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; 
D. The birds have different mating seasons.
Explanation; 
-Different species of birds have different mating or breeding seasons. Evolution has played a role in adjusting the timing of avian(birds) breeding seasons to maximize the number of young produced. The breeding season depends on a number of factors, for example In the temperate, subarctic, and arctic zones, the overriding factor is the availability of food. This varies across all different species of birds, irrespective of other similarities they may have. 
 
        
                    
             
        
        
        
Answer:
a layer or a series of layers of rock in the ground. , 
a level or class to which people are assigned according to their social status, education, or income.
Explanation:
 
        
                    
             
        
        
        
Answer:
self-copying molecules ate the primordial soup
Explanation:
 
        
             
        
        
        
Answer:
Unicellular 
Explanation:
Some organisms are microscopic and consist of only 1 cell