Summary 1 We examined in situ diversity and distribution of vascular epiphytes, as well as site environmental variables at six sites along a continuous elevational gradient (30‐2600 m a.s.l.) of old-growth forest in Costa Rica. 2 A total of 555 species of vascular epiphytes from 130 genera of 53 families were identified to species or morphospecies. The ferns were the most diverse group, with 138 species, followed by orchids (112 species). Cloud forest at 1000 m was the richest site, representing the maximum of a pronounced mid-elevation peak in epiphyte species richness. 3 Spatial randomizations of recorded elevational ranges suggest that the overall elevational richness pattern of most epiphyte groups on this transect is substantially influenced by the mid-domain effect (MDE, the mid-elevation overlap of large-ranged species). Among the environmental factors considered (rainfall, temperature and canopy light environment), only rainfall was significantly correlated with richness. 4 Different patterns of richness for vascular epiphytes and for trees indicate that mechanisms differ between life forms. 5 We collected 26% of the estimated epiphyte species of Costa Rica along a single mountain transect. This, together with the finding that different groups and life forms varied in the elevation at which species richness peaked, highlights the need to conserve the few remaining intact elevational gradients in Latin America.

Vascular epiphyte distribution patterns: explaining the mid-elevation richness peak

Aim To document the elevational pattern of epiphyte species richness at the local scale in the tropical Andes with a consistent methodology.

Location  The northern Bolivian Andes at 350–4000 m above sea level.

Methods  We surveyed epiphytic vascular plant assemblages in humid forests in (a) single trees located in (b) 90 subplots of 400 m2 each located in (c) 14 plots of 1 ha each. The plots were separated by 100–800 m along the elevational gradient.

Results  We recorded about 800 epiphyte species in total, with up to 83 species found on a single tree. Species richness peaked at c. 1500 m and declined by c. 65% to 350 m and by c. 99% to 4000 m, while forests on mountain ridges had richness values lowered by c. 30% relative to slope forests at the same elevations. The hump-shaped richness pattern differed from a null-model of random species distribution within a bounded domain (the mid-domain effect) as well as from the pattern of mean annual precipitation by a shift of the diversity peak to lower elevations and by a more pronounced decline of species richness at higher elevations. With the exception of Araceae, which declined almost monotonically, all epiphyte taxa showed hump-shaped curves, albeit with slightly differing shapes. Orchids and pteridophytes were the most species-rich epiphytic taxa, but their relative contributions shifted with elevation from a predominance of orchids at low elevations to purely fern-dominated epiphyte assemblages at 4000 m. Within the pteridophytes, the polygrammoid clade was conspicuously overrepresented in dry or cold environments. Orchids, various small groups (Cyclanthaceae, Ericaceae, Melastomataceae, etc.), and Bromeliaceae (below 1000 m) were mostly restricted to the forest canopy, while Araceae and Pteridophyta were well represented in the forest understorey.

Main conclusions  Our study confirms the hump-shaped elevational pattern of vascular epiphyte richness, but the causes of this are still poorly understood. We hypothesize that the decline of richness at high elevations is a result of low temperatures, but the mechanism involved is unknown. The taxon-specific patterns suggest that some taxa have a phylogenetically determined propensity for survival under extreme conditions (low temperatures, low humidity, and low light levels in the forest interior). The three spatial sampling scales show some different patterns, highlighting the influence of the sampling methodology.

Diversity patterns of vascular epiphytes along an elevational gradient in the Andes

Epiphytes are a characteristic component of tropical rainforests. Out of the 25 000 orchid species currently known to science, more than 70% live in tree canopies. Understanding when and how these orchids diversified is vital to understanding the history of epiphytic biomes. We investigated whether orchids managed to radiate so explosively owing to their predominantly epiphytic habit and/or their specialized pollinator systems by testing these hypotheses from a statistical and phylogenetic standpoint. For the first approach, species numbers of 100 randomly chosen epiphytic and terrestrial genera were compared. Furthermore, the mean number of pollinators per orchid species within the five subfamilies was calculated and correlated with their time of diversification and species richness. In the second approach, molecular epiphytic orchid phylogenies were screened for clades with specific suites of epiphytic adaptations. Epiphytic genera were found to be significantly richer in species than terrestrial genera both for orchids and non-orchids. No evidence was found for a positive association between pollinator specialization and orchid species richness. Repeated associations between a small body size, short life cycle and specialized clinging roots of twig epiphytes in Bulbophyllinae and Oncidiinae were discovered. The development of twig epiphytism in the first group seems repeatedly correlated with speciation bursts.

