Intra- and interspecific relations within an epiphyte community in a Mexican humid montane forest.

Hietz, P. and U. Hietz-Seifert.
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Bromeliaceae, Epiphyte associations, Mexico, Nearest neighbor analysis, Orchidaceae, Peperomia
Studies on epiphytic vegetation are scarce. Most have been made on a regional scale or by comparing different host trees or locations within a tree. We present an analysis on a very small scale, which may be a powerful tool for describing and understanding community structure and organization. One hundred and eight photographs of oak branch or stem sections, some 50 to 100 cm long, were analyzed, and the nearest neighbors of the 1,843 specimens of vascular epiphytes, belonging to 39 species, were recorded. The non-randomness of species associations was calculated as *2 values of 2 x 2 contingency tables. Not surprisingly, many species were their own nearest neighbors. The significance of having a neighbor of the same species, i.e., the degree of clustering, however, differed between groups and may be interpreted in terms of mobility of diaspores and specificity of substrate requirements. Generally, clustering decreased in the following order: orchids, Peperomia spp., most bromeliads, and non-creeping ferns. Three orchid species showed an extremely high incidence of interspecific association, which we suppose to be the result of sharing the same mycorrhizal partner. Weaker associations of different species may be explained by their preferring similar zones in the trees or, possibly, by some species serving as seed traps or nurse plants.