Masters Degrees (Ecology)

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Aspects of fruit digestion and selection in selected Southern African avain frugivores.
(2014) Zungu, Manqoba Moses.; Downs, Colleen Thelma.
Fruit-frugivore interactions play a central in maintaining the structure and diversity of ecosystems through their effects on seed dispersal. Because fruit selection and thus fruit removal represents the first stage in the seed dispersal process, understanding factors affecting fruit selection can play an important role in the formulation of sound conservation efforts especially light of the on-going habitat change. However, to date, the research is inconclusive as to factors affecting fruit selection as results have revealed inconsistent and controversial with a huge variation in fruit selection patterns between species and within individuals of the same species. The huge inter- and intra-specific variation in fruit selection patterns precludes any generalizations on fruit selection notwithstanding the research effort addressing the issue. One factor that could be attributed to this pattern is that most studies on fruit selection patterns in frugivorous birds have studied fruit attributes or physiological adaptations of frugivores to fruits in isolation. Because fruit profitability is affected by both pre- and post-ingestional factors, studying these factors in isolation deprives us of fresh insights into the fruit-frugivore interaction. Therefore by relating the physiological aspects of frugivores to fruit characteristics, this study aims to provide a link between the physiology of birds and their feeding ecology. Cape white-eyes (Zosterops virens), red-winged starlings (Onychognathus morio) and speckled mousebirds (Colius striatus) were used for this study. In the first part of this thesis, transit times and digestive efficiencies of birds fed equicaloric glucose and sucrose artificial fruit diets of varying concentrations were determined. Three concentrations were used: low (6.6%), medium (12.4%) and high (22%). Digesta transit times of birds increased with an increase in concentration for all diets but were generally higher on glucose diets. This finding has been widely reported in other similar studies. The increase in digesta transit times with an increase in sugar concentration may be due to high nutrient density on high concentration diets which require a longer processing time. Intake rates, on the other hand, decreased with an increase in sugar concentration. The inverse relationship between food intake and nutrient levels has often been attributed to compensatory feeding which posits that birds respond to nutrient dilution by increasing intake to allow a constant flux of assimilated energy. Indeed, speckled mousebirds and Cape white-eyes maintained a constant assimilated energy intake on sucrose diets by modulating food intake rates. The apparent assimilation efficiencies of glucose diets for all species were comparable and typical of those found in other frugivorous birds. However, red-winged starlings displayed low assimilation efficiencies for sucrose diets and lost significant body mass on all sucrose diets. The lack of significant sucrase activity in this species was attributed to this finding. This study showed the importance of digestive physiology in explaining fruit selection patterns in frugivorous birds. The second part of this thesis assessed the deterrence effects of tannins which are ubiquitous secondary compounds in plant material and are known for their ability to bind to protein which reduces nitrogen availability in the diet. In this study, birds were fed artificial fruit diets containing varying levels of tannins (0%, 2.5% and 5%) in paired choice tests. It was predicted that tannins would have no effect at low concentrations but at higher concentrations would act as deterrents although the levels at which they would become deterrents would differ among species. Red-winged starlings preferred the control diet, were indifferent to the medium tannin diet and were deterred by the high tannin diet whereas speckled mousebirds and Cape white-eyes were not deterred at all concentrations. The discrepancy in the results was attributed to differences in taste sensitivity, tolerance levels and detoxification mechanisms of secondary compounds between species. Occasional geophagy and consuming a broad diet were also implicated in producing the results obtained. Plant secondary compounds in fruits are diverse and their effects are similarly diverse and there is a possibility that different groups of secondary compounds generate disparate effects. Similar studies on other types of secondary compounds may thus contribute towards a broader understanding of the role of secondary compounds in mediating fruit-frugivore interactions. Overall, this study showed how diet affects ability to handle secondary compounds in fruits. The third part of this thesis addressed the influence of ethanol concentration on fruit selection in frugivorous birds. Because ethanol is ubiquitous in fruits and its concentration is positively correlated to fruit sugars, it has been suggested that because frugivores could use its odour to locate fruiting plants, they should select fruit with high ethanol concentrations. The aim of this study was to test this hypothesis by determining whether frugivorous birds show a preference for fruit laden with alcohol at levels equivalent to those of over-ripe fruits. Birds were provided with two artificial fruit diets in pairwise choice tests: an experimental diet containing 1% ethanol and an artificial fruit diet with no ethanol. For all species, there were no significant differences in the amount of fruit consumed between the two food types. These findings provided corroborating evidence to the suggestion that birds are unlikely to prefer over-ripe fruits compared to ripe fruits due to the negative impacts associated with ingesting ethanol at high concentrations. However, it could be possible that the lack of preference observed in this study was because the ethanol concentrations used were too low to be detected. Overall, this study suggests that at high concentrations, ethanol in fruits acts as a deterrent rather than an attractant. The last part of this thesis was conducted to determine the use of taste and olfaction by red-winged starlings in making foraging decisions. To determine whether they use taste in fruit selection, they were concurrently offered a control artificial fruit diet with another artificial fruit diet flavoured with different concentrations of ethanol and various fruit essences. To test whether they were able to use olfaction to locate food, they were provided with two choices: artificial fruit suspended over either banana and orange fruit essences and ethanol of varying concentrations or a control artificial fruit (without essence). It was hypothesized that (1) red-winged starlings have tasting ability which helps them in selecting fruits to feed on and that (2) red-winged starlings use olfaction to locate food. Results were consistent with the first hypothesis but inconsistent with the second one. Thus, red-winged starlings use taste when selecting fruits to feed on but do not use olfaction to locate fruit sources. The latter was unexpected because birds with olfactory bulb sizes similar to theirs exhibit advanced olfactory abilities. It was speculated that the lack of olfactory abilities in starlings could be attributed to the fact that this study was conducted outside of this species’ breeding season when olfactory abilities were likely to be lowest and also to that olfactory abilities may not have been important at the scale investigated in this study. Overall, the study showed that the sense of taste in birds plays an important role in making foraging decisions than currently appreciated. Overall, this thesis demonstrated the value of relating physiological attributes of frugivores to fruit attributes in acquiring deeper understanding of fruit-frugivore interactions. One particular advantage of the methodology employed in this study was that it controlled for covariance among fruit characters and also removed the confounding effects of as seed size and secondary compound composition. The shortcoming of this approach is related to the applicability of the results to the field conditions. Therefore an approach combining laboratory and field observations may produce results that may be important in informing us about how to manage our ecosystems.
Aspects of Nile crocodile (Crocodylus niloticus) population ecology and behaviour in Pongolapoort Dam, KwaZulu-Natal.
(2015) Summers, Mark Kai.; Downs, Colleen Thelma.
