Periodic Reporting for period 3 - DrivenByPollinators (Driven by mutualists: how declines in pollinators impact plant communities and ecosystemfunctioning)
Reporting period: 2022-09-01 to 2024-02-29
Global environmental change is disrupting mutualisms between organisms worldwide. Recent findings show that pollinator declines can affect plant community composition, but we know little about when such shifts are to be expected, and the impact they have on ecosystem functioning. Plant species composition is the major driver of ecosystem functions. Correlations between plant traits related to pollination and plant traits related to other important functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning if pollinator loss affects plant communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Using a landscape-scale experimental approach combined with observational gradients, mesocosm experiments and modelling, the DrivenByPollinators research programme, for the first time, opens up to empirical investigation the impact of pollinator declines on plant community composition and the plant-mediated impact on ecosystem functioning in real landscapes. The overarching objectives structure the project into workpackages and corresponding research platforms:
(1) Set up a network of long-term research plots in landscapes differing in pollinator abundance to measure the changes in plant reproduction over successive years, and assess experimentally how herbivory and soil fertility mediate these effects.
(2) Explore the individual processes linking pollinators, plant communities and ecosystem functioning using long-term experiments controlling pollinator, herbivore and nutrient availability, focusing on a sample of plant species covering both species dominant in the plot network and a diversity of functional traits.
(3) Assess the context-dependence of pollinator-mediated plant community determination by building and applying models integrating observational and experimental data, and combining with existing spatially-explicit pollinator models to demonstrate the applicability to assess agri-environmental measures.
(1) Set up a network of long-term research plots in landscapes differing in pollinator abundance to measure the changes in plant reproduction over successive years, and assess experimentally how herbivory and soil fertility mediate these effects.
(2) Explore the individual processes linking pollinators, plant communities and ecosystem functioning using long-term experiments controlling pollinator, herbivore and nutrient availability, focusing on a sample of plant species covering both species dominant in the plot network and a diversity of functional traits.
(3) Assess the context-dependence of pollinator-mediated plant community determination by building and applying models integrating observational and experimental data, and combining with existing spatially-explicit pollinator models to demonstrate the applicability to assess agri-environmental measures.
The project implementation during the period covered the start-up phase (September 2019 to May 2020) which included initiating project communication, the successful recruitment of researchers (one Postdoc and two PhD students), field assistants for 2020, preparation of project-adapted internal workflows for handling samples, as well as the set-up of the two empirical research platforms and purchasing consumables. These include in WP1 a network of 18 sites differing in the landscape context (share of arable land-use and composition of non-arable land-use in a 1000m radius around the sites), in which research plots (pollinator reduction and control subplots) have been established for at least the duration of the project (until 2024). In WP2, a cage experiment with 48 cages has been established at a single site, where newly established grassland vegetation is exposed to a full-factorial combination of pollinators, herbivores and nutrient levels (also at least until 2024). In June to September 2020, the first season of data collection on the empirical research platforms was conducted, including plant and insect surveys, seed set, biomass, and plant-insect interactions. From October 2020 to February 2021, laboratory-based work (identification/analysis of insect, plant and soil samples) was conducted, first preliminary analysis and results for the data from 2020 were communicated at a conference, and the second field season (spring-summer 2021) was planned. The second field season was conducted March to September 2022, recording the same data types as above, as well as a campaign to record pollination-related plant traits in WP1 and WP2. From October 2021 to February 2021, in addition to the identification/analysis of insect, plant and soil samples, we quantified the seed production, seed damage and seedling density and composition (from seed traps) from both WP1 and WP2. Work in WP3 has been initiated in 2020 by contributing to an assessment of the transferability of using prior data from crop pollinators (Blasi et al. 2021) and continued development of spatially-explicit models for central-place foragers. The availability of WP1 data has allowed us to start with building of statistical models (pollinator communities and plant-insect interactions). Over the course of 2020 and 2021 a review paper covering the landscape-scale land-use pollinator plant community ecosystem functioning relationships has been written, submitted and reviewed, it is currently prepared for resubmission.
The main results achieved so far support the effectiveness of the experimental treatments (WP1: reduced pollinator access; WP2: large differences in pollinator visitation between pollinator treatments, differences in herbivore densities) as well as effects of the landscape gradients in WP1 that are pollinator-group specific (bumblebees showing different patterns than solitary bees, hoverflies and other flies) and differ between pollinators and herbivorous insects. Analyses of effects on flower visitation and on plant reproductions (seed production, seed damage, seedling density and composition) are ongoing.
The main results achieved so far support the effectiveness of the experimental treatments (WP1: reduced pollinator access; WP2: large differences in pollinator visitation between pollinator treatments, differences in herbivore densities) as well as effects of the landscape gradients in WP1 that are pollinator-group specific (bumblebees showing different patterns than solitary bees, hoverflies and other flies) and differ between pollinators and herbivorous insects. Analyses of effects on flower visitation and on plant reproductions (seed production, seed damage, seedling density and composition) are ongoing.
In assessing conditions under which a trait-mediated cascade linking pollinators, plants and ecosystem functions emerges, we are addressing a major gap in our understanding of community and ecosystem ecology. The study of pollinator effects on plants has largely been confined to impacts on single individuals, or single-species populations. DrivenByPollinators addresses community-level impacts and ecosystem functioning with landscape-scale studies and mesocosms experiments, supported by modelling spatially-explicit plant-herbivore-pollinator interactions that will help validate the findings beyond the case-study limits.