Authors: Bianca Unglaub Jasmin Ruch Marie E Herberstein Jutta M Schneider
Publish Date: 2013/03/08
Volume: 67, Issue: 5, Pages: 785-794
Abstract
A reduced predation risk is considered to be a major adaptive advantage of sociality While most studies are concerned with nonpredatory prey species groupliving predators are likely to face similar threats from higherorder predators We studied the relationship between group size and predation risk in the subsocial crab spider Diaea ergandros by testing predictions from theoretical models including attack abatement as well as the formation of protective retreats In a field survey we found predatory clubionid spiders in 35 of the D ergandros nests and as predicted nest size did not correlate with predator presence In a subsequent laboratory experiment we observed survival probability nest construction activity and feeding behaviour including weight development between groups of different sizes as well as in the absence or presence of a predator Large groups had an advantage in terms of survival and growth compared to smaller groups or single individuals They also built significantly larger nests than smaller groups supporting the idea of protective retreat formation being an adaptive benefit to group living Even though clubionids did attack D ergandros they did not significantly affect overall mortality of D ergandros The feeding experiment showed that spiders fed on a larger proportion of flies in the presence of a predator However these groups gained significantly less weight compared to the control groups indicating that the potential predators not only act as predators but also as food competitors constituting a twofold cost for D ergandrosWe thank Theo Evans for fruitful discussions prior and during the project Moreover we thank Raelene Giffney for help with weighing the spiderlings Andrew P Allen and Stano Pekár for the statistical advice and two anonymous reviewers for constructive comments on the manuscript BU would like to express her special thanks to Michael Zorawski for his support during the entire project BU was funded by the German Academic Exchange Service DAAD through a PROMOS scholarship JR was funded by an International Scholarship of Macquarie University
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