College of Agriculture, Engineering and Science

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Characterization of rainfall over the Limpopo province, South Africa, for the period 1990 to 2020.
(2024) Moumakwe, Peter Lesiba.; Dube, Lawrence Thembokwakhe.
The Limpopo Province is home to a large rural population which is highly dependent on rainfed agriculture. Although extensive research has been undertaken to understand rainfall variability over South Africa, a better understanding of the localized rainfall characteristics and variability remains crucial for decision-makers and the livelihoods of the local community. The study aims to investigate rainfall variability and trends over the Limpopo province, understand the distribution (both spatial and temporal) of seasonal rainfall characteristics, and also establish the relationship between seasonal rainfall characteristics with larger modes of climate variability (i.e. El Niño Southern Oscillation (ENSO), and Southern Indian Ocean Dipole (SIOD)). High-resolution Climate Hazard Group Infrared Precipitation with Station Data (CHIRPS) 0.05° gridded data spanning the duration 1990-2020 was employed to analyze the spatial distribution of rainfall over the Limpopo province. In this study dry spells (pentads with < 5 mm rainfall), moderate (rainfall ranging from 10-30 mm per day) and heavy wet days (rainfall > 30 mm per day) were analyzed. Standardized Anomaly Index (SAI) was used to understand the relationship between rainfall characteristics and anomalies. The Mann-Kendall test was also used to determine the trends of seasonal rainfall characteristics over the province. The Pearson correlation was used to establish the association between seasonal rainfall characteristics (dry spells, moderate and heavy wet days) and large modes of variability (ENSO and SIOD). The results of this study show that seasonal rainfall exhibits high spatial and temporal variability over the study period. Throughout the extended summer season (October-March (ONDJFM)), dry spells migrate from the north of Vhembe and Capricorn to the northeast of Mopani, with their frequency and extent increasing from early summer (October-November) to late summer (February-March). The distribution of these rainfall characteristics follows that of mean annual rainfall. Of all periods, December-January (DJ) receives the highest frequency of moderate wet days with a larger spatial extend ranging from 6-13 days in the high-lying escarpment of Vhembe, west of Mopani, south-east of Capricorn, Waterberg, and Greater Sekhukhune. The highest heavy wet day frequency is also observed in the DJ period, over the high-lying escarpment of Vhembe, west of Mopani, south-east Capricorn and north of Greater Sekhukhune records heavy wet days ranging from 3-7 days. The results of the Mann-Kendall trend test revealed a statistically significant decreasing trend in dry spells during DJ and February-March (FM) over the entire Limpopo province. Statistically significant moderate wet day trends were observed during ON over north and east of Mopani, south-east of Capricorn, and west of Mopani district, whereas during the DJ periods, statistically significant increasing trends are recorded over the south-east of Vhembe and northwest of Mopani. During DJ, statistically significant increasing heavy wet day trends are observed over Vhembe, Greater Sekhukhune, and west of Waterberg. The relationship between seasonal rainfall characteristics and rainfall anomalies was observed. The results show that the inter-annual variability of seasonal rainfall characteristics does not always reflect in seasonal rainfall totals/anomalies. This shows that anomalies overlook the isolated impact of seasonal rainfall characteristics. The relationship between seasonal rainfall characteristics and large modes of variability was observed. A strong negative correlation with moderate wet days over the high-lying escarpment in the Vhembe district and south of the Mopani district. However, a complex relationship was observed between the inter-annual rainfall characteristics and large modes of variability. The results showed that not all La Nina years or positive phase SIOD phase equate to wet seasons. Furthermore, years with neutral ENSO and SIOD phases still exhibited above-average wet days.
Community diversity and composition of ground-dwelling arthropods in major habitat types of the KwaZulu-Natal Sandstone Sourveld.
(2023) Mhlongo, Nokukhanya.; Tsvuura, Zivanai.; Munyai, Thinandavha Caswell.
