I think the fitness landscape is too complicated to justify that kind of assessment. Even with the non-universal qualifier "usually". I think a more correct statement would be to replace "usually" with "can be", and mention the possibility of it also being disadventageous or disasterous. At this point the entire statement becomes somewhat meaningless, though. Maybe it should just be "too complex to assess without a study per-ecosystem; it depends".

I'm sure someone more familiar with the research can express all of this mathematically and and confirm of deny the existance of an overall, cross-cutting model. It may even be common knowledge in evo bio/ecology/etc.

All I can mention on my phone right now is "keystone species", "s curve", and "wolf/rabbit populations". (or was it elk?) anyway, the latter search term leads to info on cyclical and highly dynamic ecologies. Check it out.