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CONTRASTING EFFECTS OF ANTS ON THE HERBIVORY AND GROWTH OF TWO WILLOW SPECIES
Author(s) -
Sipura Mika
Publication year - 2002
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2002)083[2680:ceoaot]2.0.co;2
Subject(s) - willow , herbivore , biology , aphid , salicaceae , predation , ecology , botany , leaf beetle , woody plant , larva
This study examines the effects of two predatory ants, Myrmica rubra L. and Formica aquilonia Yarr. on the herbivory and growth of two phytochemically different willow species: low‐salicylate Salix phylicifolia L. and high‐salicylate Salix myrsinifolia Salisb. The net influence of ants on willow growth will depend on a balance between the benefits ants provide to the plant through predation on herbivores and the costs to the plant through the protection of aphids. Using both field observations and experimental manipulations of the densities of ants and tended aphids, I tested the hypothesis that this balance differs between the two willow species. On both observational and experimental willows, I followed the insect densities throughout one growing season and measured leaf damage and willow growth. The results from both data sets suggest that the effects of ants on the herbivory and consequent growth of these willows differ. Especially F. aquilonia had a positive effect on the growth of S. phylicifolia , whereas the effect on S. myrsinifolia was negligible or even slightly negative. These differences can be derived from three factors: (1) the ant‐tended aphid Pterocomma salicis L. was very abundant on both willow species, leading to strong negative impact of ants on the willows, (2) S. myrsinifolia harbored lower densities of leaf‐chewing insects, which made the positive effect of ants through reduced leaf damage less likely, and (3) the dominant leaf‐chewing herbivore on S. myrsinifolia , a leaf beetle Phratora vitellinae L., is chemically defended against predatory ants, being thus less preyed on than the predominating generalist leaf‐chewing herbivores on S. phylicifolia . Furthermore, when ants were not attending aphids, they even facilitated P. vitellinae , apparently by removing other predators. This study provides one explanation for the debate of whether ants benefit or harm plants: differences in herbivore resistance of plants may lead to diverging or even opposite results in tritrophic interactions between plants, their herbivores, and predatory ants.