Research Articles (Botany and Zoology)
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- ItemAcacia 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.
- ItemAcademic 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, AnneThe 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.
- ItemAdapting 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, CinoMuch 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.
- Item‘African dinosaurs’ : permanent new exhibition at the South African Museum(AOSIS OpenJournals, 2010-08) Anderson, BruceThe 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).
- ItemAfrican 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.
- ItemAlien 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.
- ItemAlien plant invasions in tropical savanna ecosystems: patterns, processes and prospects(Springer, 2010-07-11) Foxcroft, Llewellyn C.; Richardson, David M.; Rejmanek, Marcel; Pysek, PetrBiological 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.
- ItemAlien 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.
- ItemAlien species in South Africa’s national parks(AOSIS OpenJournals, 2011-08) Spear, Dian; McGeoch, Melodie A.; Foxcroft, Llewellyn C.; Bezuidenhout, HugoInvasive 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.
- ItemAliens 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.
- ItemAn analysis of the recent fire regimes in the Angolan catchment of the Okavango Delta, Central Africa(SpringerOpen [Commercial Publisher], 2022-07) Van Wilgen, Brian W.; De Klerk, Helen M.; Stellmes, Marion; Archibald, SallyBackground: This paper presents an analysis of fire regimes in the poorly studied Angolan catchment of the Okavango Delta in Botswana. We used MODIS data to examine the frequency and seasonality of fires over 20 years (from 2000 to 2020) in three dominant vegetation types (miombo woodlands, open woodlands and grasslands, and short closed to open bushlands), and in areas where people were present, and where they were absent. Results: The median fire return intervals for both open woodlands and grasslands and short bushlands were relatively short (1.9 and 2.2 years respectively). In miombo woodlands, fires were less frequent (median return periods of 4.5 years). Human population density had no discernible effect on the fire return intervals, but about 14% of the miombo woodlands experienced no fires over 20 years. Ongoing shifting cultivation within miombo woodlands has led to structural changes and the introduction of fire into this vegetation type where fires were rare or absent in the past. About 12% of the miombo did not burn during the period examined where people were present, whereas close to 20% of the sites remained unburnt where people were absent. This suggests that people did not change the fire return interval in any of the vegetation types studied, but that they altered the amount of the landscape that is flammable in miombo vegetation. Fires occurred between June and September, with a peak in the late dry season (August and September). Conclusions: Historical research indicates that late dry-season fires are detrimental to miombo woodlands, and our analysis suggests that degradation in parts of the catchment has led to the introduction of fire to this previously firefree and fire-sensitive vegetation type. Deforestation of miombo woodlands, and the consequent introduction of fire, is a cause for concern with respect to the ecological stability of the Okavango Delta. Managers should therefore aim to protect the remaining closed-canopy miombo stands from further clearing and to attempt to shift the timing of burns to the early dry season to reduce their intensity.
- ItemAnt assemblages have darker and larger members in cold environments(Wiley, 2016) Bishop, T. R.; Robertson, M. P.; Gibb, H.; Van Rensburg, B. J.; Braschler, B.; Chown, S. L.; Foord, S. H.; Munyai, T. C.; Okey, I.; Tshivhandekano, P. G.; Werenkraut, V.; Parr, C. L.ENGLISH ABSTRACT: Aim In ectotherms, the colour of an individual’s cuticle may have important thermoregulatory and protective consequences. In cool environments, ectotherms should be darker, to maximize heat gain, and larger, to minimize heat loss. Dark colours should also predominate under high UV-B conditions because melanin offers protection. We test these predictions in ants (Hymenoptera: Formicidae) across space and through time based on a new, spatially and temporally explicit, global-scale combination of assemblage-level and environmental data. Location Africa, Australia and South America. Methods We sampled ant assemblages (n5274) along 14 elevational transects on three continents. Individual assemblages ranged from 250 to 3000 m a.s.l. (minimum to maximum range in summer temperature of 0.5–35 8C). We used mixed-effects models to explain variation in assemblage cuticle lightness. Explanatory variables were average assemblage body size, temperature and UVB irradiation. Annual temporal changes in lightness were examined for a subset of the data. Results Assemblages with large average body sizes were darker in colour than those with small body sizes. Assemblages became lighter in colour with increasing temperature, but darkened again at the highest temperatures when there were high levels of UV-B. Through time, temperature and body size explained variation in lightness. Both the spatial and temporal models explained c. 50% of the variation in lightness. Main conclusions Our results are consistent with the thermal melanism hypothesis, and demonstrate the importance of considering body size and UVB radiation exposure in explaining the colour of insect cuticle. Crucially, this finding is at the assemblage level. Consequently, the relative abundances and identities of ant species that are present in an assemblage can change in accordance with environmental conditions over elevation, latitude and relatively short time spans. These findings suggest that there are important constraints on how ectotherm assemblages may be able to respond to rapidly changing environmental conditions.
