One, two, three: portable sample size in agricultural research

Determination of sample size (the number of replications) is a key step in the design of an observational study or randomized experiment. Statistical procedures for this purpose are readily available. Their treatment in textbooks is often somewhat marginal, however, and frequently the focus is on just one particular method of inference (significance test, confidence interval). Here, we provide a unified review of approaches and explain their close interrelationships, emphasizing that all approaches rely on the standard error of the quantity of interest, most often a pairwise difference of two means. The focus is on methods that are easy to compute, even without a computer. Our main recommendation based on standard errors is summarized as what we call the 1-2-3 rule for a difference of two treatment means

First insights into the phylogeny of the subgenus Cryobius Chaudoir, 1838 (Coleoptera: Carabidae: Pterostichus)

The past climatic changes caused repeated distribution shifts within insect populations leading to a highly diverse fauna in the mountain regions, which have acted as a refuge for many groups. There, some taxa have adapted to high altitudes and cold climatic conditions. One of those is the highly diverse and Holarctic subgenus Cryobius Chaudoir, 1838 (Carabidae: Pterostichus) including both locally and widely distributed species. Isolated and morphologically divergent populations of the same species led to the description of many subspecies. Until now, there has been no comprehensive work concerning the phylogeny of Cryobius, and genetic data on this taxon are sparse. This study is the first to provide insights into the molecular phylogeny of this subgenus, focusing on species from the Pyrenean and Cantabrian mountain systems. Cryobius specimens were sequenced targeting mitochondrial and nuclear genes. A molecular phylogeny was then built, merging the new data with genetic data from online public databases. All species of Cryobius included in this study form a monophyletic clade within Pterostichus. The synonymy of the two former taxa Pyreneorites and Haptoderus with Cryobius is confirmed by this study. Cryobius of the Pyreneo-Cantabrian area are closely related. Moreover, several well-supported clades of local species were found. The results further indicate a relation between Nearctic and Eastern Palearctic Cryobius, in agreement with the theory of faunal and floral colonization of North America via the Bering land bridge