I like all the thoughts presented but I keep returning to Eric's wise words, "same sized BG and Tilapia". This qualifier is essential to the comparison because size is the most important variable for either species with respect to their own resistance to predation. Size, by and large, is more important than species. Larger prey are more resistant to predation than smaller ones. It would be acceptable to ignore species and consider only size when projecting susceptibility to predation. Size has a lot to do with concepts like relative speed for example. There is a lot out there on the subject of the size of prey.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers