Spatial competition induces the mobilization of morula cells in the colonial ascidian Didemnum perlucidum (Tunicata: Didemnidae)

The effects of spatial competition among colonial marine organisms are often evident in the contact zones between colonies. These effects are especially pronounced when the interaction results in overgrowth or necrosis of one of the competitors. Ascidians, one of the dominant taxonomic groups in subtidal sessile communities, have specialized morula cells that provide a defense against microbial infections. Injuries resulting from interspecific competitive interactions might also act as a stimulus for this defensive mechanism. Therefore, we expected to see the recruitment of morula cells in tissues near competitor contact zones. To test the hypothesis that spatial competition elicits this immune response, we placed colonies of the ascidian Didemnum perlucidum from southeastern Brazil in four different types of competitive situations: (1) overgrowth of the competitor, (2) stand-off interactions, (3) overgrowth by the competitor, and (4) free of competitors. Our results indicate that competitive interactions increase the population of morula cells in contact zones, as more cells were observed in interactions that resulted in the overgrowth of individuals of D. perlucidum, and fewer cells were observed in colonies that were free of competitors. We identified the defensive function of the morula cells by showing the presence of the enzyme phenoloxidase within its vacuoles. Phenoloxidase is a widespread enzyme among animals and plants, and is frequently used in defense by synthesizing toxic quinones from polyphenol substrates. This is the first study to document the presence of morula cells in didemnid ascidians and the mobilization of these cells by spatial competition by heterospecifics, and one of the first studies to identify phenoloxidase activity in morula cells.

Food Competition in a Semi-Free-Ranging Cebus apella Group

The competitive regime faced by individuals is fundamental to modelling the evolution of social organization. In this paper, we assess the relative importance of contest and scramble food competition on the social dynamics of a provisioned semi-free-ranging Cebus apella group (n=18). Individuals competed directly for provisioned and clumped foods. Effects of indirect competition were apparent with individuals foraging in different areas and with increased group dispersion during periods of low food abundance. We suggest that both forms of competition can act simultaneously and to some extent synergistically in their influence on social dynamics; the combination of social and ecological opportunities for competition and how those opportunities are exploited both influence the nature of the relationships within social groups of primates and underlie the evolved social structure. Copyright (c) 2008 S. Karger AG, Basel

Particle Competition and Cooperation in Networks for Semi-Supervised Learning

Semi-supervised learning is one of the important topics in machine learning, concerning with pattern classification where only a small subset of data is labeled. In this paper, a new network-based (or graph-based) semi-supervised classification model is proposed. It employs a combined random-greedy walk of particles, with competition and cooperation mechanisms, to propagate class labels to the whole network. Due to the competition mechanism, the proposed model has a local label spreading fashion, i.e., each particle only visits a portion of nodes potentially belonging to it, while it is not allowed to visit those nodes definitely occupied by particles of other classes. In this way, a "divide-and-conquer" effect is naturally embedded in the model. As a result, the proposed model can achieve a good classification rate while exhibiting low computational complexity order in comparison to other network-based semi-supervised algorithms. Computer simulations carried out for synthetic and real-world data sets provide a numeric quantification of the performance of the method.

Intraspecific competition in Zabrotes subfasciatus: Physiological and behavioral adaptations to different amounts of host

The effects of competition on populations of the bean weevil Zabrotes subfasciatus were analyzed during 41 generations under different competition levels. Three competition environments were established by maintaining the number of couples (6) and varying the amount of available host seeds: HC, high (limited availability of host: 1.35 g); IC, intermediate (intermediate availability of host: 6 g); and LC, low competition (abundance of host: 36 g). It was found that the distribution of the eggs laid on grains was different among treatments: in LC, for example, although females showed high fecundity (35.4 +/- 5.6 eggs/female) the number of eggs laid on each grain was small (1.2 +/- 0.4 eggs on each seed), thus avoiding larval competition of their offspring; whereas in HC treatment, females showed low fecundity (27.04 +/- 4.5 eggs/female) but laid many eggs on each grain (15.03 +/- 4.3 eggs). There were no changes in the ability to respond to different amounts of host via oviposition behavior (egg distribution) during 41 generations. However, HC females had more offspring than LC females under HC conditions. This suggests that HC insects evolved toward higher fitness in crowded conditions. In addition, after inverting the competition level, insects behaved independently of the treatment conditions they experienced through generations, thus showing that oviposition behavior is flexible. Taken together, our results show that Z. subfasciatus presents a broad range of behavioral and physiological responses which allows for quick and reversible adjustments to sudden changes in the amount of resources.

