My take is there's too much diversity for a simple answer, there's a hundred different answers for different species, different natural nuances of feeding, reproduction, and survival strategies, different kinds and degrees of social structure or social interaction, or cooperation vs. solitary behavior. Some predators are social, some aren't, some grazers are social, some aren't. For some species it's seasonal, circumstantial, hormonal, etc.
Right now I have two species of Geophagus, sveni and mirabilis. The sveni are more easygoing, more social, spend more time shoaling. The mirabilis, though a bit smaller, are definitely bossier and shoal only briefly and occasionally (with the sveni). Only two of the mirabilis, so maybe that explains they're being less social (doesn't explain them being bossier), but I've seen other people say the same thing about mirabilis not being that social. I haven't seen wild mirabilis video but I've seen wild sveni video and they were shoaling in a fairly large group. I've seen something similar in other genera, species within the genus can vary a lot in aggression or social behavior.
Then there are the studies showing differing individual 'personalities' within a given population of the same species. For example, shyness vs. boldness has been studied frequently and in many fish species. Studies on some species imply the differences are variable and context dependent, while studies of other species show differences that are heritable and consistent with individuals. Just one example:
https://pubmed.ncbi.nlm.nih.gov/28350493/
Right now I have two species of Geophagus, sveni and mirabilis. The sveni are more easygoing, more social, spend more time shoaling. The mirabilis, though a bit smaller, are definitely bossier and shoal only briefly and occasionally (with the sveni). Only two of the mirabilis, so maybe that explains they're being less social (doesn't explain them being bossier), but I've seen other people say the same thing about mirabilis not being that social. I haven't seen wild mirabilis video but I've seen wild sveni video and they were shoaling in a fairly large group. I've seen something similar in other genera, species within the genus can vary a lot in aggression or social behavior.
Then there are the studies showing differing individual 'personalities' within a given population of the same species. For example, shyness vs. boldness has been studied frequently and in many fish species. Studies on some species imply the differences are variable and context dependent, while studies of other species show differences that are heritable and consistent with individuals. Just one example:
https://pubmed.ncbi.nlm.nih.gov/28350493/
