The emergence of camouflage (to avoid detection) and aposematism (to advertise unprofitability via warning signals) are two common antipredator colour strategies that have repeatedly evolved through natural selection globally. The coexistence of both strategies seems to indicate that each is successful under different circumstances, however, theories describing how ecological variables influence the presence of each strategy are largely untested. In this study, authors investigated this relationship by conducting a large-scale analysis across six continents using artificial moths as a proxy for testing each antipredator strategy.
The researchers pinned more than 15,000 paper moths to trees with meal worms as a reward across 21 locations to assess wild avian predation. They used three colour variants to mimic camouflaged targets, targets with typical warning colours and targets with atypical warning colours, as well as testing for the impact of latitude, illumination, predator community, prey community and visual environment on predation. GBIF records were used to inform which butterfly and moth species were present in each location to then calculate the ratio of each colour strategy per area. They then used GBIF-derived metrics to assess whether the local prevalence of warning or cryptic prey influences predator responses.
The results showed that anti-predator colouration effectiveness is highly context dependent. Camouflage was most effective initially under high predator competition and low light conditions but became less effective over time as predators learned where and when cryptic prey is common. In contrast, warning coloration is more stable but still affected by predator competition, which increases early predation and slows predator learning. Atypical warning signals are disadvantaged where typical ones dominate.
Overall, the study determined that predator competition is the most significant factor in shaping both strategies, suggesting camouflage may be less stable and more sensitive to environmental change than warning coloration over evolutionary time.