@article{LohmannTietjenBlaumetal.2012, author = {Lohmann, Dirk and Tietjen, Britta and Blaum, Niels and Joubert, David F. and Jeltsch, Florian}, title = {Shifting thresholds and changing degradation patterns: climate change effects on the simulated long-term response of a semi-arid savanna to grazing}, series = {Journal of applied ecology : an official journal of the British Ecological Society}, volume = {49}, journal = {Journal of applied ecology : an official journal of the British Ecological Society}, number = {4}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0021-8901}, doi = {10.1111/j.1365-2664.2012.02157.x}, pages = {814 -- 823}, year = {2012}, abstract = {1. The complex, nonlinear response of dryland systems to grazing and climatic variations is a challenge to management of these lands. Predicted climatic changes will impact the desertification of drylands under domestic livestock production. Consequently, there is an urgent need to understand the response of drylands to grazing under climate change. 2. We enhanced and parameterized an ecohydrological savanna model to assess the impacts of a range of climate change scenarios on the response of a semi-arid African savanna to grazing. We focused on the effects of temperature and CO2 level increase in combination with changes in inter- and intra-annual precipitation patterns on the long-term dynamics of three major plant functional types. 3. We found that the capacity of the savanna to sustain livestock grazing was strongly influenced by climate change. Increased mean annual precipitation and changes in intra-annual precipitation pattern have the potential to slightly increase carrying capacities of the system. In contrast, decreased precipitation, higher interannual variation and temperature increase are leading to a severe decline of carrying capacities owing to losses of the perennial grass biomass. 4. Semi-arid rangelands will be at lower risk of shrub encroachment and encroachment will be less intense under future climatic conditions. This finding holds in spite of elevated levels of atmospheric CO2 and irrespective of changes in precipitation pattern, because of the drought sensitivity of germination and establishment of encroaching species. 5. Synthesis and applications. Changes in livestock carrying capacities, both positive and negative, mainly depend on the highly uncertain future rainfall conditions. However, independent of the specific changes, shrub encroachment becomes less likely and in many cases less severe. Thus, managers of semi-arid rangelands should shift their focus from woody vegetation towards perennial grass species as indicators for rangeland degradation. Furthermore, the resulting reduced competition from woody vegetation has the potential to facilitate ecosystem restoration measures such as re-introduction of desirable plant species that are only little promising or infeasible under current climatic conditions. On a global scale, the reductions in standing biomass resulting from altered degradation dynamics of semi-arid rangelands can have negative impacts on carbon sequestration.}, language = {en} } @article{BlaumSchwagerWichmannetal.2012, author = {Blaum, Niels and Schwager, Monika and Wichmann, Matthias C. and Rossmanith, Eva}, title = {Climate induced changes in matrix suitability explain gene flow in a fragmented landscape - the effect of interannual rainfall variability}, series = {Ecography : pattern and diversity in ecology ; research papers forum}, volume = {35}, journal = {Ecography : pattern and diversity in ecology ; research papers forum}, number = {7}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0906-7590}, doi = {10.1111/j.1600-0587.2011.07154.x}, pages = {650 -- 660}, year = {2012}, abstract = {In fragmented landscapes, the survival of species and the maintenance of populations with healthy genetic structures will largely depend on movement/dispersal of organisms across matrix areas. In this article, we highlight that effects of fragmentation and climate change occur simultaneously and may enhance or mitigate each other. We systematically analyzed the effect of increasing interannual variation in rainfall on the genetic structure of two neighbouring small mammal subpopulations in a fragmented savanna landscape. The effect of interannual rainfall variation is analyzed for two contrasting scenarios that differ in mean annual rainfall and are both close to a dispersal threshold. Scenario 1 (low mean annual rainfall) lies slightly below this threshold and scenario 2 (high mean annual rainfall) slightly above, i.e. the amount of rainfall in an average rainfall year prevents dispersal in scenario 1, but promotes gene flow in scenario 2. We show that