Spider predation on floral visitors and herbivores, balance between mutualism and antagonism

Abstract

Spiders-plant interactions are usually complex and affect their host plants in multiple ways. The lynx spider Peucetia viridans camouflages to hunt flower visitors and herbivores potentially reducing the levels of herbivory and reproduction of their host plant. Plus, these green spiders are usually associated with plant species presenting trichomes, which usually facilitate the spider predation. We determined the balance of this double interaction on the forb Ruellia nudiflora in a dry forest of Costa Rica. In three different sites we performed an experiment changing the spider color to red to determine whether the increment on the spider detectability affects pollinators visitation frequency. We also estimated spider, pollinators and herbivores abundance and the levels of herbivory, trichomes density and fruit set. The presence of the spider was not associated to a decrease in pollinators visitation or fruit set. Spiders were associated to plants with low trichomes density. Herbivory was higher in plants with spiders than in plant without them, however, plants with low herbivory level and without spiders presented higher trichomes density. Sites differed in their assemblages of pollinators and herbivores but this did not affect the interactions studied. This is the first study showing that the spider P. viridans is associated with plants of the same species with low trichome density. If this spider affects pollinators visitations, the adaptive value of trichomes would be double; they reduce herbivory and repel the presence of pollinators predators. These results highlight the relevance of studying both mutualistic and antagonistic interactions to determine their relative importance.