design for rare but life-saving catches

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doi: 10.1098/rspb.2005.3114 , 1587-1592 272 2005 Proc. R. Soc. B Samuel Venner and Jérôme Casas Spider webs designed for rare but life-saving catches Supplementary data ml http://rspb.royalsocietypublishing.org/content/suppl/2009/02/12/272.1572.1587.DC1.ht "Data Supplement" References http://rspb.royalsocietypublishing.org/content/272/1572/1587.full.html#related-urls Article cited in: http://rspb.royalsocietypublishing.org/content/272/1572/1587.full.html#ref-list-1 This article cites 27 articles, 2 of which can be accessed free Email alerting service here right-hand corner of the article or click Receive free email alerts when new articles cite this article - sign up in the box at the top http://rspb.royalsocietypublishing.org/subscriptions go to: Proc. R. Soc. B To subscribe to This journal is © 2005 The Royal Society on November 7, 2010 rspb.royalsocietypublishing.org Downloaded from
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Spider webs designed for rare but life-saving catches Samuel Venner 1, * and Je ´ro ˆme Casas 2 1 Laboratoire de Biome ´trie et Biologie E ´ volutive, Universite ´ Claude Bernard—Lyon 1, UMR CNRS 5558, 43 Boulevard du Novembre 11 1918, 69622 Villeurbanne Cedex, France 2 Institut de Recherche en Biologie de l’Insecte, Universite ´ Franc ¸ois Rabelais, IRBI UMR CNRS 6035, Parc Grandmont, 37000 Tours, France The impact of rare but positive events on the design of organisms has been largely ignored, probably due to the paucity of recordings of such events and to the difficulty of estimating their impact on lifetime reproductive success. In this respect, we investigated the size of spider webs in relation to rare but large prey catches. First, we collected field data on a short time-scale using the common orb-weaving spider Zygiella x-notata to determine the distribution of the size of prey caught and to quantify the relationship between web size and daily capture success. Second, we explored, with an energetic model, the consequences of an increase in web size on spider fitness. Our results showed that (i) the great majority of prey caught are quite small (body length less than 2 mm) while large prey (length greater than 10 mm) are rare, (ii) spiders cannot survive or produce eggs without catching these large but rare prey and (iii) increasing web size increases the daily number of prey caught and thus long-term survival and fecundity. Spider webs seem, therefore, designed for making the best of the rare but crucial event of catching large prey. Keywords: orb-web spider; web efficiency; web size; web evolution; rare events; large prey 1. INTRODUCTION Rare but crucial events may shape traits in many organisms. Most studies that have been carried out have examined rare events of negative impact. For example, seashore organisms adapt their size, body shape and their attachment forces to rare waves of unusually large amplitude ( Gaines & Denny 1993 ; Denny 1995 ). The whole concept of a ‘safety factor’ in plant and animal biomechanics refers to these rare events, which can have devastating effects ( Friedland & Denny 1995 ; Niklas 1997 ). In contrast, the impact of rare but positive events
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