Grasslands constitute over 25% of the global land surface and close to one-third of southern Africa. Natural and semi-natural grasslands are recognized globally for their high biodiversity value and their important contribution to the provision of ecosystem services, including provisioning services such as carbon sequestration, water catchments, and grazing for livestock and wildlife. Nonetheless, grasslands are consistently reduced and threatened by anthropogenic activities and invasive alien plants. Invasive alien plants may hinder the growth of natural vegetation by overconsumption of resources. The impact of invasive alien plants on natural vegetation may indirectly affect plant-to-animal interactions such as specialized pollination and seed dispersal syndromes which may ultimately disturb ecosystem processes. The Sandstone Sourveld in KwaZulu-Natal province of South Africa is a threatened grassland ecosystem as a result of various anthropogenic disturbances. Knowledge of arthropod response to differences in habitat types may be essential for an improved understanding of the structure and functioning of ecosystems, which is relevant for informing conservation practice. The aim of this study was to investigate the composition and diversity patterns of ground-dwelling arthropods (ants, beetles, Orthopterans, and spiders) in three habitat types (forest, intact grassland, and disturbed grassland) at Springside and Tanglewood Nature Reserves, which occur in the KwaZulu-Natal Sandstone Sourveld (KZNSS). The objectives were: (i) to document the response of the ground-dwelling arthropod community in different habitat types, (ii) to determine the impacts of seasonal change on the abundance and richness of ground-dwelling arthropods at the two sites, and (iii) to determine the correlation between the distribution of ground-dwelling arthropods and soil characteristics in the KZNSS. Ground-dwelling arthropods were sampled in Springside and Tanglewood Nature Reserves using pitfall traps in each habitat type. Soil parameters in the habitats were also assessed. Analysis of variance was used to test for differences in arthropod morphospecies richness and abundance viii across the habitat types and between seasons. The Shannon-Weiner diversity index was computed and used to compare the diversity of ground-dwelling arthropods between the two sites and among habitat types. Ground-dwelling arthropods showed varying patterns in response to habitat characteristics and the disturbance gradient at Springside and Tanglewood. Intact grassland was the most diverse habitat in both Springside and Tanglewood. In Tanglewood, the abundance of ants was greater in disturbed grassland which consisted of a variety of alien invasive shrubs, the high abundance was explained by the “intermediate disturbance hypothesis”. However, alien invasion showed more negative than positive impacts on the abundance and composition of ground-dwelling arthropods when there was a significant decrease in the abundance and composition of ants, beetles and spiders. Species richness of ants and beetles was higher in the wet than dry season whereas Orthopterans and spiders showed no significant difference between seasons. In all arthropod groups, a greater number of species were correlated to soil potassium, soil pH, and soil bulk density. Overall, the intact grassland had the highest species richness and abundance followed by the forest and lastly the disturbed grassland. The greater abundance of ants, beetles, and spiders in the pristine grasslands of KZNSS shows that there is still a need to conserve the remnants of the KZNSS vegetation. Therefore, the conservancy management is urged to consider the eradication of alien invasive plants. Future studies are recommended to consider the volant and vegetation canopy arthropods as they are all interdependent with ground-dwelling arthropods to form a whole community of arthropods in an ecosystem.
Concurrent spatiotemporal ecology of African lions and spotted hyenas and the potential for inter- and intraspecific interactions in semi-arid and wetland ecosystems.
(2022) Barker, Nancy Ann.; Slotow, Robert Hugh.
Intraguild interactions among apex predators can potentially influence carnivore population densities and distribution, which may have profound effects on trophic processes within ecosystems. Coexisting carnivores are able to mitigate such interactions through behavioural mechanisms that promote spatiotemporal separation. Despite increasing research which highlights the occurrence and prevalence of competitive interactions between African lions (Panthera leo) and spotted hyenas (Crocuta crocuta), studies that incorporate the effects of such interactions on lion and hyena space use patterns are limited. Interactions among sympatric carnivores reveal how predators utilize spatial and temporal partitioning strategies within jointly used areas, and elucidate the spatiotemporal patterns enabling species coexistence between them. Thus, an understanding of how inter- and intragroup interactions drives the movement responses of apex predators has important implications for the structure and function of large carnivore communities, and their conservation. We used remote tracking data to investigate aspects of the ecology and behaviour of lions and spotted hyenas, with an emphasis on the spatiotemporal patterns among coexisting populations. Both lions and spotted hyenas mediated the potential for interference competition through subtle differences in temporal activity, fine-scale habitat use differentiation, and localized reactive-avoidance behaviours. Recursivity to, and duration of time at, locales of high competitor probabilities, were similar among female lions and both sexes of hyenas, but different for male lions. Our findings of lion space-use patterns across arid and mesic environments indicated the seasonal influences of competitive interactions with competitors (spotted hyenas), in that lions selected for, and chose to move through areas with a lower probability of competitors during the dry season. Dyadic interactions among lions and spotted hyenas illuminates how hyenas effectively reduced their potential of interactions with lions by utilizing spatiotemporal partitioning strategies and local reactive avoidance behaviours within shared space use areas. Quantifying the types of movement behaviour between competitors highlights the type of interaction occurring in a dyad and enhances our understanding of the potential effects of interspecific interactions among large carnivore space-use patterns within an apex predator system. Both lions and spotted hyenas exploit different behavioural strategies resulting in fine-scale spatiotemporal segregation among shared space-use areas enabling the two species to co-exist, and show adaptability across heterogeneous and homogeneous environments. Such findings are essential in understanding the behavioural choices made by members of a guild that subsequently affects population dynamics and community structure of multi-species food networks.
Conservation genetics of the Hooded vulture Necrosyrtes monachus.
(2023) Le Roux, Rynhardt.; Willows-Munro, Sandi.; Van Vuuren, Bettine.; Thompson, Lindy Jane.
