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Fine-scale population dynamics help to elucidate community assembly patterns of epiphytic lichens in alpine forests
Abstract and Figures
We examined the main and interactive effects of factors related to habitat filtering, dispersal dynamics, and biotic interactions, on tree-level population dynamics of a subset of species composing the epiphytic lichen pool in an alpine forest. We tested these processes evaluating the population size of 14 lichen species on six hundred and sixty-five trees within a 2 ha plot located in a high elevation alpine forest of the eastern Italian Alps. Our results indicate that community assembly patterns at the tree-level are underpinned by the simultaneous effects of habitat filtering, dispersal, and biotic interactions on the fine-scale population dynamics. These processes determine how the single species are sorted into community assemblages, contributing to tree-level community diversity and composition patterns. This corroborates the view that the response of lichen communities to environmental gradients, in terms of compositional and diversity shifts, may reflect differential species responses to different drivers.
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... Several studies have evaluated lichen responses in terms of shifts in species climate suitability, species richness and community composition (Ellis et al., 2007(Ellis et al., , 2014Hurtado et al., 2019;Nascimbene, Casazza, et al., 2016). In contrast, the effect of climate change on co-occurrence patterns among species that could be related to complex species interactions has received less consideration or has been only indirectly addressed (Nascimbene, Ackermann, et al., 2016). Biotic interactions play a major role in shaping species niches, fitness and adaptation to new environments (Hargreaves et al., 2020;Tomiolo et al., 2015;Wiens, 2011). ...
... Second, in our study system, the gradient of forest structure is relatively short, reflecting homogeneous management conditions across the study area (di Bolzano, 2010). Third, our sampling design intended to mainly reveal the effect of climatic conditions on epiphytic lichen communities, targeting only mature trees, and thus avoiding the variability in species richness and composition related to a gradient of tree ages (Nascimbene, Ackermann, et al., 2016). ...
... These lichens are able to rapidly form a dense lichen cover on trunks that may improve the water retention capacity of the substrate, providing more suitable micro-habitat conditions for species with small or thin thalli that have a low water holding capacity (Merinero et al., 2014). It is emblematic the case of Hypogymnia physodes (L.) Nyl. that contributes to the species composition of several lichen communities in montane-subalpine coniferous forests (Nascimbene, Ackermann, et al., 2016). In contrast, crustose, sexually reproducing species, as well as fruticose lichens, are segregated in their modules and behave as habitat specialists. ...
Several studies have evaluated lichen responses in terms of shifts in species climate suitability, species richness and community composition. In contrast, patterns of co‐occurrence among species that could be related to complex species interactions have received less consideration. Biotic interactions play a major role in shaping species niches, fitness and adaptation to new environments. Therefore, considering the specific relationships among co‐occurring species is essential to further deepen our knowledge of biodiversity response to climate change. In this perspective, the analysis of lichen ecological networks across elevational gradients may provide a powerful tool to understand how communities are structured and how biotic interactions are modulated by changing climatic conditions.
We evaluated the contribution of environmental and species biological attributes to the structure of epiphytic lichen–host tree networks. Specifically, we studied lichen communities considering two different network levels: the whole lichen community, and groups of lichen species that presented similar biological traits. In this framework, we (a) characterized the structure of the epiphytic lichen–host tree networks; (b) assessed how network structure varied with climate, forest attributes and community trait diversity and (c) evaluated the role that biological traits played in the connections established between co‐occurring lichens.
On the one hand, results indicate that epiphytic lichen communities are dominated by local segregation, suggesting habitat specialization among lichens within their host tree, and that climatic conditions and, to a lesser extent, lichen diversity are the main drivers of community assemblage. On the other hand, the role of lichen species in the networks depends on their particular biological traits, supporting the hypothesis that biological traits contribute to shape network structure by influencing the ability of the species to interact between each other. These findings warn about the potential impact of climate change on epiphytic lichen communities.
Synthesis. This study builds towards a better understanding of lichen community assembly and on biodiversity response to climate change in forest alpine ecosystems. In particular, our results highlight the value of lichen–tree networks to inform about assemblage processes acting at different organizational levels and indicate that lichens might become one of the most threatened groups under global change scenarios.
... Habitat quality can include factors such as presence of particular tree species if some lichen species have preferred substrates, tree size, tree age, bark texture and pH, or presence of holes and cracks [7][8][9][10][11][12][13][14]. Diameter of the tree at breast height (DBH) is often used as a proxy for tree size [15] or age [16] and has been positively correlated with lichen species richness in mangrove forests in New Zealand [6], Mediterranean oak forests [4] and deciduous forests in Sweden [17]. ...
... The average number of lichen species per tree is positively correlated with DBH. This has been found in other studies (6,4,15) and is usually attributed to habitat quantity and quality and a longer time for colonization if DBH is taken as a proxy for tree age. Not all sites with trees with high average DBH had more species per tree (e.g., Site 15, Cornwall Park), which supports the idea that distance from the coast may be more critical than tree size or age. ...
The spatial distribution of corticolous lichens on the iconic New Zealand pōhutukawa (Metrosideros excelsa) tree was investigated from a survey of urban parks and forests across the city of Auckland in the North Island of New Zealand. Lichens were identified from ten randomly selected trees at 20 sampling sites, with 10 sites classified as coastal and another 10 as inland sites. Lichen data were correlated with distance from sea, distance from major roads, distance from native forests, mean tree DBH (diameter at breast height) and the seven-year average of measured NO2 over the area. A total of 33 lichen species were found with coastal sites harboring significantly higher average lichen species per tree as well as higher site species richness. We found mild hotspots in two sites for average lichen species per tree and another two separate sites for species richness, with all hotspots at the coast. A positive correlation between lichen species richness and DBH was found. Sites in coastal locations were more similar to each other in terms of lichen community composition than they were to adjacent inland sites and some species were only found at coastal sites. The average number of lichen species per tree was negatively correlated with distance from the coast, suggesting that the characteristic lichen flora found on pōhutukawa may be reliant on coastal microclimates. There were no correlations with distance from major roads, and a slight positive correlation between NO2 levels and average lichen species per tree.
