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  • 1
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    Fire and simulated herbivory have antagonistic effects on resistance of savanna grasslands to alien shrub invasion
    Wiley ; 2015
    In:  Journal of Vegetation Science Vol. 26, No. 1 ( 2015-01), p. 114-122
    Details
    In: Journal of Vegetation Science, Wiley, Vol. 26, No. 1 ( 2015-01), p. 114-122
    Abstract: Resistance of the native community has been identified as an important factor limiting invasion success and invader impact. However, to what extent resistance interacts with disturbance to control invasion success remains unclear. We studied the interaction between biotic resistance, fire and small‐scale disturbances mimicking those of large mammalian herbivores (hoof action and grazing) on invasion success of the alien shrub C hromolaena odorata . Location Hluhluwe‐iMfolozi Park, South Africa. Methods We performed a seedling transplant experiment in a savanna grassland. We manipulated the grass layer by clipping (grazing), created small‐scale soil disturbances (hoof action) and transplanted seedlings under native tree canopies to assess potential nursing effects. Subsequently, we burned half of our plots. We assessed the effect of fire and small‐scale disturbances on seedling growth, survival and biomass allocation. Results Seedling survival of C . odorata was 26% in undisturbed savanna grassland, reducing to 5% post‐fire. Small‐scale disturbances increased seedling biomass and survival and modified biomass allocation, whereas fire greatly reduced seedling survival. Root allocation increased in response to grass clipping, while stem allocation decreased. Tree shading increased seedling survival in the absence of fire, but greatly reduced post‐fire survival. Conclusions Grass communities in savannas exert a high level of biotic resistance to C . odorata invasion. However, small‐scale disturbances, mimicking those of large mammalian herbivores, can facilitate the invasion of C . odorata in savanna grassland both directly, by creating micro‐sites for establishment, and indirectly, by reducing the negative effect of fire. Thus, small‐scale disturbances may aid the long‐term persistence of woody species invading grass‐dominated systems.
    Type of Medium: Online Resource
    ISSN: 1100-9233 , 1654-1103
    URL: Issue
    URL: Article
    DOI: 10.1111/jvs.2015.26.issue-1
    DOI: 10.1111/jvs.12208
    RVK:
    WA 15000
    Language: English
    Publisher: Wiley
    Publication Date: 2015
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  • 2
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    A sharp floristic discontinuity revealed by the biogeographic regionalization of African savannas
    Wiley ; 2019
    In:  Journal of Biogeography Vol. 46, No. 2 ( 2019-02), p. 454-465
    Details
    In: Journal of Biogeography, Wiley, Vol. 46, No. 2 ( 2019-02), p. 454-465
    Abstract: In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas. Location We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18° N to 33° S and from 17° W to 48° E. Taxa We focused on native woody species. Methods We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis‐)similarity‐based approach. Results We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro‐units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/West macro‐unit and the South/East macro‐unit. This floristic discontinuity matches to the High (i.e. N & W) and Low (S & E) division of Africa previously proposed by White ( ) and which tracks climatic and topographical variation. In the N & W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S & E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African. Main conclusions The proposed pan‐African classification of savannas and woodlands might assist the development of coordinated management and conservation policies.
    Type of Medium: Online Resource
    ISSN: 0305-0270 , 1365-2699
    URL: Issue
    URL: Article
    DOI: 10.1111/jbi.2019.46.issue-2
    DOI: 10.1111/jbi.13475
    Language: English
    Publisher: Wiley
    Publication Date: 2019
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  • 3
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    Structural diversity and tree density drives variation in the biodiversity–ecosystem function relationship of woodlands and savannas
    Wiley ; 2021
    In:  New Phytologist Vol. 232, No. 2 ( 2021-10), p. 579-594
    Details
    In: New Phytologist, Wiley, Vol. 232, No. 2 ( 2021-10), p. 579-594
    Abstract: Positive biodiversity–ecosystem function relationships (BEFRs) have been widely documented, but it is unclear if BEFRs should be expected in disturbance‐driven systems. Disturbance may limit competition and niche differentiation, which are frequently posited to underlie BEFRs. We provide the first exploration of the relationship between tree species diversity and biomass, one measure of ecosystem function, across southern African woodlands and savannas, an ecological system rife with disturbance from fire, herbivores and humans. We used 〉 1000 vegetation plots distributed across 10 southern African countries and structural equation modelling to determine the relationship between tree species diversity and above‐ground woody biomass, accounting for interacting effects of resource availability, disturbance by fire, tree stem density and vegetation type. We found positive effects of tree species diversity on above‐ground biomass, operating via increased structural diversity. The observed BEFR was highly dependent on organismal density, with a minimum threshold of c . 180 mature stems ha −1 . We found that water availability mainly affects biomass indirectly, via increasing species diversity. The study underlines the close association between tree diversity, ecosystem structure, environment and function in highly disturbed savannas and woodlands. We suggest that tree diversity is an under‐appreciated determinant of wooded ecosystem structure and function.
