ROLE OF SURFACE WOUNDS AND BROWN ALGAL EPIPHYTES IN THE COLONIZATION OF ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FRONDS BY VERTEBRATA LANOSA (RHODOPHYTA)1

Ascophyllum nodosum (L.) Le Jol. forms extensive beds in wave‐sheltered, rocky intertidal habitats on the northwestern Atlantic coast. This fucoid seaweed is host to an obligate red algal epiphyte, Vertebrata lanosa (L.) T. A. Chr. [=Polysiphonia lanosa (L.) Tandy], and two facultative brown algal epiphytes, Elachista fucicola (Velley) Aresch. and Pylaiella littoralis (L.) Kjellm. Although V. lanosa can occur throughout most of the length of host fronds, it largely predominates in midfrond segments. The two brown algal epiphytes are restricted to distal segments. Through field experiments conducted in Nova Scotia, Canada, we tested the hypothesis that surface wounds are required for the colonization of distal segments of host fronds by V. lanosa. Distal tissues normally have a smooth surface because of their young age (A. nodosum fronds grow apically). By creating small wounds that mimicked grazing wounds distributed elsewhere on host fronds, we demonstrated that V. lanosa can colonize distal frond segments during the growth and reproductive season (summer and autumn). Approximately half of the artificial wounds were colonized by V. lanosa during this time. The experimental exclusion of both brown algal epiphytes from distal frond segments did not affect colonization by V. lanosa. Thus, we conclude that the absence of surface irregularities on distal segments of host fronds, specifically small wounds, is the main factor explaining the absence of V. lanosa there. We propose that further experimental work clarifying epiphyte distribution in host beds will enhance our ability to understand the functional role of epiphytes in intertidal ecosystems.     

THE RED ALGAL EPIPHYTES MICROCLADIA COULTERI AND M. CALIFORNICA (RHODOPHYCEAE,CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytes Microcladia californica Farl. and M. coulteri Harv. was examined by studying the interface with their respective basiphytes and by cross-inoculation experiments. Microcladia californica attaches only to the surface of its single basiphyte Egregia menziesii (Aresch.) Turn. whereas M. coulteri penetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross-inoculation experiments show that Microcladia californica is not able to colonize the basiphytes of M. coulteri, Iridaea and Prionitis, or Ulva. The mechanisms by which these algae restrict the growth of epiphytes include short life-span, “cuticle peeling” and chemical defense. Microcladia coulteri, which naturally colonizes Iridaea and Prionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of why Egregia is the exclusive substratum for M. californica remains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive to M. californica spore settlement and growth.     

Diversity of phlorotannin profiles among sargassasacean species affecting variation and abundance of epiphytes

In general, epiphytes have detrimental effects on the growth of their basiphytes due to competition for light and nutrients. Therefore, basiphyte species must expend energy suppressing epiphytes. Some studies suggest that phlorotannins, i.e. brown algal polyphenols, prevent colonization by epiphytes, whereas others question their allelopathic function because there is not necessarily a negative correlation between epiphyte abundance and the phlorotannin content of the basiphyte algae. Various phlorotannin components are found in brown algal species, thus we hypothesized that the antifouling activities of polyphenolic compounds may differ and that the analysis of phlorotannin profiles could be useful for estimating their ecological functions. We surveyed the epiphyte richness in the apical portions of 373 thalli from 15 sargassacean species, demonstrating that the variation and abundance of epiphyte species differed remarkably among the basiphyte species. However, there was a weak negative correlation between the density and total phlorotannin content of the basiphyte algae in only one of the 18 epiphyte species. The interspecific differences in the phlorotannin profile were characterized by quantitative ¹H nuclear magnetic resonance spectroscopy (qNMR), and four major groups were categorized based on cluster and principal component analyses of polyphenolic signals in the qNMR spectra. The epiphyte Neosiphonia harveyi was more abundant on Sargassum hemiphyllum, S. patens and S. piluliferum than on other basiphyte species, and these three species were similar according to the cluster analysis. These results suggest that some phlorotannin components may be more effective for antifouling; thus interspecific differences in the phlorotannin profile could affect the variation and abundance of epiphytes.     

