Initiation and spread of escape waves within animal groups

The exceptional reactivity of animal collectives to predatory attacks is thought to be due to rapid, but local, transfer of information between group members. These groups turn together in unison and produce escape waves. However, it is not clear how escape waves are created from local interactions, nor is it understood how these patterns are shaped by natural selection. By startling schools of fish with a simulated attack in an experimental arena, we demonstrate that changes in the direction and speed by a small percentage of individuals that detect the danger initiate an escape wave. This escape wave consists of a densely packed band of individuals that causes other school members to change direction. In the majority of cases this wave passes through the entire group. We use a simulation model to demonstrate that this mechanism can, through local interactions alone, produce arbitrarily large escape waves. In the model, when we set the group density to that seen in real fish schools, we find that the risk to the members at the edge of the group is roughly equal to the risk of those within the group. Our experiments and modelling results provide a plausible explanation for how escape waves propagate in Nature without centralised control

Predators attacking virtual prey reveal the costs and benefits of leadership.

A long-standing assumption in social behavior is that leadership incurs costs as well as benefits, and this tradeoff can result in diversified social roles in groups. The major cost of leadership in moving animal groups is assumed to be predation, with individuals leading from the front of groups being targeted more often by predators. Nevertheless, empirical evidence for this is limited, and experimental tests are entirely lacking. To avoid confounding effects associated with observational studies, we presented a simulation of virtual prey to real fish predators to directly assess the predation cost of leadership. Prey leading others are at greater risk than those in the middle of groups, confirming that any benefits of leading may be offset by predation costs. Importantly, however, followers confer a net safety benefit to leaders, as prey leading others were less likely to be attacked compared with solitary prey. We also find that the predators preferentially attacked when solitary individuals were more frequent, but this effect was relatively weak compared with the preference for attacking solitary prey during an attack. Using virtual prey, where the appearance and behavior of the prey can be manipulated and controlled exactly, we reveal a hierarchy of risk from solitary to leading to following social strategies. Our results suggest that goal-orientated individuals (i.e., potential leaders) are under selective pressure to maintain group cohesion, favoring effective leadership rather than group fragmentation. Our results have significant implications for understanding the evolution and maintenance of different social roles in groups.his work was supported by Natural Environment Research Council Independent Research Fellowship NE/K009370/1 and Leverhulme Trust Grant RPG-2017-041 V (to C.C.I.)

IMPACTS ON FAST-START PERFORMANCE: HOW DO GROUP SIZE AND HABITAT DEGRADATION ALTER THE ESCAPE BEHAVIOR OF A SCHOOLING CORAL REEF FISH?

Escaping predation is essential for species survival, but prey must effectively match their response to the perceived threat imposed by a predator. Fish evaluate their surroundings using several sensory stimuli, including olfactory, visual, auditory, and mechanical cues. A range of taxa use the fast-start response to evade predators, including fishes, sharks, and larval amphibians. While the fast-start response (rapid bursts of swimming) is extensively studied in solitary fishes, the factors that mediate the collective escape response in schools of fish have historically been investigated far less. To address this knowledge gap, the collective escape behavior and individual escape performance of schools of the tropical damselfish species Chromis viridis, a common gregarious and coral-associated coral reef fish species found throughout the Indo-Pacific, were investigated. The first data chapter explored the theory of optimal group size, comparing various sized groups of fish. Fish strategically adjusted their escape response in coordination with other group mates, validating the connectivity within conspecific schools. The second data chapter investigated how degrading coral health influences antipredator behavior in fish schools. Habitat degradation was revealed to have a negative effect on schooling, and the combination of a chemical alarm cue intensified this impact. While the singular effect of a chemical alarm acted as a prewarning to strengthen the fast-start

Cognitive Control of Escape Behaviour

When faced with potential predators, animals instinctively decide whether there is a threat they should escape from, and also when, how, and where to take evasive action. While escape is often viewed in classical ethology as an action that is released upon presentation of specific stimuli, successful and adaptive escape behaviour relies on integrating information from sensory systems, stored knowledge, and internal states. From a neuroscience perspective, escape is an incredibly rich model that provides opportunities for investigating processes such as perceptual and value-based decision-making, or action selection, in an ethological setting. We review recent research from laboratory and field studies that explore, at the behavioural and mechanistic levels, how elements from multiple information streams are integrated to generate flexible escape behaviour

Animating Predator and Prey Fish Interactions

Schooling behavior is one of the most salient social and group activities among fish. They form schools for social reasons like foraging, mating and escaping from predators. Animating a school of fish is difficult because they are large in number, often swim in distinctive patterns that is they take the shape of long thin lines, squares, ovals or amoeboid and exhibit complex coordinated patterns especially when they are attacked by a predator. Previous work in computer graphics has not provided satisfactory models to simulate the many distinctive interactions between a school of prey fish and their predator, how does a predator pick its target? and how does a school of fish react to such attacks? This dissertation presents a method to simulate interactions between prey fish and predator fish in the 3D world based on the biological research findings. Firstly, a model is described by representing a school of fish as a complex network information flow with structural properties. Using this model, a predator fish targeting isolated peripheral fish is simulated. Secondly, the escape behavior state machine model and escape maneuvers exhibited by fish schools are described. The escape maneuvers include compact, avoid, fast avoid, skitter, fountain, flash, ball, split, join, herd, vacuole, and hourglass are identified in the biological studies. This proposed escape behavior animation model can free an animator from dealing with the low-level animations but instead, control the fish behavior on a higher level by modifying a state machine and a small set of system parameters. With the state machine and relatively few system parameters, the proposed system is stable, predictable, and easy to tune, which represent important properties for animators to control the outcome. This system is developed in Unity (3D). In addition, a plug-in is also developed for full-fledged graphics tool Blender software to simulate escape maneuvers. The animator has to simply select escape maneuvers, adjust parameters and work on animating predator using keyframe method. It does not deal with the state machine model. The proposed model is useful not only in generating group behaviors but also in scientific visualization tool for studying fish behavior

