Shovelnose sturgeon exhibit predator avoidance behaviour in the presence of a hungry predator

An experiment was designed to test whether age‐0 shovelnose sturgeon (Scaphirhynchus platorynchus) exhibited predator avoidance behaviour in response to a channel catfish (Ictalurus punctatus) predator. It was hypothesized that shovelnose sturgeon would not exhibit any innate predator avoidance behaviour because previous reports have shown a congener of the shovelnose sturgeon, the pallid sturgeon (S. albus), to be an unfavourable prey item for channel catfish. The results, however, indicated that shovelnose sturgeon generally avoided space occupied by the catfish predator and spent a greater proportion of time in the predator avoidance zone within the experimental tank. Bitten fish, in particular, spent a greater period of time in the predator avoidance zone. Of all sturgeon used in this experiment (N = 30), 73% swam within the fork length (350 mm) of the catfish predator. The results seem to indicate that shovelnose sturgeon were initially oblivious to the risk of predation by the catfish predator, but after interaction (e.g. being chased or bitten) appeared to display predator avoidance behaviour. Predator avoidance behaviour in shovelnose sturgeon may thus be suggested as a learned rather than an innate behaviour.     

Swimming behaviour of Daphnia clones: differentiation through predator infochemicals

We studied variation in small-scale swimming behavior (SSB)in four clones of Daphnia galeata (water flea) in response topredator infochemicals. The aim of this study was 3-fold. First,we tested for differences in SSB in Daphnia; second, we examinedthe potential of differences in SSB to explain survival probabilityunder predation; and third we tested the effect of differencesin SSB on survival under predation. Four treatments were applied:one kairomone-free control, one Chaoborus- (phantom midge) andone Perca (perch)-conditioned treatment, and a mixed treatmentcontaining both infochemicals. All of the three tested behavioralparameters (swimming speed, trajectory length and vertical distribution)were affected by the presence of the Chaoborus infochemical,and swimming speed and vertical distribution were also affectedby the presence of Perca infochemical. The effect of the treatmentwas interfered with by a clone effect: genetic differences werepronounced in all traits. These results illustrate that clonescan be responsive in only a subset of traits. The general theorythat clones are either responsive or non-responsive is not validfor SSB. The outcome of the predation trial confirms that adecrease in activity is a main factor in lowering Daphnia vulnerabilityto Chaoborus predation.     

Evolution of predator avoidance in a Daphnia population: evidence from the egg bank

Dormant propagule pools (egg banks) of zooplankton populations that accumulate in sediments provide biological archives of past conditions and enable the investigation of evolutionary changes in populations over relatively long periods of time (many decades). This study examined the egg bank of a Daphnia pulicaria population in a lake that has been stocked annually with rainbow trout (a zooplanktivore) since 1961. Resting eggs from sediments from the 1920s to 2001 (determined by ²¹⁰Pb dating) were hatched and established as isofemale clonal lines. The phototactic behavior (a proxy for vertical migration behavior) of clones was assessed in the presence and absence of fish kairomones to evaluate the hypothesis that the heavy and consistent level of predation imposed by the stocked trout would have selected for clones that are more negatively phototactic. In addition, exposure to kairomones was expected to induce stronger negative phototaxis for all clones relative to control conditions. The behavior of clones derived from resting eggs from the trout era (after 1961) was significantly more negatively phototactic than it was for pre-trout era clones. Kairomone exposure induced a more negative phototactic response in clones from both eras, but the response was much greater for the pre-trout era clones. These results suggest that the consistently high level of predation by trout over several decades has selected for a conservative (less plastic) vertical migration strategy in which Daphnia maintain a deep daytime distribution with or without the presence of chemical cues from fish predators.     

Foraging strategy and predator avoidance behaviour: an intraspecific approach

Relationships between predator avoidance behaviour (scanning and flocking) and foraging were studied in Calidris alpina, to test predictions regarding the effect of foraging techniques on such behaviours. The scanning hypothesis predicts that individuals with a tactile hunting technique and individuals with a visual hunting technique (both continuous searchers) do not differ in any variable related to scanning behaviour. The flocking hypothesis predicts that visually hunting individuals witl tend to form smaller flocks than tactile-foraging individuals. The two continuous feeding strategies did not differ among individuals in vigilance rate, nor in vigilance time or mean scan duration. However, with respect to flocking behaviour, visual foragers differed from tactile foragers in foraging flock size. The relationships between flocking behaviour and foraging strategy are discussed. The pattern found at the intraspecific level are the same as those found at interspecific level.     