Similarity of epiphyte biomass distribution on Posidonia and artificial seagrass leaves

Epiphyte biomass on Posidonia australis Hook f. and artificial seagrass leaves was analysed in relation to distance from leaf tip at different time periods following the autumnal shedding. The distribution pattern indicated no significant difference in the exponential nature of biomass increase.Similarities between epiphyte biomass distribution on real and artificial leaves is consistent with the hypothesis that biomass distribution on real leaves is not influenced significantly by metabolic interactions between host plant and epiphytes. Although a time component is involved in epiphyte biomass accumulation, the major factor in determining epiphyte biomass distribution is the relative position along the leaf.     

Long‐term changes of the vascular epiphyte assemblage on the palm Socratea exorrhiza in a lowland forest in Panama

Question: What are the qualitative and quantitative long‐term changes in the vascular epiphyte assemblage on a particular host tree species? Location: Lowland rain forest of the San Lorenzo Crane Plot, Republic of Panama. Methods: We followed the fate of the vascular epiphyte assemblage on 99 individuals of the palm Socratea exorrhiza by three censuses over the course of five years. Results: The composition of the epiphyte assemblage changed little during the course of the study. While the similarity of epiphyte vegetation decreased on individual palms through time, the similarity analysed over all palms increased. Even well established epiphyte individuals experienced high mortality with only 46% of the originally mapped individuals surviving the following five years. We found a positive correlation between host tree size and epiphyte richness and detected higher colonization rates of epiphytes per surface area on larger trees. Conclusions Epiphyte assemblages on individual S. exorrhiza trees were highly dynamic while the overall composition of the epiphyte vegetation on the host tree species in the study plot was stable. We suggest that higher recruitment rates, due to localized seed dispersal by already established epiphytes, on larger palms promote the colonization of epiphytes on larger palms. Given the known growth rates and mortality rates of the host tree species, the maximum time available for colonization and reproduction of epiphytes on a given tree is estimated to be ca. 60 years. This time frame will probably be too short to allow assemblages to be ever saturated.     

DISTRIBUTION OF ALGAL EPIPHYTES ACROSS ENVIRONMENTAL GRADIENTS AT DIFFERENT SCALES: INTERTIDAL ELEVATION,HOST CANOPIES,AND HOST FRONDS1

Understanding epiphyte distribution in coastal communities is important because these organisms affect many others directly or indirectly. Yet, their distribution has been considerably less studied than that of their hosts and other primary‐space holders. Identifying major sources of variation in epiphyte abundance is thus still a need. Environmental gradients help predict species distribution and are pervasive on marine shores. In this study, we test the notion that environmental gradients across intertidal elevation, throughout host canopies, and along host fronds explain a large variation in the abundance of sympatric epiphytes. Our model system was the assemblage of Ascophyllum nodosum (L.) Le Jol. and its epiphytes Vertebrata lanosa (L.) T. A. Chr. [= Polysiphonia lanosa (L.) Tandy], Elachista fucicola (Velley) Aresch., and Pylaiella littoralis (L.) Kjellm. On the coast of Nova Scotia (Canada), we found evidence of a spatial segregation among these species at almost all scales. While the red epiphyte V. lanosa was more common at high‐ and midintertidal elevations (peaking at midelevations) and on middle segments of host fronds, the brown epiphytes E. fucicola and P. littoralis were more common at low elevations and restricted to distal segments of host fronds. Canopy habitat affected abundance only for V. lanosa, which was more common within the host canopy than on its periphery at midelevations. Since the studied gradients are related to predictable changes in abiotic factors, the identification of likely causes behind the observed patterns was facilitated. Our study ends by proposing abiotic and biotic factors that deserve priority in the experimental testing of the forces structuring this assemblage.     

