Pollinators, not predators, affect florivore survival in Cirsium arvense (Asteraceae) reveals an experiment based on Structural Causal Modelling

Predators can affect plant fecundity by interfering with plant-pollinator or plant-herbivore interactions. While these indirect effects are usually studied in isolation, new insights can be obtained by studying multiple interactions between predators, pollinators, herbivores, and plants within a single framework. Here we applied this approach to understand the cascading effect of predatory insects on the fecundity of Cirsium arvense via their interaction with pollinators and florivores. This study focused on endophagous florivores, specifically on pre-dispersal seed predators. We used an integrated approach of combining simulation modelling with field experimentation. We first designed our experiment and then validated it through a generative simulation model, using sensitivity analysis to assess the expected statistical power of our experimental design. The sensitivity analysis confirmed that our experiment was robust enough to detect weak effects. Despite this, our field experiment did not reveal any cascading effects of predators on plant fecundity. However, we discovered that florivores in this system depend on pollinators to complete their life cycle, highlighting an overlooked link between these interactions. Our study demonstrates the usefulness of simulation models in designing ecological studies and emphasises the need to consider indirect effects in multitrophic systems.