Competition 119 



used as a source of food by odier organisms. However, the food chain 

 from bacteria or algae to the larger fishes does not consist of a single series 

 of hnks, but many. A few of these food chains may be dominant during 

 one season or under certain environmental conditions while others may 

 replace them at another time or season. Thus, at certain times, foods more 

 suitable for one species of fish may be more abundant than at other times. 

 This may be reflected in changes in condition, growth rate, and in stand- 

 ing crop of the fish. 



Larimore^- could not show definite food competition between large- 

 mouth bass and warmouths inhabiting the same lakes, although these two 

 species often fed on similar types of organisms. Warmouths tended to 

 feed on organisms on soft bottoms in shallow waters and along banks 

 while largemouths fed more on the surface organisms and free swimming 

 forms in deeper or more open parts of the lakes. 



Studies of the food habits of closely related fishes may show similarities, 

 yet with certain important differences. Ball and Tanner ^ in studying the 

 foods of bluegills and pumpkinseed sunfish from the same waters, dis- 

 covered that the pumpkinseeds selected a larger proportion of molluscs 

 and hard-bodied insects than did the bluegills; while the bluegills ate 

 larger amounts of aquatic vegetation than did the pumpkinseeds. The 

 selection of these types of foods by bluegill X pumpkinseed hybrids was 

 intermediate between the two parent species. Both parent types were 

 feeding upon about the same range of foods, but distinct preferences for 

 certain types were clearly evident. 



In fishes of widely different food habits, such as largemouth bass and 

 bluegills, there may be some evidence of food competition at times and 

 under certain conditions. For example, bass and bluegills in one pond 

 competed for insects when fish or crayfish were not available for the 

 bass.^^ Under these conditions, however, bass ate more flying insects and 

 bluegills more larval aquatic forms. In this particular situation, it was 

 impossible to evaluate the degree of competition between these two 

 species. 



Competition for Space 



When fish are forced to compete for living space, there is evidence that 

 in some species (and perhaps all species) growth rate and reproduction 

 are affected adversely. Anyone who has kept goldfish or tropical fish in 

 aquaria indoors and then has placed these fish in an outdoor pool during 

 a summer period, has had a demonstration of the change in growth rate 

 brought about by increased space. Usually, a part of the increased growth 

 rate is due to an improved diet, but even where aquarium fishes are 

 receiving a completely balanced diet, their growth appears to be affected 

 by the amount of space for each fish. 



