A classic study frequently taught in undergraduate courses involves Pisaster ochraceus and its ability to regulate the abundance of california mussels in the intertidal zone of marine systems. When P. ochraceus is removed, the system (which is limited in available space) is quickly dominated by the california mussel. When P. ochraceus is present, the intertidal community is more diverse because the mussels are 'kept in check'. Thus, P. ochraceus, through its predation on the mussels, exhibits a disproportionately large effect on the system. Another example involves the regulatory control of urchin populations by sea otters, which left unchecked, can overgraze kelp forests.

If this is the sort of thing you had in mind, Niklas, I recommend reading about keystone species. See also the following article: http://onlinelibrary.wiley.com/doi/10.1046/j.1523-1739.1995.09040962.x/abstract

Thank you, these are the kind of studies I am looking for. I am familiar with both studies you mentioned. I did not consider the keystone species angle, yet, but will do it now. 

My interest is more focused on sharks and fish.