Prey Search Research Articles

Optimization of Fractional Order PID Controller Using Grey Wolf Optimizer

This paper presents a novel evolutionary technique to optimize the parameters of fractional order controller for controlling two classes of systems: time-delay and higher-order system. The evolutionary technique known as grey wolf optimizer is used to tune both integer and fractional order controllers. The grey wolf optimizer searches for the optimum solution in the following manner, i.e. encircling, hunting, attacking the prey and finally search for the new prey consecutively if exists. To certify these various procedure, the performance indices like integral square error, integral absolute error, integral time-weighted square error, and integral time-weighted absolute error are minimized for the authenticity. Moreover, the proposed algorithm is validated and compared with well-established techniques.

Bird Use of Bobwhite Brush Shelters on a Conservation Reserve Program Field

Northern bobwhite (Colinus virginianus) are known to use constructed brush shelters. The establishment of artificial shelters is a common practice in grasslands where woody cover is lacking. We evaluated the use of brush shelters by bobwhite and other bird species in a Conservation Reserve Program (CRP) field. Twenty-seven species of birds were observed at brush shelters versus 10 species at control sites. No species occurred exclusively at control sites. Brush shelters in CRP had positive effects on avian communities by providing sites for vocalizing, prey search, loafing, and nesting.

Sneak peek: Raptors search for prey using stochastic head turns

The strategies by which foraging predators decide when to redirect their gaze influence both prey detection rates and the prey's ability to detect and avoid predators. We applied statistical analyses that have been used to study neural decision-making for gaze redirection in primates to 3 species of predatory birds with different sizes, visual systems, habitats, and hunting behaviors: the Northern Goshawk (Accipiter gentilis), Cooper's Hawk (A. cooperii), and Red-tailed Hawk (Buteo jamaicensis). The timing of head saccades was measured during visual searches using field video recordings of foraging raptors, and during a variety of behaviors using a miniature camera mounted on the head of a Northern Goshawk. The resulting statistical distribution of latencies (time between successive head saccades) was compared to predictions from various models proposed to describe visual search strategies. Our results did not support models that assume a constant probability of gaze redirection per unit time, a constant time for “giving up” on the visual search, or an initial setup time before visual search initiation. Instead, our data were fit best by a log-normal distribution, consistent with the raptors stochastically changing their gaze direction on the basis of accumulated environmental information. Specifically, this suggests that saccade initiation arises from a neural computation based on detection of a threshold level of a dynamically updated decision signal that encodes noisy sensory data, similar to the processes inferred from previous studies of visual search strategies in primates. The only significant between-species difference we found was a slower mean gaze-redirection rate for 2 larger species compared to the Cooper's Hawk, even though the latter has hunting behavior and maneuverability similar to that of the Northern Goshawk. Head-saccade latencies measured for a Northern Goshawk during different behaviors showed that the bird changed gaze direction significantly less frequently, on average, while perched than while in motion.

First capture success in two dimensions: The search for prey by a random walk predator in a comprehensive space of random walks

Random walk models are an important tool used for understanding how complex organisms redistribute themselves through space and time in search of targets such as food, shelter, or mates. These walks are easily studied with agent-based models, which can be used to ask which search strategy is best according to some efficiency metric. Current studies however, generally do not consider the full range of potential random walks, success metrics, and constraints on the walker, and implementation details vary widely. It is therefore difficult to compare results across studies. In this paper, we investigate predator search behaviour in a comprehensive space of key movement variables that allows the predator to select from a continuum of random walks ranging from Brownian walks (BWs) to correlated random walks (CorRWs) which include directional persistence, to composite random walks (ComRWs) which feature intensive and extensive search modes (ISMs and ESMs), and finally to more complex correlated composite random walks (CCRWs). We specifically focus on the search behaviour of a predator between the initiation of a search for a prey item and the first successful acquisition of a prey target: we call this interval the “search-to-capture” event. We measure the predator's success against three metrics of energetic cost: (1) the time elapsed, (2) the distance travelled, and (3) an equally weighted combination of time and distance. In addition, we explore the effect of three different constraints on the predator: (1) hunting success in the extensive search mode, (2) detection radius when in the extensive search mode, and (3) prey density. Our work confirms the broadly held notion that CCRW movement patterns should always outperform BWs, but find instructive cases where other walks are superior. We also show that, within the CCRW category, there is a wide range of possible walks and rank these according to measures of energetic cost. Our work also offers insights into the evolutionary pressures surrounding the “search-to-capture” event, and suggests that CCRW predators with low hunting success in one movement mode experience higher evolutionary pressures and are thus more likely to adopt a nearly optimal random walk. Our work highlights the need for comprehensive studies that examine several aspects of random walks simultaneously.

