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The Orchidaceae shows remarkable diversity in form and function and has long contributed to the development of evolutionary theory.

To understand the ecological and evolutionary drivers of this species rich family, we use a global database to explore the frequency of different breeding systems, means of pollinator attraction, and pollinator specificity, and how these features vary geographically and by growth habit.

We compiled data on the reproductive strategies of 2921 orchid species representing all subfamilies and 23 of 24 tribes. We tabulated information on habit, breeding and mating systems, means of pollinator attraction, and the number and identity of pollinators. ecological and functional specialisation in the use of pollinators were calculated. Patterns of reproductive biology by habit, geography, and phylogeny were analyzed graphically and statistically.

The majority of orchid species are pollinator-dependent (76 %). Only 12 % are self-incompatible, most of which are epiphytes from three subtribes of the Epidendroideae. Pollinator attraction based on rewards occurs in 54 % of the species, whereas 46 % employ some means of deceit. The most prevalent animal groups in orchid pollination are Hymenoptera and Diptera. Whether measured by ecological or functional specialization indices, orchids generally have highly specific pollinator interactions (median number of pollinator species = 1, mean = 3). Pollinator specificity is on average lower for species that offer pollinator rewards, occur in multiple continental regions, and for those in Northern America.

Our global analysis revealed that most species exhibit high level of pollinator specificity, regardless of how pollinators are attracted. The trend of specialized pollination systems applies to terrestrial and epiphytic species, and most major geographic regions. While our database reveals impressive knowledge gains, extensive gaps in basic observations of orchid reproductive biology exist, particularly in tropical regions and among diverse lineages of fly-pollinated species.

Keywords:

breeding systems, floral deception, pollinator rewards, mating systems, Orchidaceae, specificity

James Ackerman

Presentation within symposium:

S-36 IV Orchid Conservation Symposium

On the various contrivances by which orchids are pollinated: 2900 species reveal global patterns in pollination strategies

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