As I was looking though some Pokedex Entries on Luvdisc, I found this very interesting one. Take a look.
Emerald Entry: Luvdisc make the branches of Corsola their nests. There is a custom from long ago of giving a Luvdisc as a gift to express one's feelings of love.
If anyone has taken Grade Nine Science, they would know like me that this connection between Luvdisc and Corsola could be viewed at as symbiosis, the close and often long-term interactions between different biological species.
Usually, symbiosis benefits both species, which would be call mutualism. If not, it would be called antagonism, which means one species is benefitted and the other is harmed, or commensalism, which means one species is benefitted and the other is neither harmed or benefitted.
Another example of this diverse look at symbiosis is between Mantine and Remoraid.
It can definately be said that the relationship between Mantine and Remoraid is commensalism with Mantine's Gold Sprite, which states:
As it majestically swims, it doesn't care if Remoraid attach to it for scavenging its leftovers
As you can see, as Remoraid feasts on the leftovers on Mantine, Mantine is completely unaffected by Remoraid's presence, thus is doesn't benefit or get harmed by Remoraid.
But the question is, what is the relationship between Corsola and Luvdisc.
First off, we can get rid of antagonism since if Corsola did get hurt from Luvdisc being in it's branches, it would probably let Luvdisc know this and have it leave.
So it's either between mutualism or commensalism.
From what I can see, Corsola doesn't really benefit from Luvdisc living in it's branches so I have to go with commensalism, with Corsola being the benefitter and Corsola getting neither gaining or lossing from this.
And it seems as Corsola wouldn't be affected if any of it's branches got broken, due to it's Ruby Pokedex Entry:
Corsola's branches glitter very beautifully in seven colors when they catch sunlight. If any branch breaks off, this Pokémon grows it back in just one night.
So overall, it can be said Corsola and Luvdisc co-exist in a peaceful manner, even if Luvdisc is getting the bigger end of the stick, or in this case, branch.