Brood chambers of a stem borer beetle modify arthropod functional diversity on its cactus host.

Phenotypic variation in plants induced by biotic stressors can have cascading effects throughout arthropod communities. Habitat modifiers increase habitat complexity, which may promote species diversity and change arthropod species composition. A taxonomic approach to describe arthropod communities together with a trait-based approach might reveal mechanisms behind taxonomic changes and consequences for ecological processes. We previously found that the mistletoe Tristerix aphyllus induces susceptibility in the cactus Echinopsis chiloensis to the stem-borer beetle Xyletomerus sp., a habitat-modifier that drills brood chambers on cactus. Further, the community of arthropods that colonized chambers on parasitized cacti was more diverse and was different in composition compared to that found in chambers of non-parasitized cacti. We do not know whether the effects of brood chambers extend to the whole mistletoe-cactus system and how the arthropod community responds to seasonal phenology of mistletoe. Here we experimentally reduced the number of brood chambers and examined the effects on taxonomic and functional richness and composition, considering mistletoe seasonal phenology. We found a positive relationship between the number of chambers and arthropod species richness, abundance and functional richness. Arthropod taxonomic and functional richness were generally higher at mistletoe flowering compared to fruiting or mistletoe senescence/cactus flowering stages. Species composition varied with chamber number and changed with mistletoe seasonal phenology. Functional composition changed with mistletoe phenology. Functional richness and species richness were positively correlated, yet, functional redundancy is likely to occur. We conclude that cascading effects initiated by mistletoe extends beyond the chamber scale, up to the plant scale. [ABSTRACT FROM AUTHOR]