The escape response of the zebra danio (Brachydanio rerio) II. The effect of experience

Naïve zebra danios (Brachydanio rerio) flee from an approaching predator when the angle subtended at the danio's eye by the predator changes at a rate greater than some characteristic threshold value. The hypothesis was tested that this value declines, and hence reactive distance increases, as a function of the number of past experiences with the predator. Artificial predators of two types, a model and a film of an approaching object, were presented to the danios daily and changes in behaviour recorded. The rate of change of visual angle at the time of response to the predator (dα/dt threshold) declined asymptotically with increasing experience. Consequently, flight distance increased asymptotically. The change was not due to growth, maturation, or increased familiarity with the testing situation. The danios apparently associated the visual characteristics of the predator with its subsequent high rate of angular growth and began to respond to these visual characteristics prior to dα/dt exceeding the threshold. The angle of escape was not affected by experience. Escape velocity increased with experience of the film predator, but not with experience of the model predator. No decrement of the learned change in reactive distance was evident after 10 days without experience with the film predator.     

Effect of predator exposure on the performance and survival of red drum (<Emphasis Type="Italic">Sciaenops ocellatus</Emphasis>)

The influence of predator exposure on the survival of hatchery red drum, Sciaenops ocellatus was investigated under laboratory conditions. Several prey-capture (attack distance, mean attack velocity, capture time, and gape cycle duration) and anti-predator (reaction distance, response distance, mean velocity, and maximum velocity) performance variables were quantified using high-speed video for juvenile red drum (25–30 mm standard length, L _S ) reared with and without predators (pinfish, Lagodon rhomboides). Univariate contrasts of prey-capture events demonstrated that attack distance (mean ± s.e.) was significantly greater in red drum reared with (1.20 ± 0.16 mm) versus without (0.65 ± 0.09 mm) pinfish predators. During anti-predator events, red drum reared with predators had approximately 300% greater reaction distance and 20%–30% greater response distance, mean velocity and maximum velocity versus fish reared without predators; however, these differences were not statistically significant. Following video assessments, a series of mortality experiments were conducted using free-ranging pinfish predators. Mortality rates (Z) ranged from 0.047 to 0.060 (Z/hr/predator) and did not differ significantly among treatments.     

Empirical studies of escape behavior find mixed support for the race for life model

Escape theory has been exceptionally successful in conceptualizing and accurately predicting effects of numerous factors that affect predation risk and explaining variation in flight initiation distance (FID; predator–prey distance when escape begins). Less explored is the relative orientation of an approaching predator, prey, and its eventual refuge. The relationship between an approaching threat and its refuge can be expressed as an angle we call the “interpath angle” or “Φ,” which describes the angle between the paths of predator and prey to the prey’s refuge and thus expresses the degree to which prey must run toward an approaching predator. In general, we might expect that prey would escape at greater distances if they must flee toward a predator to reach its burrow. The “race for life” model makes formal predictions about how Φ should affect FID. We evaluated the model by studying escape decisions in yellow-bellied marmots Marmota flaviventer, a species which flees to burrows. We found support for some of the model’s predictions, yet the relationship between Φ and FID was less clear. Marmots may not assess Φ in a continuous fashion; but we found that binning angle into 4 45° bins explained a similar amount of variation as models that analyzed angle continuously. Future studies of Φ, especially those that focus on how different species perceive relative orientation, will likely enhance our understanding of its importance in flight decisions.     

The ontogeny of escape behavior,locomotor performance,and the hind limb in Sceloporus woodi

