The interaction of thorns and symbiotic ants as an effective defence mechanism of swollen-thorn acacias |
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Authors: | Linsey Stapley |
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Institution: | (1) Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK Fax: +44-1223-336676; e-mail: is208@cus.cam.ac.uk, GB |
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Abstract: | Evidence is provided for the interaction of ants (Crematogaster spp.) and thorns as a means of defence against browsing mammals for one species of African myrmecophyte, Acacia drepanolobium. Two experiments were conducted using goats as representative mammalian browsers. In the first experiment, the defences of
individual branches were manipulated in order to assess the effectiveness of ants and thorns both on their own and together
as anti-herbivore defences. It was shown that ants on their own are more effective defences for a single branch than having
neither ants nor thorns, but ants from a single branch do not add significantly to the effectiveness of thorns as an anti-herbivore
defence. The second experiment looked at the effect of a whole tree of ants and how they interacted with thorns in the defence
of the tree. It was shown that ants from a whole tree do significantly add to the effectiveness of thorns as an anti-herbivore
defence. In all cases, the goat refused to go back to and feed from a tree whose ants had just attacked it. Thorns on their
own, however, do not act as total browsing deterrents. They slow down the rate of feeding but animals may compensate for this
by feeding for longer periods of time. The interaction of a whole tree of ants and thorns is a very effective browsing deterrent
which causes the animal to stop feeding almost immediately, therefore keeping the amount of foliage lost to a minimum. These
results provide support for the hypothesis that the ant-acacia relationship (in the case of A. drepanolobium) evolved at least partly because of pressure from browsing mammals.
Received: 20 October 1997 / Accepted: 28 February 1998 |
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Keywords: | Thorns Acacia ants Defence Mammals Herbivory |
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