Dynamics of Aggregation and Emergence of Cooperation

Abstract

Aggregation is one of the most basic social phenomena, and many activities of social insects are linked to it. For instance, the selection of a valuable site and the spatial organization of the population are very often by-products of amplifications based on the local density of nestmates. The patterns of aggregation are very diverse, ranging from the gathering of all animals in a unique site to their splitting between several ones. One might question how these multiple patterns emerge. Do ants actively initiate the formation of such patterns by modulating the emission of an attracting signal such as the trail pheromone? Alternatively, do patterns result from quantitative changes in the duration of interaction between animals once they have reached the gathering site, without any active modulation of the communications? To discuss these questions, we present two empirical studies: the gregarious behavior of cockroaches (Blatella) and self-assembly in the weaver ant (Oecophylla). Through experimental and theoretical studies, we show how a single behavior-the resting time-leads to a collective choice in both species. This behavior is a response to the density of conspecifics and can also be modulated by heterogeneities in the environment. In weaver ants, it allows the colony to focus the formation of chains in a given area among several potential sites. In cockroaches, it allows the gathering of individuals in particular shelters, depending on the proximity between strains. These results are discussed with emphasis on the role of aggregation processes in the emergence of cooperativity and task allocation.

Predicting Dynamical Crime Distribution From Environmental and Social Influences

“…A successful robbery event, for instance, whereby an offender received cash from a victim and was never arrested or punished for it, is a kind of positive feedback which creates the conditions for similar/repeat crimes at the same locale and ultimately clustering at some places, and not others [27]. This is similar to the results of many studies on the aggregation behavior of social animals: they preferentially cluster at favorable locations but, because the individuals are also attracted toward each other, (1) they tend to aggregate at only one or a few among all the favorable locations, and (2) they can sometimes form a stable aggregate at an unfavorable location if a large enough groups has been formed there by chance [16,18,28]. In the criminological context, this would explain why not all high-risk locations-as predicted by RTM-become crime hotspots, and why low-risk locations may turn into hotspots in rare cases [11].…”

“…Similar feedback loops driven by past events and social information have been found to create clustering in unicellular organisms, insects, fish, birds, and mammals [13][14][15], even in uniform environmental conditions. However the final location of the cluster is highly dependent on the structure of the environment: clusters are more likely to originate at attractive places for the organisms, and the positive feedback process will promote the disproportionate concentration of individuals at some of the attracting places only (sometimes at a single one) while others will be abandoned [13,[16][17][18]. In addition, once this process has reached its stable state, the probability of starting a new cluster elsewhere-even at another attractive location -is low [13].…”

Aggregation Behaviour as a Source of Collective Decision in a Group of Cockroach-Like-Robots

“…Indeed, aggregation is a step towards much more complex collective behaviours because it favours interactions and information exchanges among individuals, leading to the emergence of complex and functional self-organized collective behaviours (for some examples, see [4]). As such it plays a keyrole in the evolution of cooperation in animal societies [6].…”

The search rate of the African weaver ant in cashew

“…The Nicholson-Baily functional response equation assumes that the population of predators searches their habitat randomly and that they do not affect each other, which may cause their searched areas to overlap. Ants are known to communicate on attracting other colony members to larger preys (Hölldobler, 1983;Wojtusiak et al, 1995;Deneubourg et al, 2002) causing an aggregated response to larger prey items (Crawley, 1992), and in that case the two assumptions fail. However, this aggregated response only seems to apply to larger prey items that cannot be carried by one or a few ants, and does therefore not apply to our situation where single or a few ants were observed to carry the food items.…”