Fine-scale spatial analysis of two plant-insect interactions: effects of landscape, resource distribution, and other insects

Context Biotic resource exploitation is a critical determinant of species’ distributions. However, it is difficult to quantify resource exploitation patterns through space and time, complicating their incorporation in spatial ecology studies. Therefore, understanding the local drivers of spatial patterns of resource exploitation may contribute to better large-scale species distribution models. Objectives We investigated (1) how the resource exploitation patterns of two trophic interactions (plant-insect) are explained by insect behaviour, resource aggregation, and potential insect-insect interactions. We also analyzed how (2) resource patch size and (3) resource accessibility in a heterogeneous landscape affected host exploitation patterns. Methods We quantified nectar robbing by insects in the genus Bombus (bumblebees) and frugivory by Brachypterolus vestitus larvae (Antirrhinum beetle) on Antirrhinum majus L. (wild snapdragons) in the Pyrenees Mountains, Catalonia, Spain. We tested hypotheses about resource exploitation by integrating spatial analyses at multiple scales. Results Both trophic interactions were aggregated, explained by the aggregation of their resource. At some scales, nectar robbing is more aggregated than the resource. Trophic interaction abundance is proportional to resource patch size, following the ideal free distribution model. Landscape features do not explain the locations exploited. Nectar robbing and frugivory occur together more often than expected. Conclusions Our findings suggest that multiple biotic and ecological spatial factors may simultaneously affect resource exploitation at a local scale. These findings should be considered when developing agricultural projects, management plans and conservation policies.