UBC Theses and Dissertations
Aspects of the feeding ecology of the garden cross-spider, Araneus diadematus Clerck Smith, Risa Barbara
A field study on the feeding ecology of juvenile cross-spiders confirmed the work of other researchers that "boom and bust" best describes the availability of prey for these spiderlings; most of the Araneus diadematus Clerck webs observed captured no prey but occasionally prey catches were very high. During the "bust" phases of prey availability cross-spiderlings were adept at switching to alternate food sources like the microorganisms that are filtered out of the air by their sticky orb-webs. This study established, for the first time, that spiderlings are able to gain substantial nutrition from this aerial plankton by eating it when they consume their old webs. Birch pollen, Betula papyrifera, lengthened the lifespan of both second and third instar spiderlings. Feeding on birch pollen also resulted in an increased frequency of webspinning for second instars and a decline in the number of 12-hour intervals required to spin a new web. Fungous spores, Cladosporium herbarum, however, provided no nutritional value and may have been deleterious. Third instar spiderlings feeding on fungus spun less frequently than both the pollen-fed and starving groups. During the "boom" phases of prey availability a functional response of cross-spiderlings was their ability to respond to increased prey density, as determined in the laboratory experiments. When an hymenopterous parasitoid Aphidius nigripes, was the prey species hungry spiderlings with no predatory experience exhibited an exponential functional response curve. However, once they had a day of capturing prey they responded with a Type 2 response. When an aphid, Macrosiphum euphorbiae, was offered as the prey species predatory experience did not have an effect and the spiderlings exhibited a Type 2 response.
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