Pongolapoort Dam is one of the largest dams in South Africa by volume. It is also home to a breeding population of Nile crocodiles (Crocodylus niloticus). Crocodiles are keystone species which play an important ecological role in their aquatic habitats but are under threat globally. Consequently the aims of this project were to investigate the population number, nesting ecology, and behavioural aspects of gaping in Nile crocodiles at Pongolapoort Dam. Data were captured from July 2014 to August 2015, where there was a marked decrease in water levels in Pongolapoort Dam due to a drought occurring throughout KwaZulu-Natal. An estimated 549 Nile crocodiles occurred in Pongolapoort Dam in 2015, an increase in population from a conservative estimate of 273 individuals in 2010. The majority (80%) of the Nile crocodile population occurred in the inlet section of the dam, and with dropping water levels, the crocodiles congregated in large numbers in the Croc Bay region of the inlet. The population structure changed from 2010 when the majority occurred in the juvenile class to the majority of the crocodiles occurring in the sub-adult and adult size class in 2014/2015. The reproductive output of a population can be an indicator of population health. Consequently nesting ecology of Nile crocodiles was investigated at Pongolapoort Dam for the 2014/2015 nesting season. A total of 38 Nile crocodile nests were found over four nesting sites in the river section of Pongolapoort Dam. Nest effort decreased from 73% in 2009/2010 to 43% in 2014/2015, with a density of 4.9 nests per kilometre in the river section. All nests were found in alluvial deposits where Phragmites australis was the dominant vegetation. Some nests were predated by water monitors (Varanus niloticus); however, two nurseries were found containing hatchlings, while many nests showed signs of being dug up by the nesting females. The N2 Bend and Buffalo Bend floodplain were the most important nesting grounds, and this was attributed to the presence of suitable nesting conditions. Gaping behaviour in Nile crocodiles has received little attention as there are conflicting ideas as to why gaping occurs. The majority of literature suggests that gaping is a thermoregulatory response aimed at cooling the head of the crocodile. We aimed to identify other possible behaviours associated with gaping, at a basking bank in Pongolapoort Dam during winter. Preliminary results suggest that gaping may be a communicative or behavioural posture brought on by the following factors; position of the crocodile relative to the water, total length of the crocodile, time of gape, degree of gape, nearest neighbouring crocodile and number of neighbouring crocodiles. Further research is needed to help understand this behaviour of Nile crocodiles and its importance in their ecology and behaviour. The study showed that the population of Nile crocodiles in Pongolapoort Dam is increasing and remains in a healthy state compared with other population in South Africa. Insights into their behaviour may be applicable to other crocodilian taxa.
Aspects of the ecology of Cape porcupines on farmlands, peri-urban and suburban areas in KwaZulu-Natal, South Africa.
(2018) Ngcobo, Samukelisiwe Princess.; Downs, Colleen Thelma.; Wilson, Amy-Leigh.
The unprecedented changes in the environmental and ecological processes of the biosphere have led some to believe that we have transitioned into a new geological era from the Holocene. This current era is known as the Anthropocene epoch, termed as such due to the unprecedented human-induced environmental change. Humans have dominated global changes in the environment and climate through the conversion of natural land-use systems into anthropogenic landscapes dominated by agriculture, urban and industrial development. The conversion and destruction of natural habitats into anthropogenic ones have caused shifts in ecosystem functions, and ultimately this has dire consequences for biological diversity globally. Although many species have gone extinct due to anthropogenic land-use changes, some have persisted and thrive within human-dominated landscapes. These species have adapted well to these landscapes, to the point whereby they have modified their behaviour to exploit anthropogenic resources, and increase in numbers. However, the expansion of human land-use into historically wildlands means that wildlife and humans will increasingly interact with one another. This is cause for concern, particularly with the projection of future anthropogenic land-use expansion and intensification. As a result, there is need to research how wildlife in human-dominated landscapes adapt and how their survival will influence human-wildlife interaction in the future. Cape porcupines, Hystrix africaeaustralis, are one of those species which have benefited from anthropogenic change of the landscape. However, due to their effectiveness in exploiting anthropogenic food and shelter resources, they have been perceived as problematic. This has led to their persecutions in certain areas, particularly within agricultural systems. But they are also becoming increasingly problematic also in suburbia. Therefore, as motivation for this study, we aim to investigate the spatial ecology of Cape porcupines in human-dominated landscapes of farmland and urban areas. This is because there is very little information on their space use and the research on Cape porcupines is outdated. Consequently, due to their potential to become conflict-causing, there is urgency to determine their spatial ecology and contribute knowledge towards their conservation and management in these landscapes. Therefore, Cape porcupine home range and habitat use along a land-use gradient were investigated. A total of fifteen individual Cape porcupines were captured and fitted with Global Positioning System (GPS) collar transmitters in farmlands of Fort Nottingham, a peri-urban estate near Howick, and in a suburban estate in Ballito, in KwaZulu-Natal, South Africa. Data obtained from the GPS transmitters were used to estimate Cape porcupine home ranges using the Kernel Density Estimator (KDE) (Chapter 2). Overall estimated Cape porcupine home ranges were very small (n = 9, mean ± SE: 39.37 ± 6.33 ha) compared with other Hystrix porcupines. Farmland Cape porcupine home ranges (24.57 ha) were the smallest relative to the peri-urban (34.61 ha) and suburban areas (45.18 ha). These results were as expected, since it has been revealed that porcupine home ranges are determined by forage availability. Consequently, these human-dominated habitats have anthropogenic food resources that are constant relative to natural resources. This means that the expansion of human-dominated landscapes will result in the contraction of Cape porcupine home ranges as they benefit from anthropogenic resources. With the aid of the radio-telemetry data, we also determined Cape porcupine habitat use in the farmland, peri-urban and suburban areas, in KwaZulu-Natal, South Africa (Chapter 3). Habitat use of Cape porcupines were investigated at the landscape-scale (2nd order of selection) and the home range-scale (3rd order of selection). Habitat use of Cape porcupines varied at the two-levels of selection, and individual Cape porcupines utilized different habitats, but generally selected the forest with bushland habitat above other habitats. We thought Cape porcupine habitat use would be determined by habitats dominated by anthropogenic food resources (crops and gardens). However, Cape porcupines utilized natural food resources although they lived in human-dominated landscapes. Their habitat use was determined by the presence of forest with bushland habitat, and to a less extent by croplands or residential gardens. This means that at this point, Cape porcupines opportunistically utilized anthropogenic food resources according to their availability. However, these results should be interpreted with caution since the study duration was limited by battery life of the GPS transmitters (~ 5 months). This study revealed that Cape porcupine showed individual variation in ranging patterns and habitat use which were likely influenced by forage availability. In addition, Cape porcupines shifted their spatial behaviour depending on the landscape they inhabited. Therefore, the behavioural flexibility of Cape porcupines enabled them to adapt to anthropogenic changing land-use and successfully persist there.
Aspects of the ecology of feral cats (Felis catus) in urban Pietermaritzburg, KwaZulu-Natal, South Africa.
(2015) Pillay, Kerushka Robyn.; Downs, Colleen Thelma.
