Social learning mechanisms compared in a simple environment

Social learning can be adaptive, but little is known about the underlying mechanisms. Many researchers have focused on imitation but this may have led to simpler mechanisms being underestimated. We demonstrate in simulation that imitative learning is not always the best strategy for a group-living animal, and that the effectiveness of any such strategy will depend on details of the environment and the animal's lifestyle. We show that observations of behavioural convergence or "traditions" might suggest effective social learning, but are meaningless considered alone

Social learning in a multi-agent system

In a persistent multi-agent system, it should be possible for new agents to benefit from the accumulated learning of more experienced agents. Parallel reasoning can be applied to the case of newborn animals, and thus the biological literature on social learning may aid in the construction of effective multi-agent systems. Biologists have looked at both the functions of social learning and the mechanisms that enable it. Many researchers have focused on the cognitively complex mechanism of imitation; we will also consider a range of simpler mechanisms that could more easily be implemented in robotic or software agents. Research in artificial life shows that complex global phenomena can arise from simple local rules. Similarly, complex information sharing at the system level may result from quite simple individual learning rules. We demonstrate in simulation that simple mechanisms can outperform imitation in a multi-agent system, and that the effectiveness of any social learning strategy will depend on the agents' environment. Our simple mechanisms have obvious advantages in terms of robustness and design costs

Effects of the topology of social networks on information transmission

Social behaviours cannot be fully understood without considering the network structures that underlie them. Developments in network theory provide us with relevant modelling tools. The topology of social networks may be due to selection for information transmission. To investigate this, we generated network topologies with varying proportions of random connections and degrees of preferential attachment. We simulated two social tasks on these networks: a spreading innovation model and a simple market. Results indicated that non-zero levels of random connections and low levels of preferential attachment led to more efficient information transmission. Theoretical and practical implications are discussed

Image scoring in ad-hoc networks : an investigation on realistic settings

Encouraging cooperation in distributed Multi-Agent Systems (MAS) remains an open problem. Emergent application domains such as Mobile Ad-hoc Networks (MANETs) are characterised by constraints including sparse connectivity and a lack of direct interaction history. Image scoring, a simple model of reputation proposed by Nowak and Sigmund, exhibits low space and time complexity and promotes cooperation through indirect reciprocity, in which an agent can expect cooperation in the future without repeat interactions with the same partners. The low overheads of image scoring make it a promising technique for ad-hoc networking domains. However, the original investigation of Nowak and Sigmund is limited in that it (i) used a simple idealised setting, (ii) did not consider the effects of incomplete information on the mechanism’s efficacy, and (iii) did not consider the impact of the network topology connecting agents. We address these limitations by investigating more realistic values for the number of interactions agents engage in, and show that incomplete information can cause significant errors in decision making. As the proportion of incorrect decisions rises, the efficacy of image scoring falls and selfishness becomes more dominant. We evaluate image scoring on three different connection topologies: (i) completely connected, which closely approximates Nowak and Sigmund’s original setup, (ii) random, with each pair of nodes connected with a constant probability, and (iii) scale-free, which is known to model a number of real world environments including MANETs

Comparative Yields of Seven Native Grasses Growing in An Ungrazed Mixed Prairie

A study was made to determine the average monthly and seasonally yields of seven native grasses as they grew in pure stands in an ungrazed mixed prairie near Hays, Kansas. The study was conducted for two growing seasons (1952-1953) on the upland, gentle hillside, steep hillside, and lowland. The study area consisted of 320 acres with gently rolling hills and steep hillsides broadening at their based to form ravines and a broad lowland. Grasses which were studied on the upland were blue grama (Boutelous gracilis (H.B.K.) Lab.), buffalo grass (Buchloe dactyloides (Nutt.) Englem.), side-oats grama (Bouteloua curtipendula (Michx.) Torr.), big bluestem (Andropogon gerardi, Vitaman), and western wheatgrass (Agropyron smithii, Rydb.). On the gentle hillside, yields were ascertained for buffalo grass, blue grama, side-oats grama, big bluestem, and little bluestem (Andropogon scoparius, Michx.). Grasses on the steep hillsides form which yields were taken were side-oats gram, big bluestem, and little bluestem. On the lowland yields were obtained from big bluestem, switchgrass (Panicum virgatum L.), and western wheatgrass. Randomly located square-foot quadrats were used to determine basal cover and yields. Fifteen or more square-foot quadrats were clipped each month (June to September) at the top of underlying mulch to determine yields of each species of grass on each site. The clipped forage was air dried, weighed and computed to pounds per acre. Average basal cover was determined for each species by many individual measurements. Height of growth was determined at each clipping period. Measurements were made of new growth prior to clipping the quadrats and also of unclipped growth outside the quadrats. Soul moisture was determined every 2 weeks to a depth of 4 feet on the upland and lowland. Samples were taken in duplicate and an average percent moisture for the two samples was recorded for each depth. Climate for the two seasons was characterized by low, uneven distribution of rainfall, deficiency of soil moisture and accompanying high temperatures and wind velocities. The two growing season were abnormally dry, each received about 11 inches of rainfall. Climate for the two seasons was characterized by low, uneven distribution of rainfall, deficiency of soil moisture and accompanying high temperatures and wind velocities. The two growing season were abnormally dry, each receiving about 11 inches of rainfall. Production of grasses usually reached a peak in late spring or early summer and then declined during the latter part of the growing season. Generally more forage was produced by June 15 than thereafter. Height of growth and yield were greatest when soil moisture became deficient. During the latter part of both seasons, except for sporadic greening, most grasses were in semi-dormancy with their leaves either rolled or folded. Generally the amount of forage produced was greatest from species which occupied the mesic areas and lowest form those of more xeric ones. The tall-grasses, while occupying less surface area than the short grasses, produced larger amount of forage due to their greater height and coarser growth. On the upland habitat about 1,000 pounds of forage was produced by the short grasses each season, while the yield of side-oats grama was somewhat higher. Big bluestem which occurred only in isolated bunches produced slightly more than 3,500 pounds per acre. The yield of western wheatgrass was slightly more than 1,500 pounds the first season and somewhat less the second season. On the gentle hillside habitat the two short grasses were again low producers. However, buffalo grass produced slightly more forage than blue grama and side-oats grama each season. The yield of little bluestem and big bluestem was somewhat comparable each season, each producing more than 2,000 pounds. Big bluestem produced the greatest yield followed by little bluestem and side-oats grama in that order on the steep hillside habitat. Big bluestem produced less forage on this habitat than on other sites while the yields of side-oats grama and little bluestem were somewhat higher. On the lowland habitat big bluestem produced about 6,013 pounds in 1952 followed by switchgrass (5,872 pounds) and western wheatgrass (4,940 pounds). 1953 yields were considerably less for each species. The amount of forage produced by each species generally increased with an increase with an increase in basal area

The impact of space and space-related activities on a local economy. a case study of boulder, colorado. part ii- the income-product accounts

Total impact of space and space related activities on local economy of Boulder, Colorado - income-product account