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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 balance between mutualism and antagonism in any given partnership. Using an obligate ant–plant mutualism, we manipulated the density of symbiotic acacia ants (Crematogaster mimosae) and

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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 plant species that giraffe may browse, to assess the possibility of acute hydrogen cyanide poisoning and condensed tannin intoxification. Condensed tannins and hydrogen cyanide concentrations

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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 seed retention time and tooth size, which are both positively correlated with body size. Infestation by bruchid beetles (Bruchidae) reduces Acacia germination. Herbivores may reduce

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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 wild population of free-ranging giraffes than did intact branches on the same plants. These differences in herbivory resulted in long term losses of branch length

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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 (Moe, Wegge & Kapela, 1990; Wilsey, 1996; Tomor & Owen-Smith 2002). Rapid resprouting initiated by fire, and reinforced by herbivory (cf. McNaughton, 1985), may contribute

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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 effectively controlled herbivory by megaherbivores (elephants and giraffes) and other large mammalian herbivores at a field site in Laikipia, Kenya since 1995. Mean spine lengths

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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 the expense of leaf mass, whilst investment in straight prickles was as much as 6% of shoot dry mass. Shoot length had significant effects on

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