Comparison of behavior between ant-dependent and independent aphids

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Behavioral and morphological comparison was made between ant-attended aphid and its independent sibling ; however, no significant difference was detected. This is probably because the ant-concerned mutualisms are often, if not always, conditional or indirect. From this view point, therefore, some ant-concerned mutualisms were studied in the present study. Main results were : 1) On the ant-visited oak trees, ant-dependent aphids considerably enhanced their population. However, the ants reduced the number of ant-independent aphids, weevils and moth larvae which were harmful to the leaves and acorns of the tress. This suggests that the ant-attended aphids are not always harmful to their host plants but there are some indirect ant-plant mutualisms via aphids. 2) Ant effects on the different life forms of moth larvae were investigated on the oak trees. While unsheltered larvae were significantly depopulated by ants, the density of larvae inhabiting hollow stalks or small spaces between stalks and scales was not remarkably affected by ants. Acorn-borers, which were seemingly well sheltered, were considerably depopulated by ants. The acorn-borers often needed more than one acorn for their full growth, and they appeared to be hunted by ants during the inter-acorn drift. 3) Trillium tschonoskii, Viola spp.and Erythronium japonicum are myrmechochorous, but their seed removal frequencies were controlled less by ants than by ground beetles which devoured the elaiosomes and eventually interfered the seed dispersal by ants. Thus, unlike specialized mutualisms where mutualistic partners might co-adapt to avoid interference by outsiders, these ants and plants are in loose mutualism where the ants are not specialized elaiosome feeders and are hardly induced to expel the outsiders.