Supernormal Stimulus as a Mimicry Strategy: the case for Epidendrum radicans (Orchidaceae)

Epidendrum radicans is a food deceptive Batesian mimic of its sympatric model species Asclepias curassavica and Lantana camara. Theoretically, food deceptive orchids should be rare with small inflorescences (Johnson et al. 1993; Weins 1978) yet in San Luis, Costa Rica E. radicans grows in large monotypic stands with individuals sporting up to 12 open flowers per inflorescence. E. radicans might attract pollinators using flower or inflorescence size as a visual supernormal stimulus also implicated in floral mimicry (Scheistl 2004). Pollinia removal of E. radicans was measured in plants with i) inflorescence sizes of two and ten growing amongst model species in patches ii) inflorescence sizes of one through eight flowers on plants growing naturally in dense stands without models iii) and unmodified and enlarged flowers. Pollinia removal was proportionally greater for flowers of smaller inflorescence sizes, and greater for unmodified flowers. E. radicans does not appear to use visual supernormal stimuli to attract pollinators. E. radicans may occur in large monotypic stands as a result of human disturbance. Continued pollinia removal in E. radicans may result from constant recruitment of naïve pollinators to the area.