Flight initiation distance describes the distance at which an animal flees during the approach of a predator. This distance presumably reflects the tradeoff between the benefits of fleeing versus the benefits of remaining stationary. Throughout ontogeny, the costs and benefits of flight may change substantially due to growth-related changes in sprint speed; thus ontogenetic variation in flight initiation distance may be substantial. If escape velocity is essential for surviving predator encounters, then juveniles should either tolerate short flight initiation distances and rely on crypsis, or should have high flight initiation distances to remain far away from their predators. We examined this hypothesis in a small, short-lived lizard (Sceloporus woodi). Flight initiation distance and escape velocity were recorded on an ontogenetic series of lizards in the field. Maximal running velocity was also quantified in a laboratory raceway to establish if escape velocities in the field compared with maximal velocities as measured in the lab. Finally a subset of individuals was used to quantify how muscle and limb size scale with body size throughout ontogeny. Flight initiation distance increased with body size; larger animals had higher flight initiation distances. Small lizards had short flight initiation distances and remained immobile longer, thus relying on crypsis for concealment. Escape velocity in the field did not vary with body size, yet maximum velocity in the lab did increase with size. Hind limb morphology scaled isometrically with body size. Isometric scaling of the hind limb elements and its musculature, coupled with similarities in sprint and escape velocity across ontogeny, demonstrate that smaller S. woodi must rely on crypsis to avoid predator encounters, whereas adults alter their behavior via larger flight initiation distance and lower (presumably less expensive) escape velocities.     

Repellent activity of catmint, Nepeta cataria, and iridoid nepetalactone isomers against Afro-tropical mosquitoes, ixodid ticks and red poultry mites

The repellent activity of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), and the main iridoid compounds (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone, was assessed against (i) major Afro-tropical pathogen vector mosquitoes, i.e. the malaria mosquito, Anopheles gambiae s.s. and the Southern house mosquito, Culex quinquefasciatus, using a World Health Organisation (WHO)-approved topical application bioassay (ii) the brown ear tick, Rhipicephalus appendiculatus, using a climbing repellency assay, and (iii) the red poultry mite, Dermanyssus gallinae, using field trapping experiments. Gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) analysis of two N. cataria chemotypes (A and B) used in the repellency assays showed that (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone were present in different proportions, with one of the oils (from chemotype A) being dominated by the (4aS,7S,7aR) isomer (91.95% by GC), and the other oil (from chemotype B) containing the two (4aS,7S,7aR) and (4aS,7S,7aS) isomers in 16.98% and 69.83% (by GC), respectively. The sesquiterpene hydrocarbon (E)-(1R,9S)-caryophyllene was identified as the only other major component in the oils (8.05% and 13.19% by GC, respectively). Using the topical application bioassay, the oils showed high repellent activity (chemotype A RD₅₀ = 0.081 mg cm⁻² and chemotype B RD₅₀ = 0.091 mg cm⁻²) for An. gambiae comparable with the synthetic repellent DEET (RD₅₀ = 0.12 mg cm⁻²), whilst for Cx. quinquefasciatus, lower repellent activity was recorded (chemotype A RD₅₀ = 0.34 mg cm⁻² and chemotype B RD₅₀ = 0.074 mg cm⁻²). Further repellency testing against An. gambiae using the purified (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone isomers revealed overall lower repellent activity, compared to the chemotype A and B oils. Testing of binary mixtures of the (4aS,7S,7aR) and (4aS,7S,7aS) isomers across a range of ratios, but all at the same overall dose (0.1 mg), revealed not only a synergistic effect between the two, but also a surprising ratio-dependent effect, with lower activity for the pure isomers and equivalent or near-equivalent mixtures, but higher activity for non-equivalent ratios. Furthermore, a binary mixture of (4aS,7S,7aR) and (4aS,7S,7aS) isomers, in a ratio equivalent to that found in chemotype B oil, was less repellent than the oil itself, when tested at two doses equivalent to 0.1 and 0.01 mg chemotype B oil. The three-component blend including (E)-(1R,9S)-caryophyllene at the level found in chemotype B oil had the same activity as chemotype B oil. In a tick climbing repellency assay using R. appendiculatus, the oils showed high repellent activity comparable with data for other repellent essential oils (chemotype A RD₅₀ = 0.005 mg and chemotype B RD₅₀ = 0.0012 mg). In field trapping assays with D. gallinae, addition of the chemotype A and B oils, and a combination of the two, to traps pre-conditioned with D. gallinae, all resulted in a significant reduction of D. gallinae trap capture. In summary, these data suggest that although the nepetalactone isomers have the potential to be used in human and livestock protection against major pathogen vectors, intact, i.e. unfractionated, Nepeta spp. oils offer potentially greater protection, due to the presence of both nepetalactone isomers and other components such as (E)-(1R,9S)-caryophyllene.     

