83 research outputs found

    Macroecology of global alpine vegetation

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    Gli ecosistemi alpini, ossia gli habitat di alta quota al di sopra della linea degli alberi, sono essenziali per il sostentamento umano e sono tra gli ambienti più minacciati dal cambiamento climatico di origine antropica. Nonostante il consenso generale sulla distribuzione e le caratteristiche ecologiche dei biomi terrestri, l'effettiva estensione e le caratteristiche bioclimatiche degli ecosistemi alpini globali sono ancora incerte. Inoltre, i pattern e le cause della diversità vegetale e del funzionamento degli ecosistemi alpini globali sono in gran parte sconosciuti. Questo lavoro rappresenta un punto di partenza per la delineazione dei pattern macroecologici dei biomi alpini globali. In primo luogo, ho creato una mappa delle aree alpine globali modellando le quote altimetriche regionali della linea degli alberi ad alta risoluzione spaziale, utilizzando dataset globali di copertura forestale. Ho usato questa mappa in combinazione con altri dataset digitali per valutare le caratteristiche climatiche degli ecosistemi alpini e determinarne i pattern di produttività primaria. In secondo luogo, ho analizzato i pattern globali di ricchezza delle specie vegetali negli ecosistemi alpini e l’influenza di fattori ambientali, geografici e storici a diverse scale spaziali. Per fare ciò, ho messo insieme un dataset globale della vegetazione alpina composto da oltre 8.900 plot, ho valutato i pattern latitudinali di ricchezza regionale e a livello di singole comunità vegetali, e li ho modellati rispetto a diversi predittori, stimati utilizzando raster globali. Infine, ho analizzato la variazione funzionale della vegetazione alpina in rapporto alla storia evolutiva e al macroclima. Per fare ciò, ho ulteriormente selezionato il suddetto dataset di plot di vegetazione alpina in base alla disponibilità di tratti funzionali e dati filogenetici. Ho valutato le strategie funzionali delle diverse specie di piante alpine e la dissimilarità funzionale della vegetazione tra grandi unità geografiche caratterizzate da diversa vegetazione planiziale dominante, macroclima e storia evolutiva. Infine, ho modellato la dissimilarità funzionale rispetto alle dissimilarità ambientale e filogenetica. Dalle analisi effettuate, è emerso che i biomi alpini coprono quasi il 3% delle terre emerse al di fuori dell'Antartide. Nonostante le differenze di temperatura tra le diverse latitudini, questi ecosistemi convergono al di sotto di una soglia di 5,9 °C di temperatura media annua e verso l'estremità più fredda dello spazio climatico globale. Al di sotto di tale soglia di temperatura, gli ecosistemi alpini sono influenzati da un gradiente latitudinale di temperatura media annua e sono differenziati dal punto di vista climatico per stagionalità e continentalità. Questo gradiente distingue lo spazio climatico dei biomi alpini globali da quello dei biomi temperati, boreali e della tundra. Sebbene i biomi alpini siano similmente caratterizzati da aree scarsamente vegetate, le ecoregioni mondiali mostrano forti differenze nella produttività della loro fascia alpina indipendentemente dalle principali zone climatiche. Inoltre, in contrasto con il ben noto gradiente di diversità latitudinale, la ricchezza di specie vegetali alpine di alcune regioni temperate dell'Eurasia è paragonabile a quella degli ecosistemi alpini tropicali. Questo pattern è principalmente spiegato dall'estensione attuale e passata delle aree alpine, dall'isolamento e dalla variazione del pH del suolo tra le diverse regioni, mentre la ricchezza delle comunità vegetali dipende da fattori ambientali locali. Infine, le specie vegetali delle aree alpine sembrano riflettere la variazione funzionale globale di tutte le piante e sono principalmente differenziate per le loro strategie di utilizzo delle risorse. Il macroclima attuale esercita un effetto limitato sulla vegetazione alpina, agendo per lo più a livello delle singole comunità vegetali e in combinazione con la storia evolutiva. Inoltre, la vegetazione alpina globale è funzionalmente indipendente dalle zone di vegetazione in cui è integrata, mostrando una forte convergenza funzionale. Nel complesso, nonostante la loro distribuzione globale e l'apparente eterogeneità, gli ambienti alpini formano un gruppo distinto di biomi funzionalmente convergenti, fortemente disaccoppiati dagli ambienti di pianura e con una storia biogeografica varia, la cui eredità può ancora essere osservata sugli attuali pattern di diversità che sono ulteriormente rifiniti da fattori locali.Alpine ecosystems, namely high-elevation habitats above the climatic treeline, are essential to human livelihoods and are among the environments with the highest vulnerability to anthropogenic climate change. Despite the overall agreement on the distribution and ecological features of terrestrial biomes, the actual extent and bioclimatic characteristics of alpine ecosystems worldwide are still uncertain. Furthermore, the patterns and drivers of plant diversity and functioning in alpine ecosystems are largely unknown at the global scale. This work represents a novel contribution to the delineation of macroecological patterns of global alpine biomes. First, I created a map of global alpine areas by modelling regional treeline elevations at high spatial resolution using global forest cover data. I used this map in combination with global digital datasets to assess the climatic characteristics of alpine ecosystems and to evaluate patterns of primary productivity. Second, I assessed the global patterns of plant species richness in alpine ecosystems and the relative effect of environmental, geographical and historical factors at different spatial scales. To do so, I compiled a global dataset of alpine vegetation consisting of more than 8,900 plots, evaluated latitudinal patterns of regional and community richness and modelled them against different predictors estimated using global raster layers. Third, I assessed the functional variation of alpine vegetation and its relationship with evolutionary history and macroclimate. I filtered the abovementioned dataset of alpine vegetation plots based on the availability of functional trait and phylogenetic data. I assessed the functional trade-offs of alpine plant species and the functional dissimilarity of alpine vegetation across large geographic units with different dominant lowland vegetation, macroclimate, and evolutionary history. Finally, I modelled functional dissimilarity against environmental and phylogenetic dissimilarity. I found that alpine biomes cover almost 3% of land outside Antarctica. Despite temperature differences across latitudes, these ecosystems converge below a sharp threshold of 5.9 °C and towards the colder end of the global climatic space. Below that temperature threshold, alpine ecosystems are influenced by a latitudinal gradient of mean annual temperature and are climatically differentiated by seasonality and continentality. This gradient delineates a climatic envelope of global alpine biomes. Although alpine biomes are similarly dominated by poorly vegetated areas, world ecoregions show strong differences in the productivity of their alpine belt irrespectively of major climate zones. Furthermore, in contrast with the well-known latitudinal diversity gradient, plant species richness of some temperate alpine regions in Eurasia is comparable to that of hyper-diverse tropical alpine ecosystems. This pattern is mainly explained by the current and past alpine area, isolation, and variation in soil pH among regions, while community richness depends on local environmental factors. Finally, plant species in alpine areas seemingly reflect the global variation of plant function and are mainly differentiated for their resource-use strategies. The current macroclimate exerts a limited effect on alpine vegetation, mostly acting at the community level in combination with evolutionary history. Alpine vegetation is also functionally independent from the vegetation zones in which it is embedded, exhibiting strong functional convergence at the global scale. Overall, despite their global distribution and apparent heterogeneity, alpine environments form a distinct group of functionally convergent biomes, strongly decoupled from lowland environments, and with a varied biogeographic history, whose legacy can still be observed on current diversity patterns which are locally refined by fine-scale factors

