Harmony and Conflict in the Living World - Alexander F. Skutch [36]
The situation among certain fish is quite different. According to a review by W. Wickler (1968), the warmer waters of the oceans contain no less than forty-two species of fish belonging to fourteen families known as "cleaners." These fish specialize in plucking from the bodies of other fish of different kinds the bacteria and external parasites that adhere to them, as well as removing loose or dead skin and particles of food. The clients, often very much larger than their attendants, even open their mouths and raise their gill covers to permit the cleaners to enter and search through the gills. The cleaners profit by eating what they remove from their clients, while the latter are benefited by this cleansing of their bodies, so that this is an excellent example of mutually beneficial symbiosis. The client fish make a practice of visiting the coral reefs where the cleaners dwell, for a periodic grooming. The latter fearlessly approach fish that could easily swallow them and gently work over their bodies, removing foreign matter. Occasionally, perhaps in consequence of a misunderstanding, a cleaner is devoured by its client.
As too often happens when a pleasant community of interests grows up in the natural world or among people strangers butt in to
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take a base advantage of the situation. One of the cleaner fish Labroides dimidiatus, is mimicked by a quite different fish, Aspidontus taeniatus, of the same size and similarly marked with wide, longitudinal black bands on a light ground. Advancing under false colors, the sharp-toothed Aspidontus, instead of grooming the client, bites pieces from its caudal fin. Despite the close resemblance of the imitator to the cleaner in appearance and mannerisms, the clients learn to distinguish them; young, inexperienced individuals appear to be the chief victims of the deception.
Another social bond is cooperation in feeding. Probably most flocking birds, from pelicans diving for fish in the ocean to swifts catching flying insects high in the air, help one another to find the richest concentrations of their appropriate food. Oceanic birds, which are often dazzling white, or black and white, can see each other from afar and, when they notice a few of their kind repeatedly plunging upon a school of small fish or a concentration of squid, hasten to join the feast. Similarly, swifts coursing over a wide area can watch each other flying above the treetops and converge on the spot where continued circling reveals the presence of many small volitant creatures. Much closer cooperation in foraging was exhibited by the Marbled Wood-Quails already mentioned. Standing almost above them, I noticed not the slightest resentment when one picked food from a space that another had just cleared by scratching, sometimes removing it almost from beneath the scratcher's body. If one found something too large to swallow all at once, it did not run away with its prize, as domestic chickens do, but amicably permitted its companions to share the item. Yet all these quails appeared equally mature and able to forage for themselves.
Many birds wander through the woodland in mixed flocks, which are especially large and diverse in tropical forests. The members of such flocks have different foraging habits: some climb over the trunks of trees, plucking insects and spiders from crevices in the bark; others ransack dead leaves lodged in crotches and tangles of vines; others glean caterpillars and spiders from living foliage; still others dart into the air for flying insects. Although the birds in these motley flocks are predominantly insectivorous rather than
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frugivorous, and so take much the same food, the help that they incidentally give one another seems to outweigh competition.