Bee diversity effects on pollination depend on functional complementarity and niche shifts

Abstract

Abstract. Biodiversity is important for many ecosystem processes. Global declines in pollinator diversity and abundance have been recognized, raising concerns about a pollination crisis of crops and wild plants. However, experimental evidence for effects of pollinator species diversity on plant reproduction is extremely scarce. We established communities with 1-5 bee species to test how seed production of a plant community is determined by bee diversity. Higher bee diversity resulted in higher seed production, but the strongest difference was observed for one compared to more than one bee species. Functional complementarity among bee species had a far higher explanatory power than bee diversity, suggesting that additional bee species only benefit pollination when they increase coverage of functional niches. In our experiment, complementarity was driven by differences in flower and temperature preferences. Interspecific interactions among bee species contributed to realized functional complementarity, as bees reduced interspecific overlap by shifting to alternative flowers in the presence of other species. This increased the number of plant species visited by a bee community and demonstrates a new mechanism for a biodiversity-function relationship (''interactive complementarity''). In conclusion, our results highlight both the importance of bee functional diversity for the reproduction of plant communities and the need to identify complementarity traits for accurately predicting pollination services by different bee communities.

Tree phylogenetic diversity promotes host–parasitoid interactions

“…Ideally, those studies would include experimental manipulations of plant MPD, hosts, and parasitoids (sensu [65]) to disentangle the mechanisms behind the bottom-up effect of MPD on host-parasitoid interactions in natural ecosystems.…”

Low functional diversity promotes niche changes in natural island pollinator communities

“…Specifically, a floral niche used by a lost pollinator functional group (or species) can potentially be filled through niche changes in other functional groups [19,20]. Moreover, competition among groups might be relaxed by group diversity loss: certain pollinators exhibit larger niche expansions and/or shifts in communities consisting of a single pollinator functional group than in those consisting of multiple groups [19,20]. Hence, functional complementarity in floral niches may decrease as pollinator functional diversity declines [20].…”

“…lost group, owing to buffering by niche expansions and/or shifts in other groups (figure 1). Second, such niche shifts in the remaining functional groups may indirectly reduce the number of pollinators visiting flowers not associated with the lost group, potentially leading to pollinator limitation [20,24]. However, altered niches in remaining groups may not always fully compensate for the lost pollination function [16,19,20].…”

“…Owing to the usually intimate associations between long-tongued pollinators and flowers with specialized floral organs, such as long corolla tube and spur ( [31,32]; figure 1), declines in long-tongued pollinators can lead to such plants becoming pollinator-limited [16,19,20,33]. However, few studies of natural ecosystems have investigated the impacts of long-tongued pollinator declines and the resulting niche changes on a whole flower community (but see Brosi & Briggs [17] and Kadoya & Ishii [22]).…”

“…Indirect impacts of pollinator loss on the floral community have been examined in experimental communities or simple natural communities [17,19,20,22,23], but these studies may not capture the full scale of changes in complex natural communities with many other pollinator groups that can respond to the reduced abundance of long-tongued species (figure 1). Ideally, these effects would be examined by experimental removal of long-tongued species in a natural ecosystem, but removing multiple native species from a pristine habitat throughout the year is both technically difficult and ethically problematic (e.g.…”