The role of intraspecific variation in physiological traits in determining vulnerability to capture in fish

Impacts of fisheries induced evolution (FIE) may extend beyond life history traits to more cryptic aspects of biology, such as behaviour and physiology. Understanding roles of physiological traits in determining individual susceptibility to capture in fishing gears, and how these mechanisms change across contexts is essential to evaluate the capacity of commercial fisheries to elicit phenotypic change in exploited populations. In particular, physiological traits related to metabolism, bioenergetics, and swim performance may affect the probability of fish interacting with a fishing gear, or successfully escaping it once it has been encountered, and so may also be under selection in commercial and recreational fisheries. Selection on these traits has the capacity to alter the physiological composition of exploited fish populations in response to fishing pressure, with consequences for the viability of fish stocks, and the sustainability of fisheries exploitation. Evaluating the capacity of fisheries to elicit phenotypic change in exploited fish stocks is complicated by the myriad different fishing gears used around the world, and their contrasting mechanisms of capture, as well as the modulating effect of environment on relationships between individual traits and capture vulnerability. This thesis made use of both laboratory and field-based experiments, alongside data collected from commercially important species in a real world fisheries context to establish mechanistic links between individual physiological traits and capture vulnerability in different gears, the degree to which these relationships may be modulated by the environment, and how fisheries selection may alter the ecological niche of exploited species. Using laboratory experiments, I investigated the role of environmental context in determining relationships between individual physiological traits and capture vulnerabilities in different gear types. Trawling simulations conducted on groups of Minnows comprised of individuals familiar with one another, and of individuals which had never seen each other before showed that social context can alter relationships between individual traits and capture vulnerability. When swimming among familiar conspecifics, a negative relationship between trawl capture vulnerability and anaerobic metabolic capacity was found, while no relationship between individual traits and capture vulnerability was found when fish faced the trawl alongside unfamiliar shoalmates. In contrast, a subsequent experiment investigating links between physiological traits of minnows and capture vulnerability in replicated trawl and trap trials found no relationship between metabolic traits and capture vulnerability in either gear at any temperature. However, the trawl still selected on fish behaviour with high activity fish at less risk of capture at all temperatures tested. These laboratory experiments are accompanied by two studies of fisheries selection in the wild. The first used a combination of lab based behavioural assays, respirometry and acoustic telemetry to investigate the capacity for two different fishing methods (gill netting and angling) to select on the physiological and behavioural traits of perch. This study found that gillnetted perch showed broader patterns of habitat use than their angled conspecifics, suggesting that gill nets selected on the spatial traits of wild fish. No differences in physiological traits between gear types was found. Finally, a similar comparative approach was used to investigate the capacity for trawling and jigging to select on contrasting ecological traits of wild cod. Jigging was found to selectively remove fish with low δ15N values, most likely through a mechanism of feeding motivation, while the trawl was found to be less selective on ecological traits. These results highlight the capacity for fishing gears to select on cryptic aspects of fish biology, such as patterns of space use, feeding motivation, and swim performance, but also show that these relationships can be strongly dependent on the external environment

Tiergemeinschaften im offenen Ozean: ein theoretischer Ansatz

Many aspects of the behavioural ecology of oceanic predators are little understood due to difficulties related to costs and reduced accessibility of their habitat. Often only certain parts and factors of an ecosystem can be studied. Hence it is important to compile results of previous research so as to extract the most possible information from what is available. In the scope of this study a review of animal grouping in the oceanic environment identified possible evolutionary drivers towards congregation in cetacea which were then quantitatively evaluated by a meta-analysis of group size correlations with a number of ecological and behavioural parameters, including habitat range, migration behaviour, prey composition, foraging depth and predation risk. The latter was quantified based on vertical and horizontal overlap of cetacea habitat with that of their predators, and from both, the probability of attack during an encounter with a predator and attack fatality. Tuna-dolphin associations were qualitatively analysed with regard to fitness benefits related to predation risk, foraging and improved navigation accuracy.Durch hohe Kosten verbunden mit der Erforschung der Hochsee und geringe Zugänglichkeit dieser Gebiete sind viele verhaltensökologische Aspekte ozeanischer Prädatoren kaum bekannt. Oft können nur Teile und bestimmte Faktoren eines Ökosystems untersucht werden. Dadurch ist es wichtig Resultate vergangener Studien so effizient wie möglich zu kompilieren um mit den Informationen die verfügbar sind den größtmöglichen Einblick zu gewinnen. Im Rahmen dieser Arbeit wurde ein Review über das Gruppenverhalten in Hochseegewässern angefertigt, der mögliche evolutionäre Haupteinflussfaktoren identifiziert. Diese sind dann quantitativ im Rahmen einer Meta-analyse von Korrelationen zwischen Gruppengröße und verschiedenen ökologischen und verhaltensspezifischen Parametern ausgewertet worden. Diese sind unter anderem Ausbreitungs- und Migrationsverhalten, Nahrungszusammensetzung, Nahrungstiefe und Prädationsgefahr. Letztere wurde auf der Basis von der Überlappung zwischen Räuber- und Beutehabitat, der Wahrscheinlichkeit, dass das Zusammentreffen mit einem Prädator zu einem Angriff führt und der Letalität eines solchen Angriffs quantifiziert. Thunfisch-Delphin Gemeinschaften sind im Hinblick auf mit der Ernährung, der Navigationspräzision und der Prädationsgefahr zusammenhängende Fitnessvorteile qualitativ untersucht worden