Content uploaded by Luz María Calvo-Irabién
Author content
All content in this area was uploaded by Luz María Calvo-Irabién on Dec 10, 2014
Content may be subject to copyright.
A preview of the PDF is not available
Seed dispersal and germination of the epiphyte Tillandsia brachycaulos (Bromeliaceae) in a tropical dry forest, Mexico
Abstract and Figures
Una necesidad crucial para el mantenimiento de las poblaciones de especies epífitas es la localización de micrositios adecuados en el árbol hospedero. Se necesita una evaluación cuantitativa de la dispersión y germinación de semillas de las epífitas del epífita para entender mejor la colonización exitosa; dicho proceso es particularmente importante en bosques secos, donde la sequía y la oligotrofía disminuyen las tasas de crecimiento poblacional. En un experimento de campo durante tres años, evaluamos la dispersión y germinación de semillas de Tillandsia brachycaulos y exploramos algunos factores ambientales que afectan estas fases del ciclo de vida. Las curvas de dispersión mostraron una variación significante, dependiendo en el año y la altura de la liberación de las semillas. El 41% de las semillas liberadas experimentalmente no fueron dispersadas y solamente cerca del 0.5% de las semillas dispersadas fueron capturadas en trampas de semillas. El número de semillas capturadas disminuyó a medida que se incrementó la distancia, la mayoría de las semillas se capturaron en los primeros 1.5 m de la fuente de semillas. Las semillas dispersadas a distancias más largas (15 m) provenían de las fuentes ubicadas a mayor altura. La germinación de semillas en el laboratorio fue mayor (98%) que la encontrada en campo (3%). Ni el año ni la altura del árbol afectó la germinación en una manera estadísticamente significativa. Las diferencias en la dispersión y la germinación de semillas entre años podrían ser causadas por la precipitación variable. El establecimiento de nuevos individuos es, al parecer, un cuello de botella importante en el crecimiento poblacional de T. brahcycaulos. Nuestros resultados muestran que la dispersión y la germinación son procesos determinantes en dicho establecimiento.
Figures - uploaded by Luz María Calvo-Irabién
Author content
All figure content in this area was uploaded by Luz María Calvo-Irabién
Content may be subject to copyright.
... The Bromeliaceae family is characterized by its great adaptability and resistance to extreme environmental conditions (Alvarado-Fajardo et al. 2013), and some of its species have been previously reported in tropical dry forests (Mondragón & Calvo-Irabien 2006;Vargas 2012;Rodríguez et al. 2012;Pizano & García 2014;Victoriano-Romero et al. 2017). Bromeliaceae comprises one of the most morphologically and ecologically distinct clade of Neotropical Angiosperms, with more than 3,100 described species, distributed among eight subfamilies (Givnish et al. 2011). ...
... The study of this phase is of fundamental importance, both for understanding the establishment of a plant community and for the survival and natural regeneration of species. In Bromeliaceae, some studies have described the morphology and anatomy of seeds (Cecchi-Fiordi et al. 1996, 2001Morra et al. 2002;Palací et al. 2004;Strehl & Beheregaray 2006;Scatena et al. 2006;Ferreira et al. 2009;Pereira et al. 2010;Magalhães & Mariath 2012;Corredor-Prado et al. 2014;Chilpa-Galván et al. 2018), as well as their post-seminal development (Pereira 1988;Scatena et al. 2006;Tillich 2007;Pereira et al. 2008Pereira et al. , 2009Pereira et al. , 2010Ferreira et al. 2009;Silva & Scatena 2011), and others have focused on their germination (Mondragón & Calvo-Irabien 2006;Mora et al. 2007;Pereira et al. 2008Pereira et al. , 2009Goode & Allen 2009;Valencia-Díaz et al. 2010;Silva & Scatena 2011;Montes-Recinas et al. 2012;Sosa-Luría et al. 2012;Chilpa-Galván et al. 2018;Duarte et al. 2018). These studies show the adaptive strategies in the environment where the species are found, contribute to the taxonomic circumscription, to the knowledge about seed germination and conservation, and to the production of seedlings for the recovery of degraded areas. ...
