Video recordings are commonly used to study the types, amount, and size of food items provided to nestling birds. However, the accuracy and repeatability of estimates of the size of food items from video recordings has not been examined. We assessed three aspects of the reliability of measuring prey size from video recordings of Great Tits (Parus major) provisioning nestlings. To test the accuracy of measurements of prey size (length and width) used to determine prey volume, we molded artificial plasticine caterpillars and compared their size and volume as determined using measurements of length and width on screenshots of video recordings (using the vertical diameter of nest‐box entrance holes as a size reference) to their actual size and volume. We also examined within‐ and among‐observer repeatability of measurements of the size and volume of actual prey items delivered to nestlings by adult Great Tits. We found that observers were able to accurately measure prey size and determine volume, with high agreement between the actual size and volume of plasticine caterpillars and the size and volume as determined from measurements made on screenshots from video recordings (rICC = 0.99). In addition, within‐ and among‐observer repeatability were also high (rICC = 0.98 and 0.93, respectively). Overall, our results suggest that the size of prey items delivered to nestlings by adults in video recordings can be accurately measured and those measurements, in turn, can be used to accurately determine the volume of those insect prey.

The composition of atmospheric particulate matter, including particle-bound polyaromatic hydrocarbons, generally shows a clear seasonal pattern which is reflected in its ecotoxicity as well. This study aimed at characterising seasonal differences in the ecotoxicity of rural aerosol samples applying both luminescent bacteria and higher plants as test organisms. Higher plant phytotoxicity was assessed by the Sinapis alba root growth inhibition test and the Vegetative Vigour Test. Different bioassays and end-points showed different sensitivity: while the Sinapis alba assay showed no toxic effect, luminescent bacteria proved an excellent screening tool, detecting no toxicity in the summer sample and the highest inhibition in the winter sample, with EC20 = 9.87%. In the case of Vegetative Vigour Test, parallel application of different end-points revealed that atmospheric particulate matter might have a Janus-faced effect: stimulation of photosynthetic pigments due to nutrient content and growth impairment due to toxic components.

Food web research needs to be predictive in order to support decisions system-based conservation. In order to increase predictability and applicability, complexity needs to be managed in such a way that we are able to provide simple and clear results. One question emerging frequently is whether certain perturbations (environmental effects or human impact) have positive or negative effects on natural ecosystems or their particular components. Yet, most of food web studies do not consider the sign of effects. Here, we study 6 versions of the Kelian River (Borneo) food web, representing six study sites along the river. For each network, we study the signs of the effects of a perturbed trophic group i on each other j groups. We compare the outcome of the relatively complicated dynamical simulation model and the relatively simple loop analysis model. We compare these results for the 6 sites and also the 14 trophic groups. Finally, we see if sign-agreement and sign-determinacy depend on certain structural features (node centrality, interaction strength). We found major differences between different modelling scenarios, with herbivore-detritivore fish behaving in the most consistent, while algae and particulate organic matter behaving in the least consistent way. We also found higher agreement between the signs of predictions for trophic groups at higher trophic levels in sites 1–3 and at lower trophic levels in site 4–6. This means that the behaviour of predators in the more natural sections of the river and that of producers at the more human-impacted sections are more consistently predicted. This suggests to be more careful with the less consistently predictable trophic groups in conservation management.

No abstract

Freshwater ecosystems are under multiple stressors and it is crucial to find methods to better describe, manage, and sustain aquatic ecosystems. Ecosystem modelling has become an important tool in integrating trophic relationships into food webs, assessing important nodes using network analysis, and making predictions via simulations. Fortunately, several modelling techniques exist, but the question is which approach is relevant and applicable when? In this study, we compare three modelling frameworks (Ecopath, Loop Analysis in R, STELLA software) using a case study of a small aquatic network (8 nodes). The choice of framework depends on the research question and data availability. We approach this topic from a methodological aspect by describing the data requirements and by comparing the applicability and limitations of each modelling approach. Each modelling framework has its specific focus, but some functionalities and outcomes can be compared. The predictions of Loop Analysis as compared to Ecopath’s Mixed Trophic Impact plot are in good agreement at the top and bottom trophic levels, but the middle trophic levels are less similar. This suggests that further comparisons are needed of networks of varying resolution and size. Generally, when data are limiting, Loop Analysis can provide qualitative predictions, while the other two methods provide quantitative results, yet rely on more data.