Department of Botany and Zoology

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The ability of terrestrial Oligochaeta to survive in ultramafic soils and the assessment of toxicity at different levels of organisation
(Stellenbosch : University of Stellenbosch, 2006-12) Maleri, Rudolf A.; Reinecke, A. J.; Reinecke, S. A.; Mesjasz-Przybylowicz, J.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.
Metals are natural elements of the earth crust usually present at low concentrations in all soils. Although many metals such as cobalt, copper, iron and zinc are essential to living organisms, at elevated concentrations most metals are toxic to organisms living in and on soils. Elevated concentrations of metals are caused either by anthropogenic deposition following remobilisation from the earth crust or are of natural origin. Ultramafic soils do not only pose unfavourable living conditions such as drought and poor organic content, these soils are also characterized by extremely high concentrations of a range of metals known to be toxic under normal circumstances. Ultramafic soils are of high ecological importance as a high proportion of endemic organisms, especially plants, live on these soils. As it is known that earthworms do occur in ultramafic soils, the aims of the present study were to investigate the abilities of earthworms to survive in these soils and the influences of elevated chromium, cobalt, copper, manganese and nickel levels. For the evaluation of the metal background conditions, soils originating from ultramafic rocks of the Barberton Greenstone Belt, Mpumalanga, South Africa were collected and different fractions representing different levels of bioavailability were analyzed for arsenic, chromium, cobalt, copper, manganese and nickel. To assess the mobile, readily available metal fraction, i.e. Ca2+- exchangeable metal cations, a 0.01 mol/L CaCl2 extraction was performed. To investigate the mobilisable metal fraction, representing the amount of easily remobilisable complexed and carbonated metal ions, a DTPA (di-ethylene-triamine-pentaacetic acid) extraction was conducted. In relation to non-ultramafic or anthropogenic contaminated soils, a far lower proportion of metals were extractable by the above mentioned extraction methods. To investigate the availability and effects of these metals on earthworms, two ecophysiologically different species were employed. Aporrectodea caliginosa and Eisenia fetida were long-term exposed to the ultramafic soils collected at the Barberton region and a control soil from a location at Stellenbosch with a known history of no anthropogenic metal contamination. The responses to the ecological stress originating in the ultramafic soils were measured on different levels of earthworm organisation. As endpoints affecting population development, cocoon production, fecundity and viability were evaluated. On individual level, growth, metal body burden and tissue distribution were investigated. As endpoints on subcellular level, the membrane integrity was assessed by the neutral red retention assay, the mitochondrial activity was measured by the MTT colorimetric assay and as a biomarker for the DNA integrity, the comet assay was performed. Focussing on manganese and nickel, the uptake by E. fetida of these metals was investigated with the exclusion of soil related properties using an artificial aqueous medium to draw comparisons to the uptake of these metals in natural soils. The possible development of resistance towards nickel was tested by exposing pre-exposed (for more than 10 generations) E. fetida specimens to ultramafic soils with concentrations of more than 4000 mg/kg nickel. The results showed that, except on the endpoint survival, which was less sensitive than all other bioassays, significant responses to the ultramafic challenge were observed in all earthworm bioassays and on all levels of organisation. The sensitivity of the responses of the earthworms towards the ultramafic conditions was not predictable by the level of organisation. The two species showed different strategies of metal elimination. In A. caliginosa, metals such as nickel, manganese and chromium were transported to the posterior section and the posterior section was subsequently pushed off by autotomization. In E. fetida, metals such as chromium and nickel were sequestered in storage compartments in the coelomic cells or fluid. Other metals, such as cobalt, were not taken up at elevated concentrations. Although an increased accumulation of nickel was observed in E. fetida specimens pre-exposed to nickel, development of resistance or cross resistance was not observed in this species. In contrast, pre-exposed specimen exposed to elevated concentrations of nickel showed a higher sensitivity in terms of survival, indicating the absence of acclimatisation or even genetic adaptation. A comparison of the two species employed indicated that A. caliginosa was less suited for the assessment of the ultramafic soils due to the high individual variation in metal body burden, the mass loss observed and the slow reproduction rate even in the control soils. This happened despite the fact that A. caliginosa was a soil dwelling species supposed to be better adapted to the soil substrate than the litter dwelling E. fetida. The toxicity of the ultramafic soils was not necessarily related to total or environmentally available amounts of the selected metals. Thus, it can be speculated that either these soils contained unidentified toxicants with resulting interactions between toxicants playing an important role or earthworms were able to remobilize metals occurring in these soils. As the singular application of an ecotoxicological endpoint did not give reliable results, especially seen over the duration of the exposures, it can be concluded that, when studying soils with such a complex composition, the utilisation of endpoints addressing different levels of organisation is necessary for the assessment of toxic stress emerging from these ultramafic soils.
