|dc.contributor.author||Whitney, Kenneth D
Spiders are known to influence plant fitness, and vice versa. Yet, it has not
been appreciated that these facultative relationships can be mutualistic. I examined the
interaction between Phryganoporus candidus, a subsocial Australian spider, and the extrafloral
nectary-bearing shrub Acacia ligulata to explore variability in mutualistic interactions
over a three-year period. Spiders enhanced seed production by reducing seed predation
by heteropterans, wasps, and weevils. Because spider colonies occupy only a fraction
of a plant’s volume, average benefits ranged from 0.4 to 6% increases in whole-plant seed
production. These benefits were strongest in years of low seed production, suggesting that
spiders may buffer plants against female reproductive failure. To evaluate benefits for
spiders, I established experimental spider colonies on three common hosts. Spider performance
(persistence and prey capture rates) on live A. ligulata and live hopbush Dodonaea
viscosa exceeded that on dead acacia, suggesting that live hosts are more beneficial than
dead hosts. Stable-isotope analyses demonstrated that colonies living on the three hosts
differed substantially in diet, providing a possible mechanism for the observed differential
suitability of hosts. However, the analyses were unable to establish conclusively that A.
ligulata extrafloral nectar was an important reward for spiders. Variability in the A. ligulata–
P. candidus system suggests that plant–spider associations, like other facultative protection
relationships, likely vary along a continuum from antagonism to mutualism.
EPA STAR Fellowship
and the Center for Population Biology (UC Davis).
Ecological Society of America
density-mediated indiredt effects
Experimental evidence that both parties benefit in a facultative plant-spider mutualism
Whitney, Kenneth D. "Experimental evidence that both parties benefit in a facultative plant-spider mutualism." (2004): http://hdl.handle.net/1911/21689.