The relationship between banking market competition and risk-taking: Do size and capitalization matter?

This paper addresses the effects of bank competition on the risk-taking behaviors of banks in 10 Latin American countries between 2003 and 2008. We conduct our empirical approach in two steps. First, we estimate the Boone indicator, which is a measure of competition. We then regress this measure and other explanatory variables on the banking "stability inefficiency" derived simultaneously from the estimation of a stability stochastic frontier. Unlike previous findings, this paper concludes that competition affects risk-taking behavior in a non-linear way as both high and low competition levels enhance financial stability, while we find the opposite effect for average competition. In addition, bank size and capitalization are essential factors in explaining this relationship. On the one hand, the larger a bank is, the more it benefits from competition. On the other hand, a greater capital ratio is advantageous for banks that operate in collusive markets, while capitalization only enhances the stability of larger banks under high and average competition. These results are of extreme importance when considering bank regulations, especially in light of the recent turmoil in the global financial markets. (C) 2012 Elsevier B.V. All rights reserved.

EFFECT OF COMPETITION ON SALIVARY CORTISOL, IMMUNOGLOBULIN A, AND UPPER RESPIRATORY TRACT INFECTIONS IN ELITE YOUNG SOCCER PLAYERS

Mortatti, AL, Moreira, A, Aoki, MS, Crewther, BT, Castagna, C, de Arruda, AFS, and Filho, JM. Effect of competition on salivary cortisol, immunoglobulin A, and upper respiratory tract infections in elite young soccer players. J Strength Cond Res 26(5): 1396-1401, 2012-The present study examined the effect of a 20-day period of competition on salivary cortisol, mucosal immunity, and upper respiratory tract infections (URTI) in young male soccer players (n = 14). The players were monitored during the main under-19 Brazilian soccer championship, in which 7 matches were played in 20 days. Saliva samples were collected in the morning of each match and analyzed for cortisol and immunoglobulin A (IgA). Signs and symptoms of URTI were assessed across the study and a rating of perceived exertion (RPE) was obtained for each match. Compared with match 1, a significant increase in player RPE was observed in matches 4-7 (p < 0.05). Significant (p < 0.05) increases in the reporting of URTI occurred between matches 2 and 3, and 6 and 7, and this was accompanied by significant decreases in salivary IgA levels. Significant (p < 0.05) correlations were also seen between the individual reports of URTI and the decrease in IgA levels in match 2 (r = -0.60) and match 6 (r = -0.65). These results suggest that decrements in mucosal immunity, as measured by salivary IgA concentrations, may lead to a greater incidence of URTI in elite young soccer players. It may be speculated that the physiological and psychological stressors imposed by training and competition in a short timeframe are major contributing factors to these responses. Thus, the monitoring of salivary IgA could provide a useful and noninvasive approach for predicting URTI occurrences in young athletes during short-term competitions, especially if frequent sampling and rapid measurements are made.

Changes in intrapopulation resource use patterns of an endangered raptor in response to a disease-mediated crash in prey abundance