The abundance and diversity of meso- and macrofauna in vineyard soils under different management practices
(Stellenbosch : Stellenbosch University, 2005-03) Nel, Werner; Reinecke, A. J.; Reinecke, S. A.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: The agricultural sector in South Africa relies heavily on the use of pesticides to protect crops against pest organisms. Pesticides can affect non-target organisms such as the meso- and macrofauna in the soil detrimentally. Since these organisms play an important role in the processes of mineralization and decomposition in the soil and contribute to soil fertility, it is important that they are protected. A large amount of published literature exists on the biological importance of soil meso- and macrofauna and the effects that various agricultural practices have on them. The main aim of this study was to investigate the influence of agricultural practices on the abundance and diversity of meso- and macrofauna in different vineyard soils. A comparative study was conducted of an organically managed, conventionally managed and an uncultivated control soil. A secondary aim was to determine the effect of these agricultural management practices on the biological activity of these animals. Soil samples were taken, from which mesofauna (Collembola and Acari) were extracted with a modified Tullgren extractor, identified and counted. Earthworms were extracted from the soil using hand sorting methods. Soil parameters such as pH, water holding capacity, organic matter content, soil texture and soil respiration were determined. Bait lamina and litter-bags were also used to help determine the biological activity within the soil. The mesofauna diversity was quantified using the Shannon Weiner diversity index, as well as a diversity index described by Cancela da Fonseca and Sarkar (1996). Differences in abundance of both the meso-and macrofauna were statistically measured using ANOVA's. Biological activity results were also interpreted using ANOV A's. Results indicate that the abundance of the meso fauna was the highest at the organically treated vineyard soil and lowest in the conventionally managed soil where pesticide application took place. The earthworms also showed the same trend as the mesofauna, but were much more influenced by seasonal changes. Biological activity, according to the bait lamina and the litter-bag results, was higher in both the conventionally and organically managed soils than in the control, but no statistical significant differences were found between the two experimental soils. The soil respiration (C02-flux), also indicating biological activity, was highest in the organically treated soil and lowest in the conventionally treated soil. The different sampling techniques used gave variable results and although the organically managed soil proved to have higher abundances of both meso- and macrofauna, the biological activity did not show the same trends. In conclusion the data did not give enough evidence as to whether organic management practices were more beneficial than conventional management practices for the maintenance of soil biodiversity.
Acacia mangium Willd : benefits and threats associated with its increasing use around the world
(Springer Open, 2019-01-29) Koutika, L.-S.; Richardson, D. M.
Background: Acacia mangium, a fast-growing tree native to parts of Indonesia, Papua New Guinea and Australia, has been cultivated outside its native environment and introduced into humid tropical lowland regions of Asia, South America and Africa over the last few decades. It is a multipurpose tree used in agroforestry, forestry and for restoration of degraded lands. It is also highly invasive in many regions where it has been introduced outside its native range. This paper reviews evidence of its obvious benefits and its negative impacts on biodiversity. Methods: A literature review on Australian acacias and especially on A. mangium was undertaken to highlight both benefits and threats associated with their increasing worldwide use outside their native ranges. Results: Through N2 fixed from the atmosphere, A. mangium improves soil fertility, especially by increasing N status and soil C accretion when introduced to N-limited areas; it thus has the potential to restore nutrient cycling in degraded systems. No studies have, however, been done to assess the effectiveness of A. mangium in restoring biodiversity of degraded lands. Most Australian acacias have traits that facilitate invasiveness, and 23 species have been recorded as invasive to date. A. mangium has been reported as invasive in Asia, Indonesia, Pacific Islands, Indian Ocean Islands, southern Africa and Brazil. Research on other invasive Australian acacias in several parts of the world has elucidated the types of impacts that are likely in different types of ecosystems and key options for mitigating impacts. Conclusions: A. mangium has the potential to restore nutrient cycling in degraded systems, but is highly invasive wherever it is planted. Many parts of the world have a large invasion debt for this species. Experience with other invasive acacias around the world suggests a suite of interventions that could be used to reduce invasions and mitigate impacts. Careful risk assessments should be undertaken prior to any new plantings of this species.
Academic leaders must support inclusive scientific communities during COVID-19
(Springer Nature, 2020) Maas, Bea; Grogan, Kathleen E.; Chirango, Yolanda; Harris, Nyeema; Lievano-Latorre, Luisa Fernanda; McGuire, Krista L.; Moore, Alexandria C.; Ocampo-Ariza, Carolina; Palta, Monica Marie; Perfecto, Ivette; Primack, Richard B.; Rowell, Kirsten; Sales, Lilian; Santos-Silva, Rejane; Silva, Rafaela Aparecida; Sterling, Eleanor J.; Vieira, Raisa R. S.; Wyborn, Carina; Toomey, Anne
The COVID-19 pandemic poses major challenges for all sectors of society, including scientists faced with abrupt disruptions and redirections of research and higher education1. The consequences of this crisis will disproportionately impact early-career scientists; especially those from communities historically underrepresented, disadvantaged and/or discriminated in the fields of environmental sciences, including women, researchers from the Global South and persons with disabilities2. We call for a collective effort by the entire scientific community, especially those in leadership positions, to respond to the short- and long-term challenges of this crisis and to protect decades of efforts to build an inclusive scientific community3.