... In our study, two variables, DBH and mean annual rain days, had a measurable effect on species richness. DBH is often used as a proxy measure of tree age [46] or overall size [47]. Variation in the diameter of the trunk of a tree affects available surface area, but also may influence the variability of the surface (bark texture and pH, water availability, presence of holes or cracks [48] and probably acts as a proxy measure of age. ...
... This has been noted in other studies of epiphytic lichens. For example, a study of epiphytic lichens in the Italian alps found that after substrate tree specificity was taken into account, tree size (DBH) and age influenced lichen species dynamics [47]. They observed that tree size affected population sizes and abundance patterns, and tree age had species-specific effects as some species prefer older or younger trees. ...
Mangrove forests of a single trees species, Avicennia marina subsp. australasica are widespread in the upper North Island of New Zealand, but there is little available information on the diversity of epiphytes such as lichens within them. A survey of 200 trees from 20 mangrove sites recorded a total of 106 lichen species from 45 genera. Two of these species are considered to be ‘Threatened’, five ‘At Risk’ and 27 ‘Data Deficient’. Multiple regression indicated that tree diameter (DBH) and mean annual rain days positively influenced site species richness. Multidimensional scaling showed that sites from the same geographical region generally formed distinct clusters. Redundancy analysis indicated that mean annual wet days, latitude and DBH measurably influenced species composition.
This study summarizes the results of a lichen floristic survey carried out in a 4 ha coniferous forest plot located on the Western side of the Latemar massif (Dolomites, South Tyrol) as a preliminary phase of a research on the small scale distribution patterns of some selected lichen species. This survey was mainly focused on epiphytic lichens, but some collections were carried out also on dead wood. Eighty-four species, including two non lichenized fungi, were found. The ecology of the species reflects the features of the forest habitat, most of them being linked to acidic substrates, preferring intermediate and well-lit conditions, intermediate moisture conditions, and avoiding eutrophication.
Metapopulation dynamics predicts that species incidences in patches are a function of colonization and extinction rates. Incidence function model finds colonization and extinction rates as a function of patch size and connectivity. Patch size and connectivity are relatively easy to estimate from the data. Fitting incidence function model is a special case of gen- eralized linear models with binomial error and logistic link function. This document explains how to fit the model in R.
Despite the fact that Italy is among the lichenologically best known areas worldwide, a national red list of lichens is still lacking. The aim of this work was to provide a red list of the epiphytic lichens of Italy which could facilitate the inclusion of lichens in national conservation plans. The evaluation of the species against International Union for Conservation of Nature (IUCN) criteria was based on data from multiple sources which represent the best available information on the epiphytic lichens of Italy. The species were assigned to the IUCN categories mainly using criteria D and B. A total of 368 species were evaluated: for 23 species, information is missing from more than 50 years and they were listed as regionally extinct, 64 as critically endangered, 75 as endangered, 74 as vulnerable, 58 as near threatened, 20 as least concern and 54 species as data deficient. Our results indicate that more than one-fourth of the epiphytic lichens of Italy are likely to be threatened, so that further research and effort are needed to include lichens in the main national conservation plans. Our results also highlight the lack of information that still hampers the rigorous evaluation of Italian lichens against IUCN criteria.
Nous avons étudié l'influence des caractéristiques de l'arbre et du peuplement sur la diversité des lichens pour 143 frênes âgés de 11 ans à plus de 140 ans dans 5 peuplements feuillus du sud de la Suède. Le nombre d'espèces de lichens sur chaque arbre variait de 2 à 30. Le diamètre du tronc était le facteur qui expliquait le plus cette variabilité ainsi que, dans une moindre mesure, l'âge de l'arbre, la couverture de la cime, la couverture de lichens et le type de peuplement. La relation positive entre la richesse en espèces et la couverture de lichens semble compatible avec une distribution au hasard des espèces et suggère que les mêmes facteurs affectent à la fois la croissance des lichens et leur établissement. La richesse en espèces n'augmentait plus avec l'âge de l'arbre au delà de 65 ans alors que la composition en espèces variait avec l'âge de l'arbre. En combinaison avec l'effet linéaire positif lié au diamètre du tronc, ces résultats suggèrent un léger effet positif de la surface quoique la richesse en espèce dans le temps soit plus attribuable au renouvellement des espèces. Nous avons aussi examiné si les lichens retrouvés sur des arbres d'âges différents avaient des traits d'histoire de vie tels que la taille des spores, la hauteur des thalles et la préférence au niveau du pH qui différaient. Les résultats indiquent que les lichens retrouvés plus fréquemment sur les vieux arbres avaient des spores plus gros et des thalles plus épais que les autres espèces ce qui suggère que la réponse des espèces de lichens à l'âge de l'arbre peut être expliquée en partie par leurs traits d'histoire de vie. Cependant, sur ce point, l'étude de l'écologie des lichens est encore à ses débuts.
