Evolution of swarming behavior is shaped by how predators attack

Animal grouping behaviors have been widely studied due to their implications for understanding social intelligence, collective cognition, and potential applications in engineering, artificial intelligence, and robotics. An important biological aspect of these studies is discerning which selection pressures favor the evolution of grouping behavior. In the past decade, researchers have begun using evolutionary computation to study the evolutionary effects of these selection pressures in predator-prey models. The selfish herd hypothesis states that concentrated groups arise because prey selfishly attempt to place their conspecifics between themselves and the predator, thus causing an endless cycle of movement toward the center of the group. Using an evolutionary model of a predator-prey system, we show that how predators attack is critical to the evolution of the selfish herd. Following this discovery, we show that density-dependent predation provides an abstraction of Hamilton's original formulation of ``domains of danger.'' Finally, we verify that density-dependent predation provides a sufficient selective advantage for prey to evolve the selfish herd in response to predation by coevolving predators. Thus, our work corroborates Hamilton's selfish herd hypothesis in a digital evolutionary model, refines the assumptions of the selfish herd hypothesis, and generalizes the domain of danger concept to density-dependent predation.Comment: 25 pages, 11 figures, 5 tables, including 2 Supplementary Figures. Version to appear in "Artificial Life

The Influence of Signaling Conspecific and Heterospecific Neighbors on Eavesdropper Pressure

The study of tradeoffs between the attraction of mates and the attraction of eavesdropping predators and parasites has generally focused on a single species of prey, signaling in isolation. In nature, however, animals often signal from mixed-species aggregations, where interactions with heterospecific group members may be an important mechanism modulating tradeoffs between sexual and natural selection, and thus driving signal evolution. Although studies have shown that conspecific signalers can influence eavesdropper pressure on mating signals, the effects of signaling heterospecifics on eavesdropper pressure, and on the balance between natural and sexual selection, are likely to be different. Here, we review the role of neighboring signalers in mediating changes in eavesdropper pressure, and present a simple model that explores how selection imposed by eavesdropping enemies varies as a function of a signaling aggregation\u27s species composition, the attractiveness of aggregation members to eavesdroppers, and the eavesdroppers\u27 preferences for different member types. This approach can be used to model mixed-species signaling aggregations, as well as same-species aggregations, including those with non-signaling individuals, such as satellites or females. We discuss the implications of our model for the evolution of signal structure, signaling behavior, mixed-species aggregations, and community dynamics

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

To boldly go:an occam-π mission to engineer emergence

Future systems will be too complex to design and implement explicitly. Instead, we will have to learn to engineer complex behaviours indirectly: through the discovery and application of local rules of behaviour, applied to simple process components, from which desired behaviours predictably emerge through dynamic interactions between massive numbers of instances. This paper describes a process-oriented architecture for fine-grained concurrent systems that enables experiments with such indirect engineering. Examples are presented showing the differing complex behaviours that can arise from minor (non-linear) adjustments to low-level parameters, the difficulties in suppressing the emergence of unwanted (bad) behaviour, the unexpected relationships between apparently unrelated physical phenomena (shown up by their separate emergence from the same primordial process swamp) and the ability to explore and engineer completely new physics (such as force fields) by their emergence from low-level process interactions whose mechanisms can only be imagined, but not built, at the current time

The position of graptolites within Lower Palaeozoic planktic ecosystems.

