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

Culture Outsmarts Nature in the Evolution of Cooperation

A one dimensional cellular automata model describes the evolutionary dynamics of cooperation when grouping by cooperators provides protection against predation. It is used to compare the dynamics of evolution of cooperation in three settings. G: only vertical transmission of information is allowed, as an analogy of genetic evolution with heredity; H: only horizontal information transfer is simulated, through diffusion of the majority\'s opinion, as an analogy of opinion dynamics or social learning; and C: analogy of cultural evolution, where information is transmitted both horizontally (H) and vertically (V) so that learned behavior can be transmitted to offspring. The results show that the prevalence of cooperative behavior depends on the costs and benefits of cooperation so that: a- cooperation becomes the dominant behavior, even in the presence of free-riders (i.e., non-cooperative obtaining benefits from the cooperation of others), under all scenarios, if the benefits of cooperation compensate for its cost; b- G is more susceptible to selection pressure than H achieving a closer adaptation to the fitness landscape; c- evolution of cooperative behavior in H is less sensitive to the cost of cooperation than in G; d- C achieves higher levels of cooperation than the other alternatives at low costs, whereas H does it at high costs. The results suggest that a synergy between H and V is elicited that makes the evolution of cooperation much more likely under cultural evolution than under the hereditary kind where only V is present.Social Simulation, Interactions, Group Size, Selfish Heard, Cultural Evolution, Biological Evolution

Sex, friends, and disease: social ecology of elk (Cervus elaphus) with implications for pathogen transmission

Many mammals are social. The most basic social behaviour is when the actions of one conspecific are directed toward another, what we call the ‘dyadic interaction’. Both intrinsic and extrinsic factors may affect an individual’s propensity to interact with other members of a population. I used a social cervid, elk (Cervus elaphus), as a model species to test the importance of intrinsic and extrinsic factors of sociality on dyadic interactions. Dyadic interactions not only form the basis for social structure and information transfer within a population, but are also routes of pathogen transmission. My objective in this thesis was thus twofold: to improve our understanding of sociobiology, but also to gain insight into how sociality may underlie the transmission of communicable wildlife disease. I used a hierarchical, autecological approach from DNA, through individual, dyad, group, subpopulation, and ultimately population to explore the effects of intrinsic factors (e.g., sex and pairwise genetic relatedness) and extrinsic factors (e.g., season, conspecific density, habitat, and elk group size) on sociality. Elk in Riding Mountain National Park (RMNP), Manitoba, Canada, are exposed to the causal agent of bovine tuberculosis (Mycobacterium bovis; TB); however, spatial variation in apparent disease prevalence suggests that TB can only persist in one subpopulation within the Park. Using the natural RMNP system and a captive elk herd that I manipulated, I explored factors that influence interaction rates and durations (as a proxy for pathogen transmission) among elk. Sexual segregation in elk results in seasonal and sex-based differences in interaction rate and duration; with interactions peaking in autumn-winter for both sexes. Female-female dyads interact more frequently than male-male dyads. However, male-male dyads interact for longer durations than do female-female dyads. Interaction rate and duration did not covary with pairwise relatedness. Conspecific density also had sex-specific results for interaction rate and duration. Whereas male-male dyadic interaction rates increase with density, female-female dyads increase until they reach a threshold and subsequently reduce their interaction rates at high density. I observed density dependence in interaction rates in experimental trials and from field data. Furthermore, social networks revealed that social familiarity (i.e., heterogeneity of interactions) can be both frequency- and- density dependent depending on the strength of the relationship (i.e., number of repeat interactions). Density also affected the likelihood that an interaction would occur; however, this was modified by vegetation association used by elk. My results reveal several ecological and evolutionary implications for information transfer and pathogen transmission. In particular, I show that seasonal inter-sex routes of transfer may exist and that transfer is likely to be density-dependent. Finally, I conclude that such transfer is modified by available resources

Group Dynamics and Landscape Features Constrain the Exploration of Herds in Fusion-Fission Societies: The Case of European Roe Deer

