Populations of epiphytic lichens under stress conditions: survival strategies

The effect of a copper-smelting plant on populations of Hypogymnia physodes and Tuckernianopsis sepincola was studied in the Middle Urals. A different population response was found between the two lichen species due to different life strategies. The pollution appears to decrease growth and developmental rate of H. physodes (a vegetatively reproducing strongly competitive species), resulting in a shift of population structure towards smaller, esorediate to low sorediate thalli. The background population of the sexually reproducing Tuckennanopsis sepincola consisted mainly of young, small thalli of a low fertility as a result of strong inter-species competition with H. physodes. At the polluted site, the sharp decrease in the abundance of H. physodes led to a shift in structure of the T. sepincola population towards larger and more fertile thalli. It may be concluded that T. sepincola benefits from air pollution by an indirect effect of the removal of a strong competitor, i.e. H. physodes.