- ItemAntarctic marine biodiversity and deep-sea hydrothermal vents(Public Library of Science -- PLOS, 2012-01) Chown, Steven L.The diversity of many marine benthic groups is unlike that of most other taxa. Rather than declining from the tropics to the poles, much of the benthos shows high diversity in the Southern Ocean. Moreover, many species are unique to the Antarctic region. Recent work has shown that this is also true of the communities of Antarctic deep-sea hydrothermal vents. Vent ecosystems have been documented from many sites across the globe, associated with the thermally and chemically variable habitats found around these, typically high temperature, streams that are rich in reduced compounds and polymetallic sulphides. The animal communities of the East Scotia Ridge vent ecosystems are very different to those elsewhere, though the microbiota, which form the basis of vent food webs, show less differentiation. Much of the biological significance of deep-sea hydrothermal vents lies in their biodiversity, the diverse biochemistry of their bacteria, the remarkable symbioses among many of the marine animals and these bacteria, and the prospects that investigations of these systems hold for understanding the conditions that may have led to the first appearance of life. The discovery of diverse and unusual Antarctic hydrothermal vent ecosystems provides opportunities for new understanding in these fields. Moreover, the Antarctic vents south of 60°S benefit from automatic conservation under the Convention on the Conservation of Antarctic Marine Living Resources and the Antarctic Treaty. Other deep-sea hydrothermal vents located in international waters are not protected and may be threatened by growing interests in deep-sea mining. © 2012 Steven L. Chown.
- ItemAnti-predator strategies of the invasive African clawed frog, Xenopus laevis, to native and invasive predators in western France(Regional Euro-Asian Biological Invasions Centre, 2019) Kruger, Natasha; Measey, John; Herrel, Anthony; Secondi, JeanENGLISH ABSTRACT: When species are translocated to a novel environment, individuals become exposed to new predators against which they may not express very efficient defences at least at an initial stage. The strength of anti-predator defence is an important parameter that may determine the ability of local communities to control the expansion of invasive populations. The African clawed frog, Xenopus laevis, is a globally invasive amphibian that has successfully established invasive populations on four continents. In its invasive distribution in western France, X. laevis encounters novel aquatic predators. Some may be related to the predators in the native range but others may belong to different taxonomic groups and not be functionally or ecologically equivalent. We tested whether naïve X. laevis tadpoles from the invasive French population exhibit anti-predator response to local predators, and whether the response depends on the degree of relatedness with predators encountered in the native range of the frog, or whether individuals may express generic neophobia to any cue they are not familiar with. We exposed naïve lab-reared tadpoles to a native non-predatory water snail, Planorbarius corneus, a native predatory beetle, Dytiscus dimidiatus, and an invasive predatory crayfish, Procambarus clarkii. We found that X. laevis tadpoles innately reduce their activity when exposed to beetle and crayfish stimulus cues, but not to snails. Reducing activity can decrease the probability of being detected by predators. This demonstrates that invasive tadpoles respond to known and novel predators regardless of the evolutionary history. Whether the produced response is always effective against a totally novel predator remains to be tested.
