Economics

An industry which has a Four Firm Concentration ratio of 20 can be characterized as one with a high degree of competition. In essence, it is highly likely that such an industry will, according to Grant (2002),  have attributes of a perfectly competitive industry  (P. 113) as follows
A large number of buyers and sellers.
Perfect knowledge and information about prices.
Homogenous product.
Little or no barriers to entry or exit.
Minimal transaction costs.
Profit maximization through the selling where marginal cost equals marginal profit.

In such an industry, an increase in the demand and consequent price for the product would imply a long term adjustment in the shape of a higher concentration ratio then before as firms that sell at relatively lower prices would take away demand from those that sell at relatively higher prices, provided that the product is not a luxury good whose value is derived from social perceptions. In the end, we will see that there has been consolidation in the industry with fewer sellers then before and less perfection as far as competition goes given the fact that new entrants will have to be able to sell at or near the same margins as the sellers with the most market share.

An industry which has a Four Firm Concentration ratio of 80 and 20 firms can be described as one, according to Grant (2002), bearing  monopolistic competition  (P.114) and it is highly likely that, according to Grant (2002), it will have the following characteristics
Large number of buyers and sellers.
Perfect information.
No barriers to entry or exit in the long run.
Differentiated products.
Independent decision making.
Market power on terms of exchange with seller.

Differences in market share and hence concentration ratios between this industry and the one analyzed before can be gaged by the fact that this industry sells a differentiated product while the former sold a homogeneous one. Hence, to a large degree price competition was not possible there while non price competition was not possible at all. Thus, according to Schweser (2008),  firms would have to rely on advantages of cost economies and non economic factors  (P. 70) like location and proximity to transport mechanisms for example as a way to garner higher volume and increase market share. However, here, firms will to a large degree, engage in non price competition as well as traditional price competition with firms that build up a brand following thriving at the expense of other firms by garnering market share or retaining any market share that they may have already created. This is how small firms will be able to survive, that is, by effectively targeting market niches and building their brand value amongst them so that the provision of a previously unfulfilled need takes away market share from other firms and results in a profit making exercise.