Essential Biodiversity Variables (EBVs) consolidate information from varied biodiversity observation sources. Here we demonstrate the links between data sources, EBVs and indicators and discuss how ...different sources of biodiversity observations can be harnessed to inform EBVs. We classify sources of primary observations into four types: extensive and intensive monitoring schemes, ecological field studies and satellite remote sensing. We characterize their geographic, taxonomic and temporal coverage. Ecological field studies and intensive monitoring schemes inform a wide range of EBVs, but the former tend to deliver short-term data, while the geographic coverage of the latter is limited. In contrast, extensive monitoring schemes mostly inform the population abundance EBV, but deliver long-term data across an extensive network of sites. Satellite remote sensing is particularly suited to providing information on ecosystem function and structure EBVs. Biases behind data sources may affect the representativeness of global biodiversity datasets. To improve them, researchers must assess data sources and then develop strategies to compensate for identified gaps. We draw on the population abundance dataset informing the Living Planet Index (LPI) to illustrate the effects of data sources on EBV representativeness. We find that long-term monitoring schemes informing the LPI are still scarce outside of Europe and North America and that ecological field studies play a key role in covering that gap. Achieving representative EBV datasets will depend both on the ability to integrate available data, through data harmonization and modeling efforts, and on the establishment of new monitoring programs to address critical data gaps.
•Terrestrial biodiversity observations can be organized into four types.•These types differ in taxonomic, geographic, and temporal coverage.•The representativeness of EBV datasets is affected by the underlying types of data.•Global datasets of population abundance are affected by the lack of long-term data.•New monitoring programs must address critical data gaps.
A general understanding of grazing effects on plant diversity in drylands is still missing, despite an extensive theoretical background. Cross-biome syntheses are hindered by the fact that the ...outcomes of disturbance studies are strongly affected by the choice of diversity measures, and the spatial and temporal scales of measurements. The aim of this study is to overcome these weaknesses by applying a wide range of diversity measures to a data set derived from identical sampling in three distinct ecosystems. We analyzed three fence-line contrasts (heavier vs. lighter grazing intensity), representing different degrees of aridity (from arid to semiarid) and precipitation regimes (summer rain vs. winter rain) in southern Africa. We tested the impact of grazing intensity on multiple aspects of plant diversity (species and functional group level, richness and evenness components, alpha and beta diversity, and composition) at two spatial scales, and for both 5-yr means and interannual variability. Heavier grazing reduced total plant cover and substantially altered the species and functional composition at all sites. However, a significant decrease in species alpha diversity was detected at only one of the three sites. By contrast, alpha diversity of plant functional groups responded consistently across ecosystems and scales, with a significant decrease at heavier grazing intensity. The cover-based measures of functional group diversity responded more sensitively and more consistently than functional group richness. Beta diversity of species and functional types increased under heavier grazing, showing that at larger scales, the heterogeneity of the community composition and the functional structure were increased. Heavier grazing mostly increased interannual variability of alpha diversity, while effects on beta diversity and cover were inconsistent. Our results suggest that species diversity alone may not adequately reflect the shifts in vegetation structure that occur in response to increased grazing intensity in the dryland biomes of southern Africa. Compositional and structural changes of the vegetation are better reflected by trait-based diversity measures. In particular, measures of plant functional diversity that include evenness represent a promising tool to detect and quantify disturbance effects on ecosystems.
Circular depressions are concave, shallow depressions found on planar landscape surfaces in the southern Namib Desert. They occur on gravelly substrates with nearly level to very slightly inclined ...surfaces. The depressions range from 6 to 10 m in diameter with centers typically depressed 10–20 cm below the level of the surrounding terrain. Locations of individual circular depressions were mapped at one site using ground-based measurements and at three additional sites using Google Earth imagery. At all sites, circular depressions are highly overdispersed with densities ranging from approximately 10–20/ha and corresponding nearest neighbor distances of 17–24 m. Large fragments of weathered calcrete and stones occur on soil surfaces surrounding circular depressions, but not within the depressions. Circular depressions at one site contained active burrow systems of Brants’ whistling rat (Paratomys brantsii). Bioturbation by these rodents contributes to the non-cohesive nature of the sandy substrate, which promotes aeolian deflation and formation of the depressions. Excavations of the burrow systems by the honey badger (Mellivora capensis) in search of rodent prey can transfer large stones and calcrete fragments from the subsurface to the surface and subsequently move those materials about the surface. Even if such sequential, horizontal displacements are in random directions, such movements can eventually yield a central, clast-free area surrounded by a peripheral zone where the clasts accumulate once they have been displaced beyond the margin of the area to which the predator is drawn in search of rodent prey. A conceptual model consisting of a two-dimensional random walk of large clasts about the surface until they are displaced from the focal “arena” of rodent occupation provides a novel explanation for origin of a spatially organized pattern that is initiated through the random displacement of those materials. Comparable microtopographic patterning associated with bioturbation in other arid and semi-arid environments may have similar origins.
