THE POTENTIAL USE OF COLEOPTERA AS BIO-INDICATOR OF ECOLOGICAL CHANGES ON REHABILITATED ASH DAMS AT THE HENDRINA POWER STATION IN MPUMALANGA

Abstract

This study was conducted on the ash dams of the Hendrina Power Station in Mpumalanga, South Africa and gives an evaluation of the insect order Coleoptera as possible indicators of environmental change associated with rehabilitated ash dams. The study deals with the possibility of using certain Coleoptera species as indicators of environmental changes as well as changes in the composition and diversity of Coleoptera assemblages. A two year sampling period was undertaken during which insects were collected by means of pitfall traps and sweepnets both on ash dams and in natural veld. A total of 191 Coleoptera morphospecies were caught of which 67 were found in natural veld and 175 on the ash dams. From the 191 species 126 morphospecies were only found on ash dams and 19 were only found in natural veld. The coleopteran families Anthicidae, Chrysomelidae and Tenebrionidae were most abundant on the ash dams while Tenebrionidae, Chrysomelidae and Curculionidae were most abundant in natural veld. Species diversity, equitability and species richness were higher for rehabilitated than for unrehabilitated ash dams and natural veld. The latter is because insects with lower abundance is less trappable in pitfall traps. Because predatory insects are opportunistic, mobile and good hunters they tend to quickly colonise unrehabilitated and newly rehabilitated ash dams to exploit the few prey insects which already colonised these areas. As the areas became more stable (at the older rehabilitated ash dams) the numbers of predators decreased. This tendency was also clear in the succession of individuals of the families Carabidae and Anthicidae. As soon as the area became more stable (stable plant communities occured with a high organic matter content) the numbers of these families decreased and numbers of other functional groups such as phytophagous insects increased. Statistical significant positive correlation was found between Coleoptera species diversity and -richness with the percentage organic matter in the soil. Species richness was negatively correlated with soil pH and percentage clay. The study therefore proved that certain beetle assemblages, especially those of the families Carabidae and Anthicidae, could be considered as indicators of disturbance. The abundance of individuals in these families tends to increase with an increase in disturbance. Abundance of the predatory beetles generally tend to increase with an increase in disturbance.