Abstract
Bilberry (Vaccinium myrtillus L.) is one of the dominant plants of the Fennoscandian boreal coniferous forest and consti- tutes a major food source for many insect herbivores. A common ant species in these forests is the wood ant Formica (Formica) aquilonia Yarrow, which preys heavily on other invertebrates within its territories. The aim of this study was to investigate whether aquilonia's predation on the insect herbivores may have indirect positive or negative effects on bilberry. Damage to the bilberry, its vegetative growth and reproduction were quantified in order to contrast localities close to (2 m) and far away from (50 m) ant nests. Close to ant nests, herbivore damage to the bilberry was significantly lower and reproductive success, i.e. proportion of flowers succeeding to berries, significantly higher. The results of this study therefore suggest that distance to aquilonia nests, and thus preda- tion from ants, can significantly affect herbivore damage to the bilberry and its reproductive success (supporting the hypothesis of a top down effect in this three-trophic-level system). Vegetative growth, i.e., density and biomass of current year shoots, and reproduc- tive investment, i.e., proportion of current year shoots with flower, of the bilberry was, however, not affected by distance to ant nests, indicating that the bilberry can also compensate for losses due to herbivory.
Highlights
The importance of trophic interactions in determining population sizes and community structure, and whether the primary control is by resources or predators has been the subject of much debate (Hunter & Price, 1992; Power, 1992; Strong, 1992; Persson, 1999; Lawton, 2000)
The aim of this study was to investigate the indirect effects of predation by F. aquilonia on herbivorous insect larvae feeding on the bilberry (Vaccinium myrtillus L.), a dominant shrub in the field layer of Scandinavian forests
My analysis suggests that distance to F. aquilonia nests, and predation pressure from ants, can significantly affect herbivore damage to bilberry and its reproductive success, supporting a top-down effect
Summary
The importance of trophic interactions in determining population sizes and community structure, and whether the primary control is by resources or predators has been the subject of much debate (Hunter & Price, 1992; Power, 1992; Strong, 1992; Persson, 1999; Lawton, 2000). According to the bottom-up view by White (1978), i.e. control by resources, the availability of different resources to the plants and the limited availability of nitrogen-rich food for herbivores influence all trophic levels. The direct effect of predation by carnivores can have a strong effect on abundance and structure of prey communities and, in a three-trophic-level food web, can affect the bottom level through indirect effects (Sih et al, 1985; Schoener & Spiller, 1996, 1999; Spiller & Schoener, 1998; Schmitz et al, 2000). Schmitz et al (2000) found in their review that in the studies which included three trophic levels, 75% reported significant indirect effects of carnivore removal on some plant variable
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