FIG. 13-6 Mil 

 butterfly. 



ch by (b) the 



plant stems (Ruiter 1955). The tell-tale shadows 

 cast by animals may be eliminated when the resting 

 animal lies lengthwise, rather than crosswise, to the 

 sun, or when they lie pressed close to the ground. 



Some animals, on the other hand, are vividly 

 marked with strikingly conspicuous patterns or 

 bright colors, and this aposematic or warning colora- 

 tion is accompanied by unpalatableness in certain 

 butterflies, bugs, beetles, ants, and birds ; stings, in 

 wasps and bees : a disagreeable odor in skunks ; or 

 some other offensive feature (Poulton 1887). There 

 is experimental evidence that such animals are actu- 

 ally avoided by predators (Finn 1895-97, Jones 

 1932, Cott 1947). However, a hungry predator is 

 less selective in its choice of food than one that has 

 recently fed. Apparently each individual carnivore 

 must have a personal experience with an animal so 

 marked before it learns to avoid it by associating the 

 coloration with the disagreeable feature. 



There are many examples of mimicry among in- 

 sects (Goldschmidt 1945). Batcsian mimicry is the 

 resemblance of a palatable species in external fea- 

 tures to an unpalatable one that in turn possesses 

 warning coloration and is the more abundant of the 

 two species. The palatable species derives benefit 

 from the relation, since predators, especially birds, 

 avoid them as well as the unpalatable ones. The vice- 

 roy butterfly mimics the disagreeable monarch butter- 

 fly and difTers strikingly from other members of its 

 own genus (Brower 1958). There is considerable 

 controversy about mimicry, however, and even the 

 classical example of the butterflies is disputed 

 (Urquhart 1957a). In Mullerian mimicry, both 

 model and mimic are unpalatable. Pooling of num- 

 bers between the two species gives more chances for 

 inexperienced birds to learn to avoid them and re- 

 duces the losses per species during the learning proc- 

 ess (Sheppard 1958). 



Some animals possess bright spots or colors so 

 placed on the body as to be deflective. The attention 

 of a pursuing predator is drawn to less vulnerable 

 parts of the body ; for instance, eyespots on the fins 



or tail of a fish. Eyespots on the wings of some but- 

 terflies and moths are concealed at rest, but when 

 flashed out by spread wings may frighten away an 

 attacking bird or other predator. . 



Concealing coloration and resemblance to other ob- 

 jects are apparently also useful to animals aggres- 

 sively. A carnivore that matches its background can 

 approach its prey undetected more easily than can a 

 conspicuously marked one. Some predators have di- 

 rective markings to confuse their prey as to the loca- 

 tion of their mouths or to allure them in various 

 ways. 



There has been considerable controversy about 

 the value of concealing coloration. McAtee (1932) 

 minimized its importance because he found both pro- 

 tectively colored and conspicuously colored species in 

 the stomach contents of the birds he examined. Prob- 

 ably few species are entirely immune to predation, but 

 if coloration to match the surroundings, mimicry of 

 some other avoided species, or peculiarities of form 

 or structure render predation even slightly less fre- 

 quent than it would otherwise be, it can well have 

 survival value and evolve as characteristic of a spe- 

 cies. 



A number of experiments in regard to concealing 

 coloration have been performed by exposing different 

 kinds of insects (Carrick 1936. Isely 1938), fish 

 (Sumner 1935), and mice (Dice 1947) to bird preda- 

 tors, with the result that those individuals that most 

 closely matched the color of their background were 

 taken less frequently than those that did not do so. 

 In a black aquarium in which equal numbers of black 

 and white mosquitofish were exposed to the preda- 

 tion of a penguin, 27 per cent of the fish eaten were 

 black and 7i per cent were white, but in a white 

 aquarium 62 per cent of the fish eaten were black 

 and only 38 per cent were white. 



RANGE OF FOOD SELECTION 



There is considerable range in the variety 

 of foods eaten by most species. Outside of parasitic 

 forms, few animals are restricted to a single species 

 for their food. Herbivorous species are often more 

 specific in their feeding habits than are carnivorous 

 forms. However, even herbivorous forms have vari- 

 ous degrees of restriction, as shown in the following 

 analysis of 240 species of plant-juice sucking aphids 

 (Clements and Shelford 1939) : 



Percentage 

 Species restricted to a single plant 



species 

 Species restricted to a single genus but 



feeding on more than one species 

 Species feeding on several different 



genera 33 



27 



40 



94 Ecological processes and dynamics 



