Close Encounters Ecosystems

The niche does not differ between self- and cross-pollinated Epipactis orchids in Europe

The ecological niche of 14 orchids is more determined by bedrock and land cover than their mating systems.

One third of orchid species are able to self-pollinate which allows orchids to reproduce without relying on pollinators. Selfing leads to low genetic variability and can restrict a species adaptability to changing environmental conditions. There are approximately 70 orchid species in the genus Epipactis which can reproduce by selfing (autogamy) or cross-pollination (allogamy), or by facultative cross-pollination. There are endangered and vulnerable orchid species within this genus and it is not entirely clear how the mating system affects the distribution and niche of different species. 

Alexandra Evans and Dr Hans Jacquemyn at KU Leuven (Belgium) modelled the ecological niches of 14 Epipactis species in Europe and found that the orchid mating system does not necessarily contribute to niche breadth and differentiation. The distribution of these orchid species mostly depended on bedrock and land cover and not on climate. This suggests that plant traits other than mating systems are more important in defining the ecological niche of Epipactis species. 

Two Epipactis orchids
Marsh Helleborine (Epipactis palustris) and E. thunbergii. Sources Hornbeam Arts/Flickr and Alpsdake/WikimediaCommons

Evans and Jacquemyn collected the distribution of 14 Epipactis species between 2000-2020 in Europe from the online database GBIF (www.GBIF.org). The scientists calculated the mean distribution area, habitat suitability, environmental variable contributions, niche breadth (e.g. the range of habitat conditions encompassed by a species’ ecological niche) in geographic space, niche breadth in environmental space and niche overlap for each species. The ecological niche of each species was estimated by the function of precipitation and temperature, altitude, soil composition, bedrock, and vegetation type. The scientists produced habitat suitability maps in Maxent, an open-access software, and determined the geographical range by drawing polygons around each species’ occurrence points. The niche breadth in geographical space was calculated for each species.

Habitat suitability maps of two selfing Epipactis species, E. fageticola and E. helleborine (top row) and two cross-pollinated species, E. albensis and E. muelleri. Source Evans and Jacquemyn, 2020

The bedrock and land cover generally determined the habitat suitability of Epipactis orchids. Broad-leaved forests, coniferous forests, non-irrigated arable lands, limestone and boulder clay associated with most species. Whilst there was no difference in the geographical range, habitat suitability,  niche breadth and niche overlap among selfing and cross-pollinated species, there was overall less variability for selfing species. The species E. microphylla, purpurata, kleinii, tremolsii, albensis and phyllanthes had more distinctive niches. 

“To conclude, our results do not support the hypothesis that autogamous species have larger ranges and wider ecological niches than facultative autogamous or allogamous species”, Evans and Jacquemyn said.

“Most of the Epipactis species with small ranges demonstrated distinctly strong associations with forests, and the dependence on forests that they developed in their evolutionary histories may have made them less able to utilise other environments, limiting their ranges.”

“Because germination and seedling establishment are critical stages in the life cycle of orchids, differences in interaction with mycorrhizal fungi may be as, or more, important than the mating system in defining the distribution range and niche breadth of orchids”, Evans and Jacquemyn said.

This study is somewhat “good news” for the Epipactis orchids as selfing does not seem to restrict their distribution while pollinator populations have been declining in Europe. Conserving forests is going to be key for Epipactis species. You can learn more about the global state of forests here: https://bit.ly/FAO_GlobalForests.

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