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Moog, J. ; Feldhaar, Heike ; Maschwitz, Ulrich:
On the caulinary domatia of the SE-Asian ant-plant Zanthoxylum myriacanthum Wall. ex Hook. f. (Rutaceae) their influence on branch statics, and the protection against herbivory.
In: Sociobiology.
Bd. 40
(2002)
.
- S. 547-574.
ISSN 0361-6525
Abstract
The rutaceous tree Zanthoxylum myriacanthum is a 'nonspecific' myrmecophyte that offers food via extrafloral nectaries (EFN) as well as nesting space for ants inside its hollow branches and twigs. A total of 33 different species of ants from 4 subfamilies were recorded on the tree. Twenty-eight (85) of these species were found nesting inside the domatia. None of these stem-nesting ant species appears to be a specialist occupant of Z. myriacarithum. Most of the nesting ant species showed no or little degree of effectiveness in anti-herbivore protection when loss of leaf area of inhabited branches is compared with those of uninhabited branches (the EFN of the latter still being accessible for ant visitors). For one ant species we could demonstrate a highly significant reduction of leaf area loss. The outcome of ant colonization on Z. myriacanthum will likely be diffuse because ant partners can vary markedly in space and time. In addition to biotic defence the tree also invests in chemical defences (e.g. oil glands) and in physical armament (spininess). The plant's investment of material in spines is extremely biased towards plant regions accessible to mammalian herbivores, indicating an economic investment in physical anti-herbivore defence. Overall, herbivory levels on Z. myriacanthum were very low, on average c. 4, suggesting a high effectiveness of the combined anti-herbivore defences. Z. myriacanthum is a tall and fast growing pioneer tree that develops entrance slits allowing ant access into the hollow stem domatia only late in its ontogeny. The formation of opening slits is usually restricted to horizontal branches, whereas the vertical stem axis bears no or few slits. The number of slits on branches increases strongly with increasing ramification, i.e. with increasing distance to crown supporting structures. Experiments indicate that branches with slits are more prone to breaking damage than branches without slits. We suggest that the spatial and temporal formation of entrance slits in Z. myriacanthum is influenced by the damage risk caused by providing self-opening domatia.