Article

Competition in lichen communities

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Abstract

Lichens are symbiotic organisms that often dominate stressful environments such as the surfaces of rock and tree bark. Whether or not competition occurs between lichens in these environments, however, is controversial. This review considers various aspects of the competitive interactions between lichens including the observational studies that suggest competitive effects may be important, the methods that have been used to study lichen competition in the field, the result of marginal contacts between lichen thalli, the attributes that may give a species a competitive advantage, and the role of competition in structuring lichen communities. These studies suggest that competition for space and light does occur in lichen communities and that individual lichen species can be excluded from a substratum as a result of competition. Moreover, competitive interactions in multi-species communities can also lead to stable assemblages of species. Future research should consider those aspects of the lichen symbiosis that may confer a competitive advantage and the factors that may promote stability in multi-species communities. Studies of competition in lichen communities may have implications for other stressful environments in which symbiotic organisms play a significant role.

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... Begon, 2006). Ésta implica un proceso lento que en algunos casos puede llegar a tardar décadas incluso centurias (Hale, 1974;Woolhouse et al., 1985;Armstrong & Welch, 2007). No es un proceso que haya sido acabadamente estudiado y requeriría de profundizar en el conocimiento de las interacciones de las especies en un marco temporal. ...
... En el caso de las comunidades de líquenes crustosos, quienes son los primeros colonizadores sobre sustratos rocosos, la disponibilidad de espacio y el acceso a la luz son recursos por los que las especies compiten (Oksanen, 1984;Stone, 1989;Hilmo, 1994;Ruchty et al., 2001;Armstrong, 2002;Armstrong & Welch, 2007). ...
... Por ello era de esperar que la condición de empate entre las especies dominantes fuera la más habitual, tal como lo corroboraron los datos obtenidos, además de coincidir con lo observado para otras especies crustosas por Pentecost (1980). El mecanismo por el cual los líquenes crustosos dejan de crecer cuando sus talos se encuentran, no ha sido estudiado aquí, pero es un tema que está en discusión actualmente (Armstrong & Welch, 2007). ...
... Intraspecific and interspecific competition is likely to have a large effect on the growth of R. geographicum and therefore, on the size of thalli (Armstrong and Welch, 2007). When lichens colonize a substratum the margins of thalli ultimately contact each other. ...
... Pentecost (1980) described several possible outcomes of lichen contact: (1) one species overgrows another, (2) neither species grows at the point of contact (‗truce' condition), and (3) one species may grow epiphytically on the other. Considerable evidence for thallus overgrowth has been obtained from field observations and experiments especially in interactions involving foliose species (Armstrong and Welch, 2007). Nevertheless, there is also evidence for cessation of growth when two lichen thalli meet, especially in crustose communities, leading to a ‗truce' condition which is likely to contribute to the formation of lichen mosaics dominated by crustose species such as Rhizocarpon. ...
... Limitations of indirect lichenometry include the likelihood that smaller thalli may coalesce to form a larger individual which could be recorded in error as the ‗largest thallus'. Thalli of the same and different lichen species can also fuse to form lichen mosaics, a common feature of many crustose lichen communities thus restricting their growth (Pentecost, 1980;Armstrong, 1984;Armstrong and Welch, 2007). Whether or not thalli fuse without leaving evidence of the original boundaries appears to depend on species with some thalli merging leaving no trace of their original boundaries (Clayden, 1997). ...
Chapter
The urban heat island (UHI), a phenomenon where urban areas are warmer than surrounding rural areas, is an urban problem which has been enhanced by the climate variability. This temperature difference between urban and rural areas occurs due to different land uses / land covers (LULC), which have distinct thermal characteristics among them. Vegetation areas increase evapotranspiration to reduce thermal loading, while urban constructed materials store and reemit incident energy into the environment. Other factors such as the urban geometry (i.e., size, shape, height, and arrangement of buildings) and the presence of anthropogenic thermal emission sources (i.e., automobile and industrial process) can affect the UHI phenomenon. Multiple environmental implications as well as changes in the biological environment can be related to UHI. In aquatic ecosystems, for example, UHI affect not only the water temperature, but also the stability of water column, biogeochemical cycles and biological activity. Thus, urban aquatic systems, usually used as a source of water for the population, are affected by the UHI phenomenon. This chapter is reviewing few concepts about the impacts of air temperature variations on urban aquatic systems: a physical and ecological overview. Therefore, concepts of physical impacts of air temperature variation on the water column stability as well as its impacts on the biological activity are described in this chapter. It also presents a summary of the theoretical background of physical processes of one important tool for the studies on UHI: the thermal remote sensing. Directions for future research to improve the monitoring of UHI impacts in urban aquatic systems such as the synergy between numerical modeling and microbiological studies are suggested.
... Many of the epiphytes identified were unique to a single tree species which is consistent with other studies in boreal woodlands (Nascimbene et al., 2009a(Nascimbene et al., , 2009bHauck, 2011;Odor et al., 2013). This could be related to species specific characteristics including bark pH and texture (Armstrong and Welch, 2007;Nascimbene et al., 2013). Highly textured bark provide shelter, increased humidity, protection from predation and attachment security (Armstrong and Welch, 2007;Ranius et al., 2008). ...
... This could be related to species specific characteristics including bark pH and texture (Armstrong and Welch, 2007;Nascimbene et al., 2013). Highly textured bark provide shelter, increased humidity, protection from predation and attachment security (Armstrong and Welch, 2007;Ranius et al., 2008). However, the textured yew bark was dominated by shade loving Chrysothrix candelaris, perhaps due to the lower light intensity (Whelan, 2008;Seawright, 2011). ...
... Tree bases are more sheltered with higher humidity and lower light intensity (Richards, 1938;Harris, 1971b;Hocking et al., 2008). Here, climax communities of Thamnobryum alopecurum and Thuidium tamariscinum or Dicranum scoparium occur (Thomas and Polwart, 1958;BBS, 2005;Mitchell et al., 2005;Armstrong and Welch, 2007). These mosses are several centimetres tall and form dense blankets completely smothering competition (Thomas and Polwart, 1958;Ratcliffe, 1968). ...
Article
Full-text available
The niches of epiphytes are widely studied and have been shown to be complex involving interspecific competition, succession and predation. This study is unique in that it applies the niche concept to moss and lichen distributions within Killarney National Park, Kerry, Ireland. We studied 75 trees between three pristine ancient woodlands and measured a range of physical and biological factors to ascertain influences on epiphyte cover. The species of tree was found as the principal determinant in community structure as it bioengineers conditions such as light, temperature and humidity that the epiphytes are reliant upon. Furthermore, the bark character and trunk circumference were important. Zonation of the epiphytes was apparent with both aspect and height on the trunk. Typically, moss dominated over lichen within a niche that was relatively sheltered. Lichen tolerated drier and lighter niches often being further up the trunk on sun facing aspects. Ultimately, there was succession up the tree mediated through competition. This study highlights the complexity and interrelatedness between biotic and abiotic factors in a relatively unstudied geographical and biological area. Understanding agents behind a population's distribution enables manipulation for conservation or sustainable exploitation.
... Intraspecific and interspecific competition is likely to have a large effect on the growth of R. geographicum and therefore, on the size of thalli (Armstrong and Welch, 2007). When lichens colonize a substratum the margins of thalli ultimately contact each other. ...
... Pentecost (1980) described several possible outcomes of lichen contact: (1) one species overgrows another, (2) neither species grows at the point of contact (‗truce' condition), and (3) one species may grow epiphytically on the other. Considerable evidence for thallus overgrowth has been obtained from field observations and experiments especially in interactions involving foliose species (Armstrong and Welch, 2007). Nevertheless, there is also evidence for cessation of growth when two lichen thalli meet, especially in crustose communities, leading to a ‗truce' condition which is likely to contribute to the formation of lichen mosaics dominated by crustose species such as Rhizocarpon. ...
... Limitations of indirect lichenometry include the likelihood that smaller thalli may coalesce to form a larger individual which could be recorded in error as the ‗largest thallus'. Thalli of the same and different lichen species can also fuse to form lichen mosaics, a common feature of many crustose lichen communities thus restricting their growth (Pentecost, 1980;Armstrong, 1984;Armstrong and Welch, 2007). Whether or not thalli fuse without leaving evidence of the original boundaries appears to depend on species with some thalli merging leaving no trace of their original boundaries (Clayden, 1997). ...
Chapter
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Legumes are widely used forage crops often grown in flooding prone areas but data about proteome changes in waterlogged plants are scarce. In the present study leaf 2-DE protein profiles of white (Trifolium repens L. cv. Haifa) and red (Trifolium pratense L. cv. Start) clovers, differing in waterlogging tolerance, were compared. Flooding was imposed on 21-day-old plants for a period of 14 days, followed by a 21 days of recovery. Plant physiological status was assessed by changes in leaf area, water content, photosynthetic parameters and total soluble protein. Maximum (Fv/Fm) and the actual (PSII) PSII efficiency were not significantly affected in both cultivars. However, non-photochemical quenching (NPQ) increased substantially in waterlogged white clover. Following 2-DE separation (pI 5-8 and 12% SDS-PAGE), 90 variable protein spots were identified using MALDI-TOF/TOF MS, resulting in reliable hits for 22 individual proteins in red and 26 - in white clover, 17 of them being common for both clovers. In both varieties a strong diminution under stress was observed in Rubisco subunits, ATP synthase subunits α and ß, oxygen-evolving enhancer protein and other chloroplastic proteins. Cytochrome b6-f complex iron-sulfur subunit exhibited opposite trends under waterlogging stress - decrease in red and increase in white clover. Several proteins manifested post-recovery over-accumulation. Results give some insight about the biochemical basis for the higher adaptation potential of T. repens under waterlogging stress.
... The presence of corticolous lichens is related to forest type, age, composition and structure, as well as to light and moisture availability (McCune et al. 1997, Campbell and Coxson 2001, Fanning et al. 2007, Johansson et al. 2010, Li et al. 2015, and wind speed and exposure (Armstrong and Welch 2007). At the scale of trees, the vertical distribution of species and the structure of the lichen communities are influenced by their poikilohydric physiology (Komposch andHafellner 2000, Normann et al. 2010). ...
... Lichens respond mainly to light and moisture (Sillet and Rambo 2000, Cleavitt et al. 2009, Li et al. 2015, which vary the base of the trunk to the crown of trees (Freiberg 1997, Freiberg and Freiberg 2000, Komposch and Hafellner 2000, Hauck et al. 2001, Holz et al. 2002, Boch et al. 2013, especially in the tropics (Komposch and Hafellner 2000). Other parameters that affect the lichen community are bark pH and structure (Hauck et al. 2001, Cleavitt et al. 2009, and, within trees of the same species, available space (tree size) and time for colonization (tree age) (Freiberg 1996, Cobanoglu and Sevgi 2009, Boch et al. 2013, as well as potential competition with other epiphytic organisms (Armstrong andWelch 2007, Cleavitt et al. 2009). Owing to this, the distribution of lichens on trees is not homogeneous, as some species live in shady and humid zones, while others thrive in brighter and drier areas, and yet others display a broader range of microenvironmental tolerance (Sporn et al. 2010). ...
... This may be due to the heterogeneity of the micro-habitats along tree trunks, given by the different height of phorophyte zones, as pointed out by various authors (Kuusinen 1994, Freiberg 1997, Fanning et al. 2007, Li et al. 2015 and, due to the intrinsic species restriction. Armstrong and Welch (2007) consider that an additional factor that defines the community structure of lichens is the distribution of each individual species in relation to their growth forms. In our study, although foliose lichens (especially those in the family Parmeliaceae) had higher overall cover than the crustose lichens (dominated by the family Graphidaceae), the latter exhibited the highest species richness. ...
Article
In the tropics, corticolous lichen richness and cover tend to increase from the trunk base to the top of the crown of trees. In this study we calculated the total beta diversity of the lichen community along a vertical gradient on Quercus laurina in Mexican cloud forest. By comparing the richness and cover of the lichens by zone, we show that foliose and fruticose lichens are a minor component of the total lichen species richness, but have a higher cover than the crustose lichens. Five zones were identified along each phorophyte (n = 15) with a diameter at breast height >40 cm. A total of 92 species were identified. Of these, 38% were found only in a single zone, 51% were shared between the different zones and 11% occurred across all zones. Species richness and cover increased from the lowest to the highest zones of the phorophytes. Dissimilarity in species composition between the zones could be explained by species replacement. An indicator species analysis revealed that only a few species, e.g. Hypotrachyna vexans, H. cf. sublaevigata and Ramalina cf. sinaloensis prefer a particular zone. The results show that the lichen community associated with Quercus laurina phorophytes is highly diverse and suggest that species richness and cover are related to the zone and the various growth forms.
... Begon, 2006). Ésta implica un proceso lento que en algunos casos puede llegar a tardar décadas incluso centurias (Hale, 1974;Woolhouse et al., 1985;Armstrong & Welch, 2007). No es un proceso que haya sido acabadamente estudiado y requeriría de profundizar en el conocimiento de las interacciones de las especies en un marco temporal. ...
... En el caso de las comunidades de líquenes crustosos, quienes son los primeros colonizadores sobre sustratos rocosos, la disponibilidad de espacio y el acceso a la luz son recursos por los que las especies compiten (Oksanen, 1984;Stone, 1989;Hilmo, 1994;Ruchty et al., 2001;Armstrong, 2002;Armstrong & Welch, 2007). ...
