Difference in Intensity of Ant Defense among Three Species of Macaranga Myrmecophytes in a Southeast Asian Dipterocarp Forest1

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Abstract
To examine interspecific variation in the intensity of ant defense among three sympatric species of obligate myrmecophytes of Macaranga (Euphorbiaceae), we measured the ratio of ant biomass to plant biomass, ant aggressiveness to artificial damage on host plants, and increase in herbivore damage on host plants when symbiont ants were removed. Increase in herbivore damage from two- and four-week ant exclusion varied significantly among the three species. The decreasing order of vulnerability to herbivory was M. winkleri, M. trachyphylla, and M. beccariana. The ant/plant biomass ratio (= rate of the dry weight of whole ant colonies to the dry weight of whole aboveground plant parts) and ant agressiveness also varied significantly among the three species; the orders of both the ant/plant biomass ratio and ant aggressiveness were the same as in the herbivory increase. These results indicated that the intensity of ant defense differs predictably among sympatric species of obligate myrmecophytes on Mac...