the temporal dynamics of the matrix was crucial for gene flow and the genetic structure of the neighbouring small mammal subpopulations. The most important result is that the increase in rainfall variability could both increase and decrease the genetic difference between the subpopulations in a complex pattern, depending on the scenario and on the amount of variation in rainfall. Finally, we discuss that the relevance of the matrix as temporarily suitable habitat may become a key aspect for biodiversity conservation. We conclude to incorporate temporal changes in matrix suitability in metapopulation theory since local extinctions, gene flow and re-colonization are likely to be affected in fragmented landscapes with such dynamic matrix areas.}, language = {en} } @article{StieglerKiemelEccardetal.2021, author = {Stiegler, Jonas and Kiemel, Katrin and Eccard, Jana and Fischer, Christina and Hering, Robert and Ortmann, Sylvia and Strigl, Lea and Tiedemann, Ralph and Ullmann, Wiebke and Blaum, Niels}, title = {Seed traits matter}, series = {Ecology and evolution}, volume = {11}, journal = {Ecology and evolution}, number = {24}, publisher = {Wiley}, address = {Hoboken}, issn = {2045-7758}, doi = {10.1002/ece3.8440}, pages = {18477 -- 18491}, year = {2021}, abstract = {Although many plants are dispersed by wind and seeds can travel long distances across unsuitable matrix areas, a large proportion relies on co-evolved zoochorous seed dispersal to connect populations in isolated habitat islands. Particularly in agricultural landscapes, where remaining habitat patches are often very small and highly isolated, mobile linkers as zoochorous seed dispersers are critical for the population dynamics of numerous plant species. However, knowledge about the quali- or quantification of such mobile link processes, especially in agricultural landscapes, is still limited. In a controlled feeding experiment, we recorded the seed intake and germination success after complete digestion by the European brown hare (Lepus europaeus) and explored its mobile link potential as an endozoochoric seed disperser. Utilizing a suite of common, rare, and potentially invasive plant species, we disentangled the effects of seed morphological traits on germination success while controlling for phylogenetic relatedness. Further, we measured the landscape connectivity via hares in two contrasting agricultural landscapes (simple: few natural and semi-natural structures, large fields; complex: high amount of natural and semi-natural structures, small fields) using GPS-based movement data. With 34,710 seeds of 44 plant species fed, one of 200 seeds (0.51\%) with seedlings of 33 species germinated from feces. Germination after complete digestion was positively related to denser seeds with comparatively small surface area and a relatively slender and elongated shape, suggesting that, for hares, the most critical seed characteristics for successful endozoochorous seed dispersal minimize exposure of the seed to the stomach and the associated digestive system. Furthermore, we could show that a hare's retention time is long enough to interconnect different habitats, especially grasslands and fields. Thus, besides other seed dispersal mechanisms, this most likely allows hares to act as effective mobile linkers contributing to ecosystem stability in times of agricultural intensification, not only in complex but also in simple landscapes.}, language = {en} } @article{SchererJeltschGrimmetal.2016, author = {Scherer, Cedric and Jeltsch, Florian and Grimm, Volker and Blaum, Niels}, title = {Merging trait-based and individual-based modelling: An animal functional type approach to explore the responses of birds to climatic and land use changes in semi-arid African savannas}, series = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, volume = {326}, journal = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-3800}, doi = {10.1016/j.ecolmodel.2015.07.005}, pages = {75 -- 89}, year = {2016}, abstract = {Climate change and land use management practices are major drivers of biodiversity in terrestrial ecosystems. To understand and predict resulting changes in community structures, individual-based and spatially explicit population models are a useful tool but require detailed data sets for each species. More generic approaches are thus needed. Here we present a trait-based functional type approach to model savanna birds. The aim of our model is to explore the response of different bird functional types to modifications in habitat structure. The functional types are characterized by different traits, in particular body mass, which is related to life-history traits (reproduction and mortality) and spatial scales (home range area and dispersal ability), as well as the use of vegetation structures for foraging and nesting, which is related to habitat quality and suitability. We tested the performance of the functional types in artificial landscapes varying in shrub:grass ratio and clumping intensity of shrub patches. We found that an increase in shrub encroachment and a decrease in habitat quality caused by land use mismanagement and climate change endangered all simulated bird functional types. The strength of this effect was related to the preferred habitat. Furthermore, larger-bodied insectivores and omnivores were more prone to extinction due to shrub encroachment compared to small-bodied species. Insectivorous and omnivorous birds were more sensitive to clumping intensity of shrubs whereas herbivorous and carnivorous birds were most affected by a decreasing amount of grass cover. From an applied point of view, our findings emphasize that policies such as woody plant removal and a reduction in livestock stocking rates to prevent shrub encroachment should prioritize the enlargement of existing grassland patches. Overall, our results show that the combination of an individual-based modelling approach with carefully defined functional types can provide a powerful tool for exploring biodiversity responses to environmental changes. Furthermore, the increasing accumulation of worldwide data sets on species' core and soft traits (surrogates to determine core traits indirectly) on one side and the refinement of conceptual frameworks for animal functional types on the other side will further improve functional type approaches which consider the sensitivities of multiple species to climate change, habitat loss, and fragmentation.}, language = {en} } @article{BlumroederEccardBlaum2012, author = {Blumroeder, J. and Eccard, Jana and Blaum, Niels}, title = {Behavioural flexibility in foraging mode of the spotted sand lizard (Pedioplanis l. lineoocellata) seems to buffer negative impacts of savanna degradation}, series = {Journal of arid environments}, volume = {77}, journal = {Journal of arid environments}, number = {2}, publisher = {Elsevier}, address = {London}, issn = {0140-1963}, doi = {10.1016/j.jaridenv.2011.10.005}, pages = {149 -- 152}, year = {2012}, abstract = {In this field experiment we investigate the impact of land use induced savanna degradation on movement behaviour of the spotted sand lizard (Pedioplanis l. lineoocellata) in the southern Kalahari. Foraging behaviour of lizards was tested in a factorial design (low vs. high prey availability) in degraded and non-degraded habitats. An interaction between habitat structure and prey availability affected movement behaviour. In degraded habitats with low prey availability and in non-degraded habitats with high prey availability the spotted sand lizard moved more like an active forager. In contrast, in degraded habitats with high prey availability and in non-degraded habitats with low prey availability lizards moved like sit-and-wait foragers. Interestingly, the behavioural flexibility of the spotted sand lizard seems to buffer extreme conditions and negative effects of land use impacts.}, language = {en} } @article{LohmannTietjenBlaumetal.2014, author = {Lohmann, Dirk and Tietjen, Britta and Blaum, Niels and Joubert, David Francois and Jeltsch, Florian}, title = {Prescribed fire as a tool for managing shrub encroachment in semi-arid savanna rangelands}, series = {Journal of arid environments}, volume = {107}, journal = {Journal of arid environments}, publisher = {Elsevier}, address = {London}, issn = {0140-1963}, doi = {10.1016/j.jaridenv.2014.04.003}, pages = {49 -- 56}, year = {2014}, abstract = {Savanna rangelands worldwide are threatened by shrub encroachment, i.e. the increase of woody plant species at the cost of perennial grasses, causing a strong decline in the productivity of domestic livestock production. Although recent studies indicate that fire might be of great importance for semi-arid and arid savanna dynamics, it is largely not applied in the management of semi-arid rangelands especially with regard to woody plant control. We used the eco-hydrological savanna model EcoHyD to simulate the effects of different fire management strategies on semi-arid savanna vegetation and to assess their longterm suitability for semi-arid rangeland management. Simulation results show that prescribed fires, timed to kill tree seedlings prevented shrub encroachment for a broad range of livestock densities while the possible maximum long-term cattle densities on the simulated semi-arid rangeland in Namibia increased by more than 30\%. However, when grazing intensity was too high, fire management failed in preventing shrub encroachment. Our findings indicate that with regard to fire management a clear distinction between mesic and more arid savannas is necessary: While the frequency of fires is of relevance for mesic savannas, we recommend a fire management focussing on the timing of fire for semi-arid and arid savannas. (C) 2014 Elsevier Ltd. All rights reserved.