Epiphyte ecology has been a recurrent topic throughout the preceding chapters but little or nothing has been said about community organization, succession, associated phytotelmata, phorophyte specificity, or influence of epiphytes on supports and other biota. Although documentation of cause and effect is scarce, it is clear that canopy-dwelling flora can help shape forest structure and economy; processes as fundamental as community-wide mineral cycling and productivity are affected. Influence on animals is no less pervasive. Without plant resources beyond those provided by earth-rooted vegetation, much of the immense and diverse fauna characteristic of humid tropical woodlands (Erwin 1983) would not exist. This chapter will emphasize the role of epiphytes as members of communities and substrata for other organisms.

Host specificity

Only the exceptional epiphyte has but one acceptable phorophyte (Table 7.1). Far more commonly, anchorage occurs on several kinds of supports, although usually not with equal frequency. Valdivia (1977) studied the distribution of 153 vascular epiphyte species on 45 different trees in east-central Mexico. Only Acacia cornigera, a myrmecophyte that is aggressively defended against other insects and encroaching vegetation by its ant colonies, hosted no epiphytes. The remaining 44 each supported more than one species; the record was 107, demonstrating that certain trees offer especially suitable crowns. Few phorophytes provide anchorage to every potential colonist, however, nor does occurrence always follow expected patterns. Aechmea bracteata is abundant on several trees in semievergreen forest in the Sian Ka'an Reserve, Mexican Yucatan (Olmsted and Dejean 1987).