The role of visitation rate and pollination efficiency in promoting pollinator complementarity

Background/Question/Methods

The concept of pollinator niche complementarity maintains that species-rich pollinator communities can provide higher and more stable pollination services as compared to species-poor communities, due to contrasting spatial and/or temporal pollination activity between groups of pollinators. Complementarity has usually been examined in pollinators' patterns of flower visitation or abundance, while largely neglecting the possibility of complementarity in patterns of single-visit contribution to fruit/seed set (pollination efficiency). However, variability in pollination efficiencies can greatly affect pollinators' overall pollination services and thus their complementarity.   

In the current study, we investigated the existence of pollinator complementarity in both visitation rates and pollination efficiencies. The study was conducted in a Mediterranean agro-natural landscape in central Israel in 43 watermelon fields cultivated for seed consumption. We studied spatio-temporal variation in pollinators' visitation activity, measured by repeated observations and netting, and pollination efficiency, measured by the fruit and seed set rates of hermaphrodite flowers exposed to a single bee visit. Visitation and pollination efficiency were measured along the day and season, and within and between fields with contrasting availability of nearby wild plants.  

Results/Conclusions

Pollinator species' visitation rates as well as single-visit fruit set efficiencies, but not seed set efficiencies, differed spatiotemporally and exhibited complementary patterns. Pollinators' visit frequencies responded differently to surrounding land use, location within field, time along the season, and time of day. Pollinators' fruit set efficiencies responded differently to time of day and ovary size.

Our study generally supports the view that diverse pollinator communities can deliver higher and more stable pollination services through spatiotemporal complementarity in both flower visitation rates and pollination efficiency. Complementarity in pollination efficiencies suggests further potential for diversity effects on crop yield, and calls for taking into account the variability in pollination efficiency along the spatiotemporal scales of the study rather than considering it as a species-specific constant trait. Noteworthy, the existence of niche complementarity does not necessarily translate into increased pollination services and crop yield; rather, the relevance and limitations of such mechanisms should be considered in light of the specific crop and management system.