KLEPTOPARASITES OR COMMENSALS - EFFECTS OF ARGYRODES-ANTIPODIANUS (ARANEAE, THERIDIIDAE) ON NEPHILA-PLUMIPES (ARANEAE, TETRAGNATHIDAE)

Argyrodes antipodianus is a small kleptobiotic spider that steals prey from webs of the large orb-weaving spider Nephila plumipes, and somet imes removes the web itself. We used experiments in a greenhouse to te st how the presence of the kleptobiont, differences in food availabili ty, and web damage affected fitness of the web owner. After 49 days, N . plumipes with four A. antipodianus on their webs gained 55% less wei ght and relocated their webs 4.5 times as often as spiders with no kle ptobionts. Increased web relocation and decreased weight gain may have resulted from reduced prey levels or from web damage by A. antipodian us. A second experiment demonstrated that hosts gained weight at the f eeding rate used in the first experiment, but not at lower rates. Web relocation rate also varied with feeding rate, but in a non-linear man ner. Web loss was evaluated in a separate experiment, by manually remo ving one-quarter of the web every 5 days for 30 days; however, neither weight gain nor rate of web relocation were affected. We conclude tha t A. antipodianus is a true kleptoparasite that can reduce the growth rate of its host N. plumipes, but that neither food theft nor web dama ge alone explain increased web relocation rates.