    Forgotten forests - issues and prospects in biome mapping using Seasonally Dry Tropical Forests as a case study

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    <p>Abstract</p> <p>Background</p> <p>South America is one of the most species diverse continents in the world. Within South America diversity is not distributed evenly at both local and continental scales and this has led to the recognition of various areas with unique species assemblages. Several schemes currently exist which divide the continental-level diversity into large species assemblages referred to as biomes. Here we review five currently available biome maps for South America, including the WWF Ecoregions, the Americas basemap, the Land Cover Map of South America, Morrone's Biogeographic regions of Latin America, and the Ecological Systems Map. The comparison is performed through a case study on the Seasonally Dry Tropical Forest (SDTF) biome using herbarium data of habitat specialist species.</p> <p>Results</p> <p>Current biome maps of South America perform poorly in depicting SDTF distribution. The poor performance of the maps can be attributed to two main factors: (1) poor spatial resolution, and (2) poor biome delimitation. Poor spatial resolution strongly limits the use of some of the maps in GIS applications, especially for areas with heterogeneous landscape such as the Andes. Whilst the Land Cover Map did not suffer from poor spatial resolution, it showed poor delimitation of biomes. The results highlight that delimiting structurally heterogeneous vegetation is difficult based on remote sensed data alone. A new refined working map of South American SDTF biome is proposed, derived using the Biome Distribution Modelling (BDM) approach where georeferenced herbarium data is used in conjunction with bioclimatic data.</p> <p>Conclusions</p> <p>Georeferenced specimen data play potentially an important role in biome mapping. Our study shows that herbarium data could be used as a way of ground-truthing biome maps <it>in silico</it>. The results also illustrate that herbarium data can be used to model vegetation maps through predictive modelling. The BDM approach is a promising new method in biome mapping, and could be particularly useful for mapping poorly known, fragmented, or degraded vegetation. We wish to highlight that biome delimitation is not an exact science, and that transparency is needed on how biomes are used as study units in macroevolutionary and ecological research.</p