Acclimation effects on thermal tolerance in ameronothrid mites at sub-Antarctic Marion Island
(Stellenbosch : Stellenbosch University, 2005-12) Deere, Jacques Andries; Chown, S. L.; Marshall, D. J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Evidence for widespread ecological impacts due to rapid climate change is on the increase, with further warming predicted over the next century. This increase in warming has lead to organisms adjusting their distribution range and where this is not possible organisms must cope with the stressful environments in a different way. One potential way to handle environmental stress is via a mechanism known as phenotypic plasticity, which allows an organism to express different phenotypes depending on the biotic or abiotic environment in a way that may alter that organism's fitness. Acclimation temperatures can potentially cause plastic (reversible and irreversible) changes in the response of individuals to stressful experimental conditions that could increase their survival. The issue of whether this acclimation will be beneficial to the organism or not remains contentious, with support offered both for and against the idea of beneficial acclimation. The aims of the investigation were to determine the thermal limits of five ameronothrid mite species (Halozetes marinus, H marionensis, H belgicae, H. fulvus and Podacarus auberti) from varying terrestrial habitats and to test whether there is beneficial acclimation on the thermal traits. Along with the beneficial acclimation hypothesis several alternative hypotheses were also tested. In addition, locomotor performance was determined as it has been suggested that locomotion performance is a reliable and practical measure of potential fitness of animals. The same hypotheses testing the effects of acclimation temperature on the thermal limits were tested on three performance traits; performance breadth, optimum speed and optimum temperature. Support for beneficial acclimation was found in the performance breadth and optimum speed traits for all species except for Halozetes marinus. For the optimum temperature trait the prediction for the compensation hypothesis was met and that of the beneficial acclimation hypothesis rejected, with the only exception again being that of H marinus. In the case of the locomotor performance traits the prediction for the beneficial acclimation hypothesis in the performance breadth and optimum speed traits are the same for that of the compensation hypothesis, therefore the overall response of the more terrestrial mite species is one of compensation. However, support for beneficial acclimation was not found in the thermal limit traits of all five species, with the higher acclimation temperatures (specifically 150 C) resulting in negative responses in LLT in H. marinus and H. belgicae, and in ULT in H. fulvus. Phenotypic flexibility varied between marine and terrestrial species. The less variable marine environment showed lower flexibility than that of terrestrial species in the performance breadth trait and optimum temperature trait, but there was a lack of variation between the marine and terrestrial species in the temperature tolerance traits. These results show that the effects of acclimation on various traits, especially fitness related traits, are complex and require more attention if the consequences are to be fully explained. This study therefore provides insight into the effects of acclimation on performance traits and thermal limit traits and has implications for the evolution of plastic responses in terrestrial arthropods.
Acoustic Spatial Capture-Recapture (aSCR) and the Cryptic Cape Peninsula Moss Frog Arthroleptella lightfooti
(Stellenbosch : Stellenbosch University, 2018-12) Louw, Marike; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Quantitative measurements of wildlife populations, such as population density, are quintessential for management and conservation. Acoustic Spatial Capture-recapture (aSCR) is a technique that is used to estimate the densities of acoustically active animals. It is advantageous to use when animals defy the use of traditional methods of population estimation by being very visually cryptic, but remaining acoustically active. Arthroleptella lightfooti is a visually cryptic moss frog with an average snout to vent length of 14.5 mm. The males call during the austral winter from seepages within a restricted range across the Cape Peninsula. The species has an IUCN status of Near Threatened. Here, the population densities of the endemic A. lightfooti are estimated across their range on the Cape Peninsula for the first time using aSCR. Multiple microphones, termed “acoustic arrays”, are deployed in the field to record the calls of the frogs. I assess the use of aSCR in terms of reliability of the density estimates by examining the standard errors as coefficients of variation (CVs) of the density estimates. A density estimate with a CV above 30% was considered unreliable. Recording calls for the aSCR analyses involved visiting more than 200 sites during 2016 and 2017, and deploying acoustic arrays at a total of 149 sites, of which a subset of 85 sampling sites was used. I examined the influence of different variables on the size of the CV, namely: the average number of calls received by the acoustic array per minute, the array formation, and the detector frequencies (the combination of different numbers of microphones across which calls were heard). In addition, I made use of an output from aSCR that is an aerial view of the estimated calling locations of frogs relative to the acoustic arrays. I overlaid this output with aerial images taken at three different sites using a drone, and I examined the microhabitat features that relate most significantly to the presence of calling A. lightfooti. When there were less than 111call.min-1 received by the array, density estimates had CVs that exceeded 30% and were therefore considered unreliable. Above this threshold, 91% of density estimates were acceptable. When calls were heard on mostly one microphone, and decreasingly heard across two, three, four, five and six microphones, the density estimates were more reliable. However, when calls were mostly picked up across a combination of one and six microphones, density estimates became less reliable. This suggests that array formations should have the microphones spaced in such a way that not all calls are detected across all the microphones or only one microphone. The presence of calling frogs was significantly related to the presence of wet, seepy patches in the microhabitat and to the absence of standing water. This is consistent with observations in the field and reflects the biological needs of the species: it has no life stages in water but needs moist areas for eggs and tadpoles to develop. The successful application of aSCR to A. lightfooti is promising in the field of population studies on cryptic species, as it can be used to evaluate the populations of other calling taxa, which holds important implications for conservation and management.
Adapting to climate change : a perspective from evolutionary physiology
(Inter-Research Science, 2010) Chown, Steven L.; Hoffmann, Ary A.; Kristensen, Torsten N.; Angilletta Jr., Michael J.; Stenseth, Nils C.; Pertoldi, Cino
Much attention has been given to forecasting the likely effects of ongoing climate change on biodiversity. A large and often contentious literature has developed about how changes in species’ ranges should be modelled and how additional biological mechanisms might be incorporated to improve their utility. Nonetheless, 2 areas stand out as relatively underappreciated: the importance of understanding a species’ physiological capacities when forecasting its response to climate change, and the likely influence that capacities for genetic change across generations and changes in plastic responses, or the lack thereof, will have on a species’ response. Although perhaps not as well developed as correlative approaches to understanding species responses to change, mechanistic approaches are advancing rapidly. In this review, we explore several of the key messages emerging from the mechanistic approach, embodied in evolutionary physiology, to understanding and forecasting species responses to climate change.
