Urbanization affects frog communities at multiple scales in a rapidly developing African city
Donnavan J.D. Kruger, Andrew J. Hamer, Louis H. Du Preez
Journal: Urban Ecosystems
Figure 1. Distribution maps of each of the seven anuran species detected over a four-season survey. Green circles are representative of the relative count data of each pond for Amietophrynus gutturalis (Ag), A. rangeri (Ar), Cacosternum boettgeri (Cb), Kassina senegalensis (Ks), Strongylopus fasciatus (Sf), Xenopus laevis (Xl) and Amietia quecketti (Aq). Green circles in last map (Po) show the locations of each of the surveyed ponds in order to compare the presence of the species distribution. Potchefstroom area excludes agricultural landscape. Black patches on the aerial image show areas of field that were burned due to accidental fires or firebreaks.
Abstract
Urbanization is worldwide among the biggest threats to amphibian populations. However, hardly any studies on the effects thereof in developing countries. Amphibian distribution and community assemblages are not well understood in aquatic and terrestrial habitats that are rapidly changing due to human modification. We conducted four surveys using three detection methods for both anuran larvae and predatory fish in 61 ponds in and around the city of Potchefstroom, South Africa. Tadpoles of eight anuran species and seven fish species were detected during the field surveys. The common river frog (Amietia quecketti) was the most abundant species, occurring in 39% of the sites, whereas the bubbling kassina (Kassina senegalensis) was detected in only one pond. The remaining six species were detected in 6.6–26.2% of the sites. Predatory fish were detected in 64% of the wetlands with mosquitofish (Gambusia affinis) and the banded tilapia (Tilapia sparrmanii) detected respectively in 44% and 43% of the sites. High species richness was associated with well-vegetated wetlands, low urban CBD surface area and conductivity, large pond areas and steeper bank slopes. Conductivity and pH showed only weak negative effects on species richness. This is the first study to quantify the effects of urbanization on frog communities in a developing city on the African continent. Our results demonstrate that both local and landscape variables affect amphibians in a small but rapidly developing city. Accordingly, management practices need to adopt a multi-scale approach if we are to conserve amphibians in African cities.
Keywords: anuran habitat; indirect gradient analysis; landscape; predatory fish; urbanization