Contrasting structural complexity differentiate hunting strategy in an ambush apex predator

Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake—LSC; high structural complexity—HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent with a prevalent ambush predation behaviour, whereas the higher activity and larger space use in the LSC lake indicated a transition to more active search behaviour. It could lead to increased prey encounter and cause better growth in the LSC lake. Our study demonstrated how differences in structural complexity mediated prominent changes in the foraging behaviour of an apex predator, which in turn may have effects on the prey community.

Contrasting structural complexity differentiate hunting strategy in an ambush apex predator

Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators has received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake – LSC; high structural complexity - HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent with a prevalent ambush predation behaviour, whereas the higher activity and larger space use in the LSC lake indicated a transition to more active search behaviour. It could lead to increased prey encounter and cause better growth in the LSC lake. Our study demonstrated how differences in structural complexity mediated prominent changes in the foraging behaviour of an apex predator, which in turn may have effects on the prey community.

Intersection of motor volumes predicts the outcome of ambush predation of larval zebrafish

ABSTRACTEscape maneuvers are key determinants of animal survival and are under intense selection pressure. A number of escape maneuver parameters contribute to survival, including response latency, escape speed and direction. However, the relative importance of these parameters is context dependent, suggesting that interactions between parameters and predatory context determine the likelihood of escape success. To better understand how escape maneuver parameters interact and contribute to survival, we analyzed the responses of larval zebrafish (Danio rerio) to the attacks of dragonfly nymphs (Sympetrum vicinum). We found that no single parameter explains the outcome. Instead, the relative intersection of the swept volume of the nymph's grasping organs with the volume containing all possible escape trajectories of the fish is the strongest predictor of escape success. In cases where the prey's motor volume exceeds that of the predator, the prey survives. By analyzing the intersection of these volumes, we compute the survival benefit of recruiting the Mauthner cell, a neuron in anamniotes devoted to producing escapes. We discuss how the intersection of motor volume approach provides a framework that unifies the influence of many escape maneuver parameters on the likelihood of survival.

Intersection of motor volumes predicts the outcome of ambush predation of larval zebrafish

The escape maneuvers of animals are key determinants of their survival. Consequently these maneuvers are under intense selection pressure. Current work indicates that a number of escape maneuver parameters contribute to survival including response latency, escape speed, and direction. This work has found that the relative importance of these parameters is context dependent, suggesting that interactions between escape maneuver parameters and the predatory context together determine the likelihood of escape success. However, it is unclear how escape maneuver parameters interact to contribute to escape success across different predatory contexts. To clarify these issues, we investigated the determinants of successful escape maneuvers by analyzing the responses of larval zebrafish to the attacks of dragonfly nymphs. We found that the strongest predictor of the outcome was the time needed for the nymph to reach the fish’s initial position at the onset of the attack, measured from the time that the fish initiates its escape response. We show how this result is related to the intersection of the swept volume of the nymph’s grasping organs with the volume containing all possible escape trajectories of the fish. By analyzing the intersection of these volumes, we compute the survival benefit of recruiting the Mauthner cell, a neuron in anamniotes devoted to producing escapes. We discuss how escape maneuver parameters interact in determining escape response. The intersection of motor volume approach provides a framework that unifies the influence of many escape maneuver parameters on the likelihood of survival.

Foraging behaviour of the endangered Australian skink (Liopholis slateri)

The foraging behaviour of the endangered Australian skink (Liopholis slateri) was investigated through detailed observation of a subpopulation of lizards during seven months of sampling. Slater’s skinks primarily exhibited ambush predation, darting from burrow entrances to distances of up to 4 m with a success rate of ~70%. The direction of darting was often straight ahead and almost always in an 180° arc in front of the burrow entrance. Juveniles foraged more frequently and further from burrows than adults. Ants were the most common prey item taken and juveniles targeted small ants as prey more often than adults and often moved further to capture these prey. The spread of introduced buffel grass (Cenchrus ciliaris) in central Australia in recent decades is a possible contributing factor to the decline of L. slateri. A wide field of view appears to be critical for the success of the sit-and-wait foraging strategy employed by the skinks and additional research is required to determine whether further encroachment of buffel grass around burrow systems will impede visibility and directly affect foraging behaviour of these skinks.