    Global patterns and drivers of alpine plant species richness

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    Aim 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

    Negative density dependence mediates biodiversity–productivity relationships across scales

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    Regional species diversity generally increases with primary productivity whereas local diversity–productivity relationships are highly variable. This scale-dependence of the biodiversity–productivity relationship highlights the importance of understanding the mechanisms that govern variation in species composition among local communities, which is known as β-diversity. Hypotheses to explain changes in β-diversity with productivity invoke multiple mechanisms operating at local and regional scales, but the relative importance of these mechanisms is unknown. Here we show that changes in the strength of local density-dependent interactions within and among tree species explain changes in β-diversity across a subcontinental-productivity gradient. Stronger conspecific relative to heterospecific negative density dependence in more productive regions was associated with higher local diversity, weaker habitat partitioning (less species sorting), and homogenization of community composition among sites (lower β-diversity). Regional processes associated with changes in species pools had limited effects on β-diversity. Our study suggests that systematic shifts in the strength of local interactions within and among species might generally contribute to some of the most prominent but poorly understood gradients in global biodiversity

    Taxonomy, species richness and biogeography of Finnish crane flies (Diptera, Tipuloidea).

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    Biodiversity is unequally spread throughout terrestrial ecosystems. The highest species richness of animals and plants is encountered around the Equator, and naturalists observe a decrease in the number of creatures with increasing latitude. Some animal groups, however, display an anomalous species richness pattern, but these are exceptions to the general rule. Crane flies (Diptera, Tipuloidea) are small to large sized, non-biting nematoceran insects, being mainly associated with moist environments. The species richness of crane flies is highest in the tropics, but these insects are species rich and abundant in all biogeographic realms, boreal and arctic biomes included. The phylogeny and systematics of crane flies are still at an early stage and somewhat controversial. New species are constantly discovered even from temperate Europe, faunistically the best known continent. Crane flies have been rather neglected group of insects in Finland. The history of Finnish crane fly taxonomy and faunistics started in 1907, the year when Carl Lundström published his two first articles on tipuloids. Within roughly 100 years there have been only a handful of entomologists studying the Finnish fauna, and the species richness and natural history of these flies have remained poorly understood and mapped. The aim of this thesis is to clarify the taxonomy of Finnish crane flies, present an updated and annotated list of species and seek patterns in regional species richness and assemblage composition. Tipula stackelbergi Alexander has been revised (I). This species was elevated to a species rank from a subspecific rank under T. pruinosa Wiedemann and T. stackelbergi was also deleted from the list of European crane flies. Two new synonyms were found: T. subpruinosa Mannheims is a junior synonym of T. freyana Lackschewitz and T. usuriensis Alexander is a junior synonym of T. pruinosa. A new species Tipula recondita Pilipenko & Salmela has been described (II). Both morphology and COI (mtDNA) sequences were used in the assessment of the status of the species. The new species is highly disjunct, known from Finland and Russian Far East. A list of Finnish crane flies was presented, including the presence of species in the Finnish biogeographical provinces (III). A total of twenty-four species were formally reported for the first time from Finland and twenty-two previously reported species were deleted from the list. A short historical review on the studies of Finnish crane flies has been provided. The current list of Finnish species consists of 338 crane flies (IV, Appendix I). Species richness of all species and saproxylic/fungivorous species is negatively correlated with latitude, but mire-dwelling species show a reversed species richness gradient (i.e. an increase in the number of species toward north). Provincial assemblages displayed a strong latitudinal gradient and faunistic distance increased with increasing geographical distance apart of the provinces. Nearly half (48 %) of the Finnish crane flies are Trans-Palaearctic, roughly one-third (34 %) are West Palaearctic and only 16 and 2 % are Holarctic and Fennoscandian, respectively. Due to the legacy of Pleistocene glaciations, endemic Fennoscandian species are problematic and it is thus concluded that there are probably no true endemic crane flies in this region. Finally, there are probably species living within Finnish borders that have hitherto remained unnoticed. Based on subjective assessment, the number of “true” (i.e. recorded + unknown species) species count of Finnish crane flies is at minimum 350.Siirretty Doriast

    How does environmental variability drive macroecological patterns of diversity in marine and terrestrial systems?

