Habitat fragmentation affects plant–arthropod interactions through connectivity loss and edge effects

Habitat fragmentation is widespread globally, but the effects of fragmentation on populations and communities are often unclear. Because species responses to fragmentation are interdependent, examining how fragmentation alters species interactions may clarify community responses to fragmentation. In a large, replicated fragmentation experiment, we tested the effects of inter-patch connectivity, patch-scale edge-to-area ratio, and within-patch distance from an edge on multiple co-occurring plant-arthropod interactions and pollination rate (measured by fruit-flower ratio). Using experimentally planted populations of the sandy-woods chaffhead Carphephorus bellidifolius, we measured three plant-arthropod interactions: plant-pollinator interactions, plant-florivore interactions, and plant-spider interactions (predators of pollinators). Connectivity increased pollinator visitation, highlighting the significance of connectivity for pollinator foraging. Across all arthropod groups, connectivity and edge-to-area ratio affected visitation more than distance from an edge. Despite the strong impact of connectivity on plant-pollinator interactions, connectivity had no effect on fruit-flower ratio, indicating that other local factors may be more significant for pollination and seed set. Taken together, we provide experimental evidence that multiple plant-arthropod interactions are altered by habitat fragmentation through connectivity loss and increased edge-to-area ratio. Incorporating species interactions into fragmentation research will strengthen understanding of the mechanisms by which fragmentation alters populations and communities.