The proportion of insect taxa carrying pollen and the taxonomic richness of pollen carried
To examine the effect of land-use intensity on the average abundance and proportion of pollen carrying insects in different land-use types and pollen richness present in each land-use and carried by different insect taxa, we constructed generalized linear mixed effects models using thelme4 package (Bates et al. 2014). In these models, either average abundance of each of the four common insect orders, proportion of insect individuals carrying pollen or pollen richness on those insect individuals was the response variable and land-use (categorical) was the fixed effect. For the pollen carrying and pollen richness models, insect order was also included as a fixed effect. We included month as a random effect to account for repeated sampling across the three time periods. All models were validated by examining the distribution of residuals plotted against fitted values, and we set a negative binomial distribution to account for overdispersion where necessary (Zuuret al. 2009). We ran separate models for each of the four most abundant insect orders (Coleoptera, Diptera, Hymenoptera and Lepidoptera), which represented 93.5% of pollen carriers and 94.5% of all sampled individuals. The sample sizes of the remaining taxa were too small for further analyses. Post-hoc multiple pairwise comparisons between land-uses and insect orders were tested using estimated marginal means (EMMs, using the emmeans package, Lenth 2018). EMMs are generated using the fitted model to make predictions over a grid of predictor combinations in order to assess the effects of individual factors. These predicted differences in abundance of individuals and proportion of pollen carrying insects from each of the four dominant insect orders between land-uses, and differences in average pollen richness by land-use type and insect order. We estimated the significance of differences between terms, using Tukey’s HSD (honestly significant difference) test with false discovery rate (FDR) corrected P values (at α = 0.05) (Verhoeven et al.2005).