MACROMOVEMENTS~«- 



Optimal range of physical and 

 chemical factors (current, sub- 

 strate, temperature, light, 

 dissolved oxygen) 



Suboptimal range of physical 

 chemical factors 



MICROMOVEMENTS 



[orientation with respect to flow and turbulence) 



MICROHABITAT SELECTION 

 [food quality, quantity) 



LOW FOOD 



Reduced feeding and 

 increased movement 



Increased respiration 

 (reduced growth) 



HIGH FOOD 



Increased feeding and 

 reduced movement 



Decreased respiration 

 (increased growth) 



Mortality increased 



LOW NUMERICAL AND/OR 

 BIOMASS DENSITY 



Mortality decreased 



t 



HIGH NUMERICAL AND/OR 

 BIOMASS DENSITY 



Figure 43. Proposed relationships between invertebrates and the factors 

 that determine their distribution and abundance (from Cummins 1972). 



68 



