Diversity of vascular epiphytes in remnant trees of the genus Ficus (Moraceae) in silvopastoral systems of southeastern Mexico

Antecedentes y Objetivos: En los sistemas silvopastoriles es posible observar árboles remanentes que proveen de hábitats y recursos a diferentes grupos de organismos. En este estudio se analizó el rol que tienen los árboles remanentes del género Ficus (Moraceae) como refugio para albergar epífitas vasculares en la Depresión Central de Chiapas, México. Métodos: Se evaluó la presencia de epífitas vasculares en tres sistemas silvopastoriles (dos con pastoreo extensivo y uno intensivo) y dos sitios de bosque tropical seco semiconservado. En cada sitio se seleccionaron árboles adultos de Ficus (20-30 individuos) en los cuales se muestrearon todas las epífitas vasculares (incluyendo hemiepífitas). Se realizaron análisis de varianza para determinar si hay diferencias en la riqueza y diversidad alfa (exponencial del índice de Shannon) entre los sitios, así como análisis multivariado para observar los cambios en la composición de especies. Resultados clave: Se encontraron 77 especies, distribuidas en 36 géneros y nueve familias. Las familias más abundantes fueron Orchidaceae, Bromeliaceae y Cactaceae. En promedio, se detectaron ca. seis especies de epífitas por árbol (máximo 19). La diversidad alfa es mayor en los árboles del bosque semiconservado en comparación con los árboles remanentes presentes en los sistemas silvopastoriles. La composición de especies es heterogénea y diferente entre los sitios del bosque semiconservado y los sistemas silvopastoriles. La mitad de las especies de epífitas fueron exclusivas a un sitio determinado, principalmente en el remanente de bosque con 15 especies. Conclusiones: Los árboles de Ficus presentan características como una corteza rugosa, ramas gruesas y casi horizontales que facilitan la colonización de epífitas y sirven como relictos de hábitat en los sistemas silvopastoriles. Por lo tanto, contribuyen al mantenimiento de la diversidad total de epífitas vasculares en paisajes altamente modificados.Background and Aims: In silvopastoral systems, it is possible to find remnant trees that provide habitat and resources for different groups of organisms. This study analyzed the role of remnant trees of the genus Ficus (Moraceae) as refuge to harbor vascular epiphytes in the Depresión Central de Chiapas (Mexico). Methods: The presence of vascular epiphytes in three silvopastoral systems (two with extensive and one with intensive grazing) and two sites of semi-conserved tropical deciduous forest was assessed. In each site, mature Ficus trees (20-30 individuals) were selected, and all vascular epiphytes were sampled (including hemi-epiphytes). An analysis of variance was conducted in order to determine differences in richness and alpha diversity (exponential of the Shannon index) among the sites, as well as a multivariate analysis to observe changes in species composition. Key results: We found 77 species, distributed in 36 genera and nine families. The most abundant families were Orchidaceae, Bromeliaceae and Cactaceae. On average, ca. six epiphyte species were found per tree (maximum 19). Alpha diversity was higher in semi-conserved forests of both localities than in remnant trees present in the silvopastoral systems. Species composition is heterogeneous and different among sites of the semi-conserved forest and the silvopastoral systems. Half of the epiphyte species were exclusive to a determined site, mainly in the semi-conserved forest with 15 species. Conclusions: Ficus trees present characteristics, such as rugose bark texture, as well as thick and almost horizontal branches, that facilitate the colonization of epiphytes and they serve as habitat relicts in silvorpastoril systems. Therefore, they contribute to the maintenance of the total diversity of vascular epiphytes in highly modified landscapes

Phylogenetic diversity and the structure of host-epiphyte interactions across the Neotropics

Understanding the mechanisms driving community assembly has been a major focus of ecological research for nearly a century, yet little is known about these mechanisms in commensal communities, particularly with respect to their historical/evolutionary components. Here, we use a large-scale dataset of 4,440 vascular plant species to explore the relationship between the evolutionary distinctiveness (ED) (as measured by the 'species evolutionary history' (SEH)) of host species and the phylogenetic diversity (PD) of their associated epiphyte species. Although there was considerable variation across hosts and their associated epiphyte species, they were largely unrelated to host SEH. Our results mostly support the idea that the determinants of epiphyte colonization success might involve host characteristics that are unrelated to host SEH (e.g., architectural differences between hosts). While determinants of PD of epiphyte assemblages are poorly known, they do not appear to be related to the evolutionary history of host species. Instead, they might be better explained by neutral processes of colonization and extinction. However, the high level of phylogenetic signal in epiphyte PD (independent of SEH) suggests it might still be influenced by yet unrecognized evolutionary determinants. This study highlights how little is still known about the phylogenetic determinants of epiphyte communities

Relación entre variables del forófito y la riqueza de epífitas vasculares en los Pantanos de Centla, Tabasco, México

