EFFECTS OF GRAVEL REMOVAL ON AQUATIC BIOTA 

 L. L. Moulton 



INTRODUCTION 



Populations of organisms are conlTolled by physical and chemical fac- 

 tors, often termed their environment, and by biological factors, including 

 predation and competition. Environmental constraints on a particular species 

 determine the usable habitat available to that population and the size of 

 the population is often restricted by the amount of usable habitat. After 

 the maximum number of individuals a particular habitat can support (termed 

 the carrying capacity) has been reached, the population cannot increase with- 

 out an increase in usable habitat. Predation and competition can act on a 

 population to limit numbers below the carrying capacity, thus undisturbed 

 populations are not necessarily fully utilizing the available habitat. 



Alterations to the habitat can alter the quality of the habitat, lead- 

 ing to direct changes in the carrying capacity, and consequently, to reduc- 

 tions in the affected populations. Decreases in habitat diversity may reduce 

 the carrying capacity for one species while leaving that for another un- 

 changed. If the two species were in competition, the reduction or removal of 

 one may al low the other species to increase. General ly, decreases in habitat 

 diversity will result in an increased carrying capacity of one species which 

 is able to efficiently utilize the more uniform habitat. Conversely, in- 

 creases in habitat diversity general ly cause increases in the number of 

 species or life history stages present as new habitat types are added. These 

 species increases are often accompanied by decreases in the populations 

 which had formerly been utilizing the more uniform, less diverse, habitat. 



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