What form of symbiosis would Moss growing on a tree be?




Check the answer key in the back of the book.

With a little imagination, I can make it fit in any of those categories.

Mutualism: A kind of symbiosis in which both parties derive advantage without sustaining injury.

Nope, can’t be that. A moss is a autotroph, as is a tree. Any interactions that are going on are only beneficial to the extent that all ecosystem interaction can be described as beneficial.

Parasitism: A form of symbioisis in which one symbiont, or parasite, receives benefit to the detriment of the other, or host.

Nah. Although some mosses will grow on the leaves of trees a mos growing on tree bark isn’t harming the tree nor the tree the moss in any meaningful way.
Commensalism: the association between commensals, or between a commensal and its host.
Commensal: An organism living with another and sharing the food, both species benefiting form the relationship, or one species benefiting and the other not being harmed.

Possibly. Moss almost certainly extracts some nutrients from the decaying tree bark. The trouble is that within a functioning ecosystem all organisms will be commensal by this standard if they are not in direct-predator prey relationships. It makes the term almost useless by redefining it as simply ‘Any two organisms that interact without either party being harmed.’

Although the relationship could be technically called commensalism it would be unusual to see it referred to that way. The moss is simply functioning as an epiphyte. Although it derived nutrients from the tree it only does so in the same way that all organisms in a forest derive nutrients from the trees: via decay and nutrient cycling. IMO is the moss is a commensal then a moose is equally a commensal.

I don’t think there’s any relationship. Moss can grow on rocks, I think? Therefore, it does not need anything from the tree. And trees grow without moss.

It’s not quite that simple Who Stole My Name. Moss will indeed grow on rocks or any other suface, and some species will grow on trees and rocks. But some species, particularly in the tropics, are specific to trees or rocks or soil or whatever.

But in general I agree. There is no particular relationship here, the moss is just acting as an epiphyte using the tree as an anchor point.

Moss doesn’t need the tree, and the tree doesn’t the moss to survive. I don’t believe a symbiotic relationship exists. Now, a classic example is the fish or worm(I forget) that lives within the anus of the sea cucumber, IIRC! Without it, neither would survive, IIRC…it’s been awhile, but it’s too funny-sounding to forget!

  • Jinx

It could be considered a form of parasitism - specifically for support - although the benefit to the moss is probably small, as is the cost to the tree.

This is clearer in the case of some other epiphytes, such as bromeliads, etc, or of vines which rely on the tree’s structure to gain access to the high light levels in the forest canopy (even though they do not rely on the tree for food). Trees must spend a lot of energy building their trunks in order to bring their leaves out of the shade of the understory. By growing on the tree, the epiphytes avoid this cost. And the aggregate weight of the epiphytes can be detrimental to the tree - limbs can break under the weight, especially after a rain, and vines can shade out and even kill the trees own foliage.