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McLaren, B. E., & Peterson, R. O. (1994). Wolves, Moose, and Tree Rings on Isle Royale. Science, 266(5190), 1555–1558.
Abstract: Investigation of tree growth in Isle Royale National Park in Michigan revealed the influence of herbivores and carnivores on plants in an intimately linked food chain. Plant growth rates were regulated by cycles in animal density and responded to annual changes in primary productivity only when released from herbivory by wolf predation. Isle Royale's dendrochronology complements a rich literature on food chain control in aquatic systems, which often supports a trophic cascade model. This study provides evidence of top-down control in a forested ecosystem.
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Griffiths, S. W., Brockmark, S., Höjesjö, J., & Johnsson, J. I. (2004). Coping with divided attention: the advantage of familiarity. Proc. Roy. Soc. Lond. B Biol. Sci., 271(1540), 695–699.
Abstract: The ability of an animal to perform a task successfully is limited by the amount of attention being simultaneously focused on other activities. One way in which individuals might reduce the cost of divided attention is by preferentially focusing on the most beneficial tasks. In territorial animals where aggression is lower among familiar individuals, the decision to associate preferentially with familiar conspecifics may therefore confer advantages by allowing attention to be switched from aggression to predator vigilance and feeding. Wild juvenile brown trout were used to test the prediction that familiar fishes respond more quickly than unfamiliar fishes to a simulated predator attack. Our results confirm this prediction by demonstrating that familiar trout respond 14% faster than unfamiliar individuals to a predator attack. The results also show that familiar fishes consume a greater number of food items, foraging at more than twice the rate of unfamiliar conspecifics. To the best of our knowledge, these results provide the first evidence that familiarity–biased association confers advantages through the immediate fitness benefits afforded by faster predator–evasion responses and the long–term benefits provided by increased feeding opportunities.
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Bugnyar, T., Stöwe, M., & Heinrich, B. (2004). Ravens, Corvus corax, follow gaze direction of humans around obstacles. Proc. Roy. Soc. Lond. B Biol. Sci., 271(1546), 1331–1336.
Abstract: The ability to follow gaze (i.e. head and eye direction) has recently been shown for social mammals, particularly primates. In most studies, individuals could use gaze direction as a behavioural cue without understanding that the view of others may be different from their own. Here, we show that hand–raised ravens not only visually co–orient with the look–ups of a human experimenter but also reposition themselves to follow the experimenter's gaze around a visual barrier. Birds were capable of visual co–orientation already as fledglings but consistently tracked gaze direction behind obstacles not before six months of age. These results raise the possibility that sub–adult and adult ravens can project a line of sight for the other person into the distance. To what extent ravens may attribute mental significance to the visual behaviour of others is discussed.
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Rizzolatti, G., Fogassi, L., & Gallese, V. (2001). Neurophysiological mechanisms underlying the understanding and imitation of action. Nat Rev Neurosci, 2(9), 661–670.
Abstract: What are the neural bases of action understanding? Although this capacity could merely involve visual analysis of the action, it has been argued that we actually map this visual information onto its motor representation in our nervous system. Here we discuss evidence for the existence of a system, the ‘mirror system’, that seems to serve this mapping function in primates and humans, and explore its implications for the understanding and imitation of action.
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Milo, R., Itzkovitz, S., Kashtan, N., Levitt, R., & Alon, U. (2004). Response to Comment on “Network Motifs: Simple Building Blocks of Complex Networks” and “Superfamilies of Evolved and Designed Networks”. Science, 305(5687), 1107d.
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Milo, R., Shen-Orr, S., Itzkovitz, S., Kashtan, N., Chklovskii, D., & Alon, U. (2002). Network Motifs: Simple Building Blocks of Complex Networks. Science, 298(5594), 824–827.
Abstract: Complex networks are studied across many fields of science. To uncover their structural design principles, we defined “network motifs,” patterns of interconnections occurring in complex networks at numbers that are significantly higher than those in randomized networks. We found such motifs in networks from biochemistry, neurobiology, ecology, and engineering. The motifs shared by ecological food webs were distinct from the motifs shared by the genetic networks of Escherichia coli and Saccharomyces cerevisiae or from those found in the World Wide Web. Similar motifs were found in networks that perform information processing, even though they describe elements as different as biomolecules within a cell and synaptic connections between neurons in Caenorhabditis elegans. Motifs may thus define universal classes of networks. This approach may uncover the basic building blocks of most networks.