Chemically induced predator avoidance behaviour in the burrowing bivalve Macoma balthica

The responses of the burrowing bivalves Macoma balthica and Cerastoderma edule to chemical cues emitted by feeding shore crabs Carcinus maenas were investigated. M. balthica held in the laboratory and exposed to chemical signals in effluent water discharging from tanks containing C. maenas fed 20 M. balthica day^− 1 reacted by increasing their burial depths from approximately 30 mm to depths of > 60 mm, over a period of several days. When the signal was removed the bivalves gradually returned to their original depth over 5 days. C. edule similarly exposed to effluent from crabs feeding on conspecifics showed no response. In an attempt to identify the signal inducing this burrowing response, M. balthica were exposed to a variety of chemical signals. Crabs fed M. balthica elicited the strongest response, followed by crabs fed C. edule. There were also small responses to effluent from crabs fed on fish, crabs previously fed on M. balthica and to crab faeces, but no responses to starved crabs, crushed M. balthica, or controls. We conclude that increased burrowing depth of M. balthica is induced by some as yet unidentified chemical cue produced by feeding crabs and is strongest when the crabs were fed on M. balthica. Unexpectedly, neither the presence of crabs themselves, nor of damaged conspecifics, was effective in eliciting a burrowing response. The mortality rates of M. balthica and C. edule selected by crabs when burrowed at normal depths and after exposure to effluent from feeding crabs were different. Crabs selected 1.5 times more C. edule than M. balthica when both species were burrowed at their normal depths, but 15 times more after the tanks had been exposed to effluent from feeding crabs for 5 days. The burrowing response of M. balthica thus appears to reduce mortality significantly by displacing predation pressure on to the more accessible C. edule.     

Group transmission of predator avoidance behaviour in a marine insect: The trafalgar effect

The approach of a predator model induces rapid changes in the locomotory behaviour of individuals at the periphery of flotillas of a marine insect, the ocean skater Halobates robustus Barber. There is an abrupt and substantial increase in velocity, frequency of turning, the number of apparently random encounters between individuals and also the frequency of changes in light reflection from the body surfaces. These behavioural responses are postulated to cause predator confusion and, less frequently, to initiate rapid, synchronous dispersal of the flotillas. Interactions between individuals in the flotillas mediate a rapid transmission of avoidance behaviour through the flotilla which, in our field experiments, greatly exceeded the speed of approach of a predator model. This behaviour (named the Trafalgar Effect) enables individuals to initiate avoidance behaviour before the approaching predator can be seen.     

Predator‐avoidance behaviour in a nocturnal petrel exposed to a novel predator

Many species of bird recognize acoustic and visual cues given by their predators and have complex defence adaptations to reduce predation risk. Recognition of threats posed by specific predators and specialized anti‐predation behaviours are common. In this study we investigated predator recognition and anti‐predation behaviours in a pelagic seabird, Leach's Storm‐petrel Oceanodroma leucorhoa, at a site where predation risk from Great Skuas Stercorarius skua is exceptionally high. Leach's Storm‐petrels breed in burrows and come on land only at night. Counter‐predator adaptations were investigated correlatively in relation to changing natural light levels at night, and experimentally in relation to nocturnal visual and acoustic signals from Great Skuas. Colony attendance by Leach's Storm‐petrels was attuned to changes in light conditions at night and was highest when nights were darkest. This behaviour is likely to reduce predation risk on land; however, specific recognition of Great Skuas and specialized defence behaviours were not found. Leach's Storm‐petrels, in particular apparently non‐breeding individuals, were entirely naïve to the threat posed by Great Skuas and were captured easily in a variety of different ways, on the ground and in the air. Lack of specialized behavioural adaptations in Leach's Storm‐petrels against Great Skuas may be because spatial overlap of breeding distributions of these species appears to be a rare and recent phenomenon.     