Epiphytism in a subtidal natural bed of Gracilaria gracilis of southwestern Atlantic coast (Chubut, Argentina)

The diversity of epiphytes, their temporal abundance variation and the anatomical structure of host–epiphyte interfaces were studied in the agarophyte Gracilaria gracilis from a natural bed in Bahía Bustamante, Chubut Province, Argentina. Twenty-nine algal species were recorded as epiphytes during 2 years of monthly sampling (March 2006–February 2008). Total epiphyte density ranged between 0.037 ind. cm^?2 (November 2006) and 39.37 ind. cm^?2 (April 2007), with higher density values throughout the second sampling year. Ceramiales species were the most abundant epiphytes. The density of Ceramium rubrum ranged from 0.09 ind. cm^?2 (52 % of the total amount) in September 2006 to 17.4 ind. cm^?2 (44.18 % of the total amount) in April 2007. Epiphyte infection was more dependent on spore recruitment and sporeling development, especially on thalli derived from fragmentation, than on seasonal environmental variations. The different infections were analysed, taking into account the epiphytic attachment strength and invasiveness and the degree of damage inflicted on the host. Calothrix confervicola was one of the most abundant species. This epiphyte, weakly attached to the host surface, generated no host tissue damage. In contrast, C. rubrum, Polysiphonia abscissa and other Ceramiales were the species that caused more damage to the host because their rhizoids penetrated the cortical portion of the host thallus, sometimes reaching the medullary tissue. Some generalisations and characterisations of the different epiphyte groups in relation to their consequences to Gracilaria spp. are presented.     

Diversity and distribution of herbaceous vascular epiphytes in a tropical evergreen forest at Varagalaiar, Western Ghats, India

Herbaceous vascular epiphytes were screened in a total sample of 13 445 trees (in 153 species) and 348 lianas (in 30 species) 30 cm girth at breast height in a 30 ha plot of tropical evergreen forest at Varagalaiar, Indian Western Ghats. Of these, 4.3% of trees and 3.7% of lianas were infested with epiphytes. Epiphyte diversity totaled 26 species in 19 genera and 10 families. Sixteen species were angiosperms in three families (Orchidaceae 54%; Piperaceae and Araceae 8%) and 10 species (38%) were pteridophytes in seven families. The orchid, Pholidota pallida was most abundant and occurred on 178 (29.6%) stems. Asplenium nidus occurred on the maximum of 62 host species. The species richness estimators employed for species accumulation curves after 100 times randomization of sample order have stabilized the curve at 18th and 19th hectares respectively for Incidence-based Coverage Estimator and Chao2. A total of 588 trees and 13 liana stems lodged epiphytes, 74% of which were evergreen species and 26% deciduous. Epiphyte density was greater (56%) in deciduous species (Bischofia javanica 30% and Vitex altissima 8%). A significant positive relationship was found between trunk size and epiphyte association. Larger epiphyte species occurred mostly on middle and larger stems and smaller epiphyte species occurred on smaller stems. The majority of epiphytes (92%) were of autochorous dispersal type, bearing capsule or dust diaspores, while the remaining species with berries and nutlets are dispersed by small vertebrates.     

A metapopulation approach to the analysis of long‐term changes in the epiphyte vegetation on the host tree Annona glabra

Question: Do vascular epiphyte species have a metapopulation structure? What are the qualitative and quantitative long‐term changes of the complete vascular epiphyte vegetation in a particular host tree species? Location: Lowland forest on Barro Colorado Island (9° 10’ N, 79°51’ W), Republic of Panama. Methods: In 1994 and 2002 we conducted a census of all vascular epiphytes growing on more than 1000 Annona glabra trees (= patches). Epiphyte species abundances were recorded at the tree level in each census. Results: The number of epiphyte individuals increased from ca. 15 000 to ca. 23 700 individuals during the census interval while the species composition on Annona glabra as a whole was rather stable. There was a strong positive relationship between occurrence in patches and local abundance of the species, and between species richness and host tree stand size. The dynamics of local populations of a given species were uncorrelated to each other; small and large local populations of most species had the same probability to go extinct. The frequency distribution of species on all host trees was not bimodal, but on a subset of heavily colonized host tree stands it was. Numbers of species and individuals were correlated with tree size which was not due to a correlation of tree size and tree age. Conclusions: As far as the most abundant epiphyte species with metapopulation structures are concerned, these species belong to diverse families, e. g. Orchidaceae, Bromeliaceae and Polypodiaceae. Even ca. 80 years after the initial establishment of the host tree species in the study area epiphytes are still in the stage of initial colonization and have not reached a steady state as indicated by the strong increase in individuals and the ongoing colonization of empty trees.     