    Type of Medium: Online Resource
    ISSN: 0028-646X , 1469-8137
    URL: Issue
    URL: Article
    DOI: 10.1111/nph.v232.2
    DOI: 10.1111/nph.17639
    Language: English
    Publisher: Wiley
    Publication Date: 2021
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    detail.hit.zdb_id: 1472194-6
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  • 4
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    Circum‐Arctic distribution of chemical anti‐herbivore compounds suggests biome‐wide trade‐off in defence strategies in Arctic shrubs
    Wiley ; 2022
    In:  Ecography Vol. 2022, No. 11 ( 2022-11)
    Details
    In: Ecography, Wiley, Vol. 2022, No. 11 ( 2022-11)
    Abstract: Spatial variation in plant chemical defence towards herbivores can help us understand variation in herbivore top–down control of shrubs in the Arctic and possibly also shrub responses to global warming. Less defended, non‐resinous shrubs could be more influenced by herbivores than more defended, resinous shrubs. However, sparse field measurements limit our current understanding of how much of the circum‐Arctic variation in defence compounds is explained by taxa or defence functional groups (resinous/non‐resinous). We measured circum‐Arctic chemical defence and leaf digestibility in resinous ( Betula glandulosa , B. nana ssp. exilis ) and non‐resinous ( B. nana ssp. nana , B. pumila ) shrub birches to see how they vary among and within taxa and functional groups. Using liquid chromatography–mass spectrometry (LC–MS) metabolomic analyses and in vitro leaf digestibility via incubation in cattle rumen fluid, we analysed defence composition and leaf digestibility in 128 samples from 44 tundra locations. We found biogeographical patterns in anti‐herbivore defence where mean leaf triterpene concentrations and twig resin gland density were greater in resinous taxa and mean concentrations of condensing tannins were greater in non‐resinous taxa. This indicates a biome‐wide trade‐off between triterpene‐ or tannin‐dominated defences. However, we also found variations in chemical defence composition and resin gland density both within and among functional groups (resinous/non‐resinous) and taxa, suggesting these categorisations only partly predict chemical herbivore defence. Complex tannins were the only defence compounds negatively related to in vitro digestibility, identifying this previously neglected tannin group as having a potential key role in birch anti‐herbivore defence. We conclude that circum‐Arctic variation in birch anti‐herbivore defence can be partly derived from biogeographical distributions of birch taxa, although our detailed mapping of plant defence provides more information on this variation and can be used for better predictions of herbivore effects on Arctic vegetation.
    Type of Medium: Online Resource
    ISSN: 0906-7590 , 1600-0587
    URL: Issue
    URL: Article
    DOI: 10.1111/ecog.v2022.i11
    DOI: 10.1111/ecog.06166
    Language: English
    Publisher: Wiley
    Publication Date: 2022
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  • 5
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    Precipitation gradients drive high tree species turnover in the woodlands of eastern and southern Africa
    Wiley ; 2023
    In:  Ecography
    Details
    In: Ecography, Wiley
    Abstract: Savannas cover one‐fifth of the Earth's surface, harbour substantial biodiversity, and provide a broad range of ecosystem services to hundreds of millions of people. The community composition of trees in tropical moist forests varies with climate, but whether the same processes structure communities in disturbance‐driven savannas remains relatively unknown. We investigate how biodiversity is structured over large environmental and disturbance gradients in woodlands of eastern and southern Africa. We use tree inventory data from the Socio‐Ecological Observatory for Studying African Woodlands (SEOSAW) network, covering 755 ha in a total of 6780 plots across nine countries of eastern and southern Africa, to investigate how alpha, beta, and phylogenetic diversity varies across environmental and disturbance gradients. We find strong climate‐richness patterns, with precipitation playing a primary role in determining patterns of tree richness and high turnover across these savannas. Savannas with greater rainfall contain more tree species, suggesting that low water availability places distributional limits on species, creating the observed climate‐richness patterns. Both fire and herbivory have minimal effects on tree diversity, despite their role in determining savanna distribution and structure. High turnover of tree species, genera, and families is similar to turnover in seasonally dry tropical forests of the Americas, suggesting this is a feature of semiarid tree floras. The greater richness and phylogenetic diversity of wetter plots shows that broad‐scale ecological patterns apply to disturbance‐driven savanna systems. High taxonomic turnover suggests that savannas from across the regional rainfall gradient should be protected if we are to maximise the conservation of unique tree communities.