Influence of rearing and experimental temperatures on predator avoidance behaviour in a freshwater pulmonate snail

1. Predicted increases in the temperature of freshwaters is likely to affect how prey species respond to predators. We investigated how the predator avoidance behaviour of the freshwater pulmonate snail Lymnaea stagnalis is influenced by the temperature at which it was reared and that at which behavioural trials were carried out. 2. Crawl‐out behaviour of juvenile snails from two populations (high predation risk versus low predation risk) reared at either 15 or 20 °C was assessed in response to predation cues (predatory fish kairomones and conspecific alarm cues) in behavioural trials at both 15 and 20 °C. 3. Trial temperature had a significant effect on the time that snails spent in avoidance, regardless of their population of origin. Crawl‐out behaviour was greater during behavioural trials at 15 °C, but there was no effect of trial temperature on the speed with which animals showed avoidance behaviour. 4. There was no interactive effect of rearing temperature (RT) and trial temperature, but the effect of RT on avoidance behaviour did differ between populations. For an RT of 15 °C, snails from the South Drain (high risk) population showed a more rapid and longer avoidance response than those from the Chilton Moor (low risk) population. In contrast, for snails reared at 20 °C, there was no difference between populations for the duration of the avoidance response and snails from Chilton Moor crawled out faster than those from South Drain. 5. Hence, whilst (predictable) differences relative to natural predation threat in crawl‐out behaviour were apparent at 15 °C, raising the developmental temperature to 20 °C eliminated or, in the case of latency, reversed these differences. This suggests that L. stagnalis populations that cohabit with predatory fish and experience high developmental temperatures may have a reduced ability to respond to fish predation risk.     

The ontogeny of antipredator behaviour in paradise fish larvae III. Size-related avoidance of predator models

A series of laboratory experiments examined the effect of the size of predator models on the behaviour of larval paradise fish Macropodus opercularis L., of different age (15 and 20 days old). In a small runway, individually tested larval paradise fish could approach a model predator of different size, with or without eyespots. The duration of approach, the number of fleeings and backings were measured. Fifteen-day-old larvae showed similar moderate level avoidance to all models but fled more in the presence of larger models. The approach behaviour in 20-day-old larvae depended on the size of the model but only if it had eyespots, and larvae fled and backed more with increasing size of the model. However, manipulation of larval length within age category had no effect on predator avoidance. Since the recognition of the two eyespots seems to be age dependent, it is hypothesized that only larvae older than 20 days will behave in a 'threat-sensitive' manner in the presence of predator models by avoiding larger ones.     

Thermal avoidance and preference in Daphnia magna

1. Water fleas (Daphnia magna) bred at 23°C were non-responsive to temperatures between 13 and 25°C.

2. At the lower (11°C) and upper limits (30°C) their klinokinetic avoidance behaviour showed a larger intraindividual than interindividual variation.

3. Thermal sensitivity for avoidance responses in D. magna was about 1.5°C.

4. For D. magna bred for one parthenogenetic generation at 14°C heat avoidance temperature was about 8°C lower, and cold avoidance temperature was about 1°C higher than in D. magna from 23°C.

5. In group experiments the animals showed some preference for the acclimation temperature.

6. Cold induced stenothermy and warm induced eurythermy in D. magna were related to the mode of reproduction.

On the implications of predator avoidance

The question to what extent predators regulate the populations of their food species has a long history of debate, and today top-down control of plankton dynamics still is a major issue in limnology. Over the last decade a fascinating extra dimension of this topic has been revealed. Fish, zooplankton and algae can sense their potential predators through chemical cues and adjust their life style in a flexible way to minimize the risk of being eaten. Although much progress has been made in elucidating the mechanisms involved, the implications of such predation avoidance for the potential of predators to reduce the abundance of their food populations are still poorly understood. Model analyses suggest that predation avoidance leads to more stable food webs in which the effects of nutrient enrichment are more evenly distributed over the trophic levels. In this article it is argued that the cost which predation avoidance usually has in terms of food conditions implies a tricky caveat in interpreting observations on predation rates and nutritional status in natural populations. Prey that sense the presence of predators and aggregates at safe sites where food conditions are poor, may appear starved and actual predation losses may be low. Such observations suggest that food limitation is the dominant force limiting their population development, but although starvation may indeed be the proximate cause of poor growth and reproduction, predation is clearly the ultimate factor involved in this situation. Thus when predation avoidance occurs, standard demographic analyses will tend to underestimate the importance of predators in regulating the dynamics of their prey in the field.     