‘African dinosaurs’ : permanent new exhibition at the South African Museum
(AOSIS OpenJournals, 2010-08) Anderson, Bruce
The new ‘African dinosaurs’ exhibit at the Iziko South African Museum in Cape Town capitalises on a fascination that almost every person – old and (especially) young – has with dinosaurs. A highway into the human imagination, dinosaurs can often be the spark that ignites the explosion we call learning; hence this National Lottery-funded exhibit is open-planned to accommodate large school groups. It is not surprising that these rock stars of natural history have been afforded the museum’s prime space in a sylvan gallery overlooking Government Avenue and stretching three floors to the roof (a space that is just big enough to accommodate a juvenile Sauropod).
African medicinal flora in the limelight
(AOSIS OpenJournals, 2011-10) Makunga, Nokwanda P.
In the past few years, African medicinal plants have received considerable attention, and it has been lamented that the documentation of the continent’s species that are used in traditional medicine lags behind China and India in terms of ‘internationally recognised phytochemical standards’. This book not only redresses this issue, but is the first to include plants from the south, north, east and west of Africa. In South Africa alone, there are over 3000 species that are used for medicinal purposes, with over 70% of the Black African population relying on medicinal flora as part of their primary health care and 84% of clinic patients confirming their preference for wildcrafted raw herbal medicines in spite of having access to western health care.1 Both traditional and Western healing systems are used – many educated Black people retain traditional practices as they are regarded as an important cultural link to their predecessors. Throughout Africa, plants are viewed as contributors to health; they are also used in religious and cultural ceremonies. The African continent has a rich biodiversity and this is matched by a commensurate proliferation of medicinal plant use. So the trade of medicinal plants in Africa is substantial, but largely informal, and consists of plant collectors as well as traders at herbal markets.
Ailanthus altissima : an assessment of its distribution at different spatial scales and options for management in South Africa
(Stellenbosch : Stellenbosch University, 2017-03) Walker, Gareth Alexander; Richardson, D. M.; Robertson, M. P.; Gaertner, Mirijam; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: The constant flow of goods into and out of cities has resulted in the proliferation of invasive species in urban areas and, because of this, cities are viewed as ‘hotspots’ for invasive species. The rise of global trade and long distance transportation will ensure that further introductions will take place in urban ecosystems. Conditions that have been altered due to human activities enable some alien species to proliferate rapidly throughout urban centres, often also spreading into natural and semi-natural areas at the urban/wildland interface. Evaluating the current distribution of an invader by analysing potential patterns in its distribution, as well as determining the potential distribution of a species over multiple landscapes and identifying factors that promote its spread, is essential for determining the full extent of an invader. Understanding 1) where a species is; 2) where a species may spread to; and 3) the factors that promote the spread of a species are all needed to gain an understanding of the biological and biogeographical preferences that facilitate the spread of the species. This is best achieved by using a multi-scale analysis that studies all aspects of an invasive species over a variety of spatial scales. This study focusses on a notorious northern hemisphere invader - Ailanthus altissima – that, although having been introduced into South Africa in 1834, is yet to replicate similar levels of invasion success. I adopted for a multi-scale analysis of the species evaluating the current and potential distribution of the species at a global scale (Chapter 1), national scale (Chapter 2) and local scale (Chapter 3). Each chapter addresses a central aim in which a number of research questions are evaluated. In Chapter 1 I assess the biogeography, distribution, and habitat suitability of A. altissima by evaluating the current and potential distribution of the species (based on climatic suitability) at both a global scale and a national scale (in South Africa). The main conclusions of this chapter are that 1) online databases (although outdated at times) provide an accurate representation of the distribution of invasive species and should therefore be accessed. This was ascertained by cross referencing a number of online databases to evaluate whether they were largely in agreement with one another in terms of the distribution of an invader; and 2) modelling the potential distribution of an invasive species based on climatic suitability serves as a good first approximation of potential species spread. Although this may be true, it was also suggested in this chapter that to accurately quantify the potential distribution of an invasive species, other distribution drivers (such as land use and human mediated disturbances) need to be incorporated into the design of a species distribution model. Chapter 2 evaluates the degree of range filling exhibited by A. altissima in South Africa and identifies areas at risk of future invasion. This chapter also identifies specific factors that promote the spread of the species at a global and national scale. I determined that at the global scale, climate had the highest influence on the distribution of A. altissima whereas at the national scale, human mediated disturbances exerted a higher influence on the distribution of the species. This chapter builds on the concepts proposed in Chapter 1 by highlighting the importance of incorporating different environmental variables at various spatial scales to identify potential invasion ‘hotspots’. I conclude that the multi-scale approach presented in this chapter enables the early detection of invasive species, preventing damage associate with their potential spread. Also, the novelty of this approach is particularly effective when it comes to analysing urban invaders. The third chapter evaluates the distribution pattern of A. altissima within the City of Cape Town by using the suburb of Newlands as a case study. In addition, it determines potential options for management at a city scale. It can be concluded that fine-scale analysis of invasive species distributions is best achieved using Geographic Information System (GIS) techniques and that such these ultimately help to identify potential areas susceptible to future invasion while delimiting unsuitable areas. I determined that A. altissima has a preference for affluent urban areas with podzolic soils that are exposed to high levels of rainfall within the City of Cape Town. Using this information, I determined that there is a large capacity for further spread by the species throughout the city. The systematic approach that we used in Newlands is an effective way of gauging the full extent of an invader and is especially effective for evaluating the population structure of a particular invasive species. Future studies should adopt this approach in conjunction with remote sensing techniques to achieve the best possible results. The final chapter of this thesis provides the overall conclusions in which all the main findings are highlighted. Altogether, the approach presented in this thesis is an effective method that could be used on other emerging, urban invaders globally. The systematic, multi-scale analysis proposed in this project showed high levels of success and it is my belief that this project achieved its desired aims.
