The Evolution of Communities 237 



third group, especially Remoropsis pallidas, feeds almost entirely 

 on ectoparasites or sea lice which the echeneids scrape from the 

 skin of the host. These three stages represent an evolution in habits 

 from commensalism in which only the echeneids benefit, to sym- 

 biosis in which both the echeneid and its host benefit (Strasburg, 

 1959). 



The mutualistic cleaning activities of Remoropsis are examples of 

 a highly developed symbiosis which may be an established working 

 relationship in every coastal marine community. Limbaugh ( 1961 ) 

 and others have shown that at least the young of many species of 

 smaller fishes and a number of small, slender shrimps habitually 

 clean a large assortment of larger fishes. The cleaners remove and 

 eat external parasites, wound tissue, and bacterial and fungus 

 growths from the fishes which are groomed. That this relationship 

 is not a casual one is demonstrated by the specializations in be- 

 havior and structure which have evolved in connection with clean- 

 ing symbiosis. The cleaners usually have bright colors and patterns 

 which contrast with their background, man set stations, and often 

 go through conspicuous acrobatic displays. They have pointed snouts 

 and tweezer-like teeth, ideal for the cleaning habit. The fish which 

 are cleaned habitually visit the same spot, often daily, and assume 

 ungainly but docile attitudes when being cleaned. In tropical waters 

 the cleaners enjoy almost complete immunity from predation by the 

 species they clean; in temperate waters the cleaners may be eaten 

 by their clientele. Limbaugh pointed out that this cleaning sym- 

 biosis may represent a relationship having a profound influence on 

 the species composition and population structure of at least the fish 

 component of all coastal marine communities. 



All of these mutualistic relationships arose only because of the 

 mixture of species in the same community and are therefore defi- 

 nitely part of community evolution. 



Protective Devices 



A conspicuous characteristic of a community is the phenomenon of 

 protective devices. These include disagreeable secretions, distaste- 

 ful substances, malodors, nettling hairs, thorns, and other devices 

 in both plants and animals, and protective form or coloration, 

 warning coloration, and mimicry in animals. These characteristics 

 confer on their possessors some protection from predation, hence 

 selection pressures leading to their evolution would follow im- 

 mediately in the footsteps of the evolution of food chains. It is 