Velocity and dominance affect prey capture and microhabitat selection in juvenile Chinook (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>)

Habitat selection is an important phenomenon that may greatly affect individual fitness. Using an artificial stream, we examined the relationship between the percentage of prey captured, reactive distance, dominance, and water velocity for juvenile Chinook Salmon (Oncorhynchus tshawytscha) from the Chena River, Alaska, and tested the fitness-based microhabitat selection model of Grossman et al. (Ecol Freshw Fish 11:2–10, 2002). Recent declines in the abundance of Chinook accentuate our need for habitat selection studies on this species. We conducted three experiments: two with single fish (1st N?=?27, fish SL 58–84 mm, 2nd N?=?14, fish SL 49–56 mm) and one with pairs of dominant and subordinate fish (N?=?10 pairs, 64–96 mm, mean difference in SL?=?7 mm). We placed individual or pairs of fish in an artificial flume and recorded reactive distance and the percent prey capture with individual dead brine shrimp (Artemia spp.) as prey. Prey were presented at 10 cm/s velocity intervals ranging from 10 to 60 cm/s; velocities found in the natural habitat. Mean reactive distance in single fish experiments (henceforth SFE) averaged 33 and 29 cm respectively, and was not related to velocity. We detected a negative, curvilinear relationship between velocity and percent prey capture. Holding velocities for juvenile Chinook were significantly lower than prey capture velocities. The Grossman et al. (Ecol Freshw Fish 11:2–10, 2002) model yielded an optimal focal-point velocity prediction of 35 cm/s for juvenile Chinook, however focal-point velocities occupied by juveniles in the Chena River averaged 12 cm/s. Predicted optimal velocities were present in the Chena River; hence, this discrepancy suggests that other factors such as distraction from drifting debris or predation risk influenced habitat selection. There were no differences in reactive distances or holding velocity/capture velocity relationships for dominant and subordinate fish; however, dominants captured significantly more prey than subordinates. Being subordinate resulted in a decrease of 61% in mean percent prey capture (the difference between what was captured by the fish alone versus the difference with a dominant), whereas the mean cost to fish with dominant rank was a 21% decline between the percentage captured alone versus that with a subordinate.     

Distance-to-cover and the escape decisions of an African cichlid fish,Melanochromis chipokae

Synopsis The risk to a prey individual in an encounter with a predator increases as the distance to protective cover increases. Prey should therefore initiate their flight to cover at longer distances from an approaching predator (i.e., sooner) and/or flee at greater velocities, as the distance to cover increases. These predictions were tested with an African cichlid fish, Melanochromis chipokae presented with a looming stimulus simulating an attacking predator. The fish varied their flight initiation distance as predicted, but there was no significant effect of distance-to-cover on escape velocity. Nevertheless, the cichlids appeared to choose a combination of flight initiation distance and escape velocity which ensured they reached cover with a constant temporal margin of safety.     

Scales of detection and escape of the sea urchin Tetrapygus niger in interactions with the predatory sun star Heliaster helianthus

Predators can simultaneously have lethal (consumption) and non-lethal (modification of traits) effects on their prey. Prey escape or fleeing from potential predators is a common form of a non-lethal predator effect. The efficiency of this response depends on the prey's ability to detect and correctly identify its predator far enough to increase the probability of successful escape, yet short enough to allow it to allocate time to other activities (e.g. foraging). In this study, we characterized the non-lethal effect of the sun star Heliaster helianthus on the black sea urchin Tetrapygus niger by assessing the nature of predator detection and the spatial scale involved both in predator detection and in the escape response. Through field and laboratory experiments we demonstrate that T. niger detects chemical cues released by H. helianthus. In the laboratory, these chemical signals can be detected at distances of up to about 50 cm. In the field, the distance traveled by urchins when escaping, after recognition of the predation risk, was also restricted to about 40 cm. Thus, considering the sizes of the predator and prey, the spatial scale of both detection and escape is comparatively small suggesting that non-lethal effects of H. helianthus (e.g. how it modifies the behavior of T. niger) should be important at local spatial scales and highly variable at the landscape scale.     

