Field evidence from Namibia does not support the designation of Angolan and Namibian subspecies of<i>Welwitschia mirabilis</i>Hook

Jacobson, Nicholas C.; Jacobson, Peter J.; Jaarsveld, E. Van; Jacobson, Kathryn M.

doi:10.1080/0035919x.2014.950187

Cited by 5 publications

(6 citation statements)

References 10 publications

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“…This ecological difference between northern and central-southern populations could suggest some level of isolation between these two units, someway in agreement with the proposal of two distinct taxa (Leuenberger, 2001). Reasons behind Leuenberger's (Leuenberger, 2001) proposal (i.e., different cone morphology) were confuted by a recent study of Jacobson et al (2014). But, unfortunately, populations from the Namibian northern sub-range were not considered in this study.…”

Section: Discussionsupporting

confidence: 81%

Potential impacts of climate change on Welwitschia mirabilis populations in the Namib Desert, southern Africa

Bombi

2018

J. Arid Land

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Climate change is threatening natural ecosystems in the Earth, and arid regions of southern Africa are particularly exposed to further drying. Welwitschia mirabilis Hook. (Welwitschiaceae) is an unusual gymnosperm tree that is recognized as an icon of the Namib Desert, southern Africa. Many aspects of its biology were investigated in the past, with a special emphasis for its physiology and adaptations, but nothing is known about its potential sensitivity to current climate changes. In this study, we adopted an approach based on distribution data for W. mirabilis and ecological niche models for clarifying the species-climate interactions and for predicting the potential impacts of climate change on W. mirabilis populations in three well-separated sub-ranges (northern, southern and central) in northwestern Namibia, southern Africa. We evidenced that the populations occurring in the northern sub-range have peculiar climatic exigencies compared with those in the central and southern sub-ranges and are particularly exposed to the impact of climate change, which will consist of a substantial increase in temperature across the region. These impacts could be represented by demographic changes that should be detected and monitored detailedly to plan efficient measures for managing populations of this important species on the long-term scale.

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Section: Discussionsupporting

confidence: 81%

Potential impacts of climate change on Welwitschia mirabilis populations in the Namib Desert, southern Africa

Bombi

2018

J. Arid Land

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“…94), there is considerable evidence for recent diversification of desert groups, particularly in the Aizoaceae, which diversified as recently as the Pleistiocene 95 . Arid-adapted C 4 grasses have also diversified widely 96 , and thus significant floristic biodiversity in SSA arid systems is associated with modern atmospheric CO 2 and climatic conditions.…”

Section: Perspectives | Insightmentioning

confidence: 99%

Future of African terrestrial biodiversity and ecosystems under anthropogenic climate change

2015

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A frican ecosystems and biodiversity are biologically and ecologically unique, attract substantial tourism revenue, and provide significant ecosystem services at local, regional and global levels. It is projected that anthropogenic climate change is likely to have adverse impacts on African ecosystems and their biodiversity 1 , but projections of impacts based on a range of methodologies diverge widely. This is partly due to contrasting scenarios of future precipitation, but much more importantly due to critical differences between approaches to modelling biodiversity impacts and their assumptions. These differences relate to the extent to which different modelling approaches incorporate the effects of atmospheric CO 2 and disturbance (fire, mammal herbivory) on ecosystem structure and productivity 2,3 , and relative strengths in accounting for temperature-versus water-related controls on biodiversity. Projections of large declines in biodiversity under combined scenarios of climate and socioeconomic development 4,5 may not take these uncertainties into account. The most recent report by the IPCC on African vegetation change 1 reflects this well in stating with high confidence that "substantial uncertainties are inherent in these projections [future changes in terrestrial ecosystems] because vegetation across much of the continent is not deterministically driven by climate alone".These issues require urgent resolution, because there are significant and immediate implications for biodiversity risk assessments, and adaptation and mitigation responses relevant for policymakers and land managers. The evidence necessary to resolve these divergences is indicative but far from adequate, primarily because of a dire lack of empirical evidence and information on both climate and atmospheric CO 2 impacts on the structure and function of waterlimited and disturbance-dependent ecosystems in tropical and subtropical climates 6,7 .More than any other continent, Africa's ecosystems are water limited 8 and disturbance driven (by wildfire and mega-herbivores) 9 , with a high representation of C 4 grass-dominated ecosystems 10,11 . Palaeoecological changes in climate and atmospheric CO 2 since the Miocene have strongly shaped the vegetation, disturbance regimes and biodiversity of these ecosystems 12 . Because the continent straddles the tropics and subtropics in both hemispheres, an enormous area over which climatic conditions are conducive to vegetation flammability emerged during the late Miocene 13 . The Projections of ecosystem and biodiversity change for Africa under climate change diverge widely. More than other continents, Africa has disturbance-driven ecosystems that diversified under low Neogene CO 2 levels, in which flammable fire-dependent C 4 grasses suppress trees, and mega-herbivore action alters vegetation significantly. An important consequence is metastability of vegetation state, with rapid vegetation switches occurring, some driven by anthropogenic CO 2 -stimulated release of trees from disturbance control. Thes...

