Mountains Biodiversity Hotspot Research Articles

Holocene vegetation dynamics and climatic fluctuations from Shuanghaizi Lake in the Hengduan Mountains, southwestern China

The Hengduan Mountains of Southwest China are considered the most biologically diverse temperate ecosystem in the world. Here, we present a ~ 10,000-year pollen record from Shuanghaizi Lake, northwestern Yunnan, which we use to reconstruct vegetation dynamics, climatic fluctuations and variability in the Indian Summer Monsoon (ISM). The results suggest that, between 10,000 and 7900 cal. yr BP, vegetation comprised mainly mixed needle- and broad-leaved forest (mostly Abies, Pinus, Quercus, and Salix), indicating a warm and humid climate, corresponding to a strong ISM. From 7900 to 6900 cal. yr BP, the mixed needle- and broad-leaved forest persisted, while an increase in Abies pollen and decrease in pollen of Pinus and Salix implies a reduction in temperature and precipitation, suggesting a slightly weaker ISM than in the preceding phase. Between 6900 and 2400 cal. yr BP, an expansion of Pinus and Quercus in mixed needle- and broad-leaved forest, together with the first occurrence of the aquatic Potamogeton, suggest a warmer and more humid climate, likely due to the strengthening monsoon, consistent with the Holocene climatic optimum. From 2400 to 970 cal. yr BP, the vegetation shifted to needle-leaved forest with sparse patches of broad-leaved forest, concurrent with a weakening ISM through the middle of this period. During the first half of the period covering 970 to 470 cal. yr BP, Abies and Picea increased and we inferred the lowest temperature and precipitation of the whole study, implying the weakest ISM. In the middle of this period, an expansion of broad-leaved trees including Quercus, Alnus, Betula and Castanopsis plus diverse herbaceous plants suggests that the climate developed towards warmer and more humid conditions, in agreement with a gradual intensification of the ISM. After 470 cal. yr BP, the vegetation became dominated by needle-leaved forest and most broad-leaved elements became intermittent. Although the climate was generally cool and dry in this period, temperature and precipitation gradually increased compared with the previous stage, indicating a slight intensification of the ISM. These findings provide a more detailed understanding of Holocene vegetation dynamics, climatic change, and the evolution of the palaeomonsoon in the Hengduan Mountains biodiversity hotspot, southwestern China.

The origin of the endemic African grasshopper family Lentulidae (Orthoptera: Acridoidea) and its climate‐induced diversification

AbstractAimForest relicts in the mountainous regions of Africa represent one of the most diverse ecosystems on our planet, but the processes that have generated this remarkable diversity are still poorly understood. We estimate divergence times for an endemic, flightless grasshopper family and reconstruct a potential scenario for their colonization of Africa to test the hypothesis that the diversity of these mountain‐top endemics has been generated by multiple fragmentations and reconnections of tropical rain forests in parallel with climatic fluctuations.LocationSub‐Saharan Africa.TaxonLentulidae (Orthoptera).MethodsWe inferred the phylogeny of 7 genera and 28 species of the Lentulidae based on COI, 16S and Histone 3 sequences by using a Bayesian approach and we also estimated divergence dates. Based on our molecular phylogeny as well as the available information on the relationship of six additional genera and local occurrence records for 120 lentulid species across Africa, we reconstruct a potential colonization scenario for most species of this group.ResultsOur findings indicate that the forest‐bound lentulids of East Africa represent a monophyletic group that originates from South Africa. We show that major splits in the phylogeny of the Lentulidae coincide with three known fragmentation events of the African rain forests (27, 16 and 9 Ma) and that lentulids subsequently diversified rapidly in parallel with the aridification and strong geological activity in East Africa.Main conclusionsOur results corroborate the diversification patterns reported for several endemic African forest‐bound animal taxa at small scales and endemic African plant taxa at larger scales, highlighting the finding that much of the biodiversity presently found in the forest relicts of the Eastern Arc Mountains biodiversity hotspot has been generated by the interplay between humid periods that allowed the spread of forest‐bound lineages across Africa and periods of aridity‐driven isolation of forests and their associated fauna.

