Effects of life phase and schooling patterns on the foraging behaviour of coral‐reef fishes from the genus Haemulon

During this study (December 2009 to December 2010), underwater visual surveys using the focal animal method were performed in the coastal reefs of Tamandaré, north‐eastern Brazil. The aim was to analyse the effects of the life phase (juvenile and adult) and schooling patterns (school and solitary) on the feeding behaviour (foraging rates and substratum preferences) of four species of the genus Haemulon (Haemulon aurolineatum, Haemulon parra, Haemulon plumieri and Haemulon squamipinna). PERMANOVA analysis (P < 0·05) indicated that ontogenetic changes and schooling patterns directly influence foraging behaviour. Schooling individuals had low foraging rates (mean ± s.d . = 2·3 ± 2·1 bites 10 min^?1) and mobility, usually remaining near the bottom; however, solitary fishes had high foraging rates (mean ± s.d . = 12·5 ± 4·6 bites 10 min^?1). Juveniles preferred feeding in the water column (75% of the total number of bites), whereas adults foraged mainly in sand (80%) and bare rock (20%). All four Haemulon species displayed similar patterns of feeding behaviour as well as preferences for foraging sites and display competition for food resources. In contrast, little is known about their habitat use and foraging behaviour over the diel cycle, particularly the newly settled and early juvenile stages.     

Comparison of the feeding habits of Eurasian otters on a fast flowing river and its backwater habitats

The diet and feeding habits of Eurasian otters Lutra lutra were studied by spraint analysis over a 2- year period, on three sections of the Drava River and three backwaters, in south-west Hungary. The primary food was fish (mean: 89.8% and 87.5% for riverine and backwater habitats, respectively); otters living in riverine habitats compared to backwaters, consumed more birds (3.9% and 0.7%, respectively), less mammals (0.5% and 0.9%, respectively), less reptiles and amphibians (5.6% and 10.2%, respectively) and less invertebrates (0.1% and 0.6%, respectively). In riverine habitats otters preyed more frequently on larger fish than in backwaters, but the main fish prey was small-sized (below 100 g in weight, 85.6% and 91.7%, respectively). On river sections they preyed more frequently on reophil (flow preferring fish, 18.9% and 3.3%, respectively), and less on stagnophil fish (stagnant waters preferring, 9.8% and 24.5%, respectively) than in backwaters. The main fish prey was eurytopic (tolerant of rivers and stagnant waters, 71.3% and 72.2%, respectively). Preference (by Ivlev's electivity index, E_i) in the Drava River for various fish guilds differed, as the otters preferred eurytopic (E_i= 0.30) and stagnophil fish (E_i= 0.24), and avoided reophil fish (E_i=−0.58). Otters did not threaten the rare, flow preferring fish species and the main diet consisted of economically unimportant species.     

The effect of prey density on foraging mode selection in juvenile lumpfish: balancing food intake with the metabolic cost of foraging

1. In many species, individuals will alter their foraging strategy in response to changes in prey density. However, previous work has shown that prey density has differing effects on the foraging mode decisions of ectotherms as compared with endotherms. This is likely due to differences in metabolic demand; however, the relationship between metabolism and foraging mode choice in ectotherms has not been thoroughly studied. 2. Juvenile lumpfish Cyclopterus lumpus forage using one of two modes: they can actively search for prey while swimming, or they can 'sit-and-wait' for prey while clinging to the substrate using a ventral adhesive disk. The presence of these easily distinguishable foraging modes makes juvenile lumpfish ideal for the study of foraging mode choice in ectotherms. 3. Behavioural observations conducted during laboratory experiments showed that juvenile lumpfish predominantly use the 'cling' foraging mode when prey is abundant, but resort to the more costly 'swim' mode to seek out food when prey is scarce. The metabolic cost of active foraging was also quantified for juvenile lumpfish using swim-tunnel respirometry, and a model was devised to predict the prey density at which lumpfish should switch between the swim and cling foraging modes to maximize energy intake. 4. The results of this model do not agree with previous observations of lumpfish behaviour, and thus it appears that juvenile lumpfish do not try to maximize their net energetic gain. Instead, our data suggest that juvenile lumpfish forage in a manner that reduces activity and conserves space in their limited aerobic scope. This behavioural flexibility is of great benefit to this species, as it allows young individuals to divert energy towards growth as opposed to activity. In a broader context, our results support previous speculation that ectotherms often forage in a manner that maintains a minimum prey encounter rate, but does not necessarily maximize net energy gain.     

