Modelling the distribution of the invasive Ziziphus mauritiana along road corridors in Zimbabwe

We investigate how human fruit consumption affects the spread of the alien invasive Ziziphus mauritiana along road corridors in northern Zimbabwe. A field survey was conducted to identify and map Z. Mauritiana stems at 25 randomly located 6‐ha plots placed along two main roads connecting the Zambezi Valley to the Highveld region. The L‐function was used to test for evidence of significant spatial clustering of the stems. The inhomogeneous point model fitted by maximum likelihood was also applied to check whether distance from the road explains variation in the number of stems per unit area. Finally, a t test was executed on log‐transformed abundance data to test for significant differences in the mean number of saplings and adults between the Zambezi Valley and the Highveld. Results of the L‐function indicated that Z. mauritiana had a clustered and linear distribution along roads both in the Zambezi Valley and Highveld regions. Results of the t test showed that the mean number of saplings per plot in the Zambezi Valley (μ₁ = 275) was three times higher than in the Highveld (μ₂ = 78), with p < 0.01. The mean number of adult trees was also significantly higher in the Zambezi Valley than in the Highveld.     

Relationship between native and exotic plant species at multiple savannah sites

We tested whether the recently proposed two‐part measure of degree of invasion (DI) of a community relating exotic proportion of cover to exotic proportion of richness can characterize patterns of plant invasions at multiple savannah sites in Southern Africa. Regression analysis was performed on transformed data to assess how this two‐part measure of DI compares to other metrics of community invasibility. The results indicate that at the plot level, the absolute cover of exotics was not significantly related to native cover for three sites out of four assessed (R² ≤ 0.17; P > 0.05). Also, at all four sites, no significant relationships were detected between native and exotic plant richness at both the 1‐m² and 400‐m² plot scales. By contrast, significant (P < 0.05) positive linear relationships were observed between exotic proportion of richness and exotic proportion of cover at all sites (R² was as high as 0.67 and 0.97 for two sites). Our results indicate that the new two‐part measure of DI is able to characterize patterns of plant invasions across plant communities in African savannahs.     

Precipitation of the warmest quarter and temperature of the warmest month are key to understanding the effect of climate change on plant species diversity in Southern African savannah

In this study, we test for the key bioclimatic variables that significantly explain the current distribution of plant species richness in a southern African ecosystem as a preamble to predicting plant species richness under a changed climate. We used 54,000 records of georeferenced plant species data to calculate species richness and spatially interpolated climate data to derive nineteen bioclimatic variables. Next, we determined the key bioclimatic variables explaining variation in species richness across Zimbabwe using regression analysis. Our results show that two bioclimatic variables, that is, precipitation of the warmest quarter (R² = 0.92, P < 0.001) and temperature of the warmest month (R² = 0.67, P < 0.001) significantly explain variation in plant species richness. In addition, results of bioclimatic modelling using future climate change projections show a reduction in the current bio‐climatically suitable area that supports high plant species richness. However, in high‐altitude areas, plant richness is less sensitive to climate change while low‐altitude areas show high sensitivity. Our results have important implications to biodiversity conservation in areas sensitive to climate change; for example, high‐altitude areas are likely to continue being biodiversity hotspots, as such future conservation efforts should be concentrated in these areas.     

Influence of termites on the soil seed bank in an African savannah

In savannah ecosystems, termites drive key ecosystem processes, such as primary production through creation of patchiness in soil nutrients availability around their nests. In this study, we evaluated the role of termites in altering the soil seed bank size, an important ecosystem component that has often been overlooked in previous work. Data on above ground vegetation and soil seed bank samples were collected from four microhabitats, that is, the wooded mound, unwooded mound, tree sub‐canopy and the open grassland matrix in a protected game reserve in south‐central Zimbabwe. The seedling emergence method was then used to identify species present in the soil samples. One‐way analysis of variance followed by Tukey's multiple comparison tests was executed to test for significant differences in plant species richness among the four microhabitats. The results indicate that plant species richness was high on wooded termite mound but did not differ between the unwooded and the sub‐canopy microhabitats. The open grassland microhabitat had the lowest plant species richness. The influence of termites on the soil seed bank composition was also life form specific. The herb and woody life forms had significantly (α = 0.05) higher species richness in the soil seed bank at wooded and unwooded termite mounds when compared to the other two microhabitats. Overall, these results imply that termites alter the soil seed bank and the findings enhance our understanding of the significant role termites play in regulating processes in savannah ecosystem.     

A new potential method to estimate abundance of small game species

This study tested the hypothesis that nonlinear transects, such as the L‐, V‐ and W‐shaped transect, which are widely used in soil sampling but rarely in ecology, may perform better in capturing habitat heterogeneity potentially resulting in more accurate small game species estimates, than straight‐line transects. To test this, we computed and compared the Normalized Difference Vegetation Index (NDVI) captured by the straight‐line, L‐shaped, V‐shaped and W‐shaped transects for Kyle Game Reserve (Zimbabwe), inside the home ranges of two small game species, namely species A and species B. These transects differed in geometry but had the same length. We also performed simulations in a geographic information system environment to compare the detection ability of the different transect geometry. One‐way analysis of variance followed by Tukey's honest significant difference test was used to test for significant differences in the mean number of detections and NDVI variance captured by each transect geometry. Simulations results indicate that for both home ranges, the V‐shaped transect resulted in significantly higher detections than the widely used straight‐line transect. Nonlinear transects also yielded higher NDVI variances than the straight‐line transect in both home ranges.     

