So I want to revise my comments a bit. I introduced two fairly stout ornates to my tank last week (week before?) and my common pleco hates them... And I ascribe that emotion because it really seems like the attacks are more territorial than they are for feeding purposes. The pleco is well fed, but the larger ornate has attempted to co-opt the pleco's favorite hiding place. The pleco will first bump and push the ornate with his nose or body and when he fails at that, he will being sucking on the ornate.
There's still zero interaction between the pleco and either my legacy senegal or the female senegal I added along with the ornates (although the senegal did mistake one of the plecos barbles for bloodworms they were both eating the other day).
As a side note, the ornates are not too fond of my pictus cats. I have two that are probably 6" long. One of them showed an obvious bite on its body and a sredded tail the other morning. So, the ornates are now back in my quarantine tank and I'm trying to decide whether they need to find a new home or if I am going to set up a bichir only tank.
Anyhow, though I'd add my update.
I almost spit beer all over my monitor