Exploitation 385 



Many other instances of poisoning are known, some of them acting 

 in a highly specific manner. The harm done in this way by one 

 species to another may be completely fortuitous in some instances, but 

 it may have evolved as a protective adaptation in others. The ecolog- 

 ical consequences of this type of antagonism, involving the produc- 

 tion of poisons or of harmful metabolites, have been discussed in fur- 

 ther detail by Lucas (1949). 



Exploitation 



We shall now turn to relations of exploitation in which the mem- 

 bers of one species benefit by the utilization of another species. The 

 most common manifestation of interspecific exploitation is the use of 

 a neighboring species as a source of food, and this will be discussed 

 under the headings of parasitism and predation. However, an or- 

 ganism may employ another species of plant or animal in the environ- 

 ment for attachment, support, or transport, as already mentioned, and 

 such activity often results in harmful consequences to the host. 



Certain highly specialized kinds of exploitation occur, and one of 

 the most astonishing of these is the enslavement of one species of ant 

 by another (Talbot and Kennedy, 1940). Polijergus is an obligate 

 slave-making ant that is unable to maintain its colony without the 

 presence of members of certain species of Formica. Volijergus work- 

 ers raid neighboring nests of Formica and carry home larvae and 

 pupae. After maturing into the worker stage, these captive ants 

 undertake feeding and nest building for their masters. Polyergus 

 ants will starve even in the presence of abundant food if this slave 

 labor is not available. 



Another special type of exploitation is that practiced by so-called 

 "parasitic birds." The cuckoo in Europe and the cowbird in the 

 United States never build nests of their own; each female lays an 

 egg in the nest established by birds of another, usually smaller, 

 species. The cowbirds' habit perhaps arose as a result of their 

 nomadic wandering after grazing animals, which left them insufficient 

 time in one place for such domestic matters as raising a family. The 

 pair of birds thus imposed upon is sometimes able to throw out the 

 foisted egg or to cover it by building a new nest bottom over it, but 

 more frequently the unwanted egg hatches out along with the host's 

 own eggs. The young cuckoo soon pushes the other fledglings out 

 of the nest, and the young cowbird is able to starve out its nest mates 

 by grabbing all the food. After the young imposter has left the nest, 

 its squawking still calls forth in its foster parents the behavior pattern 



