Arthropods in several orders use traps to capture prey. Such trap-building predators expend most of their foraging energy prior to any prey contact. Nevertheless, relative investments in trap construction and actual prey capture may vary among trap builders, and they are likely to face a trade-off between building very effective but energetically costly traps and building less effective traps requiring faster reaction times when attacking prey. We analysed this trade-off in a field experiment by comparing the prey capture behaviour of four different sympatric web-building spiders (Araneae: Araneidae, Nephilidae, Tetragnathidae, Theridiidae) with the retention times of five different prey types in the webs of these spiders. Retention times differed greatly among webs and among prey types. The vertical orb webs retained prey longer than the horizontal orb web and the sheet web, and active prey escaped more quickly than less active prey. Among spiders with orb webs, the spider with the web that retained prey for the shortest time was the fastest to capture prey, thus confirming the expected trade-off between building long-retaining webs and attacking slowly versus building short-retaining webs and attacking more rapidly. The sheet web, however, neither retained prey for an appreciable period of time nor facilitated rapid prey capture. We suggest that this low capture effectiveness of sheet webs is compensated by their lower maintenance costs.

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We tested the hypothesis that coffee systems with organic management have higher spider diversity by comparing a control (rainforest area) and two coffee systems, one with organic and the other with conventional management. Spiders were sampled every two weeks over three months during the dry season and three months during the rainy season in 2000. Spider alpha diversity was analyzed using Shannon and Simpson indices. We also used the Cody index for beta diversity and cluster analysis for analyzing changes in species abundance hierarchies. 2261 individuals were collected (including juveniles and adults) representing 20 families, 56 genera and 97 species. In most cases the alpha diversity indices showed no relation between management gradient and spider diversity. When compared across seasons, spider diversity differed significantly only in organic management. Species turnover among the three sites (Cody index) was highest between the two coffee farms but not so clearly in the dry vs. rainy season; the conventional management shared the fewest species with the forest. Cluster analysis showed changes in abundance hierarchy related to management type. Our results did not support the proposed hypothesis of a direct positive correlation between management gradient and alpha spider diversity. In contrast, beta diversity showed that management and seasons influenced species composition.

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