Searching for prey in a three‐dimensional environment: hierarchical movements enhance foraging success in northern elephant seals

Summary Foraging theory predicts that predators adjust their movements according to the spatial distribution of prey. Since prey is often patchily distributed, area‐restricted search (ARS) behaviour, characterized by sinuous search paths of predators with increased turning frequency, should be effective in foraging. However, it remains unclear whether ARS behaviour actually enhances foraging success in free‐ranging animals, especially in marine animals that forage in a three‐dimensional (3D) environment. Here, we reconstructed 3D dive paths of a highly pelagic marine predator, the northern elephant seal (n = 3), with multisensor data loggers that recorded depth, tri‐axis acceleration, tri‐axis magnetism and swim speed. We identified spatial scales of volume‐restricted search (VRS, termed for 3D ARS) behaviour using spherical first‐passage time analysis on 3D dive paths, accompanied with quantifying feeding rates in VRS by using mandible accelerometers that recorded feeding events. Seals exhibited VRS behaviour at two spatial scales (radius of spheres): small‐VRS (8–10 m) and large‐VRS (17–19 m). Most feeding events occurred in VRS zones (78 and 86% for small and large‐VRS, respectively), although VRS accounted for a small proportion of bottom phase of dives in distance travelled. This suggests a strong link between VRS behaviour and foraging success. There was a hierarchical structure to the VRS; most small‐VRS (95%) were nested within large‐VRS (i.e. nested VRS). Importantly, nested VRS had significantly higher feeding rates than non‐nested VRS, because nested VRS contained small‐ and large‐VRS with higher and lower feeding rates, respectively. These results suggest that seals forage on mesopelagic prey in a hierarchical patch system where high‐density patches at small scales are nested within low‐density patches at larger scales. We demonstrated that seals employed scale‐dependent, hierarchical 3D movements and that underwater fine‐scale sinuous movements (i.e. VRS) were strongly linked to higher foraging success, particularly within nested VRS zones. We suggest that seals enhanced foraging success by employing hierarchical movements that possibly reflect the hierarchical property of prey distribution. Although recent studies advocate that optimal searching behaviour would be scale‐independent (e.g. Lévy walk), our study suggests that scale‐dependent processes are important components of successful foraging behaviour.

Trophic structure and function in the larva of predatory muscid flies (Diptera, Muscidae)

Assessed multiple times over a 100-year period, yet poorly understood, we provide a new view of trophic structure and function in predatory muscid larvae based on Phaonia goberti (Mik) and Phaonia subventa (Harris) (Diptera, Muscidae). Trophic structure and function were investigated by morphological analysis, direct observation and filming. Larvae search for prey using a compartmentalised body. The rear compartment grips the substrate, while the middle one turns to the sides and the front one grabs prey. Two feeding mechanisms were recorded, sucking and lunging. Sucking occurs when the head is anchored inside the prey, and fluids are ingested using the pump in the head skeleton. Lunging is the head moving forwards and backwards, coordinated with lowering and raising of the mandibles during which fluids and tissue are gathered into the cup-shaped, oral cavity prior to sucking in. These mechanisms rely on prey being pierced, and this is achieved by a remarkable structural and functional partnership between the pseudocephalon, mandibles and accessory sclerites. The partnership involves tightening the integument of the prey between the oral bars and disengaging the mandible hooks to pierce it. Due to connections between the oral bars and pseudocephalon, the hooks do not extend from their sheaths except when piercing, an unusual feature in larvae of the Cyclorrhapha (Diptera).

