Elevational gradients of species diversity, breeding system and floral traits of orchid species on Réunion Island

Abstract

Aim This research investigates changes in orchid species composition and diversity, plant breeding system and floral traits along an elevational gradient spanning 2300 m (200-2500 m).Location The study was conducted on Réunion Island (Mascarene Islands, Indian Ocean).Methods Data on the distribution of 135 orchid species from 35 genera were gathered from 121 localities situated between 200 and 2500 m a.s.l. For each locality, 500-m transects were walked and each orchid species was recorded. Measures of species diversity (species richness, a modified Shannon diversity index and the modified Shannon equitability index) were related to altitude using ordinary least-squares regression. Species turnover and elevational gradients in species composition were determined by: (1) relating scores of detrended correspondence analysis to altitude using ordinary least-squares regression, and (2) relating Sørensen similarity indices to differences in altitude using Mantel tests. Finally, the average proportion of species displaying similar floral traits or showing the same breeding system were compared among altitudinal zones.Results Species richness per transect ranged from 1 to 36 species (mean 14.3) and decreased significantly with increasing altitude. Similarly, species evenness decreased significantly with increasing altitude. Around 50% of all orchid species were rare (occurred in fewer than 5% of all localities), and only a few occurred in more than 50% of all localities. Orchid species composition changed continuously with altitude, indicating turnover of species with increasing altitude. Analogously, orchid breeding systems and floral traits also changed with altitude. Relatively more auto-pollinating species were found at high altitudes compared with mid-and low-altitude sites where animal-pollinated species were most abundant. Species characterized by a cleistogamous pollination system were found almost exclusively in high-altitude sites, whereas the proportion of species displaying floral traits related to pollination by longtongued moths (sphinx) and flies sharply decreased with increasing altitude.Main conclusions Environmental conditions associated with altitude exert a large influence on orchid species composition and the distribution of orchid breeding systems. Our results revealed a high proportion of auto-pollinating species, and confirm earlier findings that auto-pollinating species are more frequent in high-altitude sites.

Elevational Pattern of Orchid Rarity and Endemism in Mt. Kalatungan, Mindanao Island, Philippines

“…The humpshaped relationship of orchid species richness with the elevational gradient as affected by microclimate variables has also been ascertained in studies conducted in Mexico [29] as well as in Himalayan regions of Nepal and Bhutan [9]. This pattern has been observed in other tropical vascular plants [6,29] including trees and other epiphytes. In the Philippines, however, ecological studies on orchids and other vascular plants remain to be scanty in the literature.…”

“…The different vegetation types may also explain the high levels of endemism. It was observed that some orchid species thriving at the very high elevation are isolated, habitatdependent and may become more specialized than those species found at lower elevation [22,6]. Eight endemic species present a new record in Bukidnon province, these include C. davaensis, Ceratostylis ramosa, Dendrobium diffusum, Dendrochilum coccineum, D. mindanaense, D. malindangense, Octarrhena parvula and Phreatia densiflora.…”

“…In tropical ecosystems, one of the major gradients that may exert large differences in plant species composition and richness is altitude. Moreover, the elevation also showed to influenced species evenness in negative relation (species evenness decreases significantly with increasing altitudes) [6]. Studies on elevational gradients have found three main patterns of species richness: first, a monotonic decrease in richness with increasing elevation, second, a ''humped'' distribution, with species richness highest near the middle of the gradient and a plateau at low elevations [7,8].…”

“…Being an excellent biological indicator of ecological changes in the ecosystem, the species richness pattern of orchids along the elevational gradient has been studied particularly in the Himalayas [9], Reunion Island [6,10] and Borneo [11]. However, in the Philippines which harbors more than 1,100 orchid species with about 80% endemism [12], ecological studies on orchid flora remains to be unexplored and understudied This study aimed to provide a checklist of the orchid flora of Mt.…”

An assessment of factors leading to the decline of Beclardia macrostachya (orchidaceae) population in Mauritius

“…), the spur nectar arises as an outgrowth from the proximal part of the labellum [9]. Beclardia macrostachya exhibit typical sphingophilous syndrome with white, spurred flowers and producing a strong scent [10,11]. Nevertheless, it has also been reported that grey white eye (Zosterops olivaceus) and olive white eye (Z. borbonicus) are the most probable pollinators of Beclardia macrostachya in Reunion Island [12].…”