SURFACE INTERACTIONS OF THE EPIPHYTIC MACROALGA HINCKSIA MITCHELLIAE (PHAEOPHYCEAE) WITH THE SHOALGRASS HALODULE WRIGHTII (CYMODOCEACEAE)1

Meadows of Halodule wrightii (Cymodoceaceae) underwent a decline in a tidal flat located at Paranaguá Bay (Parana, SE Brazil). This decline appeared to be related to an overgrowth of the epiphytic macroalga Hincksia mitchelliae (Harv.) P. C. Silva (Phaeophyceae). In order to characterize the type of epiphytism between the alga and its plant host, we compared two samples from the beginning and end of the algal overgrowth via electron and optical microscopes. The investigation revealed that at both sampling periods, there was an epiphytism of type II, which is due to an infection of epiphytes strongly attached to the surface of the host but not associated to any apparent direct host‐tissue damage. The presence of plasmodesmata between the cells of Hincksia only in the late stage of the host–epiphyte interaction indicated a change in the vegetative organization of Hincksia in relation to its host to improve nutrient absorption and distribution through the epiphyte cells. This is the first report on plasmodesmata in H. mitchelliae. The proposed mechanisms with which the algal epiphytes lead seagrasses to death are shadowing by adhesion on Halodule surface and disruption of its osmoregulatory system. Our findings have implications for the conservation and management strategies of seagrass ecosystems.     

Defense mechanisms of sargassacean species against the epiphytic red alga Neosiphonia harveyi

Flora diversity and abundance of epiphytes are specific to their basiphyte species and may relate to variations in the defensive abilities of basiphytes. Thus, investigating the interactions between epiphytes and basiphytes is useful for a better understanding of the biological impact of epiphytism and the survival strategies of basiphytes. We examined the epiphyte density on five sargassacean species at six locations between two study sites, which showed that the epiphytic red alga Neosiphonia harveyi was remarkably less abundant on Sargassum siliquastrum at all locations. To assess its defense mechanism against N. harveyi, we performed bioassays of phlorotannins, which are considered effective in deterring fouling, by culturing sargassacean blades with N. harveyi carpospores and observed the process by which sargassacean blades remove epiphytes. When the carpospores were incubated with various concentrations of dissolved phlorotannins, settlement and germination were inhibited only at the highest concentrations (>0.1 g · L^?1), and this effect did not significantly differ among the five sargassacean species. When the carpospores were combined with blades from the five species, many of the spores attached and germinated on every blade. Because N. harveyi penetrated rhizoids into basiphyte tissues, cuticle peeling observed in all five sargassacean species could not remove this epiphyte after germination. However, in S. siliquastrum, the blade tissues around the germlings became swollen and disintegrative, and were removed together with the germlings. The spores normally grew on the dead blades, suggesting that the tissue degradation of S. siliquastrum is triggered by the infection of N. harveyi.     

Patterns in the diversity and distribution of epiphytes and vines in a New Zealand forest

