing experimentally these conditions. In a first stage two macroalgae (Palmaria palmata and Laminaria digitata) were tested. P. miliaris showed a stronger preference for P. palmata and over a year-long experiment both urchins progressively preferred P. palmata. Seasonal variations in the chemical composition of P. palmaria were observed in the Bay of Brest: total carbohydrates were important and the relative maximum (about 50%) was reached between February and August; the lipid level was low and had a relative maximum of about 1% in June and August. Total protein in P. palmaria was high compared to other seaweeds: the maximum value (25%) was observed in June, which was probably due to the maintenance of nitrogen nutrient in the bay.In the second stage of the study, seasonal changes in biochemical components of ingestion and absorption of the two sea urchins were followed in the laboratory using a monospecific diet of P. palmaria. The patterns of total carbohydrates and lipid absorption were very similar for both sea urchin species. Carbohydrates were absorbed strongly and uniformly, year round. Lipid absorption mimicked the lipid nutrient pattern in the food source. Only changes in protein absorption varied slightly between the two urchin species. Protein absorption was maximal for both species in February and June, but the quantity of absorbed protein was significantly higher in P. miliaris than in P. lividus during February. This increase was concomitant with protein storage in the sea urchin gonads, which peaked in February for P. miliaris and in June for P. lividus. P. lividus had a higher gonad production efficiency, based on gonad yield. The comparison between in situ data and the experimental results suggests that an algal diet more nitrogenous than the in situ algal food source would benefit the herbivorous P. lividus, rather than the more omnivorous species P. miliaris. Although P. milaris has been described as a species with large gonad production potential, P. lividus appears to be a more suitable species for echiniculture conditions.     

异色瓢虫对与本土蚜虫共存的外来扶桑绵粉蚧的搜寻和捕食行为

[目的]外来入侵物种作为猎物可能影响本土广谱捕食者的搜寻和捕食行为.本研究旨在揭示异色瓢虫Harmonia axyridis对与本土豌豆修尾蚜Megoura japonica混合发生的外来入侵扶桑绵粉蚧Phenacoccus solenopsis的搜寻和捕食行为.[方法]试验前对异色瓢虫设两个饲喂猎物种类处理:用扶桑绵...