African vulture species have experienced rapid population declines, due to many anthropogenic threats. Hooded vultures are no exception and have experienced dramatic declines and are now listed as Critically Endangered on the IUCN Red Data list. Two subspecies of Hooded vulture have been described : Necrosyrtes monachus monachus which occurs in West Africa and Necrosyrtes monachus pileatus which occurs in East and southern Africa. The two subspecies differ in their feeding behaviour and morphology supporting the validity of the subspecies status. However, the validity of this taxonomic grouping is still being questioned. Clarifying the taxonomic status of the subspecies is important as if the two subspecies are genetically distinct then they should not be managed as a single species and current conservation policies would need to be updated. In addition, there is limited information available on many aspects of Hooded vulture life history including the factors affecting reproduction in the wild. In Chapter 2 I use microsatellite data collected from across the distributions of the two subspecies and Approximate Bayesian Computation (ABC) to test the hypothesis that the two subspecies are genetically distinct and should be elevated to separate species. In Chapter 3 I examine the genetic variation present in the South African Hooded vulture population. This population only includes 100-200 individuals and is at the edge of the southern range of the species. The conservation value of peripheral populations is debatable as these populations are often isolated and smaller with genetic drift and inbreeding leading to reduced genetic variability. In contrast, studying the genetic diversity in range-edge populations is important for understanding range shifts and adaptive capacity under climate change. These edge populations could potentially also retain unique genetic diversity which helps with the adaptation of species to different environments. Vulture colonies act as “food finding information hubs” allowing for the exchange of information regarding potential food resources. This explains, in part, the high-levels of relatedness often found within colonies as close relatives are more likely to tolerate the cost of sharing food by increasing their inclusive fitness. Hooded vultures are tree nesters with a single breeding pair per tree. In Chapter 4 I use the genetic data to test if individuals nesting close to each other are closely related and if the same individuals use the same nest over multiple years. The analyses conducted in Chapter 2 did not support the existence of the two subspecies classification, due to different demographic events experienced between the two groups. The next factor indicating that there is no subspeciation is the contemporary gene flow that is still seen between the population (m = 0.188) and the little variance seen between the two subspecies (11.9%). Structure analysis also does not support the formation of two distinct subspecies. Thus, this study supports the claim made by Mundy 2021 that it is size cline and not speciation. In Chapter 3 the genetic data did not support the hypothesis that the small South African population was genetically depauperate, instead the results show that the South African population contained similar levels of genetic diversity (Ho = 0.495) to that recorded for the Ghanaian population (Ho = 0.315) where Hooded vultures are more abundant. Levels of heterozygosity were similar to those recorded for other species of Old World vultures such as Cape Vultures (Gyps coprotheres, Ho = 0.380), and Bearded vultures (Gypaetus barbatus Ho = 0.400 – 0.480), but differed from the Griffon Vulture (Gyps fulvus Ho = 0.530 – 0.600) found in Europe. Worryingly, both populations of Hooded vultures show elevated levels of inbreeding and relatedness. The bottleneck analysis for both populations show no sign of a recent bottleneck and a normal L shaped distribution for both populations. In Chapter 4 breeding pairs were not found to reuse the same nests over multiple years. A negative correlation was seen between genetic distance and geographical distance (R2 = 0.0117; p-value = 0.012) the closer related individuals thus tend to nest further away from each other. The spatial autocorrelation shows a positive correlation between genetic and geographical distance between distance classes 8 km – 16km, 32 km – 40km and then between 88 km – 112km, but no clear support for increased relatedness between closer nesting individuals. Thus no support is seen for the formation of loose colonies to function as food finding information sharing hubs. African vultures are facing a number of challenges and most species are considered of conservation concern. Despite this limited genetic data is available for many species. This study aimed to fill this knowledge gap by generating and analysing microsatellite data for the Critically Endangered Hooded vulture to answer a number of key hypotheses. As such this study makes an important contribution towards the conservation of Hooded vultures across Africa.
Feeding dynamics of invasive (Tarebia granifera) and native (Melanoides tuberculata) freshwater gastropods.
(2020) Naidoo, Senine.; Carrasco, Nicola Kim.; Miranda, Nelson Augusto Fernandes.
Tarebia granifera has invaded several South African estuaries, outnumbering native gastropods such as Melanoides tuberculata. Comparative feeding dynamics can aid in estimating and understanding invasion impacts. This study aimed to explore the feeding dynamics of these gastropods with the use of two different approaches. Stable Isotope Analyses (SIAs) were used to investigate the dietary preferences and niche overlaps in the St Lucia Estuary, while Functional Response Experiments measured the relationship between the consumption rate of a food resource and its availability. These experiments were run both with and without the presence of heterospecific chemical cues (secondary metabolites secreted by either species) to determine whether chemical cues influence the functional responses of T. granifera and M. tuberculata. Mixed species experiments were also conducted to observe individual behaviour (active, inactive and feeding) over time and measure resource consumption when both species are placed together under high and low food availability. The SIA showed that both gastropods exhibited generalist diets, however, due to niche partitioning, there was no significant difference in their dietary niche overlap. In the FR experiments, both species exhibited Type II FRs and had similar feeding rates. However, in the presence of heterospecific chemical cues, M. tuberculata exhibited a higher feeding rate at high food availabilities, whereas T. granifera showed efficient feeding dynamics under limited food resources. In the mixed species experiments, T. granifera spent more time feeding under low food availability while M. tuberculata spent more time feeding under high food availability. This study showed that in certain conditions (e.g. high resource availability) the alien species did not always have a feeding advantage. A multiple method approach is recommended when assessing ecological impacts of invasive species.
The performance and spatial ecology of the critically endangered black rhinoceros, diceros bicornis l., population in iThala game reserve, KwaZulu Natal, South Africa.
(2020) Greaver, Catherine Caroline.; Slotow, Robert Hugh.
