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.