Small-scale spatial patterns determine ecological relationships: an experimental example using nectar production rates

The structuring of populations at small scales has important consequences f or ecological relationships and may contribute to the maintenance of geneti c diversity within populations. As an example we tested the effects of vari ation in nectar production rates (NPR) on pollinator visitation in experime ntal populations of Echium vulgare with different spatial arrangements. Bum blebees discriminate between groups of plants with different NPRs only when these groups are separated by distances larger than 6 m. Within groups, pl ants with high and low NPR receive similar numbers of approaches. Plants wi th high NPR increase the average number of approaches to all plants in the group; therefore, plants with low NPR benefit from nectar-rich plants nearb y. These results demonstrate that the effects of NPR on pollinator service depend on the spatial structuring of the population. We suggest that this m ay help to explain the large genetic differences in NPR that we find for E. vulgare at our study site.