Ensuring the persistence of populations of endangered species requires an understanding of, and response to, the causes of population declines. Species occurring in small populations are vulnerable to stochastic problems that are environmental, demographic, or genetic in nature, and can reduce survival as much as the threats of habitat degradation. Critically endangered black rhinoceros, Diceros bicornis, populations have declined throughout Africa since 1960, but, more recently, numbers are increasing at a continental level, but remain lower than three generations ago. The south-central black rhinoceros, Diceros bicornis minor is considered critically endangered and are found primarily in protected areas. To ensure the persistence of the species, management efforts have focussed on live-harvesting and translocation of individuals from certain sub-populations to populate additional reserves, whilst monitoring involved collecting demographic data (births, deaths, density, and sex and age structure) that could be used to improve conservation management of this species. This study was initiated to determine population estimates, growth rate, and fecundity over time, as well as sex and age structure and age-specific probabilities of survival, using 18 years (1990–2008) of long-term sightings data from Ithala Game Reserve, KwaZulu-Natal, South Africa. I also wanted to determine if mortality occurrences were associated with social or environmental factors, or as a result of management interventions. There was no significant difference in the sex ratios at birth, although the proportion of females in the population was 0.58. There was strong evidence for density-dependent regulation, with density in conception year a key driver of population ii performance (birth rate). The population does not appear to be at ecological carrying capacity; however, social effects are delaying conception. The model analyses showed that social interactions carried more weight than environmental factors on mortality, with a strong association between mortality and intensity of use, as well as mortality and management removals from the population. The mechanism of density dependence in Ithala Game Reserve is through mortality that is associated with increased social interactions, rather than from resource limitations. To mitigate density-dependent social effects, my study recommends an adaptive management strategy of pre-selecting individuals with known information on their social behaviour and context, before removal from the reserve, so as to maintain stability in the social organization of the population. In the absence of restoring linkages between populations of black rhinoceros, the translocation of black rhinoceros is a primary tool to mimic how meta-population dynamics would play out across the landscape. However, careful monitoring to enhance understanding of social factors, particularly black rhinoceros male behaviour, should be intensified to allow strategic translocation of individuals in such a way that negative density dependent effects are mitigated.
Phylogenetic diversity, host specificity and geographic distribution of avian malaria in Africa.
(2022) Van Zweiten, Sam Falcon.; Willows-Munro, Sandi.
Abstract available in PDF.
Pre-release evaluation of the flea beetle Heikertingerella sp. (Coleoptera: Galerucinae: Alticini), a potential biological control agent for the invasive weed Tecoma stans L. (Bignoniaceae) in South Africa.
(2024) Madire, Lulama Gracious.; Olckers, Terence.; Simelane, David Okhi.
The root-feeding beetle Heikertingerella sp. (Coleoptera: Chrysomelidae) was introduced into quarantine in South Africa for evaluation as a biological control agent of the invasive tree Tecoma stans L. (Bignoniaceae). Larval feeding damages the roots, potentially reducing the weed’s growth and reproduction. Pre-release studies in quarantine included several aspects. Studies on the beetle’s biology and host specificity were conducted to confirm its safety for release in South Africa. The impact of varying beetle densities on plant fitness was assessed to determine its likely impact in the field. The effect of local climate on the beetle’s potential to establish throughout the weed’s range in South Africa was predicted using climate-modelling software. The interaction between Heikertingerella sp. and a leaf-feeding agent already established in South Africa was investigated. Finally, the effect of host-plant age and nutrient enhancement on mass-rearing activities was studied, to optimize beetle numbers for releases. The beetle proved host specific resulting in the granting of permission for its release in South Africa. There were significant reductions in plant growth and biomass accumulation in the beetle-exposed plants, relative to the controls, indicating that Heikertingerella sp. is sufficiently damaging. Climate matching revealed that Heikertingerella sp. is likely to perform best at coastal sites in South Africa, with the colder, more inland, areas within the weed’s range proving less suitable. The beetle proved compatible with a defoliating agent established in South Africa, with evidence of positive interactions that are likely to enhance their combined impact on the weed. Trials involving plants of varying age and nutritional enhancement revealed that 3-year-old plants, which were supplemented by either medium or high levels of fertilizer, were best suited for F1 progeny production and therefore for the mass-rearing of Heikertingerella sp. for releases. The results of this study should also benefit other countries in Africa and elsewhere in the world, where the plant is invasive.
The impact of land-use change on arthropod diversity along an arid elevational gradient.
(2022) Mkhungo, S'phesihle.; Munyai, Thinandavha Caswell.; Foord, Stefan Hendrik.
