Group size, individual role differentiation and effectiveness of cooperation in a homogeneous group of hunters.

The emergence of cooperation in wolf-pack hunting is studied using a simple, homogeneous, particle-based computational model. Wolves and prey are modelled as particles that interact through attractive and repulsive forces. Realistic patterns of wolf aggregation readily emerge in numerical simulations, even though the model includes no explicit wolf-wolf attractive forces, showing that the form of cooperation needed for wolf-pack hunting can take place even among strangers. Simulations are used to obtain the stationary states and equilibria of the wolves and prey system and to characterize their stability. Different geometric configurations for different pack sizes arise. In small packs, the stable configuration is a regular polygon centred on the prey, while in large packs, individual behavioural differentiation occurs and induces the emergence of complex behavioural patterns between privileged positions. Stable configurations of large wolf-packs include travelling and rotating formations, periodic oscillatory behaviours and chaotic group behaviours. These findings suggest a possible mechanism by which larger pack sizes can trigger collective behaviours that lead to the reduction and loss of group hunting effectiveness, thus explaining the observed tendency of hunting success to peak at small pack sizes. They also explain how seemingly complex collective behaviours can emerge from simple rules, among agents that need not have significant cognitive skills or social organization.

Wolf-pack (Canis lupus) hunting strategies emerge from simple rules in computational simulations.

We have produced computational simulations of multi-agent systems in which wolf agents chase prey agents. We show that two simple decentralized rules controlling the movement of each wolf are enough to reproduce the main features of the wolf-pack hunting behavior: tracking the prey, carrying out the pursuit, and encircling the prey until it stops moving. The rules are (1) move towards the prey until a minimum safe distance to the prey is reached, and (2) when close enough to the prey, move away from the other wolves that are close to the safe distance to the prey. The hunting agents are autonomous, interchangeable and indistinguishable; the only information each agent needs is the position of the other agents. Our results suggest that wolf-pack hunting is an emergent collective behavior which does not necessarily rely on the presence of effective communication between the individuals participating in the hunt, and that no hierarchy is needed in the group to achieve the task properly.

Cholesterol-dependent regulation of nitric oxide production: potential role in atherosclerosis.

Atherosclerosis is preceded by cholesterol-induced diminution in vascular nitric oxide (NO) production and proatherogenic changes in endothelial cell function. Careful dissection of the steps involved in regulating endothelial nitric oxide synthase (eNOS) activity has revealed that cholesterol-induced caveolin expression reduces NO production by stimulating the production of inhibitory caveolin eNOS complexes.

Kennel enrichment: exercise and socialization of dogs.

In the last 50 years, there has been a growing need for storage and management systems for the production and maintenance of large numbers of dogs. Unwanted dogs and strays, detained in kennels, stay for various lengths of time. Large kennels also produce dogs for sale as companion animals, for the service dog industry (police and guide dogs), for biomedical research, and for use by dog food companies. Across the United States, literally tens of thousands of dogs are born in kennels and spend their lives in kennels. The laboratory dog, the kennel dog, the service dog, and the companion dog are in an evolutionary transition period, accompanied by concomitant adaptation to stresses signaled by a high frequency of genetic disease and behavioral abnormalities. For kennel enrichment programs, such as socialization and exercise, the modern kenneled dog is a genetically moving target. Specific recommendations apply neither to all breeds nor to the variations within a single breed.

Observations on assistance dog training and use.

Trained service dogs assist and also add pride, self-reliance, and personal satisfaction to an individual's daily life. However, well-bred, trained dogs are very expensive. To explore decreasing the cost of a service dog by increasing the number of dogs successfully completing training, the authors analyzed tasks that service dogs are expected to perform, measuring some of the inherent physical stresses the dogs encounter and considering training techniques to better prepare the dogs for more successful completion of tasks. Observing working dogs, the authors found that undue stress was placed on many of the dogs while performing tasks; that motivational gestures for performance were not fully extended; and that, many times, handlers did not instruct the dogs properly. The working dogs observed often were required to perform tasks that put them at risk of injury and performance failure. Important future considerations for training and handling working dogs will include proper training of handlers and a better understanding of the complexities of the instinctive and physical capabilities and limitation of dogs.

The effect of breakfast on social behavior and brain amine metabolism in vervet monkeys.

Two groups of vervet monkeys were fed, on alternate days, either before or after a morning observation period. This enabled us to determine changes in behavior when the animals were fed a nutritionally balanced breakfast of monkey chow. Feeding did not alter the proportion of behaviors that were social or non-social, but had a marked effect on individual behaviors. Feeding increased active behaviors among the adult animals except for the vervets who were lowest in the social hierarchy in each cage. For some of the individual behaviors that were altered by feeding, the changes were most marked early on in the observation period, when the animals were still feeding. Other behavioral changes were seen only later in the observation period, a time course consistent with a food-mediated change in brain biochemistry. A parallel biochemical experiment showed that feeding decreased the levels of tryptophan and 5-hydroxyindoleacetic acid in the CSF. Our data indicate that feeding can influence both brain biochemistry and behavior. The behavioral changes may be influenced by social and psychological factors as well as changes in brain biochemistry.

Hyperthermia in running sled dogs.

Hyperthermia, as measured by increase in rectal temperature, was studied in a group of 22 adult mongrel sled dogs that had been selectively bred for high-speed (up to 33 km/h) races 16-50 km in distance. Under normal working conditions, rectal temperature in the sled dogs increased significantly during initial 15-20 min of run (gathered gallop) after which temperature usually stabilized or decreased slightly. Amount of increase in rectal temperature was correlated directly with ambient temperature but not with speed or distance. Significant differences in degree of hyperthermia were found among dogs but these differences were not correlated with such factors as sex, size, coat color, weight, or genetic history. Training was found to significantly diminish amount of increase in rectal temperature during work. Data from the present study were compared to those of other laboratory investigations and relationships of heat storage and radiative surface area to body weight are discussed.