Answer: I believe the answer is mountains.
The baby-boom generation is a generation that has had much different lifestyle than the previous generation, or rather the generation of their parents. The rights of the men and women have become equal, as well as the earnings. The marriage has been delayed for later stages of life, also having less children, and relatively high divorce rates.
On the long run, this generation will have a negative demographic impact on the United States. The reason for that is that the birthrates of this generation have dropped significantly, and it is also representing a large portion of the population, so as they age they will contribute to aging population.
An aging population can have serious economic and social impact, as the percentage of people that take money from the pension funds will increase significantly relative to the people that work. Also, as the baby-boomers age, the healthcare will be overrun by them, as deep age and diseases often goes hand to hand, so the expenses for the healthcare will be enormous.
The answer to the question above is sedimentary rock. The sedimentary rock, from the words themselves, are formed from the deposition of sediments and their subsequent cementation. The word sedimentation is a collective name for the process that cause minerals and organic particles to settle down.
They could adapt to live together so that for example one starts eating only seaweed while the other starts eating only organic matter so they don't compete for food. They could also adapt like when squirrels are separated into those who eat on trees and those who eat on the ground. The 2 urchin types could split into those who eat of the ground and those that eat what floats and drifts.