    Type of Medium: Online Resource
    ISSN: 0906-7590 , 1600-0587
    URL: Article
    DOI: 10.1111/ecog.06720
    Language: English
    Publisher: Wiley
    Publication Date: 2023
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    detail.hit.zdb_id: 1112659-0
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  • 6
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    The generality of cryptic dietary niche differences in diverse large-herbivore assemblages
    Proceedings of the National Academy of Sciences ; 2022
    In:  Proceedings of the National Academy of Sciences Vol. 119, No. 35 ( 2022-08-30)
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 119, No. 35 ( 2022-08-30)
    Abstract: Ecological niche differences are necessary for stable species coexistence but are often difficult to discern. Models of dietary niche differentiation in large mammalian herbivores invoke the quality, quantity, and spatiotemporal distribution of plant tissues and growth forms but are agnostic toward food plant species identity. Empirical support for these models is variable, suggesting that additional mechanisms of resource partitioning may be important in sustaining large-herbivore diversity in African savannas. We used DNA metabarcoding to conduct a taxonomically explicit analysis of large-herbivore diets across southeastern Africa, analyzing ∼4,000 fecal samples of 30 species from 10 sites in seven countries over 6 y. We detected 893 food plant taxa from 124 families, but just two families—grasses and legumes—accounted for the majority of herbivore diets. Nonetheless, herbivore species almost invariably partitioned food plant taxa; diet composition differed significantly in 97% of pairwise comparisons between sympatric species, and dissimilarity was pronounced even between the strictest grazers (grass eaters), strictest browsers (nongrass eaters), and closest relatives at each site. Niche differentiation was weakest in an ecosystem recovering from catastrophic defaunation, indicating that food plant partitioning is driven by species interactions, and was stronger at low rainfall, as expected if interspecific competition is a predominant driver. Diets differed more between browsers than grazers, which predictably shaped community organization: Grazer-dominated trophic networks had higher nestedness and lower modularity. That dietary differentiation is structured along taxonomic lines complements prior work on how herbivores partition plant parts and patches and suggests that common mechanisms govern herbivore coexistence and community assembly in savannas.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.2204400119
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2022
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  • 7
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    Restoration of a megaherbivore: landscape‐level impacts of white rhinoceros in K ruger N ational P ark, S outh A frica
    Wiley ; 2014
    In:  Journal of Ecology Vol. 102, No. 3 ( 2014-05), p. 566-575
    Details
    In: Journal of Ecology, Wiley, Vol. 102, No. 3 ( 2014-05), p. 566-575
    Abstract: Megaherbivores have been lost from most ecosystems world‐wide, and current increases in poaching of rhino and elephant spp. threaten their status in the systems where they still occur. Although megaherbivores are said to be key drivers of ecosystem structure and functioning, empirical evidence is strongly biased to studies on A frican elephant. We urgently need a better understanding of the impact of other megaherbivore species to predict the consequences of megaherbivore loss. We used a unique ‘recolonization experiment’ to test how a megagrazer, white rhinoceros, is affecting the structure of savanna grasslands in K ruger N ational P ark ( KNP ). With a 30‐year record of rhinoceros distribution, we quantified how they recolonized KNP following their re‐introduction. This allowed us to identify landscapes with high rhino densities and long time since recolonization versus landscapes with low rhino densities that were recolonized more recently but were otherwise biophysically similar. We recorded grassland heterogeneity on 40 transects covering a total of 30 km distributed across both landscapes. We used two proxies of grassland heterogeneity: % short grass cover and number of grazing lawn patches. Grazing lawns are patches with specific communities of prostrate‐growing stoloniferous short grass species. Short grass cover was clearly higher in the high rhino impact (17.5%) than low rhino impact landscape (10.7%). Moreover, we encountered ~20 times more grazing lawns in the high rhino impact landscape. The effect of rhino on number of lawns and on short grass cover was similar to the two dominant geologies in KNP , basalt‐derived versus granite‐derived soils. Synthesis . We provide empirical evidence that white rhinoceros may have started to change the structure and composition of KNP 's savanna grasslands. It remains to be tested if these changes lead to other ecological cascading effects. However, our results highlight that the current rhino poaching crisis may not only affect the species, but also threaten the potential key role of this megaherbivore as a driver of savanna functioning.
