Signal design of a sensory exploiter: balancing foraging benefit and predation cost.
In a signal communication system, besides legitimate signalers and receivers, many organisms generate false signals to mimic the important signals the receivers are searching for, and lure the receivers to act in ways that are beneficial to these exploiters. Exploiters play an important role in the signal communication system, but relevant studies are rare. In this study, I investigate how orb-weaving spiders exploit the visual communications between angiosperms and pollinator insects. Appearance of angiosperms in terrestrial ecosystems led to an increase in diversity of insect pollinators. The increase of insect diversity subsequently resulted in the increase of spider diversity, and associated with such phenomenon were evolutionary changes in web-associated hunting behaviors and body coloration. Previous studies show that pollinator insects prefer flowers with certain visual properties, such as symmetry, dark centers, radiating stripes, disruptive patterns and peripheral dots. Recently, the coloration of spiders has been empirically demonstrated to be highly visible to prey and is visually attractive to them. In this study, I focus on how an spider exploiter, the giant wood spider Nephila pilipes, is involved in the visual interactions of angiosperms and insect pollinators. In the field, I used dummies mimicing the body coloration of spiders to test whether manipulating chromatic properties and arrangement patterns of body coloration will affect the prey attraction rate. The results showed that dummies mimicing the real spider lured prey successfully. Changing the arrangement of yellow spots did not significantly affect prey attraction rates and predator attack rates of dummies. Altering the chromatic property of spider body coloration reduced the attractiveness of dummies. These results suggest that chromatic property of spider color signal seemed to be more important than its arrangement pattern. Furthermore, dummies with an increased yellow spot area lured more insects, but they also experienced more predator attacks. Such results indicate that yellow body coloration is an important insect-luring signal for spiders. However, the cost of such a signal is that its intensity is also positively associated with predation risk. Therefore, the current body coloration pattern of N. pilipes might reflect a trade-off between foraging benefit and predation cost.
Updated: Mar-10-2014 01:22:51 (Taiwan, GMT+08:00).