The effect of size on the timing of visually mediated escape behaviour in staghorn sculpin Leptocottus armatus

The effect of prey size on the timing of the startle response in the sculpin Leptocottus armatus was investigated. Escape responses were triggered visually by a looming image obtained using a computer‐generated animation of an approaching black disk. The results showed that apparent looming threshold ( T _AL, i.e. the threshold at which the rate of change of the visual angle subtended by predator frontal profile onto the prey's eye triggers an escape response by the prey) decreased with increasing prey size. Distance travelled within a fixed time was unaffected by size. Theoretical considerations suggest that larger prey would need to travel a longer distance (and so they would need more time) in order to move their whole body outside the predator's approaching gape. Therefore, the scaling of T _AL may be explained by taking into account both ultimate and proximate considerations that need not be mutually exclusive. At an ultimate level, lower T _AL in larger fish may be explained in terms of offsetting the disadvantage of offering a larger volume to be intercepted by the predator. At a proximate level, T _AL may be related to the fish's visual acuity, which is higher in larger fish.     

The Visually Mediated Escape Response in Fish: Predicting Prey Responsiveness and the Locomotor Behaviour of Predators and Prey

The outcome of predator-prey encounters is determined by a number of factors related to the locomotor and sensory performance of the animals. Escape responses can be triggered visually, i.e. by the magnifying retinal image of an approaching object (i.e. a predator), called the looming effect, and calculated as the rate of change of the angle subtended by the predator frontal profile as seen by the prey. A threshold of looming angle (ALT, the Apparent Looming Threshold) determines the reaction distance of a startled fish, which is proportional to the attack speed of the predator and its apparent frontal profile. Optimal tactics for predator attacks as well as consideration on their functional morphology are discussed in relation to ALT. Predator optimal attack speeds depend on predator morphology as well as the prey ALT. Predictions on the scaling of ALT suggest that ALT may increase (i.e. implying a decrease in reaction distance) with prey size in cases in which predator attack speeds are high (i.e. > 4 L/s in a 1-m long predator), while it may be relatively independent of prey size when predators attack at lower speeds. The issue of scaling of ALT is discussed using examples from field and laboratory studies. While the timing of the escape is a crucial issue for avoiding being preyed upon, the direction of escape manoeuvres may also determine the success of the escape. A simple theoretical framework for optimal escape trajectories is presented here and compared with existing data on escape trajectories of fish reacting to startling stimuli.     

Formation of the compression zone in a plasma flow generated by a magnetoplasma compressor

Processes occurring in a plasma flow generated by a magnetoplasma compressor (MPC) during the formation of the compression zone are discussed. The paper presents results of measurements of the spatial distribution of the electric current in the plasma flow, the temporal and spatial (along the flow) distributions of the plasma density, and the profiles of the velocity of individual flow layers along the system axis. The spatial distribution of the electromagnetic force in the flow is analyzed. It is shown that the plasma flow is decelerated when approaching the compression zone and reaccelerated after passing it. In this case, the plasma flow velocity decreases from ν = (2–3) × 10⁷ cm/s at the MPC output to ν < 10⁶ cm/s in the region of maximum compression and then again increases to 10⁷ cm/s at a distance of 15–17 cm from the MPC output. In some MPC operating modes, a displacement of the magnetic field from the compression zone and the formation of toroidal electric current vortices in the plasma flow after passing the compression zone were detected.     

The effectiveness of post-contact defenses in a prey with no pre-contact detection

Most empirical and theoretical papers on prey–predator interactions are for animals with long-range detection, animals that can detect and react to predators long before these touch the prey. Heavy-bodied and chemically defended harvestmen (Arachnida, Opiliones) are an exception to this general pattern and rely on contact to detect arthropod predators. We examined the interactions between the Brazilian wandering spider Ctenus ornatus with harvestmen (Mischonyx cuspidatus) or control prey (Gryllus sp. and M. cuspidatus immature, both with soft integuments). Considering a prey–predator system in which fleeing from or reacting to a predator at a distance is not possible, we predicted both a high survival value of near-range defense mechanisms and that mortality would be higher in the absence of such defense mechanisms. We also expected the predator to behave differently when interacting with harvestmen or with a control prey without such defense mechanisms. Our results from laboratory experiments partially matched our predictions: First of all, histological sections showed that the integument of adult harvestmen is thicker than that of immature harvestmen and that of crickets. Adult harvestmen were less preyed upon than the control prey; the heavy armature increases the survival rate but the secretions from the scent glands do not. The predator did behave differently when attacking harvestmen compared to crickets. Despite the large size difference between predator and harvestmen, the protection provided by the armature allowed some of the harvestmen to survive encounters without pre-contact detection, thus greatly reducing the reliance on long-range detection to survive encounters with predators. Harvestmen call for theoretical and empirical work on prey–predator interactions that take into account the possibility that prey may not detect the predator before contact is established.     