We tested which factors explain the distribution pattern of the epiphytic moss Neckera pennata on three spatial scales using the framework of generalized linear models. First, we tested which factors explained its occurrence in forest stands in a 2500 ha landscape. At this scale, we also tested the effect of the historic landscape structure. We recorded its occurrence in all suitable stands. The occurrence probability increased with increasing present quantity of Acer platanoides, and with increasing present and past quantity of Fraxinus excelsior. The probability also increased with increasing connectivity to occupied stands. However, the connectivity to stands present in 1977 (recorded from infra-red aerial photographs) explained more of the variation. This suggests that the regional metapopulation size of N. pennata has decreased during the past decades, and that its present distribution pattern reflects the age of the remaining stands, and the distribution of past dispersal sources in the landscape. Second, we tested which factors explained the occurrence and abundance on individual trees in three forest stands. Neckera pennata mainly occurred on Acer and Fraxinus stems. The most important variable in explaining occurrence probability was connectivity to surrounding occupied trees, which probably reflects the restricted dispersal range in this species. The abundance on occupied trees was also explained by this variable. The occurrence probability and abundance also increased with increasing tree diameter, probably reflecting the time that a tree has been available for colonization and the time since colonization, respectively. The occurrence probability and abundance furthermore decreased on strongly leaning (and deteriorating) trees. The occurrence probability increased with increasing bark roughness, probably reflecting increasing suitability regarding bark chemistry and moisture. Third, we tested its vertical distribution on occupied trees. The main distribution was below 1.6 m.
Metapopulation dynamics have received much attention in population bi-ology and conservation. Most studies have dealt with species whose population turnover rate is much higher than the rate of patch turnover. Models of the dynamics in such systems have assumed a static patch landscape. The dynamics of many species, however, are likely to be significantly affected by the dynamics of their patches. We tested the relative im-portance of local conditions, connectivity, and dynamics of host tree patches on the meta-population dynamics of a red-listed epiphytic moss, Neckera pennata, in Sweden. Repeated surveys of the species and its host trees were conducted at three sites over a period of six years. There was a positive effect of connectivity, and colonizations mainly occurred in the vicinity of occupied trees. Colonizations were also less likely on strongly leaning trees. Local extinctions sometimes occurred from small trees with low local abundances but were most often caused by treefall. Simulations of the future (100 years) dynamics of the system showed that the metapopulation size will be overestimated unless the increased local ex-tinction rate imposed by the dynamics of the trees is accounted for. The simulations also suggested that local extinctions from standing trees may be disregarded in dynamic models for this species. This implies that the dynamics of N. pennata can be characterized as a patch-tracking metapopulation, where local extinctions are caused by patch destruction.
Tree and stand level variables affecting the species richness, cover and composition of epiphytic lichens on temperate broad-leaved
trees (Fraxinus excelsior, Quercus robur, Tilia cordata, Ulmus glabra, and U.laevis) were analysed in floodplain forest stands in Estonia. The effect of tree species, substrate characteristics, and stand and
regional variables were tested by partial canonical correspondence analysis (pCCA) and by general linear mixed models (GLMM).
The most pronounced factors affecting the species richness, cover and composition of epiphytic lichens are acidity of tree
bark, bryophyte cover and circumference of tree stems. Stand level characteristics have less effects on the species richness
of epiphytic lichens, however, lichen cover and composition was influenced by stand age and light availability. The boreo-nemoral
floodplain forests represent valuable habitats for epiphytic lichens. As substrate-related factors influence the species diversity
of lichens on temperate broad-leaved trees differently, it is important to consider the effect of each tree species in biodiversity
and conservation studies of lichens.
Predicting which species will occur together in the future, and where, remains one of the greatest challenges in ecology, and requires a sound understanding of how the abiotic and biotic environments interact with dispersal processes and history across scales. Biotic interactions and their dynamics influence species' relationships to climate, and this also has important implications for predicting future distributions of species. It is already well accepted that biotic interactions shape species' spatial distributions at local spatial extents, but the role of these interactions beyond local extents (e.g. 10 km(2) to global extents) are usually dismissed as unimportant. In this review we consolidate evidence for how biotic interactions shape species distributions beyond local extents and review methods for integrating biotic interactions into species distribution modelling tools. Drawing upon evidence from contemporary and palaeoecological studies of individual species ranges, functional groups, and species richness patterns, we show that biotic interactions have clearly left their mark on species distributions and realised assemblages of species across all spatial extents. We demonstrate this with examples from within and across trophic groups. A range of species distribution modelling tools is available to quantify species environmental relationships and predict species occurrence, such as: (i) integrating pairwise dependencies, (ii) using integrative predictors, and (iii) hybridising species distribution models (SDMs) with dynamic models. These methods have typically only been applied to interacting pairs of species at a single time, require a priori ecological knowledge about which species interact, and due to data paucity must assume that biotic interactions are constant in space and time. To better inform the future development of these models across spatial scales, we call for accelerated collection of spatially and temporally explicit species data. Ideally, these data should be sampled to reflect variation in the underlying environment across large spatial extents, and at fine spatial resolution. Simplified ecosystems where there are relatively few interacting species and sometimes a wealth of existing ecosystem monitoring data (e.g. arctic, alpine or island habitats) offer settings where the development of modelling tools that account for biotic interactions may be less difficult than elsewhere.
In the last two decades, interest in species distribution models (SDMs) of plants and animals has grown dramatically. Recent advances in SDMs allow us to potentially forecast anthropogenic effects on patterns of biodiversity at different spatial scales. However, some limitations still preclude the use of SDMs in many theoretical and practical applications. Here, we provide an overview of recent advances in this field, discuss the ecological principles and assumptions underpinning SDMs, and highlight critical limitations and decisions inherent in the construction and evaluation of SDMs. Particular emphasis is given to the use of SDMs for the assessment of climate change impacts and conservation management issues. We suggest new avenues for incorporating species migration, population dynamics, biotic interactions and community ecology into SDMs at multiple spatial scales. Addressing all these issues requires a better integration of SDMs with ecological theory.
