An RTSP proxy for implementing the IPTV media function using a streaming server
- Authors: Shibeshi, Zelalem S , Terzoli, Alfredo , Bradshaw, Karen L
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/429136 , vital:72562 , https://www.informatica.si/index.php/informatica/article/view/383
- Description: Multimedia content delivery in IMS, including IPTV, is handled by a separate unit, the Media Function (MF), made up of media control and media delivery units, which in the case of IPTV are the Media Control Function (MCF) and Media Delivery Function (MDF), respectively. According to the different specifications of an IMS based IPTV architecture, the User Equipment (UE) is expected to use the RTSP protocol as a media control protocol to interact with the MCF, and obtains delivery of media from the MDF using the RTP protocol. This also means that the streaming session needs to be initiated from the media controller on behalf of the user but the delivery of media is sent to the UE from the media deliverer (media server). Due both to the lack of free and open source Media Servers and the availability of free and open source Streaming Servers, the ideal choice for the delivery of multimedia services, including IPTV, by the research community is Streaming Servers. Nevertheless, because of denial of service attacks and other issues, most streaming servers do not allow a different location for the session setup request and the delivery of media in the streaming session. In other words, most streaming servers are not designed to be controlled by some other entity other than the RTSP client that consumes the media. This makes it difficult to have a separate media control unit for IPTV service in IMS if one wanted to use a streaming server as an MDF unit. So, while waiting for streaming servers to work in this manner, it is better to find a work around in order to use streaming servers to develop and test IPTV services in IMS environments. For this purpose we propose another component (an RTSP proxy and relay unit) as part of the IPTV MF and to mediate between the MCF and MDF. This unit correctly relays media control commands from the MCF to the MDF and RTP packets from the MDF to the UE. It also helps in the implementation of other streaming functionalities that are required for IPTV service delivery, but which are not implemented in the current open source streaming servers. Additional services can also be easily implemented with the help of this unit. This will facilitate the development of an IPTV service using readily available open source streaming servers and help researchers to evaluate their proposals on new services they would like to develop. In this paper we show how this RTSP proxy unit can be integrated into the Media Function of the IPTV architecture to ease the media delivery process of an IMS based IPTV service.
- Full Text:
- Date Issued: 2012
Are arts events a good way of augmenting the economic impact of sport?: The case of the 2010 FIFA world cup and the national arts festival in South Africa
- Authors: Snowball, Jeanette D
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71430 , vital:29848 , https://econrsa.org/system/files/publications/working_papers/wp294.pdf
- Description: Despite the debate about whether arts consumers are also sports consumers, many countries have used cultural events to leverage further tourism spending from sports events, the most famous example being the cultural Olympics. This paper reports the findings of research conducted at the 2010 South African National Arts Festival, which was specifically timed to coincide with SoccerWorld Cup matches being played in a nearby city. Of the 600 interviews conducted with Festival-goers, only 23% reported also attending World Cup soccer matches. Regression analysis revealed that, while there is some overlap between arts and sports attendees, their demographics and consumption habits are significantly different. However, consumption outside of major events showed somewhat more overlap. This suggests that staging cultural events at the same time as major sporting events is not an ideal strategy, since they tend to compete with, rather than complement, each other.
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- Date Issued: 2012
Baseline isotope data for Spirodela sp.: nutrient differentiation in aquatic systems
- Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444502 , vital:74246 , https://doi.org/10.1016/j.watres.2012.03.063
- Description: The excessive addition of nitrogen to watersheds is recognized as one of the main causes of the global deterioration of aquatic ecosystems and an increasing number of studies have shown that δ15N signatures of macrophytes may reflect the N-loading of the system under investigation. This study investigated isotopic equilibration rates and concentration level effects of KNO3 and cow manure nutrient solutions on the δ15N and δ13C signatures, C/N ratios, % N and % C of Spirodela sp. over time, to determine the feasibility of their use in monitoring anthropogenic N-loading in freshwater systems. Spirodela δ15N signatures clearly distinguished between nutrient types within 2 days of introduction, with plants grown in KNO3 showing extremely depleted δ15N values (−15.00 to −12.00‰) compared to those growing in cow manure (14.00–18.00‰). Isotopic equilibration rates could not be determined with certainty, but plant isotopic differentiation between nutrient regimes became apparent after 2 days and started to equilibrate by day 4. Concentration level effects were also apparent, with Spirodela tissue displaying more depleted and enriched δ15N values in higher concentrations of KNO3 and cow manure respectively.
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- Date Issued: 2012
Bridging and enriching top-down and participatory learning: The case of smallholder, organic conservation agriculture farmers in Zimbabwe
- Authors: Mukute, Mutizwa
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/432967 , vital:72919 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/122261"
- Description: This article discusses the combined use of top-down and participatory learning approaches during the course of a 42-month organic conservation agriculture project that is being implemented in eight districts of Mashonaland East Province in Zimbabwe. The initial 18-month project was extended by a further 24 months in order to build on what had been achieved by deepening organic conservation agriculture practices, by increasing the understanding of, and access to, markets, and by expanding farmer agency. The top-down approach involves farmer representatives, known as ‘access farmers’ in the project, undergoing training at training centres and then returning to their respective farmer associations to train other farmers in what they have learnt. Participatory learning includes farmer-to-farmer learning within and among associations, and trainers learning from, and acting on, farmer experiences. Expansive learning, which combines, and goes beyond, both approaches and allows for joint learning, innovation and agency, has been used to support the associations to learn about, practise and benefit from organic conservation agriculture. This was stimulated by change laboratory workshops being conducted with each of the 32 farmer associations formed during the first 18 months of the project. The main argument in the present article is that combining these seemingly opposite approaches to learning is feasible and is essential for accelerating practice-oriented changes in agriculture. The concept that appears to enable this linkage is dialectics.