... Por ello era de esperar que la condición de empate entre las especies dominantes fuera la más habitual, tal como lo corroboraron los datos obtenidos, además de coincidir con lo observado para otras especies crustosas por Pentecost (1980). El mecanismo por el cual los líquenes crustosos dejan de crecer cuando sus talos se encuentran, no ha sido estudiado aquí, pero es un tema que está en discusión actualmente (Armstrong & Welch, 2007). ...
Article
Full-text available
Interspecific competition determines the distribution of species and the structure of communities. Crustose lichens are the first colonizers on rocky substrates and they compete among themselves for space and light. Previous studies have mentioned three possible situations resulting from the interaction that occur by contact between thalli of different species of lichens: species that grow over the other (+), species that are killed or retract (-), or the stop of the growth of both species at the contact point (□). We analyzed the interactions between crustose lichens that colonize urban walls. On a transect of 30 m traced on the wall of a building in La Plata (Argentina), with sampling units of 20x20 cm (n=20), we recorded species coverage and the type of contact between the lichen thalli of different species. We estimated richness and relative frecuency. The average coverage of the community was 83 ± 8.6% and the absolute species richness was eight. The dominant species were Flavoplaca austrocitrina and Caloplaca teicholyta that were recorded in all sampling units. The remaining species had frequencies ≤ 50% and ≤ 1% coverage. All contacts involve some dominant. Among them, the most frequent interaction was the stop of growth (□), which occurred in 82% of contacts. Overgrowth (wins (+) - loss (-)) occurred in the 18% of contacts, always positive for the dominant. It is concluded that among the observed species, in this community, the two dominant species have equal competitive ability and suppress the rest. F. austrocitrina had advantage in colonizing the substrate.
... Intraspecific and interspecific competition is likely to have a large effect on the growth of R. geographicum and therefore, on the size of thalli (Armstrong and Welch, 2007). When lichens colonize a substratum the margins of thalli ultimately contact each other. ...
... Pentecost (1980) described several possible outcomes of lichen contact: (1) one species overgrows another, (2) neither species grows at the point of contact (‗truce' condition), and (3) one species may grow epiphytically on the other. Considerable evidence for thallus overgrowth has been obtained from field observations and experiments especially in interactions involving foliose species (Armstrong and Welch, 2007). Nevertheless, there is also evidence for cessation of growth when two lichen thalli meet, especially in crustose communities, leading to a ‗truce' condition which is likely to contribute to the formation of lichen mosaics dominated by crustose species such as Rhizocarpon. ...
... Limitations of indirect lichenometry include the likelihood that smaller thalli may coalesce to form a larger individual which could be recorded in error as the ‗largest thallus'. Thalli of the same and different lichen species can also fuse to form lichen mosaics, a common feature of many crustose lichen communities thus restricting their growth (Pentecost, 1980;Armstrong, 1984;Armstrong and Welch, 2007). Whether or not thalli fuse without leaving evidence of the original boundaries appears to depend on species with some thalli merging leaving no trace of their original boundaries (Clayden, 1997). ...
... This leads to successional sequences of lichen community composition (Degelius 1964, 1978, Rogers 1988, Hilmo 1994, Wirth et al. 1999. Young top-layer branches may host lichen communities consisting of a limited set of fast colonizing early-successional species (Rogers 1990), while lichen communities on old branches, representing late stages of succession with high cover, may have lost species due to the exclusion by more competitive lichens and/or bryophytes (Armstrong andWelch 2007, Fritz 2009). As a consequence, lichen diversity is expected to increase from the top-layer downwards to regions where species of different successional stages co-occur before it decreases again (Degelius 1964, Hilmo 1994, thus creating a hump-shaped pattern, referred to as mid-succession peak (Johansson et al. 2007). ...
... genus Lecanora and Caloplaca). Another typical trait for pioneers is the ability to efficiently disperse propagules in order to colonize new sites (Rogers 1990, Armstrong andWelch 2007). The presence of apothecia did also explain the compositional gradient, with species developing apothecia being more prevalent on younger branches. ...
Preprint
Full-text available
Forest canopies are hotspots of biodiversity even in temperate forests but which and how many ecological mechanisms contribute to the high diversity remains elusive. This biodiversity is not distributed evenly throughout the complex fractal structures formed by individual tree crowns. They are non-stationary, constantly expose new surface habitat via growth, and create contrasting abiotic conditions. These features give rise to a range of vertical gradients in habitat optimality, heterogeneity, available surface area and time for succession - all known to be mechanisms shaping diversity patterns. Using a canopy crane facility and epiphytic lichens on Fraxinus excelsior and Quercus robur as model system, we aim to assess the relative importance as well as the interplay of these mechanisms in shaping biodiversity patterns within tree canopies by detecting their distinct mechanistic fingerprints. Lichen species richness exhibited a hump-shaped vertical pattern, skewed towards the top of the crown. This pattern was observable at both the level of individual plots and that of aggregate height layers and it was correlated with lichen cover. Also, a vertical gradient in species composition was found and could be related to species traits known to reflect successional niches such as dispersal mode and growth form. Habitat heterogeneity and available surface area have been found to have little effect on vertical lichen diversity patterns. We conclude that the vertical lichen diversity patterns in the tree crown are mainly shaped by the successional accumulation of species along a branch age gradient and a pronounced vertical gradient in environmental optimality from harshly exposed young branches at the top crown over suitable habitats with a balance in light and humidity towards the limiting light conditions in the dim understory. At the level of the whole canopy, successional and environmental niche dynamics jointly operate to generate lichen diversity.
... Here we present a pair of studies, one observational and one experimental, of a saxicolous lichen community in New Mexico, USA, intended to determine whether a competition-colonization trade-off exists among several species (or species complexes) in a natural community and to describe the relationship between disturbance and diversity. Saxicolous lichens are an amenable system for such an investigation and have been used to study community patterns in a number of other studies (e.g., Armstrong 2002, Armstrong and Welch 2007, Gjerde et al. 2012. Because, at our site, the main resource lichens compete for is space on rocks, and they rarely experience predation (T. ...
... Although the foliose Xanthoparmelia often overgrows the crustose, C. contorta, C. contorta can persist without light underneath Xanthoparmelia for many years until Xanthoparmelia inevitably flakes off. Though we could not directly observe the mechanisms of competitive replacement with this study, previous studies have suggested that a number of different traits affect competitive outcomes in lichens (reviewed in Armstrong and Welch 2007), including overgrowth ability (Pentecost 1980), high growth rates (Armstrong 1984), high lobe density or thickness (Lawrey 1984), rate of thallus fragmentation (Pentecost 1980, Woolhouse et al. 1985, and allelopathy (Beschel and Weidick 1973). ...
Conference Paper
Full-text available
Background/Question/Methods The Intermediate Disturbance Hypothesis (IDH) has been frequently invoked over the last 30 years, with its simple prediction based on a tradeoff between colonization and competition. Despite many documented patterns of species diversity that appear consistent with the IDH, few studies actually test presumed underlying mechanisms. On the rocky slopes of the mountains in southwestern New Mexico, as many as 12 common species of saxicolous lichens co-occur. As shards of rock flake off due to weathering, lichens are removed and bare rock is made available for colonization; as a result, lichen cover decreases with increasing disturbance. One hundred 1 m2 plots were censused in 1978 to quantify the diversity of these lichen communities as a function of disturbance. Additionally, ten 10 x 10 cm paired plots were established, with one plot disturbed with a chisel to remove 100% of the rock face and the other plot left undisturbed. A 32-year photographic record of the paired plots allowed us to (1) determine if tradeoffs between colonization rates and competitive ability are consistent with the IDH, and (2) use this unique dataset to observe the underlying processes involved in competition and colonization. Results/Conclusions The 1 m2 plots revealed that lichen diversity did, in fact, result in a unimodal relationship with percent lichen cover (i.e. disturbance), consistent with the IDH. Using the long-term photographic data, we found tradeoffs between competition and colonization ability, with some species having high colonization rates into cleared plots and relatively poor competitive ability in undisturbed plots. However, the strength of the trade-off for each species is inversely correlated with patterns of overall species occurrence. We observed that the best support for the putative mechanisms behind the IDH comes from relatively rare species and propose that this may be a feature of many other disturbed communities.
... Lichens do not seem to exhibit specific biotic interactions such as found in plant pollination and seed dispersal, and the niche dimensions along which competition acts are presumed to be largely limited to the availability of space and to abiotic growth factors such as nutrients and microclimate (Lawrey 1981;John & Dale 1989). In lichens, a commonly used proxy to determine niche overlap or ecological equivalency, and hence competition, is the nearest neighbour approach, the observation of thalli growing side by side (Lawrey 1981;John 1989;Armstrong & Welch 2007). ...
... This result showed that each individual tree hosted multiple distantly related genotypes, which is consistent with the patterns we would expect from the competition-relatedness hypothesis (Cahill et al. 2008). Several studies showed that competition between lichen thalli does occur at local level, as they are limited by the availability of space on the substrate (Armstrong 1986;Armstrong & Welch 2007;Pastore et al. 2014). However, crustose lichens such as Graphis scripta are also known for their slow growth, which prevents their use in a manipulative experiment to illustrate competitive interactions (Lange 1990;Armstrong & Bradwell 2010). ...
Article
Full-text available
The ‘competition-relatedness’ hypothesis postulates that co-occurring taxa should be more distantly related, because of lower competition. This hypothesis has been criticized for its dependence on untested assumptions and its exclusion of other assembly forces beyond competition and habitat filtering to explain the co-existence of closely related taxa. Here we analyzed the patterns of co-occurring individuals of lichenized fungi in the Graphis scripta complex, a monophyletic group of species occurring in temperate forests throughout the Northern Hemisphere. We generated sequences for three nuclear ribosomal and protein markers (nuLSU, RPB2 , EF-1 ) and combined them with previously generated sequences to reconstruct an updated phylogeny for the complex. The resulting phylogeny was used to determine the patterns of co-occurrences at regional and at sample (tree) scales by calculating standard effect size of mean pairwise distance (SES.MPD) among co-occurring samples to determine whether they were more clustered than expected from chance. The resulting phylogeny revealed multiple distinct lineages, suggesting the presence of several phylogenetic species in this complex. At the regional and local (site) levels, SES.MPD exhibited significant clustering for five out of six regions. The sample (tree) scale SES. MPD values also suggested some clustering but the corresponding metrics did not deviate significantly from the null expectation. The differences in the SES.MPD values and their significance indicated that habitat filtering and/or local diversification may be operating at the regional level, while the local assemblies on each tree are interpreted as being the result of local competition or random colonization.
... Propagula dispersed by wind, random arrival on a substrate and then the influence of preemptive competition between thalli are the mechanisms leading to community establishment on rocks. The demonstrated competition in lichen guilds (Armstrong & Welch 2007) is mostly preeemtive (Hestmark et al. 2007) in nature but it is not the only species interaction observed among lichen thalli. Competition is largely overrated since biotic interactions include other negative and positive types such as parasitism or facilitation. ...
... Lichens are considered stress tolerant organisms according to Grime classification (1979) and competition plays an important role in community structure (Armstrong & Welch 2007) but co-occurrence analysis has failed to extract competition mechanism as important for saxicolous lichen communities. If equiprobable null models are used, nestedness and co-occurrence scores such as C-score produce similar, significant results; under less liberal null models this correlation does not hold (Ulrich et al. 2009) as our results indicate too. ...
Article
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The assemblage of saxicolous lichenized fungal communities in Măcin Mountains National Park was assessed during a biodiversity study developed between 2006 and 2008. Fifty three species of saxicolous lichenized fungi were identified on Hercynic granites and granitoid outcrops characterized by intense weathering process. Apparently, competition was not the main mechanism in community assemblage as calculated C score showed (non-significant difference between mean calculated and simulated score). Niche overlap assessment showed that lichens avoided competition by spatial niche partition (mean Pianka index of 0.07 for sampling quadrats and 0.20 for locations). The estimation of nestedness index (N=0.63 at local scale and N=0.88 at sampling quadrat scale) indicated that local communities were subsets of a larger, regional scale metacommunity. Similarities in community composition across locations were assessed by means of Ward algorithm, results indicating that the most dissimilar communities were encountered at Pietrele Mariei, a residual inselberg and Suluc foothill. Conservation of saxicolous communities containing endangered species such as Umbilicaria grisea, critically endangered Ramalina obtusata and vulnerable Acrocordia gemmata, Pertusaria hemisphaerica, Pertusaria pertusa will be challenged in the future by anthropogenic impact coming from agriculture, sheep grazing and quarries operating in the proximity of the reserve area.
... Like facilitation interactions, competition is somewhat more accepted as an important contributor to community development in nonvascular epiphytic plants and lichens than in vascular epiphytes (e. g., Armstrong and Welch, 2007;Peck and Frelich, 2008). Competition was the topic of 35 % of epiphytic bryophyte studies and 31 % of epiphytic lichen studies (Fig. 1). ...
... Spreading, dense genera such as Rhytiadelphus and Isothecium show patterns consistent with this model in temperate rainforests (Peck and Frelich, 2008;Woods et al., 2019). Successional replacement consistent with competition is found in epiphytic bryophytes in temperate rainforests (Peck and Frelich, 2008;Ruchty et al., 2001;Stone, 1989) and in epiphytic lichen communities (Armstrong and Welch, 2007;Ellis, 2012) where some species overgrow and exclude earlier species (Fig. 2F). McCune (1993) proposed the "similar gradient hypothesis" for successional replacement in epiphytes, wherein lichens are pushed towards the tops of coniferous trees because of competition with bryophytes. ...