... The production of seedlings maintains the genetic variability of the species, which is an important ecological factor for studies of recovery of degraded areas (Pereira et al. 2008). Several studies found epiphyte seeds to germinate in the field at rates between 0% and 10%, while in vitro they reach high percentages (Mondragón & Calvo-Irabien 2006;Toledo-Aceves & Wolf 2008;Goode & Allen 2009). Considering this, it would be necessary to carry out studies to evaluate the effectiveness of Bromeliaceae seeds or seedlings for the restoration in tropical dry forest. ...
Drastic changes in dry tropical forest result in the loss of biological components and reveal the importance of studies on the biology of species living in it. The present study aimed to describe seed morphoanatomy, germination and post-seminal development of Bromeliaceae species in fragments of tropical dry forest in Sucre, Colombia. Seven species representing Bromelia and Tillandsia genera were evaluated. The results provide characteristics related to the habitat of each species and contribute to distinguish the genera evaluated: fruit and seed measurements, seed shape, plumose appendage, testa characteristics, and the aleurone layer, embryo endosperm ratio, types of reserves, constriction zone in the embryo and type of post-seminal development. Characteristics of plumose appendages and the presence of vascular bundles in the embryo also contribute to distinguish Tillandsia species. In T. elongata and T. flexuosa, high number of seeds per fruit (> 100), morphoanatomical aspects, high germination (> 92%) and plant formation (> 77%) percentages, and higher germination rate values (> 4.5) give them the potential capacity for establishment in this environment. Our results provide information with taxonomic and ecological relevance for bromeliads in dry tropical forest.
... In nonvascular epiphytes and epiphytic lichens, several observational studies and a few experiments show an important role of dispersal limitation (e.g., Sillett et al. 2000), environmental filtering based on species traits , and epiphyte-epiphyte biotic interactions in shaping community assembly (reviewed in Ellis 2012, Antoine 2004, Spicer andWoods 2022). For both epiphytic and terrestrial plants, the earliest life stage transitions are key bottlenecks to individual survival and community development (Harper 1977, Ackerman et al. 1996, Zotz and Vollrath 2002, Mondragon and Calvo-Irabien 2006, Victoriano-Romero et al. 2017. ...
... We did not add any water, nutrients, or growth hormones (cf. laboratory germination experiments; Arditti 1967; Arditti and Ghani 2000; Mondragon and Calvo-Irabien 2006). We also did not affix the seeds to the subplot, unlike other seed field experiments (Mondragon and Calvo-Irabien 2006, Hietz et al. 2012, Ruiz-Cordova et al. 2014, Shao et al. 2017, Vergara-Torres et al. 2018 because our goal was to expose the epiphytes to in situ processes. ...
... laboratory germination experiments; Arditti 1967; Arditti and Ghani 2000; Mondragon and Calvo-Irabien 2006). We also did not affix the seeds to the subplot, unlike other seed field experiments (Mondragon and Calvo-Irabien 2006, Hietz et al. 2012, Ruiz-Cordova et al. 2014, Shao et al. 2017, Vergara-Torres et al. 2018 because our goal was to expose the epiphytes to in situ processes. Glue can also diminish the germination of seeds (Ruiz-Cordova et al. 2014). ...
