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COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.
Author(s) -
LACK ANDREW J.
Publication year - 1982
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1982.tb03316.x
Subject(s) - centaurea , biology , botany , asteraceae
SUMMARY Observations are presented on: (a) the numbers of insects foraging on Centaurea scabiosa and Centaurea nigra per available capitulum of each species; (b) the numbers of insect visits to each capitulum of C. scabiosa and C. nigra in 30 min intervals; (c) the numbers of insect visits to rayed capitula compared with ray less capitula; (d) the number of successful pollinations. The study was carried out on the Devil's Ditch, Cambridgeshire where C. nigra is rayless, and on Hod Hill, Dorset where C. nigra is rayed, with a few results from a garden trial set out in the Cambridge Botanic Garden. In the counts of insects in each area of the Devil's Ditch the numbers recorded feeding on each Centaurea species per capitulum were approximately proportional to the nectar reward of each species. On Hod Hill the number of insect visits to C. nigra plants from which rays had been removed was half to three‐quarters of the number of visits to rayed capitula. This is very similar to the difference on the Devil's Ditch between the number of visits to C. scabiosa (rayed) and C. nigra (rayless), and this difference may therefore be a result simply of the possession of ray florets in C. scabiosa but not in C. nigra. The difference between the two species on Hod Hill was greater ( C. scabiosa receiving two to three times as many visits as C. nigra) although C. nigra possesses ray florets and therefore resembles C. scabiosa. Some bees were observed visiting C. scabiosa selectively on Hod Hill but none did so on the Devil's Ditch. On the Devil's Ditch both species had similar numbers of styles successfully fertilized on nearly all dates. Hod Hill on most dates a similar number of styles was fertilized in each species, but on a few dates C. scabiosa had more successful fertilizations than C. nigra. It is concluded that competition for pollinators is not a strong selective factor in Centaurea on the Devil's Ditch but may be a factor promoting the later flowering and the possession of ray florets in C. nigra on Hod Hill. Competition for pollinators may have been more important as a selection pressure in the past when less suitable habitat was available.