The richness, uniqueness and strength of plant-pollinator interactions at field and landscape scales
We investigated the impact of land-use on plant-pollinator interactions at different scales (field and landscape scales) by comparing the relative effects of land-use (proportion of natural habitat and habitat diversity) at the field-scale (100 m radius) and landscape-scale (500 m radius). Specifically, we tested the effects of land-use at different scales on pollen-insect interaction richness, uniqueness and strength using generalised linear mixed-effects models (GLMMs) with the “glmmTMB” function in the glmmTMB package (Brooks et al.2017). In these models, either interaction richness, uniqueness or strength was the response variable and field-scale land-use (i.e. site where insects were collected, categorical), landscape-scale proportion of natural habitat (at 500 m radius) (continuous) and landscape-scale habitat diversity (Shannon diversity index, continuous) were the fixed effects. We included site identity as a random effect to account for the dependent data structure of multiple sites within land-use categories. We used a Poisson distribution truncated at zero for interaction richness, a Poisson distribution for interaction uniqueness and a Gamma distribution for interaction strength. We did not detect overdispersion in the Poisson models. We also tested for covariance between fixed effects in each model using a modified version of the “vif” function in the car package (Fox et al. 2016). Variance inflation factor values were low (< 3 in all models).