The role of body shape and edge characteristics on the concealment afforded by potentially disruptive marking
Section snippets
Experimental Protocol
A Microsoft Visual Basic Express® 2008 (Microsoft Corp., Seattle, WA, U.S.A.) program presented cryptic moth targets superimposed on photographs of trees on a computer screen to volunteer human subjects (Webster, Callahan, Godin, & Sherratt, 2009). All participants were visitors to Carleton University's Maxwell MacOdrum Library, where the testing took place. Computer monitors (1900 × 1200 pixels) were rotated to a portrait orientation to display high-resolution grey-scaled tree images (1600 × 800
Experiment 1
We observed a significant main effect of moth target coloration (presence/absence of edge-intersecting patches) on both target survivorship (Table 1, Fig. 3a) and target search time (Table 1, Fig. 3b). Therefore, the presence of edge-intersecting patches is associated with heightened survivorship and, of those targets that were discovered, a longer search time before detection. There was also a significant main effect of boundary visibility on both moth target survivorship (Table 1, Fig. 3a)
Discussion
Our study builds on the body of evidence that edge markings on prey affect their rate of detection by visually hunting predators (Cuthill et al., 2000; Cuthill et al., 2005; Cuthill & Székely, 2009; Fraser et al., 2007, Merilaita and Lind, 2005, Schaefer and Stobbe, 2006, Stevens et al., 2006, Stevens et al., 2009). However, it remains uncertain whether edge markings on prey increase their concealment through their effect on disrupting edge detection or through some other visual or cognitive
Acknowledgments
We are very grateful to the staff of Carleton University's Maxwell MacOdrum Library for their hospitality in hosting our human-predator experiments and to the students who participated in these experiments. All authors designed the experiment and were involved in writing the manuscript. R.J.W. ran the experiment and performed the analysis. This research was supported by Discovery grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to J.-G.J.G. and T.N.S. We
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