    Type of Medium: Online Resource
    ISSN: 0022-0477 , 1365-2745
    URL: Issue
    URL: Article
    DOI: 10.1111/jec.2014.102.issue-3
    DOI: 10.1111/1365-2745.12218
    Language: English
    Publisher: Wiley
    Publication Date: 2014
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  • 8
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    Contrasting impacts of an alien invasive shrub on mammalian savanna herbivores revealed on a landscape scale
    Wiley ; 2017
    In:  Diversity and Distributions Vol. 23, No. 6 ( 2017-06), p. 656-666
    Details
    In: Diversity and Distributions, Wiley, Vol. 23, No. 6 ( 2017-06), p. 656-666
    Abstract: Habitat loss and fragmentation is one of the main drivers of defaunation, that is the loss of large mammals. Biological invasions could be drivers of such phenomenon. However, their impact on large herbivore communities has not been studied to our knowledge. We made use of a landscape‐scale control programme of one of the world's worst invaders, the shrub Chromolaena odorata , as a natural experiment to assess how this alien invader affects habitat use by 14 species of ungulates in an African savanna. Location Hluhluwe‐ iM folozi Park, KwaZulu‐Natal, South Africa. Methods At the height of the invasion in 2004, a large‐scale control programme was initiated that successfully reduced densities of C. odorata across the park. We estimated mammalian herbivore habitat and patch use by dung counts and the presence and density of C. odorata along 24 line transects with a total length of 190 km during the peak of the invasion (2004) and a decade after the initiation of a successful control programme (2014). To account for differences in herbivore assemblies between habitats and the preferential invasion of closed savanna woodlands, we analysed the recolonization of previously invaded patches by herbivores based on the change in dung abundance. Results Herbivore species differed in how they responded to invaded patches of this non‐native shrub. Grazers were the most negatively affected, especially those that avoid predators by running. Browsers were negatively impacted only at the highest invasive shrub densities. Some species, especially bushpig, positively selected invaded patches. Main conclusions Large herbivores varied in their response to invasion with differences in impact depending on feeding strategy and predator avoidance strategy, but the majority of ungulates responded positively to the removal of this invasive shrub.
    Type of Medium: Online Resource
    ISSN: 1366-9516 , 1472-4642
    URL: Issue
    URL: Article
    DOI: 10.1111/ddi.2017.23.issue-6
    DOI: 10.1111/ddi.12547
    Language: English
    Publisher: Wiley
    Publication Date: 2017
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  • 9
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    Linking functional traits to impacts of invasive plant species: a case study
    Springer Science and Business Media LLC ; 2015
    In:  Plant Ecology Vol. 216, No. 2 ( 2015-2), p. 293-305
    Details
    In: Plant Ecology, Springer Science and Business Media LLC, Vol. 216, No. 2 ( 2015-2), p. 293-305
    Type of Medium: Online Resource
    ISSN: 1385-0237 , 1573-5052
    URL: Article
    DOI: 10.1007/s11258-014-0437-5
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2015
    detail.hit.zdb_id: 1364679-5
    detail.hit.zdb_id: 1479167-5
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  • 10
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    Plant traits poorly predict winner and loser shrub species in a warming tundra biome
    Springer Science and Business Media LLC ; 2023
    In:  Nature Communications Vol. 14, No. 1 ( 2023-06-28)
    Details
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 14, No. 1 ( 2023-06-28)
    Abstract: Climate change is leading to species redistributions. In the tundra biome, shrubs are generally expanding, but not all tundra shrub species will benefit from warming. Winner and loser species, and the characteristics that may determine success or failure, have not yet been fully identified. Here, we investigate whether past abundance changes, current range sizes and projected range shifts derived from species distribution models are related to plant trait values and intraspecific trait variation. We combined 17,921 trait records with observed past and modelled future distributions from 62 tundra shrub species across three continents. We found that species with greater variation in seed mass and specific leaf area had larger projected range shifts, and projected winner species had greater seed mass values. However, trait values and variation were not consistently related to current and projected ranges, nor to past abundance change. Overall, our findings indicate that abundance change and range shifts will not lead to directional modifications in shrub trait composition, since winner and loser species share relatively similar trait spaces.
    Type of Medium: Online Resource
    ISSN: 2041-1723
    URL: Article
    DOI: 10.1038/s41467-023-39573-4
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2553671-0
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