Eastern European countries are considered a stronghold for the continent's farmland biodiversity. The abundance of farmland birds is one important element of this biodiversity. At the end of the 20th ...century, member states of the European Union (EU) experienced serious population declines of farmland birds due to agricultural intensification, which was not observed in the Eastern European nonmember states. In 2004, 10 mostly Eastern European countries acceded to the EU. It is thus important to ask whether this historical step resulted in changes of agricultural production and, in turn, in farmland bird populations. Here we used annual crop yields and monitoring data on farmland bird abundance in an Eastern European new EU‐member state and showed that agricultural production intensified and farmland bird populations declined steeply after country's EU accession. These results indicate that entering EU's Common Agricultural Policy caused significant deterioration of farmland biodiversity in a once biodiversity‐rich region.
•Bird communities were surveyed in stands of non-native and native trees.•Bird species richness increased with increasing vegetation heterogeneity.•Non-native tree stands were impoverished in habitat ...specialists and canopy foragers.•The gradient broadleaved-coniferous stands determined bird community composition.•Tree origin is of less importance for birds compared to basic stand characteristics.
Forest management affects stands’ vegetation structure, which influences bird communities. Since the effects of forest practices are usually more pronounced if the exotic tree species are planted, we surveyed bird communities and mapped the vegetation structure in stands of non-native broad-leaved and coniferous trees, black locust and black pine, in a central European country, the Czech Republic. By means of spatial analysis – generalized least squares models – we investigated whether the positive relationship between bird species richness in various ecological groups and vegetation heterogeneity is weakened by an assumed negative effect of the exotic tree origin. Further, we tested whether the bird community composition is more impacted by tree origin (native and non-native) than forest type (coniferous and broad-leaved) using multivariate direct gradient redundancy analyses. We found that total bird species richness, species richness of habitat specialists, ground foragers and foliage gleaners significantly increased with increasing vegetation heterogeneity after taking tree origin into account. Since there was higher vegetation heterogeneity in non-native tree stands, we suggest that the potential benefits of this higher heterogeneity were suppressed by some other (unmeasured) characteristics (e.g. limited food supply) of these stands, which might also be the reason for lower richness of habitat specialists and canopy foragers. The most important gradient in the bird community composition was from broad-leaved to coniferous stands irrespective of tree origin. The effect of tree origin was expressed as the secondary gradient, albeit still significant. It seems that the birds’ adaptations to different leaf morphology play more important role in structuring bird communities than the influence of tree origin. Our results indicate that the forest management should focus on the increase of the vegetation heterogeneity in native tree stands to maximize total bird species richness, and on avoiding establishment of non-native tree plantations to prevent loss of habitat specialist birds.
Ecological specialization provides information about adaptations of species to their environment. However, identification of traits representing the relevant dimensions of ecological space remains ...challenging. Here we endeavoured to explain how complex habitat specializations relate to various ecological traits of European birds. We employed phylogenetic generalized least squares and information theoretic approach statistically controlling for differences in geographic range size among species. Habitat specialists had narrower diet niche, wider climatic niche, higher wing length/tail length ratio and migrated on shorter distances than habitat generalists. Our results support an expected positive link between habitat and diet niche breadth estimates, however a negative relationship between habitat and climate niche breadths is surprising. It implies that habitat specialists occur mostly in spatially restricted environments with high climatic variability such as mountain areas. This, however, complicates our understanding of predicted impacts of climatic changes on avian geographical distributions. Our results further corroborate that habitat specialization reflects occupation of morphological space, when specialists depend more on manoeuvrability of the flight and are thus more closely associated to open habitats than habitat generalists. Finally, our results indicate that long distance movements might hamper narrow habitat preferences. In conclusion, we have shown that species' distributions across habitats are informative about their positions along other axes of ecological space and can explain states of particular functional traits, however, our results also reveal that the links between different niche estimates cannot be always straightforwardly predicted.
