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Stabilimenta attract or camoflauge

Stabilimenta attract or camoflauge - Behavioral Ecology Vol...

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Behavioral Ecology Vol. 10 No. 4: 372–376 Do stabilimenta in orb webs attract prey or defend spiders? Todd A. Blackledge and John W. Wenzel Department of Entomology, Ohio State University, Columbus, OH 43210, USA Orb-weaving spiders are ideal organisms for the study of conflict between behavioral investments in foraging and defense because their webs provide physical manifestations of those investments. We examined the impact of including stabilimenta, designs of bright-white noncapture silk, at the center of orb webs for foraging and defense in Argiope aurantia. Our findings suggest that stabilimentum building is a defensive behavior, supporting the ‘‘web advertisement’’ hypothesis that the high visibility of stabi- limenta can prevent birds from flying through webs. Yet, spiders often do not include stabilimenta in their webs, indicating that a serious cost is associated with them. We also show, through comparison of paired webs with and without stabilimenta, that stabilimenta reduce the prey capture success of spiders by almost 30%. This demonstrates the potential impact that defensive behaviors of spiders can have on their foraging success and suggests that much of the variation in stabilimenta may be accounted for by a cost–benefit trade-off made when including stabilimenta in webs. Key words: aposematic signal, Argiope, foraging–defense trade-offs, predator–prey, silk, spider webs. [Behav Ecol 10:372–376 (1999)] C onflict between foraging and predator avoidance can have a profound impact on the behavior of organisms (Lima and Dill, 1990; Sih, 1980; Stephens and Krebs, 1986). Animals may forage in lower energy patches that have re- duced risks of predation (Gilliam and Fraser, 1987; Holomuz- ki, 1986; Lima, 1985; Lima et al., 1985) or engage in defensive behaviors that reduce their foraging efficiency within patches, such as vigilance or hiding (Rothley et al., 1997; Schmitz et al., 1997; Sih et al., 1992; Skelly, 1995). Ultimately, this conflict results in a suite of foraging and defense strategies, each of which may be selectively advantageous in different environ- ments. This may lead to selection for the ability of organisms to actively manipulate the trade-offs they make in changing environments (Rothley et al., 1997; Turner, 1997). Before the adaptive value of varying strategies in different environments can be studied, it is essential to identify the costs and benefits of the behaviors when organisms adopt those strategies. Orb-weaving spiders provide an ideal model for the study of conflict between behavioral investment in foraging and de- fense because their webs are physical manifestations of their behaviors. The orb web is clearly a tool used in foraging (Eberhard, 1990), but the sticky silk and additional silk struc- tures such as barrier webs can also serve as defenses against predators (Cloudsley-Thompson, 1997; Edmunds and Ed- munds, 1986; Higgins, 1992; Rayor and Uetz, 1990; Tolbert, 1975). Unlike the transient behavioral trade-offs between for- aging and defense made by animals engaging in vigilance or hiding, making a web is unique because the trade-off it rep- resents is constant over the course of a single day. Yet spiders
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