Judith Botha

Competition and facilitation are fundamental concepts in ecology, but evidence for the strength and direction of interspecific interactions within trophic levels is difficult to obtain, particularly in large assemblages of free‐ranging animals. We investigated abundance patterns and interspecific associations among 10 African savannah herbivores by implementing a multispecies hierarchical distance‐sampling model with a variance–covariance matrix that accounted for (i) imperfect detection; (ii) habitat preferences; and (iii) ‘indirect’ associations (i.e., shared/contrasting associations between two species mediated by any third species). Animal groups were more likely to go undetected at sampling locations with more woody vegetation. Herds of all species were less numerous on sandier soils and far from water, while associations with NDVI and woody vegetation were mixed. Positive associations dominated the correlations among species (before accounting for ‘indirect’ associations), and ‘direct’ pairwise associations after accounting for habitat preferences were generally weaker (correlation for all species pairs <|0.55|); the strongest positive correlation was between white rhino and warthog (0.47, posterior probability = 95%). The lack of strong negative associations among species is consistent with coexistence theory's premise that intraspecific competition outweighs interspecific competition. The directions of the weaker ‘direct’ pairwise interactions were largely consistent with biological mechanisms proposed or identified in previous work.

Freshwater macroinvertebrates, often used as indicators of environmental quality for freshwater ecosystems, may be compromised by microplastics (MPs). We investigated MPs occurring in benthic filter feeder, predator, and grazer macroinvertebrates collected from the catchment-independent but adjacent Olifants and Sabie rivers of Kruger National Park as duplicates. We counted 369 MPs in 376 organisms (1.0 n/organism) with a mean of 8.8 n/organism, 8.5 n/organism, and 0.16 n/organism in filter feeders, predators, and grazers, respectively. Based on MP colour, size, and morphotype, significant differences in proportional compositions between predatorial macroinvertebrates and all other macroinvertebrates in both rivers preclude predatorial macroinvertebrates as a proxy indicator for the other macroinvertebrates. Proportional compositions of MP characteristics in macroinvertebrates differed in all respects between the two adjacent rivers, except for one aspect. Microplastic morphotypes occurred in equal proportions in macroinvertebrates of both rivers, suggesting biological selection based on morphotype but not MP colour or size. We found little evidence of trophic transfer between feeding guilds. Of the six polymer types observed (n = 50), butyl and chlorobutyl dominated. Waste mismanagement, single-use plastics, inefficient wastewater treatment plants, mining, and road transportation may be the major MP pollution sources that need mitigation. Microplastics in freshwater ecosystems of nature conservation areas need more attention due to high biodiversity that may be exposed.

Maintaining and improving the state of biodiversity is a primary factor guiding management activities in conservation areas, including protected areas (PAs) and other effective area-based conservation measures (OECMs). Due to the complex nature of conservation programs, a common management approach cannot be prescribed. Robust monitoring programs supporting management activities are required to evaluate the state of species and habitats. However, limited resources, poor data management practices, and competing requirements of stakeholder groups increase the challenges that must be addressed through realization of monitoring programs. We propose a framework of seven basic questions to guide conservation area managers to implement effective biodiversity monitoring techniques. The result is identification of indicators, site characteristics, and resources to promote the development of a biodiversity monitoring program. We call for adoption of a strategic guideline providing this framework to harmonize decision making processes across national and international networks. Implementation of this robust framework will support comparative monitoring data, contributing to systematic approaches for adaptive management in PAs and OECMs and improving the body of knowledge surrounding global biodiversity.

Mokala National Park (MoNP) has a history of arboricide use through South African National Parks (SANPs) having bought commercial game farmland for its establishment in 2007. Tebuthiuron arboricide is known to have been applied for controlling bush densification during the period 1996 to 2004. Persistent negative impacts on MoNP vegetation, which are ascribed to the historical arboricide use, have prompted this investigation from 2016 to 2017. Bioassay experiments employing as test plants the tree species Vachellia erioloba and Vachellia tortilis, the shrub species Senegalia mellifera and the grass Tragus berteronianus were conducted in a glasshouse. Growth responses of these species were assessed upon their exposure to a tebuthiuron concentration range that simulated expected levels in MoNP soil soon and long after application. Chemical analysis as well as bioassay with the test species Lycopersicon esculentum (tomato) were performed on soil samples collected from three depths (0−30, 30−60 and 60−90 cm) of the soil profile at two sites in MoNP where tebuthiuron was applied in the past. The three woody test species showed differential, negative growth response to tebuthiuron, and even growth of the grass species (T. berteronianus) was affected at the higher concentrations. Evidence provided by the tomato bioassay and analysis performed on soil samples collected in situ points to the putative presence of tebuthiuron, more than a decade after the last use of arboricides for controlling bush densification. Conservation implications: If the reported evidence of the presence of phytotoxic residue of tebuthiuron in soil of MoNP would be substantiated through further research, such findings could at least partly explain the failure of natural recruitment of vegetation in those areas where the woody component was degraded because of arboricide application more than a decade ago.