With changing land use such as urbanization, certain species thrive and are successful despite changes in the modified landscapes. Therefore, study of the ecology, adaptations and survival of these species in an urban context is warranted. Often these species include alien invasive species. An example is the feral cat (Felis catus). The negative effects caused by feral cats generally include impacts on native species of wildlife because of their highly predatory nature and their ability to spread zoonotic diseases. Furthermore, it often becomes a public nuisance occurring at high densities in urban areas. Consequently the aspects of the ecology of feral cats were studied from March 2014 to June 2015 in an urban mosaic in Pietermaritzburg, KwaZulu-Natal, South Africa. The research was also undertaken to propose and assist with an effective management strategy that was deemed necessary to control high densities of feral cats existing in urban Pietermaritzburg. Feral cats were trapped and fitted with GPS-GSM-UHF tracking collars in order to determine their home and core range sizes within the urban mosaic containing varying degrees of green and urban areas. Additionally, the disease prevalence in feral cats was also documented by collecting blood samples from feral cats occurring in many areas of the greater Pietermaritzburg area. The information gained in this study allowed compilation of feral cat management recommendations and strategies in order to control the increasing feral cat communities already established in Pietermaritzburg. Feral cat telemetry data showed that availability and abundance of food resources were the primary influencing factors affecting feral cat home range size and distribution as core areas contained at least one supplemental feeding site. There was considerable overlap of feral cats within the core areas. Overall home range size of feral cats was small but varied with individual cats. There was considerable overlap between and within the sexes. There were no significant differences in range size between sexes nor between day and night. However, diurnal ranges were generally smaller than nocturnal range sizes. Generally male feral cats had larger home ranges than female feral cats and nocturnal activity was higher across genders. Feral cats used urban areas more than green areas suggesting that the urban environment supports larger numbers of feral cats. The disease prevalence in feral cats tested was generally low. However, some tested positive for Feline Leukaemia Virus (FeLV) (28.6%) and for Feline Immunodeficiency Virus (FIV) (7.1 %). There was no occurrence of Feline Corona Viruses (FCoV) in feral cats tested in Pietermaritzburg. The location of feral cats within the city had a significant effect on prevalence of FeLV infection in feral cats tested. The findings of this study of feral cats in the urban mosaic of Pietermaritzburg showed that feral cats’ habitat use and home range were mainly affected by supplemental food resources. Furthermore, disease prevalence in feral cats tested was generally low. Thus efficient, cost-effective and realistic methods need to be implemented to control high densities of feral cats in this urban area require the use of a low-key supplemental feeding programme with a combined sterilization programme. This proposed strategy should be adopted and sustained with involvement of all concerned stakeholders to ensure that the welfare and population of the cats is well managed and humanely controlled particularly as this is an alien, invasive species. Additionally, all cats that test positive for any disease should be removed from the population to stop the spread of diseases to other feral or domestic cats in urban areas of Pietermaritzburg.
Aspects of the urban ecology of the Spotted Thick-knee (Burhinus capensis)
(2021) Josiah, Kyrone Kent.; Downs, Colleen Thelma.
Abstract available in PDF.
Assessing the success of red-billed oxpecker translocations as a conservation tool in KwaZulu-Natal, South Africa.
(2016) Jordaan, Maryna.; Downs, Colleen Thelma.; Combrink, Leigh.
There are numerous factors that contribute to a bird species becoming threatened and in need of increased conservation efforts in order to survive. Compared with fossil records, current extinction rates are much higher than expected, which emphasizes the need for conservation. Conservation translocations aim to increase the survival of threatened species by ameliorating their possibility of extinction, and contribute either to educational, scientific or supportive purposes in this. Reintroductions or translocations are a well-established method for increasing a species’ distribution and for restoring their historical range. Translocations are defined as human-mediated movements of organisms from one area and released in another. A translocation is only considered successful when a population is self-sustained through breeding of the released individuals and does not require intervention. Oxpeckers are African passerines from the starling lineage. Historically, red-billed oxpeckers (Buphagus erythrorhynchus) had a distributional range that extended from Eritrea to Somalia, through south-eastern Sudan to Zimbabwe and into the former Transvaal, Natal and Eastern Cape Provinces, South Africa. Oxpecker populations became threatened in South Africa in the early years of the 20th century. In southern Africa, red-billed oxpeckers became Near-Threatened as a result of cattle dips with substances toxic to the birds, and because of a significant decrease in their large game host species. Conservation efforts in the 1980s onwards have attempted to deal with the factors causing their demise. In 2002, The Endangered Wildlife Trust began translocating red-billed oxpeckers to areas where they had gone locally extinct, in an attempt to increase their current distribution and population in South Africa. Consequently, we documented and reviewed the various capture and quarantine methods, conducted since 1988 to the present, in the various translocations of red-billed oxpeckers. We also highlighted lessons learnt from these translocation events. To determine how successful these translocations were, we compared changes in the Southern African Bird Atlas Project (SABAP) reporting rate data and determined the presence or absence of red-billed oxpeckers at all the 24 translocation release sites in KwaZulu-Natal (KZN). In SABAP 1, data on species occurrences were collected at the Quarter Degree Grid Cell (QDGC) level. In SABAP 2, this was refined to pentads, where nine pentads are in one QDGC. Therefore, the reporting rate comparison was done at QDGC level. Prior to these translocations, red-billed oxpeckers were absent from all these sites. Specifically, we conducted transect surveys to determine red-billed oxpecker’s population estimates in Ithala Game Reserve (IGR) and Tembe Elephant Park (TEP). We also netted and ringed red-billed oxpeckers at these sites to obtain morphological and genetic data and to determine their breeding status. Furthermore, we distributed an online questionnaire to determine public perceptions on red-billed oxpecker’s range expansion in South Africa. We analysed the SABAP data using general linear modelling and the survey data using the Distance Programme in R Studio. There was a significant increase in reporting rates of red-billed oxpeckers in southern Africa since the end of SABAP1 in 1991 with several new areas where they had established. This was again confirmed from landowners reporting the first observation made of red-billed oxpeckers on their respective properties. Reporting rates at the specific translocated release sites had also increased. Twenty-four per cent of the QDGCs (n = 170) showed an increase in reporting rates in southern Africa, however, 36% of the QDGCs showed a decrease in reporting rates (n = 258). Fourteen per cent of the QDGCs (n = 100) showed new areas colonized by red-billed oxpeckers. In South Africa, red-billed oxpeckers had colonised several new areas, particularly near areas where reporting rates had increased. Twenty-six per cent of the QDGCs showed areas where red- billed oxpeckers were absent and had gone locally extinct (n = 187); however these areas were mostly in Botswana and Zimbabwe. We determined that habitat, host preference and host herd size were important factors when calculating population densities of red-billed oxpeckers. Detection probabilities for red-billed oxpeckers were highest in open bush habitat and where large herds were present. In IGR, red-billed oxpeckers were seen in 8% (n = 33) of the total of 391 observations made. In TEP, red-billed oxpeckers were observed in 6% (n = 24) of the total 378 observations made. In both IGR and TEP all red-billed oxpeckers we trapped and ringed had not been previously ringed and some had brood patches supporting their successful reproduction there. To date, a total of 24 reintroduction events and 13 population reinforcements have taken place, with a total of 1359 red-billed oxpeckers translocated in South Africa. The increase in reports of red-billed oxpecker sightings, especially at release sites and on nearby land, showed the importance of translocations for the conservation of oxpeckers. In addition, the placement of artificial nest boxes has increased the likelihood of red-billed oxpeckers breeding at their new translocated site. The recent down-grading of red-billed oxpeckers from Near Threatened to Least Concern, and the data collected in our study support the success of translocation as a conservation tool for this species. Translocations of red-billed oxpeckers in South Africa should be considered one of the more successful of such programmes as indicated by its success.
Assessing the trade of reptile species in the South African pet trade.
(2021) Mantintsilili, Asekho.; Downs, Colleen Thelma.; Shivambu, Tinyiko Cavin.; Shivambu, Ndivhuwo.
