Strong antiapostatic selection against novel rare aposematic prey - PubMed (original) (raw)

Strong antiapostatic selection against novel rare aposematic prey

L Lindström et al. Proc Natl Acad Sci U S A. 2001.

Abstract

The evolution of aposematism, a phenomenon where prey species conspicuously advertise their unprofitability to predators, is puzzling. How did conspicuousness evolve, if it simultaneously increased the likelihood of an inexperienced predator to detect the prey and presumably kill it? Antiapostatic selection, where rare prey is predated relatively more often, is considered as another major difficulty for aposematism to evolve. However, the risk of being conspicuous in low frequencies has not been experimentally tested. We designed an experiment to test how frequency (4%, 12%, 32%) of conspicuous aposematic prey and its dispersion type (solitary vs. aggregated) affect an initial predation risk of the prey and in avoidance learning of predators. Wild great tits (Parus major) were predators on artificial prey in a "novel world." The relative mortality of aposematic prey was antiapostatic, thus the frequency-dependent predation was most severe at low frequencies. In all frequencies, aggregated aposematic prey survived better than solitary prey. Surprisingly, learning was not determined by a fixed number of unpalatable prey eaten, but at low frequencies fewer aposematic individuals eaten generated predators' avoidance learning. However, per-capita risk for the prey remained highest at low frequencies. Our results underscore the problems of initial evolution of rare conspicuous morphs. Aggregated prey suffered less from predation, indicating selective advantage of aggregation over solitary living for a conspicuous individual.

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Figures

Figure 1

Figure 1

The mean (± SE) initial relative risk of predation on aposematic prey within the first five encountered prey items, in the first trial. □ represent solitary treatments and ● aggregated treatments. The line of unity indicates that the prey is eaten at the same rate that it is presented.

Figure 2

Figure 2

The mean (+ SE) relative risk of predation on 2 consecutive days in three different frequencies (a) in solitary and (b) in aggregated treatment. The random line indicates where aposematic prey is eaten at the same frequency it was presented.

Figure 3

Figure 3

The mean (± SE) cumulative sum of aposematic prey eaten within the experiment according to the dispersion type, (a) solitary and (b) aggregated. Equal number of prey (altogether 200) was presented on both day 1 and day 2. Birds were allowed to eat 50 prey items each day. Both experimental days are divided into five sections and the numbers of aposematic prey eaten within these sections (10 eaten prey items each) are presented cumulatively. Thus, the 1 refers to the number of aposematic prey eaten within the first 10 consumed prey, 2 within the first 20 etc., and 10 referring to the number of aposematic prey eaten in the whole experiment.

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