전기물고기의 방해 회피 반응 모델링과 응용

In this paper, we suggest a phase difference algorithm inspired by weakly electric fish. Weakly electric fish is a fish which generates electric field though its electric organ in the tail. The weakly electric fish search for prey and detect an object by using electrolocation. The weakly electric fish have Jamming Avoidance Response (JAR) to avoid jamming signal. One of pulse-type weakly electric fish Gymnotus carapo also have JAR to reduce the probability of coincidence of pulses. We analyze this response signal and design the phase difference algorithm. We expect that simple algorithm inspired by weakly electric fish can be used in many engineering fields.

Bidirectional Echolocation in the Bat Barbastella barbastellus: Different Signals of Low Source Level Are Emitted Upward through the Nose and Downward through the Mouth

The Barbastelle bat (Barbastella barbastellus) preys almost exclusively on tympanate moths. While foraging, this species alternates between two different signal types. We investigated whether these signals differ in emission direction or source level (SL) as assumed from earlier single microphone recordings. We used two different settings of a 16-microphone array to determine SL and sonar beam direction at various locations in the field. Both types of search signals had low SLs (81 and 82 dB SPL rms re 1 m) as compared to other aerial-hawking bats. These two signal types were emitted in different directions; type 1 signals were directed downward and type 2 signals upward. The angle between beam directions was approximately 70°. Barbastelle bats are able to emit signals through both the mouth and the nostrils. As mouth and nostrils are roughly perpendicular to each other, we conclude that type 1 signals are emitted through the mouth while type 2 signals and approach signals are emitted through the nose. We hypothesize that the “stealth” echolocation system of B. barbastellus is bifunctional. The more upward directed nose signals may be mainly used for search and localization of prey. Their low SL prevents an early detection by eared moths but comes at the expense of a strongly reduced detection range for the environment below the bat. The more downward directed mouth signals may have evolved to compensate for this disadvantage and may be mainly used for spatial orientation. We suggest that the possibly bifunctional echolocation system of B. barbastellus has been adapted to the selective foraging of eared moths and is an excellent example of a sophisticated sensory arms race between predator and prey.

Roadkills of vertebrate species in the Pampa Region, South Brazil

Human activities such as the construction and use of highways interfere with the ecological dynamics of wildlife. The presence of roads affects three main effects on wild vertebrates: barrier, avoidance and roadkills, which the last is definitely the most noticeable. In this sense, the identification of the impacts of roads on wildlife can contribute to the establishment of actions that promote wildlife conservation. This study aimed to estimate the loss of fauna of terrestrial vertebrates by roadkills on a highway (BR-290) in Sao Gabriel, in Rio Grande do Sul, in the Brazilian Pampa; and to identify the ecological characteristics of the species most frequently run over. The study was conducted in a 12 km stretch of the BR-290 highway in the municipality of Sao Gabriel. The sampled highway is located in the Pampa biome domains. The sampling lasted six months, twice a week, from September 2009 to February 2010. The research group covered the stretch of road by car, with an average speed of 50 km/hour. Although 39 species have been recorded in our study, roadkills were concentrated in a few species within each taxonomic group. Apparently, the Pampa biome species are accustomed to move through areas with undergrowth vegetation, where the road cannot represent an obstacle for displacement. If, on the one hand, this condition reduces the road barrier effect, on the other hand, it increases the exposure of species to road mortality. Our results indicate that terriculous species and highly mobile species of reptiles and mammals are more susceptible to collisions in the study area. For birds, the main factor seems to be the low flight altitude associated with the search for prey on the highways.

