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cannibalism did not significantly increase the fitness of adult female A. bruen- nichi: neither the number of clutches, nor clutch size or hatching success were affected by consumption of males. Araneae composed an insignificant per- centage of the total prey biomass of A. bruennichi in this study (Tab. 3) and in other studies (Becker 1982; Nentwig 1985; Malt 1996a; Szymkowiak & al. 2005; Ludy 2007).

Daily catch of prey

The rate of predation upon larger-sized prey (>3 mm in length) on three con- secutive days is presented in Tab. 3. The table shows that, on average, 1.09

l a r g e r - s i z e d p r e y w e b

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w a s c a p t u r e d . T h i s v a l u e i s a n u n d e r e s t i m a t e

due to the fact that only larger-sized insects have been recorded in Tab. 3. Appart from larger-sized prey, some tiny insects (dipterans, aphids and thrips of 13 mm lenth), each weighing 12 mg, are regularly entangled in the webs. Large orb-weaving spiders tend to ignore such tiny insects as food (which is in agreement with foraging theory) and many researchers came to the con- clusion that exclusively the larger-sized insects trapped in the webs should be considered to be prey (e.g., Robinson & Robinson 1970, 1973; Uetz & al. 1978; Murakami 1983). [Some of the tiny insects ignored by the adult female orb-weavers are removed (eaten) by conspecific males that enter female webs during the reproductive periode (Becker 1982; Bradley 1993) and/or by theridiid kleptoparasites that habitually invade large orb-webs in the more southern areas of the globe (e.g., Vollrath 1979; Higgins 1987; Grostal & Walter 1997; Kerr 2005).] According to Nentwig (1985, 1987) the tiny insects belong to the spiders' diet, too. He stated that the tiny insects caught in orb- webs are often too weak to free themselves; they die undetected and remain attached to the web. Orb-weaving spiders such as A. bruennichi which rebuild their web daily and eat the old silk in order to recycle the web proteins, also eat these attached small insects (Peakall 1971; Nentwig 1987; Malt 1996a). Though tiny insects were not recorded in my prey census (see above), the cap- ture rate of prey of all sizes can be estimated based on Tab. 3, if the average ratio of the numbers of large-sized to small-sized prey caught in the webs is known. The average ratio of the number of larger-sized to small-sized prey caught by the webs of adult female A. bruennichi was approx. 20% : 80% (based on a series of prey collections with a total of >900 prey items), sug- gesting that the total capture rate (including tiny prey) may have been 5 x 1.01 p r e y w e b - 1 d a y - 1 = a p p r o x . 5 p r e y w e b - 1 d a y - 1 . I n a m o s t r e c e n t G e r study, Ludy (2007) monitored adult female A. bruennichi webs continuously m a n f i e l d


Martin Nyffeler

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