The alarm vocalizations of Brants' whistling rat, Parotomys Brantsii
(Stellenbosch : Stellenbosch University, 2001-12) Le Roux, Aliza; Cherry, M. I.; Jackson, T. P.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: The alarm calls of a colonial rodent, Brants' whistling rat (Parotomys brantsii), were investigated at Goegap Nature Reserve in the Northern Cape, South Africa. At this site P. brantsii occurs in sympatry with the congeneric P. littledalei, and the alarm calls in response to humans was compared between the two species. Parotomys brantsii's typical call in reaction to a human is a simple whistle, characterized by an initial upward frequency sweep and high frequency plateau, whereas the alarm whistle of P. littledalei has three overlapping components. Parotomys littledalei's calls are significantly shorter and lower in dominant frequency than those of P. brantsii, and have a significantly wider frequency bandwidth. These distinctions were attributed to species discrimination and habitat preferences. The acoustic adaptation hypothesis is supported in part, as P. littledalei, which inhabits a closed habitat in comparison with P. brantsii, has calls which are lower in frequency than P. brantsii calls, but contrary to the hypothesis, P. brantsii calls show less frequency modulation than those of P. littledalei. The high pitch of both species' vocalizations may be a convergent feature making the callers difficult for predators to locate. The alarm call repertoire of P. brantsii was investigated by presenting members of the P. brantsii colony with models of some typical predators, a raptor and puff adder, as well as a human observer. Virtually no variation was detected in the structure of alarm whistles elicited by different predators, indicating that P. brantsii did not identify different predator types by means of vocalizations, even though behavioural responses showed that P. brantsii do distinguish between different predators and non-predators. Note duration varied in conjunction with the physical reaction of the caller. When the caller bolted towards safety, the whistle was significantly shorter than when it remained aboveground. During an encounter with a snake or far-off human the caller would utter relatively long duration calls, signifying a low-risk situation, while highrisk situations such as a nearby human or raptor provoked short calls, emitted just before the whistling rat bolted underground. I regard P. brantsii's alarm call repertoire as a graded "urgency-based" system, indicating threat level perceived rather than predator type. This system is widespread among ground squirrels and is usually associated with animals inhabiting a two-dimensional environment. Playback experiments were conducted to determine the meaning of alarm calls to conspecifics, focusing specifically on the effect of variation in single call duration and function of alarm-calling bouts. All alarm calls induced heightened vigilance in receivers, but the behavioural response did not differ between short and long single calls. Multiple calls lead to significantly longer periods of high vigilance than single calls even after calling bouts have ended, showing that one of the functions of multiple calls is to maintain high vigilance in conspecifics for relatively long periods. The non-iconic nature of their alarm calls and the undiscriminating response of receivers to different calls emphasizes the importance of contextual clues in the communication system of animals living in an open habitat like that of P. brantsii.
Alien plant invasions and native plant extinctions : a six-threshold framework
(Oxford University Press on behalf of the Annals of Botany Company, 2016-07-15) Downey, Paul O.; Richardson, David M.
Biological invasions are widely acknowledged as a major threat to global biodiversity. Species from all major taxonomic groups have become invasive. The range of impacts of invasive taxa and the overall magnitude of the threat is increasing. Plants comprise the biggest and best-studied group of invasive species. There is a growing debate; however, regarding the nature of the alien plant threat—in particular whether the outcome is likely to be the widespread extinction of native plant species. The debate has raised questions on whether the threat posed by invasive plants to native plants has been overstated. We provide a conceptual framework to guide discussion on this topic, in which the threat posed by invasive plants is considered in the context of a progression from no impact through to extinction. We define six thresholds along the ‘extinction trajectory’, global extinction being the final threshold. Although there are no documented examples of either ‘in the wild’ (Threshold 5) or global extinctions (Threshold 6) of native plants that are attributable solely to plant invasions, there is evidence that native plants have crossed or breached other thresholds along the extinction trajectory due to the impacts associated with plant invasions. Several factors may be masking where native species are on the trajectory; these include a lack of appropriate data to accurately map the position of species on the trajectory, the timeframe required to definitively state that extinctions have occurred and management interventions. Such interventions, focussing mainly on Thresholds 1–3 (a declining population through to the local extinction of a population), are likely to alter the extinction trajectory of some species. The critical issue for conservation managers is the trend, because interventions must be implemented before extinctions occur. Thus the lack of evidence for extinctions attributable to plant invasions does not mean we should disregard the broader threat.