Epiphytes are a unique group of plants that live nonparasitically on other plants (hosts) and constitute approximately one-fifth of Neotropical vascular plant diversity. However, the processes governing early epiphyte community assembly are poorly understood and have scarcely been experimentally tested. Here, we use an in situ experiment in the cloud forest of Santa F, Panama, to evaluate the extent to which host substrate texture regulates early epiphyte establishment. We experimentally varied the surface roughness of native wood substrates, applied bromeliad and orchid seeds to the substrates, and monitored emergence of epiphyte seedlings and their persistence for a year. Rougher substrates facilitated higher initial abundance of epiphyte seedlings; after two months, 81% of the 1,934 total germinated epiphytes occurred on the substrates with experimentally added roughness. Via photo analysis, we also show that epiphytes disproportionately established early on in the experimental grooves, wherein 71% more epiphytes per unit area occurred within 1.5 mm of the grooves than on nearby smooth surfaces. While epiphyte cohort survival rates differed between rough and smooth substrates in the first six months, more than 99% of all seedlings died after one year, regardless of experimental roughness treatment. Only 10 seedlings survived through the end of the experiment. Our results suggest that while substrate texture explains some variation in early epiphyte emergence, roughness alone is not sufficient to explain epiphyte persistence to adulthood. Moreover, our results highlight the importance of removal processes (e.g., wind, rain, animals) in structuring early epiphyte community assembly. Variation in substrate texture may contribute to differences in epiphyte diversity and community composition within- and among-host tree species, but more experiments are needed to disentangle removal processes from substrate-mediated host affinity.
... In Bromeliaceae, the second-most species-rich plant family in the Neotropics (Ulloa Ulloa et al. 2017), seed germination (i.e. sexual reproduction) plays an important role in the population dynamics of many species (Benzing 1978;García-Franco and Rico-Gray 1991;Santos 2001;Sampaio et al. 2002;Pinheiro and Borghetti 2003;Winkler et al. 2005Winkler et al. , 2007Lenzi et al. 2006;Mondragon and Calvo-Irabien 2006;Nunes-Freitas and Rocha 2007;Paggi et al. 2007;Mantovani and Iglesias 2008;Toledo-Aceves and Wolf 2008;Bader et al. 2009;Toledo-Aceves et al. 2012;Wagner et al. 2013;Müller et al. 2017). The ecology of germination has not been extensively described in this family (Smith and Downs 1974;Müller et al. 2017;Males 2018), and, to our knowledge, there has been no study analysing the effects of the light environment where the mother plant lived on seed germination for any bromeliad species. ...
... Although asexual reproduction may be important in bromeliads population dynamics (Villegas 2001;Sampaio et al. 2002Sampaio et al. , 2004Sampaio et al. , 2005Ticktin and Nantel 2004;Ticktin 2005;Duarte et al. 2007;Nunes-Freitas and Rocha 2007;Rogalski et al. 2007;Mantuano and Martinelli 2008;Barberis et al. 2020), germination is a key 'bottleneck' in the determination of species distributions (Müller et al. 2017) and bromeliads are not the exception (Mondragon and Calvo-Irabien 2006). The results found in this study may help understand the links between certain aspects of the regeneration niche of Bromelia serra and the distribution of its individuals in Schinopsis balansae xerophytic forests. ...
Context Some plant species show within-generational and trans-generational phenotypic plasticity associated with the light environment for germination traits. In bromeliads, light affects the seed germination of several species, but there is no study analysing the effects of the light environment where the mother plant lived on seed germination. Bromelia serra inhabits the understorey of xerophytic forests, where individuals could be conditioned by the heterogeneous light environment because its cover and abundance are negatively associated with tree basal area and woody vegetation cover. Aims To analyse the effect of the light environment on seed germination of B. serra, considering also the light environment where the mother plant lived. Methods In four patches from three different sites in a stand of a Schinopsis balansae forest, 48 fruiting plants of B. serra were harvested. Canopy openness was obtained from a hemispherical photograph taken above each plant. From each infructescence, half of the seeds from five fruit were kept in light conditions and the remaining seeds in dark conditions in a germination room. Key results There was no effect of the light environment where mother plants lived on seed germination, but the light environment in the germination room positively affected germination variables. Conclusions The positive effect of light on seed germination of B. serra might explain the spatial distribution of individual plants in these xerophytic forests. Implications These results have enhanced our understanding of the regeneration and distribution of understorey herbaceous species in these South American forests.
