Ecological role of a flower-dwelling predator in a tri-trophic interaction in northwestern Patagonia

Abstract

Flower-dwelling predators may play several ecological roles depending on their effects on the reproductive success of the plants that they use to forage. However, tri-trophic interactions often are context-dependent highlighting the importance of assessing both the overall top-down effect on plant fitness and predator behavioral and physiological attributes that shape that outcome. We studied the effect of the flower-dwelling crab spider Misumenops pallidus on the perennial herb Anemone multifida in a low-thicket in Northwestern Patagonia. We measured pollinator visitation frequency, florivory rate, plant fitness, spider abundance, and spider's physiological (e.g. camouflage) and behavioral attributes (e.g. host selection, fidelity) that aid to define its possible ecological role. Misumenops pallidus showed a generalist diet (mostly pollinators), camouflage strategies, and intraspecific selection for plants bearing higher number and longer trichomes. Additionally, it displayed host-fidelity with long periods of permanence in the selected host plant, occupying ∼25% of plant population. However, the presence of these spiders did not affect pollinator visitation rate, florivory or plant fitness, indicating a commensalism role. Our findings suggested that the asymmetric benefit in this plant-spider association may be attributed to a combination of factors. In particular, the low-to-moderate spider abundance, generalist diet and cryptic camouflage; all of which weaken the top-down effect on pollinators and plant fitness, especially whenever ecological redundant pollinators are present. However, temporal and/or spatial variation on spider population might enhance this asymmetric benefit for the spider, potentially changing its role from commensalism to antagonism.