Genetic control of migratory behaviour in birds

Although it has long been suspected that biannual migration in birds has a direct genetic basis, only in the last decade have details of the inheritance of behavioural traits such as migratory activity and directional preferences been demonstrated. A model has now been developed to estimate how inexperienced first-time migrants manage to reach their unknown winter quarters on the basis of inherited spatio-temporal programs. Furthermore, in obligate partial migrants the decision to migrate or not has been shown to have a strong genetic base. Migratoriness and sedentariness in partial migrants have been shown to have a high potential for rapid evolution. A recent set of results has suggested that novel migratory habits can evolve in less than 25 years. A possible consequence is that environmental changes, including 'greenhouse' effects, might considerably alter avian migration systems by acting on genetic variation for migratory tendencies.     

Anti-predator behaviour of native prey (Daphnia) to an invasive predator (Bythotrephes longimanus) is influenced by predator density and water clarity

Hydrobiologia - Bythotrephes longimanus is an invasive zooplankton predator, negatively impacting zooplankton abundance and diversity in North American lakes. Previous studies have shown that...     

Components of Daphnia feeding behaviour

Measurements of filter limb beat rate, mandible movement rate,and bolus swallowing rate from individual Daphnia magna arecollated with the grazing rates of groups of animals free-swimmingunder similar conditions. Significant effects of temperature,food concentration and angular light distribution are recorded,and the data are interpreted in the light of possible mechanismscontrolling the cladoceran feeding process.     

The role of differential reinforcement in predator avoidance learning

Little is known about how predator recognition develops under natural conditions. Predispositions to respond to some stimuli preferentially are likely to interact with the effects of experience. Convergent evidence from several studies suggests that predator-nai;ve tammar wallabies (Macropus eugenii) have some ability to respond to vertebrate predators differently from non-predators and that antipredator responses can be selectively enhanced by experience. Here, we examined the effects of differential reinforcement on responses to a model fox (Vulpes vulpes), cat (Felis catus) and conspecific wallaby. During training, tammars experienced paired presentations of a model fox and a simulated capture, as well as presentations of a wallaby and a cat alone. Training enhanced responses to the fox, relative to the conspecific wallaby, but acquired responses to the two predators did not differ, despite repeated, non-reinforced presentations of the cat. Results suggest that experience interacts with the wallabies' ability to perceive predators as a natural category.     

Interclonal proteomic responses to predator exposure in Daphnia magna may depend on predator composition of habitats

Phenotypic plasticity, the ability of one genotype to express different phenotypes in response to changing environmental conditions, is one of the most common phenomena characterizing the living world and is not only relevant for the ecology but also for the evolution of species. Daphnia, the water flea, is a textbook example for predator‐induced phenotypic plastic defences; however, the analysis of molecular mechanisms underlying these inducible defences is still in its early stages. We exposed Daphnia magna to chemical cues of the predator Triops cancriformis to identify key processes underlying plastic defensive trait formation. To get a more comprehensive idea of this phenomenon, we studied four genotypes with five biological replicates each, originating from habitats characterized by different predator composition, ranging from predator‐free habitats to habitats containing T. cancriformis. We analysed the morphologies as well as proteomes of predator‐exposed and control animals. Three genotypes showed morphological changes when the predator was present. Using a high‐throughput proteomics approach, we found 294 proteins which were significantly altered in their abundance after predator exposure in a general or genotype‐dependent manner. Proteins connected to genotype‐dependent responses were related to the cuticle, protein synthesis and calcium binding, whereas the yolk protein vitellogenin increased in abundance in all genotypes, indicating their involvement in a more general response. Furthermore, genotype‐dependent responses at the proteome level were most distinct for the only genotype that shares its habitat with Triops. Altogether, our study provides new insights concerning genotype‐dependent and general molecular processes involved in predator‐induced phenotypic plasticity in D. magna.     

Direct distributional response in Daphnia pulex to a predator kairomone

The hypothesis that zooplankton are capable of direct and differentiatedbehavioural responses to different biotic factors was tested.A multichamber flow-through technique enabled predeterminedfood levels of the green alga Scenedesmus acutus to be maintainedconstant throughout the experiments. By adding water from aculture of fourth instar Chaoborus flavicans larvae to one ofthe end chambers, a concentration gradient of the chemical substancewas established across the parallel chambers. Evidence is presentedfor a direct avoidance response in the water flea Daphnia pulexto a substance released by the predatory midge C.flavicans.This response occurs in the absence of visual cues and is independentof food availability. Finally, the results indicate that swarmingin D.pulex may occur in the absence of both light and predatorscent, but is influenced by food concentrations.