Title: Global patterns and drivers of alpine plant species richness
AbstractAim
Alpine ecosystems differ in area, macroenvironment and biogeographical history across the Earth, but the relationship between these factors and plant species richness is still unexplored. Here, we assess the global patterns of plant species richness in alpine ecosystems and their association with environmental, geographical and historical factors at regional and community scales.
Location
Global.
Time period
Data collected between 1923 and 2019.
Major taxa studied
Vascular plants.
Methods
We used a dataset representative of global alpine vegetation, consisting of 8,928 plots sampled within 26 ecoregions and six biogeographical realms, to estimate regional richness using sample‐based rarefaction and extrapolation. Then, we evaluated latitudinal patterns of regional and community richness with generalized additive models. Using environmental, geographical and historical predictors from global raster layers, we modelled regional and community richness in a mixed‐effect modelling framework.
Results
The latitudinal pattern of regional richness peaked around the equator and at mid‐latitudes, in response to current and past alpine area, isolation and the variation in soil pH among regions. At the community level, species richness peaked at mid‐latitudes of the Northern Hemisphere, despite a considerable within‐region variation. Community richness was related to macroclimate and historical predictors, with strong effects of other spatially structured factors.
Main conclusions
In contrast to the well‐known latitudinal diversity gradient, the alpine plant species richness of some temperate regions in Eurasia was comparable to that of hyperdiverse tropical ecosystems, such as the páramo. The species richness of these putative hotspot regions is explained mainly by the extent of alpine area and their glacial history, whereas community richness depends on local environmental factors. Our results highlight hotspots of species richness at mid‐latitudes, indicating that the diversity of alpine plants is linked to regional idiosyncrasies and to the historical prevalence of alpine ecosystems, rather than current macroclimatic gradients.
Margaroni, Sofia; Petersen, Kurt B.; Gleadow, Roslyn; Burd, Martin(
, Journal of Biogeography)
AbstractAim
Separation of regeneration niches may promote coexistence among closely related plant species, but there is little evidence that regeneration traits affect species ranges at broad geographical scales. We address patterns of co‐occurrence within the genusSelaginella, an ancient lineage of free‐sporing, heterosporous, vascular plants. Specifically, we ask whether differences between species in spore size are associated with the extent of overlap in their geographical ranges, a measure of opportunity for ecological interaction.
Taxon
Selaginella(Selaginellaceae: Lycopodiales).
Methods
We used quantile regression to examine the relationship of spore size ratios (pairwise ratios for megaspores and microspores of co‐occurring species) to the area of range overlap and to latitude for a worldwide sample of 112Selaginellaspecies. Phylogenetically informed tests of statistical significance were used for each percentile relationship examined in the quantile regressions.
Results
Large pairwise disparities in megaspore sizes were significantly associated with large range overlap. Disparities also tended to be larger at low latitudes. Microspore size differences, in contrast, were unrelated to shared range area or latitude.
Main conclusion
Megaspore size appears to affect coexistence at a broad regional scale amongSelaginellaspecies, in at least some cases. The pattern is consistent with some degree of competitive structuring of size‐related aspects of dispersal and establishment of propagules among some co‐occurring species. Habitat complexity, such as open microsites within otherwise closed and shaded vegetation, seems likely to promote reproductive niche separation and may account for the latitudinal structure inSelaginellaspore sizes.
Roots and rhizospheres host diverse microbial communities that can influence the fitness, phenotypes, and environmental tolerances of plants. Documenting the biogeography of these microbiomes can detect the potential for a changing environment to disrupt host‐microbe interactions, particularly in cases where microbes buffer hosts against abiotic stressors. We evaluated whether root‐associated fungi had poleward declines in diversity, tested whether fungal communities in roots shifted near host plant range edges, and determined the relative importance of environmental and host predictors of root fungal community structure.
Location
North American plains grasslands.
Taxon
Foundation grasses –Andropogon gerardii, Bouteloua dactyloides, B. eriopoda, B. gracilis,andSchizachyrium scopariumand root fungi.
Methods
At each of 24 sites representing three replicate 17°–latitudinal gradients, we collected roots from 12 individuals per species along five transects spaced 10 m apart (40 m × 40 m grid). We used next‐generation sequencing of ITS2, direct fungal culturing from roots, and microscopy to survey fungi associated with grass roots.
