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Unformatted text preview: Size dependent occurrence of different types of web decorations and a barrier web in the tropical spider Argiope argentata (Fabricius 1775) (Araneae Araneidae) G ABRIELE U HL 1 Universitt Bonn Institut fr Zoologie, Abteilung Neuroethologie, Endenicher Allee 11-13, D-53115 Bonn, Germany Received 7 February 2007, accepted 11 September 2007 Web decorations occur in a wide range of spiders and are con- structed using various materials such as leaves, carcasses or silk. Silk decorations, so called stabilimenta, have attracted most attention since they are an obvious feature of the webs of several orb web species and are highly visible to the human eye. Silk decorations are mainly disc- shaped, linear or cruciate. The functions of silk decorations remain a controversial issue. More comparative and experimental work is needed, apart from the assessment of environmental prerequisites for the con- struction of web decorations. I collected data on the occurrence and type of silk decorations, along with a measure of body size, for a population of the tropical spider Argiope argentata (Fabricius 1775) in the Bijagual biological reserve in Costa Rica. In addition, I recorded whether a barrier web was present or not. I found that whether a discoid or cruciate deco- ration was produced significantly depended on body size: smaller spiders constructed mainly discoid decorations whereas larger spiders construct- ed at least part of a cruciate decoration or none at all. Barrier webs pre- dominantly occurred in smaller spiders and were rarely present in larger spiders. The data contradict those of an earlier census performed on the Galapagos Islands, which suggested that the difference in biotic and abi- otic environmental parameters not only causes differences in variability of web building behaviour but near complete reversal. KEY WORDS: St Andrews cross spider, stabilimentum, web decoration, bar- rier web, ontogenetic changes, plasticity, predator-prey rela- tionship. Correspondence: PD Dr. Gabriele Uhl, Phone: 0049 (0)228 73 5557, Fax: 0049 (0)228 73 5556 (E-mail: email@example.com). Tropical Zoology 21: 97-108, 2008 98 G. Uhl INTRODUCTION So called web decorations or stabilimenta are interesting features of webs of a wide range of orb web spiders. Spiders can decorate their web by including leaves, pieces of plant material, leftovers from previous meals, egg sacs or only silk material, which in one or the other combination was suggested to camouflage the spider (H ERBERSTEIN et al. 2000a, E BERHARD 2003). However, decorations that consist only of silk have attracted most attention. Silk decorations occur in at least 22 genera (S CHARFF & C ODDING- TON 1997) and are arranged in various patterns on the web, mostly occurring as cruciate, linear, discoid, spiral, or irregular silk material. The function of these structures has remained the subject of considerable controversy with little consensus. The functions best studied are prey attraction, protection little consensus....
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