... Los árboles remanentes son importantes porque contribuyen al mantenimiento de una porción de la diversidad de las epífitas en el paisaje (Barthlott et al., 2001;Werner et al., 2005;Hietz et al., 2006;Poltz y Zotz, 2011). Sin embargo, la configuración del sistema silvopastoril dificulta los flujos de semillas e intercambio genético de las epífitas entre los fragmentos de bosque y los árboles remanentes (Zotz y Vollrath, 2003;Flores-Palacios y García-Franco, 2006;Mondragon y Calvo-Irabien, 2006). Por ello, las comunidades de epífitas se empobrecen paulatinamente con el tiempo de aislamiento y con el aumento de la distancia hacia los remanentes de los bosques (Werner y Gradstein, 2008;Köster et al., 2009;Poltz y Zotz, 2011;Werner, 2011;Einzmann et al., 2016). ...
... Las especies epífitas de cactáceas tienen una alta capacidad de adaptación a la falta de disponibilidad de agua debido a su metabolismo ácido de las crasuláceas (CAM, por sus siglas en inglés) y a su capacidad de almacenamiento de reservas de agua y nutrientes (Andrade y Nobel, 1997). Se anticipaba la contribución a la riqueza total de la familia Bromeliaceae, ya que muchas de sus especies han desarrollado adaptaciones morfológicas y ecofisiológicas (p.ej., mayor cantidad de tricomas espe-cialmente en bromelias atmosféricas, presentan metabolismo de fotosíntesis CAM y tienen hojas arrosetadas que retienen agua en sus tanques) que les permite colonizar los bosques tropicales secos (Mondragon y Calvo-Irabien, 2006;Chilpa-Galván et al., 2013. Esto a pesar de las condiciones ambientales estresantes que imperan en estos bosques en comparación con sus contrapartes más húmedos (p.ej., sequía más severa, menor humedad y mayor radiación solar). ...
... Another plausible explanation for the predominance of Tillandsia in the dry forests studied is their anemochore dispersion, with plumose diaspores, which allow them to fall faster and therefore be more likely to establish near the mother plant, in comparison to winged diaspores, which can travel large distances from mother plants (Benzing, 1990). Moreover, when the height of the host increases, they can reach distances of up to 15 m (Bernal, Valverde, & Hernández-Rosas, 2005;Ibarra-Manríquez, Sánchez-Garfias, & González-García, 1991;Mondragón & Calvo-Irabien, 2006), allowing their distribution along with vertical distribution in the host, increasing their tolerance to dry environments. ...
Host traits partly determine the abundance and species richness of epiphytes in tropical forests. It has been proposed that older trees with rough bark and evergreens often house more individuals and more epiphytic species than those with thin, smooth, and peeling bark, which harbor few epiphytes. We hypothesize (i) that epiphytes are more abundant and species‐rich in the more shaded forest, which is related to bark roughness, and (ii) that epiphytes are distributed in the middle of the host, where microenvironmental conditions are more favorable to survival. We evaluated abundance, species richness, and vertical distribution of epiphytes in two tropical dry forests, according to the deciduousness and basal area of the trees. Moreover, we selected the most abundant epiphytes to test whether their distribution is related to a specific bark type and examine their vertical distribution in two dry forests. We distinguished a high abundance and species richness of epiphytes in the deciduous forest, although basal area and host species richness were higher in the semi‐deciduous forest. In both forests, we found a positive relationship between epiphyte abundance and basal area. Higher abundance of epiphytes was related to the predominance of Tillandsia schiedeana, a drought‐adapted species, in both forests. Unexpectedly, epiphytes abundantly colonized Bursera simaruba, a host with peeling bark and a very branched crown, where small individuals of T. schiedeana colonized abundantly toward the top of the crown. Our results show the importance of the tropical dry forest, particularly, B. simaruba, in maintaining epiphyte diversity in terms of T. schiedeana colonization. Small individuals of the bromeliad Tillandsia schiedeana colonize abundantly toward the top of the crown of Bursera simaruba, a peeling host from tropical dry forests.
