Responses of the ichthyofauna to urbanization in two urban areas in Southeast Brazil

In this study, we evaluated the trophic structure and composition of the ichthyofauna in streams from non-urbanized and urbanized areas in two municipalities with approximately 30,000 inhabitants. We sampled fish fauna in nine pool-run stretches, four located in urban and five in non-urban areas. We adapted a physical habitat index (PHI) that summarized the physical attributes of the habitat, and a fish-based biotic integrity index (IBI) for the trophic structure of fish assemblage. Higher median scores of habitat parameters characterized non-urban stretches owing to better riparian vegetation and shading, bank stability and larger substrates. Diversity, richness and evenness indexes, as well as the abundance and biomass comparison (ABC), did not differ between urban and non-urban areas. The PHI was significantly correlated with the IBI and a non-metric multidimensional scaling (NMDS) analysis showed differences in the composition of the ichthyofauna. These results illustrated a common process in fish assemblages subjected to environmental impact, in which the generalist species replaced more specialist species, altering the species composition but maintaining a similar community structure. In general, the species responses were dependent on their trophic plasticity and foraging habitats. We showed that in a gradient of habitat alteration, species composition and thophic structure are better indicators of degradation than simple diversity indexes. We also discuss the implications of the urbanization in small towns toward changes in the species composition of freshwater fish, and the utilization of biotic and abiotic characteristics to document these changes.     

The Burden of Labour Costs in Mexico

Abstract. We analysed labour costs in Mexico and evaluated their impact in terms of firm performance. Using a new survey, we studied how firms chose to conduct a firing procedure (i.e. mandatory payment, negotiation, or legal dispute) and the actual costs derived from that decision. We found that firms that negotiate have, on average, lower costs. This may mean that workers subvaluate the legal benefits. Moreover, legal disputes may increase firing costs by 50 per cent. We contributed to the analysis of the impact of such costs on employment and found that, when firms negotiate or pay higher costs, this decreases the level of employment. We also analysed the impact of Social Benefits on employment using an industrial survey. We found that a 10 per cent increment in these benefits may have a negative long‐term impact of 9 per cent on the level of employment.     

Revised GRASP with path-relinking for the linear ordering problem

The linear ordering problem (LOP) is an NP\mathcal{NP}-hard combinatorial optimization problem with a wide range of applications in economics, archaeology, the social sciences, scheduling, and biology. It has, however, drawn little attention compared to other closely related problems such as the quadratic assignment problem and the traveling salesman problem. Due to its computational complexity, it is essential in practice to develop solution approaches to rapidly search for solution of high-quality. In this paper we propose a new algorithm based on a greedy randomized adaptive search procedure (GRASP) to efficiently solve the LOP. The algorithm is integrated with a Path-Relinking (PR) procedure and a new local search scheme. We tested our implementation on the set of 49 real-world instances of input-output tables (LOLIB instances) proposed in Reinelt (Linear ordering library (LOLIB) 2002). In addition, we tested a set of 30 large randomly-generated instances proposed in Mitchell (Computational experience with an interior point cutting plane algorithm, Tech. rep., Mathematical Sciences, Rensellaer Polytechnic Institute, Troy, NY 12180-3590, USA 1997). Most of the LOLIB instances were solved to optimality within 0.87 seconds on average. The average gap for the randomly-generated instances was 0.0173% with an average running time of 21.98 seconds. The results indicate the efficiency and high-quality of the proposed heuristic procedure.