Land-use change is a major threat to global biodiversity. The rapid growth of the human population has resulted in increased landscape modifications and habitat loss. The impact includes reduced species diversity, ecosystem instability, altered species interactions and altered food webs. Land-use has increased drastically in mountainous areas, mainly through agriculture and human settlements. Mountains support approximately one-third of the terrestrial diversity and host half of the global biodiversity hotspots. The high variation in habitat structure and microclimates, within short distances allows mountains to support high species diversity. This study aimed to investigate the impact of increasing land-use change, elevation, and season on selected arthropod diversity, and community composition along the Western Soutpansberg mountain range in Limpopo province of South Africa. The objectives of the study were to determine spider and ant diversity patterns along the mountain. Secondly, to determine the role of land-use, elevation, and season in structuring the diversity of both taxa. Lastly, to compare the composition of spider and ant assemblages across the various sites and identify indicator species for monitoring land-use change in the study area. A standardized pitfall trap survey was used to sample ants and spiders along an elevational transect that stretches across the southern and northern aspects of the mountain. The elevational transect (800 m a. s. l – 1700 m a. s. l) was made up of 18 sites, some of which have undergone human transformation mainly through agriculture and settlements. Sampling took place during the dry season (September 2019) and wet season (January 2020). Generalized linear mixed models with Poisson error distributions were used to determine the impact of land-use, elevation, season on spider and ant species richness and activity. Community composition was analyzed using NMDS (non-metric multidimensional scaling), PERMANOVA and ANOSIM analyses. Land-use had a positive effect on spider and ant diversity as the transformed sites had significantly higher species richness and activity for both taxa, particularly the agricultural sites and human settlement. However, species evenness was significantly lower in the transformed sites and higher in the natural sites. Species richness and activities for both taxa were highest at the low elevations. Spider diversity was higher in the dry season, but ants peaked in the wet season. Spider and ant assemblages were highly distinct between the land-use types and elevations. Ant assemblages remained similar between the seasons, while spider composition was slightly different across the two seasons. Spider and ant assemblages in the transformed sites were highly uneven which indicates a large disproportion in the number of individuals within the species found in transformed sites. It also indicates high species dominance, which is driven by the disturbance-tolerant species. One spider species, Copa flavoplumosa, was identified as an indicator species for the Eucalyptus plantations. All land-use types had an ant indicator species, which was either Monomorium damarense and/or Lepisiota sp.02 (spinosior gp.). High species dominance displayed by spider and ant assemblages in the modified habitats might have adverse effects on native and endemic communities. Because dominant and disturbance-tolerant species are likely to increase if more natural land is converted. This study was the first to investigate the impact of land-use changes at the Soutpansberg mountain range. The results indicate that landuse change had a positive effect on arthropod species richness and activity. However, species evenness was negatively affected. Although the land-use changes at Soutpansberg can increase the diversity of certain species, the potential to sustain the populations over the long term is unknown. Therefore, further assessments and monitoring of diversity in the region is recommended to understand the long-term impact of land-use and for informed decision making and strategy in conservation efforts.
The marine aquarium trade in South Africa: a vector for alien invasive species?
(2019) Wehr, Gitte Kirsten.; Macdonald, Angus Hector Harold.; Sink, Kerry.
Biological invasions are increasingly recognized as a primary threat to biodiversity. Global transport and trade play an important role in the movement of alien species around the world, and as transport and trade have intensified over the decades, so too has the number of alien species introductions. As preventing the introduction of harmful species is a more cost-effective and efficient method to managing biological invasions, it is imperative that scientific studies are aimed at identifying the pathways responsible for introductions. The marine aquarium trade is an ever-growing business globally and only up until recently has been identified as a major pathway for the introduction of alien species. Except for the notorious cases of the invasive lionfish, Pterois volitans, and seaweed, Caulerpa taxifolia, the role of the aquarium trade towards the introduction of alien marine organisms has been largely unevaluated. With popularity rising for the marine aquarium hobby in South Africa, it is of concern that the trade remains predominantly unregulated. This study aims to investigate the risk posed by the marine aquarium trade as a pathway for the introduction of alien invasive species in South Africa. One such vector examined in this study is live rock: any type of rock or dead coral skeleton encrusted with, and containing within its crevices, a wide variety of marine organisms, including colourful sessile invertebrates and encrusting algae. A combination of morphological and DNA barcoding molecular identifications, based on the phylogenetic inference of mitochondrial cytochrome c oxidase subunit 1 (COI) and internal transcribed spacer region (ITS) sequence data, was used to assign identifications to 174 taxa harvested from imported Indonesian and Kenyan live rock. Of the 6 diverse phyla identified, one alien species was flagged as harmful due to its successful invasion of other ecosystems in the world: the glass sea anemone Aiptasia pulchella. Non-target DNA amplification of live rock associated taxa exposed the coral pathogenic bacteria Vibrio spp., further suggesting that the marine aquarium trade is also a pathway for the introduction of pathogens. A second component of the study involved the assessment, via formal survey, of the role that pet stores and hobbyists play in the introduction and transmission of marine organisms around South Africa. Irresponsible aquarium pest disposal methods and informal trading pathways were revealed highlighting the need for an education intervention to promote responsible aquarium ownership skills. The third part of the study entailed a national stock inventory of marine aquarium traded fish and revealed that the number of species traded is vast (n = 228) and that 60 % are alien to South African waters. Although the strength of this vector was not defined, this study confirms that the marine aquarium trade is a pathway for the introduction of alien and potentially invasive organisms and serves as the foundation for future research into marine aquarium trade vectors in South Africa. The findings and conclusions presented here should be considered by biosecurity monitoring and management initiatives.
Towards understanding alien floristics within an urban matrix: the case of Durban, South Africa.
(2021) Appalasamy, Minoli.; Ramdhani, Syd.; Naidoo, Sershen.
