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

Abstract

ABSTRACTTo examine interspecific variation in the intensity of ant defense among three sympatric species of obligate myrme‐cophytes ofMacaranga(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 wasM. winkleri, M. trachyphylla, andM. beccariana.The antip/ant 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 onMacaranga.In addition to the interspecific difference in the total intensity of ant defense, when symbiont ants were excluded, both patterns of within‐plant variation in the amount of herbivore damage and compositions of herbivore species that caused the damage differed among species. This suggests that the threeMacarangaspecies have different systems of ant defense with reference to what parts of plant tissue are protected and what herbivorous species are avoided by ant defense. Thus, it is important to consider the interspecific variation in ant defense amongMacarangaspecies to understand the herbivore community onMacarangaplants and the mechanisms that promote the coexistence of multipleMacarangamyrmecophytes.