Connectivity is a fundamental concept that is widely utilised in spatail ecology. The majority of connectivity measures used in the recent ecological literature only consider the nearest neighbour patch/population, or patches within a limited neighbourhood of the focal patch(a buffer). Meta-analysis suggests that studies using nearest neighbour connectivity measures are much less likely to find statistically significant effects of connectivity than studies that use more complex measures. Here we compare simple connectivity measures in their ability to predict colonisation events in two large and good-quality empirical data sets. The nearest neighbour distance to an occupied patch is found to be an inferior measure. Buffer meaaures do far better, but their performance is found to be sensitive to the estimate of buffer radius. For highly fragmented a habitats, the best and most consistent performance is found for a measure that takes into account the size of the focal patch and the sizes and distances to all potential source populations. When experimenting with reduced data sets, it was discovered that the nearest neighbour measures fail to find a statistically significant effect of connectivity for a large range of data set sizes for which the more complex measures still detect a highly significant effect. We conclude that the simplicity of a nearest neighbour measure is not an adequate compensation for poor performance.
The classical Poisson, geometric and negative binomial regression models for count data belong to the family of generalized linear models and are available at the core of the statistics toolbox in the R system for statistical computing. After reviewing the conceptual and computational features of these methods, a new implementation of hurdle and zero-inflated regression models in the functions hurdle() and zeroinfl() from the package pscl is introduced. It re-uses design and functionality of the basic R functions just as the underlying conceptual tools extend the classical models. Both hurdle and zero-inflated model, are able to incorporate over-dispersion and excess zeros-two problems that typically occur in count data sets in economics and the social sciences—better than their classical counterparts. Using cross-section data on the demand for medical care, it is illustrated how the classical as well as the zero-augmented models can be fitted, inspected and tested in practice.
Lichen symbioses represent a major way of life among the Fungi. Almost one-fifth of all known fungal species are lichenized, and about 1500 species of lichens contain cyanobacterial photobionts, most of which belong to the genus Nostoc . Despite extensive studies, many basic aspects of their biology
AimPatterns of epiphytic lichen diversity along elevational gradients covering the range of Norway spruce forests were analysed. The roles of water and energy variables in shaping the observed species–elevation relationship were tested, as well as how growth form and photobiont type distribution varied along the gradient.LocationSouth Tyrol, northern Italy.Methods
Eight sites were selected spanning the elevational range of spruce forests (900–1900 m a.s.l.) and the regional rainfall gradient. At each site, a pair of forest stands (one mature even-aged and one multilayered) was selected at three elevation steps. Epiphytic lichens were surveyed according to European guidelines for lichen diversity monitoring. Explanatory variables indicative of both forest structure and climate were included in the models.ResultsA positive relationship was found between number of species and elevation. This reflected the physiological response of epiphytic lichens to the main climatic factors, trait selection being the mechanism that determined the response at community level. Nonlinear species–temperature and trait–temperature relationships predicted that major changes may be expected in the intermediate part of the gradient. Lichens with a Trentepohlia algal partner were more frequent at lower elevations and proved to be sensitive to environmental factors indicative of forest structure. Lichen growth forms had contrasting patterns related to temperature, crustose species richness being enhanced by increasing values, and alectorioid and foliose lichens by decreasing values. Alectorioid lichens were also negatively influenced by rainfall.Main conclusionsIn a climate change scenario, lichen diversity in alpine regions will probably not benefit from an increase in air temperature in the same way as flowering plants. Monitoring variations in the proportions of growth form and photobiont type may represent a tool for detecting the effects of climate change on lichen species.
Epiphytic lichens are a functionally important and species-rich component of Alpine forests,
including several species of conservation concern. Their dependence on specific host
trees predicts that forests with different tree species composition host different lichen
communities, enhancing lichen diversity in forest landscapes. In this study, we tested for
the first time the effect of forest type on patterns of epiphytic lichen diversity, in the Italian
Alps. We sampled the main forest types of the South Tyrol, a typical Alpine region of Italy.
We also assessed the influence of factors related to forest structure and climatic conditions.
Our results demonstrate that different forest types host statistically different
lichen communities, suggesting that the conservation of lichen diversity is entrusted to the
maintenance of forest landscape heterogeneity, including forest types of minor economic
value and rural habitats. The highest number of species was found in grazed larch forests
and in high-elevation spruce forests, while the poorest pool was found in low-elevation
spruce forests, beech forests and Scots pine (Pinus sylvestris) forests. High-elevation
spruce forests also had the highest number of red-listed lichens, as the non-intensive
management of these forest type allows the establishment of a rich lichen biota. Our
results also emphasize the role for lichen conservation of some forest types that are of
minor economic importance, such as oak (Quercus pubescens), riparian, and silver-fir (Abies
alba) forests. This can also apply to grazed larch (Larix decidua) forests that are maintained
by traditional farming, which shape one of the most pleasing aspects of the Italian Alpine
landscapes.
Nitrogen (N) deposition has increased globally over the last 150 years and further increases are predicted. Epiphytic lichens decline in abundance and diversity in areas with high N loads, and the abundance of lichens decreases along gradients of increased deposition. Thus, although N is an essential nutrient for lichens, excessive loads may be detrimental for them. However, these gradients include many correlated pollutants and the mechanisms behind the decline are thus poorly known. The aim of this study was to assess effects of N deposition, alone, on the epiphytic lichen community composition in a naturally N‐poor boreal forest. For this purpose, whole spruce trees were fertilized daily with N at five levels, equivalent to 0.6, 6, 12.5, 25, and 50 kg N ha−1 yr−1, during four consecutive growing seasons (2006–2009), and changes in the abundance of lichens were monitored each autumn from the preceding year (2005). The studied lichen communities were highly dynamic and responded strongly to the environmental perturbation. N deposition detectably altered the direction of succession and reduced the species richness of the epiphytic lichen communities, even at the lowest fertilization application (6 kg N ha−1 yr−1). The simulated N deposition caused significant changes in the abundance of Alectoria sarmentosa, Bryoria spp., and Hypogymnia physodes, which all increased at low N loads and decreased at high loads, but with species‐specific optima. The rapid decline of A. sarmentosa may have been caused by the added nitrogen reducing the stability of the lichen thalli, possibly due to increases in the photobiont: mycobiont ratio or parasitic fungal attacks. We conclude that increases in nitrogen availability, per se, could be responsible for the reductions in lichen abundance and diversity observed along deposition gradients, and those community responses may be due to physiological responses of the individual species rather than changes in competitive interactions.
