A generalist species is able to survive in a wide variety of environmental conditions and can make use of lots of different resources. Generalist species have a big niche. Humans, rabbits, house flies, and raccoons would all fall under the generalist species list. 
A specialist species can only thrive is a small variety of environmental conditions and/or only has a limited diet. Specialist species have a small niche. Pandas, koalas, and salamanders would all fall under the specialist species list. 
 
        
             
        
        
        
From a modern genetic perspective, this is defined as evolution. 
        
             
        
        
        
Answer:
The amount of energy at each trophic level decreases as it moves through an ecosystem. As little as 10 percent of the energy at any trophic level is transferred to the next level; the rest is lost largely through metabolic processes as heat.
Explanation: