No abstract

The diversity, abundance and frequency of vascular epiphytes on the lower trunk were compared between two host groups of a Mexican cloud forest: angiosperm trees (n = 72) and tree ferns (n = 28). The bark of the five most frequent host trees and the root mantle of the two tree ferns were analysed for their thickness, water content, water retention capacity and pH. A total of 55 epiphyte species and 910 individuals were found on the 27 host species. On hosts with a dbh range of 5–10 cm, epiphytes were significantly more diverse (4.3±0.9 species per host) and more abundant (12.5±2.2 individuals per host) on tree ferns than on angiosperm trees (1.9±0.2 species per host and 3.9±0.6 individuals per host). However, these differences were not significant for the dbh class of 10–20 cm, because epiphyte numbers increased on angiosperm trees with larger host size, but not in tree ferns. Most epiphyte species had no preference for any host group, but four species were significantly more frequent on tree ferns and two species on angiosperm trees. The higher epiphyte diversity and abundance on tree fern trunks of the smallest dbh class is attributed to their presumably greater age and to two stem characteristics, which differed significantly between host groups, the thicker root mantle and higher water retention capacity of tree ferns. These bark characteristics may favour germination and establishment of epiphytes.

Alaska to Ecuador mega-experiment shows seeds are more likely to be munched toward the tropics and lowlands, as Darwin predicted.

Las Pteridófitas de Chile continental están representadas por 116 especies nativas (43 géneros, 20 familias), y en Argentina continental por 346 (86 géneros, 27 familias). Ambos países comparten 89 especies (41 géneros, 20 familias). La menor diversidad pteridofítica y el mayor endemismo en Chile (11,2 %) que en Argentina (3,5 %) están relacionados probablemente con extinciones históricas y su actual aislamiento geoclimático. Sin embargo, se destaca que el endemismo en los helechos es cinco a seis veces menor que en Angiospermas. Los géneros con más especies en Argentina son Thelypteris (34), Asplenium (32), Cheilanthes (21), Blechnum (19) e Hymenophyllum (16). Los dos últimos también son los más diversificados en Chile (Hymenophyllum, 18 y Blechnum, 10). En la región estudiada la diversidad muestra incrementos latitudinales opuestos, concentrándose en tres centros, dos subtropicales en el noroeste y noreste de Argentina y uno templado-lluvioso en el sur argentino-chileno alrededor de los 40º latitud sur. Los tres centros de diversidad concentran el 93 % de las especies y el 95 % de los endemismos, compartiendo pocas especies entre ellos. En los centros subtropicales las familias Aspleniaceae, Polypodiaceae, Pteridaceae, Thelypteridaceae y Selaginellaceae son sus componentes más importantes, y comparten un gran número de especies con Bolivia y Brasil, respectivamente. El centro templado sur tiene una menor diversidad pteridofítica, pero se hallan en él mayor cantidad de endemismos (77 %) que en los centros subtropicales, a consecuencia de un fuerte aislamiento. Sin embargo, presenta altos índices de similitud e intercambio florístico entre ambas vertientes de Los Andes. Allí las Blechnaceae y Hymenophyllaceae son las familias mejor representadas. Los taxa que presentan una distribución disyunta encontrándose en los tres centros de diversidad, nos indican que la pteridoflora del Cono Sur fue históricamente más extensa y continua, y que sus límites han retrocedido a causa de los impactantes cambios climáticos y geomorfológicos que sucedieron durante el Terciario y el Pleistoceno.

in growth rates. To investigate I measure trunk growth rates, we studied a population of Alsophila firma at Las Canadas, Huatusco, State of Veracruz, Mexico. We measured leaf traits monthly for 26 mo and trunk height at the beginning and end of the study. Alsophila firma showed a unique seasonal pattern of leaf phenology, shedding its leaf pinnules when they are yellow or still green during the wet season, and 50-70% of plants stay leafless for at least 1 mo, after which strongly asynchronous leaf flush occurs. This ?e to evade higher herbivore pressure of the wet season and to t from higher light levels in the understory during the dry season when a proportion of canopy ), and 25% of the plants were fertile. Mean annual trunk growth was 17.1 ± 0.85 cm. Based on "srns (>10 m) are at least 60 yr old.The tree fern families of Cibotiaceae, Cyatheaceae and Dicksoniaceae together comprise over 640 species worldwide (Smith et ah, 2006) of which approximately 180 species occur in the neotropics (Tryon and Tryon, 1982). The neotropical center of diversity extends from the mountain ranges of Costa Rica and Panama to the Andes of Bolivia and Venezuela, with 40-50 species per country. In Mexico, there are 18 species of tree ferns (Mickel and Smith, 2004).Tree ferns are striking elements of the tropical forest vegetation and have attracted attention of ecologists for decades (