Alien plant invasions in tropical savanna ecosystems: patterns, processes and prospects
(Springer, 2010-07-11) Foxcroft, Llewellyn C.; Richardson, David M.; Rejmanek, Marcel; Pysek, Petr
Biological invasions affect virtually all ecosystems on earth, but the degree to which different regions and biomes are invaded, and the quality of information from different regions, varies greatly. A large body of literature exists on the invasion of savannas in the Neotropics and northern Australia where invasive plants, especially African grasses, have had major impacts. Less has been published on plant invasions in African savannas, except for those in South Africa. Negative impacts due to plant invasions in African savannas appear to be less severe than in other regions at present. As savannas cover about 60% of the continent, with tens of millions of people relying on the services they provide, it is timely to assess the current status of invasions as a threat to these ecosystems. We reviewed the literature, contrasting the African situation with that of Neotropical and Australian savannas. A number of drivers and explanatory factors of plant invasions in savannas have been described, mostly from the Neotropics and Australia. These include herbivore presence, residence time, intentional introductions for pasture improvements, fire regimes, the physiology of the introduced species, and anthropogenic disturbance. After comparing these drivers across the three regions, we suggest that the lower extent of alien plant invasions in African savannas is largely attributable to: (1) significantly lower rates of intentional plant introductions and widespread plantings (until recently); (2) the role of large mammalian herbivores in these ecosystems; (3) historical and biogeographical issues relating to the regions of origin of introduced species; and (4) the adaptation of African systems to fire. We discuss how changing conditions in the three regions are likely to affect plant invasions in the future.
Alien reptiles and amphibians in South Africa : towards a pragmatic management strategy
(Academy of Science of South Africa -ASSAf, 2008-02) Van Wilgen, Nicola J.; Richardson, David M.; Baard, Ernst H. W.
Biological invasions are a growing problem in South Africa. Many alien species have been introduced for various reasons and through multiple pathways over the past few centuries. Invasive alien reptiles and amphibians (herpetofauna) are not yet a major problem in the country. However, escalating difficulties with invasive species in these groups worldwide, and changing circumstances in South Africa, suggest a high risk of increased problems in the future. This paper reviews key issues pertaining to invasive alien herpetofauna worldwide and discusses how risk assessment can be used as part of an effective biosecurity strategy for South Africa. Nearly 300 species of alien herpetofauna have already been imported into the country via the pet trade and are being kept in captivity. There is a need to consider the potential threat of these species, and others still to be introduced, in line with practices in other countries where formal risk assessment policies are in place to separate potentially invasive species from those that are unlikely to be problematical. New legislation in South Africa seeks to regulate activities involving alien species, but exactly how this will be done has yet to be finalized. Each province in South Africa currently has its own legislation with different requirements; this causes many problems. Records of permit applications are also poor, complicating attempts to compile accurate inventories and to discern trends in imports and permit allocations. We define a pragmatic framework for dealing with alien reptiles and amphibians in South Africa. The framework identifies key issues facing the country and considers how the situation and advances elsewhere in the world can be used to set priorities. We propose that a risk assessment protocol be implemented for categorizing species as permissible or prohibited for import and trade. Accurate data are needed on the alien species already in South Africa.
Alien species and propagules in the Antarctic : movements through space and time
(Stellenbosch : University of Stellenbosch, 2009-03) Lee, Jennifer Elizabeth; Chown, Steven L.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post‐dispersal processes because of the difficulties of measuring propagule pressure and the detecting of newly established species. Here the Antarctic is used as a model system in which to quantify the initial dispersal of alien species and investigate the factors that contribute to the establishment and range dynamics of alien species once they have arrived in the region. Human movements are known to transport alien species into the Antarctic, some of which have successfully established and had wide ranging consequences in recipient ecosystems. Considering terrestrial flora, this research found that over 700 seeds from 99 taxa, including some species known to be invasive, are transported into the Antarctic each year in association with South African National Antarctic Programme (SANAP) passenger luggage and cargo. The first ever assessment of propagule drop‐off indicated that 30‐50% of these propagules will enter the recipient environment. Further results suggested that the construction of the British Antarctic Survey Halley VI station will facilitate the transport of over 5000 seeds from 34 taxa into the region, making this a significant pathway for introductions. Propagule pressure due to SANAP logistics is also considerable for marine species. Fouling assemblages on the external hull surfaces of the SANAP resupply vessel, the SA Agulhas, form only once the vessel’s anti‐fouling paint has been damaged by travel through sea ice and are characterised by low diversity. Ice scour prevents fouling assemblages from being transported to the Antarctic continent, but assemblages remain largely intact when travelling to sub‐Antarctic Islands. In the sea‐chests of the vessel populations of a known invasive, Mytilus galloprovincialis, were found with some individuals having survived transportation to the Antarctic region on multiple occasions. Once species have overcome initial dispersal barriers, they face further ecological and physiological challenges in order to establish in the recipient region. The parasitoid wasp Aphidius matricariae was first recorded on Marion Island in 2001. Surveys around the island show that adult abundance and the frequency of aphid parasitism are highest adjacent to a common anchor point of the SA Agulhas and decline away from this region. Genetic diversity was low, suggesting that the population was established from a single introduction. This highlights that high propagule pressure is not necessary for successful establishment of introduced invertebrates. Another species that has overcome the dispersal barrier is the terrestrial slug Deroceras panormitanum, which was introduced to Marion Island in the 1970’s and has since spread throughout much of the coastal habitat of the island. For this species range limits are set by intolerance of low temperature and salinity, and abundance structure is characterized by patches and gaps which are associated with this species inability to tolerate dry conditions. To prevent further alien introductions in the region, targeted management of high risk pathways is required. In addition, increased vigilance is needed to detect and manage newly established aliens before their ranges expand.
