The effects of the invasive weed Arundo donax on insect biodiversity in the Kruger National Park

Arundo donax is an invasive weed which was recently discovered on the Sabie River in Kruger National Park and like many invasives it is thought to reduce biodiversity in its invaded environment. In this experiment we looked at the effects of the invasive weed on insect biodiversity in a riparian environment. We compared the species richness of A. donax to the native reed, Phragmites mauritianus and to a mixed vegetation environment. We found that A. donax did not significantly decrease the number of individuals or number of species found in pitfall traps. Biological diversity indices showed, however, that there was in fact a higher diversity in the A. donax insect populations. We also took measurements of the insect diversity of the three vegetation types by beating the reeds and analyzing the insects that fell out. We found a lower species richness in A. donax than in P. mauritianus. This can be explained by the fact that one species of ant is dominating P. mauritianus on the ground but dominating A. donax in the upper layers of the reed. This, in turn, says that the dominating species is pushing out other species accounting for a lowered diversity that might otherwise be found. In our study, A. donax did not significantly affect the biodiversity of insects overall found on P mauritianus within a riparian ecosystem.