Despite the negative impacts that the pet trade has on the native and non-native biodiversity, economy and human health, the research suggests that the demand for pets and the extent of trade in live animals as pets has increased dramatically over the years. As a result, many species, including reptiles, have been translocated and introduced into new or non-native environments. Some of these have established feral populations, become invasive and are causing significant environmental and socio-economic impacts on non-native environments. Reptiles are among the most popular groups of animals in the pet trade industry globally. Trade in pet reptiles in South Africa is large and one of the major pathways through which non-native species, including invasive species, are introduced into the country. Despite this, little is known about the dynamics of the wildlife trade in pet reptiles globally. To understand the dynamics of the global trade in pet reptiles, we carried out a comprehensive literature search to gather relevant information from reptile pet trade-based publications. We further compiled a list of traded pet reptiles from all South African physical pet stores and online advertising websites to determine which species are traded, pose an invasion risk and have potential environmental and socio-economic impacts. We found a total of 39 publications based on the reptile pet trade from 1994 – 2021 worldwide. Our analyses revealed that the research effort was not uniform globally, with the majority (63.6%) of all relevant studies originating from three continents (Asia, Europe, and North America). Moreover, the United States of America (North America) and Indonesia (Asia) produced the greatest research outputs (12.1% each) compared with other countries across the world. We found at least 1140 reptile species belonging to 60 families involved in the global pet trade, with invasive red-eared slider Trachemys scripta elegans being the most frequently studied species (number of studies = 23/39). Of the recorded species, at least 79 are invasive, 46 endangered, 29 critically endangered, while only 546 are CITES-listed. In terms of reptile species sold in South Africa, we recorded a total of 2771 individuals representing 88 unique reptiles, 69 from physical pet stores and 18 from online advertising websites. KwaZulu-Natal, Gauteng and Western Cape Provinces had the highest number of pet stores and online advertising websites; therefore, they subsequently recorded the highest number of pet reptiles compared with other provinces. Physical pet stores were found to have the highest number of species compared to online trade. Of the recorded species, 76 are nonnative, and 15 of these are invasive to South Africa. Moreover, only 32 pet reptiles are listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). For current distributions, red-eared slider Trachemys scripta elegans, P. guttatus, and Western diamondback rattlesnake Crotalus atrox had the largest predicted climatic suitability. The future predictions for the latter two species were predicted to increase, while red-eared slider suitability shifted. Some species, such as Burmese pythons Python bivittatus, showed low invasion risk based on climatic suitability. However, given their large body size, history of invasion and their popularity in the pet trade, they are most likely to escape or be released from captivity and become invasive. A total of 76 reptile species were assessed for environmental and socio-economic impacts using the Generic Impact Scoring System (GISS), Environmental Impact Classification for Alien Taxa (EICAT), and Socio-Economic Impact Classification for Alien Taxa (SEICAT). Using GISS, we found that 13 species had environmental impacts (E_GISS), while 11 species had socio-economic impacts (SE_GISS). For EICAT and SEICAT, 13 species had environmental impacts, and eight had socio-economic impacts, respectively. The most popular pet species, red-tailed boa Boa constrictor, green iguana Iguana iguana, P. bivittatus, T. elegans, and central bearded dragon Pogona vitticeps had impacts in all the three scoring schemes. The later species and corn snake (Pantherophis guttatus) scored the highest for all impact schemes. Species sold in high numbers, with large climatically suitability and potential impacts, are more likely to establish feral populations and become invasive should they escape or be released from captivity. We, therefore, recommended that the trade in pet reptiles should be constantly monitored to avoid new introductions and the implications that the pet trade may have to the country.
Assessment of the current ecological integrity of the uMngeni River, KwaZulu-Natal, South Africa, using fish community structures and attributes of the Labeobarbus natalensis (Castelnau, 1861) populations.
(2019) Dlamini, Pumla Vanessa.; Downs, Colleen Thelma.; O'Brien, Gordon Craig.
Rivers are the main source of freshwater water for human communities and provide people with numerous ecosystem services such as water purification, transportation, power generation, food supply, and water for domestic, agricultural and industrial use. Water resources, and the ecosystem services they provide, are particularly important in developing countries, such as South Africa. The uMngeni River, is a strategic resource that provides water to two of the largest cities in KwaZulu-Natal Province (the uMgungundlovu and eThekwini municipalities), with more than four million people, making it socio-economically important. As such, to maintain sustainability the protection of the river is important. However, in South Africa and KwaZulu-Natal, the impact of anthropogenic activities has made riverine ecosystems one of the most threatened types of ecosystems in the world. The use of fish as key indicators of the ecological state of aquatic ecosystems is well established as their vulnerability to environmental change, mobility, longevity and relative ease of species identification make them good indicators. This study evaluated the current ecological integrity of the uMngeni River in KwaZulu-Natal using multiple lines of evidence including fish communities and the state of Labeobarbus natalensis (the KwaZulu-Natal yellowfish) populations, and environmental variables. The research was undertaken in the major man-made lakes (dams) in the uMngeni River (namely Midmar, Albert Falls, Nagle and Inanda Dams) and in the rivers of the uMngeni Catchment. Abiotic lines of evidence investigated included water quality and habitat, while the biotic lines of evidence included fish community structures and attributes of the population of L. natalensis. Fish community structures at eight selected River Eco-status Monitoring Programme (REMP) sites in the uMngeni catchment were considered. This included consideration of how the fish communities responded to changes in a range of environmental variables and alien fishes using the Fish Response Assessment Index (FRAI), we were able to determine that the ecological integrity of the uMngeni River decreases in a downstream gradient from the upper reaches of the catchment to lower reaches, due the synergistic effect of multiple anthropogenic stressors. The multivariate analyses indicated that the anthropogenic impacts responsible for shifts in fish community structures, and the associated ecological integrity of the river were related to changes in instream habitats and water quality stressors primarily. Most of the environmental changes identified can be linked to flow modifications and land use activities throughout the uMngeni catchment. Assessments of attributes of the L. natalensis populations from large instream impoundments in the uMngeni River (namely Midmar, Albert Falls, Nagle and Inanda Dam) resulted in diminishing wellbeing of the populations of this endemic migratory fish progressively both in abundance and structure, down the length of the catchment. The quality and quantity of water diminished down the catchment gradient with this gradient and the effect of the barriers themselves can partially be attributed to the impaired state of the populations. Impoundments are not preferred by juvenile and young L. natalensis that prefer shallow riffle habitats that are lacking in dams, the occurrence of many predatory alien fishes in the dam can also be attributed to the absence of small yellowfish in the dams. The outcomes of this study can contribute to the sustainable management and development of conservation plans for the rivers and dams in the uMngeni catchment. Major stressors that should be mitigated include the barrier effect and operation or flow releases from the large dams and smaller weirs etc. that cause river fragmentation in the catchment. It is recommended that management plans for the conservation of the fishes in the catchment should be developed which is achievable as the current supply of resources in the catchment is balanced with the demand for use. Fish passages should be established in all of the dams in the uMngeni River to allow migratory fish free passage along the river and to re-establish river connectivity processes. Additionally, the removal of redundant weirs or partial man-made barriers is recommended to alleviate the effects of fragmentation particularly on the yellowfish in the catchment. More research is required to understand the migratory requirements of fishes in the catchments and the cost-benefit of mitigating river fragmentation to achieve a sustainable balance between the use and protection of resources in the catchment. Finally, the study has identified water quality and flow stressors that are negatively affecting the wellbeing of the fish communities in the catchment. The water quality stressors derived from land-based activities and associated management of flows in the catchment must be improved to attain a sustainable balance between the use and protection of the resources of the uMngeni Catchment.
Development and application of novel ornithological survey methods for the detection of cryptic avian indicator species that predict grassland health.
(2021) Beaumont, Stuart Nicholas.; Downs, Colleen Thelma.