Spatial distribution of <Emphasis Type="Italic">Vachellia karroo</Emphasis> in Zimbabwean savannas (southern Africa) under a changing climate

Climate change projections in southern Africa show a drier and a warmer future climate. It is not yet clear how these changes are going to affect the suitable habitat of bush encroacher woody species in southern African savannas. Maximum Entropy niche modelling technique was used to test the extent to which climate change is likely to affect the suitable habitat of Vachellia karroo in Zimbabwe based on six Global Climate Models (GCMs) from Coupled Model Intercomparison Project Phase 5 (CMIP5) and two Representative Concentration Pathways (RCPs) for the 2070s. An overlay analysis was then performed in a Geographic Information System based on the current and future bioclimatically suitable areas for the respective GCMs and RCPs. This was done to determine the potential effect of climate change on the focal species. Results show that temperature related variables are more important in explaining the spatial distribution of V. karroo than precipitation related variables. In addition, results indicate an overall increase in the modelled suitable habitat for V. karroo by the 2070s across the GCMs and RCPs considered in this study. Specifically, the suitable habitat of V. Karroo is projected to increase by a maximum of 57,594 km² signifying a 69% increase from the current suitable habitat (83,674 km²). The suitable areas are projected to increase in eastern, western and south eastern parts of Zimbabwe. These results imply that improved understanding of the response of woody species to a changing climate is important for managing bush encroachment in savanna ecosystems.     

COL-3, a Chemically Modified Tetracycline,Inhibits Lipopolysaccharide-Induced Microglia Activation and Cytokine Expression in the Brain

Microglia activation results in release of proinflammatory molecules including cytokines, which contribute to neuronal damage in the central nervous system (CNS) if not controlled. Tetracycline antibiotics such as minocycline inhibit microglial activation and cytokine expression during CNS inflammation. In the present study we found that administration of chemically modified tetracycline-3 (COL-3), inhibits lipopolysaccharide (LPS)-induced microglial and p38 MAPK activation, as well as the increase in TNF-α, but not IL-1β expression, in the brains of BALB/c mice. COL-3 has been described to have no antibacterial activity. We observed that COL-3 had no activity against a Gram-negative bacteria, Escherichia coli; however surprisingly, COL-3 had antibacterial activity against a Gram-positive bacteria Staphylococcus aureus, with a minimum inhibitory concentration of 1 mg/ml. Our data show that COL-3 has some antibacterial activity against S. aureus, inhibits LPS-induced neuroinflammation, and displays potential as a therapeutic agent for treatment of conditions involving CNS inflammation.     

Accuracy assessment of MODIS active fire products in southern African savannah woodlands

Satellite remote sensing offers a cost‐effective method for monitoring fire occurrence in savannah systems, for proper fire management. However, the ability of satellite fire products to detect active fire is known to vary depending on the terrestrial ecosystems and sensor characteristics. In this study, the overall accuracy, kappa coefficient of agreement and true skill statistic (TSS) were used to assess the accuracy of two MODIS fire products (MOD14A1 and MCD14ML) to detect active fire at two savannah woodland sites dominated by Baikiaea plurijuga and Brachystegia spiciformis in Zimbabwe. In both sites, MOD14A1 with a coarse spatial resolution of 1 km had a poor index of agreement with ground fire data (kappa = 0, TSS = 0 and overall accuracy ≤ 0.4). By contrast, a moderate to strong agreement between MCD14ML and active fires measured on the ground was observed at both study sites (overall accuracy ≥ 0.7, kappa ≥ 0.6 and TSS ≥ 0.6; Table  1 ). It was therefore concluded that MCD14ML, with a spatial resolution of 375 m, is a more suitable product for detecting active fires in both Baikiaea plurijuga and Brachystegia‐dominated savannah woodlands of southern Africa compared to MOD14A1.     

Monitoring African buffalo (Syncerus caffer) and cattle (Bos taurus) movement across a damaged veterinary control fence at a Southern African wildlife/livestock interface

We test the extent to which fence damage or fence permeability (resulting from human and elephant damage) influences patterns of cattle and buffalo movement at the periphery of Gonarezhou National Park, Zimbabwe. We used spoor data to detect and compare the frequency of cattle and buffalo movement across the fence boundary. Results show that spoor proportions for cattle were significantly higher on fence partially damaged by humans than buffalo spoor. Conversely, buffalo spoor proportions were significantly higher on sections with totally removed fence as a result of elephant damage. Results suggest that cattle and buffalo use different sections of the damaged fence.     

Decadal changes in mean annual rainfall drive long‐term changes in bush‐encroached southern African savannas

Bush encroachment can have profound effects on the ability of savanna ecosystems to provide goods and services to society. It is therefore crucial to understand the key drivers of bush encroachment in savannas. In this study, we test whether decadal changes in mean annual rainfall significantly explain changes in the dominant patch size as well as the density of bush patches at six protected savanna sites located along a rainfall gradient in Zimbabwe. We first performed Maximal Overlap Discrete Wavelet transform within the intensity‐dominant scale theoretical framework on multi‐temporal aerial photographs and high spatial resolution satellite imagery to objectively detect changes in the dominant patch dimension as well as the intensity of bush cover over a 40‐year period at six test sites. We then pooled the data and performed regression analysis relating changes in dominant scale and intensity to decadal changes in mean annual rainfall in order to deduce a possible connection between dynamics of bush encroachment and rainfall variability. Our results indicate a significant nonlinear relationship between changes in the dominant scale and decadal changes in mean annual rainfall (R² = 0.85, F₁₃ = 35.96, P < 0.01). In contrast, the relationship between decadal changes in mean annual rainfall and changes in intensity was weak and not significant (R² = 0.29, F₁₃ = 2.69, P = 0.106). These results imply the importance of annual rainfall in explaining long‐term changes in the dominant scale of woody patches. However, mechanisms other than rainfall probably explain changes in the intensity of bush cover, and this needs further investigation.