Varying benefits of generalist and specialist camouflage in two versus four background environments

Abstract

Background-matching camouflage is a well-established strategy to reduce detection, but implementing this on heterogeneous backgrounds is challenging. For prey with fixed color patterns, solutions include specializing on a particular visual microhabitat, or adopting a compromise or generalist appearance, matching multiple backgrounds less well. Existing studies suggest both approaches can succeed, but most consider relatively simple scenarios, where artificial prey appear against two backgrounds differing in a single visual characteristic. Here, we used computer-based search tasks with human participants to test the relative benefits of specializing and generalizing for complex targets, displayed on either two or four types of naturalistic backgrounds. Across two background types, specialization was beneficial on average. However, the success of this strategy varied with search duration, such that generalist targets could outperform specialists over short search durations due to the presence of poorly matched specialists. Over longer searches, the remaining well-matched specialists had greater success than generalists, leading to an overall benefit of specialization at longer search durations. Against four different backgrounds, the initial cost to specialization was greater, so specialists and generalists ultimately experienced similar survival. Generalists performed better when their patterning was a compromise between backgrounds that were more similar to each other than when backgrounds were more different, with similarity in luminance more relevant than pattern differences. Time dependence in the relative success of these strategies suggests that predator search behavior may affect optimal camouflage in real-world situations.

Keywords: background matching; camouflage; crypsis; generalist; specialist.

Figure 1

Schematic to show how the targets were created from the backgrounds. Two random backgrounds were selected (a leaf background A and a grass background B in this example, top row) and then blended in the Fourier domain in three different ways: 25% background A and 75% background B (left middle), 50% background A and 50% background B (center middle), and 75% background A and 25% background B (right middle). A randomly placed triangular “moth” target was then cut out from each blended background (bottom row).

Figure 2

Top: loading screen for the online experiment. Bottom: example trials, showing the same target on the two different backgrounds used to create it (left a leaf background, right a bark background).

Figure 3

Survival probability for specialist and generalist targets over time in Experiment 1. Specialist targets are either more similar to background A (75% from background A) or background B (25% from background A), and would be expected to have equivalent survival. Generalist targets (50% condition) should be equally well matched on both backgrounds A and B. Crosses indicate censored (time out) data, and the shaded line indicates the 95% CI. The inset shows a zoomed-in section of the main curve, between 1 and 2 s, in order to highlight the crossover effect (see also the Supplementary Materials for a graph showing the summarized data for this time period for each condition).

Figure 4

Survival probability of specialist and generalist targets over time in Experiment 1, split into cases where the background pairs are less similar than the median difference (left) or more similar than the median difference (right). Specialist targets are either more similar to background A (75% from background A) or background B (25% from background A), and would be expected to have equivalent survival. Generalist targets (50% condition) should be equally well matched on both A and B. Crosses indicate censored (time out) data, and the shaded line indicates the 95% CI.

Figure 5

Survival probability of specialist (S) and G2 or G4 generalist targets over time in Experiment 2, with a zoomed-in section over the first 2 s of searching (inset), to show the differences in this time period more clearly. Crosses indicate censored (time out) data, and the shaded line indicates the 95% CI.