Biotic interactions exert considerable influence on the distribution of individual species and should, thus, strongly impact communities. Implementing biotic interactions in spatial models of community assembly is therefore essential for accurately modelling assemblage properties. However, this remains a challenge due to the difficulty of detecting the role of species interactions and because accurate paired community and environment data sets are required to disentangle biotic influences from abiotic effects.
Here, we incorporate data from three dominant species into community‐level models as a proxy for the frequency and intensity of their interactions with other species and predict emergent assemblage properties for the co‐occurring subdominant species. By analysing plant community and field‐quantified environmental data from specially designed and spatially replicated monitoring grids, we provide a robust in vivo test of community models.
Considering this well‐defined and easily quantified surrogate for biotic interactions consistently improved realism in all aspects of community models (community composition, species richness and functional structure), irrespective of modelling methodology.
Dominant species reduced community richness locally and favoured species with similar leaf dry matter content. This effect was most pronounced under conditions of high plant biomass and cover, where stronger competitive impacts are expected. Analysis of leaf dry matter content suggests that this effect may occur through efficient resource sequestration.
Synthesis . We demonstrate the strong role of dominant species in shaping multiple plant community attributes, and thus the need to explicitly include interspecific interactions to achieve robust predictions of assemblage properties. Incorporating information on biotic interactions strengthens our capacity not only to predict the richness and composition of communities, but also how their structure and function will be modified in the face of global change.
We measured the water holding capacity per area (WHCA;mgH2O/cm2), and thus the
saturating rainfall (mm), for sympatric cyano- (Lobaria scrobiculata and Pseudocyphellaria
crocata) and cephalolichens (Lobaria pulmonaria) along canopy height gradients in boreal
rainforests, to quantify the importance of specimen size, photobiont type and branch
height as WHCA drivers. Size increased WHCA by a factor of four. Cyanolichens had 1.5
times higher WHCA than cephalolichens. Finally, branch height significantly increased
WHCA for the Lobaria species. Reported responses are consistent with higher optimal
rainfall requirements for reproducing versus juvenile specimens, and for cyanolichens
versus those with green algal photobionts. Increased WHCA with height in the canopy is
consistent with acclimation to stronger evaporative demands. The results highlight the
link between rainfall patterns and maximal sizes realized for a given lichen species and
habitat, and extend our understanding of why the cyanolichen/green algal lichen-ratio
increases in forests with increasing rainfall.
The forest canopy is fundamentally important in biodiversity conservation and ecosystem function. Cryptogamic epiphytes are dominant tree bole and canopy elements in temperate and boreal forests, though remain neglected by mainstream forest ecology. This review makes ecological information on cryptogamic epiphytes available to a non-specialist audience, to facilitate their integration in forest biodiversity and ecosystem studies more generally. The review focuses specifically on lichen epiphytes, highlighting their diversity and ecosystem role. A principal task is to explore pattern and process in lichen epiphyte diversity – species composition and richness – therefore demonstrating the utility of lichens as an ecological model system. The review examines key themes in previous research. First, the extensive literature used to resolve species response to, and community turnover along environmental/resource gradients, consistent with the habitat niche. Second, the evidence for dispersal-limitation, which may constrain community composition and richness in isolated habitats. Third, these two processes – the habitat niche and dispersal-limitation – are used to explain stand-scale diversity, in addition to the role of neutral effects (habitat area). Fourth, the review moves from a taxonomic (pattern) to a functional (process) perspective, considering evidence for autogenic succession evidenced by competition and/or facilitation, and non-random trends in life-history traits. This functional approach provides a counter-point to an assumption that lichen epiphyte communities are unsaturated and non-competitive, a situation which would allow the long-term accumulation of species richness with temporal continuity. Finally, the review explores landscape-scale impacts on lichen epiphytes, with recommendations for conservation.
The effect of management related factors on species richness of epiphytic bryophytes and lichens was studied in managed deciduous-coniferous mixed forests in Western-Hungary. At the stand level, the potential explanatory variables were tree species composition, stand structure, microclimate and light conditions, landscape and historical variables; while at tree level host tree species, tree size and light were studied. Species richness of the two epiphyte groups was positively correlated. Both for lichen and bryophyte plot level richness, the composition and diversity of tree species and the abundance of shrub layer were the most influential positive factors. Besides, for bryophytes the presence of large trees, while for lichens amount and heterogeneity of light were important. Tree level richness was mainly determined by host tree species for both groups. For bryophytes oaks, while for lichens oaks and hornbeam turned out the most favourable hosts. Tree size generally increased tree level species richness, except on pine for bryophytes and on hornbeam for lichens. The key variables for epiphytic diversity of the region were directly influenced by recent forest management; historical and landscape variables were not influential. Forest management oriented to the conservation of epiphytes should focus on: (i) the maintenance of tree species diversity in mixed stands; (ii) increment the proportion of deciduous trees (mainly oaks); (iii) conserving large trees within the stands; (iv) providing the presence of shrub and regeneration layer; (v) creating heterogeneous light conditions. For these purposes tree selection and selective cutting management seem more appropriate than shelterwood system.
