Using presence-absence data to establish reserve selection procedures that are robust to temporal species turnover

Previous studies suggest that a network of nature reserves with maximum efficiency (obtained by selecting the minimum area such that each species is represented once) is likely to be insufficient to maintain species in the network over time. Here, we test the performance of three selection strategies which require presence-absence data, two of them previously proposed (multiple representations and selecting an increasing percentage of each species' range) and a novel one based on selecting the site where each species has exhibited a higher permanence rate in the past. Multiple representations appear to be a safer strategy than selecting a percentage of range because the former gives priority to rarer species while the latter favours the most widespread. The most effective strategy was the one based on the permanence rate, indicating that the robustness of reserve networks can be improved by adopting reserve selection procedures that integrate information about the relative value of sites. This strategy was also very efficient, suggesting that the investment made in the monitoring schemes may be compensated for by a lower cost in reserve acquisition

Quasispecies evolution in general mean-field landscapes

I consider a class of fitness landscapes, in which the fitness is a function of a finite number of phenotypic "traits", which are themselves linear functions of the genotype. I show that the stationary trait distribution in such a landscape can be explicitly evaluated in a suitably defined "thermodynamic limit", which is a combination of infinite-genome and strong selection limits. These considerations can be applied in particular to identify relevant features of the evolution of promoter binding sites, in spite of the shortness of the corresponding sequences.Comment: 6 pages, 2 figures, Europhysics Letters style (included) Finite-size scaling analysis sketched. To appear in Europhysics Letter

New Abundances for Old Stars - Atomic Diffusion at Work in NGC 6397

A homogeneous spectroscopic analysis of unevolved and evolved stars in the metal-poor globular cluster NGC 6397 with FLAMES-UVES reveals systematic trends of stellar surface abundances that are likely caused by atomic diffusion. This finding helps to understand, among other issues, why the lithium abundances of old halo stars are significantly lower than the abundance found to be produced shortly after the Big Bang.Comment: 8 pages, 7 colour figures, 1 table; can also be downloaded via http://www.eso.org/messenger

An Error-Components Three-Stage Least-Squares Model of Investment Allocation by Farm Households

This paper is an assessment of patterns of investment by farm households via an econometric model adapted from a land allocation approach of Holt (1999). This analysis will shed light on the importance of different classes of assets to farm household well-being, and show the reaction of farm households to a variety of market, international and government effects.Farm Management,