Multifractal anisotropic swimming: the optimal foraging behaviour of grouper larvae

It was hypothesized that the Malabar grouper Ephinephelus malabaricus larvae have developed search patterns adapted to the distribution of their prey to maximise their net energy intake per unit time. Analysis of the swimming behaviour of E. malabaricus larvae in both the presence and absence of Artemia sp. nauplii is presented to test this hypothesis. A method derived from turbulence studies (the moment function of the displacements) was used to characterize the behaviour. The results revealed that larval swimming pattern was multifractal (intermittent and long‐range‐correlated) and isotropic (i.e. uniform in all directions) in the presence of prey, but multifractal and anisotropic (i.e. more frequent long displacement on the vertical axis) in the absence of prey. It is suggested that the search behaviour observed in the absence of prey is an adaptive response to prey distribution pattern, which is often characterised by multifractality and anisotropy (i.e. larger patches on the horizontal axes). In the presence of prey, E. malabaricus shifted to intensive search behaviour. Other possible contributors to the observed patterns are discussed. It is concluded that multifractality and anisotropy of swimming patterns observed in the experiment are mainly explained in an optimal foraging theory framework.     

Interplay of individual interactions and turbidity affects the functional response of three-spined sticklebacks Gasterosteus aculeatus

The effects of turbidity, size and the presence of conspecifics on the functional response, feeding latency and activity in the three-spined stickleback Gasterosteus aculeatus were examined. A significant interaction between standard length and presence of conspecifics demonstrated an increase in attack rates of larger individuals in the presence of conspecifics. Attack rate was also higher in turbid water. Feeding latency decreased with prey concentration and presence of conspecifics, but was not affected by turbidity. Activity level did not change with prey levels, but increased with turbidity. These results can help to better understand how individual flexibility in the functional response can affect prey mortality according to environmental perturbation and social interaction at the level of the predator.     

Artificial dietary regime may impair subsequent foraging behaviour of hatchery-reared turbot released into the natural environment

When offered a size range of shrimp Crangon crangon , fewer naïve reared turbot Scophthalmus maximus fed than did wild fish, and those that fed took smaller prey. Analysis of feeding behaviour indicated differences between wild and naïve reared fish in the motivation to feed on novel prey and in prey recognition and capture efficiency. Feeding efficiency and motivation increased with experience and reared fish achieved the feeding rate of wild fish within the 9 days of the experiment. The 'creep' style of approach to shrimp was innate to naïve reared turbot. A comparative feeding experiment confirmed that experienced reared fish ate more prey than naïve reared fish. Naïve reared turbot selected pellets and attacked stones preferentially to shrimp, in contrast to wild and experienced reared fish, which selected shrimp. Stones were attacked due to the memory of pellet-like visual characteristics and this behaviour persisted in some reared fish for at least 6 weeks, illustrating a cost of memory in which changing environmental conditions cause previously learnt information to become misleading. The experimental data also demonstrated that differences may arise in the prey and feeding behaviour of wild and naïve reared fish, but that such differences diminish with experience.     

Individual variation in the foraging strategies of young yellow perch (Perca flavescens) from the Ottawa River

Differences in the foraging strategies among young individuals of the yellow perch (Perca flavescens) were observed in the laboratory by using two kinds of food (Daphnia and brine shrimp) separately and together. Individuals differed significantly in their ability for feeding attempts, time interval between two consecutive feeding attempts, feeding angles, regurgitation rate, and number of unsuccessful attempts and in their food preference. It is concluded that there are individuals with different foraging strategies. Variability in foraging strategies within single species populations is important because it may explain how the conspecific individuals may differ in their overall feeding behaviour.     

Influence of chorion ingestion on the performance of Ascia monuste and its association with cannibalism

1. In some lepidopterans, the newly hatched caterpillars feed on chorion (animal protein) as their first food. This is also a frequent behaviour of newly hatched caterpillars of Ascia monuste. 2. According to some parameters tested (time for pupation, number of adults, male imago weight, and fifth‐instar ingestion), chorion ingestion by first‐instar larvae affects adult performance positively. The ingestion of ultraviolet‐sterilised chorion provided the same positive effect on performance. It is thus suggested that young caterpillars may be benefiting from chorion nutritionally, and that chorion ingestion is a chain of events that leads to positive effects on insect performance. 3. Cannibalism in A. monuste was observed in newly hatched caterpillars and is related to the chorion ingestion behaviour. A condition for this to occur was the interval of time of hatching, which means that, if a group of caterpillars hatches very much before another group, once the caterpillars have ingested the chorion of their own eggs, there is a tendency for them to ingest the chorion of other eggs (including unhatched eggs) and, consequently, practice cannibalism. 4. Ascia monuste immatures are considered to be herbivorous, however it is important to know that they eat animal tissue (chorion and conspecific eggs).     

