Data from: Facilitation and biodiversity jointly drive mutualistic networks

1. Facilitation by nurse plants increases understorey diversity and
supports ecological communities. In turn, biodiversity shapes ecological
networks and enhances ecosystem functioning. However, whether and how
facilitation and increased biodiversity jointly influence community
structure and ecosystem functioning remains unclear. 2. We performed a
field experiment disentangling the relative contribution of nurse plants
and increasing understorey plant diversity in driving pollination
interactions. Both the presence of nurse shrubs as well as increased
understorey plant diversity increased pollinator diversity and visitation
rates. While nurse and understorey diversity effects on pollinator
visitation rates did not interact, the effects of increasing understorey
plant diversity on pollinator diversity were stronger in the absence than
in the presence of shrubs, meaning that nurse shrubs attenuated the
effects of high understorey diversity and buffered the effects of low
understorey diversity. 3. We also found positive complementarity effects
among understorey species as well as complementarity between nurse plants
and understorey species at high diversity. Results also indicate negative
selection effects, suggesting that species with generally few pollinators
benefit the most in the polyculture, while a species (possibly the nurse
plant) with generally lots of pollinators does not. The corresponding
changes in pollination networks with the experimental treatments were due
to both changes in the frequency of visits and turnover in pollinator
community composition. 4. Synthesis Plant–plant facilitative systems,
where a nurse plant increases understorey plant diversity, are common in
stressful environments. Here, we show that these facilitative systems
positively influence mutualistic interactions with pollinators via both
direct nurse effects and indirect positive effects of increasing plant
diversity. Conserving and supporting nurse plant systems is crucial not
only for maintaining plant diversity but also for supporting ecosystem
functions and services.