The anthropogenic pressure on South African grasslands to meet the needs of the burgeoning human population has exposed them to extensive permanent transformation and degradation. Indicator species may identify changes in the grassland ecosystem. One such indicator species for natural sourveld grassland condition in South Africa is the red-winged francolin (Scleroptila levaillantii), whose population density is negatively correlated to grazing intensity and annual burning. Pointing dogs (Canis lupus familiaris) have been used extensively to aid ecologists in detecting these and other cryptic gamebirds to establish abundance. Here, a reliable method was developed to count cryptic gamebirds in the Greater uMgeni Vlei Expansion Area, KwaZulu-Natal Midlands, South Africa, where the route through a survey site was flexible. A variation to the existing distance sampling technique was proposed where the dog global positioning system (GPS) track was the transect line. The study investigated the effect of varying environmental conditions on the distance from which a pointing dog could reliably and consistently detect a bird and allow calculating a detection distance based on influential environmental variables. Between March – October 2021, using pointing dogs fitted with GPS devices, controlled and uncontrolled trials were conducted on Japanese quail (Coturnix japonica) and red-winged francolin in their natural habitat, respectively, to establish the environmental conditions that affect detectability and the detection distance from which a dog can detect a bird of known location. A total of 21 surveys were conducted (August 2020 – October 2021), on four survey sites by one or two pointer dogs fitted with GPS devices, to establish the population densities and territory of red-winged francolin. Individual area of search, established from the detection distance based on nominal wind speed and GPS track, was calculated. The redundancy in area of search enabled the evaluation of relative proficiency of detection of red-winged francolin. Of the environmental variables monitored, only nominal wind speed significantly influenced detection distance, where an increase of one-knot wind strength resulted in an increase in detection distance by 0.64 m. This enabled an area of search, considerate of influential environmental conditions, to be derived and the probability of detection within that search area = 1. Results showed significantly better precision and accuracy when surveying with two dogs when compared with one dog. The calculation of detection distance, where the probability of detecting a bird at this distance = 1, addresses the bias of varying scenting conditions. The established area of search, where the probability of detecting a bird within this area = 1, addresses the situation where known coveys in an area of known size remain undetected. Since the area of search is independent of time spent searching and normalised for redundancy, the bias introduced by varying physical aptitude is mitigated. Consideration for the application of this method should be given to the environmental conditions under which the surveying is planned since the detection distance function is derived for conditions at the present study sites. These techniques, based on a variable survey route through the survey site, may be used by citizen scientists to assist land managers, conservationists, and ecologists in establishing the abundance of red-winged francolin, contributing to burning and grazing regime management to enhance conservation efforts for the species.
Eco-physiological aspects of invasive common myna.
(2015) Senoge, Ntaki Donald.; Downs, Colleen Thelma.
Abstract not available.
The ecology of black-backed jackal (Canis mesomelas) on farmlands in the Midlands of KwaZulu-Natal, South Africa.
(2014) Humphries, Bruce David.; Downs, Colleen Thelma.; Ramesh, Tharmalingam.; Hill, Trevor Raymond.
Agricultural development is progressively being attributed as a cause of biodiversity loss. Despite this development, some species do successfully inhabit these transformed habitats and benefit from increased food and resource availability. Therefore it is important to understand how and why species persist in those altered landscapes to conserve remaining biodiversity. Black-backed jackals are an abundant mesopredator with an apparent success to these changing agricultural environments. An understanding of their ecology in agricultural areas can provide important ecological information on the species and elucidate possible reasons why this mesopredator is capable of adapting and surviving in agricultural lands. From 2013 to 2014, a study was conducted on the ecology of the black-backed jackal Canis mesomelas in the Midlands of KwaZulu-Natal, South Africa. The study examined the home range, habitat use and diet of the species. In addition species characteristics and conflict of black-backed jackal from a landowner’s perspective were determined. It was found that rodents comprised the most consumed item of prey by black-backed jackal, followed by domestic livestock. There was a significant diversity of prey species in the diet indicating the opportunistic and generalist nature of the species. The home range movements of the species were relatively large compared to previous studies on the species and juveniles generally had larger home ranges than adult males and females. Habitat selection within home ranges indicated jackals preferred bushlands in winter and spring, and croplands in summer and autumn. Landowner’s reported regular predation on livestock by the species and suggest the increasing intensity of agriculture provides a greater food source of jackals. Some farmers used mitigation strategies in an attempt to prevent livestock losses, however, 32 % of farmers confessed to having poor disposal techniques for dead animals. This study provides important ecological information on black-backed jackal as a mesopredator species. Information on the spatial movement and diet of jackals in this study highlighted the variability in ecology of the species, providing information on the species’ persistence and success in agricultural areas. Furthermore, feedback from farmers emphasised the importance of having collaboration between farmers to control jackal predation and reduce human-wildlife conflict.
Ecology of the South African giraffe (Giraffa camelopardalis giraffa) across a land-use gradient in central KwaZulu-Natal, South Africa.
(2020) Nyathi, Memeli Jefrey Jethro.; Downs, Colleen Thelma.; Calverley, Peter Markham.
Abstract available in pdf.
The effects of fragmentation and forest structural components on the diversity of forest bird species in Durban, South Africa.
(2018) Maseko, Mfundo Sibongakonke Terrance.; Downs, Colleen Thelma.; Ehlers Smith, Yvette Cathrine.; Ehlers Smith, David Alan.
The pressure to meet the demands of the growing human population has resulted in the conversion of a large proportion of the Earth’s natural habitats into modified landscapes. With increasing urbanisation, generalist species may persist and thrive within the anthropogenically-modified landscapes, whereas specialist species are likely to decline in numbers and possibly become extinct. Consequently, this affects biodiversity and threatens the long-term functioning of the ecosystem as some species’ functional traits are lost. Therefore, understanding the ecological requirements of species with various functional traits to persist within human-modified landscapes is crucial for biodiversity conservation. The present research was conducted in the urban mosaic of Durban (eThekwini Municipality), KwaZulu-Natal, South Africa. The landscape of the study region comprised of extensive patches of Indigenous Forest and Thicket/Dense Bush. Previous research has highlighted the dramatic loss of natural forests within Durban as a result of anthropogenic activities, such as tourism-orientated development and human settlements. However, only a few studies have documented the threats that losing these coastal forests pose to wildlife, particularly birds. With the loss of forests and increasing urbanisation in Durban, the present study aimed to investigate the (i) forest fragmentation effects via patch size and isolation distance of habitat patches on the diversity of forest birds (ii) differences in vegetation structures of Indigenous Forest (hereafter IF) and Thicket/Dense Bush (hereafter TDB; a secondary forest habitat representing regenerating IF) with the aim of showing their importance in the provisioning of habitat and a diversity of niches and resources for avian species in Protected Areas (PAs) within an urban mosaic. During the southern Africa breeding season between October 2016 and March 2017, we conducted bird point-count surveys in IF and TDB patches within five PAs within eThekwini Municipality. We further recorded microhabitat vegetation structure at each survey point. We recorded a total of 75 bird species. Furthermore, we recorded the species richness per patch as overall species richness, and then calculated the functional diversity of the community recorded as a difference matrix of each species’ functional traits. Principally, we found that taxonomic richness was not affected by increasing isolation distance between forest patches, and that habitat patch size positively influenced taxonomic richness and functional diversity. Furthermore, the number of avian forest specialist species increased with patch size, probably because of the diverse environmental niches and resources present in larger patches. Secondly, the overall vegetation structures and species richness of IF and TDB did not differ significantly. However, the presence of avian specialist species in TDB survey sites was of interest because TDB vegetation structure was not predicted to be ideal habitat for forest specialist species, as TBD was expected to represent secondary forested habitat. The lack of significant differences in vegetation structures between IF and TBD, and the provisioning of forest specialist species in TBD led us to conclude that the TDB in our study region is at an advanced stage of regeneration into IF. Overall, the present study highlighted the diverse avian species that may exist within the urban mosaic forests, provided that availability of specialised niches persist. Therefore, the findings of this study highlight the conservation importance of natural landscapes in human modified landscapes. Furthermore, they emphasize the necessity of legally protecting both forest and thicket dense bush.
