A mathematical model of a food web helps you better understand portions, and track the structure of how the web is flowing. The food web could also help because it helps predict things.
        
             
        
        
        
The answer is density-dependent factor
        
                    
             
        
        
        
size hence streams  are little and rivers are bigger than streams because a stream connects between two or more rivers
mark brainliest please   :)
 
        
             
        
        
        
Genetic variation is advantageous because it enables some individuals and, therefore, a population, to survive despite a changing environment.
        
             
        
        
        
Teperature
Ph level
Substrate concentration
Not sure if these are physical but hope it helped.