Interspecific competition is assumed to play an important role in the ecological differentiation of species and speciation. However, empirical evidence for competition's role in speciation remains ...surprisingly scarce. Here, we studied the role of interspecific competition in the ecological differentiation and speciation of two closely related songbird species, the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (Luscinia luscinia). Both species are insectivorous and ecologically very similar. They hybridize in a secondary contact zone, which is a mosaic of sites where both species co‐occur (syntopy) and sites where only one species is present (allotopy). We analysed fine‐scale habitat data for both species in both syntopic and allotopic sites and looked for associations between habitat use and bill morphology, which have been previously shown to be more divergent in sympatry than in allopatry. We found that the two nightingale species differ in habitat use in allotopic sites, where L. megarhynchos occurred in drier habitats and at slightly higher elevations, but not in syntopic sites. Birds from allotopic sites also showed higher interspecific divergence in relative bill size compared to birds from syntopic sites. Finally, we found an association between bill morphology and elevation. Our results are consistent with the view that interspecific competition in nightingales has resulted in partial habitat segregation in sympatry and that the habitat‐specific food supply has in turn very likely led to bill size divergence. Such ecological divergence may enhance prezygotic as well as extrinsic postzygotic isolation and thus accelerate the completion of the speciation process.
Ecological character displacement is a process of phenotypic differentiation of sympatric populations caused by interspecific competition. Such differentiation could facilitate speciation by ...enhancing reproductive isolation between incipient species, although empirical evidence for it at early stages of divergence when gene flow still occurs between the species is relatively scarce. Here we studied patterns of morphological variation in sympatric and allopatric populations of two hybridizing species of birds, the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (L. luscinia).
We conducted principal component (PC) analysis of morphological traits and found that nightingale species converged in overall body size (PC1) and diverged in relative bill size (PC3) in sympatry. Closer analysis of morphological variation along geographical gradients revealed that the convergence in body size can be attributed largely to increasing body size with increasing latitude, a phenomenon known as Bergmann's rule. In contrast, interspecific interactions contributed significantly to the observed divergence in relative bill size, even after controlling for the effects of geographical gradients. We suggest that the divergence in bill size most likely reflects segregation of feeding niches between the species in sympatry.
Our results suggest that interspecific competition for food resources can drive species divergence even in the face of ongoing hybridization. Such divergence may enhance reproductive isolation between the species and thus contribute to speciation.
In migratory birds, increasing temperatures have been linked to earlier arrival to breeding sites, enabling an earlier start of breeding and leading to changes in abundance. Long-term population ...trends may thus reflect a species capacity to respond to climate change. However, when a species is more abundant, it is also more easily detectable by observers, leading to an earlier detection of its arrival. Therefore, investigations of the drivers of shifts in apparent arrival dates to breeding sites and population trends remain challenging. Here, we formulate predictions aiming to disentangle the different drivers, analysing spring arrival dates and population changes of 52 migratory birds in a Central European country, the Czech Republic, from 1994 to 2017. If shifts in arrival dates are driven by increasing spring temperatures, migrants should arrive earlier in a warmer year and their abundance should increase in the subsequent year due to earlier breeding. If earlier migrant arrival results from their increased detectability caused by higher abundance, then migrants should arrive earlier in the same years when their abundance is high. We found clear support for the former prediction, indicating that climate change drives the earlier arrival of migrants irrespective of changes in their detectability. Moreover, species advancing their arrival to a greater degree had more positive population trends, and responses to rising spring temperatures in the Czech Republic became weaker with increasing migration distance. Therefore, climate change drives population trends of migratory species according to their capacity to adjust their arrival date to variations in spring temperatures.
It has been proposed that divergence in the gut microbiota composition between incipient species could contribute to their reproductive isolation. Nevertheless, empirical evidence for the role of gut ...microbiota in speciation is scarce. Moreover, it is still largely unknown to what extent closely related species in the early stages of speciation differ in their gut microbiota composition, especially in non-mammalian taxa, and which factors drive the divergence. Here we analysed the gut microbiota in two closely related passerine species, the common nightingale (Luscinia megarhynchos) and the thrush nightingale (Luscinia luscinia). The ranges of these two species overlap in a secondary contact zone, where both species occasionally hybridize and where interspecific competition has resulted in habitat use differentiation.