Invasive alien plant species (IAPs) represent a major threat to biodiversity loss and ecosystem functioning globally. Alien species can take advantage of changes in ecosystems brought about by natural and non-natural disturbances and compete with indigenous species for resources. Urban areas are becoming increasingly susceptible to plant invasions due to increasing anthropogenic activity levels as urban human populations increase and changing climatic conditions that favour alien species. If uncontrolled, IAP impacts can bring about the transformation of natural habitats and exclusion of indigenous species. Given the limited financial and human resources available for IAP monitoring and control in developing countries like South Africa, increased efforts to monitor the prevalence of IAPs more efficiently and identify the drivers of invasiveness within cities is urgently needed to prioritise urban green spaces and species for monitoring and control interventions. Frameworks to monitor alien invasions, identify their drivers and impacts and prioritise sites and species for control of alien plants have been limited in the urban context, particularly within developing countries such as South Africa. Where these frameworks have been developed, there are challenges of them not being equally effective at different geographic scales and across different habitats. Furthermore, these frameworks often also suffer the weakness of not capturing the multi-dimensionality of plant invasiveness. This inspired the current study, which aimed to inform the design of an evidence-based framework that aids in prioritising urban green spaces and alien species for monitoring and control interventions by carrying out a set of inter-related investigations that addressed the following research questions: (1) What are the major environmental drivers of alien species (particularly IAPs) distribution? (2) Are alien and indigenous plant functional diversity (FD) and alien-indigenous co-occurrence patterns influenced by non-natural disturbance? (3) What is the influence of non-natural disturbance on the alien and indigenous soil seed bank (SB) floristics? and (4) Can selected seed physical and/or chemical traits be used as potential indicators of IAP persistence in natural SBs? These research questions were addressed using a case study approach: plants occurring within selected natural green spaces in an urban matrix in the rapidly developing city of Durban (eThekwini Metropolitan Area [EMA]), located within the Maputaland-Pondoland-Albany biodiversity hotspot in subtropical KwaZulu-Natal, South Africa. Classical vegetation survey techniques were used to identify and quantify (in terms of richness, density and diversity) aliens within 30 natural green spaces in the study area. Levels of non-natural disturbance were quantified using a scoring matrix, and soil SB samples were collected from each site. Cumulatively, 80 alien plant species were identified, of which 35 are presently categorised as IAPs in the EMA. Once it was established that IAP species richness and density were significantly positively related to disturbance level, selected parameters measured (viz. alien species richness and density) were used to develop an Alien Invasive Index (AII), the utility of which was validated in terms of its ability to discriminate between sites with low and high levels of invasiveness. The findings demonstrate the value of integrating the data generated using vegetation surveys and Geographic Information Systems to monitor and prioritise urban green spaces for alien control interventions. Importantly, the results suggest that the AII could assist in identifying invasive plant hotspots within urban areas. In a related study, alien and indigenous floristic patterns were probed further by comparing alien and indigenous species richness, density, diversity (alpha and functional), and species co-occurrence levels at the 30 sites in relation to non-natural disturbance levels. The ratio of alien to indigenous species was 1:1.5, with Asteraceae being the most dominant family. The relationship between species richness and alpha diversity differed for alien and indigenous species. Alien species were found to have higher FD, except for reproductive mode. Additionally, FD was significantly related to disturbance levels, alien species richness, and alien plant density. Co-occurrence data showed that alien-indigenous species pairs cooccur at high levels in urban spaces. Three notable alien-indigenous pairs (Centella asiaticaConyza sumatrensis, Centella asiatica-Solanum mauritianum and Bidens pilosa-Commelina erecta) co-occurred at more than 40% of sites, while two alien-alien pairs (Solanum mauritianum-Lantana camara and Conyza sumatrensis-Tagetes minuata) co-occurred at more than 50% of sites. The positive interactions between different alien species identified here contribute to the growing amount of evidence that supports the Invasional Meltdown Hypothesis (IMH). The results also showed that non-natural disturbance might lead to high levels of alien plant species diversity and facilitatory alien-alien and alien-indigenous species interactions. Understanding co-occurrence patterns could help design alien control programmes that focus on reducing alien-alien facilitation. For the study examining alien and indigenous species soil SBs in relation to nonnatural disturbance across the 30 sites, samples collected were processed using a modified seedling emergence method, incubated under greenhouse conditions (with irrigation), and monitored for one year. Germinants were identified and quantified, and comparisons were made between the soil SB and standing vegetation (SV). Cumulatively, 70 species belonging to 20 families were identified within the SB, with a higher presence of indigenous (60%) than alien species (40%). Overall, the SB flora was dominated by graminoids. Of the 70 species found in the SB, 69 were shared with the SV. Irrespective of the disturbance level, indigenous was higher than alien plant density within the SB. The findings of this study have implications for managers of urban green spaces since alien species in SBs could exploit niches created by disturbances, promoting urban invasions. In the final investigation, seeds of five IAPs were buried for two years at an experimental site to mimic seed burial within natural SBs. Additionally, the seeds of these species were characterised in terms of selected morphological and anatomical (seed mass, seed size, seed coat thickness) and chemical traits (estimated lipid content and changes in lipid melting properties). This study was designed to assess whether seed physical and/or chemical traits can be used as potential indicators of IAP persistence in natural SBs. Batches of buried seeds were exhumed every three/six months for viability (germinated seeds + seeds that