Differences facilitating the coexistence of two sympatric, orb-web spiders, Argiope aurantia Lucas and Argiope trifasciata (Forskal) (Araneidae, Araneae)
Differences facilitating the coexistence of two sympatric, orb-web spiders, Argiope aurantia Lucas and Argiope trifasciata (Forskal) (Araneidae, Araneae)
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Date
1977
Authors
Taub, Marilyn Lorraine
Advisor
Morse, Douglass H.
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Abstract
Two closely-related, sympatric, orb-web spiders, Argiope aurantia
and Argiope trifasciata, take prey which differ in size. In accordance
with the often-assumed direct relationship between the size of predators
and their prey, A. aurantia is larger than A. trifasciata at any
single point in time, largely a result of their asynchronous reproductive
cycles. The ratio of their sizes exceeds the 1.28 proposed by Hutchinson
(1959) for coexistence. Vertical and horizontal differences in their
use of the microhabitat also occur and may further reduce the overlap
in their use of food or reduce the frequency of interspecific interactions.
In this study, vertical stratification of webs occurred only late in
the season, with A. aurantia higher than A. trifasciata. These results
contrast with those of Enders (1974), probably due to different densities
of the two species in our study areas.
Experiments show that the differences in the size of prey taken
by these Argiope spiders were due, in part, to dissimilarities in the
filtering properties of their webs and to differences in the ability of
the two species to capture prey of the same relative size. However,
the differences were mainly due to the spiders' rejection of a large
and different portion of the available prey.