Competition Between Three Saxicolous Species of Parmelia (Lichens)

Summary Fragments of three foliose, saxicolous lichens were glued in 5 × 5 cm plots on pieces of slate in the field, either in monoculture or paired in 1:1 mixtures with each of the other two species. A preliminary experiment suggested that glueing did not influence the radial growth of the lichen fragments. No species eliminated another after 3 years but the growth (total area in mm2) of Parmelia saxatilis and P. glabratula ssp. fuliginosa was reduced significantly in the mixtures with P. conspersa; the growth of P. glabratula ssp. fuliginosa was reduced significantly in the mixture with P. saxatilis compared with their growth in monoculture. The results suggest that the three lichens show interference by competition for space and light in the following order of competitive ability: P. conspersa > P. saxatilis > P. glabratula ssp. fuliginosa. A high radial growth rate and the ability to overgrow a thallus may be important competitive attributes in foliose lichens and the results also suggest that competition can reduce the abundance of a lichen and lead to distribution patterns in the field.