- ItemAntibacterial, antioxidant and tyrosinase-inhibition activities of pomegranate fruit peel methanolic extract(BioMed Central, 2012-10) Fawole, Olaniyi A.; Makunga, Nokwanda P.; Opara, Umezuruike L.Abstract Background This study evaluated, using in vitro assays, the antibacterial, antioxidant, and tyrosinase-inhibition activities of methanolic extracts from peels of seven commercially grown pomegranate cultivars. Methods Antibacterial activity was tested on Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Klebsiella pneumonia) using a microdilution method. Several potential antioxidant activities, including radical-scavenging ability (RSA), ferrous ion chelating (FIC) and ferric ion reducing antioxidant power (FRAP), were evaluated. Tyrosinase enzyme inhibition was investigated against monophenolase (tyrosine) and diphenolase (DOPA), with arbutin and kojic acid as positive controls. Furthermore, phenolic contents including total flavonoid content (TFC), gallotannin content (GTC) and total anthocyanin content (TAC) were determined using colourimetric methods. HPLC-ESI/MSn analysis of phenolic composition of methanolic extracts was also performed. Results Methanolic peel extracts showed strong broad-spectrum activity against Gram-positive and Gram-negative bacteria, with the minimum inhibitory concentrations (MIC) ranging from 0.2 to 0.78 mg/ml. At the highest concentration tested (1000 μg/ml), radical scavenging activities were significantly higher in Arakta (83.54%), Ganesh (83.56%), and Ruby (83.34%) cultivars (P< 0.05). Dose dependent FIC and FRAP activities were exhibited by all the peel extracts. All extracts also exhibited high inhibition (>50%) against monophenolase and diphenolase activities at the highest screening concentration. The most active peel extract was the Bhagwa cultivar against monophenolase and the Arakta cultivar against diphenolase with IC50 values of 3.66 μg/ml and 15.88 μg/ml, respectively. High amounts of phenolic compounds were found in peel extracts with the highest and lowest total phenolic contents of 295.5 (Ganesh) and 179.3 mg/g dry extract (Molla de Elche), respectively. Catechin, epicatechin, ellagic acid and gallic acid were found in all cultivars, of which ellagic acid was the most abundant comprising of more than 50% of total phenolic compounds detected in each cultivar. Conclusions The present study showed that the tested pomegranate peels exhibited strong antibacterial, antioxidant and tyrosinase-inhibition activities. These results suggest that pomegranate fruit peel could be exploited as a potential source of natural antimicrobial and antioxidant agents as well as tyrosinase inhibitors.
- ItemAnuran fauna of the Lesotho Highlands in the Khatse Dam catchment area and Jorodane River region(AOSIS, 1996) Van Dijk, D. E.Surveys were made of the anuran fauna of the Khatse Dam catchment area in the Lesotho Highlands, and of the region between the Central Mountains and the Thaba Putsoa Range which would be affected by Phase IB of the Lesotho Highlands Water Scheme, if implemented. The Khatse Dam is at present filling. Seven species of anurans were encountered in the Khatse Dam catchment, and five of them also in the valley to the south-west. Four taxa occur all around central Lesotho, but one, the Gariep toad, has its south-eastern limit on the Drakensberg Escarpment, and another, Gray's frog, shows indications in Lesotho, as elsewhere, of being distinct from the typical taxon. Two taxa are endemic to the mountains of the Lesotho region, the one being more rheophilic and more wide-spread. The remaining anuran, previously unknown in Lesotho, is now recorded from the highly characteristic, strongly rheophilic tadpoles, as Heleophryne. The various available habitats and the associated anurans are reviewed. Features of the reproductive cycles, are noted. Dispersal and isolation are outlined. Reference is made to the most probable additions to the anuran fauna which further collecting might reveal. The probable impact of the Khatse Dam is discussed.
- ItemApplications of cytokinins in horticultural fruit crops : trends and future prospects(MDPI, 2020-08-22) Aremu, Adeyemi O.; Fawole, Olaniyi A.; Makunga, Nokwanda P.; Masondo, Nqobile A.; Moyo, Mack; Buthelezi, Nana M. D.; Amoo, Stephen O.; Spichal, Lukas; Dolezal, KarelCytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.