stained positively following a Tetrazolium Chloride Test). Seed mass, size and coat thickness differed significantly across species, with Canna indica having the biggest and heaviest seeds of all species and the thickest seed coat. Solanum mauritianum had the smallest and lightest seed, with one of the thinnest seed coats. Results showed decreases in viability for four species (Canna indica, Melia azedarach, Senna didymobotrya, and Ricinus communis), while Solanum mauritianum maintained a 100% viability throughout the experimental period. However, while the viability of C. indica, R. communis, and S. didymobotrya was dominated by germinable seeds before burial, as viability declined with an increase in burial time, viability was dominated by seeds that were not germinable but stained positively. Melia azedarach differed slightly, where viability declined with burial time, but the majority of the seeds that were viable remained germinable. The longest ageing rate based on P50 was observed for C. indica (lowest estimated lipid content), while M. azedarach had the shortest ageing rate (highest estimated lipid content). Decreases in germination over time for C. indica, R. communis, M. azedarach, and S. didymobotrya led to changes in either/both enthalpy of melting of the lipid, and the temperature of the lipid melt, which could be related to different seed deterioration mechanisms when buried. This study did not identify significant relationships between the seed physical and/or chemical traits and SB longevity using the traits investigated. This could be explained by the relatively low number of species and traits studied and/or the phenotypic plasticity associated with seed post-harvest physiology in wild species. Nevertheless, the study gave rise to the beginnings of a conceptual continuum of IAP seed bank longevity, which, once populated with data for more species, could supplement the criteria currently used for assessing species invasiveness. As mentioned earlier, alien plant invasions are a major challenge for developing countries, particularly in urban settings. In countries like South Africa, the management of IAPs is complicated by heterogeneous combinations of non-natural disturbances, site-specific levels of disturbance intensity, and diverse vegetation types and associated species richness. The results clearly show that IAPs thrive under high levels of non-natural disturbance in urban green spaces and that alien and indigenous species can co-occur in various vegetation types. The AII was able to identify alien hotspots within the study area and may represent a useful tool for conservation practitioners/land managers. Lantana camara and Solanum mauritianum emerged as the most problematic IAPs currently in the study area. It was also evident that disturbance levels play a role in soil SBs of alien and indigenous species richness and plant density, and some problematic IAPs, notably S. mauritianum, can persist in SBs for long periods due to morphological, anatomical, and chemical traits. The results generated were used to design a multi-disciplinary and multi-dimensional framework that aids in prioritising sites and species for alien plant monitoring and control within urban areas. The methods proposed for assessing the prevalence and drivers of alien plant species and the indicators identified as potential indicators of their impacts in the framework can assist land managers, practitioners, and researchers develop recommendations and actions for alien plant monitoring and control in urban areas. The framework is designed to supplement and aid, and not replace, existing EMA policies/guidelines for alien plant control by preceding their planning and preparation phases. It could also help in developing new approaches to monitoring alien plant species in urban spaces.
Utilising GIS and remote sensing to assess the impacts of the invasive Rubus cuneifolius on veld grazing capacity.
(2023) Mnikathi, Ayanda Pretty.; Kirkman, Kevin Peter.; Sibanda, Mbulisi.
This study was motivated by the heavily invasion of Rubus cuneifolius (bramble) in the Mistbelt grasslands of KwaZulu-Natal province of South Africa, particularly at Wakefield Farm. When not effectively managed, bramble invasion results in dire consequences, including the reduction of veld grazing capacity. The initial steps in managing invasive alien plants (IAPs) in rangelands involves understanding their distribution and extent. This requires a suitable satellite data with optimal temporal, spectral and spatial resolution, a task that necessitates accurate and feasible mapping of IAPs. In this regard, this study aimed to assess the utility of Sentinel-2 multispectral imager in mapping the spatial distribution of bramble and assessing its impact on veld grazing capacity. This overarching aim was addressed using two specific objectives. The first objective was to test the capabilities Sentinel-2 Multispectral Imager (MSI) in detecting and mapping bramble during the senescence period. To address this objective, four sets of spectral features (all spectral bands, mNDVI, mSR and combined inputs) and the Discriminant Analysis algorithm were used to test the utility of Sentinel-2 MSI’s in detecting bramble during the senescing stage. Inputs were tested when red edge bands were included in the analysis (inclusive bands) compared to when they were excluded from the analysis (exclusive bands). The second objective was to assess the impacts of bramble invasions on grass production, species diversity and dominance. To address this objective, grass biomass and species data we gathered and dry weight rank (DWR) and double sampling techniques were utilised. A relationship between the estimated biomass and the actual biomass was determined in the invaded and the uninvaded patches. Then, Shannon-Wiener diversity index and the Simpson’s Index were used to calculate species diversity and dominance, respectively. Results showed that bramble could be detected using Sentinel-2 MSI to an overall accuracy of 89.33% with red edge derived mNDVI being the most influential discrimination variable. Furthermore, results showed a significant relationship between the estimated and the actual biomass as well as a higher total biomass in the invaded patches. In uninvaded patches, species diversity was higher while dominance was lower and in the invaded patches species diversity was lower while dominance was higher. This study highlights that Sentinel-2 MSI's red edge bands are well-suited for discriminating invasive alien plants, particularly bramble, in rangelands during annual senescence. Additionally, it emphasizes that bramble invasion diminishes the value of rangelands by reducing the productivity of palatable grass species.
Vegetative propagation of Corymbia henryi and its hybrids in South Africa through cuttings and mini-grafting techniques.
