Terrestrial and epiphytic orchids exhibit different diversity and distribution patterns along an elevation gradient of Mt. Victoria, Myanmar

Abstract

Orchids have been long fascinating biologists and ecologists because of their remarkable range of life history strategies, floral and vegetative morphology, pollination syndromes, and symbiotic fungi. However, the diversity and distribution patterns of orchids remain unclear in several regions, seriously hindering the understanding of orchid diversity and their maintenance mechanisms. In this study, species richness, abundance, and environmental conditions of epiphytic and terrestrial orchids were investigated along an elevation gradient of Mt. Victoria, Myanmar, ranging from 600 to 3000 m with 200-m intervals. A binary species-based network was structured between epiphytic orchids and their hosts to further address the effect of hosts on orchid distribution. In total, 94 orchid species were recorded, including 58 epiphytic and 36 terrestrial orchids. A hump-shaped pattern of epiphytic orchid richness occurred along the elevation gradient, with the highest richness at ca. 2200 m, whereas terrestrial orchid richness follows a monotonous decrease. Both elevation and slope significantly affected the species composition and diversity of epiphytic and terrestrial orchids, while terrestrial orchids were also affected by herb coverage. The network between epiphytic orchids and their hosts exhibited a low level of connectance, and significant nestedness with a high level of modularity and specialization. Interactions in the network were heterogeneously distributed among hosts, as Lithocarpus variolosus, Rhododendron arboretum, and Lyonia ovalifolia hosted a wide variety of orchid species and hence played an important role in maintaining the diversity pattern of epiphytic orchids, while the bulk of species exhibited few interactions. Twenty epiphytic orchids (such as Sunipia grandiflora, Liparis viridiflora, Porpax grandiflora and Liparis tsii), which were only attached to specific host species, may be exposed to a high risk of extinction with the intensification of human activities. This study provides basic data for the conservation and management of orchids in Mt. Victoria, Myanmar.