Article
Biotic interactions are widely accepted as an important driver of ecological and evolutionary patterns, contributing to the structure of systems as diverse as tropical tree seedlings, intertidal barnacles, and wildflower-pollinator networks. Species interactions within a trophic level, such as competition and facilitation, can drive patterns of community change over time, yielding both fundamental ecological theories of succession as well as insight vital to predicting biodiversity conservation priorities. One system in which biotic interactions are poorly explored is epiphytes, or structurally dependent, non-parasitic organisms. This is a topic of broad interest because epiphytes—including vascular plants, bryophytes, and lichens—exist in practically all terrestrial ecosystems throughout the world. From lichens acting as pollution-sensitive indicator species in urbanized landscapes, to the multimillion-dollar commercial market for horticultural bromeliads, to tropical orchids representing striking examples of rapid speciation, epiphytes make substantial contributions to theory, biodiversity, ecosystem services, and the global economy. This review is the first to broadly synthesize the underlying biotic interactions important to epiphyte ecology and evolution. We first draw from theory to discuss where and when biotic or abiotic processes are likely stronger drivers of epiphyte dynamics. We then systematically review the literature across the major interaction modes, highlighting areas where different groups of epiphytes (e.g., vascular versus nonvascular) and ecosystems have contrasting patterns or expectations. Throughout, we illustrate where research efforts have focused and where large gaps in knowledge exist. Our review is organized around the major biotic interactions, rather than the specific organisms interacting with the epiphytes, to highlight general processes and set epiphytism within the framework of ecological and evolutionary theory. Our review encompasses pollination and dispersal, intratrophic facilitation and competition, mycorrhizal mutualisms, epiphyte-host interactions, parasitism and pathogens, and herbivory, focusing on the impact of these interactions on the epiphyte. Finally, we provide a simple conceptual framework distilling open questions in the field, expand our findings to the community and ecosystem level, and summarize the biodiversity conservation implications of ignoring biotic interactions in epiphytes. Our synthesis brings together currently disparate literature from tropical and temperate systems on vascular and nonvascular plants and lichens. We hope our review stimulates further research and inspires cross-disciplinary collaboration.
... A change in the environment to a less than optimal condition may inhibit lichen growth to such an extent that thalli rapidly fragment and disappear from a substratum (McCarthy 1989, Armstrong 2017a). In addition, the environment can act more indirectly by altering the competitive balance among different species thus changing the composition of a community (Armstrong and Welch 2007). Second, knowledge of environmental growth effects is important in 'lichenometry', a technique which uses lichens to estimate the surface age of a substratum or archaeological remains (Locke et al. 1979, Innes 1985, Matthews 1994, Benedict 2009). ...
... A second decision is whether to use an absolute or relative growth rate measure. Hence, RaGR is a useful indicator of how quickly a species may cover a substratum and may be directly related to the competitive ability of a species (Armstrong and Welch 2007). In other circumstance, however, it may be the efficiency of a growth process under different conditions which may be important, e.g., the efficiency of the thallus as a producer of new growth and hence, a measure of RGR can be applied to any basic absolute measure. ...
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The quantitative analysis of plant growth ('plant growth analysis', PGA) has been particularly valuable in investigations of the development of higher plants and the influence of environmental factors on growth. This review describes various aspects of a PGA modified for application specifically to lichens and is illustrated with special reference to the growth of the common foliose lichen Xanthoparmelia conspersa (Ehrh. Ex Ach.) Hale. Hence, this review considers: (1) methods of measuring growth, (2) terms, abbreviations and units, (3) variability in measures of absolute and relative growth, (4) the growth rate size curve and growth models, and (5) practical considerations including aspects of experimental design and statistical analysis. Most studies of the growth of X. conspersa and other lichens have used absolute measures of growth such as radial growth rate (RaGR) or dry weight gain (DWG) whereas relative growth rate (RGR) measures such as 'unit annulus rate' (UAR) may be more sensitive and informative. There are a number of considerations when carrying out lichen growth analysis including: (1) which aspect of growth to measure, (2) how to express growth, (3) the experimental design, as different sources of variation may be present which influence statistical 'power', and (4) the statistical analysis of the data.
... The influence of climate change on the distribution of saxicolous lichen communities would be mainly caused by an increase in temperature and changes in precipitation patterns whereas the main influence of microsite characteristics on temperature would be due to boulder surface slope inclination and aspect which affects sun incidence and capture of precipitations. Saxicolous lichen communities are also influenced by geochemical composition of rocks and the surface area of the substrate among others (Armesto and Contreras 1981;Armstrong and Welch 2007;Kuntz and Larson 2006;Rajakaruna et al. 2012). These variables must be kept fixed or considered as co-variables to study main effects. ...
... The community composition revealed an expected relation with altitude and secondarily with others environmental variables -mainly slope throughout the whole gradient and aspect at the lower altitudes. Presumably, some species that have a wide tolerance to environmental conditions cannot grow in microhabitat with better conditions due to competitive exclusion (Armstrong and Welch 2007). Although our study did not evaluate competition we can provide indirect evidence. ...
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The extent to which small shifts among local topographic microsites could mitigate the effects of larger-scale climate change in arctic–alpine systems including mountain top organisms is largely unknown. This study is among the first to evaluate the relative contribution of microsite and altitude as a proxy for climate change on saxicolous lichen communities. We registered 107 lichen species in 54 boulders ranging from 900 to 2700 m.a.s.l. and in a large array of microsites in central Argentina. Communities ordinated along NMS multivariate analysis axes 1, 2 and 3 presented a cumulative R² of 80%. The three axes were explained by altitude with axis 1 only being explained by altitude. Axis 2 was also explained by slope and aspect whereas axis 3 was explained by the interaction of altitude with aspect indicating that aspect was important only at lower altitudes but not at the mountain top. Lichen cover and richness were similar throughout the altitudinal gradient. We interpret that under a climate warming scenario, lower altitude species occupying pole ward facing slopes will have to migrate upwards while at the mountain top—for most communities—there still is scope for microsite segregation to compensate climate change.
... In comparisons to all other genera, Usnea and Xanthoparmelia have developed unique sets of strategies to exploit a much wider range of habitats. Informally known as "old man beard lichens, " Usnea species have a bushy or pendulous growth form that allows them to minimally attach to the substrate surface, while exploiting a vast "empty" three-dimensional space to capture extra carbon dioxide and moisture 31,32 . These lichens also produce predominantly usnic acid, which was shown to reflect extra sunlight and consequently protect algal cells inside 33 . ...
Article
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1 Renewed interests in macroevolutionary dynamics have led to the proliferation of studies on diversification processes in large taxonomic groups, such as angiosperms, mammals, and birds. However, such a study has yet to be conducted in lichenized fungi – an extremely successful and diverse group of fungi. Analysing the most comprehensive time-calibrated phylogenies with a new analytical method, we illustrated drastically different diversification dynamics between two hyper-diverse families of lichenized fungi, Graphidaceae and Parmeliaceae, which represent more than a fourth of the total species diversity of lichenized fungi. Despite adopting a similar nutrition mode and having a similar number of species, Graphidaceae exhibited a lower speciation rate, while Parmeliaceae showed a sharp increase in speciation rate that corresponded with the aridification during the Oligocene-Miocene transition, suggesting their adaptive radiation into a novel arid habitat. Recent advances in phylogenetic reconstruction and comparative methods have renewed interest in macroevolutionary dynamics of large taxonomic groups, such as in plants 1–3 , mammals 4 , and birds 5. These studies have provided additional insights into timing and processes of diversification – a research program that has traditionally been pursued from a mostly paleontological perspective 6. However, these recent methodological advances enable us to shed light on diversification processes in organisms with little or no fossil record. Lichens – symbiotic associations of fungi with algae and/or cyanobacteria – represent an extremely successful nutritional mode in the fungi, allowing a heterotrophic fungal partner to expand their ecological range without relying on " external " sources of energy. Nearly one-fifth of all fungi are lichen-forming 7
... This suggests that intraspecific competition would promote species diversity by shaping more diverse niches when intraspecific aggregation increases. The inference of greater diversity in aggregated communities is also supported by traditional ecological theory (i.e., not considering gap formation), as species clumping reduces interspecific contact, thereby retarding competitive exclusion 47 . This is confirmed by numerous experiments with annual species 21,45,46 . ...
Article
Gap disturbance is assumed to maintain species diversity by creating environmental heterogeneity. However, little is known about how interactions with neighbours, such as competition and facilitation, alter the emerging gap patterns after extreme events. Using a spatially explicit community model we demonstrate that negative interactions, especially intraspecific competition, greatly promote both average gap size and gap-size diversity relative to positive interspecific interaction. This suggests that competition would promote diversity maintenance but also increase community invasibility, as large gaps with a wide size variety provide more diverse niches for both local and exotic species. Under interspecific competition, both gap metrics interestingly increased with species richness, while they were reduced under intraspecific competition. Having a wider range of species interaction strengths led to a smaller average gap size only under intraspecific competition. Increasing conspecific clumping induced larger gaps with more variable sizes under intraspecific competition, in contrast to interspecific competition. Given the range of intraspecific clumping in real communities, models or experiments based on randomly synthesized communities may yield biased estimates of the opportunities for potential colonizers to fill gaps. Overall, our “static” model on gap formation offers perspectives to better predict recolonization opportunity and thus community secondary succession under extreme event regimes.
... Letharia and Oropogon) have a more limited range of suitable algal partners. While sampling additional groups of epiphytic fruticose and saxicolous foliose lichens will be necessary to confirm this general pattern, we hypothesize that the three-dimensional growth form created by fruticose lichens may require less common specialized algal partners adapted to cope with increased exposure, relative to foliose lichens that occur in a largely two-dimensional space (Armstrong & Welch 2007;McEvoy et al. 2007). However, while saxicolous foliose lichens sampled for this study generally had lower specificity than fruticose lichens, foliose genera Parmelina and Parmotrema both showed specificity values comparable to those of fruticose genera, highlighting that extrapolations of specificity based on growth form may not be appropriate. ...
Article
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Microbial symbionts are instrumental to the ecological and long-term evolutionary success of their hosts, and the central role of symbiotic interactions is increasingly recognized across the vast majority of life. Lichens provide an iconic group for investigating patterns in species interactions; however, relationships among lichen symbionts are often masked by uncertain species boundaries or an inability to reliably identify symbionts. The species-rich lichen-forming fungal family Parmeliaceae provides a diverse group for assessing patterns of interactions of algal symbionts, and our study addresses patterns of lichen symbiont interactions at the largest geographic and taxonomic scales attempted to date. We analysed a total of 2356 algal internal transcribed spacer (ITS) region sequences collected from lichens representing ten mycobiont genera in Parmeliaceae, two genera in Lecanoraceae and 26 cultured Trebouxia strains. Algal ITS sequences were grouped into operational taxonomic units (OTUs); we attempted to validate the evolutionary independence of a subset of the inferred OTUs using chloroplast and mitochondrial loci. We explored the patterns of symbiont interactions in these lichens based on ecogeographic distributions and mycobiont taxonomy. We found high levels of undescribed diversity in Trebouxia, broad distributions across distinct ecoregions for many photobiont OTUs and varying levels of mycobiont selectivity and specificity towards the photobiont. Based on these results, we conclude that fungal specificity and selectivity for algal partners play a major role in determining lichen partnerships, potentially superseding ecology, at least at the ecogeographic scale investigated here. To facilitate effective communication and consistency across future studies, we propose a provisional naming system for Trebouxia photobionts and provide representative sequences for each OTU circumscribed in this study.
... Understanding the ecological processes that control species distributions is a central theme in biogeography. For lichen epiphytes, these processes represent a network of effects, including 1) the abiotic environment, 2) the symbiotic relationship expressed as specificity, selectivity and access to compatible photobionts for thallus establishment and growth, and 3) an interspecific interaction among lichens, as competition (Armstrong and Welch 2007), or possibly as facilitation including the 'seeding' of photobionts into bark microhabitats by asexual lichens as suggested by the core-fringe hypothesis (Rikkinen et al. 2002). We discuss the effect of the abiotic environment, and symbiotic and interspecific interactions, below. ...
Article
Understanding how the biodiversity response to climate change will be modifi ed at ecological scales, e.g. by species interactions, is a major challenge. Lichen epiphytes – the close interdependent relationship between a heterotrophic fungus and photosynthetic partner (photobiont) – are used here to explore how interaction regimes (between lichen species, and between lichens and their photobionts) explain distribution patterns along spatial climatic gradients. To do this we tested fi eld evidence for the ‘ core-fringe hypothesis ’ , which proposes a facilitative interaction; sexually-reproducing and sporedispersed lichens with a requirement for resynthesis with a compatible photobiont ( Nostoc ) are facilitated by the prior establishment of asexual lichens which disperse both the fungus and photobiont together. We used two closely related Nephroma species which diff er in their reproductive mode – N. laevigatum (sexual spore-dispersed) and N. parile (asexual) – and compared their occurrence along a bioclimatic gradient to local habitat factors, including the co-occurrence of asexual lichens which have shared specifi city for compatible Nostoc genotypes. Th e results showed that: 1) N. laevigatum is signifi cantly more likely to occur on trees that have already been colonised by asexual lichens with shared specifi city for Nostoc , supporting the core-fringe hypothesis, while 2) N. parile is independent of this association (strengthening the core-fringe hypothesis), with its response to a precipitation gradient modifi ed by microhabitat factors. Th is positive test for the core-fringe hypothesis demonstrates how interaction regimes can fundamentally alter expectations under climate change. Th ere is an assumption that spore-dispersed lichen species could more easily track their suitable bioclimatic space through fragmented habitat, compared to asexual species with larger and heavier propagules. However, the establishment of spore-dispersed lichen epiphytes into new habitat may be limited by the dispersal rates of asexual species, which act as key facilitators.
