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Daily catch of prey of A. bruennichi compared to other orb-weavers

My estimate of the daily catch of appro


90 mg prey web

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d a y - 1 f o r A . b r u e n


nichi is comparable to that of Robinson & Robinson (1970) for the tropical orb- weaver Argiope argentata in Panama. These authors estimated that an adult

female A. argentata caught, on average, 1.63 larger-sized prey web

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11 -- which translates to 89 mg (fresh weight) prey web day (overall mean of a

one year census). Robinson & Robinson (1970) may have overlooked some of the smallest insects in their prey census, as they themselves admit. But it is known from other field work in Panama that tiny insects comprise, on average, roughly 10% of the total prey biomass of A. argentata (Nentwig 1985). Taking this into account it can be estimated that the average catch of prey biomass of adult female A. argentata in Robinson & Robinson's study may have been



1 0 0 m g w e b - 1 d a y

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if tiny prey were included


It can be estimated that the average daily prey catch of 90100 mg by an adult female Argiope equals approx. 20% of the spider's body weight, assum- ing a spider weight of 400500 mg (see data on spider weights by Robinson & Robinson 1970; Carrel & Heathcote 1976; Friedel & Nentwig 1989). Kajak (1971), wo surveyed 950 webs in Polish grasslands over a two year period, found that the average daily prey catch of web-building spiders equalled approx. 18% of the spider's body weight. From a prey catch of 90100 mg w e b - 1 d a y - 1 a n A r g i o p e c a n i n g e s t a t l e a s t 4 5 5 0 m g f o o d s p i d e r - 1 d spiders' energy requirements thereby being fully met, evidenced by high reproductive success (compare Robinson & Robinson 1970; Bradley 1993; Leborgne & Pasquet 2005; Nyffeler unpubl.). A food ingestion rate of 4550 a y - 1 , t h e m g s p i d e r - 1 d a y - 1 e q u a l s a p p r o x . 1 0 % o f t h e s p i d e r ' s b o d y w within the range of energy requirement estimates known for other spider taxa (see Foelix 1996). e i g h t w h i c h i s

The similarity of the daily catch of prey of A. bruennichi (this study) and A. argentata (study by Robinson & Robinson 1970) obviously reflects the fact that these are two similar-sized orb-weavers (see Hormiga & al. 2000) with similar energy requirements. In several studies it was found that the average prey capture rate of orb-weavers of similar size did not differ significantly if different locations were compared (e.g., Higgins 1987; McNett & Rypstra 1997). This was demonstrated beautifully by Higgins (1987) who compared prey capture of the orb-weaver Nephila clavipes in two different habitat types in Texas. Spiders at the two locations differed significantly in the types of prey captured and the contribution of each prey type to the total prey bio- mass. Despite these differences, the number of prey and the estimated weight of prey captured by the spiders was not different between the two locations


Martin Nyffeler

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