Abstract Plants that rely on other plants for support (i.e. epiphytes and vines) are common in many forest ecosystems. However, they are poorly understood relative to terrestrial plants, especially in the Southern Hemisphere. To help bridge this gap, we evaluated the diversity and distribution of vascular epiphytes and vines on seven common tree species in a conifer‐broadleaf forest on New Zealand's North Island. Ground‐based surveys of 274 host trees were used to test whether epiphyte and vine diversity increased with tree diameter, and whether diversity‐diameter relationships differed among host tree species. Occurrence patterns of individual epiphyte and vine species were also assessed. We first evaluated the accuracy of ground‐based inventories by comparing surveys of trees made from the ground to those made from a canopy walkway. On average, 1 in 10 species of epiphytes and vines were unseen from the ground. However, sampling accuracy did not differ among the three host tree species growing along the walkway, suggesting unbiased comparisons could be made between hosts. Results from ground‐based surveys showed that species diversity of epiphytes and vines increased with host tree diameter. However, epiphytes showed stronger diversity‐diameter relationships than vines. Epiphyte diversity increased markedly in four host species and less strongly in the remaining three host species. Conversely, vines showed weak diversity‐diameter relationships in all host species. Occurrence patterns of individual species helped to explain diversity‐diameter relationships. All common epiphyte species occurred more frequently on large trees, regardless of host species, but occurrence patterns in most vine species were unrelated to tree size. Rather, the vines often showed strong host ‘preferences’. Overall results illustrate a rich diversity of distributional patterns in New Zealand's epiphytes and vines, and suggest that a similarly diverse set of ecological and evolutionary processes are responsible for them.     

Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds

It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus.     

Host trait preferences and distribution of vascular epiphytes in a warm-temperate forest

To illustrate the ecological factors and process leading to the observed diversity patterns of vascular epiphytes, we examined the effect and importance of host tree traits on epiphyte richness and spatial aggregation of epiphytes. The study was conducted in warm-temperate forest in Japan. The recorded host traits were diameter, height, species, habitat topography, and growth rate, and we analyzed the effects and importance of these traits on three species groups: total epiphytic species, epiphytic orchid species, and epiphytic pteridophyte species. Diameter and species of host trees had the greatest influence on epiphytes and their magnitudes were roughly similar in all species groups. Growth rate and topography were less important than host size and species. Growth rate had a negative effect on all three groups, and topography was important for pteridophytes. Epiphyte richness did not exhibit clear spatial aggregation. Our results suggest that size, stability, and quality of the host are equally important in determining epiphyte colonization.     

Reti trofiche e flussi di energia nei sistemi a fanerogame marine

Abstract

Food webs and energy flow in seagrass ecosystems. A review on the pathways in the food webs of seagrass ecosystems, both tropical and temperate, with a particular emphasis to Mediterranean Posidonia oceanica meadows is given. Three main pathways of energy transfer from primary producers (host plant and algal epiphytes) were identified: i) the plant itself through photosynthetic tissue; ii) the leaf detritus which in some species forms a litter compartment; iii) the algal epiphytes of leaf blades. The detritus and epiphyte ways are the most common, but they can be differently important according to the season and the spatial patterns of the meadows.     

Structure of the Epiphyte Community in a Tropical Montane Forest in SW China

Vascular epiphytes are an understudied and particularly important component of tropical forest ecosystems. However, owing to the difficulties of access, little is known about the properties of epiphyte-host tree communities and the factors structuring them, especially in Asia. We investigated factors structuring the vascular epiphyte-host community and its network properties in a tropical montane forest in Xishuangbanna, SW China. Vascular epiphytes were surveyed in six plots located in mature forests. Six host and four micro-site environmental factors were investigated. Epiphyte diversity was strongly correlated with host size (DBH, diameter at breast height), while within hosts the highest epiphyte diversity was in the middle canopy and epiphyte diversity was significantly higher in sites with canopy soil or a moss mat than on bare bark. DBH, elevation and stem height explained 22% of the total variation in the epiphyte species assemblage among hosts, and DBH was the most important factor which alone explained 6% of the variation. Within hosts, 51% of the variation in epiphyte assemblage composition was explained by canopy position and substrate, and the most important single factor was substrate which accounted for 16% of the variation. Analysis of network properties indicated that the epiphyte host community was highly nested, with a low level of epiphyte specialization, and an almost even interaction strength between epiphytes and host trees. Together, these results indicate that large trees harbor a substantial proportion of the epiphyte community in this forest.     

