Variations in Avian Species and Functional Diversity in Different Habitat Types in a Vulnerable Savannah Ecosystem in Ghana

Most research on avian functional diversity in the tropics is focused on forest and agroecosystems, leaving a gap in knowledge about the effects of habitat types on functional diversity in savannah landscapes. Savanna ecosystems are fragile and are under threat of anthropogenic destruction, particularly in developing Sub-Saharan Africa and could be eliminated in the face of the ever-increasing human population exacerbated by the changing climate. This study investigated the influence of the three major habitat types (grassland, riparian forest, woodland) on bird species and functional diversity in the Mole National Park (MNP) in Ghana. We used the line transect method to survey birds along 39 transects, each 1 km in length, and collected data on environmental variables along the same transects. Data from these surveys was used to estimate species and functional diversity indicators. We found significant variations in species and functional diversity measures between the three habitat types in the MNP. These variations were significantly influenced by species abundance and environmental covariates. Diversity measures were particularly higher in the riparian forest habitats compared to the woodland and grassland, with the latter being the least diverse habitat both functionally and species wise. The results of this study suggest that the avifauna assemblages in MNP are largely influenced by the riparian forest and are important for ecosystem function and stability. We recommend management efforts to intensify the protection of such vital habitats of the Mole National Park from illegal human activities, especially the rising removal and export of rosewoods (Dalbergia nigra) around the park. Further research on the avian community composition and structure in the MNP is recommended.

Stream pollution causes aggregation of wintering insectivorous birds through increased aquatic emergence

Cross-boundary prey subsidies can propagate the effects of human impacts from streams to terrestrial ecosystems, but effects during winter are poorly known. Here I focused on this season and investigated the effects of pollution due to a sewage treatment plant (STP) on aquatic insect emergence and wintering insectivorous birds in a Swiss stream. At sites downstream of the STP, a combination of nutrient (phosphorus), organic (biochemical oxygen demand), and thermal pollution led to higher aquatic emergence compared to upstream sites (6× higher). In turn, the higher emergence led to a strong aggregational response by wintering insectivorous birds (8× higher linear densities compared to upstream sites). Polluted sites also had a different bird assemblage, which included rare wintering species that forage largely on aerial insects. A comparison between the polluted (downstream) sites and a nearby unpolluted stream produced similar differences. The magnitude and consistency of the effects illustrate how strongly stream alterations can propagate to birds through changes in aquatic emergence. Moreover, the results provide insights into the responses of linked stream-terrestrial food webs to other environmental issues that cause warming and/or pollution, including urbanization and climate change.

Quantifying the contribution of riparian soils to the provision of ecosystem services

Riparian areas, the interface between land and freshwater ecosystems, are considered to play a pivotal role in the supply of regulating, provisioning, cultural and supporting services. Most previous studies, however, have tended to focus on intensive agricultural systems and only on a single ecosystem function. Here, we present the first study which attempts to assess a wide range of ecological processes involved in the provision of the ecosystem service of water quality regulation across a diverse range of riparian typologies. Specifically, we focus on 1) evaluating the spatial variation in riparian soils properties with respect to distance with the river and soil depth in contrasting habitat types; 2) gaining further insights into the underlying mechanisms of pollutant removal (i.e. pesticide sorption/degradation, denitrification, etc.) by riparian soils; and 3) quantify and evaluate how riparian vegetation across different habitat types contribute to the provision of watercourse shading. All the habitats were present within a single large catchment and included: (i) improved grassland, (ii) unimproved (semi-natural) grassland, (iii) broadleaf woodland, (iv) coniferous woodland, and (iv) mountain, heath and bog. Taking all the data together, the riparian soils could be statistically separated by habitat type, providing evidence that they deliver ecosystem services to differing extents. Overall, however, our findings seem to contradict the general assumption that soils in riparian area are different from neighbouring (non-riparian) areas and that they possess extra functionality in terms of ecosystem service provision. Watercourse shading was highly habitat specific and was maximal in forests (ca. 52% shade cover) in comparison to the other habitat types (7-17%). Our data suggest that the functioning of riparian areas in less intensive agricultural areas, such as those studied here, may be broadly predicted from the surrounding land use, however, further research is required to critically test this across a wider range of ecosystems.