... Although most epiphytes are anemochorous and release their diaspores from high above the ground, which makes long-distance dispersal much more likely than in small terrestrial herbs (Tackenberg 2003), most seedlings establish close to their mother plant Mondragón & Calvo-Irabien 2006;Paggi et al. 2010). Since epiphytes may as easily disperse into a tree in close proximity as to the other side of the crown of the same tree, a group of neighbouring trees is also a meaningful spatial unit. ...
1. Despite the ecological importance of vascular epiphytes in the tropics, even basic information on the processes that form epiphyte communities is scarce. This is partially due to an almost complete lack of long‐term studies. 2. Here, we present data that was collected in three consecutive censuses over 21 years in a monospecific host tree system that is about 100 years old and interpret them in an empirical‐ and a metapopulation/metacommunity framework. 3. We documented an ongoing increase in abundance and diversity at the level of the entire system (metacommunity) and at the level of communities (all epiphytes growing on individual Annona glabra tree stands). This was also reflected at the population level; >2/3 of the species showed positive population growth rates. Similarly, colonisation of empty Annona trees was still ongoing, with the most abundant species being also the first to colonise empty trees. The community composition of colonised trees became more similar with time. In all three censuses, habitat size of epiphytes explained much of the variation in species richness among stands (groups of trees with individual trees within 25 m of each other) and overall abundant species tended to be more abundant at the stand scale. The species frequency distribution was unimodal, regardless of whether considering all stands or only stands with very large epiphyte communities, indicating that the metacommunity still has not reached an equilibrium phase. Similarly consistent in both census intervals, population growth rates decreased with increasing population size with substantial asynchrony among populations. 4. Synthesis: In contrast to a typical herbaceous plant community, this epiphyte metacommunity is still expanding after one century of development. Our study shows that previously reported short‐term patterns of epiphyte community dynamics hold true in the long term. It remains to be shown, however, whether results from this monospecific host tree system are really representative for epiphyte community dynamics in more diverse tropical forests.
... Additionally, an increase in dispersal limitation leading to an overrepresentation of anemochorous species should not impact our overall conclusions given that the relative abundance in the community is not a factor in our analyses.Therefore, it remains to be seen how increased dispersal limitation and differences in dispersal syndrome may influence assemblages of accidental epiphytes and facultative hemiepiphytes. However, clues from obligate epiphytes elsewhere suggest high levels of dispersal limitation may be an important factor in species abundance(Ackerman et al., 1996;Mondragón and Calvo-Irabien, 2006;Victoriano-Romero et al., 2017), especially within forest interiors(Cascante-Marín et al., 2009). ...
Aims
Shade‐tolerant tree species often produce larger seeds with greater energetic resources to cope with light limitation. On the other hand, shade‐intolerant species often produce smaller seeds with greater dispersal potential to colonise lighter, more‐disturbed areas of forest. We test the hypothesis that small‐seeded species utilise an alternative recruitment strategy in a southern temperate rainforest by establishing epiphytically on the trunks of tree ferns.
Location
Wellington region, North Island of New Zealand
Methods
To assess whether small‐seeded tree species rely on tree fern epiphytism for recruitment we quantified relative abundances of both epiphytic and terrestrial subpopulations in 14 woody plant species across a range of seed sizes. We used a paired study design where we surveyed all 3727 woody plants occurring on 322 tree ferns and in matching forest floor plots of equivalent area. Using a linear model, we then assessed the relationship between species’ seed size and their epiphytic tendency (arboreality).