Biomass accumulation and shading effects of epiphytes on leaves of the seagrass, Heterozostera tasmanica, in Victoria,Australia

A method is described for estimating the rate of accumulation of epiphyte biomass on leaves of the seagrass, Heterozostera tasmanica (Martens ex Aschers.) den Hartog and for estimating the effect of epiphyte biomass on photosynthesis of the seagrass. Epiphyte biomass was determined by comparison of the weight per unit area of epiphyte-covered and epiphyte-free leaf blades. Epiphyte weight increased as age of the seagrass leaves increased. Linear regression on epiphyte biomass vs. leaf age estimated the rate of biomass accumulation. Rates varied from 5.7 to 104 μg epiphyte dry weight per cm² of leaf surface per day at three sites in Western Port and Port Phillip Bay, Victoria. Rates of accumulation of epiphyte biomass were generally higher during December through March (summer) than in May (autumn), August (winter) or October (Spring). Light attenuation by epiphytes increase linearly with biomass. The rate of biomass accumulation of epiphytes was compared with leaf growth rate, ambient photon flux density in H. tasmanica beds and the photosynthesis—photon flux density curve of H. tasmanica. This comparison demonstrated that epiphyte biomass can accumulate fast enough to shade H. tasmanica leaves and significantly reduce the time (to less than one half of the leaf life span) in which positive net photosynthesis of the leaf blade is possible.     

Effect of epiphytism on reproductive and vegetative lateral formation in the brown, intertidal seaweed Ascophyllum nodosum (Phaeophyceae)

In the brown alga Ascophyllum nodosum (L) Le Jolis, a common species on sheltered Northern temperate rocky shores, gametes are produced in receptacles that emerge from small depressions (lateral pits) along the branched frond. These lateral pits are also the preferred settling site for the obligate epiphyte Polysiphonia lanosa (L) Tandy. Therefore, epiphytism can be expected to interfere with host reproductive output. The present study investigated the potential impact of the epiphyte on A. nodosum in two series of laboratory experiments that measured: (i) the direct shading of the host plant underneath an epiphyte canopy; and (ii) the development of receptacles in clean and epiphytised A. nodosum segments (excised from individual fronds) over a 6 month period. These experiments showed that light reaching emerged fronds underneath a dense epiphyte cover was reduced by 40%, and this was independent of the degree of desiccation the epiphyte experienced. Concurrently, in the growth study with epiphytised A. nodosum segments (segments with one clean and one epiphytised lateral pit) total receptacle biomass per epiphytised fragment was significantly reduced compared with clean segments (0.52 g and 1.25 g per gram of frond segment, respectively), although this effect was only significant in A. nodosum from sheltered shores. However, expressed as biomass per lateral pit, receptacle biomass in the remaining clean lateral pits in epiphytised segments was significantly increased in segments from both shores, demonstrating that A. nodosum can at least partially compensate for the loss of production resulting from epiphytism.     

Nutrient induced changes in the species composition of epiphytes on Cladophora glomerata Kütz. (Chlorophyta)

Cladophora glomerata is a widely distributed filamentous freshwater alga that hosts a complex microalgal epiphyte assemblage. We manipulated nutrients and epiphyte abundances to access their effects on epiphyte biomass, epiphyte species composition, and C. glomerata growth. C. glomerata did not grow in response to these manipulations. Similarly, nutrient and epiphyte removal treatments did not alter epiphyte biovolume. Epiphyte species composition, however, changed dramatically with nutrient enrichment. The epiphyte assemblage on unenriched C. glomerata was dominated by Epithemia sorex and Epithemia adnata, whereas the assemblage on enriched C. glomerata was dominated by Achnanthidium minutissimum, Nitzschia palea and Synedra spp. These results indicate that nutrients strongly structure epiphyte species composition. Interactions between C. glomerata and its epiphytes were not affected by epiphyte species composition in our experiment but may be when C. glomerata is actively growing.     

Contribution of peeling host for epiphyte abundance in two tropical dry forests in the “El Cielo Biosphere Reserve”, Mexico

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.