The reaction distance of a planktivorous fish (<Emphasis Type="Italic">Scardinius erythrophthalmus</Emphasis>) and the evasiveness of its prey (<Emphasis Type="Italic">Daphnia pulex </Emphasis>×<Emphasis Type="Italic"> pulicaria</Emphasis>) under different artificial light spectra

Artificial light at night may affect mortality risk in prey from visually oriented predators because the effect of the artificial light spectrum may differ for a predator’s visual prey detection and for prey evasiveness. To test this, we conducted two types of experiment. First, we assessed the reaction distance and swimming speed of juvenile rudd (Scardinius erythrophthalmus) allowed to forage on juvenile Daphnia pulex?×?pulicaria under three artificial light sources: halogen, high pressure sodium (HPS), and metal halide bulbs, at the same light intensity. Second, we assessed the evasiveness of D. pulex?×?pulicaria under the same artificial light sources and in darkness (as a control), in the presence and absence of chemical information on predation risk (kairomones) of juvenile rudd. We found that while both reaction distance and swimming speed of fish was greater under halogen compared to HPS, and similar under metal halide light compared to halogen and HPS, the evasiveness of Daphnia was greater under halogen and HPS-generated light than under metal halide light. The results suggest a possible mismatch of Daphnia’s behavioural response under metal halide light to predicted predation risk, and thus a possible threat to predator–prey balance in a lake ecosystem.     

The carabid <Emphasis Type="Italic">Pterostichus melanarius</Emphasis> uses chemical cues for opportunistic predation and saprophagy but not for finding healthy prey

The sentinel prey method can quantify predation pressure in various habitats. Real prey is assumed to more realistically mimic the predator experience but the predator can rarely be identified. Artificial prey made of plasticine may lack real chemical cues, but provides information about predator identity. However, the relationship between predation pressure registered by artificial versus real prey is not clear. We tested the relative attractiveness of artificial caterpillars, and intact, wounded, or dead larvae of the cabbage moth (Mamestra brassicae) for the carabid predator Pterostichus melanarius Illiger (Coleoptera: Carabidae). P. melanarius adults were attracted to dead caterpillars more than to live or wounded ones. Coating artificial caterpillars with caterpillar haemolymph increased their attractiveness. However, predators were not attracted more to healthy, real caterpillars than to “untreated” artificial ones. We conclude that using artificial caterpillars does not underestimate predation pressure by this carabid on healthy caterpillars.     

Predator identification and effects of habitat management and fencing on depredation rates of simulated nests of an endangered population of Hermann’s tortoises

Nest predation has been identified as the main threat behind the negative population dynamics in chelonian species and in particular in the native Iberian population of the Western Hermann’s tortoise Testudo hermanni hermanni. This endangered subspecies is found within the Albera Nature Reserve, where this study was performed. We selected three formerly high-density tortoise areas to carry out different trials whose aims were to: (1) identify nest predator species, (2) test the success of reducing the shrub cover to reduce nest predation in potential new nesting areas, and (3) assess fencing efficiency to exclude predators. For the first objective, camera-trapping was used to identify nest predators, with sardines and artificial tortoise nests as lures. We obtained 825 pictures of possible predators and demonstrated that the beech marten was the most abundant predator in the study areas, followed by the badger and the wild boar. For the second objective, predation of artificial nests was compared between plots managed for shrub reduction (27 plots of 4, 25, and 100?m²) and a natural nesting area (nine control plots of 100?m²). Predation was strong in the managed plots (43.6% after 48?h and 99.6% after 144?h) but highest in the control area (100% after 48?h). Surprisingly, predation occurred at an even faster pace when we repeated the trial with a single artificial nest (in order to reduce odor intensity). Finally, we compared predation rates between eight fenced and eight unfenced plots of 100?m². Fencing was partially effective to control nest predation because it excluded all the main predator species except the beech marten, which learned to go through it. Since the nest predation threat to this endangered population is critical, new strategies are needed to control nest predation by taking into account the ability of predators to learn nest location.     

