Organisms with advantageous adaptations are more likely to survive and reproduce than organisms without the advantageous adaptations. this phenomenon is known as natural selection. in order for natural selection to occur,

Natural selection refers to the phenomenon by which the species in a population possessing the tendency to get adapted in a condition enhance in numbers in comparison to those who exhibit fewer adaptation capacities over a number of generations.  

In other words, it can be stated as the non-random and differential development of distinct genotypes function to sustain favorable variant and to eradicate less favorable variants. Some of the conditions are required for the process of natural selection to take place.  

These are heredity, reproduction, variation in individual characters, and variation in the fitness of organisms among the members of the population. If the conditions are met, then the phenomenon of natural selection occurs by default.  

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.