Use Setup to set up the ecosystem, Forever to run it, and Pollution to demonstrate the effects of humans polluting the otter's environment which kills them.
Interestingly, 61% of the time otters are being killed by sharks, so there is a 61% chance that a shark will kill an otter. There are 4 species and trophic levels modelled below. The limiting factors in the environment are size and space as there is a limit as to how big species can get, and how far they can go about. Probability is used when determining the size of an Otter or Shark litter.