Sex-specific foraging behaviour in a seabird with reversed sexual dimorphism: the red-footed booby

Most hypotheses attempting to explain the evolution of reversed sexual dimorphism (RSD) assume that size-related differences in foraging ability are of prime importance, but the studies on sex-specific differences in foraging behaviour remain scarce. We compare the foraging behaviour of males and females in a seabird species with a RSD by using several miniaturised activity and telemetry loggers. In red-footed boobies males are 5% smaller and 15% lighter than females, but have a longer tail than females. Both sexes spend similar time on the nest while incubating or brooding. When foraging at sea, males and females spend similar time foraging in oceanic waters, forage in similar areas, spend similar proportion of their foraging trip in flight, and feed on similar prey—flying fishes and flying squids—of similar size. However, compared to males, females range farther during incubation (85 km vs. 50 km), and furthermore feed mostly at the extremity of their foraging trip, whereas males actively forage throughout the trip. Males are much more active than females, landing and diving more often. During the study period, males lost mass, whereas females showed no significant changes. These results indicate that males and females of the red-footed boobies differ in several aspects in their foraging behaviour. Although some differences found in the study may be the direct result of the larger size of females, that is, the slightly higher speeds and deeper depths attained by females, others indicate clearly different foraging strategies between the sexes. The smaller size and longer tail of males confer them a higher agility, and could allow them to occupy a foraging niche different from that of females. The higher foraging effort of males related to its different foraging strategy is probably at the origin of the rapid mass loss of males during the breeding period. These results suggest that foraging differences are probably the reason for the differential breeding investment observed in boobies, and are likely to be involved in the evolution and maintenance of RSD.     

Infestation of coconut fruits by Aceria guerreronis enhances the pest status of the coconut moth Atheloca subrufella

The coconut mite, Aceria guerreronis (Acari: Eriophyidae) and the coconut moth, Atheloca subrufella (Lepidoptera: Phycitidae), exploit the same habitat—meristematic region underneath the coconut fruit perianth. The coconut fruit perianth, however, is a tight structure allowing free colonisation of the meristematic region of the fruit only by small arthropods such as the eriophyid and tarsonemid mites. Fruits infested by the mites develop different levels of necrosis around the perianth providing access to colonising larvae of the coconut moth, which bore the fruit under the perianth resulting in fruit abortion. Based on field observations, we hypothesise that A. subrufella will colonise coconut fruits only if they exhibit damage on the perianth such as the necrosis caused by the coconut mite. Fruits with and without necrosis were collected from different production areas located in three different states along the Brazilian Atlantic coast and inspected for infestation with coconut moth larvae. In the laboratory, coconut fruits with and without necrosis were offered to moths for oviposition preference and tested for colonisation by neonate and third instar larvae. The results showed that the moths showed no preference for fruits with or without necrosis for oviposition and, hence, neonate larvae have to go under the perianth bract to reach the meristematic region of the fruit. However, neonate larvae were unable to colonise fruits without necrosis (0%) compared to 23% and 60% of fruit colonisation success when exhibiting mite necrosis or mechanical damage, respectively. Similar results were found with respect to older coconut moth larvae. Thus, the data support the hypothesis that the indirect interaction through previous fruit colonisation and necrosis caused by the coconut mite allows the larvae of A. subrufella to be a key pest of coconut fruits.     

Temporal pattern in foraging behaviour of the Indian pond heron,Ardeola grayii at Ratanpur,Chhattisgarh, India

In avian population, the biological clock is synchronized with the photoperiod as a significant time cue. However, information on feeding behaviour of the Indian Pond Heron, Ardeola grayii at Ratanpur, Chhattisgarh, India is not available. In present study we examined the effect of ‘time of the day’ and ‘photoperiod’ on daytime feeding behaviour of A. grayii at Ratanpur (85º17’E longitude and 22º3’N latitude), Chhattisgarh, India. The different feeding techniques of A. grayii, were recorded for two consecutive days each during long days (May and June 2014) and during short days (December 2014 and January 2015). One-way ANOVA (using SPSS 16.0) was applied to find out the effects of ‘photoperiod’ and ‘time of the day’ on daytime feeding activity with respect to frequency of feeding techniques. The rhythms in daytime feeding activity were evaluated using the Cosinor rhythmometry at 24 h and 12 h. The present study revealed that the A. grayii adopted three major techniques viz., slowly walking, probing and striking on which the slowly walking and striking was popularly used feeding technique as compared to the probing technique during the feeding. Moreover, the A. grayii is found to be bimodal viz., morning and evening type during both of long and short days. Furthermore, bird was more active during short day as compared to the long day.     

Examining the link between dietary specialization and foraging modes of stream‐dwelling brown trout Salmo trutta

The aim of this study was to explore differences in dietary specialization across two foraging modes (benthic v. surface‐drift foraging) of stream‐dwelling brown trout Salmo trutta. The degree of inter‐individual niche variation within each foraging mode was high, but the dietary specialization was maintained between foraging modes. This study supports the view that if aquatic invertebrates are more abundant and accessible than surface prey, the individuals will not specialize on surface prey (surface‐drift foraging).     