Alien species in South Africa’s national parks
(AOSIS OpenJournals, 2011-08) Spear, Dian; McGeoch, Melodie A.; Foxcroft, Llewellyn C.; Bezuidenhout, Hugo
Invasive alien species (IAS) are one of the major threats to biodiversity in protected areas and pose a significant management challenge (see Allen, Brown & Stohlgren 2009; Pyšek, Jarošík & Kučera 2002). One of the first steps towards managing IAS in protected areas is establishing which alien species are present, followed by ongoing surveillance and prevention efforts to combat new introductions (Foxcroft et al. 2009). Information on the identity and traits of alien species is needed for conducting risk assessments and prioritising species for control, as well as for monitoring management effectiveness in preventing new introductions (McGeoch et al. 2010). It also provides a first step towards monitoring the extent of occurrence of alien species in national parks.
Aliens in Antarctica : accessing transfer of plant propagules by human visitors to reduce invasion risk
(Elsevier, 2014) Huiskes, H. L.; Gremmen, N. J. M.; Bergstrom, D. M.; Frenot, Y.; Hughes, K. A.; Imura, S.; Kiefer, K.; Lebouvier, M.; Lee, J. E.; Tsujimoto, M.; Ware, C.; Van de Vijver, B.; Chown, S. L.
Despite considerable research on biological invasions, key areas remain poorly explored, especially ways to reduce unintentional propagule transfer. The Antarctic represents a microcosm of the situation, with the numbers of established non-native species growing. Information to help reduce potential impacts is therefore critical. We measured the propagule load of seeds, and fragments of bryophytes and lichens (the number of other plant or animal fragments was too low to draw any conclusions) carried in the clothing and gear of visitors to the Antarctic, during the 2007/08 austral summer. Samples were collected from different categories of visitors associated with national research programs and tourism and different categories of clothing and gear, new as well as used. We also collected information about the timing of travel and the regions visitors had travelled to prior to Antarctic travel. Seeds were found in 20% and 45% of tourist and science visitor samples, respectively. For bryophyte and lichen fragments the proportions were 11% and 20%, respectively. Footwear, trousers and bags belonging to field scientists were the highest risk items, especially of those personnel which had previously visited protected areas, parklands/botanic gardens or alpine areas. Tourists who visited rural/agricultural areas prior to travel, and/or travel with national programs or on smaller tourist vessels had the highest probability of transferring plant propagules. Travel either during the boreal or austral autumn months increased the probability of propagule presence. Our assessment is applicable to other areas given evidence of propagule transfer patterns in those areas that are broadly similar to those documented here. The current work provides a sound evidence base for both self-regulation (e.g. taking care of personal equipment) and organization-based regulation (e.g. issuing guidelines and holding regular inspections) to reduce propagule transfer of plants to the Antarctic.
All-in-one : physics, chemistry and ecology are essential fields to thermal ecologists
(International Biogeography Society, 2018) Clusella-Trullas, Susana
The book clearly targets principles that are essential for understanding the relationship between temperature and organisms and does not represent a book for applications on how to do measurements or complex tasks in thermal ecology. Principles of Thermal Ecology is a guiding book to get a solid knowledge of the building blocks that form the field of thermal ecology and does a brilliant job of achieving this. These building blocks and the relationships between physiology and ecology, as well as concepts that include larger scale patterns of life and diversity, will also be of great value to biogeographers and to wider audiences.
Amphibian conservation in an urban park : a spatial approach to quantifying threats to Anura on the Cape peninsula
(Stellenbosch : Stellenbosch University, 2017-12) Ebrahim, Zishan Cassiem; Measey, G. J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Species’ threat assessments produce generalized threat impact scores, often by considering regional-scale representations of threats. Cities, on the other hand, produce municipal-scale, high resolution data that are proxies for threats; furthermore, cities in mega-diverse regions are home to a high number of threatened species. Prioritization of conservation action is biased for where more information is known (about the ecosystem), and where a positive outcome can be anticipated. Eight Cape peninsula amphibian species have a threatened conservation status. They are isolated on highlands or are restricted to remnant and suburban habitats, dependent on both urban and protected terrestrial and freshwater habitats found in the City of Cape Town and Table Mountain National Park. In Chapter Two, I used spatial data (shapefiles) to represent threats in a Geographic Information System to spatially define threats to eight amphibian species (five lowland, three upland). I used two approaches: weighted and un-weighted by a threat impact-score, to produce five indices of local threats. The Micro Frog (Microbatrachella capensis) is assessed as the most threatened peninsula frog species by three of the five indices considered. The results show that for lowland species, the threat-class of greatest extent is ‘Residential and commercial development’. The three lowland species most exposed to this threat are M. capensis (100% exposed to potential development), Breviceps gibbosus (55.6% of its 8.5 km2 putative peninsula distribution), and Sclerophrys pantherina (38.4% of its 199.7 km2 distribution). The Compounded and the General Threat Index correlate to the (global) Redlist Index (P < 0.05); but no correlation to the regional Red Listing, indicating congruency of threats and threat status. The Critically Endangered Table Mountain Ghost Frog (Heleophryne rosei) is torrent adapted, and found only on the Table Mountain massif. CapeNature monitors tadpoles, and SANParks monitors (selected) stream parameters. In Chapter Three, I analyse water-habitat monitoring data (controlled for altitude) to show where threats of habitat alteration, drought, or temperature extremes may affect the H. rosei metapopulation. Permanence of water-flow and water temperature are shown to be very highly significant predictors of tadpole presence (p = 0.0005, r = 0.78). The lower the water temperature, the more likely tadpoles are present. Streams with a mean summer temperature greater than 17.2°C (n=3) at 400 to 300 meters above sea level were found to have no tadpoles at this altitude. Permanence of water flow is significant, as tadpoles need more than one year to reach metamorphosis. Summer water temperatures over an average of 17.2°C should be a red-flag for management authorities responsible for bulk-water supply, threat mitigation efforts, and biodiversity conservation. Spatial indices of threat are useful to illustrate the relative exposure to threats at a local (city) scale. Threats to different lowland amphibians are similar (e.g. residential and commercial development), which varies from the mutual threats to different upland amphibians. Fundamental to stream species’ conservation is water supply and demand management, while upland terrestrial species are most affected by veld age and invasive alien flora. Some threats are common for both areas (e.g. invasive alien species). Key words: Threat impact score, threatened areas, GIS, habitat loss, amphibians, Table Mountain National Park, Cape Town, environmental water requirement, water temperature, habitat.
