Doug asked:The dark one is not killing the the green one? Or are they fusing together?
The dark one is maybe another ascomycete which are parasites and is more than likley feeding off of the lichen, which too consists of an ascomycete which feeds off of the carbohydrates produced by the algae contained there in.
Rik replied:Ken, can you explain a bit more about what it means to be "controlled parasitism" versus "symbiotic relationship"?
There is a good arguement for both sides Rik, however, my feelings towards there not being a symbiotic or mutalistic union, stems from the findings, theory, or suggestions of one Simon Schwendener, a German, who was first to discover the dual nature of lichens (1869). He states that the fungi, which is an ascomycete and is acoustomed to living off of another organisms work, actually traps the algae for its own purpose in survival because it cannot produce any nourishment of its or on its own. Thinking of this and what you have already stated about photobionts;
But many of the photobionts, of which there are relatively few kinds, are often found free-living, not necessarily in the same environments
leads me to think that if the algae can exist apart from the fungi in certain environments and do it quite well, then why would they need the ascomycete to help them along. Then again there are some enviornments that the algae cannot obviously survive without the aide of the fungi. So, yes it is true here that the fungi does indeed aide in extending the range of the algae but for what purpose does it do the algae any good and so that leads me back to Schwendener's idea of it being a case of the fungi entrapping the algae and using it for its own purpose. You may want to search S. Schwendener and read up on his work in lichenology to better understand what I am getting at. Anyway I hope I have not confused things and still there is an argument for both sides of the fence.