We analysed the gut microbiota from the proximal, middle and distal part of the small intestine in both sympatric and allopatric populations of the two nightingale species using sequencing of bacterial 16S rRNA. We found small but significant differences in the microbiota composition among the three gut sections. However, the gut microbiota composition in the two nightingale species did not differ significantly between either sympatric or allopatric populations. Most of the observed variation in the gut microbiota composition was explained by inter-individual differences.
To our knowledge, this is the first attempt to assess the potential role of the gut microbiota in bird speciation. Our results suggest that neither habitat use, nor geographical distance, nor species identity have strong influence on the nightingale gut microbiota composition. This suggests that changes in the gut microbiota composition are unlikely to contribute to reproductive isolation in these passerine birds.
Recent studies show differences in population trends between groups of species occupying different habitats. In Czech birds, as well as in many other European countries, populations of forest species ...have increased, whereas populations of farmland species have declined. The aim of our study was to test whether population trends of particular species were related to finer bird-habitat associations within farmland and forest birds. We assessed bird-habitat associations using canonical correspondence analysis based on data from a 400 km long transect across the Czech Republic. We calculated population trends of 62 bird species using log-linear models based on data from a large-scale annual monitoring scheme, which covers the time series from 1982 to 2005. Within forest birds, species with a closer association with lowland broad-leaved forest have had more positive population trends, whereas species with a closer association with montane and coniferous forest revealed more negative population trends. We attribute these opposite trends to the gradual replacement of coniferous forests by deciduous ones, which took place in the Czech Republic during recent decades. Our analyses revealed a hump-shaped relationship within farmland birds, species most closely associated with farmland habitat revealing the most negative trends, whereas species with intermediate association to farmland habitat showed the most positive population trends. Such a pattern can be explained by the abandonment of previously cultivated areas followed by the spread of unmanaged meadows and scrubland. Changes in quantity or quality of preferred habitats may thus represent major drivers of observed bird population changes.
There have been several attempts to build a unified framework for macroecological patterns. However, these have mostly been based either on questionable assumptions or have had to be parameterized to ...obtain realistic predictions. Here, we propose a new model explicitly considering patterns of aggregated species distributions on multiple spatial scales, the property which lies behind all spatial macroecological patterns, using the idea we term 'generalized fractals'. Species' spatial distributions were modelled by a random hierarchical process in which the original 'habitat' patches were randomly replaced by sets of smaller patches nested within them, and the statistical properties of modelled species assemblages were compared with macroecological patterns in observed bird data. Without parameterization based on observed patterns, this simple model predicts realistic patterns of species abundance, distribution and diversity, including fractal-like spatial distributions, the frequency distribution of species occupancies/abundances and the species-area relationship. Although observed macroecological patterns may differ in some quantitative properties, our concept of random hierarchical aggregation can be considered as an appropriate null model of fundamental macroecological patterns which can potentially be modified to accommodate ecologically important variables.
Climate change is one of the most important recent forces modulating the structure of ecological communities worldwide. Although a number of studies have documented climatically induced altitudinal ...range shifts, with species move upwards with increasing temperature and tracking their climatic optima, an examination of interspecific variability in such altitudinal shifts remains unexplored. Using a unique dataset on the altitudinal distribution of birds in a central European mountain range, collected with constant effort and methodology over more than 20 years, we examined the effects of particular species' ecological traits on interspecific variability in altitudinal range shifts. We predicted that shifts would be greater in species with narrower European climatic niches, breeding in open habitats, feeding on insects and originally breeding at lower altitudes. Patterns of the shifts differed within the time period studied. In the first decade, no climate change was observed and species did not show any direction in their altitudinal shifts. In the second decade, local spring temperatures increased and species moved to higher altitudes. These altitudinal shifts were related to species' habitat preferences, with open habitat species shifting to higher altitudes than forest species. The effect of other predictors was relatively small. The habitat effects imply either stronger self-regulation of the forest microclimate compared to open habitats, with forest species less forced to move upwards, or a delayed shift in the alpine timberline due to the slow growth of trees. In the latter case, forest species would face unfavourable climatic conditions and at the same time be constrained by the limited distribution of their habitat. Our study shows that species' ecology can considerably alter the actual outcome of the impacts of ongoing climate change in mountain areas.
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