Results
Arboreality scores differed both between species and between life history stages. Seed size predicted arboreality regardless of life history stage, with small‐seeded species more likely to occur arboreally than larger‐seeded ones. However, the effect of seed size decreased predictably in later life history stages. Seed size also predicted arboreality when the model was re‐run using subsets of data restricted to common understorey tree ferns.
Conclusion
Interspecific differences in the epiphytic establishment of New Zealand tree species are pronounced, with only smaller‐seeded species able to use this regeneration niche. Small‐seeded species, especially Weinmannia racemosa , appear to be utilising an alternative recruitment strategy by establishing epiphytically on tree fern trunks.
... The main factor that affects epiphytic occurrence might be the dispersal mode of a species (Schimper 1888). Limited seed dispersal has been shown to be a major limitation of the abundance in tropical epiphytes (Ackerman et al. 1996;Mondragon and Calvo-Irabien 2006;Cascante-Marín et al. 2009). However, we are not aware of any attempt to relate dispersal traits to species abundance of accidental epiphytes. ...
Background: Accidental epiphytism is common among vascular plants in forest ecosystems around the globe. A frequent observation in surveys of accidental epiphytes is the occurrence of few species with high epiphytic abundance, while most co-occurring terrestrial species are rarely found as epiphytes.
Aims: Based on the general assumption that water is the major limiting factor for epiphytic plants, we hypothesised that differences in drought resistance of accidental epiphytes explain the difference in epiphytic abundances.
Methods: We exposed 16 species with different epiphytic abundance in central Europe to experimentally induced drought during germination and growth of juvenile plants.
Results: Drought resistance differed substantially among species but did not correlate with their epiphytic abundance, neither during germination nor during juvenile growth.
Conclusions: In central Europe, accidental epiphytes are usually found on moss cushions or in accumulated arboreal soil on their host tree. In such water-storing substrates, water availability might be less limiting than it is for obligate epiphytes that typically grow on bare bark, which would explain the lack of a correlation between drought resistance and epiphytic abundance of the studied species. Hence, other factors must explain the consistent differences in epiphytic abundance, e.g. dispersal traits and mass effect.
en Tropical non-self-supporting plants such as hemiepiphytes and nomadic vines are model organisms for disentangling biotic and environmental correlates which influence their occupancy patterns. We inventoried >4000 individuals from >3000 trees ranging from 1 to 200 cm diameter at breast height (DBH) in a northeastern Amazonian upland forest to address how tree (phorophyte) size, edaphic factors and recruitment strategy influence occupancy, diversity, and compositional patterns of two vascular non-self-supporting plant functional groups. Hemiepiphytes germinate on phorophytes prior to establishing soil connections, whereas nomadic vines initiate their life cycle on the forest floor and subsequently climb phorophytes for crown access, abandoning roots replaced by adventitious connections which may reach the ground. Our results show that larger phorophytes (≥30 cm DBH) supported more species for both hemiepiphytes and nomadic vines. However, nomadic vines' occupancy probabilities saturated faster at smaller stem sizes than that of hemiepiphytes indicating differential preferences for stem sizes among the two functional groups. For smaller phorophytes (<30 cm DBH), soil correlations were stronger with nomadic vines than hemiepiphytes, whereas no significant differences were detected among functional groups in relation to edaphic factors for larger (≥ 30 cm DBH) ones. Finally, a small core group of species showed disproportionately greater abundances among large phorophytes suggesting that autogenic processes differentially promote survivability. Such interactions among phorophyte size and edaphic factors may result from the contrasting ecological requirements of hemiepiphytes and nomadic vines at the recruitment stage, demonstrating the necessity for elaborate demographic-based studies to better understand these complex plant–plant interactions.