Pit-builder vs non-pit-builder: advantage of trap building strategy in antlion larvae does not mean greater behaviour diversity

Predators use different foraging modes, ranging from active to ambush predation. We investigated the predatory behaviour of two antlion species, the pit-builder Euroleon nostras and the non-pit-builder Neuroleon microstenus, both considered as ambush predators but with different predatory strategies. Since the pit-builders evolved from non-pit-builders, we focused on the similarities and differences in behavioural patterns and capture success. We found that most behavioural patterns occur in both species, although the non-pit-builder’s behaviour is less stereotypic and exhibits more behavioural patterns than in the pit-builder when comparing behaviour from prey introduction to jaw set without pit-construction. In N. microstenus, two distinct behavioural sequences were noted, which depend on the method of prey carcass clearing. This is the first report describing two methods of prey-carcass clearing in a non-pit-builder: tossing or dropping the prey. We also noted the presence of camouflage in the non-pit-builder, considered as an important mechanism in anti-predator tactics.

Variation in the diet of the Lataste's viper Vipera latastei in the Iberian Peninsula: seasonal, sexual and size-related effects

Several life-history traits may increase vulnerability of species to extinction. Among snakes, ambush predation and dietary specialisation are factors that increase this vulnerability. European viper species, genus Vipera, display such traits and are categorised as endangered in several parts of its range. For their conservation management, a deeper knowledge of their ecology and habitat use is highly relevant. One of the species with less ecological data is the Lataste's viper Vipera latastei, a species which lives in the Iberian Peninsula and northwestern Africa. Here, we describe its diet based on the analysis of gut content of 435 museum specimens plus nine bibliographic data from the entire Iberian range. The species showed seasonal and ontogenetic shift in diet but no sexual variations. Feeding activity (percentage of vipers with prey) was low in accordance with its ambush predation tactics, being lower in spring than in summer and autumn. Prey spectrum included two main (reptiles and small mammals), and three sporadic, types of prey (arthropods, amphibians and birds). The consumption of reptiles and mammals was seasonal; the former decreased in occurrence from spring to autumn, whereas the latter showed an opposite pattern. There was an ontogenetic shift in the diet: juveniles fed mainly on reptiles and arthropods, whereas adult vipers progressively substitute this prey with insectivores, and the largest vipers primarily foraged on rodents and birds. Our results suggest that the seasonal variation in prey type was related to prey availability, whereas the ontogenetic shift was linked to gape limitation. The apparently wide prey spectrum of V. latastei must therefore be examined, taking into account that there are seasonal and ontogenetic dietary variations as well as geographic differences, the latter probably driven by climatic contrasts into the Iberian Peninsula. This new data of the endangered Iberian V. latastei can aid the effective conservation management of this species.

Effect of habitat complexity and predatory style on the capture success of fish feeding on aggregated prey

When offered a choice between open water and a ‘vegetated’ area of an aquarium (artificial sea grass), mysid (Paramesopodopsis rufa) swarms always selected open water. In contrast, juvenile and adult sea horses, Hippocampus abdominalis, which feed by ambush predation, always selected vegetated areas even when their mysid prey occurred in the adjacent clear water. Lunging predators, Australian salmon (Arripis trutta), always preferred open water to vegetated regions of the tank. Increasing vegetation density, i.e. from low to medium habitat complexity had a positive effect on capture success of juvenile and adult sea horses feeding on mysid swarms. However, number of attacks by juvenile sea horses, but not adults, was significantly reduced in higher density vegetation. Number of attacks by Australian salmon decreased as vegetation density increased but capture success, nonetheless, increased. Density of vegetation did not significantly affect the number of unsuccessful attacks by adult sea horses. Whereas proportion of unsuccessful attacks increased with vegetation density for juvenile sea horses, it decreased for juvenile salmon. This result is thought to be due to the fact that high vegetation densities disrupt structure of the prey swarm, itself a defensive formation, leaving a large number of more vulnerable small groups. Cohesive escape responses of a large swarm are likely to be a more effective defence against a lunging predator than against an ambush predator whose strategy is to use stealth to avoid provoking escape responses. Dense vegetation will militate against this strategy.

Feeding Ecology of the Tasmanian Spotted Skink, Niveoscincus Ocellatus (Squamata: Scincidae)

The feeding ecology of the spotted skink, Niveoscincus ocellatus, was examined over a 6-month period, from October to March, with additional data from one sample in midwinter. The investigation considered feeding activity, dietary composition and foraging strategy. Feeding activity,measured by stomach fullness, was unrelated to age, sex or reproductive status and showed little variation during the warmer months; in winter feeding was greatly reduced. N. ocellatus exhibits flexible foraging behaviour; a wide variety of terrestrial arthropods is taken opportunistically in accordance with a wide ranging foraging strategy. However, the consistent occurrence of cryptic and hidden prey indicates that active search foraging is also utilised. No evidence for ambush predation was found and, unlike many other small skinks, few arboreal or aerial prey are included in the diet, even though the habitat is rock scree and woodland where such prey abound. No evidence for any in a specific partitioning of diet based on kind or size of prey was obtained although a slight, but significant, correlation exists between maximum prey size and lizard size.