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Epiphytism and pollinator specialization: drivers for orchid diversity?

Clearance and fragmentation of tropical montane forests in the Highlands of Chiapas, Mexico (1975-2000)

Aim Although vascular epiphytes are important components of species richness and complexity of Neotropical forests, vascular epiphytes are under-represented in large scale biogeographical analyses. We studied the diversity, biogeography and floristic relationships of the epiphytic flora of the Yasuno´ region (Western Amazonia) in a Neotropical context, with special emphasis on the influence of the Andean flora on floristic composition and diversity of surrounding lowland forests. Location Western Amazonian lowland rainforest, Tiputini Biodiversity Station (0� 38¢ S7 6� 09¢ W, 230 m a.s.l., 650 ha), Yasuno´ National Park, Ecuador. Methods We compared the vascular epiphyte flora of Yasuno´ with 16 published Neotropical epiphyte inventories. Secondly, based on a floristic database with records of more than 70,000 specimens of vascular epiphytes from the Neotropics the elevational composition of eight selected inventories was analysed in detail. Results The vascular epiphyte flora of Yasuno´ is characterized by a very high species richness (313 spp.). A moderate portion of species is endemic to the Upper Napo region (c. 10%). However, this figure is much higher than previous analyses primarily based on woody species suggested. Geographical ranges of these species match with a proposed Pleistocene forest refuge. Compared with Northern and Central Amazonian sites, Western Amazonian epiphyte communities are characterized by a higher portion of montane and submontane species. Species richness of vascular epiphytes at the sites was correlated with the amount of rainfall, which is negatively correlated with the number of dry months. Main conclusion Recent and historic patterns of rainfall are the driving forces behind diversity and floristic composition of vascular epiphytes in Western Amazonia: high annual rainfall in combination with low seasonality provides suitable conditions to harbour high species richness. The proximity to the Andes, the most important centre of speciation for most Neotropical epiphytic taxa, in combination with the climatic setting has allowed a continuous supply of species richness to the region. At least for epiphytes, the borderline between the Andean and Amazonian flora is much hazier than previously thought. Moreover, the comparatively moist climate in Western Amazonia during the Pleistocene has probably led to fewer extinctions and/or more speciation than in more affected surrounding lowlands.

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Diversity and biogeography of vascular epiphytes in Western Amazonia, Yasuní, Ecuador

Aim We aim to assess regional patterns in the distribution and species richness of vascular epiphytes with an emphasis on forests that differ in altitude and the amount of rainfall. Location Tropical America, in particularly the 75000 km2 large state of Chiapas in southern Mexico at 14.5-18.0o N. Chiapas is diverse in habitats with forests from sea-level to the tree-line at approximately 3800 m altitude and with annual amounts of rainfall ranging from 800 to over 5000 mm. It is also one of the botanical best-explored regions in the tropics. Methods First we give an overview of epiphyte inventories to date. Such epiphyte surveys were mostly carried out on the basis of surface area or individual trees and we discuss their problematic comparison. Applying a different methodological approach, next we used 12276 unique vascular epiphyte plant collections from Chiapas that are deposited in various botanical collections. The locality data were georeferenced and compiled in a relational database that was analysed using a Geographic Information System. To compare the number of species between inventories that differed in the numbers of records, we estimated the total richness, SChao, at each. Results We recorded 1173 vascular epiphyte species in 39 families (23 angiosperms), comprising c. 14% of all confirmed plant species in the state. About half of all species were orchids (568). Ferns and bromeliads were the next species rich groups with 244 and 101 species, respectively. Most species were found in the Montane Rain Forest and in the Central Plateau. Trees of different forest formations, rainfall regimes, altitudes and physiographic regions supported a characteristic epiphyte flora. Main conclusions We were able to confirm the presumed presence of a belt of high diversity at mid-elevations (500 - 2000 m) in neotropical mountains. In contrast to predictions, however, we observed a decrease in diversity when the annual amount of rainfall exceeded 2500 mm. The decrease is attributed to wind-dispersed orchids, bromeliads and Pteridophyta that may find establishment problematical under frequent downpours. In the wet but seasonal forests in Chiapas, this decrease is not compensated by plants in the animal-dispersed Araceae that are abundant elsewhere. We presume that in addition to the annual amount of rainfall, its distribution in time determines the composition of the epiphyte community.

Flamenco-S Alejandro

Papers

Patterns in species richness and distribution of vascular epiphytes in Chiapas, Mexico