Abstract in Spanish is available with online material
RESUMO
es Las hemiepífitas y lianas nómades son plantas tropicales que no se sostienen a sí mismas y sirven como organismos modelo para desenredar las correlaciones bióticas y ambientales que influyen en sus patrones de ocupación. Inventariamos más de 4000 individuos en más de 3000 árboles que van desde 1 a 200 cm de diámetro a la altura del pecho (DAP) en un bosque de tierras altas en el noreste de la Amazonía para abordar cómo el tamaño del árbol (forófito), los factores edáficos y la estrategia de reclutamiento influyen en la ocupación, diversidad y patrones de composición de dos grupos funcionales de plantas vasculares no autosuficientes. Las hemiepífitas germinan en los forófitos antes de establecer conexiones con el suelo, mientras que las lianas nómades inician su ciclo de vida en el suelo del bosque y subsecuentemente trepan a los forófitos para acceder a la copa, abandonando las raíces reemplazadas por conexiones adventicias que pueden llegar al suelo. Nuestros resultados muestran que los forófitos más grandes (>30 cm DAP) soportaron más especies tanto para hemiepífitas como para lianas nómades. Sin embargo, las probabilidades de ocupación de las lianas nómadas se saturaron más rápido en tamaños de tallo más pequeños que las hemiepífitas, lo que indica preferencias diferenciales por los tamaños de tallo entre los dos grupos funcionales. Para los forófitos más pequeños (<30 cm DAP), las correlaciones del suelo fueron más fuertes con las lianas nómades que con las hemiepífitas, mientras que no se detectaron diferencias significativas entre los grupos funcionales en relación con los factores edáficos para los más grandes (> 30 cm DAP). Finalmente, un pequeño grupo central de especies mostró abundancias desproporcionadamente mayores entre los forófitos grandes, lo que sugiere que los procesos autógenos promueven la supervivencia de manera diferencial. Tales interacciones entre el tamaño de los forófitos y los factores edáficos pueden resultar de los requisitos ecológicos contrastantes de las hemiepífitas y las lianas nómades en la etapa de reclutamiento, lo que demuestra la necesidad de elaborar estudios demográficos para comprender mejor estas complejas interacciones planta-planta.
The phenology of vascular epiphytes, which account for about 10 % of the world's flowering plants and perform important ecological functions, has been just partially explored. Since phenology is a key tool for the management and conservation of species, the objective of this review was to synthesize the information published so far about the phenology of vascular epiphytes, detect gaps of knowledge, and suggest future lines of investigation to understand the underlying mechanisms. We conducted an online search for articles in Google Scholar and in the ISI Web of Science database from 1800 to 2020, with different combinations of keywords. 107 studies addressing the phenology of different holoepiphyte species were found; 88 % of the studies were performed in the Neotropic, especially in tropical and subtropical wet forests. The phenology of only ca. 2 % (418 spp.) of all reported holoepiphyte species has been explored. There is a bias toward the study of the flowering and fruiting phenology in members of the Orchidaceae (192 spp.) and Bromeliaceae (124 spp.) families. In general, the vegetative and reproductive phenology of epiphytes tends to be seasonal; however, there is a huge gap in our understanding of the proximate and ultimate factors involved. Future research should explicitly focus on studying those factors.
