Abstract
Abstract Intensification of agriculture has been one of the major drivers for biodiversity loss in recent decades. Pollinators, which serve an important role in pollinating crops as well as wild plants, have shown a decline in species richness. Flower strips can be used to support pollinators in agro-ecosystems, however the question remains as to how their design can be optimized in order to best benefit pollinators. Increasing plant species diversity has been shown to be beneficial for pollinators, and it is often suggested that functional traits are driving this relationship. Therefore, increasing plant functional diversity could be a tool to support pollinator abundance and diversity. As experimental evidence on this relationship is scarce, we developed a field study with experimental sown flower strips with four functional diversity levels, based on multiple flower traits and with equal plant species richness. We monitored vegetation development, as well as the flower-visiting pollinator community and their interaction networks with flowers. We were able to create a functional diversity gradient while controlling for plant species richness and evenness. However, in contrast to our expectations, pollinator species richness and evenness were not influenced by functional diversity, and increasing functional diversity even resulted in lower flower visitation rates. Network stability metrics showed no effect or negative relationships with functional diversity. We conclude that increasing functional diversity was not the key for supporting pollinators in wildflower strips. Our results also suggest that, for a constant amount of flower resources, increasing plant functional diversity and thus decreasing redundancy of potential pollinator feeding niches, decreases the amount of flower resources present per feeding niche. As pollinator species tended to have less overlap in their feeding niches in flower strips with increased functional diversity, this may lead to a reduction of flower resources available for pollinator species with a more specialized feeding niche.
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