Species interactions have long been predicted to increase in intensity towards the tropics and low elevations, due to gradients in climate, productivity, or biodiversity. Despite their importance for understanding global ecological and evolutionary processes, plant-animal interaction gradients are particularly difficult to test systematically across large geographic gradients, and evidence from smaller, disparate studies is inconclusive. By systematically measuring post-dispersal seed predation using 6980 standardized seed depots along 18 mountains in the Pacific cordillera, we found that seed predation increases 18% from the Arctic to Equator and 16% from 4000 masl to sea level. Clines in total predation, likely driven by invertebrates, were consistent across tree-line ecotones and in continuous forest, and were better explained by climate seasonality than by productivity, biodiversity, or latitude. These results suggest that species interactions play predictably greater ecological and evolutionary roles in tropical, lowland, and other less seasonal ecosystems.One Sentence Summary: Post-dispersal seed predation increases from the Arctic to the Equator and from high elevations to sea level. Main Text:Few biological patterns are as striking as latitudinal and elevational changes in biotic communities. Biodiversity and ecosystem productivity increase dramatically toward low latitudes (1, 2) and elevations (3,4). Biologists have long speculated that greater diversity and productivity should generate corresponding increases in the intensity of species interactions (5-7). However, tests for gradients in interaction intensity (8)(9)(10)(11)(12) or their expected ecological and evolutionary signatures (e.g. density dependence 13, 14, defenses 15, 16) find contradictory results. While latitude and elevation are often considered analogues, their effects on interaction strength are rarely tested together. This likely contributes to the variability of experimental results, and limits our understanding of their joint effects on global patterns in species interactions.More intense interactions toward low latitudes and elevations underpin several iconic biogeographic hypotheses. Antagonistic species interactions are thought to maintain high tropical diversity by limiting species dominance (the Janzen-Connell hypothesis; 17, 18), amplify tropical diversity by accelerating speciation (7,19), and play a predictably greater role in determining species' warm (low-latitude and elevation) vs. cool range limits (5,6). For example, stronger tropical seed predation-an interaction that shapes plant communities and distributions (20, 21)-is proposed to explain the greater tropical diversity of trees (14,17,18) and adaptations for seed defense (22). The strength and predictability of interaction gradients is therefore pivotal to understanding their role as macroevolutionary and biogeographic agents.Despite an outsized role in theory, assessing the generality of interaction gradients is hampered by constraints of existing evidence (23). Mos...

In ferns, leaf traces in the petioles are sometimes surrounded by a circumendodermal band (CB), a cell layer of varying structure and arrangement. We studied the CB of 89 fern species from 53 genera and 28 families, and its correlation with leaf trace configuration, leaf dissection and life form, to explore its anatomical diversity, possible origin and suitability for fern systematics. The cells of the CB always contain tannins in their lumina and their walls, but lack lignin and suberin. Cell wall thickness varies among species and may prove to be useful for fern systematics. The occurrence of the CB correlates with a larger number of vascular strands in the leaf trace and a lower degree of leaf dissection, but not with life form. Cystopteridaceae is the earliest branching family with a CB. The exclusive presence of the CB in nine of the most derived fern families supports the hypothesis of a single origin before the divergence of the two major clades of eupolypods. The discontinuity or absence of the CB in some species of derived families (e.g. Polypodiaceae, subfamily Polypodioideae) is interpreted as a secondary loss. Possible functions of the CB are discussed. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169, 596–610.

A population of the giant leather fern Acrostichum danaeifolium was observed during an 18-mo period at La Mancha (19°36′00″N, 96°22′40″W), Veracruz, Mexico. The study site was 230 m from a brackish-water lagoon, in the understorey of the mangroves, which are dominated by Avicennia germinans (Avicenniaceae). Acrostichum danaeifolium showed a clumped distribution pattern, and one third of the population became fertile during this time. Plants had a mean number of 9.4 ± 0.45 sterile leaves, which developed continuously at a rate of 14.6 ± 0.44 leaves y −1 . The mean life span of sterile leaves was 7.7 mo. Although soil water was always available, phenological patterns of fertility, leaf production and leaf growth were strongly correlated with the seasonal climate. Individual leaf growth and leaf size increased significantly during the rainy season. Fertile leaves emerged exclusively from April to August and had a mean life span of 4.1 mo. Spore release was restricted to the wet season, when conditions for germination were favourable. Environmental triggers of fertility are discussed and phenological patterns are compared with ferns and angiosperms from other habitats.Resumen: Se observó una población de Acrostichum danaeifolium durante 18 meses en La Mancha (19°36′00″N, 96°22′40″W), Veracruz, México. El sitio del estudio distaba unos 230 m de una laguna de agua salobre, en el sotobosque de un manglar, que es dominado por Avicennia germinans (Avicenniaceae). Se observó una distribución agrupada de A. danaeifolium, y de la población aproximadamente un tercio de las plantas estuvieron en estado fértil. Las plantas tenían un número promedio de 9.4 ± 0.45 hojas estériles. Estas se desarrollaron continuamente durante todo el año con una formación promedia de unas 14.6 ± 0.44 hojas por año. La longevidad de hojas estériles fue de 7.7 meses. Aunque agua siempre estaba disponible en el suelo, los patrones fenológicos de fertilidad y la producción y el crecimiento de las hojas fueron fuertemente correlacionadas con el clima estacional. El crecimiento individual y el tamaño de las hojas aumentaron significativamente durante la estación lluviosa, y las hojas fértiles brotaron exclusivamente de abril a agosto y sobrevivieron 4.1 meses. Las esporas fueron liberadas únicamente durante la estación húmeda, cuando las condiciones para la germinación eran favorables. Se discuten factores medioambientales que pueden inducir la fertilidad y se comparan los patrones fenológicos con helechos y angiospermas de otros hábitats.