Bumble bee pollination of the sticky catchfly in a fragmented agricultural landscape

Abstract

Seed set and pollinator activity of bumble bees were examined in a fragmented population of sticky catchfly (Viscaria vulgaris). We focused on the potential effect of the spatial distribution of plant individuals at three hierarchical 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 patches and islets were study design parameters, whereas isolation at the patch and islet level and size at the tussock level were treated in the analysis 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 range of bumble bees in the study area. While islet size seemed to be unimportant, both pollinator activity and seed set increased with increasing patch and tussock size, whereas the frequency of aborted seeds decreased. The increased seed set of larger and presumably older patches and tussocks indicate that to maximize viability of a fragmented, perennial herb population, it is important to minimize local disturbance so that individual subpopulations may develop over time.