... Lichen establishment may be influenced by competition, facilitation, photobiont availability, and predation, in addition to the above mentioned variables for habitat quality. Competition includes here the replacement of species during succession, overgrowth by other species, and a structuring of communities due to space and light availability (Lawrey, 1991;Armstrong & Welch, 2007). Herbivore predation of diaspores or young thalli fragments has been suggested to stop or reduce establishment success (Scheidegger et al., 1995;Asplund & Gauslaa, 2008). ...
... One of them proposes that competitive interactions among species lead to non-random co-occurrence patterns. The competition is one of the most important mechanisms in structuring a community and its diversity (Armstrong & Welch 2007). Keddy (2001) defines it as the negative effect of an organism on another for the consumption or the access control to a resource that is limited in its avai- lability. ...
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This study aims to determine lichens co-occurrence patterns on five phorophyte species in the montane rainforest of Gran Piedra, Santiago de Cuba. In each plot, all trees of these five species: Gomidesia lindeniana, Coccoloba wrightii, Clusia tetrastigma, Dendropanax arboreus and Brunellia comocladifolia were surveyed. On the 51 sampled phorophyte trees, 53 lichen species were found. Only Gomidesia lindeniana and Coccoloba wrightii exhibited probabilities for the C-score and CHECKER indices significantly higher than expected by chance; consequently, lichens co-occurrence are non-random on these phorophytes. For Dendropanax arboreus , Clusia tetrastigma and Brunellia comocladifolia the null hypothesis for these indices was not rejected. The enhanced of frequency of lichen species, increase the number of species pairs forming a checkerboard distribution. In conclusion, lichen species co-occurred less often than expected by chance, although this pattern was not similar for all phorophytes species.
... Low lichen colonization rates have been explained by increased landscape-level fragmentation and loss of suitable old-growth habitat (Snäll et al. 2005), lichen dispersal limitations (Snäll et al. 2005), competition from bryophytes and large foliose lichens resulting in over-growth of smaller lichens and impaired establishment (Armstrong and Welch 2007), and gastropod grazing on Lobaria (Asplund et al. 2010). The availability and quality of the habitat may also have changed substantially over longer time scales, resulting in delayed species extinctions ('extinction debt' sensu Tilman et al. (1994). ...
Article
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Incorporating functional values in biodiversity monitoring systems could add novel perspectives of the status of biodiversity in conservation areas. Stable frequencies of large foliose nitrogen-fixing cyanolichens likely have positive effects on the nitrogen budget of forests and provide food, material and shelter for invertebrates, gastropods and birds. Stable volumes of deadwood and frequencies of associated fungi provide an important supporting function for ecosystem services such as nutrient cycling, carbon storage and soil formation. Based on regional monitoring data from boreal old-growth forest nature reserves and key habitats, we tested for changes in the frequency of various functionally important substrates and species over time. We detected significant reductions in the frequency of indicator cyanolichens occurring on deciduous trees already after 10 years in key habitats, despite non-significant changes in their host substrates. Frequencies of indicator pendulous lichens Alectoria sarmentosa and Bryoria nadvornikiana had also decreased in key habitats, despite overall stable volumes of large conifer host trees. Lichen reductions were more pronounced in the smaller key habitats compared to the larger formally protected nature reserves, likely due to degrading fragmentation and isolation effects. In contrast to these lichens, the average frequencies of old-growth forest indicator fungi decaying coniferous deadwood and common fungi on deciduous trees (Fomes fomentarius) and coniferous trees (Fomitopsis pinicola) remained unchanged. The studied cyanolichens and fruiting fungi generally had similar extinction rates over 10 years, whilst only cyanolichens had substantially lower colonization rates. Amid a severely fragmented landscape, conservation areas seem to struggle in preserving some of the basic old-growth forest values.
... An example is the phenol protection by lecanoric acid, which controls the growth of the mycobiont Nectria parmeliae (Lawrey 2000). Lichenized fungi show better tolerance toward the inhibitory effect of secondary lichen substances than nonlichenized fungi (Armstrong and Welch 2007). The epiphytic lichen Hypogymnia physodes affects wood-consuming fungi, thereby protecting the own substrate from decomposition (Henningsson and Lundstrom 1970). ...
Article
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Lichen secondary metabolites can function as allelochemicals and affect the development and growth of neighboring bryophytes, fungi, vascular plants, microorganisms, and even other lichens. Lichen overgrowth on bryophytes is frequently observed in nature even though mosses grow faster than lichens, but there is still little information on the interactions between lichens and bryophytes. In the present study, we used extracts from six lichen thalli containing secondary metabolites like usnic acid, protocetraric acid, atranorin, lecanoric acid, nortistic acid, and thamnolic acid. To observe the influence of these metabolites on bryophytes, the moss Physcomitrella patens was cultivated for 5 weeks under laboratory conditions and treated with lichen extracts. Toxicity of natural mixtures of secondary metabolites was tested at three selected doses (0.001, 0.01, and 0.1 %). When the mixture contained substantial amounts of usnic acid, we observed growth inhibition of protonemata and reduced development of gametophores. Significant differences in cell lengths and widths were also noticed. Furthermore, usnic acid had a strong effect on cell division in protonemata suggesting a strong impact on the early stages of bryophyte development by allelochemicals contained in the lichen secondary metabolites. Biological activities of lichen secondary metabolites were confirmed in several studies such as antiviral, antibacterial, antitumor, antiherbivore, antioxidant, antipyretic, and analgetic action or photoprotection. This work aimed to expand the knowledge on allelopathic effects on bryophyte growth.
... Vertical distribution patterns have been related mainly to microclimate (e.g., solar radiation and humidity) and the interaction between canopy microclimate and canopy structure (McCune et al. 1997;Goward 1998;Campbell and Coxson 2001), as well as bark chemistry (Kermit and Gauslaa 2001;Fritz 2009). Furthermore, biotic factors such as gastropod grazing (Asplund et al. 2010) and competition from bryophytes and large foliose lichens (Scheidegger et al. 1995;Armstrong and Welch 2007) can shape lichen distribution within tree canopies. Very few Scandinavian studies, except Gauslaa (1997), have focused on lichen population attributes at different canopy heights in coniferous stands. ...
Article
All specimens of three foliose lichens (Lobaria pulmonaria (L.) Hoffm., n = 725; Lobaria scrobiculata (Scop.) DC., n = 6613; Pseudocyphellaria crocata (L.) Vain., n = 1237) and two pendulous lichens (Alectoria sarmentosa (Ach.) Ach., n = 441; Ramalina thrausta (Ach.) Nyl., n = 990) were collected from 160 random Picea abies (L.) H. Karst. branches (2-15 m above the ground) in three spruce-dominated boreal rainforests in Norway. Maximum diameter (foliose lichens), length (pendulous lichens), and reproductive structures were quantified in each thallus. The effects of measured tree and branch variables on abundance and reproduction were tested by generalized linear mixed models with binomial errors (binomial GLMM) and zero-altered (over-dispersed) Poisson generalized linear mixed models (ZAPGLMM). Lobaria pulmonaria, P. crocata, and R. thrausta occurred predominantly in the lower canopy, whereas the remaining species were also common at higher levels. The portions of thalli producing soredia and (or) isidia were 60%, 22%, and 14% for P. crocata, L. scrobiculata, and L. pulmonaria, respectively. Isidiate and (or) sorediate L. pulmonaria thalli occurred mainly on low, dead branches, whereas sorediate L. scrobiculata and P. crocata occurred at all heights. The occurrence of small P. crocata, <5 mm, decreased by branch height and small L. scrobiculata, <5 mm, increased with branch length and decreased with tree age. Upper branches supported a significant part of the total populations of studied lichens and are, thus, important when evaluating epiphyte conservation status.
... Ecologically, the function of lichen metabolites is to protect the thallus and the photobiont by counteracting biotic factors such as competitive organisms (Armstrong and Welch, 2007), herbivores (P€ oykk€ o et al., 2010), and abiotic factors such as photoprotection (Kov a cik et al., 2011;Loh ezic-Le D ev ehat et al., 2013), as well as the allelopathic effects on other organisms competing for space (Lokajov a et al., 2014); however, the latter effects in nature were recognised as a controversial issue by Asplund and Wardle, (2017). Apart of the above, the presence of these compounds is considered as agents that enable lichens to colonize almost all permanent habitats on our planet (Moln ar and Farkas, 2010). ...
Article
An analysis of data from experimental studies investigating the effect of powdered thalli, extracts and secondary metabolites from 25 lichen species on the growth dynamics of the mycelia of 36 species of macromy-cetes classified into different trophic groups (pathogens, saprotrophs and mycorrhizal fungi) is presented. Since various methods have been used to extract lichen substances, thereby preventing a direct comparison of results, a critical review was undertaken. The results of studies, depending on the adopted methodology of fungal culture and supplementation of active substances, indicated that natural ecological processes can be regulated by biochemical compounds from lichens and that they have a wide range of potential effects. Experiments have revealed that the strongest inhibitory activity against macromycetes is produced by Cetra-ria islandica, Evernia prunastri, Hypogymnia physodes, Pseudevernia furfuracea and Cladonia species, and those fungi most susceptible to lichen substances include, Gloeophyllum sepiarium, Macrolepiota procera, Paxillus involutus and Stereum sangunoilentum. Limited experimental studies on the effects of lichen substances on macromycetes that have been carried out worldwide may prompt more detailed research focused on explaining the role of lichens in the natural environment, particularly in forests. The conclusions obtained from this work underline the wide range of allelopathic effects which depend upon dose-effect phenomenon of lichen substances tested as homogenates, lichen extracts and individual secondary metabolites. They also show the role of underestimated primary as well as secondary metabolites as a mixture of lichen substances and their effects on ecological processes. Full text available under https://authors.elsevier.com/c/1fKCt_5oYGckAN
... Varying levels of secondary metabolite production by lichen thalli will also have an effect on the environment in distribution of allelopathic compounds influencing competition among cryptogams as well as germination and growth of vascular plants (Armstrong and Welch 2007;Lawrey 1995), Collembolans and Dipterans (Miller et al. 2008), and the growth of intrathalline bacterial communities (Bates et al. 2011), which have been shown to vary across a lichen thallus (Mushegian et al. 2011). The spatial configuration of noncryptogam communities may be shaped at small and large spatial scales depending on the levels and types of sec- Fig. 6. ...
Article
The Precambrian Shield supports a diversity of cryptogams where environmental conditions predict their distribution. Moisture and light are thought to affect secondary metabolite production in lichens, leading to a hypothesis of chemical communities that may be independent of species assemblages. Hypotheses were that habitats will be characterized by lichen secondary metabolites and that lichen and bryophyte species composition will also distinguish among habitats. Lichens and bryophytes were sampled from six quadrats from each of two sites within each of three habitats (rock faces, rock outcrops, and forest floors). This study showed strong relationships among species assemblages, secondary metabolites, and types of habitat. Species abundance, cover, and species richness also differed among habitats. Individual secondary metabolites could differentiate among three habitats, suggesting that certain metabolites such as usnic and squamatic acids would more likely be found in habitats such as dry exposed rock outcrops than in moist shaded habitats. Individual analyses suggested that some secondary metabolites may serve multiple functions in a habitat, such as triterpenes, while others may have more specific functions, such as salazinic acid, where environmental features may be important for secondary metabolite production. Further investigation of specific metabolites is needed to understand their roles in adaptation.
... It is also noticeable that H. erythromma can overcome the occupation of the surface of the rocks by foliose species like X. elegans. Most of the studies have noticed a succession from the crustose species, the first to colonize a substrate, to the foliose ones (Armstrong & Welch 2007). In the present study, foliose species are still excluded by crustose, redesigning the succession in the Antarctic environment. ...
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Antarctica is one of the most extreme environments on the planet considering the climatic conditions. This greatly limits the development of plants, and is reflected in slow growth, especially in the lichens present in this environment. Haematomma erythromma is a nitrophile lichen easily identifiable by its color and was the species chosen to evaluate growth in Antarctica. Using a plastic sheet, squares of 20 x 20 cm were placed on eight different rocks with crustose lichen communities and the species found were drawn in 1992 and in 2012. The location chosen for the survey was Stinker Point, on Elephant Island, north of the South Shetland Archipelago. After 20 years and evaluating 178 thalli, H. erythromma grew 0.2 to 0.7 mm/year, one of the slowest among Antarctic lichens. The thallus growth is mainly oriented West/Northwest, against prevailing wind direction, probably due to nutrient carried form a penguin rockery nearby. New thalli formed during this evaluation and the old ones also grew to connect each other, resulting in a confluent larger thallus. The new thalli grew mostly over Xanthoria elegans (Link.) Th. Fr., Rhizoplaca aspidophora (Vain.) Redón and Buellia spp. demonstrating that H. erythromma is capable of colonize areas with other lichen species coverage. The growth to be confluent with other thalli and the wind orientation are novelties to this species of lichen.
... It thus seems likely that, when one of these lichen morphotypes is established first, it spreads rapidly and hampers the colonization of the other morphotype. Armstrong and Welch [86] showed that lichen species may be excluded from a substrate through competition and that competitive interactions in diverse lichen communities can lead to the establishment of stable species groups. Competition may also account for the fact that the greater number of lichen morphotypes observed in the center of the ENP did not result in greater richness or cover. ...