(2019) Mkhize, Millicent Smisele.; Laing, Mark Delmege.
Eucalyptus species are the most commonly planted hardwood species in South Africa, composing 42% of the total plantation area in the country but as the forestry planation areas in South Africa are not expanding, the only way to increase timber supply is to use the available land productively. This also increases the demand to efficiently propagate eucalyptus species, in an easy and economically viable way. This can be achieved through optimising vegetative propagation techniques which ensures mass multiplication of superior genotypes/phenotypes and the maintenance of individual characteristics in order to ensure that a plant is genetically identical to the original/donor plant. Spotted gum (Corymbia species) and their inter-specific hybrids have been identified as promising taxa for commercial forestry in South Africa due to their superior survival and growth across a broad range of edaphic and climatic conditions. The major benefits of these hybrids include superior growth characteristics, disease and insect resistance and frost tolerance, making them desirable for propagation. The hybrids of Corymbia torelliana and C. citriodora are some of the extensively used Corymbia hybrids since they combine frost tolerance (C. citriodora) and disease resistance (C. torelliana). The widely used vegetative propagation techniques include propagation through rooted cuttings and grafting. The aim of the study was to investigate the vegetative propagation of Corymbia henryi (C. henryi) hybrids through the rooting cuttings, and the grafting of C. henryi. The propagation of the hybrids through cuttings was carried out in three experiments, comparing cutting material collected from coppice stumps and ramets. The cuttings were collected from 14 C. henryi hybrid genotypes grown in Zululand. The cuttings were maintained in a rooting tunnel for four weeks before being placed in greenhouse conditions to acclimatize to the natural environment. The use of ascorbic acid (AA) (40 mg L-1) with Seradix® 2 (IBA 3g kg-1) yielded the highest rooting incidence, ranging from 37.5-55.5%, with the lowest rooting resulting from the application of propiconazole with Seradix®2 (IBA 3g kg-1) at >2%. The combination of AA with IBA has shown to be synergistic, since AA acts by protecting the rooting hormone from oxidation therefore allowing it to enhance tolerance of the plants to greenhouse conditions and alleviate stress. The cuttings selected from coppice had a higher rooting survival than those collected from hedge material. The genotype had an effect on the rooting success of cuttings, with the highest rooting percentage occurring with C. torelliana x C. citriodora subsp. variegata hybrids, with rooting ranging from 25-70%, while a C. torelliana x C. henryi hybrid had the least rooting success (%). The Corymbia species are considered difficult-to-root therefore the results have shown that these species can be propagated through rooting if the better rooting hybrid genotypes are selected. There is still a need to perform more trials to test the genotypes that have been found to root better in order to reach the commercial requirements of rooting rate of 70% and above. The propagation through grafting allows for the union of more than one genotype, whether belonging from the same species or different species and offers propagation of species which may be hard-to-root therefore cannot be produced through cuttings. The grafting experiment was carried out to optimize grafting techniques by comparing mini-grafting and conventional grafting techniques for Corymbia henryi. The rootstocks were grown and maintained at the ICFR nursery until time of grating. The scion material was collected from the Zululand region from C. henryi provenance mix. The grafting and mini-grafting was carried out in the grafting tunnel at the Institute for Commercial Forestry Research (ICFR) nursery, which had continuous mist for the duration of the experiments. The methods applied on the grafts were cleft and splice grafting. The evaluations made were based on the grafting method applied, comparing age of the grafts (mini- grafting and conventional grafting) and the effect of different treatments applied onto the grafts which included the control treatment, use of Parafilm® to tie the graft union, covering the grafts with polyethylene plastic (for one week) and use of an antitranspirant, Vapor Guard®. The control treatment, where grafts were tied with Parafilm® had the highest graft survival (33.3%), with the lowest graft survival on grafts covered with polyethylene plastic (%).Grafting onto four- month old seedlings(mini-grafting) had the highest survival at 55.6%, compared to grafting onto 10-month old seedlings (conventional grafting), with a survival of 22.2%. Mini-grafting has been tested over some species due to its ease of handling and is being evaluated for its potential in the propagation of Corymbia henryi. This type of grafting offers advantages of efficient management of plants that are grown in the nursery, allowing ease in irrigation, nutrition and pest disease control. The use of younger seedlings allows for grafting to be a commercially viable technique due the reduced time to grow the plant, flexible and pliable cambium layers of younger rootstocks and rapidness of grafting these younger seedlings. Mini-grafting was evaluated with the use of commercially available anti-transpirants and antioxidants, to assess effect of these treatments on graft success. The different ancillary treatments applied were the control, use of Parafilm® to tie the graft union, the use of anti-transpirants such as Nu-Film 17®, Vapor Gard® and Greenstim®, and the use of an antioxidant, ascorbic acid. Foliar application of ascorbic acid had the highest graft survival (60%) compared to the other treatments applied. The use of anti-transpirants in grafting of C. henryi was not successful therefore more research needs to be done on the commercially available anti-tranpirants in alleviating water stress in Eucalyptus species, as each crop may have different requirements for anti-transpirant application and doses may differ from one crop to another. Vegetative propagation of Corymbia henryi and its hybrids shows some potential for future use, but more research needs to be done to optimise these techniques to be able to have an impact on the commercial scale and in research outputs.

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