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    INFLUENCES OF RIPARIAN LAND-USES ON HABITAT USE AND INTERSPECIFIC COMPETITION OF STREAM-DWELLING SALAMANDERS: EVIDENCE FROM BLUE RIDGE & PIEDMONT

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    Human-induced disturbances can result in persistent influences on ecosystems, including habitat loss and biogeographical changes. Global amphibian decline, a consequence of habitat degradation, is among prime conservation concerns. To better understand causes of the amphibian crisis, investigations a multiple levels of biological organization - behavior, communities, and landscapes - is imperative. I investigated the responses of stream-associated Plethdontid salamanders of the Blue Ridge and Piedmont of the Southeastern US to historical and current land uses in the riparian zone and watershed to determine, (1) change in the community structure and mechanisms driving the change and uses operating at different spatial-temporal scales; (2) competition between two sympatric species with different body sizes, natural histories, and differential sensitivity for habitat alterations (black-bellied and northern dusky salamanders) in the context of riparian land uses. I surveyed low-order streams for salamanders, estimated 15 habitat variables and current and historical land-cover at riparian and watershed scale for each sampling site. Forested streams were more diverse than non-forested streams. Two assemblages were evident: disturbance avoiders (forest-dependent, large-bodied, disturbance-sensitive species) and disturbance tolerators (cosmopolitan, small-bodied, disturbance-resistant species); each assemblage composed of 80% and 20% of the regional species pool, respectively. Riparian zone characteristics (canopy cover, canopy height, leaf-litter cover) and stream geomorphology (bank complexity, stream substrate heterogeneity, sedimentation) were dramatically altered by land uses, rendering streams unsuitable for most salamanders. Historical land uses at both riparian- and watershed-scale influenced current populations and community structure of salamanders. Piedmont protected areas with crop-farming legacies were the most species-deprived since intensive agriculture can lead to lasting effects including soil erosion, sedimentation, increased discharge, and destabilization of stream banks. My experiment on competition revealed marked differences in microhabitat associations of focal species across riparian land uses. Black-bellied salamanders competitively dominated the use of stream channel over northern dusky salamanders in forested and agricultural streams. Northern dusky salamanders competitively displaced black-bellied salamanders from stream banks in urban streams. Riparian anthropogenic disturbances negatively affected the large-bodied habitat specialists and favored small-bodied habitat generalists. Terrestrial anthropogenic disturbances can modify stream habitats and, result in the exclusion of disturbance-sensitive species, ultimately leading to biotic homogenization. Conservation of stream salamander community should be strengthened with protection and restoration of riparian forests and degraded stream habitats; land-use regulations at the watershed scale; establishment of connectivity among riparian forests; and introduction of Best Management Practices for farmlands and timberlands

    Global change and the future of avian diversity

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    Biodiversity in the Anthropocene is declining at an alarming rate. Both ecological and evolutionary components of biodiversity are critical for determining the processes that have led to the biogeographic patterns of biodiversity we see today, as well as understanding the impacts of global change on communities and ecosystems. Here, I use unique trait datasets, and phylogenetic relationships, to explore extant and future patterns of avian biodiversity. In the first part of this Thesis, I interrogate global-scale biogeographic patterns of avian diversity, by using avian traits to reveal how species fill and expand niche space. I show that evolutionary history, rather than contemporary environment, drives patterns of extant global trait diversity. In the second part I assess the impact of species extinctions on this diversity and examine whether the loss of trait and phylogenetic diversity is greater than predicted by species loss alone. I find that not only is trait homogenisation expected across the whole Avian class, but that this is borne out spatially, with the majority of biome and ecoregion assemblages predicted to experience a significant reduction in morphological diversity with important consequences for ecosystem functioning. Finally, given that Anthropogenic land-use change is experienced most intensely in the tropics, I move from a broad to local spatial scales, and highlight that the protection of secondary forests should be seen as a priority for the conservation of tropical biodiversity. Overall, this Thesis helps to further our understanding of the origins of biodiversity, and in the face of global change, its conservation
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