Genomic insight into “sky island” species diversification in a mountainous biodiversity hotspot

Abstract“Sky island” species diversification contributes greatly to mountainous biodiversity. However, the underlying genomic divergence and the inferred drivers remain largely unknown. In this study, we examined the diversification history of five diploid species with three exclusively endemic to the sky islands (mountains) of the Himalaya–Hengduan Mountains biodiversity hotspot. All of them together comprise a clade of the genus Eutrema (Brassicaceae). We resequenced genomes of multiple individuals of the found populations for each species. We recovered the inconsistent phylogenetic relationships between plastome and nuclear‐genome trees for one species. Based on nuclear population genomic data, we detected high genetic divergence between five species with limited gene flow. Four species seemed to diverge mainly through geographical isolation, whereas one arose through hybrid origin. The origins of the sampled five species were dated to within the late Miocene when mountains were uplifted and climates oscillated. All species decreased their population sizes since the inferred origin of each species initially, but only two of them expanded after the Last Glacial Maximum. Together, these findings suggest that geographic isolation plays an important role in driving the sky island species diversification of the sampled species in addition to the occasional gene flow that might have led to the hybrid origin of some sky island species, similar to the species diversification of sea islands.

A taxonomically broad metagenomic survey of 339 species spanning 57 families suggests cystobasidiomycete yeasts are not ubiquitous across all lichens.

Lichens are fungi that enter into obligate symbioses with photosynthesizing organisms (algae, cyanobacteria). Traditional narratives of lichens as binary symbiont pairs have given way to their recognition as dynamic metacommunities. Basidiomycete yeasts, particularly of the genus Cyphobasidium, have been inferred to be widespread and important components of lichen metacommunities. Yet, the presence of basidiomycete yeasts across a wide diversity of lichen lineages has not previously been tested. We searched for lichen-associated cystobasidiomycete yeasts in newly generated metagenomic data from 413 samples of 339 lichen species spanning 57 families and 25 orders. The data set was generated as part of a large-scale project to study lichen biodiversity gradients in the southern Appalachian Mountains Biodiversity Hotspot of southeastern North America. Our efforts detected cystobasidiomycete yeasts in nine taxa (Bryoria nadvornikiana, Heterodermia leucomelos, Lecidea roseotincta, Opegrapha vulgata, Parmotrema hypotropum, P. subsumptum, Usnea cornuta, U. strigosa, and U. subgracilis), representing 2.7% of all species sampled. Seven of these taxa (78%) are foliose (leaf-like) or fruticose (shrubby) lichens that belong to families where basidiomycete yeasts have been previously detected. In several of the nine cases, cystobasidiomycete rDNA coverage was comparable to, or greater than, that of the primary lichen fungus single-copy nuclear genomic rDNA, suggesting sampling artifacts are unlikely to account for our results. Studies from diverse areas of the natural sciences have led to the need to reconceptualize lichens as dynamic metacommunities. However, our failure to detect cystobasidiomycetes in 97.3% (330 species) of the sampled species suggests that basidiomycete yeasts are not ubiquitous in lichens.

Zehneria tuberifera (Cucurbitaceae), a new species from Taita Hills, Kenya

A new plant species in the genus Zehneria (Cucurbitaceae) is here described and illustrated. The species was collected at Taita Hills tropical montane forests in Kenya, a fragment of the larger Eastern Arc Mountains biodiversity hotspot. The new species, Zehneria tuberifera, is similar to Z. oligosperma and Z. longiflora, but distinguished by its tuberous rhizome and subcoriaceous leaf blades. Furthermore, it has scattered bristles along the midrib on the adaxial surface of its young leaf blades, a shorter receptacle tube, a trilobed disk in the male flower, solitary or 2-clustered female flowers, and up-to-20-flowered and subumbelliform male inflorescences.

