I wondered the same thing; I suppose it depends on how frequent those kinds of mass extinction events are. You might end up with two species: 1. The kinds that

I wondered the same thing; I suppose it depends on how frequent those kinds of mass extinction events are. You might end up with two species: 1. The kinds that clump and are subject to rare mass extinctions, but get along well enough otherwise. 2. The kinds that are really good at avoiding converging obstacles by avoiding clumps. Edit: I just realized that the clumps are kind of a communication network and eventually you might be able to get a kind of clump that either is able to quickly evade converging obstacles or be self-sacrificing to save a part of the whole.