Web decoration is important in mediating foraging site fidelity as well as prey availability and predation risk in an orb-web spider

Animals may consider both biotic and abiotic factors in foraging site choice. Among the biotic factors, food availability and predation risk are two widely reported important factors in determining foraging site fidelity. Their earlier investments, such as those retreat-building species’ efforts in retreats construction, however, have been largely ignored. The orb-web spider Cyclosa monticola constructs a long column of masquerading detritus decoration in its web for predator avoidance purpose. This detritus decoration also functions as a retreat. However, the role of the detritus decoration for its foraging site fidelity is unknown. By manipulating three factors, presence of detritus decoration, prey availability, and predation risk to the spider webs in the field, we show that the self-constructed detritus decoration is as important as prey availability and predation risk in mediating web site fidelity. In addition, the web area also has a significant impact to the foraging site fidelity of the spider, those with larger webs were more likely to leave after being manipulated. However, other factors such as spider body size, decoration length, and rain all have no significant impact. Our study may strengthen the current understanding of the movement and foraging of animals, especially those building retreats.

Methods
Field observations

动物在选择觅食位点时，会同时考量生物与非生物两类因素。在生物因素中，猎物可获得性与捕食风险是两项被广泛报道的、决定觅食位点保真度的关键因子。然而，动物此前的投资行为——例如筑隐蔽所类物种在构筑隐蔽所时付出的努力——却长期被学界忽视。圆网蛛山地尘蛛（Cyclosa monticola）会在其蛛网中构筑一列长条形的伪装性碎屑装饰，用于躲避天敌；该碎屑装饰同时也可作为隐蔽所使用。但这类碎屑装饰对于其觅食位点保真度的作用仍不明晰。本研究通过野外操控三个变量——蛛网是否带有碎屑装饰、猎物可获得性以及蜘蛛面临的捕食风险——开展实验，结果表明：该蜘蛛自行构筑的碎屑装饰，在调控觅食位点保真度方面的重要性，与猎物可获得性及捕食风险相当。此外，蛛网面积也会对该蜘蛛的觅食位点保真度产生显著影响：蛛网面积更大的个体在经操控后更易离开原位点。而蜘蛛体型、装饰长度以及降雨等其他因素则未表现出显著影响。本研究或可加深学界对动物（尤其是筑有隐蔽所的物种）的移动与觅食行为的现有认知。
研究方法
野外观察