Effects of land restoration on the habitat integrity of rivers based on biological water quality and habitat condition assessments with a focus on the eThekwini Municipality, Durban, South Africa.
(2024) Magudu, Kholosa.; Downs, Colleen Thelma.; Burnett, Matthew James.
Riparian ecosystems are natural areas that offer an extensive range of ecosystem services. Their functionality aids in diverting and mitigating the impacts of surface water runoff, thereby reducing soil erosion. Riparian ecosystems also play an important role in sequestering nutrients and organic matter. The degradation of river systems impairs riparian ecosystem health and results in dysfunction, lack of ecosystem services provision and other deleterious effects. This study examined the effect of restoring riparian habitats across two study sites in Durban, Ethekwini Municipality, South Africa. The study aimed to a) measure and assess habitat integrity across three river systems as a result of reforestation efforts, and b) monitor the biological water quality using the Mini Stream Assessment Scoring System (MiniSASS) and the Index of Habitat Integrity indices. In addition, a systematic review was undertaken to provide an introduction and background to ecological restoration work involving freshwater ecosystems in the general South African context. The Index of Habitat Integrity and MiniSASS data were collected over ten months at two sites reforested by eThekwini Municipality, which were compared with data collected from a third river site used as the reference. Two sampling points were selected per site (namely upstream and downstream). It was predicted there would be a significant difference in MiniSASS scores between river sites under reforestation and reference sites not exposed to reforestation. However, it was found that MiniSASS and Index of Habitat Integrity scores differed between and across sites. The reference site had the highest scores. The sites with greater habitat integrity had improved ecological conditions based on macroinvertebrate responses to anthropogenic disturbances. This study highlighted the important role of naturally functioning riparian habitats in cleaning water and provides a baseline for reforestation impact monitoring, as well as informing local governance strategies for restoring degraded rivers in urban areas.
Evaluating multiple stressors on aquatic ecosystems in an urban environment.
(2024) Ngcobo, Nolwazi Blessed.; Downs, Colleen Thelma.
The issue of compromised aquatic ecosystems is a global dilemma; with existing and new stressors emerging, freshwater ecosystems continue to degrade tremendously. Multiple stressors exist in aquatic ecosystems, from invasive species to overexploitation of aquatic resources, habitat degradation, flow modifications and pollution. The uMsunduzi catchment in Pietermaritzburg, KwaZulu-Natal Province, South Africa, is one such stressed freshwater body. The present study was undertaken to determine the major threats to aquatic ecosystems and the possible strategies to mitigate the factors that compromise freshwater biodiversity, health, and ecological status. The first problem was to investigate the impact of anthropogenic barriers along the longitudinal pathway of the rivers. Hence, an extensive literature review on managing river barriers was conducted. This systematic review showed a need for river connectivity restoration projects in Africa, particularly in South Africa. The Northern Hemisphere countries are more advanced in restoring river connectivity by removing barriers or retrofitting fishways. A prevalence of physical barriers in the uMsunduzi catchment was found, and most barriers did not have fishways or fish passage structures. The fish communities, together with their associated habitat features, within the uMsunduzi mainstem and tributaries, were assessed to deduce which environmental factors influence the fish communities' structures in the system. There was a clear indication of a decline in species diversity and deterioration of the ecological health of the uMsunduzi catchment. Of the 18 expected fish species, according to the Freshwater Biodiversity Information System (2023), only 50% of these were caught. This is concerning, especially as the “near threatened” (IUCN status) Enteromius gurneyii (redtail barb) was not caught, and Amphilius natalensis (Natal mountain catfish) was caught once in low abundance. The uMsunduzi River had a highly deteriorated ecological integrity per the Fish Response Assessment Index (FRAI) scores, especially close and downstream of the city centre where the industrial areas are concentrated. Similarly, there is a great deal of microbial contamination, putting the uMsunduzi River in a matter of public health. There was also a significant presence of magnesium, calcium and fatty acids. In conclusion, the connectivity, ecological health and water quality of the uMsunduzi catchment were compromised, giving a clarion call for mitigation and management actions on the systems.
Fleshy-fruited invasive plant species in KwaZulu-Natal, South Africa: native avian seed dispersal and impact assessment.
(2019) Bitani, Nasiphi.; Downs, Colleen Thelma.
Globally, alien plant species have been recognised as a major threat to biodiversity. The increased global trade and travel have resulted in the increased introduction of new species. Direct or indirect introductions of alien invasive plant species result in altered ecosystem functioning, negatively affect economies, human health and wellbeing. In forest systems, habitat fragmentation has major impacts on biodiversity including the facilitation of alien invasions. Habitat alteration creates disturbance zones that are associated with increased invasion success. South Africa, like other parts of the world, is severely affected by alien plant species. Fleshy-fruited invasive species are amongst the most damaging invasive species with major environmental, social and economic impacts. Fleshy-fruited invasive plant species integrate into local seed dispersal networks and form mutual relationships with local avian seed dispersers leading to increased invasion potential. The success of avian mediated seed dispersal is influenced by the functional traits of both the plant and avian seed dispersers. Considering the negative impacts of fleshy-fruited alien invasive species it is important to understand ecological processes leading to their successful spread and if high priority species are being targeted for management to guide policy and conservation. Understanding avian mediated dispersal is important as it gives insights into the species that could promote alien plant invasion. The aim of the present study was to assess avian seed dispersal, and ecological and socio-economic impacts of fleshy-fruited alien invasive plant species. The objectives were to (1) predict avian seed dispersers of fleshy-fruited alien invasive plant species; (2) determine the assemblage of native avian species potentially dispersing the seeds of Lantana camara; and (3) determine the socio-economic and ecological impacts of fleshy-fruited alien invasive plant species. Firstly, we predicted the avian seed dispersers of fleshy-fruited invasive plant species in the Indian Coastal Belt Forest of KwaZulu-Natal Province, South Africa using functional traits of avian species (body mass, gape width, bill length, degree of frugivory, foraging strategy, abundance and habitat specificity) and fleshy-fruited invasive plants (crop size, fruit size, seed size, number of seeds, plant height, plant habitat, fruiting period and derived invasiveness score). The results showed that small, abundant forest generalist avian species were potentially effective dispersers of fleshy-fruited invasive species. Fleshy-fruited invasive plant species that were more likely to persist in the disturbed Indian Coastal Belt Forest through avian-mediated seed dispersal were small-seeded, open habitat plants with relatively longer fruiting duration. Secondly, we assessed the role of native avian species in the potential dispersal of a highly invasive shrub Lantana camara of the family Verbenaceae in Pietermatzburg, KwaZulu-Natal, South Africa. Avian species visiting L. camara were observed and potential dispersal distances estimated. The results showed that native avian species were potential seed dispersers of L. camara were mostly relatively small, moderately frugivorous avian species. The dark-capped bulbul (Pycnonotus tricolor) showed relatively high visitation frequencies to L. camara and was more likely the main effective dispersers of the plant. Potential seed dispersal distances were shown to range from 9 to 45 km and long distance seed dispersal distances were shown to be rare and only limited by rarely large avian frugivores. Lastly, we assessed the ecological and socio-economic impacts of fleshy-fruited invasive species using the generic impact scoring system. The results showed that fleshy-fruited invasive plant species have both socio-economic and environmental impacts. The highest environmental impacts were shown to be on ecosystem and vegetation, or plant and the highest socioeconomic impacts were on agriculture, forest production and human health. The results presented in this thesis provide essential insights into the importance of avian mediated seed dispersal in the invasion of fleshy-fruited invasive plant species. The findings of the study also highlight the importance of predictive approaches in informing the management of invasions and showed fleshy-fruited invasive plant species with high socio-economic and ecological impacts. Knowledge of species with high impacts will help in guiding resource allocation and preventing the introduction of high-risk species. Also, ecologists and other decision-makers should consider ecological processes that are leading to the spread of invasive plant species in management practices or plans.
