Are giraffes pollinators or flower predators of Acacia nigrescens in Kruger National Park, South Africa?

Abstract

We examined the relationship between giraffes (Giraffa camelopardalis) and Acacia nigrescens in Kruger National Park, South Africa, to determine whether these tall ungulates may be providing a pollination service for the trees, or are simply flower predators. We quantified florivory and subsequent fruit set in the presence and absence of giraffes. Acacia nigrescens flowers are clearly a substantial dietary component for giraffes. Although A. nigrescens flowers contain almost three times as much condensed tannin as leaves, giraffes consume large quantities of flowers (∼85% of flowers within reach), resulting in distinct browse lines on the trees. This substantial florivory is detrimental to the overall fecundity of A. nigrescens, with significantly reduced fruit set at heights on trees that are accessible to giraffes. Fruit set increased above the reach of giraffes, suggesting successful pollination by insects. Giraffes were effectively flower predators of A. nigrescens in the season we examined.