Coping with the epiphytic existence: pollination strategies.

Ackerman, J.D.
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epiphytic flowering plants, pollination strategies, euglossine bees
Populations of epiphytic flowering plants are often composed of scattered individuals or small, hyperdispersed clusters. These characteristics create conditions for pollination somewhat different from that encountered by many terrestrial plants. For example, plant distribution and size constraints imposed by the epiphytic habit may have limited floral apparency or competitiveness for adequate pollinator service. To cope with these problems, epiphytes employ one of several specialized pollination strategies which involve deception, or exclusive or unique reqards. Each of the specialized strategies is probably most efficient for diffusely distributed species and may have either a terrestrial or an epiphytic origin. In one system, plants produce few flowers per day for long periods. the blossoms contain a high quality reqard which is exclusively accessible to large traplining pollinators. In another, pollinator attraction is based on deceit which by-passes constraints directly imposed by pollinator foraging energetics. The deception may exploit sexual, feeding or egg-laying behaviors of their pollinators. A third strategy employed by many neotropical epiphytes is pollination by male euglossine bees. The flowers produce fragrances which serve as specific attractants and perhaps precursors to sex pheromones of the bees. Pollination occurs when male bees arrive and collect the fragrance compounds. All three strategies are not unique to epiphytes. Both terrestrials and epiphytes with shared size and dispersion constraints seem to have more specialized pollination biologies than their more densely populated and floriferous neighbors. The dispersion-specialization hypothesis generates testable predictions, some of which are presented.