Results
Root‐associated fungi did not follow the poleward declines in diversity documented for many animals and plants. Instead, host plant identity had the largest influence on fungal community structure. Edaphic factors outranked climate or host plant traits as correlates of fungal community structure; however, the relative importance of environmental predictors differed among plant species. As sampling approached host species range edges, fungal composition converged in similarity among individual plants of each grass species.
Main conclusions
Environmental predictors of root‐associated fungi depended strongly on host plant species identity. Biogeographic patterns in fungal composition suggested a homogenizing influence of stressors at host plant range limits. Results predict that communities of non‐mycorrhizal, root‐associated fungi in the North American plains will be more sensitive to future changes in host plant ranges and edaphic factors than to the direct effects of climate.
Historical processes that shaped current diversity patterns of seaweeds remain poorly understood. Using Dictyotales, a globally distributed order of brown seaweeds as a model, we test if historical biogeographical and diversification patterns are comparable across clades. Dictyotales contain some 22 genera, three of which,Dictyota,LobophoraandPadina, are exceptionally diverse. Specifically, we test whether the evolutionary processes that shaped the latitudinal diversity patterns in these clades are in line with the tropical conservatism, out‐of‐the‐tropics or diversification rate hypotheses.
Location
Global coastal benthic marine environments.
Taxon
Dictyotales (Phaeophyceae).
Methods
Species diversity was inferred using DNA‐based species delineation, addressing cryptic diversity and circumventing taxonomic problems. A six‐gene time‐calibrated phylogeny, distribution data of 3,755 specimens and probabilistic modelling of geographical range evolution were used to infer historical biogeographical patterns. The phylogeny was tested against different trait‐dependent models to compare diversification rates for different geographical units as well as different thermal affinities.
Results
Our results indicate that Dictyotales originated in the Middle Jurassic and reach a current peak of species diversity in the Central Indo‐Pacific. Ancestral range estimation points to a southern hemisphere origin of Dictyotales corresponding to the tropical southern Tethys Sea. Our results demonstrate that diversification rates were generally higher in tropical regions, but increased diversification rates in different clades are driven by different processes. Our results suggest that three major clades underwent a major diversification burst in the early Cenozoic, withDictyotaandPadinaexpanding their distribution into temperate regions whileLobophoraretained a predominantly tropical niche.
Main conclusions
Our results are consistent with both the tropical conservatism hypothesis, in which clades originate and remain in the tropics (Lobophora), and the out‐of‐the‐tropics scenario, where taxa originate and expand towards the temperate regions while preserving their presence in the tropics (Dictyota,Padina).
Malanson, George P.; Testolin, Riccardo; Pansing, Elizabeth R.; Jiménez‐Alfaro, Borja(
, Journal of Biogeography)
AbstractAim
Area and environmental heterogeneity together explain most patterns of species diversity but disentangling their relative importance has been difficult. Here, we empirically examined this relationship and parsed their relative importance, and that of the heterogeneity—effective area trade‐off, at different spatial scales and in different spatial representations in simulations.
Location
Alpine grasslands of 23 mountain ranges of southern and central Europe.
Taxon
Vascular plants.
Methods
We developed metrics of climatic and edaphic heterogeneity, using principal components analyses and the shoelace algorithm, and added elevation range. We applied commonality analysis to partition the unique and shared explanation of the observed vascular plant species richness among selected metrics. A simulation was developed to separate the relative importance of area and heterogeneity at different extents and representations of spatial nestedness, and the heterogeneity—effective area trade‐off was evaluated by altering spatial discreteness.
Results
The explanation of the observed regional richness was shared by area and heterogeneity. The simulation revealed that heterogeneity was consistently more important, but less so among smaller areas. This qualitative pattern was maintained regardless of whether and how nestedness was represented. The heterogeneity–effective area trade‐off occurred in a few simulations of more discrete habitats.
Main Conclusions
Scale dependence may account for discrepancies among past empirical studies wherein environmental heterogeneity has usually outweighed area in the explanation of species richness; and it is not affected by nestedness. The potential heterogeneity–effective area trade‐off may be limited to locations where the environmental heterogeneity is quite discrete or if the added environment is beyond the niches of any species in the potential pool. The significant importance of area per se in small territories indicates that microrefugia, even with an unlikely full range of heterogeneity, will suffer local extinctions in the face of climate change.
