Abstract
Insect communities consist of aposematic species with efficient warning colours against predation, as well as abundant examples of crypsis. To understand such coexistence, we here report results from a field experiment where relative survival of artificial larvae, varying in conspicuousness, was estimated in natural bird communities over an entire season. This takes advantage of natural variation in the proportion of naive predators: naivety peaks when young birds have just fledged. We show that the relative benefit of warning signals and crypsis changes accordingly. When naive birds are rare (early and late in the season), conspicuous warning signals improve survival, but conspicuousness becomes a disadvantage near the fledging time of birds. Such temporal structuring of predator–prey relationships facilitates the coexistence of diverse antipredatory strategies and helps explain two patterns we found in a 688-species community of Lepidoterans: larval warning signals remain rare and occur disproportionately often in seasons when predators are educated.
Highlights
Insect communities consist of aposematic species with efficient warning colours against predation, as well as abundant examples of crypsis
Absolute survival of prey may be linked to variations in alternative prey availability[14,15]: in times of high insect abundance, per capita survival can increase despite breeding efforts of birds, causing high predator activity. Such factors have an impact on the absolute values of survival that can be expected, we focus here on changes in relative survival between prey types, as this determines the direction of selection
We estimated seasonally varying survival differences among the three different larval types by fitting a set of candidate models to data and estimating their support based on Akaike information criteria (AIC)[24,25] (Table 1)
Summary
Insect communities consist of aposematic species with efficient warning colours against predation, as well as abundant examples of crypsis To understand such coexistence, we here report results from a field experiment where relative survival of artificial larvae, varying in conspicuousness, was estimated in natural bird communities over an entire season. Absolute survival of prey may be linked to variations in alternative prey availability[14,15]: in times of high insect abundance, per capita survival can increase despite breeding efforts of birds, causing high predator activity Such factors have an impact on the absolute values of survival that can be expected, we focus here on changes in relative survival between prey types, as this determines the direction of selection (that is, whether warning colours or crypsis is favoured[16,17]). These patterns of relative survival matches data on fledging times of passerine birds (main predators of larvae in vegetation), which suggests that juvenile fledging time increases the relative attack rate towards conspicuous larvae
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