Invasive tree species detection in the Eastern Arc Mountains biodiversity hotspot using one class classification

Eucalyptus spp. and Acacia mearnsii are common exotic tree species in eastern Africa that have shown (strong) invasive behavior in some regions. Acacia mearnsii is considered a highly invasive species that is replacing native species and Eucalyptus spp. are known to consume high amounts of groundwater with suspected effects on native flora. Mapping the occurrence of these species in the Taita Hills, Kenya (part of the Eastern Arc Mountains Biodiversity Hotspot) is important as there is lack of knowledge on their occurrence and ecological impact in the area. Mapping methods that require a lot of fieldwork are impractical in areas like the Taita Hills, where the terrain is rugged and the infrastructure is poor. Our aim was hence to map the occurrence of these tree species in a 100 km2 area using airborne imaging spectroscopy and laser scanning. We used a one class biased support vector machine (BSVM) classifier as it needs labeled training data only for the positive classes (A. mearnsii and Eucalyptus spp.), which potentially reduces the amount of required fieldwork. We also introduce a new approach for parameterizing and setting the threshold level simultaneously for the BSVM classifier. The second aim was to link the occurrence of these species to selected environmental variables. The results showed that the BSVM classifier is suitable for mapping Acacia mearnsii and Eucalyptus spp., holding the potential to improve the efficiency of field data collection. The introduced parametrization/threshold selection method performed better than other commonly used approaches. The crown level F1-score was 0.76 for Eucalyptus spp. and 0.78 for A. mearnsii. We show that Eucalyptus spp. and A. mearnsii trees cover 0.8% and 1.6% of the study area, respectively. Both species are particularly located on steeper slopes and higher altitudes. Both species have significant occurrences in areas close to the biggest remaining native forest patch (Ngangao) in the study area. Nonetheless, follow-up studies are needed to evaluate their impact on the native flora and fauna, as well as their impact on the water resources. The maps created in this study in combination with such follow-up studies could serve as base data to generate guidelines that authorities can use to take action in handling the problems these species are causing.

Ecosystem change in the South Pare Mountain bloc, Eastern Arc Mountains of Tanzania

Palaeoecological evidence is used to investigate climatic and anthropogenic drivers of vegetation and fire dynamics through the past ~1200 years in the Eastern Arc Mountains, Tanzania. Pollen and charcoal analyses are supported by a chronology derived from five accelerator mass spectrometry ages, a137Cs activity profile and marker horizons from two exotic pollen taxa. Pollen indicator taxa are used to develop a series of environmental indices, and compared with fluctuations in key timber species, and a fire history reconstruction. Prior to AD 1274, the ecosystem is characterised by moist montane forest that is somewhat anomalous with other East African records, providing evidence for the persistence of a mesic environment and ecosystem resilience of the Eastern Arc Mountains. An open drier forest type is recorded from AD 1275 to 1512, resulting from regional aridity; when the aforementioned buffering ability was exceeded and ecosystem resilience curtailed. Maize appears from ~AD 1737, possibly associated with the regional expansion of agriculture to supply the ivory trade. The peak of the caravan trade in the mid-19th century, and later colonial administration, coincides with intensified human impacts, specifically forest clearance suggested by substantial declines in the timber tree Ocotea. Following independence, there are tentative signals of montane forest recovery, which coincide with the establishment of forest reserves, and associated timber bans. Palaeoecological understanding of historical ecosystem change in the Eastern Arc Mountains biodiversity hotspot is vital to build informed conservation and forest management policies for a future characterised by growing human populations coupled with changing climate–ecosystem relationships.

Biogeography of Shangri-la flora in southwestern China

Shangri-la region of southwestern China is within the Hengduan Mountains biodiversity hotspot and is exceptional in floral diversity. Based on intensive field investigations and herbarium specimens, 6807 species of native seed plants from 1297 genera and 166 families were recognized. The flora is dominated by families and genera with cosmopolitan and north temperate distributions, including Apiaceae, Asteraceae, Ericaceae, Fabaceae, Gentianaceae, Lamiaceae, and the genera Pedicularis, Rhododendron, and Salix, which contribute up to 73.15 % of the total number of species, but only make up a small portion of the total number of families and genera. Families and genera with fewer species more commonly have tropical distributions, while East Asian and Chinese endemic families and genera are mostly monotypic and oligotypic, and contribute little to the floristic diversity of the region. It is revealed that the flora of Shangri-la might have evolved through rapid speciation mainly from families and genera of cosmopolitan and north temperate distributions with the uplift of the Himalayas and climatic oscillations after the late Tertiary. The macroevolution of the flora in the Shangri-la region interpreted by floristic patterns is well supported by phylogeographic studies on plant taxa in Hengduan-Qinghai-Tibet Plateau regions.

