We analysed the combined effects of pollination and seed predation on seed
set of Centaurea jacea in 15 landscapes differing in structural complexity.
In the centre of each landscape, a patch of Centaurea plants was establish
ed for standardized measurements of flower visitation, seed predation and s
eed set. Both the number of flower-visiting bees and the proportion of flow
er heads damaged by seed predators increased,,vith landscape complexity, wh
ich was measured as the proportion of semi-natural habitats. The mean numbe
r of seeds per flower head did not increase with the proportion of semi-nat
ural habitats, presumably because of the counterbalancing effects of pollin
ation and seed predation. For a subset of undamaged flower heads, the numbe
r of seeds per flower head was positively correlated with the number of flo
wer visits. Further reasons for the unexpected failure to detect a correlat
ion between landscape complexity and seed set appeared to be changes in flo
wer-visitor behaviour and the contrasting responses of honeybees and wild b
ees to habitat context. Landscape analyses at eight spatial scales (radius
of landscape sectors, 250-3000 m) showed that different groups perceived th
e landscape at different spatial scales. Changes in pollinator numbers coul
d be explained only at small scales (up to 1000 m), while the seed predator
s also responded to large scales (up to 2500 m).