it depends on the intelligence level of the animal I'd think.  Think about how some animals mate for life while others do not - or how - mammals were mainly mentioned. I don't know about the invertebrates but I'm assuming some of these mammals are reasoning just not as long-term as we do then again octopus are very very smart and invertebrates so it really could even be down to the species sometimes.. they don't get married etc. their lives are beautiful but they have to think about survival much more frequently and solving disputes in their own way.