}, language = {en} } @article{TabaresMapaniBlaumetal.2018, author = {Tabares, Ximena and Mapani, Benjamin and Blaum, Niels and Herzschuh, Ulrike}, title = {Composition and diversity of vegetation and pollen spectra along gradients of grazing intensity and precipitation in southern Africa}, series = {Review of palaeobotany and palynology : an international journal}, volume = {253}, journal = {Review of palaeobotany and palynology : an international journal}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0034-6667}, doi = {10.1016/j.revpalbo.2018.04.004}, pages = {88 -- 100}, year = {2018}, abstract = {Understanding vegetation-modern pollen relationships is essential to provide confidence in fossil pollen reconstructions of long-term vegetation changes in savanna ecosystems. In this paper we compare the taxonomical composition and the diversity (Hill NO, N1, N2) of vegetation and modern pollen along precipitation and local grazing-intensity gradients in Namibian savannas. Modern pollen was extracted from surface soil samples collected from 5 x 5 m plots distributed along four 500 m gradients. Vegetation was surveyed in each plot. The results show a high correspondence between vegetation and pollen data in terms of composition. Precipitation and grazing explain a significant although low proportion of compositional change in the vegetation and pollen spectra. We identified pollen taxa as indicators of grazing pressure such as Limeum, Alternanthera, and particularly Tribulus. Correspondence between vegetation and pollen data in terms of taxa richness (NO) is limited, probably because of the influence of landscape heterogeneity and openness, as well as low pollen concentrations. In contrast, the effective numbers of common and dominant taxa (N1, N2) are consistent among the different datasets. We conclude that in spite of limitations, modern pollen assemblages can reflect changes in vegetation composition, richness and diversity patterns along precipitation and grazing gradients in savanna environments. (C) 2018 Elsevier B.V. All rights reserved.}, language = {en} } @article{MarquartEldridgeGeissleretal.2020, author = {Marquart, Arnim and Eldridge, David J. and Geissler, Katja and Lobas, Christoph and Blaum, Niels}, title = {Interconnected effects of shrubs, invertebrate-derived macropores and soil texture on water infiltration in a semi-arid savanna rangeland}, series = {Land degradation \& development}, volume = {31}, journal = {Land degradation \& development}, number = {16}, publisher = {Wiley}, address = {Chichester, Sussex}, issn = {1085-3278}, doi = {10.1002/ldr.3598}, pages = {2307 -- 2318}, year = {2020}, abstract = {Many semi arid savannas are prone to degradation, caused for example, by overgrazing or extreme climatic events, which often lead to shrub encroachment. Overgrazing by livestock affects vegetation and infiltration processes by directly altering plant composition (selective grazing) or by impacting soil physical properties (trampling). Water infiltration is controlled by several parameters, such as macropores (created by soil-burrowing animals or plant roots) and soil texture, but their effects have mostly been studied in isolation. Here we report on a study, in which we conducted infiltration experiments to analyze the interconnected effects of invertebrate-created macropores, shrubs and soil texture (sandy soil and loamy sand) on infiltration in two Namibian rangelands. Using structural equation modeling, we found a direct positive effect of shrub size on infiltration and indirectly via invertebrate macropores on both soil types. On loamy sands this effect was even stronger, but additionally, invertebrate-created macropores became relevant as a direct driver of infiltration. Our results provide new insights into the effects of vegetation and invertebrates on infiltration under different soil textures. Pastoralists should use management strategies that maintain a heterogeneous plant community that supports soil fauna to sustain healthy soil water dynamics, particularly on soils with higher loam content. Understanding the fundamental functioning of soil water dynamics in drylands is critical because these ecosystems are water-limited and support the livelihoods of many cultures worldwide.