The habitat preference and spatial distribution within a habitat of Guzmania monostachia, Catopsis berteroniana, C. floribunda and C. nutans were examined. These epiphytic bromeliads are not randomly distributed but are patchy, confined to Fraxinus caroliniana-Annona glabra swamps. Distribution within the habitat is subject to a number of constraints: temperature and light gradients, aspect, location of host species in the habitat and distribution among hosts. Host morphology is also an important distribution factor. The number of principal vertical stems produced by a single tree (DBH) or the basal area of all host plants per clump were positively correlated with abundance of all epiphytic species. Host DBH had little effect on species abundance, except for the number of C. nutans per stem. The 4 species were distributed over vertical stem gradients in the following sequence (low-high): Guzmania, C. nutans, C. floribunda and C. berteroniana. The distribution of Guzmania and Catopsis is patchy because of clumping in preferred habitats, habitat constraints, and host morphology. Seeds and seedlings were more abundant on epiphytic bryophytes than on exposed bark. -from Author
1 The influence of dispersal patterns on the local distribution and abundance of the mistletoe, Phrygilanthus sonorae (Loranthaceae) is investigated. 2 Mistletoe and host distributions were measured at several subsites at two field sites in Baja California. Dispersal patterns were determined both by bird observation and the locations of dispersed seeds. The observed correlations between patterns of dispersal and patterns of mistletoe infection are interpreted by treating the mistletoe population as a metapopulation of the mistletoes on individual trees. 3 Mistletoe seeds were dispersed artificially to test experimentally for differences in the establishment success of mistletoe seedlings between individuals within a host species or between host species. No evidence was found for individual differences in susceptibility of hosts within a site or for host specific races of Phrygilanthus sonorae. 4 Sites and subsites differed dramatically in frugivore sets, dispersal patterns and the relative density of host trees (relative to all large trees and shrubs in the community). 5 A number of patterns of mistletoe distribution are explained by dispersal. Within subsites, the proportion of a size class infected by mistletoes (cohort occupancy) increases with the size of the class. This size-occupancy relationship is predicted from a metapopulation model with patch (tree) turnover. Subsites within sites differ in the slope of the size-occupancy relationship and in the overall proportion of hosts infected by mistletoes (overall occupancy). These differences between subsites are explained by differences in the proportion of mistletoe seeds that are dispersed off the parent host tree and the efficiency of the off-tree dispersal, but not by overall dispersal efficiency. 6 Differences in mistletoe establishment success, adult mistletoe mortality and host turnover do not explain the observed patterns of infection.
We report the results of the first complete samples of all plant species and individuals for any lowland tropical forest in the world. The three forests sampled are in western Ecuador; Rio Palenque, Jauneche, and Capeira are, respectively, wet, moist, and dry forests. In each forest we sampled all vascular plants in a 0.1-ha area. At wet forest Rio Palenque, nontree habit groups make up most of the sampled species and individuals. Over a third of the species and almost half the individual plants are epiphytes, 13 percent of the species are terrestrial herbs, 10 percent are shrubs, and 9 percent nonepiphytic climbers. The moist and dry forest samples have many fewer species, largely due to many fewer epiphytes. The new data are compared with the most diverse 0.1-ha samples from elsewhere in the world. Our wet forest sample is by far the most species-rich such sample yet recorded and would remain so even if all tree species were excluded from the data.
A new hypothesis is given to account for the maintenance of higher tree species richness at lower latitudes, which does not invoke the influence of animals. Vine and epiphyte loads of wet, lowland forest canopy increase dramatically at low latitudes, and these loads may be an important cause of the high tree fall rates of such tropical forests. The perennial patchwork of disturbance generated by high tree fall rates could maintain forest as a perpetual preclimax mosaic, increasing the diversity of sapling environments, and reducing the frequency of long-term competitive interactions between adjacent individuals.
The epiphyte communities of a Costa Rican cloud forest make up a conspicuous portion of the canopy, especially on large canopy dominants. Non-destructive sampling methods were used to assess the composition, biomass, and nutrient concentration of live and dead epiphytes on representative host trees to determine the mineral capital contained in the epiphyte components of the standing vegetation. Epiphyte standing crop on a single large Clusia alata (Guttiferae) tree is 141.9 kg. The nutrient capital (in g) is: N = 3062; P = 97; K = 678; Ca = 460; Mg = 126; Na = 207. Using information on forest structure and epiphyte distribution, stand-level estimates of epiphyte mat nutrient capital were made. Although epiphyte biomass constitutes less than 2 percent of total elfin forest ecosystem dry weight, the nutrients they contain are equivalent to up to 45 percent of nutrients contained in ecosystem foliage of similar ecosystems. Assessment of epiphyte nutrient capital gives a more complete and accurate idea of the aboveground vegetation pools, and supports the idea that epiphytes may play a greater role in ecosystem nutrient dynamics than has been previously considered.