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“…The present diversity is minimal. Though the diversification of gene pools is clearly visible at the molecular level, it is hard to distinguish even the two subspecies morphologically in the field, whereas cultivation under identical conditions did allow us to distinguish the two subspecies 7,8 . This relatively low level of diversification could support the hypothesis that only one common ancestor settled the refuge and has since diversified at a slow rate.…”

Section: Adaptive Diversification Within the Refuge?mentioning

confidence: 99%

“…Leuenberger observed morphological differences in the male strobili (cone length, color and wax cover, surface sculpturing, bract morphology and connation, peduncle length) and allopatric distribution of greenhouse plants of the dioecious species cultivated under identical conditions. Jacobson et al 8 questioned the validity of the two subspecies but studied only populations belonging to the Namibian subspecies. Therefore, their results neither support nor reject Leuenberger’s proposal.…”

Section: Introductionmentioning

confidence: 99%

“…For Angola, Kers based the map records on Taborda de Morais 12 , who mentioned a population 8 km NE of the Rio de Sao Nicolau (= Rio Bentiaba), which is at 14.26°S. Jacobson et al 8 reported a N limit south of the Bentiaba River, while Henschel et al 13 reported 14.9°S, which is close to Moçâmedes (Namibé) at the latitude of Moscas Bay/Baba. Kers 11 interpreted the biogeography as disjunct: “Most of the localities are so clearly separated from each other geographically that it is not even possible to imagine a gene exchange between them.” Giess 14 published a few additional locations.…”

Section: Introductionmentioning

confidence: 99%

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Welwitschia: Phylogeography of a living fossil, diversified within a desert refuge

Jürgens

Oncken

Oldeland

et al. 2021

Sci Rep

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Welwitschia mirabilis is one of the most extraordinary plant species on earth. With a fossil record of 112 My and phylogenetically isolated within the order Gnetales, the monotypic genus Welwitschia has survived only in the northern Namib Desert in Angola and Namibia. Despite its iconic role, the biogeography, ecological niche, and evolutionary history of the species remain poorly understood. Here we present the first comprehensive map of the strongly disjunct species range, and we explore the genetic relationships among all range fragments based on six SSR markers. We also assess the variation of the environmental niche and habitat preference. Our results confirm genetic divergence, which is consistent with the hypothetical existence of two subspecies within Welwitschia. We identify an efficient geographical barrier separating two gene pools at 18.7°S in northern Namibia. We also identify further diversification within each of the two subspecies, with several different gene pools in ten isolated range fragments. Given the presence of well-isolated populations with unique gene pools and the association with different bioclimatic variables, rock types, and habitats within arid river catchments, we can hypothesize that the present intraspecific diversity may have evolved at least in part within the present refuge of the northern Namib Desert.

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Field evidence from Namibia does not support the designation of Angolan and Namibian subspecies ofWelwitschia mirabilisHook

Cited by 5 publications

References 10 publications

Potential impacts of climate change on Welwitschia mirabilis populations in the Namib Desert, southern Africa

Potential impacts of climate change on Welwitschia mirabilis populations in the Namib Desert, southern Africa

Future of African terrestrial biodiversity and ecosystems under anthropogenic climate change

Welwitschia: Phylogeography of a living fossil, diversified within a desert refuge

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