Jan Marek Kaczmarek

Amphibians are among the most endangered groups of vertebrates worldwide; therefore, effective population monitoring is crucial for understanding the factors driving these unfavourable trends. In this study, we evaluated the effectiveness of fully automated passive acoustic monitoring in estimating the distribution and population size of the European green toad (Bufotes viridis)—an anuran species in which males vocalize intensively during the breeding season. We conducted visual counts with human observers, recorded the soundscape using autonomous sound recorders, applied automatic call detection, and calculated soundscape complexity using acoustic indices adjusted to the frequency range of European green toad vocalizations. Our algorithm generated a calling intensity index, which detected 36% of calls with 96% precision. The calling intensity index showed a significant correlation with the number of calls detected manually (r = 0.727). Additionally, we found moderate but significant correlations between acoustic indices (Acoustic Complexity Index and Bioacoustic Index) and both the manually and automatically detected call counts. The calling intensity index and acoustic indices did not significantly correlate with the number of males counted by human observer, but they reflected the phenological changes in species’ reproductive activity. Our study demonstrates that passive acoustic monitoring enables the assessment of presence and distribution of the European green toad, as well as daily and seasonal patterns in calling activity. However, due to the specific biology and ecology of the species, calling intensity alone is insufficient for accurately estimating male abundance.

The efficiency of aposematic colouration of prey is based on the innate bias or facilitation of avoidance learning of predators. In many toxic bufonids, larvae are uniformly black, which is considered a warning signal. We compared fish predation on normal (black) and ‘transient albino’ (greyish) common toad Bufo bufo tadpoles that did not differ in toxicity or activity. In a two-stage experiment, each fish was presented with tadpoles of one colour in the first trial and the other colour in a subsequent trial. While tadpoles sampled by fish were typically not ingested, some died from injuries. The attack rate did not differ between tadpole phenotypes nor trials, irrespective of which phenotype was the first exposed to the fish. However, during the second trial, the sampled tadpoles, independent of colouration, were mouthed by fish for shorter periods and tadpole mortality decreased. The duration of mouthing also declined with an increasing number of attacks during subsequent trials. We conclude that in single-species prey populations, black tadpole colouration is not a warning signal as it does not accelerate predator learning about prey unprofitability. Our results indicate that with growing experience, predators sample potentially toxic prey more cautiously. This may explain why natural selection does not eliminate aposematic morphs even if predators continuously sample conspicuous prey.

Some new cases of anomalies in wild Bufotes viridis from Western Poland are presented together with a discussion of their potential causes and a comparison with similar cases from the literature. The anomalies in question are color aberrations (pre- and post-metamorphic) and developmental pathologies (pre–metamorphic). The color anomalies include an ochre patch in a juvenile, leucism and albinism in both tadpoles and juvenile individuals. Developmental pathologies described in this paper include gigantism, edema, curvature of tail, and asymmetric bodies.

Associational effects such as “associational resistance” or “aposematic commensalism” may facilitate the subsequent evolution of mimicry. However, such effects are usually expected to be contingent on a spatiotemporal co-occurrence of defended and undefended species. Associational resistance may emerge in communities of larval anurans where tadpoles of different species share a generalized morphology but vary in chemical defences. In Europe, the marsh frog Pelophylax ridibundus reproduces in fish-containing habitats that earlier in the season can be used by the common toad Bufo bufo, a species with chemically defended larvae. In a mesocosm experiment, we investigated if the associational protection against predation provided by the defended species could be strong enough to last even after the defended prey metamorphose and leave the system. We expected that the higher abundances (both absolute and relative) of chemically defended B. bufo in the tadpole assemblage exposed to predation by the common carp Cyprinus carpio prior to the occurrence of P. ridibundus tadpoles would be related to the increased later survival of P. ridibundus in the presence of the same fish. The tadpoles of P. ridibundus were highly vulnerable to predation during a 2-week cohabitation with fish. We found no relationship between the survival of P. ridibundus and the absolute density or relative proportion of B. bufo. Although associational effects may be ecologically relevant in aquatic animal communities, they apparently require the co-presence of the defended prey in fish-tadpole interactions.

Introduction: Despite the growing number of studies describing digit ratio patterns in tetrapods, knowledge concerning certain basic issues is still scarce. In lower vertebrates such as tailless amphibians (Anura), the numbering of individual fingers on the forelimbs and their homology with the fingers of other vertebrates pose an unsolved problem. Based on reviewed data on anuran limb development, we argue that the correct finger numbering scheme should be based on the assumption that the first finger, not the fifth finger, was reduced on the forelimbs. We analyzed the digit ratio in the common toad (Bufo bufo, Bufonidae), a species characterized by well-developed sexual dimorphism whereby females are larger than males, using both numbering schemes present in the literature.Results: We found that the digit ratio on hindlimbs differed significantly between the sexes only in the cases of left 2D:3D, with lower digit ratios in females, and of left 3D:4D, with lower digit ratios in males. We found that sex was the only significant variable for forelimbs, differentiating 2D:3D on the left forelimb, with lower digit ratios in females; 2D:4D on the right forelimb, with lower digit ratios in males; and 3D:4D on both forelimbs, with lower digit ratios in males. These results relate to variant II reflecting the hypothesis that the first digit was reduced during phylogenesis. There was no relationship between the body size (SVL) of individuals and any digit ratio, excluding 2D:4D on the right forelimbs in models with age variables. Additionally, for a subset of data where individual age was known, the models indicated that age was linked to significant differences in 2D:4D and 3D:4D on the left hindlimbs, while age, SVL, and sex influenced 2D:4D on the right forelimbs.Conclusion: We emphasize the importance of the problem of the correct numbering of forelimb digits in Anura and, under the assumption that it was the fifth digit that was reduced, argue that earlier results on digit ratio in this group should be interpreted with caution. The detected relationship between digit ratio and age in amphibians expands our knowledge, indicating that the age of individuals should be included in future digit ratio studies. This relationship may also apply to studies using digit ratio as a noninvasive indicator of endocrine disruption in amphibians.

