Biologichni Studii / Studia Biologica

Background. The species and taxonomic diversity of biotic communities are directly related to changes in the environment. The more diverse an ecosystem is in terms of its biotic and abiotic components, the more complex are its functional structure and the relationships between species and habitats. The restoration of species and taxonomic diversity in ecosystems affected by anthropogenic impacts of varying intensity takes place under different scenarios. This is illustrated by the analysis of the structural and functional characteristics of bird communities in montane and lowland river ecosystems in Zakarpattia. The key component of these bird communities is the ecological group of wetland species, which was analysed by the number and abundance of species, and changes of species composition in the past 100 years.
Materials and Methods. The bird communities of the middle course of the montane Uzh River and of the lowland Botar River were analysed in 1994–2002 and 2016–2020, and in 2014–2015, respectively, in the breeding season (April–June). Birds were counted during route surveys. The width of the survey stripes was 100 m (50 m on both sides of the route). A 13 km-long section of the middle course of the Uzh River was exami­ned in two different habitats: 7 km in natural and 6 km in urbanised areas. Additionally, a 17 km-long lowland section of the Botar River was studied, which included channelised parts and riverbed ponds as well as 6 km of the preserved natural riverbed and floodplain. In total, a 308 km-long route was surveyed. For statistical analysis of data obtained during the study of birds on the Uzh and Botar Rivers, Pearson’s chi-squa­red test was used. Calculations were performed using Microsoft Excel.
Results and Discussion. During the breeding season, 81 bird species (of 65 gene­ra, 35 families, and 14 orders) were recorded in the valley of the middle Uzh River, and 81 species (of 58 genera, 33 families, and 15 orders) in the lowland course of the Botar River. The structural and functional characteristics of the bird communities of both rivers are reflected in the proportion, population density, and presence status (resident or migratory) of each species, in the combination of ecological groups, and in the trophic and spatial structure of the community. All of these parameters depend on the diversity of habitats in these river ecosystems and characterise the carrying capacity of the environment.
In terms of ecological groups, the bird community of the middle Uzh is dominated by forest species, both in species richness (45.7 %) and density of individuals per km² (52.6 %). Wetland (17.3 %) and forest-steppe species (18.5 %) are also well represented. Species of anthropogenic landscapes, in addition to forest species, also have a relatively high population density (21.7 %). Within the lowland part of the Botar River, the bird community is dominated by forest and wetland species (32 % and 29.6 %, respectively), but the highest population density is characteristic of forest-steppe species (32.6 %), followed by forest and wetland species (27 % and 18.6 %, respectively). Birds of anthropogenic landscapes are the least represented by both species richness (6.2 %) and population density (7.6 %). Despite the dramatic transformation of the Botar River in the twentieth century due to the creation of an irrigation system, wetland bird species, compared to the Uzh River, have a significant proportion by both their number and density. This is due to the specific structural features of habitats and ecological niches of the montane and lowland river ecosystems. The difference in living conditions between the mountain river and the lowland river is significant for wetland bird species (χ² = 5,2; p <0.05 ).
With regard to spatial distribution, the dominant group in the bird community of the middle Uzh is the hollow-nesting species (26.5%), followed by tree-nesting and ground-nesting species (23.5 % each). Hollow-nesting species also predominate by population density (32.1 %), whereas urban-nesting birds are sub-dominants (21.8 %). In contrast, the bird community of the lowland Botar River is dominated by ground-nesting species (35.3 %), although the proportion of tree- (23.5% ) and shrub-nesting (19.1 %) species is also relatively high. In terms of population density, the dominant species are hollow-nesting (34.1 %), whereas the sub-dominants are ground-nesting (31.4 %).
In terms of trophic specialisation, the bird community of the Uzh River is dominated by carnivores both by species richness (65.4 %) and population density (48.4 %). In the bird community of the Botar River, however, carnivores notably dominate by species composition (70.3 %), but omnivores dominate by population density (50.6 %). Ground-nesting carnivores and omnivores make up a significant proportion of wetland bird species, the functional role of which is clearly noticeable in this community. The bird community in the middle Uzh River is dominated by forest-dwelling hollow-nesting carnivores, which inhabit the strip of riverine willow and poplar forests.
Conclusion. The analysis of the structural and functional characteristics of bird communities in the montane and lowland river ecosystems of Zakarpattia, which in the twentieth century underwent anthropogenic transformation to varying degrees, illustrates the main differences between these ecosystems. Anthropogenic impacts associated with the drainage and loss of much of the natural floodplain of both rivers led to a decline in the species diversity of wetland birds. However, the compensation for the loss of bird diversity of the two rivers occurred under different scenarios. These differences lie in habitat conditions, carrying capacity, and the previous history of species diversity.