Despite the large number of movement studies, the constraints that grouping imposes on movement decisions remain essentially unexplored, even for highly social species. Such constraints could be key, however, to understanding the dynamics and spatial organisation of species living in group fusion-fission systems. We investigated the winter movements (speed and diffusion coefficient) of groups of free-ranging roe deer (Capreolus capreolus), in an agricultural landscape characterised by a mosaic of food and foodless patches. Most groups were short-lived units that merged and split up frequently during the course of a day. Deer groups decreased their speed and diffusion rate in areas where food patches were abundant, as well as when travelling close to main roads and crest lines and far from forests. While accounting for these behavioural adjustments to habitat features, our study revealed some constraints imposed by group foraging: large groups reached the limit of their diffusion rate faster than small groups. The ability of individuals to move rapidly to new foraging locations following patch depression thus decreases with group size. Our results highlight the importance of considering both habitat heterogeneity and group dynamics when predicting the movements of individuals in group fusion-fission societies. Further, we provide empirical evidence that group cohesion can restrain movement and, therefore, the speed at which group members can explore their environment. When maintaining cohesion reduces foraging gains because of movement constraints, leaving the group may become a fitness-rewarding decision, especially when individuals can join other groups located nearby, which would tend to maintain highly dynamical group fusion-fission systems. Our findings also provide the basis for new hypotheses explaining a broad range of ecological patterns, such as the broader diet and longer residency time reported for larger herbivore groups

Predation and antipredator tactics of nesting black brant and lesser snow geese

Coloniality and nest defence were examined in black brant Branta bernicla nigricans and lesser snow geese Chen caerulescens caerulescens. Increased nest density had no effect on nest survival, egg survival, or likelihood of partial clutch predation in snow geese. In brant, nest survival declined as nest density increased in 1992 and with increased distance from shore in 1993. Brant with conspecific nearest neighbours were less likely to suffer partial clutch predation in 1993, but not in 1992. Egg survival in brant increased with nest density in 1993, but decreased as density increased in 1992, however, the decrease occurred only in nests with three or four eggs. Nesting at high densities, in central positions, or far from shorelines commonly travelled by glaucous gulls Larurs hyperboreus and parasitic jaegers Stercorarius parasiticus, the primary egg predators in this study, did not provide geese with a nest or egg survival advantage because effects were lacking in snow geese and were inconsistent and contradictory in brant. Female snow geese had very high nest attendance and both sexes had high territory attendance so snow goose nests were rarely unattended during incubation. Brant had lower nest attendance than snow geese, and due to a lack food near their nests, brant left their territories to feed resulting in lower territory attendance as well. Although male brant were capable of defending the nest from avian predators and usually remained on their territories when females were absent, males were less effective defenders than incubating females. Increased vigilance and decreased resting by female brant as incubation progressed provided support for the prediction, from parental investment theory, that nest guarding effort would increase with offspring age, but there were no changes in male brant or in snow geese. However, declining nest and territory attendance by female brant and males of both species contradicted predictions from parental investment theory but were consistent with an increased need to forage as nutrient reserves declined through incubation as expected due to energetic constraints

Western Burrowing Owl Predation in an Urban Setting in California: Do California Ground Squirrel Calls Reduce Risk?

Western burrowing owls are found in ground squirrel burrows throughout the urbanized landscape of the South San Francisco bay area, where they are threatened by habitat loss and degradation, prey limitation and predation. Previous research has characterized effects of habitat loss and prey-base limitations on owls, but the interplay between ground squirrels, owls and their predators has not yet been studied. The objective of this study was to assess the rate and types of predation interactions faced by Western burrowing owls and the extent to which California ground squirrels help burrowing owls reduce risk through alarm calling at Moffett Federal Airfield in northern Santa Clara County, California. From June through August 2012 and April through June 2013, over 100 hours of direct observations and 14,540 hours of camera trapping observations yielded seven owl takes by species including red-tailed hawk, red fox, striped skunk, common raven, and snake species. Although the ratio of squirrels to owls was 74:26, ground squirrels were observed responding to predator approaches before owls 58.8% of the time, while burrowing owls responded first 28.4% of the time. Burrowing owls reacted to 65.5% of squirrel alarm calls, while squirrels responded to only 25.8% of owl alarms. This research suggests healthy ground squirrel populations may provide important predator-avoidance services in burrowing owl habitat, and that predation should be of greater concern to burrowing owl conservation. And ground squirrels are needed to determine the extent of predation protection via alarm calls