The adults of three ground-beetle species were induced to discharge defensive secretions into vials. The secretions were obtained by CH₂Cl₂ extraction. Altogether 11 compounds were identified by GC-MS analysis. Calosoma sycophanta possesses 10 defensive compounds, Carabus ullrichii seven, while Abax parallelepipedus has six compounds. Methacrylic, tiglic and isobutyric acids were present in all samples. The first two organic compounds were predominant in the extracts of Abax parallelepipedus. Methacrylic acid and salicylaldehyde were the major compounds in extracts of Calosoma sycophanta. Methacrylic and angelic acids were the major components in extracts of Carabus ullrichii. Propanoic acid was detected for the first time in the family Carabidae and in all animals. 2-Methyl butyric, angelic and benzoic acids were found for the first time in the subfamily Carabinae. Our finding of butyric acid is its first precise identification in the Carabinae subfamily. 2-Methyl butyric, angelic, crotonic, senecioic and benzoic acids were found for the first time in a European groundbeetle species. The compounds detected in the defensive secretions serve as protection against predators.

Classic theories on assembly rules and food-web structure are species-centered, so they largely ignore intraspecific variation. Intraspecific trophic variation, however, might be of key importance in understanding community organization. Here we study the variability of isotopic niche spaces of ground beetles and its consequences for the trophic structure of beetle assembly. Stable isotopes ratios (δ¹³C and δ¹⁵N) were measured in 1156 specimens of carabids belonging to 59 species inhabiting 20 island and two mainland sites of the Masuria Lakeland in northern Poland. Carabid species belonged to three different trophic guilds (named “phytophages”, “decomposer feeders” and “generalist predators”). However, this division is not sharp due to high intraspecific variability of isotopic signatures, which indicates the use of very different types of resources by conspecific individuals inhabiting different sites. As a consequence, most species studied did not differ significantly in the isotopic niche space. This high niche overlap corroborates the view that resource competition is not a major factor shaping the composition of ground beetles communities. Future studies should take into account the complex trophic structure of beetle assemblages and explore the intraspecific niche variability of ground beetles.

During the period 2000–2012 we witnessed a general increase in the Baltic grey seal (Halichoerus grypus) population size. Population growth has, however, ceased in the northern sea areas. The accompanying changes to age structure during this time suggest a reduced female pregnancy rate. In this study, we used hunted individuals to examine the ovulation and pregnancy rates of seals from different age classes and years. We examined the presence of corpus luteum, corpus albicans and placental scars from seals killed before the implantation period and fetuses after the implantation period. The pregnancy rate derived from the presence of corpus albicans or placental scars in the pre-implantation period was similar to that based on fetuses. Thirty-three percent of females ovulated at the age of 3 years, 81% at the age of 4 years and 99% thereafter. The pregnancy rate was lower among 4–5-year-old females (0.54–0.56) than among 6–24-year-old females (0.77–0.86), being highest in 7–11-year-old females. The pregnancy rate of 6–24-year-old females decreased from 0.89 in 2000–2004 to 0.66 in 2005–2011 and correlated negatively with population size. The decreased pregnancy rate suggests that grey seal numbers in the northern part of the Baltic Sea may be today close to the carrying capacity of the environment.

In Europe, muskrat is an invasive species that can profoundly affect lake ecosystems. We developed a landscape-based prediction model for the occurrence of muskrat based on 237 muskrat and 236 randomly selected lakes within the distribution range of muskrat in northern Sweden. We analyzed the importance of slope and cover of vegetation types for the occurrence of the muskrat at 12 spatial scales (50–1000 m) from the lakeshores. Logistic regression models that incorporated slope and percentage cover of swamps, meadows and lakeshore meadows successfully predicted the occurrence of muskrat. The importance of the predictor variables changed with increased distance from the shoreline. Our results were confirmed with an independent data set (n = 29) from the southern distribution range of the muskrat in Sweden. The prediction model can be used to assess the risk of muskrat occurrence in lakes as well as for the development of muskrat-related conservation measures.

The relationship between total length (L, cm) and weight (W, kg) in the large northern pike (Esox lucius) was investigated using a dataset comprising 802 specimens weighing between 1 and 18.8 kg caught during fishing competitions. The applying the data to the equation W = aL^b, yielded a = 6.648 × 10^-6 and b = 3.0217. Weight residuals fluctuate during the fishing season, likely due to conditions of the fish, probably associated with gonad development. Additionally, the equations including maximum girth (G, cm) — W = aG^b and W = a(L × G)^b — were fitted using a subset of record fish totalling 186 specimens. Comparison of the equations W = aL^b and W = aG^b showed that weight was better described by maximum girth (AIC = 624.9) rather than by length (AIC = 690.0), but the best fit was obtained with the equation W = a(L × G)^b (AIC = 566.3) with the parameters a = 2.426 × 10^-3 and b = 0.974.

Studies on the mechanisms of speciation and maintenance of lineages have paid great attention to hybridization between species because this process is considered an important source of variability and evolution. In recent years, the use of molecular markers has provided more detailed information on the distribution and magnitude of hybridization in natural populations. Here we present a phylogenetic analysis using one mitochondrial and one nuclear DNA segment as molecular markers in two closely related lizard species, Tupinambis merianae and T. rufescens, which are present in a continuous area including allopatric and sympatric populations. Consensus trees obtained with the mitochondrial gene showed two well-supported clades. Some individuals clustered with one of the species in the tree obtained with mitochondrial DNA, and with the other species in the tree recovered using the nuclear gene, demonstrating the occurrence of hybridization between these species. Hybrid individuals were captured in the area of sympatry, suggesting the existence of a hybrid zone in the contact area of the distribution ranges of these two lizards, which corresponds to the ecotone between Dry Chaco and Espinal. This work presents the first evidence of natural hybridization within the genus Tupinambis.