}, language = {en} } @article{ReinhardGeisslerBlaum2022, author = {Reinhard, Johanna E. and Geißler, Katja and Blaum, Niels}, title = {Grass and ground dwelling beetle community responses to holistic and wildlife grazing management using a cross-fence comparison in Western Kalahari rangeland, Namibia}, series = {Journal of insect conservation : an international journal devoted to the conservation of insects and related invertebrates}, volume = {26}, journal = {Journal of insect conservation : an international journal devoted to the conservation of insects and related invertebrates}, publisher = {Springer}, address = {Dordrecht}, issn = {1366-638X}, doi = {10.1007/s10841-022-00410-6}, pages = {711 -- 720}, year = {2022}, abstract = {Savannahs are often branded by livestock grazing with resulting land degradation. Holistic management of livestock was proposed to contribute to biodiversity conservation by simulating native wildlife grazing behaviour. This study attempts the comparison of the impact of a holistic management regime to a wildlife grazing management regime on grass and ground-dwelling beetle species diversity on neighboring farms in Namibian rangeland. Results show that the response of biodiversity in species richness and composition to holistic management of livestock differs substantially from wildlife grazing with a positive impact. From a total of 39 identified species of ground-dwelling beetles (Coleoptera: Tenebrionidae, Carabidae) from 29 genera, eight species were found to be indicators for holistic management of livestock and three were found to be indicators for wildlife grazed rangeland. Observations suggest that holistic management of livestock may contribute to biodiversity conservation, but the differential effect of grazing management on species assemblages suggests that livestock grazing cannot replace native wildlife herbivory. Implications for insect conservation An adaptive management strategy such as holistic management used in this study shows the potential to support high beetle biodiversity. Holistic management of livestock thus aspects in favour for a sustainable form of grazing management for insect conservation even though it does not functionally replace grazing by native wildlife.}, language = {en} } @article{BerryDammhahnBlaum2023, author = {Berry, Paul E. and Dammhahn, Melanie and Blaum, Niels}, title = {Keeping cool on hot days}, series = {Frontiers in ecology and evolution}, volume = {11}, journal = {Frontiers in ecology and evolution}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-701X}, doi = {10.3389/fevo.2023.1172303}, pages = {13}, year = {2023}, abstract = {Long-lived organisms are likely to respond to a rapidly changing climate with behavioral flexibility. Animals inhabiting the arid parts of southern Africa face a particularly rapid rise in temperature which in combination with food and water scarcity places substantial constraints on the ability of animals to tolerate heat. We investigated how three species of African antelope-springbok Antidorcas marsupialis, kudu Tragelaphus strepsiceros and eland T. oryx-differing in body size, habitat preference and movement ecology, change their activity in response to extreme heat in an arid savanna. Serving as a proxy for activity, dynamic body acceleration data recorded every five minutes were analyzed for seven to eight individuals per species for the three hottest months of the year. Activity responses to heat during the hottest time of day (the afternoons) were investigated and diel activity patterns were compared between hot and cool days. Springbok, which prefer open habitat, are highly mobile and the smallest of the species studied, showed the greatest decrease in activity with rising temperature. Furthermore, springbok showed reduced mean activity over the 24 h cycle on hot days compared to cool days. Large-bodied eland seemed less affected by afternoon heat than springbok. While eland also reduced diurnal activity on hot days compared to cool days, they compensated for this by increasing nocturnal activity, possibly because their predation risk is lower. Kudu, which are comparatively sedentary and typically occupy shady habitat, seemed least affected during the hottest time of day and showed no appreciable difference in diel activity patterns between hot and cool days. The interplay between habitat preference, body size, movement patterns, and other factors seems complex and even sub-lethal levels of heat stress have been shown to impact an animal's long-term survival and reproduction. Thus, differing heat tolerances among species could result in a shift in the composition of African herbivore communities as temperatures continue to rise, with significant implications for economically important wildlife-based land use and conservation.}, language = {en} }