Using information theory as a substitute for stepwise regression in ecology and behavior

In ecological and behavioral research, drawing reliable conclusions from statistical models with multiple predictors is usually difficult if all predictors are simultaneously in the model. The traditional way of handling multiple predictors has been the use of threshold-based removal-introduction algorithms, that is, stepwise regression, which currently receives considerable criticism. A more recent and increasingly propagated modelling method for multiple predictors is the information theoretic (IT) approach that quantifies the relative suitability of multiple, potentially non-nested models based on a balance of model fit and the accuracy of estimates. Here, we examine three shortcomings of stepwise regression, subjective critical values, model uncertainty, and parameter estimation bias, which have been suggested to be avoided by applying information theory. We argue that, in certain circumstances, the IT approach may be sensitive to these issues as well. We point to areas where further testing and development could enhance the performance of IT methods and ultimately lead to robust inferences in behavioral ecology.     

Mapping of tritium emissions using absorption vapour samplers

Püspökszilágy Radioactive Waste Treatment and Disposal Facility (RWTDF) is a typical near-surface engineered repository designated to store low- and intermediate-level wastes from various institutes, research facilities and hospitals in Hungary. Two automatic combined ¹⁴C–tritium sampling units installed at the facility sample the air 2 m above surface. The one installed near the vaults detects tritium (T) activities two orders of magnitude higher than the far reference sampling unit. To localize the T emissions, 19 small absorption vapour samplers filled with silica gel were settled onto the ground surface. After the saturation of the silica gel, the water was recovered and its T concentration was measured with a low-background liquid scintillation counter. The absorption vapour samplers are cheap, simple and easy-to-use. We present the samplers and the T distribution map constructed from the data, which helps to localize the T emission.     

The LUCAS topsoil database and derived information on the regional variability of cropland topsoil properties in the European Union

Approximately 20,000 topsoil samples were collected in 25 European Union (EU) Member States (EU-27 except Bulgaria and Romania) with the aim to produce the first coherent pan-European physical and chemical topsoil database, which can serve as baseline information for an EU wide harmonized soil monitoring. The soil sampling was undertaken within the frame of the Land Use/Land Cover Area Frame Survey (LUCAS), a project to monitor changes in the management and character of the land surface of the EU. Soil samples have been analysed for basic soil properties, including particle size distribution, pH, organic carbon, carbonates, NPK, cation exchange capacity (CEC) and multispectral signatures. Preliminary studies show the outstanding potential of the dataset for enhancing the knowledge base on soils in the EU. The current paper provides an introduction to the LUCAS Topsoil 2009 project and provides an example of data applicability for cropland assessment by highlighting initial results for regional and national comparisons.     

Nutritional correlates and mate acquisition role of multiple sexual traits in male collared flycatchers

The information content of a sexual signal may predict its importance in a multiple signal system. Many studies have correlated sexual signal expression with the absolute levels of nutrient reserves. In contrast, the changes of nutrient reserves associated with signal expression are largely unknown in the wild due to technical limitations although they are important determinants of signal information content. We compared two visual and eight acoustic sexual traits in male collared flycatchers to see whether the nutritional correlates of expression predict the role of the signal in sexual selection. We used single point assays of plasma lipid metabolites to estimate short-term changes in nutritional state in relation to sexual trait expression during courtship. As a measure of sexual selection, we estimated the relationship with pairing latency after arrival in a 4-year dataset. Males which found a mate rapidly were characterized by large wing and forehead patches, but small song strophe complexity and small figure repertoire size. Traits more strongly related to pairing latency were also more closely related to changes in nutrient reserves. This indicates a link between signal role and information content. Small wing patches and, surprisingly, complex songs seemed to indicate poor phenotypic quality and were apparently disfavoured at mate acquisition in our population. Future studies of the information content of sexual traits, especially dynamic traits such as song, may benefit from the use of plasma metabolite profiles as non-invasive indicators of short-term changes in body condition.     

The relationship between maternal ornamentation and feeding rate is explained by intrinsic nestling quality

In altricial birds, parental feeding is essential, and its amount may depend on the quality of both parents. A relationship between parental quality and feeding rate is generally attributed to an active adjustment by parents in order to retain good quality mates or ensure high fitness through raising high-quality offspring. However, the behaviour and need of young may also change with parental quality, and this may affect parental behaviour. A further problem is that most studies have investigated post-hatching parental investment in relation to the secondary sexual signals of males, but not females. In a cross-fostering experiment, we examined the feeding rates of rearing parents in relation to the size and ornamentation of both original and rearing parents in collared flycatchers (Ficedula albicollis). Using this setup, we could examine whether the observed feeding patterns were the results of the decision of the parents based on their own and their partner’s traits or the constraints imposed by the behaviour or need of offspring. When correcting for clutch size and year, we found that feeding rate of both foster parents correlated with the wing patch size of the original female. This implies that original maternal quality had an offspring-mediated indirect effect on investment of foster parents, that is intrinsic nestling quality may constrain parental feeding decisions. This explanation should not be overlooked in future studies on preferential parental investment, and our results also point out that maternal ornaments deserve more attention in such studies.     