A 22 570-year record of vegetational and climatic change from Wenhai Lake in the Hengduan Mountains biodiversity hotspot, Yunnan, Southwest China

Abstract. The Hengduan Mountains, with their strong altitudinal vegetation zonation, form a biodiversity hotspot which offers the potential for comparison between sites in order to understand how this zonation arose and how it has responded to climate change and human impacts through time. This paper presents a 22 570-year pollen record of vegetational and climatic change based on a core 320 cm in depth collected from Wenhai Lake on Jade Dragon Snow Mountain, one of the highest peaks in the Hengduan Mountains region of Yunnan, Southwest China. From 22 570 to 21 140 cal yr BP, the vegetation was dominated by broad-leaved forest (comprising mainly Quercus, Betula and Castanopsis), accompanied by needle-leaved forest (mainly Pinus and Abies), indicating a rather cold and dry climate relative to the present followed by cold and wet conditions. In the period between 21 140 and 19 350 cal yr BP, the vegetation was still dominated by broad-leaved forest and needle-leaved forest as before but with a notable increase in Betula pollen and a sharp decrease in Quercus pollen, implying a relatively cold and dry climate with several fluctuations in humidity. The period 19 350 to 17 930 cal yr BP was a transition stage from broad-leaved forest to needle-leaved forest, with a dramatic decrease in Quercus pollen and a maximum reading for Abies pollen, reflecting the coldest and driest climate since 22 570 cal yr BP. The expansion in needle-leaved forest dominated by Pinus and Abies (22 570–17 930 cal yr BP) along with an increase of Betula might correspond to the Last Glacial Maximum (LGM; the start of the LGM perhaps occurred prior to the basal age of the core). Between 17 930 and 9250 cal yr BP, needle-leaved forest declined and broad-leaved forest began to increase at first, suggesting increases in temperature and humidity, while towards the end of the period, needle-leaved forest expanded and broad-leaved forest shrank, indicating a colder and drier climate, possibly corresponding to the Younger Dryas. From 9250 cal yr BP to the present, the vegetation has been dominated by needle-leaved forest (comprising mainly Pinus, Abies and Tsuga), interspersed with broad-leaved Quercus and Betula, reflecting a significant decline in humidity from the early to late Holocene. During this period, human activity likely increased in this region, with impacts on the vegetation such as a distinct decrease in Pinus and Quercus pollen and an increase in Polygonaceae pollen in the upper 30 cm of the core. The marked decline in Quercus pollen compared with the early stage of this period, in particular, in the Wenhai core can be correlated with that observed in the Haligu core (situated about 2 km away) between 2400 cal yr BP and the present.

Floral diversity and community structure in Pedicularis (Orobanchaceae)

A pervasive hypothesis at the interface of ecology and evolution is that biotic interactions contribute to regional biodiversity by accelerating adaptation and speciation. We investigated this question in the context of closely related, bumble bee‐pollinated plants (Pedicularis spp.) in the Hengduan Mountains of south‐central China, where they exhibit spectacular levels of richness, endemism, and floral diversity. Because these species co‐occur frequently, flower synchronously, and share pollinators during the brief reproductive season, we predict that pollinator‐mediated interactions may influence their community assembly and evolutionary diversification. If disparity in floral traits reduces competitive interactions between species, as would happen if floral isolation mitigates reproductive interference caused by heterospecific pollen flow, then species with dissimilar flowers should co‐occur more often, yielding greater floral diversity at local scales than expected by chance. Moreover, if such interactions have repeatedly driven character displacement, then floral traits should exhibit homoplasy, the phylogenetic signature of labile evolution. We present evidence supporting these predictions, and find that local species richness is best explained by a model including both floral diversity and phylogenetic distance. Our results suggest that a dynamic mosaic of pollinator‐mediated interactions among Pedicularis in the Hengduan region promotes ecological sorting through recurrent selection against reproductive interference, causing rapid species turnover at local scales, and accelerating the rate of floral divergence among species. Together these processes may have contributed to the remarkable accumulation of florally diverse species of Pedicularis endemic to the Hengduan Mountains biodiversity hotspot.

