Ecosystems need producers because they are the start of the food chain. 
Producers are consumed by first consumers, the second consumers and so on.
 
        
             
        
        
        
Answer: (A) the time that two species have been evolving independently.
Explanation: The molecular clock is figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when<u> two or more life forms.</u>
 
        
                    
             
        
        
        
Answer:
Mother is dominant with tall trait XRXR
Father is recessive with short trait XrY