The relationship between thallus mass, surface area and apothecium production in Umbilicaria rigida
Gregersen, Inger K.; Hegseth, Marit Nøst Hestmark; Kongsbak, Ruth H.; Moe, Therese; Fosholt,
The relationship between thallus mass, surface area and apothecium production in the alpine, saxicolous umbilicate lichen Umbilicaria rigida was investigated. There is a very strong and significant relationship between an increase in thallus mass and an increase in upper surface area. The relationship is strictly linear, adding 2 mm2 to the upper surface area for each 1 mg added to the mass, and does not exhibit allometric change from small to large individuals. There is a moderately strong and significant relationship between the two size parameters (mass, upper surface area) and the number of apothecia produced on the upper surface. The relationship is linear and does not indicate increased allocation to reproduction with increased size. However, the thalli have to reach a certain minimum size to produce apothecia (= 30 mg), indicating the existence of a developmental threshold for reproduction. Thalli up to 660 mg may however be without apothecia. The observations indicate that thallus size is a fairly good predictor of current reproductive status in this lichen.