Importance of freshwater systems and eels in the uMngeni and uThukela catchments, KwaZulu-Natal, South Africa: community perspectives.
(2023) Nkomo, Mxolisi Nhlakanipho.; Downs, Colleen Thelma.
Globally, the conservation status of inland fishery resources and freshwater systems is vulnerable, threatening communities' livelihoods dependent on freshwater harvested species. Few studies have reported on the economic and cultural contributions of catadromous eels (Anguilla spp.) in southern Africa, particularly in South Africa. Beyond using freshwater systems for domestic purposes and meeting basic needs, people use rivers for socio-cultural purposes such as; cultural (cleansing), spirituality (healing), and religion (baptism). This study was undertaken to determine if human activities impact the African anguillids eel populations in the local communities of uThukela and uMngeni catchments and management areas in KwaZulu-Natal. A systematic review was conducted on global studies, with an emphasis on southern Africa, that report on the human perspective on the value of anguillid eels when in freshwater systems. In the southern African region, the available literature focused on the distribution of anguillid eels, habitat loss, and a report on the drastic decline of anguillid eels in KwaZulu-Natal's freshwaters where the Anguilla marmorata, A. mossambica, A. bengalensis, and A. bicolor occur. The studies from the northern hemisphere were rich in reports of eel harvesting (wild catches) and export, which was lacking in the southern African region. The systematic review showed a scarcity of knowledge regarding anguillid eels’ association with spirituality, spirituality, culture, and subsistence in South Africa. Secondly, people’s perceptions of the importance of eel species in freshwater fisheries were assessed using a questionnaire along water courses in the uMngeni and uThukela catchments and ecological management areas, KwaZulu-Natal. A total of 154 people were interviewed (66% males, 34% females); the majority of these participants were isiZulu-speaking, which contextualises the findings to the area of KwaZulu-Natal, uThukela and uMngeni management ii areas in particular. The fishing of eels was found in both catchments, with 74% (of the n = 102) being subsistence fishers (with only one female fisher), and 41% of these subsistence fishers specifically targeted eels. All the fishers that targeted eels depended on freshwater eel catches for income because of the relatively high demand and value. Some fishers caught and sold eels to traditional healers who used their products of medicinal products for different uses. Thirdly, the use of freshwater eels (Anguilla spp.) was assessed beyond harvesting them to sell or consume. In particular, using a questionnaire, the spiritual and cultural values of African freshwater eels and their associated freshwater environment in the uMngeni and uThukela catchments were investigated. A total of 154 people from different communities were interviewed along these river systems during 2021 and 2022. In the different communities within catchments, participants reported a number of different beliefs associated with eels and rivers. The responses showed that people valued clean rivers for various cultural, religious, and recreational activities. Some valued eels as they were associated with their beliefs. People who use freshwater for their respective cultural and spiritual, fishing, and domestic purposes voiced a considerable challenge in using freshwater systems, water pollution and water contamination from industrial waste or eutrophication from agricultural waste. Without community participation, there is no guaranteed sustainability of the water resources for the spiritual and cultural values of freshwater eels and freshwater systems. Community leaders and water management bodies must engage with communities in identifying important river uses (domestic, fisheries), and their contribution to spiritual and cultural practices. This will ensure long-term sustainable use and protection of inland water and fisheries resources associated with cultural and spiritual beliefs in KwaZulu-Natal. Freshwater eels hold a crucial aspect in the lives of traditional healers, some local fishers, and the general public, iii those that have knowledge of the use of these species. The study has shown that these species are still under-studied in KwaZulu-Natal, and most people have little understanding of the economic and cultural values, leading to less appreciation of these species by most people, mostly nonfishers.
Macroinvertebrates as ecological indicators of the wellbeing of the lower uMvoti and Thukela Rivers, KwaZulu-Natal, South Africa.
(2018) Tenza, Ntombiphumile Perceverence.; O'Brien, Gordon Craig.; Downs, Colleen Thelma.
The excessive use of water resources and climate change stressors is impacting the quality and quantity of surface aquatic ecosystems in South Africa, a semi-arid country. Although South Africa is considered to be a developing nation, riverine ecosystems have already been transformed and impacted on to meet human needs. This has altered the ecological characteristics of the rivers of which more than 70% are now threatened. The National Water Act (NWA) of South Africa and associated National Water Resource Strategy (NWRS) advocates the establishment of a suitable balance between the use and protection of water resources to ensure sustainability. The implementation of NWA and NWRS is limited in some South African rivers and the quality of these vulnerable ecosystems continues to deteriorate. Knowledge is needed to evaluate the response of the riverine ecosystems to changes in environmental variables so that we can understand the socio-ecological consequences of the continued deterioration of our resources and best manage them when resource demand exceeds supply. This study focusses primarily on lower uMvoti and Thukela Rivers along with their associated tributaries (Ntchaweni and Mandeni Streams). These rivers are among the highly threatened ecosystems and that can be attributed to water resource use stressors including overexploitation, invasion by exotic species, industrial pollution and effluents, extensive agricultural practices, mining activities, increased urbanization as well as social and economic development in peri-urban and urban centres. These stressors have been identified as determinants of the degradation of aquatic biodiversity and they result in the loss of key ecosystem services. Aquatic macroinvertebrates are good ecological indicators that have been used internationally to establish robust bio-monitoring lines of evidence or tools for the monitoring and management of river ecosystems. Today a suite of international and local lines of evidence incorporating macroinvertebrates are available to evaluate the wellbeing of macroinvertebrates communities, their response to environmental variable changes and the wellbeing of the rivers they occur in. To implement the use of macroinvertebrate communities as ecological indicators of the evaluation of the wellbeing of the uMvoti and Thukela Rivers, aquatic insects, mollusks, fresh water crustaceans, annelids, and other aquatic invertebrate communities were characterised. These use of these ecological indicators is well established due to: (1) the knowledge of the tolerances of taxa to different water quality, quantity and habitat stresses, (2) the high diversity of taxa that are representative of a wide range of river ecosystem types and (3) they are abundant, easy to collect (visible to the naked eye) and easy to identify. Two community metric measure tools namely the South African Scoring System (SASS, version 5) and the Macroinvertebrate Response Assessment Index (MIRAI) were used to evaluate the wellbeing of macroinvertebrate communities of the lowland uMvoti and Thukela Rivers in this study. The ecological integrity of both rivers were found to be adversely impacted and their integrity state ranged mostly from class C (moderately modified) to class E/F (seriously or extremely modified). Reduced habitat heterogeneity and altered water quality were found to be driving factors that cause the degradation in macroinvertebrate communities. Multivariate statistical analyses were used to evaluate the responses of macroinvertebrate communities to water resource use activities associated with the uMvoti and Thukela Rivers. In the early part of the study period many intolerant macroinvertebrate taxa contributed to the structure of communities. However, towards the latter part of the study, pollution tolerant taxa dominated communities. Both rivers also showed a decreasing trend in estimated macroinvertebrates estimated abundance and number of taxa. In the uMvoti River this can be attributed to the combined effect of the urban runoff, effluence discharge from the Gledhow sugar mill and Sappi Stanger Mill, informal settlements and agricultural activities. Results reported from the Thukela River can be ascribed to the synergistic effects of water quality stressors associated with the Isithebe Industrial complex, wastewater treatment works, effluent from the Sappi mill, sugarcane plantations as well as domestic use by local communities. The outcomes of this study showed that there is not sufficient protection and management measures afforded to the systems. The requirements of the National Water Act to establish a sustainable balance between the use and protection of the water resources in the system is not being achieved. No action is being taken to mitigate pollution from major sources in the study area. Thus, an appropriate management plan and its implementation is urgently needed, with monitoring activities, to mitigate these stressors and attain a balance between use and protection of these socio-ecologically important ecosystems. Failure to implement effective management plans may result in continued deterioration of the wellbeing of the ecosystem and potential loss of biodiversity, ecosystem services and functions that these rivers provide.