Effect of the change of leaf angle arrangement on productivity of maize (Zea mays L.) stands

Leaf angles, frequency distribution of leaf area inclinations, leaf area index, amount of intercepted radiation, biological, vegetative and grain yields and grain yield proportion of biological yield were determined in maize stands of two population densities, 55 555 plants ha^?1 (S ₁), and 80 000 plants ha^?1 (S ₂). Also the effect of the artificial change of leaf angle upon these indices was studied. We classified normal maize stand (N) as the interstage between a planophile and a plagiophile type of canopy, that with artificially changed leaf angle (V) as an erectophile type of canopy. The relative interception of the incoming radiation in the variantsV S ₁ andV S ₂ was lower than in the variantsN S ₁ andN S ₂. The variantsV in comparison with variants N increased grain yield and biological yield.     

Microcalorimetric investigations of the metabolism of yeasts. growth in batch and chemostat cultures on ethanol medium

Summary In the presence of protein, Hansenula polymorpha cultivation medium exhibits a maximum volumetric mass transfer coefficient, k_La, as function of the employed antifoam agents (soy oil and Desmophen 3600). With diminishing superficial gas velocity this maximum disappeas.Symbols E_G Relative gas holdup - k_La Volumetric mass transfer coefficient (s^–1) - w_SL Superficial liquid velocity (cm s^–1) - w_SG Superficial gas velocity (cm s^–1)     

A new mathematical equation relating activation energy to bond angle and distance: A key for understanding the role of acceleration in lactonization of the trimethyl lock system

AM1 semi-empirical molecular orbital and ab initio HF at the 6-31G level calculations for the lactonization processes of 12 different hydroxy acids (1a-1l) which differ in their structural features have been conducted. The calculations obtained reveal the following: (1) The rate-limiting step in the lactonization process is formation of a tetrahedral intermediate and not its collapse as was previously reported. (2) The rate-limiting step in both the acid-catalyzed and uncatalyzed lactonization is composed of two successive steps: approach of the hydroxyl toward the carbonyl carbon until it reaches a distance of 1.4 -1.5 Å, followed by proton transfer from the ether-type oxygen to one of the hydroxyls in the tetrahedral intermediate. Calculations of the activation energies for formation of the tetrahedral intermediate in the 12 hydroxy acids studied indicate: (1) A linear relationship exists between the change in enthalpic energy (E) and the ratio of the attack angle (nucleophilic-oxygen/carbonyl-carbon/αλπηα-carbon) to the distance (nucleophilic-oxygen/carbonyl-carbon) termed α/r; (2) The slope (S) of E vs. α/r plots depend on the nature of the hydroxy acids. Furthermore, plots of S values against the experimental rate values (log k_exp) show a linear correlation with a high correlation coefficient. The combined results suggest that hydroxy acids with low S values have high k_exp values due to enthalpic proximity effects.     

Predator-induced take-off strategy in great tits (Parus major)

When birds are attacked by predators the initial take-off is crucial for survival. The strategy in the initial phase of predator evasion is probably affected by factors such as body mass and presence of cover and conspecifics, but it may also be a response to the character of the predator''s attack. In choosing an angle of flight, birds face a trade-off between climbing from the ground and accelerating across the ground. This is, to our knowledge, the first study investigating whether the attack trajectory of a raptor affects the take-off strategy of the prey bird. First-year male great tits (Parus major) adjusted take-off angle to a model predator''s angle of attack. Birds attacked from a steep angle took off at a lower angle than birds attacked from a low angle. We also compared take-offs at dawn and dusk but could not find any measurable effect of the diurnal body mass gain (on average 7.9%) in the great tits on either flight velocity or angle of ascent.     

Visual Mechanism determining Flight Distance in Zebra Danios (<Emphasis Type="Italic">Brachydanio rerio</Emphasis> Pisces)

HERSHEL WEINBERGER¹ conjectured that animals may be able to estimate the time to collision with an approaching object in the absence of knowledge of the size, velocity or distance of the object. The question arises whether prey animals use this mechanism to detect and avoid predators.