Background and Aims: Vascular epiphytes are rare elements of mangrove-dominated forests because sea salinity causes extreme conditions that difficult their establishment. In southern Mexico, most of the studies about the relationships between epiphytes and phorophytes have been carried out in montane forests, while the mangrove forests have received little attention. Our aim was to analyze the relationships between epiphytic species richness and the phorophyte characteristics of Rhizophora mangle, an endangered species under the NOM-059-SEMARNAT- 2010, in the “Pantanos de Centla” Biosphere Reserve located in the north-east of the state of Tabasco. Methods: The relation between species richness of epiphytes and several variables of the phorophytes, such as the aerial root coverage, diameter at breast height (DBH) and height, was evaluated using linear regression models. In addition, phorophytes were divided into five vertical zones to analyze the vertical distribution of the epiphytes using the Sørensen and Margalef indexes. Key results: Seventeen species of epiphytes were recorded. Orchidaceae and Bromeliaceae were the families with the highest species richness (six each). The most representative genus was Tillandsia (Bromeliaceae) with five species. The epiphytic species richness was significantly correlated with phorophyte aerial root coverage and DBH. The phorophyte zones I and III were the most similar because they shared 47% of all recorded species. The zone I (aerial roots) showed the highest epiphyte species richness. In the zone V (outer portion of the canopy) only Selenicereus testudo (Cactaceae) was registered, a species that was found in all five zones of the phorophyte. The mangrove area studied has a relatively high epiphyte richness in spite of the high salinity present in its flooded habitat. Conclusions: Epiphytic species richness was determined by the variation in size of the phorophytes. The aerial roots of R. mangle are an additional niche for the colonization of epiphytes and not just a supporting structure for the unstable soil of the mangrove ecosystem.Antecedentes y Objetivos: Las epífitas vasculares son elementos poco comunes en manglares debido a que la salinidad del agua de mar impone condiciones extremas que dificultan su establecimiento. En el sur de México se han realizado estudios sobre las relaciones epífitas-forófito, principalmente en bosques montanos, pero hay pocos trabajos enfocados en los manglares. El objetivo de este trabajo fue analizar las relaciones entre la riqueza de epífitas y las características de los forófitos de Rhizophora mangle, especie amenazada de acuerdo a la NOM-059-SEMARNAT-2010, en la Reserva de la Biosfera “Pantanos de Centla”, ubicada en el noreste del estado de Tabasco. Métodos: Se evaluó la relación entre la riqueza de epífitas y algunas variables de los forófitos, como la altura, el diámetro a la altura del pecho (DAP) y la cobertura de raíces aéreas, mediante modelos de regresión lineal. Además, los forófitos se dividieron en cinco zonas verticales para analizar la distribución vertical de las epífitas aplicando los índices de Sørensen y Margalef. Resultados clave: Se registraron 17 especies de epífitas. Orchidaceae y Bromeliaceae fueron las familias con mayor riqueza (seis especies cada una). El género más representativo fue Tillandsia (Bromeliaceae) con cinco especies. La riqueza de epífitas estuvo significativamente relacionada con la cobertura de raíces aéreas y el DAP de los forófitos. Las zonas I y III de los forófitos fueron las más similares ya que compartieron 47% del total de las especies registradas. La zona I (raíces aéreas) fue la más rica en especies de epífitas. En la zona V (parte exterior de la copa) solo se encontró a Selenicereus testudo (Cactaceae), especie también hallada en el resto de las zonas. El área de manglar estudiado presenta una riqueza relativamente alta de epífitas pese a la alta salinidad presente en su hábitat inundado. Conclusiones: La variación de los tamaños de los forófitos determinó la riqueza de epífitas. Las raíces aéreas de R. mangle son un nicho adicional para la colonización de epífitas y no solamente sirven como soporte al suelo inestable del ecosistema de manglar

An Assessment of the Spatial Variability of Tropical Swamp Forest along a 300 km Long Transect in the Usumacinta River Basin, Mexico

The provision of valuable ecosystem services by tropical swamp forests (mainly carbon sequestration and storage in biomass and soil) explains their ecological importance. Current efforts toward the conservation of these ecosystems, however, face strong limitations as their spatial variation is largely unknown, particularly in regions where they occur over large areas. Here, we analyze the α-diversity (i.e., effective number of species or true diversity) and community structure variability of three tropical swamp forest communities distributed along an approximately 300 km long portion of the Usumacinta River Basin, southern Mexico. We sampled eighty-three 625-m2 plots to characterize the diversity and structural attributes of the woody plant communities. We recorded 2302 individuals belonging to 60 species and 25 families. Both α-diversity and structural attributes differed significantly among the three communities. The most inland community stood out for having the highest α-diversity for three true diversity values. Interestingly, the mangrove Rhizophora mangle L. was one of the dominant species, both in the swamp forest located closest to the coast and in the community farthest away from the sea. Basal area and density of individuals also had their maxima in the most inland swamp forest. The diversity and structural differences observed among the examined swamp forests seem to be related to contrasting environmental conditions, such as water salinity, distance to the coastline, and the hydrological dynamics of the Usumacinta River. We emphasize the urgency to conserve R. mangle populations in the swamp forest located farthest away from the coast due to its unusual habitat association, which appears to be a relictual condition

Conservation status of vascular epiphytes in the neotropics

The Neotropical realm hosts some of the Earth’s most species-rich biodiversity hotspots, with vascular epiphytes significantly contributing to this diversity, regionally accounting for up to 39% of the vascular flora. However, many regions of the Neotropics where epiphytic species of restricted distribution are reported coincide with threatened ecosystems, such as the tropical montane cloud forest. Moreover, epiphytes may be especially vulnerable to land use and climate change impacts due to their dependence on host trees. We assessed the conservation status of vascular epiphytes in the Neotropics for the families that represent over 80% of the global epiphyte diversity (Araceae, Bromeliaceae, Orchidaceae, Piperaceae, and Polypodiaceae) and identified geographical centres of accumulation of threatened epiphyte species. We gathered information from free-access web repositories, specific epiphytic plant databases, and scientific and grey literature. We assessed the extinction risk of 11,446 epiphyte species following IUCN Red List guidelines, using Criterion B (geographic range size). We found nearly 60% (6,721 species) to be threatened, with 1,766 critically endangered (CR), 3,537 endangered (EN), and 1,418 vulnerable (VU). The threatened species are mainly found in the centres of endemism of vascular epiphytes in Central America, the northern Andes, and the Atlantic Forest. Our study emphasises that the centres of threatened species largely coincide with diversity hotspots, highlighting epiphytes as an especially vulnerable group that requires urgent conservation actions