Many chemically defended aposematic species are characterized by relatively low toxin levels, which enables predators to include them in their diets under certain circumstances. Knowledge of the conditions governing the survival of such prey animals—especially in the context of the co‐occurrence of similar but undefended prey, which may result in mimicry‐like interactions—is crucial for understanding the initial evolution of aposematism. In a one‐month outdoor experiment using fish (the common carp Cyprinus carpio) as predators, we examined the survival of moderately defended aposematic tadpole prey (the European common toad Bufo bufo) with varying absolute densities in single‐species prey systems or varying relative densities in two‐species prey systems containing morphologically similar but undefended prey (the European common frog Rana temporaria). The density effects were investigated in conjunction with the hunger levels of the predator, which were manipulated by means of the addition of alternative (nontadpole) food. The survival of the B. bufo tadpoles was promoted by increasing their absolute density in the single‐species prey systems, increasing their relative density in the two‐species prey systems, and providing ample alternative food for the predator. Hungry predators eliminated all R. temporaria individuals regardless of their proportion in the prey community; in treatments with ample alternative food, high relative B. bufo density supported R. temporaria survival. The results demonstrated that moderately defended prey did benefit from high population densities (both absolute and relative), even under long‐term predation pressure. However, the physiological state of the predator was a crucial factor in the survival of moderately defended prey. While the availability of alternative prey in general should promote the spread and maintenance of aposematism, the results indicated that the resemblance between the co‐occurring defended and undefended prey may impose mortality costs on the defended model species, even in the absence of actual mimicry.

The expansion of energy crops such as miscanthus Miscanthus x giganteus has changed the habitat of European farmland birds. However, most studies on the subject are based in Western Europe. We surveyed the avian community in a sample bioenergy landscape in Poland to investigate the pattern of use of the crop by birds in Central Europe. During a year-long survey, 80 species were noted, with 32 sighted in miscanthus. The number of bird sightings was negatively correlated with the area covered by miscanthus in study plots. In contrast to results from Western Europe, most woodland-generalist bird species tended to avoid miscanthus. Farmland species (e.g. the corn bunting Miliaria calandra; the tree sparrow Passer montanus; the starling Sturnus vulgaris; the yellowhammer Emberiza citrinella) were less frequently sighted in the crop than in other habitats. Only a few species were sighted more often in miscanthus than in other habitats, e.g. the marsh warbler Acrocephalus palustris; the reed bunting Emberiza schoeniclus; the whinchat Saxicola rubetra. The potential impact of expanded miscanthus cropping on bird communities in Central and Eastern Europe may diverge from predictions derived from studies based in Western Europe due to differing habitat preferences and bird densities between the regions. For a majority of farmland species, the crop may constitute only a suboptimal, supplementary habitat, with only a few birds potentially adapting to the exploitation of bioenergy plantations.

In Batesian mimicry, a species lacking defences against predators benefits from mimicking the aposematic signal of a defended species, while the model may incur the costs of reduced defensive efficacy. Similar reciprocal indirect effects may emerge even when the signal is not mimicked; termed associational effects, such interactions are well known in plants sharing herbivores but have received little attention in animal studies. We investigated associational interactions in a system where unequally defended prey (chemically defended Bufo bufo and undefended Rana temporaria tadpoles), sharing general morphology but not an aposematic signal, were exposed to predation by the carp Cyprinus carpio along a gradient of relative prey abundance. In the absence of fish, the assemblage composition had no effect on the survival of Rana, while that of Bufo decreased with increasing abundance of Rana. Fish reduced the survival of tadpoles from both species. However, increased relative abundance of Bufo in the community led to enhanced survival in both Bufo and Rana. Increasing relative proportions of heterospecifics reduced metamorph mass only in Bufo, indicating greater sensitivity to interspecific competition compared to Rana; the effect was reduced in the presence of fish. Our results show that undefended non-mimetic prey enjoy reduced predation with increasing relative abundance of chemically defended prey, which in turn suffer greater mortality with an increasing proportion of the undefended species. Associational resistance/susceptibility, driven by current assemblage composition, not by selection for resemblance, can shape the dynamics of mixed communities of defended and undefended prey in the absence of mimicry.

The development of cellulosic bioethanol and other second-generation (2G) biofuels has gone through various phases during the last few years. The prospect of technological breakthroughs stimulates extensive research on turning cellulose into bioethanol or biodiesel. Agricultural or forestry residues and some plants, referred to as ‘lignocellulosic energy crops’ or ‘second generation (2G) energy crops’ can provide feedstock for new types of biofuels. The impact of lignocellulosic energy crops on farmland birds has been relatively well studied. This is surprising since the technology of converting these crops into fuel has so recently been developed. However, we believe that some questions regarding potential bird use of 2G energy crops have still not been answered. In Europe, most research has been carried out in agricultural areas of Western Europe. However, Central & Eastern Europe host the highest densities of farmland birds and, in general, the highest biodiversity. There is huge potential for 2G energy cropping due to large areas of mainly marginal land. We have outlined possible discrepancies between the results obtained from W. Europe and potential relationships between birds and 2G energy crops in Central Europe.