Article
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Habitat fragmentation affects lichen communities by inducing edge effects, although the dispersal of pollutants by pesticide drift from commercial crops may also provoke alterations in community structure, due to the varying sensitivity of lichen morphotypes to pollutants. In this context, we tested the hypothesis that lichen morphotype richness and diversity, and the percentage area of the trunks covered by different lichen morphotypes are modified significantly at the edges of fragments of Cerrado vegetation inserted within the agricultural matrix. We evaluated habitat fragments representing different Cerrado formations (Cerradão, Cerrado sensu stricto, and seasonal semi-deciduous forest) as well as the Emas National Park, a prominent Cerrado conservation unit. We used Generalized Linear Mixed Models (GLMMs) to test the potential of the models compiled using a mixture of phytosociological and environmental parameters, including the species, the height of the host plant (H), the circumference of its stem at breast height (CBH), total chlorophyll (TC), bark fissuring (BF) and pH, and illuminance (Lum), to explain the observed variation in the lichen morphotype richness and the percentage cover of the trunks by corticolous lichen morphotypes at the center and edge of the fragments. The central areas invariably had a greater diversity of morphotypes in all the fragments. The morphotypes considered highly sensitive to disturbance were not observed in edge areas, confirming a clear edge effect, as well as the influence of pesticide drift from the adjacent farmland matrix, on the structure of the lichen community. At both the edge and center sites, the larger trees (higher CBH) with less fissured bark tended to have the greatest diversity of lichen morphotypes, and more acidic barks had the greatest lichen cover. The models tested indicated that the variable tree species is an important determinant of the observed patterns of lichen morphotype richness and cover, either on its own or in association with pH or CBH + pH. The analyses also indicated that all the variables tested are important in some way for the definition of the percentage cover of the host trunks. The present study contributes to the understanding of the diversity of the corticolous lichen communities in the remaining fragments of Cerrado vegetation and the effects of the agricultural matrix on this community. The lichen may thus play a role as indicators of impact on other species, these organisms may provide important insights for the further investigation of the disturbance caused by the agricultural matrix on the communities of other groups of organisms.
... They are equipped to tolerate desiccation and extreme habitat conditions and can scavenge free radicals due to the presence of oxidoreducatase enzymes like peroxidases and laccases as studied in Peltigeralean lichens (Laufer et al. 2006;Liers et al. 2011;Beckett et al. 2013a, b). These enzymes also act as allelochemics, protecting the Peltigeralean lichens from the detrimental phenolic compounds produced by other organisms (Armstrong and Welch 2007;Beckett et al. 2013a, b). ...
Chapter
The key features of sustainable agriculture which include crop improvement, control of pests and diseases, and maintenance of soil fertility have largely been augmented by microbial application. These microorganisms and their consortia have largely been utilized as bioremediative and biocontrol agents as well as natural bioindicators. Algae also help in conserving environment by sequestering carbon dioxide directly from atmosphere and are used in production of biofuels and biorefinery products. Also commercial production and extraction of a large array of bioactive compounds like fatty acids (PUFA, EPA, and DHA), bioflavonoids, carotenoids, polyphenols, asperfumoid, phomoenamide from them have been reported to show antibacterial, antifungal, antiviral, and insecticidal properties besides diverse therapeutic uses. The role of algae–fungal associations and their role in the sustainable agriculture have been elaborated in this chapter. With the advancement of biotechnology, the biostimulatory potential of microbes particularly the algal and fungal communities has been thoroughly studied and manipulated, but more innovative approaches are indeed required for an ecofriendly environment and better tomorrow.
... Alelopatia: Sekundárne metabolity lišajníkov plnia aj funkciu alelochemikálii a hrajú dôležitú úlohu v boji o priestor a slnečné žiarenie, ktoré je dôležité pre fotosyntézu (Armstrong & Welch 2007). Často ovplyvňujú rast a vývin susediacich lišajníkov, machov a cievnatých rastlín ako aj mikroorganizmov (Lawrey 1995;Macías et al. 2007;Romagni et al. 2004;Rundel 1978). ...
Article
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Lichens produce many unique chemical compounds, known also as secondary metabolites. They play an important role in photobiont as well as mycoboint defense of, e. g. photoprotection, antiherbivoral, antiviral, antibacterial, cytotoxic, antitumor activities. They can be used also as allelochemicals, antipyretics or analgetics. Secondary metabolites participate in chelating process because they can immobilize xenobiotics – such as metals. This review summarizes basic applications, where secondary metabolites can be used.
... Some exceptions do exist, as in the case of various Fusarium species, and these parasites attack a variety of lichens and are tolerant of many lichen defense compounds [7]. Moreover, several species of Caloplaca are known to have parasitic phases in their life cycles during which they take over other crustose lichens [8,9]. A killer is the basidiomycete Athelia arachnoidea, which has been shown to attack and destroy Lecanora conizaeoides lichen [10]. ...
Article
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A lichen body is formed most often from green alga cells trapped in a net of ascomycetous fungi and accompanied by endolichenic or parasitic fungi, other algae, and symbiotic or free-living bacteria. The lichen’s microcosmos is inhabited by mites, insects, and other animals for which the lichen is a source of food or a place to live. Novel, four-segmented dsRNA viruses were detected in saxicolous Chrysothrix chlorina and Lepraria incana lichens. Comparison of encoded genome proteins revealed classification of the viruses to the genus Alphachrysovirus and a relationship to chrysoviruses from filamentous ascomycetous fungi. We propose the names Chrysothrix chrysovirus 1 (CcCV1) and Lepraria chrysovirus 1 (LiCV1) as acronyms for these viruses. Surprisingly, observation of Chrysothrix chlorina hybridization with fluorescent-labelled virus probe by confocal microscope revealed that the CcCV1 virus is not present in the lichen body-forming fungus but in accompanying endolichenic Penicillium citreosulfuratum fungus. These are the first descriptions of mycoviruses from a lichen environment.
... But even though we need to go beyond growth forms to better identify growth factors, it must be borne in mind that they are useful ecological concepts when researchers want to generalize and predict: for example, crustose lichens can colonize harsher habitats (Rogers, 1990) while foliose and fruticose species are good competitors in less demanding environments (Armstrong, 1993;Armstrong & Welch, 2007). In tropical latitudes, the lower temperatures and higher photosynthetic rates of mid altitudes favor foliose and fruticose species (Ceron & Quintero, 2009), but only crustose species can grow in the more demanding conditions of high altitudes (Rai, Khare, Baniya, Upreti, & Gupta, 2015). ...
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Lichens are traditionally divided into short “crustose”, intermediate “foliose” and tall “fruticose” types, a practice that hides a growth continuum. Substrate, temperature and water are thought to affect vertical growth, but such factors are difficult to measure, because, for example, the water actually available to lichens does not match rainfall patterns or even ground water levels. To reliably assess the effect of those factors, I recorded temperature, moisture, and substrate in and under individual terricolous lichen colonies in 60 fixed quadrats on April, August, October, and December of 2015 (Cerro de la Muerte, Costa Rica, 9°33′N; 83°45′W). The measurements were taken inside the colonies themselves (rather than on the general environment), covering an annual cycle of the relatively simple páramo habitat, where animals and vegetation have less impact than in lower ecosystems. The hypotheses were that lichens would grow taller on softer, warmer, and moister ground; on the Caribbean versant; and on the rainy season. Results matched the hypotheses, with one exception: lichens on soft ground were not taller than those on rock. Caribbean colonies were, on the average, 7 cm taller than those on the drier Pacific versant. Physiologically available water seems to be the main determinant of lichen vertical growth: more water means taller lichens and greater protection from climatic change for both the lichens and their microcommunities.
... But even though we need to go beyond growth forms to better identify growth factors, it must be borne in mind that they are useful ecological concepts when researchers want to generalize and predict: for example, crustose lichens can colonize more extreme habitats (Rogers, 1990) while foliose and fruticose species are better competitors in less demanding environments (Armstrong, 1993;Armstrong & Welch, 2007). In tropical latitudes, the lower temperatures and higher photosynthetic rates of mid altitudes favor foliose and fruticose species (Ceron & Quintero, 2009), but only crustose species can grow in the more demanding conditions of high altitudes (Rai, Khare, Baniya, Upreti, & Gupta, 2015). ...
Preprint
Full-text available
Lichens are traditionally divided into short "crustose", intermediate "foliose" and tall "fruticose" types, a practice that hides a growth continuum. Substrate, temperature and water are thought to affect vertical growth, but such factors are difficult to measure, because, for example, the water actually available to lichens does not match rainfall patterns or even ground water levels. To reliably assess the effect of those factors, I recorded temperature, moisture, and substrate in and under individual terricolous lichen colonies in 60 fixed quadrats on April, August, October, and December of 2015 (Cerro de la Muerte, Costa Rica). The measurements were taken inside the colonies themselves (rather than on the general environment), covering an annual cycle of the relatively simple paramo habitat, where animals and vegetation have less impact than in lower ecosystems. The hypotheses were that lichens would grow taller on softer, warmer, and moister ground; on the Caribbean versant; and on the rainy season. Results matched the hypotheses, with one exception: lichens on soft ground were not taller than those on rock. Caribbean colonies were, on the average, 7 cm taller than those on the drier Pacific versant. Physiologically available water seems to be the main determinant of lichen vertical growth: more water means taller lichens and greater protection from climatic change for both the lichens and their microcommunities.
... In addition, adjacent vascular plants can also influence lichen symbiosis through their effects on soil properties and lichen development, and competition for resources (e.g. space and light) (Armstrong & Welch, 2007;O'Bryan et al., 2009;Bowker et al., 2016;Gauslaa et al., 2020). Increasing plant litter cover could reduce light that reaches the soil surface and therefore the available lichen habitat (Bowker et al., 2005). ...
Article
․Lichens play crucial roles in sustaining the functioning of terrestrial ecosystems; however, the diversity and ecological factors associated with lichenized soil fungi remain poorly understood. ․To address this knowledge gap, we used a global field survey including information on fungal sequences of topsoils from 235 terrestrial ecosystems. ․We identified 880 lichenized fungal phylotypes across nine biomes ranging from deserts to tropical forests. The diversity and proportion of lichenized soil fungi peaked in shrublands and dry grasslands. Aridity index, plant cover and soil pH were the most important factors associated with the distribution of lichenized soil fungi. Further, we identified Endocarpon, Verrucaria and Rinodina as some of the most dominant lichenized genera across the globe, and they had similar environmental preferences to the lichenized fungal community. In addition, precipitation seasonality and mean diurnal temperature range were also important in predicting the proportion of these dominant genera. Using this information, we were able to create the first global maps of the richness and the proportion of dominant genera of lichenized fungi. ․This work provides new insight into the global distribution and ecological preferences of lichenized soil fungi, and supports their dominance in drylands across the globe.
... Lichens segregate secondary metabolites to the substrate to disadvantage their competitors. These secondary metabolites represent allelochemicals, which negatively influence vascular plants, mosses, or even lichens nearby (Armstrong & Welch, 2007;Molisch, 1938). As mosses and lichens have a long evolutionary history of allelopathic relations, they achieved survival strategies for cohabitation. ...
Article
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Lichens and mosses often share the same environmental conditions where they compete for substrate and other essential factors. Lichens use secondary metabolites as allelochemicals to repel surrounding plants and potential rivals. In mosses, endoreduplication leads to the occurrence of various ploidy levels in the same individual and has been suggested as an adaptation to abiotic stresses. Here, we show that also biotic factors such as usnic acid, an allelochemical produced by lichens, directly influenced the level of ploidy in mosses. Application of usnic acid changed the nuclei proportion and significantly enhanced the endoreduplication index in two moss species, Physcomitrella patens and Pohlia drummondii. These investigations add a new aspect on secondary metabolites of lichens which count as biotic factors and affect ploidy levels in mosses.
... Las diferencias de diversidad encontradas entre estos dos tipos de bosques pueden explicarse mediante otros factores distintos a la apertura del dosel o el grado de perturbación, como son la edad de los árboles (Armstrong & Welch 2007;Nascimbene et al. 2009;Johansson et al. 2010), el microclima (Li et al. 2015) o la calidad del área adyacente (Cardós et al. 2016). Sin embargo, también se puede indicar que la altura de los árboles también juega un rol, como ha sido mostrado por Prather et al. (2018), quienes mostraron que un 80% de la comunidad liquénica puede ser registrada en la parte baja de los árboles (hasta 1,9 m de la base) y un 68% de la diversidad se encuentra representada en la parte del dosel de árboles de altura mayores a 50 m. ...
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The Rucamanque Park houses some of the remnants of the Roble-Raulí-Coigüe mixed forest in Central South Chile. Cortical lichens were monitored in Renoval and in the Original Remnant Forest of Nothofagus obliqua (Mirb.) Oerst. We found differences in specific richness by tree species and between the Renoval (13 species) and the Original Remnant (7 species). The variables that affect the greatest richness are discussed, suggesting that the structure of the forest may play a key factor.
... This may explain the luxuriant occurrence of the crustose form and, thus, unlike lichens that benefit from a lush supply of water from sea spray and therefore may not be restricted to the flat crustose form (like Cladonia litoralis Gumboski and Eliasaro that have a cushion-like form and protrude up to 2.5 cm aboveground; Gumboski and Eliasaro 2011), the crustose form facilitates the acquisition of a high water supply by dew. However, it also increases the risk of competition over light (Armstrong and Welch 2007), but nevertheless, with water being the most limiting factor in deserts, the advantage of the crustose form for enhancing dew formation is evident. To maximize however fog interception, an upright position of the thalli, normal to the droplets flux, is required (Rundel 1978), as well as narrow and finely dissected thalli, i.e., high ratio of surface area to volume (Gauslaa 2014;Armstrong 2017), all yielding an advantage to the fruticose lichens in fog interception. ...
Article
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Main conclusion The expansion of crustose lichens in the Negev is principally determined by dew and that of fruticose lichens by fog. Crustose and fruticose lichens are largely adapted to dew and fog, respectively. Abstract Although crustose and fruticosea lichens were shown to efficiently use dew and fog, the link between their expansion and the occurrence of dew and fog has never been shown experimentally. This is also the case for the Negev Desert Highlands, where (i) dewless habitats were not inhabited by lichens and (ii) an increase in fruticose lichens with high-altitude fog-prone areas was noted, leading us to hypothesize that the expansion of crustose and fruticose lichens is mainly linked to dew and fog, respectively. Experiments aiming to compare the non-rainfall water (NRW) were conducted. We used cloths attached to 7 cm-high cobbles to mimic crustose lichens (MCL), cloths placed horizontally aboveground to evaluate the amount of NRW without the presence of the cobble (CoP), cloths attached to a wire scaffold mimicking fruticose lichens (MFL), and cloths attached to glass plates (CPM) that served as a reference. Substrate temperatures were compared to the dew point temperature. In addition, sprinkling experiments, which mimicked fog under variable wind speeds (0.9, 1.4, 3.3 and 5.7 m s⁻¹), were also conducted. NRW followed the pattern: MCL ≈ CPM > CoP > > MFL. While MCL yielded substantially higher amounts of NRW (0.09 mm) in comparison to MFL (0.04 mm) during dew events, similar amounts were obtained by both substrates (0.15–0.16 mm) following fog. However, fog interception increased substantially with wind speed. The findings may explain the expansion of crustose lichens in extreme deserts benefiting mainly from dew (but also fog), and the proliferation of fruticose lichens in fog-prone areas, especially when accompanied by high-speed winds. While (mainly) high proliferation of crustose lichens may serve as bioindicators for dew in extreme deserts, fruticose lichens may serve as bioindicators for fog.
... The growth of the green algae Chlamydomonas was dithered by usnic acid (Schimmer and Lehner, 1973). In the case of mosses such as Ceratodon purpureus, Funaria hygrometrica, and Mnium cuspidatum, the germination of their spore and the growth of the protonema were severely impaired by metabolites such as 4-O-methylated depsides and evernic and squamatic acids (Armstrong and Welch, 2007). Mosses such as Anomodon attenuatum and Hedwigia ciliata and the liverwort Porella platyphylla also face inhibition of their propagation by the lichen Porpidia albocaerulescens (Heilman and Sharp, 1963). ...
Chapter
Lichen is an interesting example of a symbiotic association between algae and fungi. Being a separate entity combining these two genres, it’s a rich repertoire of unique secondary metabolites. Lichens generally grow in the alpine and polar regions of the globe and face stressful environmental cues. Therefore, they accumulate high amounts of distinctive metabolites that maintain hydrophobicity and absorb UV. It helps them to survive under harsh conditions. These compounds also play a significant role in ecological interactions and regulation of the synergism between symbionts. In this chapter, we offer an overall scenario of the important secondary metabolites identified in lichens that have pharmaceutical properties. Moreover, those metabolites have also described that have paved the lichen’s path in curing several human diseases. To obtain secondary metabolites from lichens, growing them is a daunting task. The axenic cultivation process of each symbiotic partner, particularly the mycobiont, is difficult. Hence, we have also mentioned the means to overcome the limitations for the supply of rare metabolites from lichens.In summary, lichens are important natural source from which different bioactive compounds can be produced.
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Symbiotic interactions are widespread in nature, but the relationship between life history, fecundity, and habitat specificity has been underexplored. This study investigated the life history strategies of foliose saxicolous lichens relative to their surrounding communities. Macrolichens were collected from 39 transects in Manitoba and Ontario. Frequency and percentage of ground cover of macrolichens, environmental variables, and numbers of apothecia and ascospores were recorded. Lichen assemblages were characterized using species similarity in a cluster analysis and ordination methods and were defined into communities using analysis of variance of the biotic variables among assemblages. Lichen life history strategies were inferred from community features, lichen fecundity, and morphological features. The general linear model determined which environmental variables may have influenced fecundity. The 81 species of macrolichens present in three lichen communities differed in species richness, with low species richness in the open mossy rock community, moderate in the grassy rock community, and high in the treed rock community. Three foliose saxicolous lichens dominated particular communities, and the life history strategy was characterized as competitive for Arctoparmelia centrifuga (L.) Hale, stress tolerant for Xanthoparmelia viriduloumbrina (Gyel.) Lendemer, and ruderal generalist for Xanthoparmelia cumberlandia (Gyel.) Hale. The proportion of sexual and asexual reproductive propagules for macrolichens showed uniformity between communities despite a significant difference in species richness. The study provides insights into the ecology of saxicolous lichens growing in the boreal forest and a characterization of lichen communities, and it shows how morphologically similar lichens can exhibit different life history strategies.
Article
Three common terricolous Toninia species (Toninia opuntioides, T. physaroides and T. sedifolia) - formerly kept under Toninia coeruleonigricans - were investigated in the same locality for comparison of various substrate parameters of their microhabitats. Classification and regression trees (CART) were used to examine the niche preference of these species. Additionally, we also examined the predictability of the colonising species given the particular characteristics of a site. More than two hundred soil samples were analysed in the respect of eight soil parameters. The classification trees revealed that the different species prefer distinct substrate types, each of which was defined by combination of 3-4 environmental variables. Carbonate content, pH, hygroscopicity, soil depth and exposition seem to be the most important predictors of abundance.
Article
Question In arid regions, the succession of biological soil crusts (biocrusts) usually accompanies substantial turnover of community composition, How interspecific interactions among biocrust forming mosses, lichens, algae and cyanobacteria change along the successional gradient is largely unknown. According to stress gradient hypothesis (SGH), the frequency or intensity of facilitative and competitive interactions within the community will vary along an environmental stress gradient, with increasing role of competition relative to facilitation undermore benign environmental conditions. In the process of biocrust succession, decreasing soil stress also occurs because of slow soil amelioration, which meets the assumption of the SGH. Therefore, we hypothesize that the changes in facilitative and competitive interactions within biocrust communities will follow the prediction of the SGH and that the nature of biocrust interactions will also change. Location Sandbinding vegetation belts for the BaotouLanzhou railway at the southeast fringe of the Tengger Desert in the Shapotou region of the Ningxia Hui Autonomous Region, western China. Methods We conducted a field evaluation at five adjacent sandbinding vegetation belts built in chronosequence to study the successional gradient. Small‐scale pattern of co‐occurrence and null models were used to evaluate the communitylevel interspecific interactions among the biocrust‐forming mosses, lichens, algae and cyanobacteria. In addition, an accessorymethod of species‐pair co‐occurrence based on null models was also applied to potentially identify the nature of the interspecific interactions within the biocrusts and for the causal investigation of these patterns. Results The strong spatial segregation of co‐occurrence pattern occurred between cyanobacteria and algae and species of mosses and lichens at early succession, and occurred among species of mosses and lichens at late succession. While the weak spatial aggregation between lichen species only occurred at the middle succession. Conclusions Negative interspecific interactions were prevalent within biocrusts throughout succession. The co‐occurrence patterns at both the community and species‐pair levels are consistent, supporting the unimodal version of the SGH that species interactions shift toward competition under extremely stressed conditions. Given the lack of research on interspecific interactions in biocrusts, our study is important for obtaining a deeper understanding of biocrust succession.
Article
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The altitudinal patterns of lichen communities in altitudinal gradients are very variable. The changes that occur along the mountains depend on climatic factors but also on microsite variables such as substrate type and aspect. The effect of altitude and aspect on richness, cover and composition of saxicolous lichens communities along an elevation gradient in extra Andean mountains from the central-west of Argentina was studied. Rock outcrops on the north and south aspect of three mountain summits distributed between 2,500 and 4,500 m.a.s.l. were sampled. Lichen species present in a 20 × 20 cm square were identified and the relative cover was measured using digital photography. Richness, cover and composition were analyzed through linear models and multivariate analysis. Fifty-eight saxicolous lichen species were identified between the three sites. Richness and cover were maximum at middle altitude. Also compositional differences among communities of each mountain summit were found. Finally, the effect of the aspect was significant at lower altitudes for cover and composition.
Thesis
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Les lichens, organismes symbiotiques associant un champignon et un partenaire photosynthétique (algue verte et/ou cyanobactérie), sont caractérisés par la biosynthèse de métabolites secondaires uniques dotés de bioactivités variées. Pour valoriser au mieux cette ressource privilégiée, des méthodes innovantes de spectrométrie de masse ont été développées dans le but de minimiser la préparation de l’échantillon et la durée des analyses. Deux techniques de spectrométrie de masse ont été évaluées en ce sens : le DART-MS et le LDI-MS. L’apport de chacune de ces deux méthodes a pu être établi sur un large panel de lichens, représentant une part importante de l’espace chimique couvert par ces organismes. Il a été démontré que des profils chimiques complets pouvaient être obtenus respectivement à partir de thalles lichéniques et d’extraits acétoniques totaux. Compte tenu de la très large utilisation de la CCM pour l’analyse chimique de lichens, les possibilités offertes par le couplage de la CCM à l’ionisation electrospray ont également été explorées. Une seconde partie de ces travaux avait pour but de cartographier la distribution des métabolites secondaires au sein du thalle lichénique. À ces fins, des analyses d’imagerie LDI ont été réalisées sur une coupe transversale d’un lichen crustacé modèle : Ophioparma ventosa. Ce lichen a été étudié en phytochimie pour identifier six napthopyranones à partir des apothécies dont quatre nouvelles structures. Les principaux métabolites de ce lichen ont pu être imagés par LDI-MSI avec une résolution spatiale de 50 μm environ. Une corrélation entre la distribution des molécules et leur rôle écologique présumé permet d’avancer des hypothèses d’écologie chimique. Des approches conjointes reliant histolocalisation et étude génétique des partenaires de la symbiose ont été entreprises. La recherche des gènes de la biosynthèse de la mycosporine sérinol chez les symbiontes isolés de Lichina pygmaea par microdissection capture laser a été initiée en ce sens. D’autres approches innovantes comme l’analyse cristallographique par diffraction de poudre par les rayons X sont également abordées dans ce document articulé autour de six publications issues de ce travail et de deux articles en cours de soumission.
Chapter
The majority of studies of the effects of environmental factors on lichen growth have been carried out in the field. Growth of lichens in the field has been measured as absolute growth rate (e.g. length growth, radial growth, diameter growth, area growth, or dry weight gain per unit of time) or as a relative growth rate, expressed per unit of thallus area or weight, e.g. thallus specific weight. Seasonal fluctuations in growth in the field often correlate best with changes in average or total rainfall or frequency of rain events through the year. In some regions of the world, temperature is also an important climatic factor influencing growth. Interactions between microclimatic factors such as light intensity, temperature, and moisture are particularly important in determining local differences in growth especially in relation to aspect and slope of rock surface, or height on a tree. Factors associated with the substratum including type, chemistry, texture, and porosity can all influence growth. In addition, growth can be influenced by the degree of nutrient enrichment of the substratum associated with bird droppings, nitrogen, phosphate, salinity, or pollution. Effects of environmental factors on growth can act directly to restrict species distribution or indirectly by altering the competitive balance among different species in a community.
Article
Lichens are traditionally divided into types such as "crustose", "foliose" and "fruticose", with different shapes and heights. Substrate, temperature and water are thought to affect lichen height, but there are few studies regarding tropical paramo lichens. Along 2015 I measured those variables in the terricolous lichens of the Cerro Buena Vista, paramo (Costa Rica, 9°33' N & 83°45' W). The measurements were taken inside the lichens and in the substrate under them, in 61 randomly located quadrats (50 x 50 cm). Lichens grew taller on (1) warmer ground, (2) wetter ground, (3) the moister Caribbean slope, and (4) the season with heavier rainfall, as expected. Apparently, atmospheric factors are more important than substrate in the determination of temperature, relative humidity and growth of lichens. Physiologically available water seems to be the main determinant of lichen vertical growth in the Buena Vista paramo.
Chapter
We explore in this chapter how biological soil crusts (biocrusts) may serve as a useful model system for studying multiple questions of interest in ecology, including biodiversity–ecosystem function relationships, positive and negative species interactions along environmental gradients, the source–sink hydrological dynamics in drylands, and ecosystem resistance and resilience. To illustrate our views, we synthesize recent and ongoing studies that are employing biocrusts as model systems to tackle these and other related questions, emphasizing the main features of biocrusts that make them special and well suited to advance ecological theory and our understanding of many important topics in community and ecosystem ecology. We complete the synthesis of the studies conducted so far with recommendations aiming to promote the use of biocrusts by community and ecosystem ecologists.
Article
Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates.
Chapter
Lichens exhibit the classic features of stress-tolerant organisms, viz. slow growth rates, considerable longevity, low demand for nutrients, and the presence of specific adaptations to survive in the most inhospitable environments on Earth. The ability of lichens to tolerate the extremes posed by deserts, polar regions, and chemically rich environments involves both morphological and physiological adaptation and changes in ecological behaviour so that species adapt to relatively protected niches within an extreme environment. This chapter discusses those aspects of the lichen symbiosis relevant to survival in extreme conditions and then describes the adaptation of lichens to (1) wet forests, (2) deserts, (3) the Arctic, (4) alpine regions, (5) Antarctica, (6) chemically rich environments, and (7) extraterrestrial environments such as outer space and Mars. It is evident that the lichen symbiosis is more tolerant to hostile conditions than its symbionts, morphological and physiological adaptations are intimately associated, and convergent evolution has resulted in similar changes in different environments.
