Abstract
The family Orchidaceae is not only one of the most diverse families of flowering plants, but also one of the most endangered plant taxa. Therefore, understanding how its species richness varies along geographical and environmental gradients is essential for conservation efforts. However, such knowledge is rarely available, especially on a large scale. We used a database extracted from herbarium records to investigate the relationships between orchid species richness and elevation, and to examine how elevational diversity in Yunnan Province, China, might be explained by mid-domain effect (MDE), species–area relationship (SAR), water–energy dynamics (WED), Rapoport’s Rule, and climatic variables. This particular location was selected because it is one of the primary centers of distribution for orchids. We recorded 691 species that span 127 genera and account for 88.59% of all confirmed orchid species in Yunnan. Species richness, estimated at 200-m intervals along a slope, was closely correlated with elevation, peaking at 1395 to 1723 m. The elevational pattern of orchid richness was considerably shaped by MDE, SAR, WED, and climate. Among those four predictors, climate was the strongest while MDE was the weakest for predicting the elevational pattern of orchid richness. Species richness showed parabolic responses to mean annual temperature (MAT) and mean annual precipitation (MAP), with maximum richness values recorded at 13.7 to 17.7°C for MAT and 1237 to 1414 mm for MAP. Rapoport’s Rule also helped to explain the elevational pattern of species richness in Yunnan, but those influences were not entirely uniform across all methods. These results suggested that the elevational pattern of orchid species richness in Yunnan is collectively shaped by several mechanisms related to geometric constraints, size of the land area, and environments. Because of the dominant role of climate in determining orchid richness, our findings may contribute to a better understanding of the potential effects of climate change on orchid diversity, and the development of conservation strategies for orchids.
Highlights
The family Orchidaceae is one of the largest and most diverse families of flowering plants, comprising of more than 24,000 species that span 800 genera worldwide [1]
We examined the records for 691 species from 127 genera of the family Orchidaceae in Yunnan
Many species were adaptable to various habitat types, 64.51% of all specimens had been collected from forests, 13.37% from grassy slopes, 8.74% from shrublands, and less than 5% each from forest edges, meadows, and open sites (Fig 2)
Summary
The family Orchidaceae is one of the largest and most diverse families of flowering plants, comprising of more than 24,000 species that span 800 genera worldwide [1] This family is considered to have the highest rate of speciation, and the highest rate of extinction [2, 3]. The rapid speciation and high species diversity within Orchidaceae is linked to the family’s specialized pollination syndromes, symbiotic associations with mycorrhizal fungi, and colonization of epiphytic habitats [2]. Because of their mycorrhizal specificity, pollinator specialization and germination limitation, many species are only distributed in specific habitats [2, 4, 5]. The variability in this diversity along those gradients is rarely examined, especially on a large scale [7, 8]
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