Collins, Courtney G.; Spasojevic, Marko J.; Alados, Concepción L.; Aronson, Emma L.; Benavides, Juan C.; Cannone, Nicoletta; Caviezel, Chatrina; Grau, Oriol; Guo, Hui; Kudo, Gaku; et al(
, Global Change Biology)
Abstract
Global climate and land use change are causing woody plant encroachment in arctic, alpine, and arid/semi‐arid ecosystems around the world, yet our understanding of the belowground impacts of this phenomenon is limited. We conducted a globally distributed field study of 13 alpine sites across four continents undergoing woody plant encroachment and sampled soils from both woody encroached and nearby herbaceous plant community types. We found that woody plant encroachment influenced soil microbial richness and community composition across sites based on multiple factors including woody plant traits, site level climate, and abiotic soil conditions. In particular, root symbiont type was a key determinant of belowground effects, as Nitrogen‐fixing woody plants had higher soil fungal richness, while Ecto/Ericoid mycorrhizal species had higher soil bacterial richness and symbiont types had distinct soil microbial community composition. Woody plant leaf traits indirectly influenced soil microbes through their impact on soil abiotic conditions, primarily soil pH and C:N ratios. Finally, site‐level climate affected the overall magnitude and direction of woody plant influence, as soil fungal and bacterial richness were either higher or lower in woody encroached versus herbaceous soils depending on mean annual temperature and precipitation. All together, these results document global impacts of woody plant encroachment on soil microbial communities, but highlight that multiple biotic and abiotic pathways must be considered to scale up globally from site‐ and species‐level patterns. Considering both the aboveground and belowground effects of woody encroachment will be critical to predict future changes in alpine ecosystem structure and function and subsequent feedbacks to the global climate system.
@article{osti_10452902,
place = {Country unknown/Code not available},
title = {Global patterns and drivers of alpine plant species richness},
url = {https://par.nsf.gov/biblio/10452902},
DOI = {10.1111/geb.13297},
abstractNote = {Abstract AimAlpine ecosystems differ in area, macroenvironment and biogeographical history across the Earth, but the relationship between these factors and plant species richness is still unexplored. Here, we assess the global patterns of plant species richness in alpine ecosystems and their association with environmental, geographical and historical factors at regional and community scales. LocationGlobal. Time periodData collected between 1923 and 2019. Major taxa studiedVascular plants. MethodsWe used a dataset representative of global alpine vegetation, consisting of 8,928 plots sampled within 26 ecoregions and six biogeographical realms, to estimate regional richness using sample‐based rarefaction and extrapolation. Then, we evaluated latitudinal patterns of regional and community richness with generalized additive models. Using environmental, geographical and historical predictors from global raster layers, we modelled regional and community richness in a mixed‐effect modelling framework. ResultsThe latitudinal pattern of regional richness peaked around the equator and at mid‐latitudes, in response to current and past alpine area, isolation and the variation in soil pH among regions. At the community level, species richness peaked at mid‐latitudes of the Northern Hemisphere, despite a considerable within‐region variation. Community richness was related to macroclimate and historical predictors, with strong effects of other spatially structured factors. Main conclusionsIn contrast to the well‐known latitudinal diversity gradient, the alpine plant species richness of some temperate regions in Eurasia was comparable to that of hyperdiverse tropical ecosystems, such as the páramo. The species richness of these putative hotspot regions is explained mainly by the extent of alpine area and their glacial history, whereas community richness depends on local environmental factors. Our results highlight hotspots of species richness at mid‐latitudes, indicating that the diversity of alpine plants is linked to regional idiosyncrasies and to the historical prevalence of alpine ecosystems, rather than current macroclimatic gradients.},
journal = {Global Ecology and Biogeography},
volume = {30},
number = {6},
publisher = {Wiley-Blackwell},
author = {Testolin, Riccardo and Attorre, Fabio and Borchardt, Peter and Brand, Robert F. and Bruelheide, Helge and Chytrý, Milan and De Sanctis, Michele and Dolezal, Jiri and Finckh, Manfred and Haider, Sylvia and Hemp, Andreas and Jandt, Ute and Kessler, Michael and Korolyuk, Andrey Yu and Lenoir, Jonathan and Makunina, Natalia and Malanson, George P. and Montesinos‐Tubée, Daniel B. and Noroozi, Jalil and Nowak, Arkadiusz and Peet, Robert K. and Peyre, Gwendolyn and Sabatini, Francesco Maria and Šibík, Jozef and Sklenář, Petr and Sylvester, Steven P. and Vassilev, Kiril and Virtanen, Risto and Willner, Wolfgang and Wiser, Susan K. and Zibzeev, Evgeny G. and Jiménez‐Alfaro, Borja and Bjorkman, ed., Anne},
}
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