Herbivore-induced changes in flower scent and morphology affect the structure of flower–visitor networks but not plant reproduction

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Abstract

Herbivory induces various responses in plants, thus altering the plants' phenotype in chemical and morphological traits. Herbivore-induced changes in vegetative plant parts, plant-physiological mechanisms, and effects on plant-animal interactions have been intensively studied from species to community level. In contrast, we are just beginning to examine herbivore-induced effects on reproductive plant parts and flower–visitor interactions, especially in a community context. We investigated the effect of herbivory at different plant developmental stages on plant growth, floral and vegetative phenotype and reproduction in Sinapis arvensis (Brassicaceae). Additionally, we tested how herbivore-induced plant responses affect flower–visitor interactions and plant reproduction in species-rich communities. Our results indicate that the timing of herbivory affects the magnitude of changes in plant traits. Herbivory in early but not in late development accelerated the plant's flowering phenology, reduced vegetative growth, increased stem trichome density and altered floral morphology and scent. These findings suggest age-dependent tradeoffs between growth, defense and reproduction. Herbivore-induced changes in flower traits also affected flower–visitor interactions in a community context with effects on the structure of flower–visitor networks. However, changes in the network structure had neglectable effects on plant reproduction, i.e. plants were able to compensate altered flower visitor behavior. Thus, herbivory is a source of intraspecific variation in reproductive traits, which can be behaviorally relevant for potential pollinators. However, plants were capable to maintain reproductive success suggesting a tolerance against herbivory. We conclude that in our study system induced direct or indirect defenses that have often been shown to decrease negative effects of herbivores on vegetative plant parts come at no costs for plant reproduction.

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