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Imaging mass spectrometry techniques have become a powerful strategy to assess the spatial distribution of metabolites in biological systems. Based on auto-ionisability of lichen metabolites using LDI-MS, we herein image the distribution of major secondary metabolites (specialized metabolites) from the lichen Ophioparma ventosa by LDI-MSI (Mass Spectrometry Imaging). Such technologies offer tremendous opportunities to discuss the role of natural products through spatial mapping, their distribution patterns being consistent with previous chemical ecology reports. A special attention was dedicated to miriquidic acid, an unexpected molecule we first reported in Ophioparma ventosa. The analytical strategy presented herein offers new perspectives to access the sharp distribution of lichen metabolites from regular razor blade-sectioned slices.
Article
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Lichens are organisms which are formed through symbiotic association of fungi and algae or cyanobacteria. Lichen produces a great variety of secondary metabolites with various biological activities including antimicrobial, antiviral, antitumour, antioxidant, antihervivore, insecticidal, allelochemical and allergenic action. These compounds play a major role in providing photoprotection against intense radiation and can be used as an important candidate for antipyretic and analgesic drugs. Lichen metabolites act as major factor in metal homeostasis and pollution tolerance of lichen. This review describes the biological activities of secondary metabolites produced from lichen.
Chapter
Lichenometry is one of the most widely used methods available for dating the surface age of various substrata including rock surfaces, boulders, walls and archaeological remains. It depends on the assumption that if the lag time before colonisation of a substratum by a lichen is known and lichen age can be estimated, then a minimum date can be obtained by measuring the diameter (or another property related to size) of the largest lichen at the site. Lichen age can be determined by variety of methods including calibrating lichen size against surfaces of known age (‘indirect lichenometry’), by constructing a growth rate–size curve from direct measurement of lichen growth (‘direct lichenometry’ ), using radiocarbon (RC) dating and from lichen ‘growth rings’. This chapter describes the following: (1) lichen growth rates and longevity, (2) methods of estimating lichen age, (3) the methodology of lichenometry and (4) applications of lichenometry. Despite its limitations, lichenometry is likely to continue to play an important role in dating a variety of surfaces and also in providing data that contribute to the debate regarding global warming and climate change.
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Saxicolous lichen vegetation on Ordovician rock at the mouth of the River Dovey, South Merionethshire, is examined in relation to aspect, slope angle, light intensity, rock porosity, rock microtopography and rock stability. A number of characteristic groups of species are recognized. The environmental factors measured are discussed in some detail. In addition, the wide tolerance of most saxicolous species is emphasized.
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The health, abundance, metal content and species richness of corticolous macrolichens and bryophytes of Quercus ilex were compared at nine roadside stations in Montseny Biosphere Reserve, 40 km NNE of Barcelona, and at a control site outside the industrial metropolis. Stations were characterized by traffic levels and the correlated parameter airborne particles. Corticolous flora at all stations was dominated by sorediate Parmelia species (P. caperata, P. soredians, P. subrudecta, P. subaurifera, P. sulcata and P. perlata). Damage, mainly due to arthropod feeding and fungal parasites, ranged from 14 to 33% of mean cover per station in the park and was 10% at the control site. Elevated levels of Pb, Zn and Cu were found in large thalli near the roadsides.
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The lichen flora was sampled at each of the five sites on a near-vertical gneiss rock face. The sites were ranked according to the degree ofweathering of the rock surface and were taken to represent different stages in a succession. The succession shows an increase in species richness and diversity over time, although the proportion of the rock face unoccupied by lichens increases at the oldest site. The succession will be driven by allogenic processes, physical weathering of the rock, facilitation, especially the effects of lichens on surface erosion, and by inhibition, through competition for space. At the oldest site mortality of lichen thalli becomes important, continually opening up new areas for recolonization and maintaining community diversity. The succession may be described by four phases: (1) colonization, (2) growth,(3) competition and (4) senescence.
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Optimal defence theory (ODT) attempts to explain variation in plant secondary compounds between different species, different growth conditions and different parts of individual plants. The theory is widely applied to vascular plants and more recently also to seaweeds. Surprisingly, ODT has gained little attention as potential explanation on the distribution of lichen secondary metabolites. In the present study, we analysed intrathalline variation in total phenol content and phenol spectra between reproductive and somatic structures of three foliose lichens, Xanthoria parietina, Vulpicida pinastri and Hypogymnia physodes. The results showed that the concentration of phenolic compounds is higher in sorediate than in non-sorediate lobe ends of V. pinastri and H. physodes as well as in apothecia of X. parietina compared to other parts of the thallus. These results were in accordance with ODT predicting higher allocation of phenols in structures that are most important for the fitness of an individual genet or ramet. This pattern was parallel in all species regardless whether the compounds originate from either acetate-mevalonate or shikimic acid pathways. Moreover, both sexual (X. parietina apothecia) and asexual (soralia of V. pinastri and H. physodes) reproductive structures were higher in phenols compared to somatic tissue.
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Thalli of Xanthoria parietina have been grown in cultures in the natural environment. In early phases of development the fungus associates with foreign algae and only later forms a symbiosis with Pseudotrebouxia. The lichen is shown to have a very effective mechanism for distribution by sexual spores followed by relichenization.
Article
Three growth-form groups of plants were distinguished: dwarf shrubs, carpet-forming cryptogams, other cryptogams. Dwarf shrubs differ widely from cryptogams, being rooted and having sparse shoots. As most of them occur on the N slopes, they are mainly associated with the mesic cryptograms. Carpet-forming cryptogams are not usually associated with each other when transect segments with the same dominant are compared. However, since lichens (Cladina spp.) are concentrated on the S slopes and bryophytes (mainly Pleurozium schreberi) on the N slopes, there are positive associations within these groups in the whole data set. The other cryptogams mainly colonize gaps in the lichen or bryophyte carpet. Such carpets form slowly on some sunny S slope sites, and there several minor species are frequent (Cladina mitis, Stereocaulon paschale, Cladonia spp). Some of the gap colonizers can persist in closed carpets (Cladonia cornuta). It is suggested that Pohlia nutans can grow near shoots of Vaccinium vitis-idaea and Polytrichum juniperinum in narrow openings in patches of Cladina stellaris.- from Author
Article
The factors associated with lobe division were studied in thalli of the lichen Parmelia conspersa (Ehrh. ex Ach.)Ach. Lobe division was studied in sequences of adjacent lobes using spatial pattern analysis. In five large thalli, lobe division within the thallus margin was randomly distributed. Correlations between the degree of lobe division, the radial growth of the lobe and lobe morphology were studied in six thalli. Lobe division was positively correlated with either lobe width or area in four thalli. Correlations were observed with radial growth or morphology of the adjacent lobes in two thalli. Dividing and non-dividing lobes were removed from large thalli and glued to pieces of slate with their tips either at the same level or in front of neighbouring lobes. Dividing lobes divided more rapidly when their tips were glued in front of their neighbours. The levels of ribitol, arabitol and mannitol were measured within a 2 mm region of the tip in dividing and non-dividing lobes on four occasions in 1994. Carbohydrate levels were significantly increased in dividing compared with non-dividing lobes. In addition, the mean size of the algal cells was greater in non-dividing compared with dividing lobes especially at the lobe base. However, the percentage of zoosporangia and aplanosporangia did not vary significantly in dividing and non-dividing lobes. These results suggest that: 1) the pattern of lobe division within the thallus margin may be random, 2) lobe division may be determined by lobe size and the location of the lobe tip relative to the neighbouring lobes and 3) there may be an increase in the productivity of lobes associated with lobe division.
Chapter
In the early days of agriculture, man must have learned of the competition among individual plants within a crop or intraspecific competition, even though his knowledge was purely in empirical terms. He must have learned by experience that if the sowing rate were sparse, his harvest would be lean, and conversely that if the seed rate were increased beyond a certain value, the plants would be spindly and poorly grown. The fuller understanding of competition among plants requires a greater knowledge of the response of plants to their environment, especially of the response to the environmental stresses created by neighbors. Plant physiologists have studied the single plant, and agronomists have looked at the whole crop, but the plant within the community has scarcely been investigated. This is a field which promises both scientific depth and great potential reward in terms of crop production.
Article
The effect of deposition of different fertilizers and of lime on lichens was investigated under field conditions. Three terricolous lichens were tested: Cladonia floerkeana, C. furcata and C. portentosa. The lichens were exposed to three types of powdered fertilizer (NPK-, N-, P-fertilizer) and lime. The applied nutrients were recorded in lichen thalli and soil. The influence on lichen growth rate and vegetation cover was estimated over 2 years. The response was a clear change in vegetation cover with an exceptional stimulating effect of NPK on the moss Polytrichum formosum. A lethal effect was observed on Cladonia floerkeana following exposure to lime. NPK and P had the most significant stimulatory effect on G. furcata. Only NPK promoted the growth of C. portentosa and P, N or Ca had a negative effect.
Article
A point quadrat sampling technique was used to define the vertical zonation of epiphytic corticolous lichens on oak and birch at Shaugh, South Devon. Small frames of ten pins were used to estimate percentage cover for the lichens species present, samples being taken from 1 m wide zones 1 m apart. Twenty-four oak and twenty-five birch trees were sampled giving a total of 106 sample zones on each tree species. Graphs of mean percentage cover against height in the tree were plotted as well as graphs of mean percentage cover against tree age at each height. A clear vertical zonation of the major species was demonstrated on both oak and birch. Parmelia caperata, P. physodes and P. sulcata have generally basal, middle and tree top distributions respectively. A close relationship between lichen cover and tree age was discovered with P. caperata apparently reaching maximum cover at 35 years, P. physodes at 20 years and P. sulcata at 10-15 years. The possible roles of microclimatological gradients, competition, and succession in maintaining this vertical zonation are discussed.
Article
Many obligate fungal pathogens of lichens, the so-called lichenicolous fungi, seem to be tolerant of antibiotic lichen secondary metabolites. However, certain lichenicolous fungi are known to be strongly inhibited by chemical defenses of lichens, even those on which they are frequently found in nature. One of these fungi is Nectria parmeliae, an obligate lichenicolous fungus that is observed on many species of lichens. Field observations of this fungus in northern Virginia indicate a marked preference for the lichen Punctelia rudecta. Laboratory studies established that N. parmeliae is incapable of growing on tissues of this lichen unless they are first washed with acetone to remove phenolic defense compounds. It was determined that N. parmeliae can grow on P. rudecta in nature after another lichen inhabitant, a species of Fusarium, enzymatically degrades lecanoric acid (LEC), the dominant lichen compound of P. rudecta. Field studies in northern Virginia demonstrate that observed lichens harboring N. parmeliae generally also harbor the Fusarium sp. Furthermore, high performance liquid chromatography (HPLC) shows that LEC is completely degraded by Fusarium in 90 days, which permits growth of N. parmeliae. Taken together, these results suggest that some obligate lichenicolous fungi cannot colonize certain lichens unless there has been prior chemical processing of these lichens.
Article
A study of lichen succession on seven rock surfaces of recent origin occurring below timberline in the North Canterbury high country, New Zealand, is described. Trends derived from data on occurrence of species, number of species, and total lichen cover were found to have a general correlation with age. Some of the variation in the values obtained could be attributed to the effect of stone size. The computing of negative exponential curves for three 40 yr old surfaces indicated that clear asymptotic levels could be defined for the relationship between numbers of species per stone and stone area. These asymptotes provide a means of eliminating variability attributable to stone size from the data, enhancing the possibility of using the general trends described as a means for dating rock surfaces. Further variation in the data appeared to be the result of environmental differences.
Article
The nearest neighbor relations of the cryptogams growing on Quercus rubra in Michigan were investigated over whole tree trunks, and over four subsections of trunks to partially eliminate the effects of microhabitat. At all scales numerous nonrandom associations were found, indicating that it is not only gross microhabitat requirements that determine these relationships. The associations were found to differ from place to place on the tree trunk. Despite sharing the same general habitat (the tree trunk), or part of the habitat (e.g., upper north side), some species and groups of species are rarely neighbors, whereas others are far more likely to coexist and therefore interact.
Article
Ascospore germination of the crustose lichens Graphis scripta and Caloplaca citrina was observed in the presence of atranorin (ATR), vulpinic acid (VUL), evernic acid (EVE) and stictic acid (STC) on buffered media ranging in pH from 4 to 7. Caloplaca citrina spore germination was much reduced in the presence of VUL, EVE and ATR. Spores of G. scripta were also severely inhibited by VUL and EVE, but were not affected by ATR. Neither species showed significant germination reductions in the presence of STC. These results, and those of previous studies, demonstrate the allelopathic potential of lichen compounds in biochemically diverse lichen communities.
Article
Germination responses of Sordaria fimicola and Cladonia cristatella ascospores were observed in the presence of three pure lichen acids on buffered media ranging in pH from 4 to 7. Acetone solutions of either vulpinic (VUL), evernic (EVE) or stictic (STC) acid were poured onto buffered agar at a concentration of 2.7 x 10-3 M and the acetone allowed to evaporate. Ascospores were deposited on the agar surface and the percent spore germination was recorded after 24 hr. Comparisons were made with control plates to which only acetone was added. Cladonia cristatella spore germination was slightly but significantly inhibited by VUL, but no inhibitory effects were observed for EVE or STC. Sordaria fimicola spores were severely inhibited by both VUL and EVE, but not STC. No pH effects on lichen compound toxicity were observed, but C. cristatella spores exhibited little germination at pH 7. Lichen acids appear to be capable of functioning as allelopathic agents in nature; however, lichenized fungi may be better able to tolerate the inhibitory effects of lichen acids than nonlichenized fungi.
