Bumble bee pollination of the sticky catchfly in a fragmented agriculturallandscape

Seed set and pollinator activity of bumble bees were examined in a fragment ed population of sticky catchfly (Viscaria vulgaris). We focused on the pot ential effect of the spatial distribution of plant individuals at three hie rarchical levels: islet level (outcrops with seminatural vegetation in the agricultural fields), patch level (aggregations of plant individuals within islets), and tussock level (plant individuals within patches). Size of pat ches and islets were study design parameters, whereas isolation at the patc h and islet level and size at the tussock level were treated in the analysi s as covariates. Isolation of islets and patches had no significant effect on the response variables (seed set and bumble bee activity). However, the isolation of islets and patches was quite small compared to the activity ra nge of bumble bees in the study area. While islet size seemed to be unimpor tant, both pollinator activity and seed set increased with increasing patch and tussock size, whereas the frequency of aborted seeds decreased. The in creased seed set of larger and presumably older patches and tussocks indica te that to maximize viability of a fragmented, perennial herb population, i t is important to minimize local disturbance so that individual subpopulati ons may develop over time.