ECOLOGICAL STUDIES ON THE DIVERSITY OF ODONATA (INSECTA) IN IPOGUN, IFEDORE LOCAL GOVERNMENT AREA, ONDO STATE, NIGERIA

Abstract

Odonata (Dragonfly and Damselfly) are particularly good indicators of freshwater ecosystem health. The constant disturbance of freshwater habitats can result in reduction of Odonata species diversity. Changes in Odonata biodiversity are influenced by human activities such as urbanization, agriculture and input of pollutants in water. This study assessed the abundance and diversity of Odonata along River Aponmu in Ipogun. A total of 906 individuals representing sixty-four (64) species and sixteen (16) genera in seven (7) families (Coenagrionidae, Lestidae, Platycnemididae, Chlorocyphidae, Calopterygidae, Libellulidae and Gomphidae) were collected and identified. Of the 906 individuals, Libellulidae had the highest percentage composition (44%) with 395 individuals out of which Trithemis arteriosa (a pollution tolerant species) had the highest number of individuals (225) and Gomphidae had the lowest percentage composition (0.03%) with 1 individual. Most of the species collected had tolerance for disturbed environment including Pseudagrion melanicterum, Paragomphus genei and Orthetrum julia. Aponmu area had the highest species diversity (Hꞌ= 2.312) while Idi area had the least species diversity (Hꞌ = 2.021). Alaasin area had the highest Simpson_d value (0.8557) and the best taxa distribution (Evenness=0.524; Equitability_J= 0.7764) which made the area a more pristine site than the other sites while Aponmu area had the least distribution (Evenness=0.3365; Equitability_J= 0.6798). Cluster analysis revealed a close similarity between the Odonata assemblages at Alaasin and Aponmu areas while that of Idi area was quite different. Analysis of variance (ANOVA) of physico-chemical parameters revealed that temperature (◦C), pH, Dissolved Oxygen (DO), turbidity (NTU), Biochemical oxygen demand (BOD), Nitrate (NO3) and Phosphate (PO4) did not show significant difference at the three sites while Electrical Conductivity (μS/cm) and Total dissolved solids (mg/L) which had moderately high mean values indicated significant difference at Aponmu area (p<0.05). Trithemis arteriosa exhibited a weak negative correlation to both temperature and Dissolved Oxygen (DO). This study has provided information on Odonata assemblage and physico-chemical parameters at River Aponmu and therefore infers that some parameters influence the abundance of some Odonata species and River Aponmu is somewhat polluted as it receives more pollutants resulting from human activities around it and could be unsafe for drinking