Search results for " Competition"
showing 10 items of 819 documents
The age and evolution of sociality in Stegodyphus spiders: a molecular phylogenetic perspective
2006
Social, cooperative breeding behaviour is rare in spiders and generally characterized by inbreeding, skewed sex ratios and high rates of colony turnover, processes that when combined may reduce genetic variation and lower individual fitness quickly. On these grounds, social spider species have been suggested to be unstable in evolutionary time, and hence sociality a rare phenomenon in spiders. Based on a partial molecular phylogeny of the genus Stegodyphus , we address the hypothesis that social spiders in this genus are evolutionary transient. We estimate the age of the three social species, test whether they represent an ancestral or derived state and assess diversification relative to s…
Biometrical and ecological observations on Cistus salvifolius L.
1993
Abstract Biometrical observations on Cistus salvifolius L. (Cistaceae), a species with a very variable morphology, are presented: data, collected in Sicily, are relative to three environments in which populations of Cistus salvifolius live: garigue, maquis, pinewood. Measurements are compared with other ones, found in the literature, and in some cases they disagree or supply useful indications. On the basis of the different light regimes in the three environments, and of the parameters in which the difference among the three populations is most evident, some observations about the reaction to shade in Cistus salvifolius were made. On the basis of the few data collected, the intraspecific di…
A note on Stackelberg competition
2011
International audience
Stackelberg equilibrium with many leaders and followers. The case of zero fixed costs
2017
Abstract I study a version of the Stackelberg game with many identical firms in which leaders and followers use a continuous cost function with no fixed cost. Using lattice theoretical methods I provide a set of conditions that guarantee that the game has an equilibrium in pure strategies. With convex costs the model shows the same properties as a quasi-competitive Cournot model. The same happens with concave costs, but only when the number of followers is small. When this number is large the leaders preempt entry. I study the comparative statics and the limit behavior of the equilibrium and I show how the main determinants of market structure interact. More competition between the leaders …
Effects of morphometric descriptor changes on statistical classification and morphospaces
2004
Ten morphometric descriptors (five pairs of form and shape parameters) are used to describe the complex morphology of the first lower molar of two morphologically similar species, Microtus arvalis and M. agrestis. These descriptors are derived either from linear measurements or from outline analysis. The effects of these different descriptors on classical analysis as used in biology or palaeobiology are explored. First, the reliability of results in statistical classification is assessed. All of the descriptors discriminate well between the two species. The initial morphometric scheme (linear or outline) does not induce marked differences in statistical classification and the major discrepa…
Correlated randomness and switching phenomena
2010
One challenge of biology, medicine, and economics is that the systems treated by these serious scientific disciplines have no perfect metronome in time and no perfect spatial architecture—crystalline or otherwise. Nonetheless, as if by magic, out of nothing but randomness one finds remarkably fine-tuned processes in time and remarkably fine-tuned structures in space. Further, many of these processes and structures have the remarkable feature of “switching” from one behavior to another as if by magic. The past century has, philosophically, been concerned with placing aside the human tendency to see the universe as a fine-tuned machine. Here we will address the challenge of uncovering how, th…
R&D, Competition and Growth with Human Capital Accumulation Revisited
2012
In this paper, we have presented a generalization of Bucci's (2003) model in which have disentangled the monopolistic mark-up in the intermediate goods sector, the intermediate goods share in the final output and the returns to specialization in order to have a better measurement of competition. Indeed, unlike Bucci (2003), in our model, the measure of competition is completely independent of the intermediate goods share in the final output and the returns to specialization. Our main finding is that, unlike Bucci (2003), we show that the competition does not play any role in growth. This result is explained by the complementarity of innovation and human capital assumed in the research produ…
Pseudo-Cut Strategies for Global Optimization
2011
Motivated by the successful use of a pseudo-cut strategy within the setting of constrained nonlinear and nonconvex optimization in Lasdon et al. (2010), we propose a framework for general pseudo-cut strategies in global optimization that provides a broader and more comprehensive range of methods. The fundamental idea is to introduce linear cutting planes that provide temporary, possibly invalid, restrictions on the space of feasible solutions, as proposed in the setting of the tabu search metaheuristic in Glover (1989), in order to guide a solution process toward a global optimum, where the cutting planes can be discarded and replaced by others as the process continues. These strategies can…
INTRA- AND INTERSPECIFIC VARIATION IN INTERNAL STRUCTURES OF THE GENUSSTENOSARINA(BRACHIOPODA, TEREBRATULIDA) USING LANDMARKS
2001
Abstract Although a number of brachiopod genera have been defined mainly from their internal structures, the fixity of those structures has rarely been investigated. Variability of the rather simple loops of two New Caledonian species of the Recent genus Stenosarina (Terebratulida), one species having a variant with endemic morphology, provides insight into the relationship between the two species. Procrustes methods based on landmarks are used. Intra-population variability is found to be of the same order of magnitude as inter-population variability. Moreover, the morphological distance between the endemic variant and the other specimens is greater than the distance between the two species…
Modelling Bacterial Dynamics in Food Products: Role of Environmental Noise and Interspecific Competition
2013
In this paper we review some results obtained within the context of the predictive microbiology, which is a specific field of the population dynamics. In particular we discuss three models, which exploit tools of statistical mechanics, for bacterial dynamics in food of animal origin. In the first model, the random fluctuating behaviour, experimentally measured, of the temperature is considered. In the second model stochastic differential equations are introduced to take into account the influence of physical and chemical variables, such as temperature, pH and activity water, subject to deterministic and random variations. The third model, which is an extended version of the second one, negl…