Mate detection in a territorial butterfly—the effect of background and luminance contrast

Many animals search for potential mates or prey using a perch-and-sally strategy. The success of such a strategy will depend on factors that affect the observer’s ability to detect a passing resource item. Intrinsic factors (e.g., eye structure and physiology) have received much recent attention, but less is known about effects on object detection in nature and extrinsic factors such as size, coloration, and speed of a passing object and the background against which the object is viewed. Here, we examine how background affects the detection of butterfly models by perched males of the butterfly Asterocampa leilia in the field. We test the hypothesis that male choice of perch site in nature will influence the contrast between the object and background against which it is viewed and that this will influence success in detecting the object. We also test the effect of contrast by manipulating the brightness of the object and presenting butterfly models of different reflectance (ranging from black to white). We found an effect of model luminance, with dark models being most likely to elicit a response regardless of background. Further, there was an effect of background type with models viewed against blue sky eliciting the highest response. Perceived luminance contrast correlates to behavior; highly contrasting objects are more frequently detected. This study expands our understanding of visual system performance and has implications for our understanding of the behavior and evolutionary ecology of perching species.

茶互利素和蚜性信息素及其组合调控大草蛉行为的效应

The tea aphid,Toxoptera aurantii( Boyer),aggregates,pierces and sucks the sap of the tea shoots. The chemical control is not practical and restricted,since the tender tea shoots are commonly used for producing quality tea leaves. The green lacewing,Chrysopa septempunctata Wesmael,is one of the most important natural enemies of the tea aphid. However,the effectiveness of using this predator to suppress tea aphid populations is limited by their dispersal behavior and inefficiency of prey search. Here,we proposed a new strategy for enhancing the biological control against thetea aphids by using the tea shoot synomones and the aphid sex pheromones as potential lacewing attractant lures. The volatiles were collected from aphid-damaged tea shoots and intact tea shoots by the headspace sampling technique,and analyzed by gas chromatography coupled with mass spectrometry.( E)-2-pentenal,benzaldehyde and α-farnesene were identified as three dominant volatile components,followed by other 13 compounds from aphid-damaged tea shoots. EAG responses by the lacewing antennae were tested on the 16 synthetic individual compounds identified from aphid-damaged tea shoots,the two known aphid sex pheromone components( nepetalactone and nepetalactol),and a synthetic mixture containing α-farnesene,benzaldehyde and nepetalactol at ratio of 2∶2∶6,at 200 !g loading dosage for each tested compound or mixture. Nepetalactol,nepetalactone,α-farnesene,( E)-2-pentenal and benzaldehyde elicited higher EAG responses than did the other identified volatile components. However,the highest lacewing EAG response was observed to the synthetic mixture of α-farnesene,benzaldehyde and nepetalactol. This synthetic blend,aphid sex-pheromone,nepetalactone and nepetalactol,blends at seven different ratios( 10∶0,9∶1,7.5∶2.5,5∶5,2.5∶7.5,1∶9,0∶10),( Z)-3-hexen-1-ol,( E)-2-pentenal,( E)-2-hexenal,benzaldehyde and α- farnesene,each at 10 mg dosage,were tested in the field. Our field trapping results showed that the synthetic blend of α-farnesene,benzaldehyde and nepetalactol was the most attractive to C.septempunctata adults,followed by nepetalactol alone and the binary blend of nepetalactone and nepetalactol at 1∶ 9 ratio,which caught more lacewings than did the other ratios of the pheromone binary blends or other individual plant volatile compounds. During the field observations,we also found that the lacewing adults were not only attracted to lure-baited tea plants to directly prey on aphids,but also oviposited to raise their larva overwintering population in the habitat with plenty of overwintering aphid eggs. The deployment of lacewing attractant lures on tea plants may provide a unique,novel,and non-traditional control strategy against the economically important tea aphids.

Selection of nectar plants for use in ecological engineering to promote biological control of rice pests by the predatory bug, Cyrtorhinus lividipennis, (Heteroptera: Miridae).

