(N/A) According to Gause's Competitive Exclusion Principle,two closely related species competing for the same resources cannot coexist indefinitely,and the competitively inferior one will eventually be eliminated.
However,in the given scenario,both species are surviving. Possible reasons include:
$1$. Resource Partitioning: The species may have evolved mechanisms to feed at different times of the day or at different depths of the aquarium,thereby reducing direct competition.
$2$. Abundance of Resources: If the supply of phytoplanktons is abundant and exceeds the combined demand of both fish populations,competition is minimized,allowing coexistence.
$3$. Niche Differentiation: Each species may occupy a slightly different ecological niche,even if they share the same food source,which prevents total competitive exclusion.