Managing nesting hawksbill turtles (Eretmochelys imbricata) on a small tropical island.
(2018) Gane, Julie Alexandra.; Downs, Colleen Thelma.; Brown, Mark.
Although human impact has caused the hawksbill turtle (Eretmochelys imbricata) to be on the brink of extinction, conservation efforts are on the increase and management strategies are being re-defined to manage the species towards rapid population increases. Numerous conservation measures have been applied and tested, with varying levels of success, to minimize threats and increase hatchling recruitment success rates. Conservation management is imperative for the survival of this species and has been shown to be easiest and most feasible at the nesting and hatching stages. On Cousine Island where this study took place, a turtle monitoring and management program was initiated in 1994 to protect nesting females and incubating eggs at the nesting and hatching stages of the lifecycle. Controversial conservation measures such as the handling of eggs, relocating clutches and application of crab proof barriers, have been applied on an ad hoc basis to minimize the high levels of mortality from natural erosion and crab predation. The merit of these practices, such as the translocation of egg clutches and the implementation of these specific barrier methods has never to our knowledge been scientifically tested using controlled experimentation. The first aim of this study was to find the most effective crab barrier method for increasing hatchling recruitment success and minimising predation rates with limited negative consequences. The second aim was to decipher crab density trends in order to offer a proxy for the number of crabs a nest might be exposed to within an area and develop beach profiles along the entire nesting beach to provide an expression of beach morphology to minimise nest loses from erosion. Finally, we analysed 10 years of nesting ecology and hatching success data with the aim of providing nesting and hatching trends to inform management decisions on Cousine Island into the future. Results across this study indicated that management measures can have both positive and negative effects on the nesting ecology and hatchling recruitment success in particular. We found that hawksbill clutches incubating without crab barriers are susceptible to losing on average a third or more eggs to crab predation than those with a crab barrier in place. Nests which were protected with netting had significantly higher hatchling recruitment success rates and nests protected with fencing had significantly lower predation rates than control nests. The use of netting, however, had a substantial cooling effect which can potentially distort natural sex ratios. Results across the entire study indicated that spatial distribution and environmental variations have an effect on embryonic development, hatchling fitness, sex determination, hatching success and the risk of predation. The hatchling recruitment success on Cousine Island was also found to be affected by nest losses each season from seasonal beach erosion. Beach dynamics were also found to be cyclical and we discovered that the nesting beach is prone to higher levels of erosion than accretion which created significant changes to beach width across the season. This study showed that when focusing turtle conservation measures at the nesting site, hatchling recruitment success can be increased by minimising mortality at the egg and hatchling stage. The aim in the long-term is to assist with the analyses of local and global population dynamics, deciphering threats and minimising the threat of extinction.
Monitoring the efficacy of a lowland instream barrier on the lower uThukela River and the importance of river connectivity.
(2023) Van Zyl, Bradley Bruce.; Downs, Colleen Thelma.
Freshwater is the key to life on earth, with rivers being the pathway that allows it to run from mountains to the ocean, performing many important functions along its way. Humans rely on the many ecosystem services that freshwater provides, such as water quantity provision for domestic, industrial, and agricultural processes, food supply, water purification, and recreation and tourism, to name a few. Water-scarce countries, such as South Africa, are particularly vulnerable to water shortage issues and require many water supply solutions, like dams, weirs, and transfer schemes, to harvest the available rainfall. The uThukela River in KwaZulu-Natal is not only an important resource within its catchment but also to external catchments through inter-basin water transfer schemes, including that of the Thukela-Vaal transfer, which feeds the economically important hub of South Africa, the Gauteng Province. The lower uThukela River is a highly stressed system, with synergistic effects from multiple stressors relating to water quality, water quantity, habitat alterations, and wildlife disturbance affecting it. Additionally, the Lower Thukela Bulk Water Supply Scheme (LTBWSS) weir was recently constructed in its lower reaches, approximately 20 km upstream of the uThukela Mouth to the Indian Ocean, to provide bulk water to surrounding local municipalities. Due to the rich diversity of fish species in the region, particularly those with marine, estuarine, and freshwater migratory patterns, a fishway was incorporated into the design of the weir to facilitate fish movements over the weir. This study evaluated the impact that the LTBWSS weir has on fish community structures in the region and additionally assessed the efficacy of the fishway in allowing fish movements through it. Various sites were selected upstream, downstream, and on the tributary Mandeni ii Stream to assess environmental variables driving fish community structures, with passive and active sampling methods used to assess the fishway's functionality. Fish collection occurred at three sites upstream of the LTBWSS weir, four sites downstream of it on the uThukela River, and two sites on the Mandeni Stream. Abiotic variables relating to water quality, velocity, depth, and habitat were collected along with fish to determine which environmental variables were driving the fish communities at these sites. Multivariate analyses indicated that available substrate and cover, the average depth, and temperature were drivers of the fish communities in the study. Upstream sites showed lower species richness compared with downstream sites, with fish communities largely made of freshwater species and few euryhaline species. Additionally, individual species showed different responses to different environmental variables. Furthermore, since the construction of the LTBWSS, the loss of previously highly abundant cichlid species has occurred in the region. This is likely because of the synergistic effects of stressors created by it, such as the disruption of fine sediment transport, water abstraction, and pollution. Passive assessment of the fishway's efficacy in catering for migratory species used PIT telemetry. Budget constraints only allowed the installation of a single PIT antenna at the upstream entrance of the fishway, which was able to assess the upstream migration of fish from downstream. The results found that only eight individuals representing three species managed to navigate the fishway during the study successfully. This included Oreochromis mossambicus, Labeo molybdinus, and Clarias gariepinus. Active sampling involved electrofishing three key locations in the fishway on a monthly basis. Results showed that small-size classes of fish largely dominated the fishway and that the downstream entrance had the highest abundances and species richness. Further research on the role of the fishway in maintaining river connectivity is recommended. iii The outcomes of this study showed the importance that water resource managers have in maintaining the resource for humans and the environment. Knowing individual species' responses to environmental variables allows their populations to be better managed. Additionally, the outcomes of this study showed the importance of river connectivity past a barrier and highlighted the need for effective fish passage solutions in South Africa. It emphasised the need to better understand the migratory requirements of local fish to build better fish passage structures. Major stressors to be addressed include the impacts caused by barriers relating to flow releases, migration blocks, and habitat alteration upstream and downstream of them. Furthermore, the proper management of fish passage structures is essential to their functionality, which includes regular monitoring of the fishway for issues such as debris blockages and swiftly finding solutions to them to ensure that no undue delays or stress may occur for migratory fish.

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