Enough is enough: The effects of symbiotic ant abundance on herbivory, growth, and reproduction in an African acacia
Understanding how cooperative interactions evolve and persist remains a central challenge in biology. Many mutualisms are thought to be maintained by ‘‘partner fidelity feedback,’’ in which each partner bases their investment on the benefits they receive. Yet, we know little about how benefits change as mutualists vary their investment, which is critical to understanding the […]
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 […]
Three–way interactions between Acacia, large mammalian herbivores and bruchid beetles ‐ a review
Large mammalian herbivores are both predators and dispersers of Acacia seeds. While some of the seeds are destroyed during passage through the herbivore’s digestive tract, others are defecated unharmed. Ingestion by large herbivores facilitates germination by scarification of the seed coat. The extent of the influence of herbivores on seed dispersal and germination depends on […]
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 […]
Delayed effects of fire on habitat use by large herbivores in Acacia drepanolobium savanna
Fire is frequently used as a wildlife management tool in savanna habitats (Trollope, 1982). Burning stimulates sprouting of plants (Vesey-Fitzgerald, 1971), improving forage quality (Komarek, 1967; Dorgeloh, 1999). Several studies have supported quantitatively what has been well known by managers for some time, namely that ungulates are attracted by resprouting vegetation in recently burned areas […]
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 […]
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 […]
Effects of natural and simulated herbivory on spine lengths of Acacia drepanolobium in Kenya
We present experimental evidence supporting the hypothesis that increased spine length in acacia species is a defense induced by herbivory. Acacia drepanolobium is the dominant tree over large areas of East Africa. Each individual tree is occupied by one of four ant species at our study site. Using two types of electric fences, we have […]
Shoot characteristics of Acacia tortilis (Forsk.) in wildlife and rangeland habitats of Botswana
Length, branch production, orientation, spinescence and biomass were measured for current shoots of Acacia tortilis shrubs in a range of habitats in Botswana. All shoot characteristics varied between individuals and between habitats with longer, less spinescent shoots produced in the habitat recently protected from wildlife. Biomass allocated to woody material increased with shoot length at […]