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Milo, R., Itzkovitz, S., Kashtan, N., Levitt, R., Shen-Orr, S., Ayzenshtat, I., et al. (2004). Superfamilies of Evolved and Designed Networks. Science, 303(5663), 1538–1542.
Abstract: Complex biological, technological, and sociological networks can be of very different sizes and connectivities, making it difficult to compare their structures. Here we present an approach to systematically study similarity in the local structure of networks, based on the significance profile (SP) of small subgraphs in the network compared to randomized networks. We find several superfamilies of previously unrelated networks with very similar SPs. One superfamily, including transcription networks of microorganisms, represents “rate-limited” information-processing networks strongly constrained by the response time of their components. A distinct superfamily includes protein signaling, developmental genetic networks, and neuronal wiring. Additional superfamilies include power grids, protein-structure networks and geometric networks, World Wide Web links and social networks, and word-adjacency networks from different languages.
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Artzy-Randrup, Y., Fleishman, S. J., Ben-Tal, N., & Stone, L. (2004). Comment on “Network Motifs: Simple Building Blocks of Complex Networks” and “Superfamilies of Evolved and Designed Networks”. Science, 305(5687), 1107c.
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Penzhorn, B. L., & Novellie, P. A. (1991). Some behavioural traits of Cape mountain zebras (Equus zebra zebra) and their implications for the management of a small conservation area. Appl. Anim. Behav. Sci., 29(1-4), 293–299.
Abstract: The social organisation of mountain zebras (Equus zebra zebra) consists of breeding herds (1 male, 2.4 females (range 1-5) and their offspring) which remain stable over many years, and bachelor groups. Foals leave their maternal herds of their own accord. In a free-ranging population the behaviour of the foals in leaving the herd is probably an adequate mechanism to prevent inbreeding, but inbreeding may occur in confined populations. Individual recognition by means of stripe pattern allows a check to be kept. Seasonal movement of mountain zebras is associated with a relative change in diet quality (as indicated by crude protein contents of preferred food plants and of faeces) between summer and winter habitats. Any conservation area should be large and varied enough to include both summer and winter habitats. Mountain zebras favour taller grass than most antelope species, harvesting their food at 50-150 mm from the ground. The existence of large populations of antelope could, therefore, be detrimental to zebras.
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Sumpter, D. J. T. (2006). The principles of collective animal behaviour. Phil. Trans. Biol. Sci., 361(1465), 5–22.
Abstract: In recent years, the concept of self-organization has been used to understand collective behaviour of animals. The central tenet of self-organization is that simple repeated interactions between individuals can produce complex adaptive patterns at the level of the group. Inspiration comes from patterns seen in physical systems, such as spiralling chemical waves, which arise without complexity at the level of the individual units of which the system is composed. The suggestion is that biological structures such as termite mounds, ant trail networks and even human crowds can be explained in terms of repeated interactions between the animals and their environment, without invoking individual complexity. Here, I review cases in which the self-organization approach has been successful in explaining collective behaviour of animal groups and societies. Ant pheromone trail networks, aggregation of cockroaches, the applause of opera audiences and the migration of fish schools have all been accurately described in terms of individuals following simple sets of rules. Unlike the simple units composing physical systems, however, animals are themselves complex entities, and other examples of collective behaviour, such as honey bee foraging with its myriad of dance signals and behavioural cues, cannot be fully understood in terms of simple individuals alone. I argue that the key to understanding collective behaviour lies in identifying the principles of the behavioural algorithms followed by individual animals and of how information flows between the animals. These principles, such as positive feedback, response thresholds and individual integrity, are repeatedly observed in very different animal societies. The future of collective behaviour research lies in classifying these principles, establishing the properties they produce at a group level and asking why they have evolved in so many different and distinct natural systems. Ultimately, this research could inform not only our understanding of animal societies, but also the principles by which we organize our own society.
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