BUTTERFLY PALATABILITY AND MIMICRY: EXPERIMENTS WITH AMEIVA LIZARDS.

Abstract

Direct demonstration of unpalatability or mimicry in nature represents a problem of great difficulty because of the rarity and complexity of the events concerned. To witness a sequence in the wild in which the same predator was observed to learn that a species was unpalatable, reject it at a later encounter and still later refuse its mimic, would be highly unlikely (Brower, 1963). For this reason the bulk of proof for unpalatability or mimicry theory does not come from direct evidence of predation but rather from indirect evidence, much of it from laboratory studies. In the laboratory, a predator may be afforded a closer, longer scrutiny of its prey than in the wild where conditions of risk, attack and lighting often vary considerably. Also, there is always the possibility that under these conditions a predator might attack and eat a prey item which it would rarely utilize in nature where a variety of food sources are available. Brower et al. (1964, 1967), Cook (1969) and Benson (1972) all obtained indirect evidence for the selective advantage of unpalatability and mimicry in the wild by using live prey in capture-recapture studies. Morrell and Turner (1970) obtained more direct evidence by testing the reaction of wild birds to artificial prey (pastry soaked in quinine). This study, however, appears to be the first direct test of unpalatability and mimicry theory using both vertebrate predators (lizards) and live prey (butterflies) in their natural habitats. Birds and lizards have long been considered to be the m inr qplptix7p n opntc rpnnnihla fnr 1hc, extreme diversity of unpalatable and mimetic forms of butterflies in nature. It is well established that birds attack and eat butterflies in the wild (Carpenter, 1937, 1941-2). Lizards are less well established as selective agents for butterflies, although good evidence does exist (Schoener, 1968; Sexton, 1960). Predators are known to differ in their susceptibility to toxins produced by different prey, and prey species often differ in the amount and type of toxins they contain (Rettenmeyer, 1970; Brower et al., 1972). Therefore, it was suspected that the preferences of one group of vertebrates (birds) might be quite different from those of another (lizards). The purposes of this study were to determine: how the preferences of lizards correspond to those of birds when offered similar prey; whether lizards readily attack and eat butterflies in nature; whether wild lizards could act as selective agents for the evolution of unpalatability or mimicry; the mechanism by which lizards recognize and avoid prey in the wild. Ameiva ameiva lizards are excellent subjects for such a study because they are insectivores, capable of taking fairly large prey (Hallinan, 1920). They and some other species of lizards appear to be predators with the capacity to learn (Sexton, 1960). Ameiva have restricted home ranges, a fact which presents a good situation for observing learning within a small localized population. These lizards occur sympatrically with butterflies previously tested with birds for palatability (Brower et al., 1963) and are fairly approachable by an observer. 'Present address: Department of Botany, University of Washington, Seattle, WA 98195.