Biological treatment of chicken feather waste for improved biogas production

A two-stage system was developed which combines the biological degradation of keratin-rich waste with the production of biogas. Chicken feather waste was treated biologically with a recombinant Bacillus megaterium strain showing keratinase activity prior to biogas production. Chopped, autoclaved chicken feathers (4%, W/V) were completely degraded, resulting in a yellowish fermentation broth with a level of 0.51 mg/mL soluble proteins after 8 days of cultivation of the recombinant strain. During the subsequent anaerobic batch digestion experiments, methane production of 0.35 Nm³/kg dry feathers (i.e., 0.4 Nm³/kg volatile solids of feathers), corresponding to 80% of the theoretical value on proteins, was achieved from the feather hydrolyzates, independently of the pre-hydrolysis time period of 1, 2 or 8 days. Cultivation with a native keratinase producing strain, Bacillus licheniformis resulted in only 0.25 mg/mL soluble proteins in the feather hydrolyzate, which then was digested achieving a maximum accumulated methane production of 0.31 Nm³/kg dry feathers. Feather hydrolyzates treated with the wild type B. megaterium produced 0.21 Nm³ CH₄/kg dry feathers as maximum yield.     

Female ornamentation and territorial conflicts in collared flycatchers (Ficedula albicollis)

Female ornaments in species with conventional sex roles often indicate individual quality, but the evolutionary forces maintaining them are less clear. Sexual competition for breeding opportunities may represent an important role for female signals, especially in polygynous species, but there is little experimental evidence for this. The wing patch size (WPS) of female collared flycatchers indicates age and body condition and predicts social mating patterns. We challenged nest-building females with decoy females of varying WPS and found that the aggressive response of residents increased with decoy WPS, suggesting a role for this female ornament in territorial competition. Our results explain why female WPS predicts territorial distances when mated to a polygynous male and indicate that the role of WPS in female competitive interactions is similar to that in males of the same population.     

Determinants of male territorial behavior in a Hungarian collared flycatcher population: plumage traits of residents and challengers

In intrasexual conflicts, contestants can rely on relative or absolute size of status badges to mediate aggressive behavior. Most studies focus on the response of focal animals to variation in status badges of their competitors; few have simultaneously considered the traits of both participants under experimental conditions. By simulating territorial intrusions, we tested the importance of two sexual traits [forehead patch size (FPS) and wing patch size (WPS)] in territorial behavior of males in a Hungarian population of the collared flycatcher, Ficedula albicollis. We presented a stimulus male to an unpaired resident male to examine whether the characteristics of the territory owner or those of the challenger were associated with the latency of the first attack of the owner, which is a good predictor of the territorial behavior in general. WPS of the stimulus male was a significant determinant of the latency of the first attack, as males with a larger WPS elicited quicker attacks from the residents than males with a small WPS. From the residents’ perspective, age appeared to influence their territorial behavior, as yearlings had shorter attack latencies than older males. Additionally, latency could be considered an individual-specific attribute because it varied consistently among males, even when the WPS of the stimulus male was controlled, and it was associated with pairing success. Contrary to findings in a Swedish population, FPS seemed to be unimportant in male–male competition in our population, which suggests population differences in the role of the two plumage traits. Our results indicate that in a territorial conflict, the characteristics of both participants are important.     

Ecotoxicity and fungal deterioration of recycled polypropylene/wood composites: Effect of wood content and coupling

Recycled polypropylene (rPP) was recovered from an industrial shredder and composites were prepared with a relatively wide range of wood content and with two coupling agents, a maleated PP (MAPP) and a maleated ethylene-propylene-diene elastomer (MAEPDM). The mechanical properties of the composites showed that the coupling agents change structure only slightly, but interfacial adhesion quite drastically. The durability of the materials was determined by exposing them to a range of fungi and, ecotoxicity was studied on the aquatic organism Vibrio fischeri. The composites generally exhibit low acute toxicity, with values below the levels considered to have direct ecotoxic effect on aquatic ecosystems (<2 toxic units). Their toxicity to V. fischeri depended on the presence of the coupling agents with larger E₅₀ values in 24-h aqueous extracts from composites containing MAPP or MAEPDM in comparison to composites without any coupling agent. Evaluation of resistance against fungal colonization and deterioration proved that wood facilitates fungal colonization. Fungi caused slight mass loss (below 3%) but it was not correlated with substantial deterioration in material properties. MAPP seems to be beneficial in the retention of mechanical properties during fungal attack. rPP/wood composites can be considered non-ecotoxic and quite durable, but the influence of wood content on resistance to fungal attack must be taken into account for materials intended for applications requiring long-term outdoor exposure.