Ecological engineering for pest management involves the identification of optimal forms of botanical diversity to incorporate into a farming system to suppress pests, by promoting their natural enemies. Whilst this approach has been extensively researched in many temperate crop systems, much less has been done for rice. This paper reports the influence of various plant species on the performance of a key natural enemy of rice planthopper pests, the predatory mirid bug, Cyrtorhinus lividipennis. Survival of adult males and females was increased by the presence of flowering Tagetes erecta, Trida procumbens, Emilia sonchifolia (Compositae), and Sesamum indicum (Pedaliaceae) compared with water or nil controls. All flower treatments resulted in increased consumption of brown plant hopper, Nilaparvata lugens, and for female C. lividipennis, S. indicum was the most favorable. A separate study with a wider range of plant species and varying densities of prey eggs showed that S. indicum most strongly promoted predation by C. lividipennis. Reflecting this, S. indicum gave a relatively high rate of prey search and low prey handling time. On this basis, S. indicum was selected for more detailed studies to check if its potential incorporation into the farming system would not inadvertently benefit Cnaphalocrocis medinalis and Marasmia patnalis, serious Lepidoptera pests of rice. Adult longevity and fecundity of both pests was comparable for S. indicum and water treatments and significantly lower than the honey solution treatment. Findings indicate that S. indicumis well suited for use as an ecological engineering plant in the margins of rice crops. Sesame indicum can be a valuable crop as well as providing benefits to C. lividipennis whilst denying benefit to key pests.

Forest type affects prey foraging of saddleback tamarins, Saguinus nigrifrons

Callitrichids can persist in secondary forests where they may benefit from elevated prey abundance. However, how tamarins forage for prey in secondary forest compared to primary forest has not been examined. Using scan and focal sampling, we compared prey foraging and capture success of two groups of Saguinus nigrifrons in north-eastern Peru: one ranging in primary forest, the other with access to a 10-year-old anthropogenic secondary forest. There was a trend for more prey search in the secondary forest, but prey feeding, capture success and size were lower compared to the primary forest. Tamarins avoided the forest floor, used vertical supports less often and searched on a lower variety of substrates in the secondary forest. In the secondary forest, tamarins did not capture flushed prey, which make up a substantial part of the total prey captures biomass in primary forests. Reduced prey capture success is unlikely to reflect reduced prey availability, since more Orthoptera were found in secondary forest through ultrasonic surveys. Therefore, the prey search activity of S. nigrifrons in young secondary forests seemed rather opportunistic, presumably influenced by altered predation patterns, vegetation structure, as well as prey diversity.Electronic supplementary materialThe online version of this article (doi:10.1007/s10329-014-0416-4) contains supplementary material, which is available to authorized users.

Risk taking not foraging behavior predicts dispersal of recently emerged stream brook charr (Salvelinus fontinalis)

Several hypotheses predict that individual differences in migration and dispersal are related to individual differences in routine behavior associated with foraging and risk taking. We tested whether short‐term dispersal of recently emerged brook charrSalvelinus fontinaliswas correlated with differences in activity during prey search in the field (a measure of foraging tactic) or in the time taken to exit a dark tube into an unfamiliar field environment (a measure of risk taking). For one sample of fish, we tested whether an individual's propensity to disperse in a standardized dispersal test in the lab was correlated with its activity during prey search and its exit times in the field. For another sample of marked, released and recaptured fish, we tested whether an individual's minimum displacement distance over 6 days in the field (a measure of dispersal in the field) was related to its propensity to disperse in the lab. For the first sample, an individual's propensity to disperse in the lab was correlated with risk taking only, but, contrary to expectation, individuals with long exit times (risk‐avoiders) dispersed farther than those with short exit times (risk‐takers). For the second sample, dispersal in the field was also correlated with propensity to disperse in the lab, but, contrary to expectation, individuals with greater displacements in the field displayed lower propensities to disperse in the lab. Our findings demonstrate that individual differences in juvenile dispersal are related to differences in risk taking behavior, but not in foraging tactic, and that the nature of this relationship can depend on environmental context. These findings are consistent with the hypothesis that individuals differing in risk taking behavior can contribute disproportionately to ecological processes involving long‐distance movement.