Conservation and sustainable forestry are essential in a multi-functional landscape. In this respect, ecological studies on epiphytes are needed to determine abiotic and biotic factors associated with high diversity. The aim of the present study was to evaluate relative sensitivity of conservation targets (epiphytic bryophytes and lichens) in relation to contrasting environmental variables (tree species, tree diameter at breast height, bark crevice depth, pH, tree inclination, pH, forest stand age, area and type) in boreo-nemoral forests. The study was conducted in Latvian 34 woodland key habitat (WKH) boreo-nemoral forest stands. Generalized linear mixed models and canonical correspondence analysis showed that tree species and tree bark pH were the most important variables explaining epiphytic bryophyte and lichen composition and richness (total, Red-listed, WKH indicator species). Forest stand level factors, such as stand size and habitat type, had only minor influence on epiphytic species composition and richness. The results of the present study indicate a need to maintain the diversity of tree species and large trees, particularly Acer platanoides, Carpinus betulus, Fraxinus excelsior, Populus tremula, Tilia cordata, Ulmus glabra and Ulmus laevis in conservation of epiphytic bryophyte and lichen communities in the future.
For several epiphyte species, dispersal limitation and metapopulation dynamics have been suggested. We studied the relative importance of local environmental conditions and spatial aggregation of species richness of facultative and obligate epiphytic bryophytes and lichens within two old-growth forests in eastern Sweden. The effect of the local environment was analyzed using generalized linear models (GLM). We tested whether species richness was spatially structured by fitting variogram models to the residuals of the GLM. In addition, we analyzed the species-area relationship (area=tree diameter). Different environmental variables explained the richness of different species groups (bryophytes vs lichens, specialists vs generalists, sexual vs asexual dispersal). In most groups, the total variation explained by environmental variables was higher than the variation explained by the spatial model. Spatial aggregation was more pronounced in asexually than in sexually dispersed species. Bryophyte species richness was only poorly predicted by area, and lichen species richness was not explained by area at all.
Background: Few studies analysing lichen diversity have simultaneously considered interactions among drivers that operate at different spatial and temporal scales.
Aims: The aims of this study were to evaluate the relative importance of host tree, and local, landscape and historical factors in explaining lichen diversity in managed temperate forests, and to test the potential interactions among factors acting at different spatial scales.
Methods: Thirty-five stands were selected in the Őrség region of western Hungary. Linear models and multi-model inference within an information-theory framework were used to evaluate the role of different variables on lichen species richness.
Results: Drivers at multiple spatial scales contributed to shaping lichen species richness both at the tree and plot levels. Tree-level species richness was related to both tree- and plot-level factors. With increasing relative diffuse light lichen species richness increased; this effect was stronger on the higher than on the lower part of the trunks. At the plot scale, species richness was affected by local drivers. Landscape and historical factors had no, or only a marginal, effect.
Conclusions: Lichen conservation in temperate managed forests could be improved if the complex interactions among host tree quality and availability, micro-climatic conditions, and management were taken into consideration.
Questions
How are the fine‐scale spatial distribution and abundance of epiphytic lichens explained by factors related to environmental filtering and local dispersal? Are spatial distribution and abundance explained by the same underlying factors across sites for: (1) each species separately; or (2) groups of species with similar dispersal strategies?
Location
Ten lowland deciduous forests at the southwest coast of N orway (60ºN, 5ºE).
Methods
We investigated the spatial distribution and abundance, given occurrence, of 15 epiphytic L obarion lichens in ten forest sites: six 1800‐m ² study sites and four 5000‐m ² study sites. We divided each site into a grid of 1‐m ² sampling units, marked all trees and recorded the abundance of individual lichen species. We assessed the relative impact of factors related to environmental filtering and local dispersal for each lichen species using multiple regressions and variation partitioning. Finally, to compare the results between species and between sites, we applied linear mixed effect models.
Results
We found that the occurrence of lichen species on a tree is explained primarily by factors related to environmental filtering. The abundance of lichen species that occur on a tree is explained by a combination of environmental filtering and local dispersal, but the relative importance of these factors was found to vary greatly between sites. We found no differences in this respect between species with different dispersal strategies.
Conclusions
Our results indicate that both environmental filtering and local dispersal dynamics are important processes explaining the distribution and abundance patterns of Lobarion lichens at fine spatial scales. However, spatial variations in environmental factors within sites interact with propagule distributions to produce a range of inter‐site variation. Accordingly, the relative importance of these two structuring mechanisms varies among sites, particularly in the case of abundance patterns. Since single‐site patterns are not readily generalized, we emphasize the importance of multiple study sites for evaluation of the role of different processes in shaping the spatial distribution patterns of species.
Written by a world renowned biologist, this volume offers a comprehensive synthesis of current research in this rapidly expanding area of population biology. It covers both the essential theory and a wide range of empirical studies, including the author's groundbreaking work on the Glanville fritillary butterfly. It also includes practical applications to conservation biology. The book describes theoretical models for metapopulation dynamics in highly fragmented landscapes and emphasizes spatially realistic models. It presents the incidence function model and includes several detailed examples of its application. Accessible to advanced undergraduate and graduate students, Metapopulation Ecology will be a valuable resource for researchers in population biology, conservation biology, and landscape ecology.
Wood‐decaying fungi are ubiquitous and functionally important organisms within forest ecosystems world‐wide, but remarkably little is known of their population dynamics in relation to the dynamics of their host substrates. Living in transient environments, where local extinctions are caused by gradual substrate (patch) destruction or deterioration due to wood decomposition, the long‐term persistence of these species requires successful colonization of new patches.
During a 6‐year period, we examined the colonization–extinction dynamics of wood‐decaying fungi ( Aphyllophorales : Polyporaceae and Corticiaceae ) in relation to the spatiotemporal distribution of host logs within a boreal old‐growth Norway spruce ( Picea abies ) forest.
