382 



Relations between Species 



benefit ( — , 0). Antibiosis, the production of harmful secretions, is 

 the outstanding example of this type of relationship. (2) Species A 

 may inflict harm by direct use of species B for its own benefit in a 

 relationship of exploitation (-]-, — ). Species A may exploit B by 

 gaining support or shelter for itself, or it may obtain nourishment di- 

 rectly from B as a parasite or as a predator. (3) Both species may be 

 harmed in a reciprocally unfavorable relationship ( — , — ). This 

 situation is commonly found in the indirect rivalry, or competition, of 

 two species for some feature of the environment that they both need 

 and that exists in short supply. The space, food, light, oxygen, or 

 other necessity taken by one species reduces the amount available for 

 the other. In some situations considerable harm is suffered by both 

 competing species; in other instances the injury may be serious for one 

 species and relatively minor for the other. A reciprocally harmful 

 effect will also occur if species A produces an antibiotic harmful to 



Fig. 10.10. Roots of strangling fig enveloping the trunk of its host in a Florida 



hammock. 



