Spiders: Webs, Behavior, and Evolution

Spiders: Webs, Behavior, and Evolution

Language: English

Pages: 508

ISBN: 0804712034

Format: PDF / Kindle (mobi) / ePub

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some combination of food abundance and the thermal environment. Spiders in less stressful habitats may judge web sites either by the total number of prey or, more probably, by the total biomass of prey. If total biomass is the criterion, the occasional occurrence of large prey at a web site will be the determining factor in judging the site (Olive 1980). Studies of the decision rules that different species employ in leaving web sites will be an invaluable addition to our knowledge of the movement

by the adults; and because juveniles are present in the fall, when temperatures are cooler and insect numbers high following the summer rains, they do not require the presence of the other features, all of which have been shown to be important to the fulfillment of the physiological and prey-availability requirements of the adults (Riechert and Tracy 1975). The depressions and shrubs used as web sites, and the litter that may be present at both types of sites, have important effects on spider

and webs with large amounts of sticky line (Nephila clavipes). The relative weights of the two types of line are not known, however. In a few cases the diameters of sticky and nonsticky lines have been measured; e.g., Denny (1976) found that in the webs of Nuctenea sclopetaria the sticky fibers have an average diameter of 1 jjim and the radial fibers an average diameter of 1.9 |xm. However, the balls of sticky material are not included in these measurements, and thus the relative costs of the two

webs of conventional aradiffer from that em- seems to Fig. 5.6. usually starting arrows method of construction, and/or function of webs of four genera in the web of Poecilopachys australasia. Viscid lines were spun from the outside in, on R6 but occasionally on R$. Each was spun in the direction indicated by the Structure, Cyrtarachneae. in at a: most a half circle, i.e., never extending around Ri. As indicated by the arrows, the Webs are approximately 80 cm in diamweb of

rarely horizontal; they were usually inclined or nearly vertical (Marples 1962; pers. obs.). This was also true of webs of Philoponella sp. B and P. undulata that were in commensal associations with other web builders. Philoponella republicana orbs in colonies were most often cies, culates inclined at angles of 40 to 6o° (Fig. 6.10). Within colonies, spiders often changed the inclination, height above ground, and compass orientation of their orbs from day to day (Fig. 6. 1 1). This suggests

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