The dynamics of the species studied were strongly influenced by both local log characteristics (within patch) and connectivity (between patch). Several species (e.g. Asterodon ferruginosus , Phellinus ferrugineofuscus , P. viticola , Phlebia centrifuga ) showed a positive effect of connectivity, mainly colonizing logs in the vicinity of previously occupied logs. This implies that some wood‐decaying fungi may be dispersal limited in terms of successful colonizations. The relative importance of patch conditions and connectivity was however, highly species specific.
Our results further illustrate the importance of life‐strategies adopted by species that are present during different stages of wood decomposition. Early colonizers were primarily affected by the stage of decomposition; secondary colonizers were affected by a variety of within patch and/or between patch variables, maintaining high species coexistence within intermediate stages of decay. Phellinus nigrolimitatus was the dominant polyporous decayer at the final stages of decomposition, clearly gaining a competitive advantage from specializing on highly decomposed wood and having very low mean annual mortality rates.
Local extinction rates were higher on small diameter logs than large diameter logs, and generally increased as decay proceeded, illustrating the importance of deterministic patch destruction due to wood decomposition.
Synthesis . The fungi‐log study system was highly dynamic, illustrating that both characteristics and spatiotemporal availability of logs are important in explaining the distribution patterns and population dynamics of wood‐decaying fungal communities. The result implies that the dynamics of some wood‐decaying fungi can be characterized as patch‐tracking metapopulations, with connectivity‐dependent colonizations and local extinctions caused by the turnover of the patches.
Deciduous trees within a coniferous forest landscape provide habitat for many organisms. Single trees in deciduous forests form dynamic patches that emerge, grow and fall, but the stands themselves are also dynamic patches established after disturbances and replaced by conifers during succession. Increased dispersal distance, as imposed by landscape fragmentation, may lead to extinctions and reduced biodiversity among species dependent on this dynamic network.
We analysed regional frequency distributions, local abundances and spatial occupancy patterns of epiphytic bryophytes in 135 deciduous forest stands in a fragmented landscape in Sweden. We used generalized non‐linear models to test whether these patterns could be assigned to metapopulation dynamics of individual epiphytes by investigating the relative importance of stand size, habitat quality, connectivity and landscape history on species occupancies and local abundances.
Most asexually dispersed species were regionally rare, and spatial species occupancy patterns suggest that this is caused by dispersal limitation. In sexually dispersed species, a strong rescue effect was indicated by a bimodal frequency distribution of the species, as well as by increasing local abundance with increasing connectivity to stands present today, or some decades ago. There was a strong positive relationship between regional frequency and local abundance of the species, and between species richness and forest stand size. Vicinity to forest edge negatively affected the local abundance of most species.
Our results clearly indicate a metapopulation structure. Sensitivity of epiphytes to habitat fragmentation is caused by decreasing forest sizes, habitat alteration at forest edges and increasing dispersal distances. Even in assumed good dispersers, increasing distances can significantly alter regional dispersal processes. A lower rescue effect leads to smaller stand population sizes with a larger extinction risk. Rapid reduction of the amount of habitat during the last decades and the expected time‐lag in species extinctions suggest that epiphytes will further decline in the future, although there may still be time for restoration programmes to prevent extinction.
Question: Are soil lichen communities structured by biotic interactions?
Location: Gypsum outcrops located next to Belmonte del Tajo, central Spain.
Methods: We sampled a total of 68 (50 cm × 50 cm) plots in gypsum outcrops from central Spain. Each plot was divided into 100 (5 cm × 5 cm) sampling quadrats, and the presence of all lichen species in every quadrat was recorded (6800 quadrats in total). We used two realistic null models to generate random communities unstructured by biotic interactions, and used them to test the hypothesis that soil lichen species co‐occur less often than expected by chance.
Results: We found fewer species combinations and less co‐occurrence than expected by chance. However, the latter result was dependent on the null model selected. The number of checkerboard pairs did not differ significantly from the null expectation.
Conclusions: Overall, our results suggest that gypsiferous soil lichen communities are structured by competitive interactions. They are consistent with studies conducted with a wide variety of taxa, and fill a gap in our knowledge of the factors driving the small‐scale distribution of these important organisms.
We investigated the variability in spatial pattern of some structural, dendrochronological and dendroclimatological features of a mixed Larix decidua-Pinus cembra forest at the timberline in the eastern Italian Alps at fine geographical and temporal scales. Forest structure variables such as stem diameter, tree height, age and tree-ring related parameters (yearly growth index, mean sensitivity, first order autocorrelation and some dendroclimatic variables) have been compared at various scale levels. We observed that most of the variables show positive autocorrelated structures due to both forest dynamics and fine-scale driving forces, probably related to microrelief. Spatial structure of yearly indexed radial growth appears sensitive to extreme climatic events. Secondary succession after past disturbances drives the forest towards a structure governed by a gap regeneration dynamics that seems to ensure the different requirements of the two main tree species present. Small spatial scale studies of forest structures, especially if integrated to dendro-ecological data, seem an efficient tool to assess the disturbance regime and species sensitivity to environmental change.
Numerous studies have successfully used topographic variables for the prediction of plant species distributions in mountainous areas. A current question is which scale optimizes the predictive power of these variables. Due to the development of airborne radar/laser scanning, very high resolution digital elevation models (VHR DEMs) with a typical resolution of 1 m have emerged, allowing an accurate estimation of surface derivatives on a fine scale. Improved understanding of the relationship between scale and predictive power, through a comparative assessment of the significance of topographic variables computed at different scales, is needed. It should help researchers in selecting an adequate scale for the computation of topographic factors and further also increase the precision of models for predicting plant species distributions, and find direct applications, such as a better estimation of potential refuges for plant species in a climate change scenario. In this context, it is worth exploring the use of VHR DEM's techniques for data acquisition.
