Adaptation of a decreaser and an increaser grass species to defoliation in semi-arid grassveld.

Abstract

Grasses have developed through natural selection to deter, escape and tolerate herbivory, and to escape and tolerate fire. In the semi-arid grassveld of the Eastern Cape, the species Themeda triandra and Sporobolus fimbriatus have been classified as Decreaser and Increaser II plants respectively. Both species have well-developed escape and tolerance mechanisms, although T. triandra readily tolerates defoliation only during the dormant season, while S. fimbriatus is adapted to tolerating defoliation throughout the year. Furthermore, T. triandra has only moderately developed deterrents to herbivory, in contrast to S. fimbriatus, where deterrents are well-developed. It follows that the Decreaser species T. triandra is adapted to relatively frequent fire and no more than modest herbivory, while the Increaser II species, S. fimbriatus, is adapted to heavy herbivory usage, but infrequent fire.

Keywords: botany; chemical deterrents; decreaser species; defoliation; eastern cape; fire; grasses; grassveld; growth patterns; herbivory; increaser species; lateral tillering; natural selection; semi-arid grassveld; south africa; sporobolus fimbriatus; themeda triandra; tolerance