- ItemAn approach to the development of a national strategy for controlling invasive alien plant species : the case of Parthenium hysterophorus in South Africa(AOSIS Publishing, 2016) Terblanche, Colette; Nanni, Ingrid; Kaplan, Haylee; Strathie, Lorraine W.; McConnachie, Andrew J.; Goodall, Jeremy; Van Wilgen, Brian W.Invasive alien species require co-ordinated strategic management if negative impacts are to be effectively avoided. Here we describe a strategy for the management of Parthenium hysterophorus L. (Asteraceae) in South Africa. P. hysterophorus is an annual herb native to tropical America, which has become invasive in over 30 countries. The strategy sets goals for (1) the prevention of spread to new areas; (2) local eradication of isolated populations; (3) containment in areas where eradication is not possible; and (4) actions to protect assets where containment is no longer an option. We developed both a national strategy to set policy and to monitor progress towards goals at a national level and an implementation plan to set goals and timeframes for their achievement at local levels. It is not clear, at this stage, whether or not the goals of the strategy are achievable because implementation will face many challenges arising from ecological features of the target plant, social and cultural practices that will influence management, inadequate levels of funding and multiple political considerations. Our strategy proposes regular assessment using high-level indicators, a practice that is widely recognised as essential but seldom implemented at a national scale. Because the outcomes are uncertain, it is vital that regular monitoring of outcomes should be instituted from the start, so that both appropriate adjustments can be made to the strategy and lessons for the implementation of similar strategies elsewhere can be derived.
- ItemArbuscular mycorrhizal colonisation modifies the water relations of young transplanted grapevines (vitis)(South African Society for Enology and Viticulture, 2004) Van Rooyen, M.; Valentine, A.; Archer, E.The effect of arbuscular mycorrhizal (AM) colonisation on the alleviation of transplantation shock in young grapevines was investigated. One-year-old grapevines (Sauvignon blanc on Richter 99), colonised with Glomus etunicatum (Becker and Gerdemann), were cultivated in an atmosphere-controlled tunnel. Water relations, leaf photosynthetic parameters and growth characters were evaluated. AM colonisation enhanced the photosynthetic performance of host plants, but had no influence on biomass and mineral nutrition of the transplanted hosts. The increased photosynthetic rates of the AM plants were related to improved water relations. Stomata] conductance, transpiration rate and midday xylem water potential were higher in the AM hosts during the transplanted period. These results indicate that AM inoculation can influence the water relations of transplanted grapevine rootstocks, thereby improving photosynthetic performance and potential survival during the initial growth stages of the host plants.
- ItemAre invasive populations characterized by a broader diet than native populations?(PeerJ, 2017) Courant, Julien; Vogt, Solveig; Marques, Raquel; Measey, John; Secondi, Jean; Rebelo, Rui; De Villiers, Andre; Ihlow, Flora; De Busschere, Charlotte; Backeljau, Thierry; Rodder, Dennis; Herrel, AnthonyBackground. Invasive species are among the most significant threats to biodiversity. The diet of invasive animal populations is a crucial factor that must be considered in the context of biological invasions. A broad dietary spectrum is a frequently cited characteristic of invasive species, allowing them to thrive in a wide range of environments. Therefore, empirical studies comparing diet in invasive and native populations are necessary to understand dietary requirements, dietary flexibility, and the associated impacts of invasive species. Methods. In this study, we compared the diet of populations of the African clawed frog, Xenopus laevis in its native range, with several areas where it has become invasive. Each prey category detected in stomach contents was assigned to an ecological category, allowing a comparison of the diversity of ecological traits among the prey items in the diet of native and introduced populations. The comparison of diets was also performed using evenness as a niche breadth index on all sampled populations, and electivity as a prey selection index for three out of the six sampled populations. Results. Our results showed that diet breadth could be either narrow or broad in invasive populations. According to diet and prey availability, zooplankton was strongly preferred in most cases. In lotic environments, zooplankton was replaced by benthic preys, such as ephemeropteran larvae. Discussion. The relative proportions of prey with different ecological traits, and dietary variability within and between areas of occurrence, suggest that X. laevis is a generalist predator in both native and invasive populations. Shifts in the realized trophic niche are observed, and appear related to resource availability. Xenopus laevis may strongly impact aquatic ecosystems because of its near complete aquatic lifestyle and its significant consumption of key taxa for the trophic relationships in ponds.