1. A long-standing question in ecology is how natural populations respond to a changing environment. Emergent optimal foraging theory-based models for individual variation go beyond the population level and predict how its individuals would respond to disturbances that produce changes in resource availability. 2. Evaluating variations in resource use patterns at the intrapopulation level in wild populations under changing environmental conditions would allow to further advance in the research on foraging ecology and evolution by gaining a better idea of the underlying mechanisms explaining trophic diversity. 3. In this study, we use a large spatio-temporal scale data set (western continental Europe, 19682006) on the diet of Bonellis Eagle Aquila fasciata breeding pairs to analyse the predator trophic responses at the intrapopulation level to a prey population crash. In particular, we borrow metrics from studies on network structure and intrapopulation variation to understand how an emerging infectious disease [the rabbit haemorrhagic disease (RHD)] that caused the density of the eagles primary prey (rabbit Oryctolagus cuniculus) to dramatically drop across Europe impacted on resource use patterns of this endangered raptor. 4. Following the major RHD outbreak, substantial changes in Bonellis Eagles diet diversity and organisation patterns at the intrapopulation level took place. Dietary variation among breeding pairs was larger after than before the outbreak. Before RHD, there were no clusters of pairs with similar diets, but significant clustering emerged after RHD. Moreover, diets at the pair level presented a nested pattern before RHD, but not after. 5. Here, we reveal how intrapopulation patterns of resource use can quantitatively and qualitatively vary, given drastic changes in resource availability. 6. For the first time, we show that a pathogen of a prey species can indirectly impact the intrapopulation patterns of resource use of an endangered predator.

Is shell partitioning between the hermit crabs Pagurus brevidactylus and Pagurus criniticornis explained by interference and/or exploitation competition?

The effect of crab behaviour on shell-use dynamics was analysed, comparing both interference and exploitation behaviours between the hermit crabs Pagurus criniticornis and Pagurus brevidactylus. Although these species exhibited microhabitat separation, with P. criniticornis dominating (100%) in sandy substrates and P. brevidactylus (80%) on rocky shores, they overlapped in the rocky shore/sand interface (P. criniticornis, 53%; P. brevidactylus, 43%). Pagurus criniticornis occupied shells of Cerithium atratum in higher frequencies (84%) than P. brevidactylus (37%), which was hypothesized to be a consequence of competitive interactions combined with their ability to acquire and/or retain this resource. The species P. criniticornis was attracted in larger numbers to simulated gastropod predation events than was P. brevidactylus, which, on the few occasions that it moved before P. criniticornis, tended to be attracted more rapidly. Interspecific shell exchanges between these species were few, suggesting the absence of dominance relationships. The shell-use pattern in this species pair is thus defined by exploitation competition, which is presumed to be intensified in areas of microsympatry. These results differ from other studies, which found that interference competition through interspecific exchanges shapes shell use, indicating that shell partitioning in hermit crabs is dependent on the behaviour of the species involved in the contests.

Non-mean-field effects in systems with long-range forces in competition

We investigate the canonical equilibrium of systems with long-range forces in competition. These forces create a modulation in the interaction potential and modulated phases appear at the system scale. The structure of these phases differentiate this system from monotonic potentials, where only the mean-field and disordered phases exist. With increasing temperature, the system switches from one ordered phase to another through a first-order phase transition. Both mean-field and modulated phases may be stable, even at zero temperature, and the long-range nature of the interaction will lead to metastability characterized by extremely long time scales.

Irreversibility by competition on a Glauber-Ising model by means of the entropy production.

An out of equilibrium Ising model subjected to an irreversible dynamics is analyzed by means of a stochastic dynamics, on a effort that aims to understand the observed critical behavior as consequence of the intrinsic microscopic characteristics. The study focus on the kinetic phase transitions that take place by assuming a lattice model with inversion symmetry and under the influence of two competing Glauber dynamics, intended to describe the stationary states using the entropy production, which characterize the system behavior and clarifies its reversibility conditions. Thus, it is considered a square lattice formed by two sublattices interconnected, each one of which is in contact with a heat bath at different temperature from the other. Analytical and numerical treatments are faced, using mean-field approximations and Monte Carlo simulations. For the one dimensional model exact results for the entropy production were obtained, though in this case the phase transition that takes place in the two dimensional counterpart is not observed, fact which is in accordance with the behavior shared by lattice models presenting inversion symmetry. Results found for the stationary state show a critical behavior of the same class as the equilibrium Ising model with a phase transition of the second order, which is evidenced by a divergence with an exponent µ ¼ 0:003 of the entropy production derivative.