Forest degradation and its impact on anuran diversity and abundance in Arun Owun, Sapele, Delta State, Nigeria

Abstract

The effects of vegetation degradation on the abundance and diversity of anuran species were investigated in Arun Owun, Delta State. Combinations of visual encounter survey (VES) and acoustic encounter survey (AES) were conducted to estimate the local anuran composition both prior to and after the clearing of vegetation at the study sites. These surveys were conducted during the wet season (June-August, 2008) and dry season (December-February, 2009). Adjacent sites were also surveyed as to ascertain the presence or absence of anuran species still in the vicinity, but not observed at the study sites. Mean totals of 27.69 and 6.53 anurans belonging to 26 species were recorded in 96 hours of combined VES and AES sampling during this study prior to the cutting of vegetation and after its cutting respectively. The highest number of species (26) was recorded during the rainy season prior to the cutting of vegetation, whereas the lowest (5) was during the dry season after the cutting of vegetation at the sites. At the adjacent sites, a total number of 64 anurans belonging to 9 species were observed in 10 hours of sampling which were no longer present at the study sites. Five (19.2%) species which could no longer be accounted for, both at the study and adjacent sites were: Phrynobatrachus plicatus, Phrynobatrachus sp, Phlyctimantis boulengeri, Silurana tropicalis and Hylarana galamensis. There was significant difference during the rainy, dry and entire seasons; at t-test calculated as 1.297, 0.793 and 1.039 respectively at (p<0.05, df = 25, t_cal = 7.436), between the time prior to vegetation cutting and post vegetation cutting. Similarly the Shannon-Wiener and Equitability indices also showed remarkable differences between these two regimes. Unfortunately, deforestation is extremely difficult to halt, as development of agriculture, infrastructure and oil exploration are seen as crucial steps to national development. Preventing the degradation of the forest fragments should be a priority and also monitoring the dynamics of anuran species in their response to habitat destruction is important. These are crucial steps in the conservation of biological diversity.

Keywords: anuran abundance, vegetation degradation, oil exploration, habitat destruction, conservation and biological diversity