Relative stability of core groups in pollination networks in a biodiversity hotspot over four years.

Plants and their pollinators form pollination networks integral to the evolution and persistence of species in communities. Previous studies suggest that pollination network structure remains nested while network composition is highly dynamic. However, little is known about temporal variation in the structure and function of plant-pollinator networks, especially in species-rich communities where the strength of pollinator competition is predicted to be high. Here we quantify temporal variation of pollination networks over four consecutive years in an alpine meadow in the Hengduan Mountains biodiversity hotspot in China. We found that ranked positions and idiosyncratic temperatures of both plants and pollinators were more conservative between consecutive years than in non-consecutive years. Although network compositions exhibited high turnover, generalized core groups – decomposed by a k-core algorithm – were much more stable than peripheral groups. Given the high rate of turnover observed, we suggest that identical plants and pollinators that persist for at least two successive years sustain pollination services at the community level. Our data do not support theoretical predictions of a high proportion of specialized links within species-rich communities. Plants were relatively specialized, exhibiting less variability in pollinator composition at pollinator functional group level than at the species level. Both specialized and generalized plants experienced narrow variation in functional pollinator groups. The dynamic nature of pollination networks in the alpine meadow demonstrates the potential for networks to mitigate the effects of fluctuations in species composition in a high biodiversity area.

Modelling agricultural expansion in Kenya’s Eastern Arc Mountains biodiversity hotspot

The Taita Hills are the northernmost part of the Eastern Arc Mountains of Kenya and Tanzania, which is one of the most important regions for biological conservation in the world. The indigenous cloud forests in this area have suffered substantial degradation for several centuries due to agricultural expansion. In the Taita Hills, currently only 1% of the original forested area remains preserved. In order to create effective policies to preserve the natural resources and biodiversity of the Eastern Arc Mountains it is crucial to understand the causes and interactions involved in the landscape changes in the most degraded areas. The research presented here aimed to understand the role of landscape attributes and infrastructure components as driving forces of agricultural expansion in the Taita Hills. Geospatial technology tools and a landscape dynamic simulation model were integrated to identify and evaluate the driving forces of agricultural expansion and simulate future landscape scenarios. The results indicate that, if current trends persist, agricultural areas will occupy roughly 60% of the study area by 2030. Agricultural expansion will likely take place predominantly in lowlands and foothills throughout the next 20 years, increasing the spatial dependence on distance to rivers and other water bodies. The main factors driving the spatial distribution of new croplands were the distance to markets, proximity to already established agricultural areas and distance to roads. Other driving forces of the agricultural expansion, as well as their implications for natural resources conservation, are discussed. Further studies are necessary to integrate the effects of population pressure and climate change on the sustainability and characteristics of local agricultural systems.

Processes of diversification and dispersion of Rice yellow mottle virus inferred from large‐scale and high‐resolution phylogeographical studies

Phylogeography of Rice yellow mottle virus (RYMV) was reconstructed from the coat protein gene sequences of a selection of 173 isolates from the 14 countries of mainland Africa where the disease occurred and from the full sequences of 16 representative isolates. Genetic variation was linked to geographical distribution and not to host species as isolates from wild rice always clustered with isolates from cultivated rice of the same region. Genetic variation was not associated to agro-ecology, viral interference and insect vector species. Distinct RYMV lineages occurred in East, Central and West Africa, although the Central African lineage included isolates from Benin, Togo and Niger at the west, adjacent to countries of the West African lineage. Genetic subdivision at finer geographical scales was apparent within lineages of Central and West Africa, although less pronounced than in East Africa. Physical obstacles, but also habitat fragmentation, as exemplified by the small low-lying island of Pemba offshore Tanzania mainland, explained strain localization. Three new highly divergent strains were found in eastern Tanzania. By contrast, intensive surveys in Cote d'Ivoire and Guinea at the west of Africa did not reveal any new variant. Altogether, this supported the view that the Eastern Arc Mountains biodiversity hotspot was the centre of origin of RYMV and that the virus spread subsequently from east to west across Africa. In West Africa, specific strains occurred in the Inner Niger Delta and suggested it was a secondary centre of diversification. Processes for diversification and dispersion of RYMV are proposed.