POPULATION-SIZE AND DENSITY EFFECTS IN POLLINATION - POLLINATOR FORAGING AND PLANT REPRODUCTIVE SUCCESS IN EXPERIMENTAL ARRAYS OF BRASSICA KABER

1 The term 'density-dependence' is often applied rather loosely to a v ariety of aspects of local abundance. 'Density' is most commonly measu red as the size of a local population and/or the (average) spacing bet ween the individuals within it. These parameters are interrelated and correlated in most natural populations. Yet species interactions and p opulation dynamics may be affected differently by these different aspe cts of abundance. 2 Field experiments were performed to tesi the effec ts of two components of local abundance on pollination in the self-inc ompatible annual plant, Brassica kaber. In one experiment, populations of uniform density but differing size were planted out, whilst in a s econd study both the density and size of populations were varied. 3 Th e number of individuals in a population had no effect on pollinator vi sitation or subsequent seed set in either experiment. 4 Population den sity, however, had strong effects on both visitation and reproductive success. 5 The position of a plant within a population had an impact o n pollinator constancy in the second experiment, but had no effect on visitation rates or reproductive success.