A quantitative test of the ‘economic’ and ‘optimal’ models of escape behaviour

A game of patience between predator and prey: waiting for opponent’s action determines successful capture or escape

When predator and prey animals face each other, preemptive actions by both sides are considered to mediate successful capture or escape. However, in spite of the general presumption, some animals, such as predatory snakes and their frog prey, occasionally remain motionless or move slowly for a while before striking or escaping, respectively. To clarify the possible advantages of this behaviour, we examined interactions between Japanese Four-lined Ratsnakes (Elaphe quadrivirgata (H. Boie, 1826)) and Black-spotted Pond Frogs (Pelophylax nigromaculatus (Hallowell, 1861)), focusing especially on kinematic features of strike behaviour of snakes and flight behaviour of frogs in close quarters. Staged encounter experiments and field observations revealed that counteractions against an opponent’s preemptive actions are effective for both snakes and frogs until a certain distance because they are hardly able to change their trajectories once they initiate strike or escape behaviours. Snakes and frogs also appropriately switched their behaviour from waiting for the opponent’s action to taking preemptive action at this threshold distance. These results suggested the occurrence of a game of patience between snakes and frogs in which they wait for the opponent’s action to achieve effective countermeasures. Our study provides new insights for predicting optimal decision-making by predators and prey and will contribute to a better understanding of their strategies.

Predatory chemical cues decrease attack time and increase metabolic rate in an orb-web spider

Animals are able to assess the risk of predation and respond accordingly via behavioural and physiological changes. Web-building spiders are in the unique situation where they reside in the middle of their web and are therefore relatively exposed to predators. Thus, these spiders might moderate either their web-building behaviour or their behaviour on the web when exposed to the threat of predation. In this study, we experimentally explored how predatory chemical cues influence foraging behaviour and metabolic rate in female of the orb-web spider, Argiope keyserlingi. We found that female spiders restricted their foraging time budget when exposed to the predatory cues from a praying mantid: they responded 11 percent and 17 percent quicker to a vibratory stimulus compare to control and non-predator cues, respectively, and spent less time handling the prey. Moreover, spiders were less likely to rebuild the web under predatory cues. Female A. keyserlingi exposed to the praying mantid cue significantly elevated their metabolic rate compared to the control group. Our findings revealed short-term modifications over two weeks of the trials in foraging behaviour and physiology of female spiders in response to predator cues. This study suggests that under predator cues the spiders move quicker and this could be facilitated by elevation in metabolic rate. Reduced foraging activity and less frequent web repair/rebuilding would also reduce the spiders’ exposure to praying mantid predators.

Are males more scared of predators? Differential change in metabolic rate between males and females under predation risk

The non-consumptive effects of predation contribute to reduce preys' fitness. In this way, predation imposes a cost to animals, not only through direct consumption, but also as an energetic cost. One way used to estimate this cost in the past has been to measure the production of CO₂ to estimate the change in metabolic rate because of predation. It has been proposed that this change is mediated by the insect stress neurohormone octopamine. Here we study the change in metabolic rate of the black field cricket (Teleogryllus commodus), and how the production of CO₂ varies when a chemical cue from a sympatric predator is added. We hypothesised that after the addition of a predatory cue, the metabolic rate will increase. Moreover, since the pressure of predation is stronger on females, we propose that females will have a greater increase in the CO₂ produce as consequence of the added cues from the predator. Our results confirmed our first hypothesis, showing an almost two-fold increase in CO₂ when the predatory cue was added. However, males were the ones that showed a greater increase, in opposition to our second hypothesis. We put these results in the context of the escape theory and, in particular, the "landscape of fear" hypothesis. Also, because the timing between the increase of metabolic rate we measure here and the release of octopamine reported in previous studies do not match, we reject the idea that octopamine causes the increase in metabolism.

Immobile defence of a frog distracts attention of approaching predators to other prey

Escape theories predict that animals remaining motionless after being detected by a predator are less successful in predation avoidance because it simply allows the predator to come closer. Nonetheless, even in such a situation, some animals often remain motionless for a while before escaping. We hypothesized that this non-immediate escape response increases the survivorship of the prey by distracting the predator’s attention to another nearby prey that indifferently comes into the visual field of the predator that is carefully and inconspicuously approaching the former prey. Staged encounter experiments using frogs and snakes as prey and predator, respectively, yielded the results that support this hypothesis. Considering the density of frogs in the field, this phenomenon is feasible under natural conditions. Therefore, remaining motionless after being detected by predator could be an effective choice for prey to avoid predation under a certain condition.

Danger comes from all fronts: predator-dependent escape tactics of túngara frogs

The escape response of an organism is generally its last line of defense against a predator. Because the effectiveness of an escape varies with the approach behaviour of the predator, it should be advantageous for prey to alter their escape trajectories depending on the mode of predator attack. To test this hypothesis we examined the escape responses of a single prey species, the ground-dwelling túngara frog (Engystomops pustulosus), to disparate predators approaching from different spatial planes: a terrestrial predator (snake) and an aerial predator (bat). Túngara frogs showed consistently distinct escape responses when attacked by terrestrial versus aerial predators. The frogs fled away from the snake models (Median: 131°). In stark contrast, the frogs moved toward the bat models (Median: 27°); effectively undercutting the bat’s flight path. Our results reveal that prey escape trajectories reflect the specificity of their predators’ attacks. This study emphasizes the flexibility of strategies performed by prey to outcompete predators with diverse modes of attack.

Distance-dependent switching of anti-predator behavior of frogs from immobility to fleeing

To avoid predation, many animals are required to appropriately switch between immobility for crypsis and fleeing for escape. We conducted two staged-encounter experiments using a frog and a snake to examine factors that affect the occurrence of immobility and fleeing, and to evaluate the efficiency of them. The first experiment demonstrated that frogs initially exhibit immobility, when snakes are moving at a long distance, and then switch from immobility to fleeing at a shorter distance even when snakes have not detected them. The second experiment demonstrated that snakes at 400–800 mm distance detect only fleeing frogs, whereas snakes at 100 mm or closer detect both immobile and fleeing frogs. Thus, the ability of snakes to detect motionless frogs depends on the distance, and the distance-dependent switching can be considered an adaptive strategy of the frog. However, a previous model predicts that cryptic prey should flee immediately on seeing a predator or not flee until being detected by the predator. To explain this discordance, we propose two factors: engagement of intensive searching mode by predator at short distance and effects of sudden fleeing at close distance. We suggest incorporating them in future theory for better understanding of anti-predator strategy.