An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms

Funktionelle Reaktionen von Konsumenten: die SSS Gleichung und ihre Anwendung

Der Zusammenhang zwischen der pro Kopf Konsumtionsrate und der Nahrungsdichte wird in der Ökologie als funktionelle Reaktion bezeichnet und ist das Thema dieser Dissertation. Jeweils zum ersten Mal seit den 70er Jahren gebe ich hier einen Überblick über sowohl theoretische als auch empirische Arbeiten zur funktionellen Reaktion. Dabei zeige ich eine Lücke in der bisherigen Theorie und fülle diese mit einem neuen Modell, der SSS Gleichung. Dieses Modell kann man beispielsweise dazu verwenden, die Auswirkungen von Beutetier-Verteidigungen auf Konsumtionsraten von Räubern vorherzusagen. Diese Vorhersagen sind korrekt im Vergleich zu den bisher einzigen existierenden entsprechenden empirischen Daten, welche hier vorgestellt werden. Eine weitere Anwendungsmöglichkeit der SSS Gleichung ist die Einteilung von Konsumenten in zwei Gruppen, handling-limitierte und verdauungslimitierte, wobei erstere für das Angreifen und die Aufnahme von Nahrung (beides zusammen wird als handling bezeichnet) mindestens so viel Zeit benötigen wie für die Verdauung; deren Konsumtionsrate wird deshalb von deren handling time bestimmt. Die meisten Konsumenten sind in ihrer Konsumtionsrate jedoch verdauungslimitiert. Sie können ‚satt’ werden und sollten daher von Zeitdruck befreit sein, wenn die Nahrung häufig genug ist, um schnell gefunden zu werden und auch die übrigen Umweltbedingungen gut sind. Eine von mir durchgeführte Analyse empirischer Daten deutet an, dass zumindest Herbivore in der Natur tatsächlich häufig von Zeitdruck befreit zu sein scheinen. Diese Analyse zeigt damit einen Schwachpunkt bisheriger Verhaltensmodelle, welche ausnahmslos vom Gegenteil, also permanentem Zeitdruck, ausgehen. In meiner Zusammenfassung empirischer funktioneller Reaktionen zeige ich, dass filtrierende Konsumenten charakteristischerweise einen bestimmten Typ funktioneller Reaktionen zeigen. Nachdem ich die SSS Gleichung dahingehend erweitert habe, dass sie die Besonderheiten von Filtrierern berücksichtigt, kann ich dieses Ergebnis erklären: Die Ursache scheint die Eigenschaft von Filtrierern zu sein, während der Nahrungssuche und -aufnahme in der Lage zu sein, weitere Nahrungspartikel zu fangen oder zu fressen und auch andere Aktivitäten auszuführen, z.B. nach Räubern Ausschau zu halten. Ich erweitere die SSS Gleichung außerdem um den sog. Konfusionseffekt. Ein solcher Effekt liegt vor, wenn ein Räuber, der mit einem Schwarm seiner Beutetiere konfrontiert ist, nicht in der Lage ist, die vielen Sinneseindrücke neuronal zu verarbeiten. Ich vergleiche die erweiterte SSS Gleichung mit empirischen Daten zur funktionellen Reaktion von ‚konfusen’ Räubern und stelle nicht nur eine qualitative, sondern auch eine quantitative Übereinstimmung fest. In diesem Abschnitt zeige ich auch, dass der Konfusionseffekt ein häufig auftretendes Phänomen ist, besonders bei taktilen Räubern und solchen visuellen Räubern, die agile Beutetiere jagen. Abschließend zeige ich weitere, bisher nicht verwirklichte Anwendungsmöglichkeiten der SSS Gleichung im speziellen und des Konzepts der funktionellen Reaktion im allgemeinen

RESPONSES OF PREDATORY MYXOBACTERIA TO PREY SIGNALING MOLECULES & FEATURES OF A PSEUDOMONAS PREY AVOIDING PREDATION

Gram-negative unicellular myxobacteria, along with their multicellular lifestyle andbiologically active specialized metabolites, are known for the predatory interactions with Gram-negative/ Gram-positive bacteria and fungi. Although myxobacterial predation range have been exploited extensively, little is known about the prey associated molecules contributing to myxobacterial predator-prey dynamics. By employing transcriptomics and untargeted metabolomics approaches, we demonstrate two structurally distinct classes of signaling molecules from Gram-negative bacterial prey elicit significant omics responses from myxobacteria, Myxococcus xanthus and Cystobacter ferrugineus. An overlapping and general response to acylhomoserine lactones, whereas a distinctive response to a quinolone signaling molecule is observed from both myxobacteria. Similarly, by employing transcriptomics and classical microbiological assays, we demonstrate higher production of molecules like pyoverdine, phenazine-1-carboxylic acid, and alginate and resistance to aminoglycosides and tetracycline antibiotics are unique to a predation survivor Pseudomonas putida phenotype. In a predator-prey co-culturing, the predatory stress from myxobacterium C. ferrugineus selects for this P. putida phenotype that eludes subsequent myxobacterial predation. Overall, our study confirms that prey associated chemical components significantly direct responses from predatory myxobacteria