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.
Psammotermes allocerus
Silvestri,
1908
is the only described species representing the genus
Psammotermes
Desneux,
1902
in Southern Africa. The large geographical range of this subterranean termite ...covers both summer and winter rainfall regimes. Deadwood is the preferred food when available, but in more arid habitats, both live and dead grasses form the major dietary component. Along the Namib Desert margins, the species’ localised herbivory creates circular bare patches known as fairy circles. For a regional phylogeographic study of this species, we sampled 65 sand termite populations within drier parts of Namibia, South Africa, and Angola. Based on combined molecular and ecological data, we found considerable genetic diversification within
P. allocerus
. Analyses of two mitochondrial markers (COI, COII), including a Bayesian inference tree, haplotype analysis and genetic distances suggest a delineation into seven highly differentiated genetic groups. The ‘Succulent Karoo’ group is additionally characterised by unique features of the royal chamber, nest and tunnel system. In conclusion, our data suggest that
P. allocerus
should be not regarded as one species but as a species complex. Termites of each analysed group ‘Northern Namib’, ‘Western Kalahari Basin’, ‘Nama’, ‘Southwestern Kalahari’, ‘East Gariep’, ‘Southern Namib’ and ‘Succulent Karoo’ should be considered as distinct species. The species name
P. allocerus
should be used for termites of the ‘Succulent Karoo’.
Land use is known to influence the diversity of vascular plants in the Miombo woodlands. However, little is known about the interaction between soil and land use in herbaceous and woody species. We ...compared the diversity of vascular plants at the plot level (20 m × 50 m) and site level for three sites in the Miombo woodlands of western Zambia subject to different levels of intensity classes of diffuse land use (e.g., livestock herbivory and selective timber harvesting). For each of the sites, twenty plots were randomly selected for assessment of species composition of vascular plant species, indicators of land-use intensity, and soil chemistry per plot. We hypothesized that the site with the lowest human impact would have the highest richness and diversity of woody and herbaceous species. At the site level, we found that richness and diversity of woody species were unaffected by land-use intensity, whereas herbaceous species richness was higher for the protected site (28 species on average per 1000 m2) than the two other sites (23 and 21 species on average per 1000 m2). At the plot level, herbaceous species richness was positively associated with woodcutting and soil pH. We interpret the positive effect of woodcutting on herbaceous species richness as the effect of lower competition by the woody component for resources such as water, nutrients, and light. With regard to the absence of any effect of land-use intensity on the richness of woody species, we conclude that in our study areas selective timber harvesting may be at a sustainable level and might even have a positive effect on the diversity of the herbaceous layer.
1. Circular bare patches occur in high numbers among the vegetation of the Namib Desert margin. There is an ongoing scientific debate on the origin of these so‐called “fairy circles” (FCs). One of ...the most frequently discussed hypotheses regards the bare patches to be the result of localised herbivory by sand termites of the genus Psammotermes (family Rhinotermitidae).
2. In all earlier publications, the fairy circles of the Namib Desert region within their entire range from Angola through Namibia to South Africa were, in principle, regarded to be of one type, albeit increasing in size towards the north. Here we present evidence that at −16.23° latitude there is an abrupt discontinuity which separates the FCs on either side from each other.
3. South of this discontinuity all studied FCs share the properties of the previously described fairy circles in Namibia and South Africa, especially the presence of Psammotermes termites.
4. In contrast, north of −16.23°S the FCs are much larger and are caused by a different and undescribed termite species, most closely related to the harvester termite genus Microhodotermes (family Hodotermitidae). The two sets of fairy circles differ in a specific set of morphological features, associated termites, and soil parameters.
5. The observed juxtaposition of the newly discovered large structures caused by a hodotermitid termite and the Psammotermes FCs caused by a rhinotermitid species is interpreted as an interesting example of convergent evolution resulting in similar ecological structures.
The fairy circles of the Namib Desert show different morphology, north and south of 16.23° southern latitude.
The giant fairy circles in the Angolan Northern Namib Desert are not caused by the sand termite Psammotermes allocerus but by an undescribed new species of the harvester termite family.
The fact that two different types of Namib fairy circles are accompanied by two different termite species supports a termite origin of fairy circles.
Aims
: Gebel Elba is an arid mountain range supporting biological diversity that is incomparable to any other region of Egypt. This mountain has a vegetation structure and floristic community similar ...to the highlands of East Africa and the southwestern Arabian Peninsula. We aimed to provide the first classification of the vegetation units on Gebel Elba and identify the environmental factors controlling their distribution.
Study area
: Wadi Yahmib and its tributaries, which drain the north-western slopes of Gebel Elba, south-eastern Egypt.
