Size does matter: larger patches of diverse floral resources increase insect pollinator density, diversity, and their pollination of native wildflowers

Insect pollinators are used extensively by farmers all over the world for crop pollination. However, the lack of floral diversity and nesting sites makes many agricultural landscapes poor habitat for insect pollinators. The addition of native wildflowers to agricultural landscapes can provide resources to support these pollinators throughout the growing season, potentially maintaining the pollination services from wild bees. However, there is little information on how much habitat is needed to support wild bees and their pollination services. We measured the response of insect pollinators to wildflower patch size by establishing twelve native flowering perennial plants in replicated plots ranging in size from 1 to 100 m². The response of flower richness, insect pollinators, and the provision of pollination services to patch size were measured across these different sized plots. We found that honey bees, wild bees, and hoverflies all respond positively to increasing flower richness, whereas particular insect pollinator groups respond differently to varying sizes of wildflower habitat. In general, wild bees were observed at higher density and diversity in the 30 and 100 m² patches. Subsequently, increasing wildflower patch size, and thus wild bee density, resulted in greater seed set in the wildflowers. Conversely, honey bees and hoverflies did not respond to wildflower patch size. We conclude that wild pollinators and the services they provide are sensitive to the richness and area of available floral resources. Establishing large areas of diverse wildflower species is necessary to support pollinators and their pollination of flowering plants in fragmented agricultural landscapes.