An assesment of the role of biotic interactions and dynamic processes in the organization of species in a saxicolous lichen community

John A.E.
Can. J. Bot.
67: 2025-2037
A saxicolous lichen community is examined for evidence of dynamic processes and biotic interactions among its members. Spatial relationships among species are examined in a series of association analyses at three scales: (i) the "nearestneighbour" scale, i.e., associations between touching thalli; (H) associations between thalli 10 and 20 cm apart; and (Ui) associations at the scale of the whole rock face. The nearest-neighbour analysis reveals fundamental differences in the way crustose and foliose thalli sample their environment; crustose lichens are more likely to have uncolonized rock as a nearest neighbour, whereas foliose lichens are more likely to contact another thallus. Associations between species at the 10- and 20-cm scales are often negative, reflecting the degree of microhabitat specificity in this community; however, intraspecific associations at the same scale are often positive, possibly indicating local dispersal processes. At the whole-rock scale, there are many positive associations indicating that, even at this larger scale, microhabitat specificity is important. Thallus-size distributions are also studied, and these indicate that recruitment into lichen populations is an ongoing process, based on the assumption that small thalli.are younger than large thalli. There is little evidence of succession to a higher plant community over most of the rocks at this 500-year-old site, and it is hypothesized that cyclic successional processes maintain this dynamic and diverse community
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