Article
At a site where the morphologically similar but chemically different Parmelia loxodes and P. verruculifera grow together, a species of Lepraria is overwhelmingly associated as an epiphyte with the latter. The nonrandom distribution of the Lepraria may result from allelopathic effects and reflect the disparate medullary chemistries of the substrate species of parmelias.
Article
Distinct patterns of species distribution upon individual rockfaces are found n a saxicolous lichen community growing on a rockslide in the Canadian Rockies. A grid system was used for sampling individual rockfaces and the likelihood of finding a species on particular parts of the rockface was analysed. Use of chemicals in the field and collection of apothecia allowed specific identification of individual lichen thalli. Lichens were divisible into three groups: those which are distributed apparently at random over the rockfaces, those which are more likely to occur on upper, outer and southerly portions of the rockfaces and those which are found more often on lower, inner and northerly portions of the rockfaces. The upper rockface surfaces are often snow-free in winter while the lower rockface group experiences deeper and more persistent snow cover. Simple microclimatic measurements suggest that temperature also differs across the surface of a rockface. It is hypothesised that lichen distributions are at least in part explained by ecophysiological adaptations to their particular microhabitat, while it is recognised that competition may also play a role in community organisation.
Article
Both competitive and non-competitive processes may strongly influence the growth of plants in a multispecific community, though the latter, particularly in experimental studies, are often overlooked. A method of analysis, based on the principles of the de Wit model, is suggested which may enable . the factors involved in both competitive and non-competitive aspects of interference between species to be identified.
Article
It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.
Article
(1) Populations of flowering male and female shoots of Mercurialis perennis were grown in three experiments under different light screens: (i) the sexes grown together in a replacement series under a screen transmitting 11 % incident light; (ii) the density of the plants varied under an 11 % light screen; and (iii) the sexes grown separately with Holcus mollis under light screens transmitting 31 % and 2% incident light. (2) In the replacement series with mixed sexes, the males grew more than the females at (male:female) 10:10 while the females grew more at 17:3 and 3:17. The sexes grew similarly in monoculture. The results for total yield of the plants suggest that competition between the sexes was less than that within them. (3) In the density experiment, the males grew more than the females as the density increased from 20 to 30 plants/box and both grew similarly at 42 plants/box. (4) It is suggested that observed uneven sex ratios in natural populations of shoots may be a result of the sexual differences in growth as the density of the plants increases. (5) In the replacement series with H. mollis under the 31 % light screens the males grew more than the females at (M. perennis: H. mollis) 3:17 while the females grew more at 17:3. These results suggest that males may persist longer in association with other species. (6) No consistent results were obtained from the H. mollis replacement series under the 2 % light screens. (7) The sexes grew similarly more under the 31 % compared to the 11 % light screens, suggesting that neither is physiologically intolerant to increased sunlight.
Article
The influence of neighbours on individual performance in natural populations of the lichenized ascomycete Umbilicaria spodochroa was investigated using three different neighbourhood models; the polygon model, the fixed radius model and the nearest neighbour model. The data set consisted of the exact position of the holdfast points of the peltate lichens within 29 sample squares in crowded populations as well as the mass, diameter, and no. of apothecia of all thalli. A total of 11246 individual thalli were sampled and measured. The predictive power of all three neighbourhood models was moderate, but highly significant for the whole data as well as within most individual sample quadrats. The nearest neighbour model had the best predictive success, closely followed by the polygon model. The fixed radius model had approximately half the power of the two other models. We suggest that the difference is due to different degrees of realism in the models. Thallus mass was commonly the performance parameter best predicted, followed by thallus diameter and number of apothecia. The predictive power of the models for these natural populations was comparable to values obtained in several laboratory studies with vascular plants. The predictive success of the three different models was strongly correlated for single populations, indicating different levels of interference in different populations.
Article
The response of internal and external extracts of fresh arboreal lichens, Alectoria sarmentosa, Bryoria fuscescens and Bryoria fremontii, and commercial usnic acid extracted from Usnea spp. and Cladonia spp. on the growth of the Ascomycetous Gremmeniella abietina types was studied in vitro. Neither internal and external extracts of the three lichen nor usnic acid had strong inhibitive effect on the growth of either type A or B of G. abietina. A slight stimulative effect due to the extracts was, however, detected: type B (isolate 12) grew faster on almost all media than type A (isolate 11), but great variation within isolates of both types existed suggesting that different types of G. abietina may have different responses to chemicals. Keywords: Gremmeniella abietina, Alectoria sarmentosa, Bryoria fuscescens, Bryoria fremontii, usnic acid, lichen toxicity.
Article
The foliose lichens of a corticolous epiphyte community were sampled using a grid of points and nearest neighbour sampling. Most species were found to have nonrandom distributions with respect to height and aspect on the tree trunk. The tendency of species to form exclusive patches and to contact other species showed large interspecific differences. Some formed monocultures and had fewer interspecific contacts than expected, while others did not form large patches and had more interspecific contacts than expected. Investigation of interspecific thallus overlaps revealed a hierarchy in which heavier species such as Flavoparmelia caperata (2.3 mg/mm2) overtop lighter ones such as Melanelia subaurifera (1.1 mg/mm2) more often than the converse is true. It is likely that being overtopped by another lichen puts a thallus at a disadvantage in competition for resources. The success of a species at overtopping another does not change according to location on the tree trunk. There was evidence that F. caperata excluded other species during succession. Key words: epiphytes, foliose lichens, thallus overlaps, interspecific competition, ecological strategies.
Article
A saxicolous lichen community is examined for evidence of dynamic processes and biotic interactions among its members. Spatial relationships among species are examined in a series of association analyses at three scales: (i) the "nearest-neighbour" scale, i.e., associations between touching thalli; (ii) associations between thalli 10 and 20 cm apart; and (iii) associations at the scale of the whole rock face. The nearest-neighbour analysis reveals fundamental differences in the way crustose and foliose thalli sample their environment; crustose lichens are more likely to have uncolonized rock as a nearest neighbour, whereas foliose lichens are more likely to contact another thallus. Associations between species at the 10- and 20-cm scales are often negative, reflecting the degree of microhabitat specificity in this community; however, intraspecific associations at the same scale are often positive, possibly indicating local dispersal processes. At the whole-rock scale, there are many positive associations indicating that, even at this larger scale, microhabitat specificity is important. Thallus-size distributions are also studied, and these indicate that recruitment into lichen populations is an ongoing process, based on the assumption that small thalli are younger than large thalli. There is little evidence of succession to a higher plant community over most of the rocks at this 500-year-old site, and it is hypothesized that cyclic successional processes maintain this dynamic and diverse community.
Article
DR GRIME replies: There is a clear difference of opinion between Newman and myself with regard to the role of root competition in natural vegetation. It would be a mistake to pursue the discussion, however, without first defining competition and placing the phenomenon in a wider but relevant context.
Article
The distribution of epiphytic lichens on branches of a stand of Picea abies has been mapped, and patterns of succession and community structure are described. Many crustose species are of particular interest since little is known about their ecological requirements (e.g. Fuscidea pusilla Tønsb., Japewia subaurifera Muhr & Tønsb. and Gyalideopsis alnicola Noble & Vězda). Numerical treatment (correspondence analysis and canonical correspondence analysis) of the species data was used to study the lichen distribution in relation to measured environmental variables. Tree age, tree height and branch height above ground are shown to be the most important variables to explain the species distribution. No significant relationship was found between branch compass point and the distribution of lichens. The species composition and cover changed from young to old trees. The largest variation in the lichen vegetation was found on the branches of young trees. A more homogeneous and stable lichen community appears on branches of mature trees. A clear zonation of the epiphytic vegetation develops as the branches grow, resulting in the occurrence of typical ‘branch-tip’ and ‘branch-base’ species. The highest number of species was recorded on the outermost part of branches before lichen cover reached the maximum. Hyperepiphytic thalli were mainly located in specific areas with high lichen cover on the branches. Lichens with reduced vitality were most common at the base of branches.
Article
Competition between crustose and squamulose lichens was investigated at two sites in Wales. At one, two competing species (Caloplaca heppiana and C. aurantia) were well matched as neither exclusively overgrew the other, while at the other site, Aspicilia calcarea competed with C. heppiana, the former usually overgrowing the latter at marginal contacts, but A. calcarea was itself overgrown at 'window' contacts. The development of a crustose lichen community in Gwynedd, Wales is briefly described. Four main factors control the development and dynamics of these communities: (a) colonization rate and density; (b) radial growth rate; (c) type of contact between species; and (d) rate of senescence.
Article
A diallel arrangement, which incorporated the essential features of the de Wit density replacement series, was employed to study the effects of competition amongst five genotypes of perennial ryegrass ( Lolium perenne ). Of the five genotypes concerned two were derived from S·24, two were collected from natural populations in South Wales, while the remaining genotype originated from S· 23. These five genotypes were grown as monocultures and in all ten binary combinations. Within each combination there were three mixture proportions, namely 75:25, 50:50 and 25:75. All mixtures and monocultures were represented by two boxes, one of which was cut at 3-week intervals (frequent cutting) the other being cut at 6-week intervals (infrequent cutting). At each cut all plants within the appropriate mixtures and monocultures were harvested individually and their dry weight recorded. The results obtained over the first 18 weeks of the experiment (i. e. the first three complete growing periods) establish that competition is occurring in nine of the ten binary combinations. Within these nine combinations competition may be classified into one of three groups: first, it may be compensatory, in which the gains and losses incurred by the two components counterbalance; secondly, it may be positive complete complementation, where the advantage gained by the stronger component is such that the mixture performance matches that of the better monoculture, and thirdly, it may be positive over-complementation, where the yield of the better monoculture is surpassed by the mixture. Further tests disclose that a long-leaved S· 24 genotype is the strongest competitor, while a short-leaved, prostrate, indigenous genotype proves to be by far the weakest competitor. Estimates of the equilibrium proportions for each genotype combination suggest that most combinations are expected to become monocultures of the strongest component, with only the combination between the long-leaved indigenous and longleaved S· 23 genotypes remaining a mixture at equilibrium. None of these equilibria coincides with the proportions required to achieve maximum productivity from a particular combination. The results are considered in relation to the known characteristics of these five perennial ryegrass genotypes, while the wider agronomic implications are also discussed.
Article
Survival strategies of 34 species of lichens from a range of substrata, climates and growth forms were examined using the triangular ordination procedure of Grime. Triangular ordination is apparently an appropriate technique to apply to lichens, all available data falling within a triangle except for two foliicolous species which are probably partial leaf parasites. Statistically significant relationships between survival strategy and growth form, mode of asexual reproduction, substratum preference, family affiliation, and diversity of secondary chemical biosynthetic pathways have been demonstrated.
Article
The extent to which biotic factors (competition, predation/disease, longevity) regulate lichen community development can be addressed by considering a number of general trends expected in higher plant successions and searching for supporting evidence from lichen studies. Four of the most frequently observed (or predicted) trends during succession are that: (1) superior competitors replace poor competitors; (2) ecologically specialized species replace generalists; (3) chemically well-defended species replace poorly-defended species; (4) long-lived species replace ephemeral species. Available evidence suggests that, for many lichen communities, competitive exclusion rarely occurs once thalli are established. This is especially true for communities that develop on the most stable habitats. An absence of competitive exclusion suggests that lichen successions are driven more by additions of colonists than by species replacements, and replacement trends observed in higher plant successions are therefore observed less frequently inlichen successions.
Article
Where two crustose lichen thalli meet at a ‘ truce ’ boundary theshape of the boundary can be used to evaluate models of how lichen growth rates change with thallus size. The application of this method to studies of intra- and interspecific competition are discussed.
Article
Lichen growth is reviewed in the context of the anatomy of the growth region, thallus morphology of crustose and foliose lichens, photosynthesis, mathematical models and their application. The Aplin & Hill model is suggested as a basis for more detailed investigation of integrated processes of growth including not only the size increase but also the general structure of the thallus and the processes which limit growth.
Article
Based on a study of photographs from two adjacent sites with closed crustose lichen mosaics on rock in Cardiganshire taken in 1959-60 and 1973, examples of overgrowth and equilibrium are provided. Ochrolechia parella overgrew Rhizocarpon obscuratum but reached an equilibrium on contact with Lecanora gangaleoides; L. gangaleoides was unable to overgrow islets of R. obscuratum included in its thallus. Coalescence of small thalli of L. gangaleoides to make a larger thallus was also observed, and growth rates for the species considered were calculated.
Article
The effect of deposition of different fertilizers and of lime on lichens was investigated under field conditions. Three terricolous lichens were tested:Cladonia floerkeanaC. furcataandC. portentosa. The lichens were exposed to three types of powdered fertilizer (NPK-, N-, P-fertilizer) and lime. The applied nutrients were recorded in lichen thalli and soil. the influence on lichen growth rate and vegetation cover was estimated over 2 years. The response was a clear change in vegetation cover with an exceptional stimulating effect of NPK on the mossPolytrichum formosum. A lethal effect was observed onCladonia floerkeanafollowing exposure to lime. NPK and P had the most significant stimulatory effect onC. furcata. Only NPK promoted the growth ofC. portentosaand P, N or Ca had a negative effect.