Herbivores are a main driver of ecosystem patterns and processes in semi-arid savannas, with their effects clearly observed when they are excluded from landscapes. Starting in the 1960s, various herbivore exclosures have been erected in the Kruger National Park (KNP), for research and management purposes. These exclosures vary from very small (1 m2) to relatively large (almost 900 ha), from short-term (single growing season) to long-term (e.g. some of the exclosures were erected more than 60 years ago), and are located on different geologies and across a rainfall gradient. We provide a summary of the history and specifications of various exclosures. This is followed by a systematic overview of mostly peer-reviewed literature resulting from using KNP exclosures as research sites. These 75 articles cover research on soils, vegetation dynamics, herbivore exclusion on other faunal groups and disease. We provide general patterns and mechanisms in a synthesis section, and end with recommendations to increase research outputs and productivity for future exclosure experiments.Conservation Implications: Herbivore exclosures in the KNP have become global research platforms, that have helped in the training of ecologists, veterinarians and field biologists, and have provided valuable insights into savanna dynamics that would otherwise have been hard to gain. In an age of dwindling conservation funding, we make the case for the value added by exclosures and make recommendations for their continued use as learning tools in complex African savannas.

Background: Although the Kruger National Park (KNP) is a protected area, it is not exempted from anthropogenically induced impacts, which often compromise river water flow and quality. Measures of river water quality in South Africa have conventionally been based on water chemistry as well as different ecological indicator groups such as fish and macroinvertebrates. Diatoms have been shown to be useful indicators of changes in water quality resulting from pollution and land-use impacts.Objectives: To determine the applicability of diatoms for hind-casting water quality in the KNP and to compare recent diatom community composition with those from the 1980s.Methods: In this study, pH and electrical conductivity (EC) were used to evaluate temporal changes in water quality of three rivers within the KNP. Additionally, we made use of historic diatom samples from three of the five perennial rivers to evaluate if diatom communities reflected changes in water conditions between 1983 and 2015.Results: Diatom community structure was significantly different between 1983 and 2015. Diatom-based index scores (SPI) indicated an improvement in water quality for the Letaba and Olifants rivers.Conclusion: Diatoms were shown to be useful indicators of current water quality and are also useful for determining temporal changes.

The Kruger National Park’s (KNP) long-running experimental burn plots (EBPs) have a history of research projects, which improve the understanding of fire in savanna ecosystems. Using data from KNP’s aerial censuses (2005–2016) and in situ dung count data (2008–2017), this study assessed (1) herbivore densities on the Satara, N’Wanetsi and Marheya EBPs, on annual, triennial and no-burn treatments and across pre-, during and post-drought climate conditions; (2) herbivore densities of these EBPs relative to their non-manipulated surroundings and (3) the extent to which distance to water and rainfall influence ungulate densities. The results revealed that herbivore mean density differed significantly between the three EBPs of Satara and across their fire treatments. N’Wanetsi showed the highest density (0.30 animals/ha), whilst the lowest was found at Marheya (0.12 animals/ha). Overall, pre-drought density was higher on the annual plots (0.56 animals/ha), whilst higher post-drought density was evidenced on the triennial plots (0.80 animals/ha). On average, there were significantly higher herbivore densities on the EBPs (2.54 animals/ha) compared to the surrounding matrix at the larger scales of the Satara management section (0.15 animals/ha) and the central KNP (0.18 animals/ha). A positive correlation between herbivore mean density estimate and distance to water was shown. However, grazer mean density across fire treatments was strongly correlated to rainfall. Conservation implications: Given the variation in fire regimes and their application, and the non-uniform and elevated herbivore densities of the EBPs, inferences from the EBPs cannot be made to the larger KNP. The trials should rather be viewed as an isolated, fire herbivory experiment. It is also recommended to align the experiment with South African National Parks’ mandate by including biodiversity parameters like small mammals and insects in the monitoring of the plots.