1. This paper describes a novel approach to modelling of metapopulation dynamics. The model is constructed as a generalized incidence function, which describes how the fraction of occupied habitat patches depends on patch areas and isolations. 2. The model may be fitted to presence/absence data from a metapopulation at a dynamic equilibrium between extinctions and colonizations. 3. Using the estimated parameter values, transient dynamics and the equilibrium fraction of occupied patches in any system of habitat patches can be predicted. The significance of particular habitat patches for the long-term persistence of the metapopulation, for example, can also be evaluated. 4. The model is fitted to data from three butterfly metapopulations. The model predicts well the observed minimum patch size for occupancy and the numbers of extinctions and colonizations per year (turnover rate). The results suggest that local populations of the three butterflies in patches of 1 ha, which may support of the order of 1000 adult butterflies, have an expected lifetime of 20-100 years.
Plant communities have traditionally been viewed as either a random collection of individuals or as organismal entities. For most ecologists however, neither perspective provides a modern comprehensive view of plant communities, but we have yet to formalize the view that we currently hold. Here, we assert that an explicit re-consideration of formal community theory must incorporate interactions that have recently been prominent in plant ecology, namely facilitation and indirect effects among competitors. These interactions do not support the traditional
individualistic perspective. We believe that rejecting strict individualistic theory will allow ecologists to better explain variation occurring at different spatial scales, synthesize more general predictive theories of community dynamics, and develop models for community-level responses to global change. Here, we introduce the concept of the integrated community (IC) which proposes that range from highly natural plant communities individualistic to highly interdependent depending on synergism among:
(i) stochastic processes,
(ii) the abiotic tolerances of species,
(iii) positive and negative interactions among plants, and
(iv) indirect interactions within and between trophic levels.
All of these processes are well accepted by plant ecologists, but no single theory has sought to integrate these different processes into our concept of communities.
1. The epiphytic vegetation of 60 stems of aspen (Populus tremula) was studied in a 16-ha forest area near Uppsala, Sweden. The cover of bryophytes and of foliose and fruticose lichens was registered at three heights (50, 100 and 150 cm) around each stem and related to tree factors: bark roughness, bark depth, tree diameter and tree age; to forest conditions: total basal area (approximates tree density including basal area of aspen), light conditions, site quality class and field-layer vegetation type; to bark chemistry: pH, total K, Ca, Mg and Na, and exchangeable K, Ca, Mg and S; and to soil chemistry: pH, total K, Na, Mg, Ca, base saturation and total acidity. 2. Canonical correspondance analysis (CCA, following ter Braak) showed that the most important factors affecting the composition of the epiphytic vegetation were field-layer vegetation type and light conditions, which were correlated with the first axis, and basal area of aspen, soil exchangeable Ca and soil exchangeable Na, which were correlated with the second axis. 3. In multiple regression analyses with individual species as dependent variables, important factors were field-layer vegetation type, bark total Na and soil exchangeable Ca. A high species number was correlated with thick bark and shady conditions. 4. There were significant correlations between bark chemistry and soil chemistry: both exchangeable bark Ca and total bark Ca were significantly correlated with soil pH in multiple regression analyses. Redundancy analysis (RDA, following ter Braak) gave similar results and revealed a positive covariation between bark factors (total Ca, exchangeable Ca, total Na,) and soil factors (pH, soil exchangeable Ca, soil exchangeable Mg). 5. The mechanisms for the connection between soil and bark chemistry are unknown, but several explanations can be postulated, of which an impact from the soil on the bark through transportation of nutrients from the tree roots to the bark seems the most likely. Since bark chemical factors are important for epiphytic species, soil properties might affect the composition of the epiphytic vegetation on Populus tremula. 6. There is a need to investigate further the bark-soil relationships and the mechanisms of possible interactions. If the epiphytic species are indirectly affected by the soil through influences on the bark, this could have consequences for conservation management intended to preserve epiphytic species as well as for the use of bryophytes and lichens as indicators of air pollution.
Interpretation of regression coefficients is sensitive to the scale of the inputs. One method often used to place input variables on a common scale is to divide each numeric variable by its standard deviation. Here we propose dividing each numeric variable by two times its standard deviation, so that the generic comparison is with inputs equal to the mean +/-1 standard deviation. The resulting coefficients are then directly comparable for untransformed binary predictors. We have implemented the procedure as a function in R. We illustrate the method with two simple analyses that are typical of applied modeling: a linear regression of data from the National Election Study and a multilevel logistic regression of data on the prevalence of rodents in New York City apartments. We recommend our rescaling as a default option--an improvement upon the usual approach of including variables in whatever way they are coded in the data file--so that the magnitudes of coefficients can be directly compared as a matter of routine statistical practice.
MuMIn: Multi-model Inference. R package version 1.9
- K Barton
Barton, K., 2013. MuMIn: Multi-model Inference. R package version 1.9.13. http://
CRAN.R-project.org/package¼MuMIn.
Lichen guilds share related cyanobacterial symbionts
- J Rikkinen
- I Oksanen
- K Lohtander
Rikkinen, J., Oksanen, I., Lohtander, K., 2002. Lichen guilds share related cyanobacterial symbionts. Science 297, 357.
- W N Venables
- B D Ripley
Venables, W.N., Ripley, B.D., 2002. Modern Applied Statistics with S, fourth ed.
Springer, New York.
Pscl: Classes and Methods for R Developed in the Political Science
- S Jackman
Jackman, S., 2012. Pscl: Classes and Methods for R Developed in the Political Science
Computational Laboratory. Stanford University. Department of Political Science,
Stanford University, Stanford, California. R package version 1.04.4. http://pscl.
stanford.edu/.