Mammalian predator–prey interaction in a fragmented landscape: weasels and voles

The relationship between predators and prey is thought to change due to habitat loss and fragmentation, but patterns regarding the direction of the effect are lacking. The common prediction is that specialized predators, often more dependent on a certain habitat type, should be more vulnerable to habitat loss compared to generalist predators, but actual fragmentation effects are unknown. If a predator is small and vulnerable to predation by other larger predators through intra-guild predation, habitat fragmentation will similarly affect both the prey and the small predator. In this case, the predator is predicted to behave similarly to the prey and avoid open and risky areas. We studied a specialist predator's, the least weasel, Mustela nivalis nivalis, spacing behavior and hunting efficiency on bank voles, Myodes glareolus, in an experimentally fragmented habitat. The habitat consisted of either one large habitat patch (non-fragmented) or four small habitat patches (fragmented) with the same total area. The study was replicated in summer and autumn during a year with high avian predation risk for both voles and weasels. As predicted, weasels under radio-surveillance killed more voles in the non-fragmented habitat which also provided cover from avian predators during their prey search. However, this was only during autumn, when the killing rate was also generally high due to cold weather. The movement areas were the same for both sexes and both fragmentation treatments, but weasels of both sexes were more prone to take risks in crossing the open matrix in the fragmented treatment. Our results support the hypothesis that habitat fragmentation may increase the persistence of specialist predator and prey populations if predators are limited in the same habitat as their prey and they share the same risk from avian predation.

Foraging activity of the snail kite, Rostrhamus sociabilis (Aves: Accipitridae) in wetlands of southern Brazil

The snail kite (Rostrhamus sociabilis) is widely distributed in the American continent. Its specialised diet consists mostly of the gastropod mollusk Pomacea sp and its foraging strategy probably varies depending on the season, prey availability, and climate factors, which can be reflected in its semi-nomad behaviour. This study was aimed at examining the hunting strategy of the snail kite, and its association with climate factors and habitat heterogeneity. Direct observations of birds between January 2010 and March 2011 in southernmost Brazil revealed that hunting was still the predominant foraging strategy (79% of records) to capture mollusks. Despite morphological specialisations to extract mollusks from the shells, the handling time (average = 92.4 s) was twice as much the time between prey search and capture (average = 55 s). The increase in the number of mollusks ingested apparently occurs when the resting time on perches or any other substrates near the hunting sites decreases between successive unsuccessful attempts. The correlation between the number of consumed preys and the climatic variables examined was low. Regarding habitat heterogeneity, our findings suggest that birds forage preferentially in marshes with low vegetation, which may increase the access to mollusks. The hunting efficiency of the snail kite was high (76 % successful attempts) compared to those of other birds of prey.

Unravelling the mysteries of a mesopelagic diet: a large apex predator specializes on small prey

Summary To gain insight into the foraging behaviour of deep diving seals, we developed a long‐term jaw‐motion recorder, which successfully measured the feeding attempts of four post‐breeding female northern elephant seals for 55–68 days during migration in the north‐east Pacific Ocean. Using the jaw‐motion recorders in conjunction with satellite tracking data, we first reveal the three‐dimensional fine‐scale distribution of deep foraging activity in the north‐east Pacific Ocean. A large number of jaw‐motion events (23 817–58 766 during 2925–4178 dives, per seal) were observed with diel patterns suggesting their dependency on small mesopelagic prey. Calculations using at‐sea field metabolic‐rate and the photographs concurrently obtained by the head‐mounted camera indicated feeding on small mesopelagic prey (10–20 g) including lantern fish (F. Myctophidae). The foraging behaviour of the northern elephant seal contrasts with echolocating toothed whales, which make fewer feeding attempts, suggesting the whales forage more selectively. We hypothesize that the continuous diving mode exhibited by this seal could be attributed to their reliance on small prey and their less efficient ‘passive sensors’ for prey search, that is, their vision or whiskers to detect prey.

Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae)

A computer reconstruction of isolated cervical vertebrae of Azhdarcho lancicollis from the Turonian of Uzbekistan allows three-dimensional model of the cervical region of the vertebral column of this animal. The relative length of cervical vertebrae (I + II VI > VII > VIII > IX) is the same as in pterodactyloids with short cervical vertebrae. An increase in neck length is provided mostly by the middle cervical vertebrae (IV–VI). In a neutral posture, the neck of azhdarchids was not straight, as often reconstructed, but S-shaped, with the maximum angles between the V–VI (20°), VI–VII (20°), and VIII–IX (17°) vertebrae. The feeding strategy of azhdarchids was probably similar to that of pelicans. In a search for prey, azhdarchids were soaring above the water surface of large inland or nearshore marine water bodies. Their prey (predominantly fish) was captured by the widely open mouth and fell into the throat sac, the presence of which is suggested by the spiral jaw joint. Prey was swallowed during the abrupt neck flexion in the posterior segment, which brought the head in an almost horizontal position. A storklike wading ecology for azhdarchids is less probable, because these clumsy on land animals were vulnerable to terrestrial predators.

Strike mechanics of an ambush predator: the spearing mantis shrimp

Ambush predation is characterized by an animal scanning the environment from a concealed position and then rapidly executing a surprise attack. Mantis shrimp (Stomatopoda) consist of both ambush predators ('spearers') and foragers ('smashers'). Spearers hide in sandy burrows and capture evasive prey, whereas smashers search for prey away from their burrows and typically hammer hard-shelled, sedentary prey. Here, we examined the kinematics, morphology and field behavior of spearing mantis shrimp and compared them with previously studied smashers. Using two species with dramatically different adult sizes, we found that strikes produced by the diminutive species, Alachosquilla vicina, were faster (mean peak speed 5.72±0.91 m s(-1); mean duration 3.26±0.41 ms) than the strikes produced by the large species, Lysiosquillina maculata (mean peak speed 2.30±0.85 m s(-1); mean duration 24.98±9.68 ms). Micro-computed tomography and dissections showed that both species have the spring and latch structures that are used in other species for producing a spring-loaded strike; however, kinematic analyses indicated that only A. vicina consistently engages the elastic mechanism. In the field, L. maculata ambushed evasive prey primarily at night while hidden in burrows, striking with both long and short durations compared with laboratory videos. We expected ambush predators to strike with very high speeds, yet instead we found that these spearing mantis shrimp struck more slowly and with longer durations than smashers. Nonetheless, the strikes of spearers occurred at similar speeds and durations to those of other aquatic predators of evasive prey. Although counterintuitive, these findings suggest that ambush predators do not actually need to produce extremely high speeds, and that the very fastest predators are using speed to achieve other mechanical feats, such as producing large impact forces.

Predator crown-of-thorns starfish (Acanthaster planci) outbreak, mass mortality of corals, and cascading effects on reef fish and benthic communities.

Outbreaks of the coral-killing seastar Acanthaster planci are intense disturbances that can decimate coral reefs. These events consist of the emergence of large swarms of the predatory seastar that feed on reef-building corals, often leading to widespread devastation of coral populations. While cyclic occurrences of such outbreaks are reported from many tropical reefs throughout the Indo-Pacific, their causes are hotly debated, and the spatio-temporal dynamics of the outbreaks and impacts to reef communities remain unclear. Based on observations of a recent event around the island of Moorea, French Polynesia, we show that Acanthaster outbreaks are methodic, slow-paced, and diffusive biological disturbances. Acanthaster outbreaks on insular reef systems like Moorea's appear to originate from restricted areas confined to the ocean-exposed base of reefs. Elevated Acanthaster densities then progressively spread to adjacent and shallower locations by migrations of seastars in aggregative waves that eventually affect the entire reef system. The directional migration across reefs appears to be a search for prey as reef portions affected by dense seastar aggregations are rapidly depleted of living corals and subsequently left behind. Coral decline on impacted reefs occurs by the sequential consumption of species in the order of Acanthaster feeding preferences. Acanthaster outbreaks thus result in predictable alteration of the coral community structure. The outbreak we report here is among the most intense and devastating ever reported. Using a hierarchical, multi-scale approach, we also show how sessile benthic communities and resident coral-feeding fish assemblages were subsequently affected by the decline of corals. By elucidating the processes involved in an Acanthaster outbreak, our study contributes to comprehending this widespread disturbance and should thus benefit targeted management actions for coral reef ecosystems.