Interspecific and temporal variation of condensed tannins and cyanide concentrations in potential dietary sources of extralimital giraffes (Giraffa camelopardalis) in the Karoo
During 2016 and 2018 four giraffe (Giraffa camelopardalis) mortalities occurred in the Karoo potentially caused by acute hydrogen cyanide poisoning. Plants have various defence mechanisms to protect themselves against herbivory, including the production of secondary metabolites such as condensed tannins and hydrogen cyanide. This study quantified condensed tannin and hydrogen cyanide production in selected Karoo […]
Thorns as induced defenses: experimental evidence
We report evidence from controlled experiments that long straight thorns deter herbivory by browsers. Cut branches of three woody species that had their thorns removed suffered significantly greater herbivory by a tethered goat than did paired intact branches. Branches on living Acacia seyal plants that had their thorns removed suffered significantly greater herbivory by a […]
Giraffes and the pollination ecology of knobthorns (Acacia nigrescens)
Giraffes (Giraffa camelopardalis) consume large quantities of knobthorn (Acacia nigrescens) flowers every year, and may be acting as pollinators. Because knobthorns flower in the late dry season, nutritionally a critical time of year for ungulates, the flowers are an important source of food for giraffes, especially since they are not physically protected against herbivory. Giraffes […]
Effects of simulated shoot and leaf herbivory on vegetative growth and plant defense in Acacia drepanolobium
Plants have considerable ability to respond to herbivory, both with (above-ground) regrowth and with increased defense. We simulated both leaf and shoot herbivory in controlled, replicated experiments on individuals of Acacia drepanolobium in Laikipia, Kenya. These experiments were carried out on individuals that had experienced different, experimentally controlled histories of large mammalian herbivory. Both forms […]
Are giraffes pollinators or flower predators of Acacia nigrescens in Kruger National Park, South Africa?
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 […]
Symbiotic ants as an alternative defense against giraffe herbivory in spinescent Acacia drepanolobium
We explore here the occurrence of aggressive ants in an apparently symbiotic relationship with the savanna tree Acacia drepanolobium and their effects on giraffe herbivory on the Athi-Kapiti Plains, Kenya. Trees taller than 1.3 m were more likely to be occupied by aggressive ants in the genus Crematogaster than were shorter trees. Ants were concentrated on shoot tips, the […]
Browsing-induced Effects on Leaf Litter Quality and Decomposition in a Southern African Savanna
We investigated the linkages between leaf litter quality and decomposability in a savanna plant community dominated by palatable-spinescent tree species. We measured: (1) leaf litter decomposability across five woody species that differ in leaf chemistry; (2) mass decomposition, nitrogen (N); and carbon (C) dynamics in leaf litter of a staple browse species (Acacia nigrescens) as […]