An analysis of the Cordylus Polyzonus complex (Reptilia : Cordylidae) in the South-Western Cape
(Stellenbosch : University of Stellenbosch, 1990-03) Badenhorst, N. C.; Mouton, P. le F. N.; Van Wyk, J. H.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.
Mouton and Oelofsen (1988) suggested that melanistic cordylid populations in the southwestern Cape represent relict, cold-adapted populations which evolved under adverse climatic conditions during the Last Glacial Period, 18000-16000 BP. The first section of this study was undertaken to test their model for the evolution of melanism in the cordylid species, Cordylus polyzonus. For this purpose, geographic character variation among populations of Cordylus polyzonus in the region south of 32°15' latitude and west of 19015' longitude was investigated. Variation in 122 external morphological characters was analysed in 306 specimens from 93 localities. Although no inter-locality variation was observed in most of the characters, a high degree of concordancy was observed in the geographical variation of three headshield characters. These three headshield characters are considered non-adaptive and can accordingly be regarded as good indicators of genealogical relationship. Since they varied together with other adaptive characters such as melanism and body size, it can be concluded that geographically isolated melanistic populations of Cordylus polyzonus represent relicts of a once larger melanistic population. The data underscore the Mouton-Oelofsen hypothesis for the evolution of melanistic cordylid taxa in the south-western Cape. A further corrolary of the Mouton-Oelofsen hypothesis, is that melanistic cordylids are presently restricted to cool enclaves. This assumption was evaluated in the second section of this study by analysing prevailing climatic conditions associated with the occurrence of extant melanistic populations of the genera Cordylus and Pseudocordylus in the southwestern Cape. Climatic data were obtained from 123 weather stations in the study-area. A close correspondence was found between the distribution of melanistic populations along the westcoast and the primary upwelling zones of the southern Benguela Current. Lower mean daily temperatures and a high incidence of advective sea fog on the adjacent coastal regions are direct effects of these cold upwelled waters. Likewise, montane melanistic populations, occurring at relatively high altitudes along the extreme western borders of the Cape Fold Mountains, also experience lower mean daily temperatures and a high incidence of orographic fog and cloud cover. Melanistic cordylid populations therefore generally have to 4. contend with relatively exposed environmental conditions of low temperature and limited solar radiation due to the filtering effect of fog and cloud cover. The fact that all the melanistic taxa in this region occur as small isolated populations limited to cool enclaves, suggests that they are presently in a contracted state under strong environmental pressure. It is postulated that palaeoclimatic conditions very similar to climatic conditions presently prevailing in these enclaves were experienced over the entire western coastal region, at least as far as the Orange River, during the Last Glacial Maximum when melanism probably evolved. Our results therefore corroborate the Mouton-Oelofsen hypothesis that isolated melanistic cordylid populations represent cold-adapted relicts. One would accordingly expect melanistic populations to posses some enhanced ability to absorb infrared radiant heat to cope with these conditions of limited sunshine and lower temperatures. In section three of this study, differences in dorsal skin reflectivity between melanistic and turquoise ~. polyzonus populations were quantified. Furthermore, the physiological ability of this species to change body colour was investigated, as well as ontogenetic colour change. Significant differences in dorsal skin reflectivity existed between melanistic and turquoise specimens in the 500-1300 mjl spectral range, demonstrating the greater heat-absorbing capacity of melanistic populations. The data underscore the MoutonOelofsen model that melanistic populations are "cold-adapted" relicts. Furthermore, ontogenetic colour change is a real phenomenon in the melanistic variation of C. polyzonus. In this respect it is unique among the melanistic cordylid taxa in that ontogenetic colour change seemingly does not occur in the other forms. Experiments to investigate short term colour change in response to different temperatures regimes, produced no conclusive results. On the other hand, seasonal colour changes could be demonstrated for both melanistic and turquoise specimens, indicating that this species has the physiological capacity to change colour. It is, however, believed that geographic colour variation in ~. polyzonus cannot be attributed to this capacity, but is rather the result of selection over time. This view is underscored by the results of section one demonstrating that, apart from colour and body size, melanistic and turquoise forms also differ in certain non-adaptive traits; suggesting that they do not belong to the same primary gene pool.

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