Spin-off of Project Creature Colonies

Start with your code from the previous ecosystem projects, pasting it in here.
Now build a system of creatures. How can they interact with each other? Can you use inheritance
to create a variety of creatures, derived from the same code base? Develop a methodology for
how they compete for resources (for example, food). Can you track a creature’s “health” much
like we tracked a particle’s lifespan, removing creatures when appropriate? What rules can you
incorporate to control how creatures are born?