Trait‐mediated Effects on Flowers: Artificial Spiders Deceive Pollinators and Decrease Plant Fitness

Abstract

Although predators can affect foraging behaviors of floral visitors, rarely is it known if these top-down effects of predators may cascade to plant fitness through trait-mediated interactions. In this study we manipulated artificial crab spiders on flowers of Rubus rosifolius to test the effects of predation risk on flower-visiting insects and strength of trait-mediated indirect effects to plant fitness. In addition, we tested which predator traits (e.g., forelimbs, abdomen) are recognized and avoided by pollinators. Total visitation rate was higher for control flowers than for flowers with an artificial crab spider. In addition, flowers with a sphere (simulating a spider abdomen) were more frequently visited than those with forelimbs or the entire spider model. Furthermore, the presence of artificial spiders decreased individual seed set by 42% and fruit biomass by 50%. Our findings indicate that pollinators, mostly bees, recognize and avoid flowers with predation risk; forelimbs seem to be the predator trait recognized and avoided by hymenopterans. Additionally, predator avoidance by pollinators resulted in pollen limitation, thereby affecting some components of plant fitness (fruit biomass and seed number). Because most pollinator species that recognized predation risk visited many other plant species, trait-mediated indirect effects of spiders cascading down to plant fitness may be a common phenomenon in the Atlantic rainforest ecosystem.

Predator crypsis enhances behaviourally mediated indirect effects on plants by altering bumblebee foraging preferences

“…We can therefore conclude that they are just avoiding flowers harbouring spiders (e.g. as in Gonçalves-Souza et al 2008). By contrast, bees encountering cryptic spiders started to avoid safe yellow flowers towards the end of the training phase ( figure 2c).…”

“…Gonçalves-Souza et al 2008), but can extend to an entire population of flowers with similar appearance (typically of the same species). In particular, we found that even though bumblebees are able to accurately detect and avoid cryptic spiders ( Ings & Chittka 2008), they chose to avoid all flowers resembling those that harboured cryptic spiders when alternative safe flower species were available.…”

“…reduction of pollinator densities through predation (Dukas 2005;Knight et al 2006). However, there is some evidence that predators can have non-consumptive indirect effects on plant fitness (Louda 1982;Gonçalves-Souza et al 2008). Gonçalves-Souza et al (2008) showed that pollinators tended to avoid flowers that contained visual predator cues (model crab spiders).…”

“…However, there is some evidence that predators can have non-consumptive indirect effects on plant fitness (Louda 1982;Gonçalves-Souza et al 2008). Gonçalves-Souza et al (2008) showed that pollinators tended to avoid flowers that contained visual predator cues (model crab spiders). As a result, flowers bearing model predators became pollen-limited and suffered from poorer seed set and reduced fruit biomass.…”

Background colour matching by a crab spider in the field: a community sensory ecology perspective

“…However, there is a lack of knowledge about the role of the chromatic and achromatic crypsis in the prey capture rate and survival rate against birds. Indeed, despite the growing number of studies using crab spider-prey interactions, there is not yet any evidence, for any prey, that decreasing chromatic and/or achromatic contrasts provides the spider with a benefit in terms of predation efficiency (Gonçalves-Souza et al, 2008;Yokoi and Fujisaki, 2009;Brechbühl et al, 2010a; Brechbühl et al, 2010b). These studies, however, revealed that the way prey behave in response to a crab spider is not only species specific but also individual specific.…”