EVOLUTION OF PREDATOR-PREY SYSTEMS - SPIDER FORAGING PLASTICITY IN RESPONSE TO THE VISUAL ECOLOGY OF PREY

Nephila clavipes, a large, orb-spinning spider, is distributed through out the Tropics and Subtropics and forages in a variety of forest, non forest, and edge habitats. In this article we show that N. clavipes sp in silks of varying spectral properties in response to both the intens ity and spectral composition of its light environment. In bright light characterized by broad irradiance spectra, N. clavipes produce a comp lex of yellow pigments that absorb light of wavelengths less than 500 nm, making their webs appear golden. In dim light and where wavelength s less than 500 nm have been eliminated, N. clavipes produce pigments that reflect light between 400 and 500 nm, making their webs appear wh ite. Because yellow serves as a superstimulus attracting both herbivor ous and pollinating insects, yellow silks may attract prey to spider w ebs. By training Trigona fluviventris, a stingless bee commonly fed on by N. clavipes, to forage at an artificial feeding site, we found tha t silk color affects insect response in two ways. First, yellow webs a ttract and intercept T. fluviventris more frequently than webs of any other color. Second, even after being intercepted once, T. fluviventri s have difficulty learning to avoid yellow webs. We propose that N. cl avipes has evolved a foraging behavior that makes use of the color cue s insects seek while foraging and that the broad distribution of N, cl avipes results from the spiders' ability to adjust the reflectance pro perties of its silks relative to its local light environment, allowing spiders to make use of whatever local populations of prey are most ab undant.