Methods
: On the basis of 169 relevés, we used TWINSPAN to classify the perennial vegetation. We calculated separate GAMs for the deciduous and evergreen species to describe the patterns for each leaf strategy type with elevation. We used CCA to quantify the relationship between the perennial vegetation and the studied environmental factors. To estimate diversity and our sampling strategy, we used rarefaction curves for species richness.
Results
: We identified seven communities along the elevational gradient of Wadi Yahmib and its tributaries. We found that each community was restricted to a confined habitat depending on its drought resistance ability. Deciduous
Vachellia
woodland was the main vegetation type on Gebel Elba, while evergreen
Olea
woodland appeared in small fragments at higher elevations. We analysed the distribution patterns of deciduous and evergreen trees along the elevational gradient. We found a turnover at 500 m, indicating a potential ecotone between the
Vachellia
and
Olea
woodlands that was occupied by a
Ficus
community. CCA revealed the importance of altitude and soil quality in determining the vegetation structure of Gebel Elba. The species richness increased with elevation as a result of reduced stress and increased water availability at the upper wadis.
Conclusions
: This study identified seven vegetation units in the study area and showed the importance of orographic precipitation, soil quality and the complex topography in determining the habitats.
Taxonomic reference
: Boulos (2009); names updated according to POWO (2019).
Abbreviations
: CCA = Canonical Correspondence Analysis; GAM = Generalized Additive Model; TWINSPANTWINSPAN = Two Way Indicator Species Analysis.
Aim
This study aimed to predict the alpha and beta plant diversity of an arid mountain based on environmental variables derived from remotely sensed and ground truth data.
Location
Gebel Elba, Egypt.
...Methods
Based on 133 vegetation plots of 100 m2, we calculated alpha (Shannon index) and beta the first ordination axis of nonmetric multidimensional scaling (NMDS1) plant diversity. Generalized additive models (GAMs) were used to map alpha and beta diversity based on various environmental variables derived from a digital elevation model, the SoilGrids dataset, and very high resolution PlanetScope satellite imagery. The predictive models for alpha and beta diversity were mapped within the northern slopes of Gebel Elba. An ANOVA post hoc test was used to compare Shannon index and NMDS1 values among plant communities.
Results
The selected models revealed the importance of altitude, landforms, solar insolation, catchment area, and modified soil‐adjusted vegetation index for Shannon diversity and NMDS1. The GAMs explained 54.9% of Shannon diversity and 80.6% of NMDS1. The predicted diversity maps showed that the mountainous area was more diverse and substantially different from the open desert. The post‐hoc test revealed a clear separation of mountain and desert vegetation.
Conclusions
Employing remotely sensed variables combined with ground truth data offers great opportunities for exploring spatial patterns of biodiversity. By mapping alpha and beta diversity, it was possible to determine the spatial distribution of plant diversity in Gebel Elba; the results highlighted the importance of the wadi systems and higher slopes of this mountain area. We expect our findings can be generalized to similar arid mountains in the region.
In this paper, we have created the first model‐based plant diversity maps for the arid mountain Gebel Elba. We found that topographical parameters and plant productivity played important roles in explaining predictive models of alpha and beta diversity on the northern slopes of this mountain. We expect that our findings can be generalized to similar arid mountains in the region.
In parts of Angola, Namibia and South Africa the sparse vegetation at the margin of the Namib Desert is often dotted with roughly circular bare patches. The origin of these “fairy circles” (FC) is ...subject of an ongoing debate. In a recent article in PPEES, Getzin et al. (2022) provided assessments of grasses and termites combined with soil moisture measurements, in and near to fairy circles in several areas in Namibia. In their interpretation they state that termite herbivory is not causing this grass death as the plants had undamaged roots. Instead they propose that the matrix grasses severely depleted the water in FCs. Here, we use a comprehensive, detailed body of measurements and assessments collated during the last 14 years to propose an alternative interpretation. We structure our interpretation with four statements, each of them based on shown evidence: (1) Long-term soil moisture measurements confirm that the soil beneath the dry topsoil of the bare patch of fairy circles contains an equal or, especially during the biologically active season, higher amount of moisture than the surrounding matrix, at any given time. The grasses of the fairy circles bare patch die during the moist phase of the first weeks after a rain, before even the soil beneath the matrix vegetation gets depleted by transpiration. (2) Within the sandy soils of fairy circle landscapes, there is no sufficiently strong “uptake –diffusion feedback” that could cause a horizontal movement of soil moisture over several meters within a few days. (3) The grasses of the fairy circles bare patch first die at the centre of the bare patch and later towards the margin. (4) The grass in the bare patch of fairy circles dies because of damage to roots due to herbivory by sand termites.
•The soil beneath the fairy circles is the moistest soil compartment in the ecosystem.•The grasses of the fairy circles bare patch die during the moist phase.•The “uptake –diffusion feedback” in the sandy soils of fairy circles is very low.•The fairy circle grasses first die at the centre of the bare patch.•The fairy circle grasses die because of damage to roots due to sand termite herbivory.
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