Indirect effects in plant-pollinator interactions: the role of exotic plants and herbivores
Date
2008
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Abstract
Flowering plants interact with a variety of other species. While numerous studies have demonstrated that pair-wise interactions between species are important factors affecting plant ecology and evolution, interaction with one species may affect the outcome of the interaction with another. I examined how pollination is influenced by both competition and herbivory. In Chapter One, I tested whether the presence of an exotic plant, musk thistle (Carduus nutans L. (Asteraceae)) influenced flower visitor behavior in relation to the native plant, bee balm (Monarda fistulosa L. (Lamiaceae)). I found that visitation rate to the native was not affected by the presence of the exotic. However, flower visitors commonly switched between the native and exotic and transferred exotic pollen to native plant stigmas. Conspecific pollen on the native plant stigmas was also reduced in the presence of the exotic. Seed set of the native plant was not affected. In a separate experiment, I examined how distance from the exotic plant influenced visitation rate to the native plant. I found that visitation rate to the native plant was reduced when the native plant was 1 and 5 meters from the exotic. However, visitation rate remained unchanged at 0 and 15 meters. This suggests that magnitude of interactions between plants through flower visitors may depend on spatial scale. In Chapter Two, I examined how the exotic plant, musk thistle, influenced visitation rate to the native plant, common harebell (Campanula rotundifolia L. (Campanulaceae)). I found that visitation rate to the native plant was reduced in the presence of the exotic plant. However, only solitary bees exhibited a reduction in visitation rate while Bombus species did not. Flower visitors did not switch between the exotic and native plants, and there were no exotic pollen grains on the native plant stigmas. Conspecific pollen deposition and seed set were not affected by the presence of the exotic plant. In Chapter Three, I explored whether the biological control Mecinus janthinus (Coleoptera) affected floral display size and visitation rate to the exotic plant Dalmatian toadflax (Linaria dalmatica (Scrophulariaceae)). In addition, I examined whether M. janthinus feeding affected female reproductive success directly or indirectly through flower visitors. I found that herbivory decreased the number of flowers and visitation rate to Dalmatian toadflax. However, I found no effect of herbivory on seed set when conducting hand-pollinations, suggesting no indirect effects of M. janthinus through flower visitors.
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Subject
exotic plants
herbivores
invasive species
plant-pollinator interactions
pollination
ecology