Contrasting effects of host tree isolation on population connectedness in two tropical epiphytic bromeliads.

PREMISE: Conversion of primary forests to pastures is a major cause of habitat fragmentation in the tropics. Fragmentation is expected to impede gene flow for many plant species that are restricted to remaining forest fragments. Epiphytes may be especially vulnerable to this effect of forest fragmentation because they depend on host trees. However, trees that remain in pastures may enhance connectivity across the landscape for epiphyte species that can thrive on such trees. To investigate this possibility, we studied the genetic structures of two such species on isolated pasture trees and surrounding forest, in relation to their local abundances in different habitat types and aspects of their reproductive biology including pollen and seed dispersal agents, and looked for evidence of increased or diminished gene flow. METHODS: We used microsatellite markers to assess geographic patterns of genetic diversity and differentiation in two epiphytic bromeliads, Catopsis nitida and Werauhia tonduziana, in the Monteverde region of Costa Rica. RESULTS: About 85% of the FST value for Catopsis nitida was found among pastures within regions, while for Weruahia tonduziana, about 80% of the FST value was contributed by differences between regions, indicating much more gene flow within regions, relative to C. nitida. CONCLUSIONS: Although there was substantial genetic differentiation among epiphyte populations, those on isolated pasture trees were not substantially less diverse than those in adjacent forests, suggesting that pasture trees may serve as "stepping stones" that help these species maintain their genetic connectedness and diversity at larger geographic scales.

Reproductive phenology of epiphytes in Monteverde, Costa Rica

Phenology of plants, or the timing of life cycle events, is important for understanding plant ecology, forest dynamics, and plant-animal interactions. In tropical forests, studies that document epiphyte reproductive phenology are relatively few because of the challenges of tracking plants that live in the canopy. Phenological patterns for 279 individuals of 7 epiphyte species were examined across 12 months in a tropical montane forest in Monteverde, Costa Rica. Epiphytes were located in one of two common tree species, Ficus tuerckheimii (Moraceae) or Ocotea tonduzii (Lauraceae). Flowering and fruiting (i.e., when ripe or unripe fruit is present on the plant) of study plants was recorded on monthly intervals, and phenology was examined as a function of the season at the study site (i.e., wet, transition, or dry season), and pollinator syndrome (bird-, or insect-pollinated) and seed dispersal syndrome (bird-, bat-, or wind-dispersed) of each plant. Though some epiphyte species flowered and fruited throughout the year, the majority showed significant seasonality in phenological events. Based on circular statistics, the timing of mean flowering of different epiphyte species varied, however, timing of mean fruiting for most species tended to occur during the wet season. Insect- and bird-pollinated species had peak flowering during the dry season and late wet season, respectively. Bird-dispersed fruits were present each month of the year with peaks from February to October and again in December. Wind-dispersed fruits were observed eight months of the year with a peak in the early wet season. The timing of epiphyte flowering coincided with flowering of large trees in the area. Epiphyte fruiting, however, is distinct from large tree fruiting. Our results demonstrate the seasonal nature of flowering and fruiting in individual epiphyte species while also highlighted the asynchronous nature of phenological events amongst the epiphyte community.

La fenología de las plantas, o el cronograma de eventos en el ciclo de vida, es importante para la comprensión de la ecología vegetal, la dinámica de los bosques y de las interacciones planta-animal. En los bosques tropicales, los estudios que documentan la fenología de las epífitas son relativamente pocos debido a los desafíos que representa darles seguimiento a las plantas que viven en el dosel. Aquí se presenta un reporte de los patrones fenológicos de 279 individuos de 7 especies de epífitas que abarca 12 meses en un bosque montano tropical en Monteverde, Costa Rica. Las epífitas se encuentran en una de las dos especies de árboles comunes, Ficus tuerckheimii (Moraceae) u Ocotea tonduzii (Lauraceae). Se registró la floración y fructificación (i.e. cuando la fruta madura o inmadura está presente en la planta) de las plantas de estudio en intervalos mensuales y examinó la fenología a través de las estaciones en el sitio de estudio (i.e. estación húmeda, transición, o seca) y el síndrome de polinizadores (ave- , o insecto-polinización ) y el síndrome de dispersión de semillas (ave-, murciélago-, o viento- dispersión) de cada planta. Aunque la mayoría de las especies de epífitas tuvieron flores y frutos durante todo el año, la mayoría mostró estacionalidad significativa en los eventos fenoló-gicos. Con base en estadísticas circulares, el tiempo de floración promedio de las especies de epífitas es variado, sin embargo, el momento de la fructificación promedio para la mayoría de las especies tiende a ocurrir durante la estación húmeda. Especies de insectos y aves de polinización tenían pico de floración durante la estación seca y la estación lluviosa tarde, respectivamente. Frutas dispersadas por aves estaban presentes todos los meses del año con picos de febrero a octubre y de nuevo en diciembre. Frutas dispersadas por el viento se observaron ocho meses del año con un pico en la temporada de lluvias temprana. El momento de la floración de las epífitas coincidió con la floración de árboles de gran tamaño en la zona. La fructificación de las epífitas, sin embargo, fue diferente de la fructificación de los árboles de gran tamaño. Nuestros resultados ponen de manifiesto el carácter estacional de la floración y fructificación de las especies epífitas individuales, además de destacar el carácter asincrónico de los eventos fenológicos entre toda la comunidad de epífitas.

Epiphytic and terrestrial mycorrhizas in a lower montane Costa Rican cloud forest.

The epiphyte community is the most diverse plant community in neotropical cloud forests and its collective biomass can exceed that of the terrestrial shrubs and herbs. However, little is known about the role of mycorrhizas in this community. We assessed the mycorrhizal status of epiphytic (Araceae, Clusiaceae, Ericaceae, and Piperaceae) and terrestrial (Clusiaceae, Ericaceae) plants in a lower montane cloud forest in Costa Rica. Arbuscular mycorrhizas were observed in taxa from Araceae and Clusiaceae; ericoid mycorrhizas were observed in ericaceous plants. This is the first report of intracellular hyphal coils characteristic of ericoid mycorrhizas in roots of Cavendishia melastomoides, Disterigma humboldtii, and Gaultheria erecta. Ericaceous roots were also covered by an intermittent hyphal mantle that penetrated between epidermal cells. Mantles, observed uniquely on ericaceous roots, were more abundant on terrestrial than on epiphytic roots. Mantle abundance was negatively correlated with gravimetric soil water content for epiphytic samples. Dark septate endophytic (DSE) fungi colonized roots of all four families. For the common epiphyte D. humboldtii, DSE structures were most abundant on samples collected from exposed microsites in the canopy. The presence of mycorrhizas in all epiphytes except Peperomia sp. suggests that inoculum levels and environmental conditions in the canopy of tropical cloud forests are generally conducive to the formation of mycorrhizas. These may impact nutrient and water dynamics in arboreal ecosystems.