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 variety of aspects of local abundance. 'Density' is most commonly measured as the size of a local population and/or the (average) spacing between the individuals within it. These parameters are interrelated and correlated in most natural populations. Yet species interactions and population dynamics may be affected differently by these different aspects of abundance. 2 Field experiments were performed to tesi the effects of two components of local abundance on pollination in the self-incompatible annual plant, Brassica kaber. In one experiment, populations of uniform density but differing size were planted out, whilst in a second study both the density and size of populations were varied. 3 The number of individuals in a population had no effect on pollinator visitation or subsequent seed set in either experiment. 4 Population density, however, had strong effects on both visitation and reproductive success. 5 The position of a plant within a population had an impact on pollinator constancy in the second experiment, but had no effect on visitation rates or reproductive success.