The effect of prey type and density on the foraging efficiency of juvenile perch, (Perca fluviatilis)

The foraging efficiency of juvenile perch (Perca fluviatilis), feeding on two types of prey, was studied in laboratory experiments. Waterfleas (Daphnia magna) and phantom midge larvae (Chaoborus flavicans) were offered in a range of densities, either separately or combined. Perch fed more efficiently on each prey type separately than when both were mixed. Foraging efficiency decreased with an increase of mixed prey density with both prey types present in equal numbers, but also when the proportion of Chaoborus increased. This could be caused by the existence of different hunting techniques, each of which is fully efficient in the presence of one prey type only. In the presence of two prey types, the predator constantly has to switch from one hunting technique to another.     

Recognition of host-specific chemical stimulants in two sympatric host races of the pea aphid Acyrthosiphon pisum

Abstract.  1. In ecological speciation , adaptation to variation in the external environment provides the crucial push that starts the process of genetic divergence and eventually leads to speciation. This emphasis on the role of ecological specialisation in speciation events has brought with it a renewed interest in its proximate mechanisms in recently diverged groups such as host races. Here, the proximate mechanisms of feeding specialisation are investigated in two host races of the pea aphid Acyrthosiphon pisum .
2. Using alfalfa and clover extracts, enclosed in diet chambers or applied on whole plants, it is shown that feeding specialisation depends on recognition of stimulants specific to the host plant, not on deterrents or toxins specific to the non-host plants.
3. Because pea aphids mate on their host plant, feeding specialisation leads to de facto assortative mating. This study suggests that behavioural recognition of host-specific chemicals, rather than avoidance of deterrents or/and plant toxins, contributes to gene flow restriction between the alfalfa and clover host races.     

Isovaleronitrile co-induced with its precursor,l-leucine,by herbivory in the common evening primrose stimulates foraging behavior of the predatory blue shield bug

Herbivore-induced plant volatiles play important roles in plant–insect and plant–plant interactions. The common evening primrose, Oenothera biennis, is often infested by the flea beetle, Altica oleracea, on which the predatory blue shield bug, Zicrona caerulea, is usually found. This observation suggests that the predatory bug can discriminate infested plants from intact ones to locate its prey. In this study, l-leucine-derived nitrogen-containing compounds [isovaleronitrile (3-methylbutanenitrile), (E/Z)-isovaleraldoxime and 3-methyl-1-nitrobutane] and some terpenes were identified as a characteristic volatile blend from herbivore-infested O. biennis leaves by gas chromatography/mass spectrometry, chemical synthesis, and incorporation assays using deuterium-labeled l-leucine. Volatile emission was also elicited by exogenous methyl jasmonate (MeJA), but not by mechanical damage. l-Leucine accumulated temporarily in O. biennis leaves after MeJA treatment prior to isovaleronitrile emission. Behavioral assays revealed that Z. caerulea showed a strong preference for herbivore-infested leaves, their volatiles, and isovaleronitrile in laboratory conditions.     

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man‐made floodplain waterbody

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man‐made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.     

Inclusion of biotic stress (consumer pressure) alters predictions from the stress gradient hypothesis

1.  The stress gradient hypothesis (SGH) predicts a shift from net negative interactions in benign environments towards net positive in harsh environments in ecological communities. While several studies found support for the SGH, others found evidence against it, leading to a debate on how nature and strength of species interactions change along stress gradients, and to calls for new empirical and theoretical work.
2.  In the latest attempt in this journal, it is successfully argued how the SGH should be expanded by considering different life strategies of species (stress tolerance versus competitive ability) and characteristics of abiotic stress (resource versus non-resource based) over wider stress gradients (opposed to low–high contrasts), but the crucial role of biotic stress by consumers is largely ignored in this refinement.
3.  We point out that consumers strongly alter the outcome of species interactions in benign and harsh environments, and show how inclusion of consumer-incurred biotic stress alters the predicted outcome of interactions along resource- and non-resource-based stress gradients for stress-tolerant and competitive benefactors and beneficiaries.
4.   Synthesis. New studies should include stress gradients consisting of both abiotic and biotic components to disentangle their impacts, and to improve our understanding of how species interactions change along environmental gradients.     

The effect of the chemical environment on interactions in groups of crayfish

Most of our knowledge of social behaviour in crustaceans stems from observations of pairs of animals engaged in conflict. Less consideration has been given to the dynamics of group behaviour. We investigated whether chemical signals affect the dynamic of groups of Cherax destructor. Animals were exposed to odours collected from male, female, moulted or dominant crayfish, or from fish. We observed agonistic encounters in the group during a 15 min period after the introduction of the odour. There was a decrease in threat behaviours when the male odour was added. We conclude from this that an olfactory stimulus can affect the dynamic of group interactions and the results suggest that the outcome is likely to be different from that obtained with paired or single individuals.