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- Date Issued: 2012
Building a Graphical Fuzzing Framework
- Authors: Zeisberger, Sascha , Irwin, Barry V W
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/429772 , vital:72638 , https://digifors.cs.up.ac.za/issa/2012/Proceedings/Research/59_ResearchInProgress.pdf
- Description: Fuzz testing is a robustness testing technique that sends malformed data to an application’s input. This is to test an application’s behaviour when presented with input beyond its specification. The main difference between traditional testing techniques and fuzz testing is that in most traditional techniques an application is tested according to a specification and rated on how well the application conforms to that specification. Fuzz testing tests beyond the scope of a specification by intelligently generating values that may be interpreted by an application in an unintended manner. The use of fuzz testing has been more prevalent in academic and security communities despite showing success in production environments. To measure the effectiveness of fuzz testing, an experiment was conducted where several publicly available applications were fuzzed. In some instances, fuzz testing was able to force an application into an invalid state and it was concluded that fuzz testing is a relevant testing technique that could assist in developing more robust applications. This success prompted a further investigation into fuzz testing in order to compile a list of requirements that makes an effective fuzzer. The aforementioned investigation assisted in the design of a fuzz testing framework, the goal of which is to make the process more accessible to users outside of an academic and security environment. Design methodologies and justifications of said framework are discussed, focusing on the graphical user interface components as this aspect of the framework is used to increase the usability of the framework.
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- Date Issued: 2012
Can contracts be both plain and precise?
- Authors: Siebörger, Ian , Adendorff, Ralph D
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123299 , vital:35425 , https://doi.org/10.2989/16073614.2011.651944
- Description: One argument against the use of plain language in legal documents is that it is impossible to convey legal meanings in plain language with the same precision as in specialist legal discourse (Hunt, 2003). We tested this claim by redrafting an extract from a lease agreement into plain English in three stages, producing three versions of the extract in progressively plainer English. We submitted these with the original lease agreement to a senior advocate to elicit his opinion on whether the plain-language versions of the extract are equivalent to the original in legal force. Various differences between the versions are analysed using lexical semantics and Systemic Functional Grammar (as described in Halliday & Matthiessen, 2004). This analysis reveals that the redrafted versions could easily be altered to eliminate the difference between them and the original extract, and that ‘plain language’ as conceived by redrafters of official documents may be easy for non-experts to read, but more difficult for experts. This demonstrates that a ‘one-size-fits-all’ approach to readability is often not tenable, and that plain-language activists can learn much from research (such as Street, 1993) which asserts the existence of a plurality of literacies.
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- Date Issued: 2012
Capturefoundry: a gpu accelerated packet capture analysis tool
- Authors: Nottingham, Alastair , Richter, John , Irwin, Barry V W
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430112 , vital:72666 , https://doi.org/10.1145/2389836.2389877
- Description: Packet captures are used to support a variety of tasks, including network administration, fault diagnosis and security and network related research. Despite their usefulness, processing packet capture files is a slow and tedious process that impedes the analysis of large, long-term captures. This paper discusses the primary components and observed performance of CaptureFoundry, a stand-alone capture analysis support tool designed to quickly map, filter and extract packets from large capture files using a combination of indexing techniques and GPU accelerated packet classification. All results are persistent, and may be used to rapidly extract small pre-filtered captures on demand that may be analysed quickly in existing capture analysis applications. Performance results show that CaptureFoundry is capable of generating multiple indexes and classification results for large captures at hundreds of megabytes per second, with minimal CPU and memory overhead and only minor additional storage space requirements.
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- Date Issued: 2012
CdTe quantum dots functionalized with 4-amino-2, 2, 6, 6-tetramethylpiperidine-N-oxide as luminescent nanoprobe for the sensitive recognition of bromide ion
- Authors: Adegoke, Oluwasesan , Hosten, Eric , McCleland, Cedric , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244393 , vital:51253 , xlink:href="https://doi.org/10.1016/j.aca.2012.01.040"
- Description: A novel bromide ion-selective modified nanoprobe sensor based on 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4AT)-functionalized CdTe quantum dots (QDs-4AT) has been developed. Fluorescence quenching of the QDs by 4AT was observed. The functionalized QDs-4AT nanoprobe allowed a highly sensitive determination of bromide ion via analyte-induced change in the photoluminescence (fluorescence recovery) of the modified QDs. A detection limit of 0.6 nM of bromide ion was obtained, while the interfering effect of other inorganic cations and anions was investigated to examine the selectivity of the nanoprobe. The linear range was between 0.01 and 0.13 μM. Combined fluorescence lifetime and electron paramagnetic resonance measurements confirmed electron transfer processes between bromide ion and QDs-4AT.
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- Date Issued: 2012
Challenges experienced in the first year of implementation of a teaching and learning virtual partnership at the University of Namibia
- Authors: Mufeti, K , Foster, Gregory G , Terzoli, Alfredo
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/431234 , vital:72756 , https://rcetj.org/index.php/rcetj/article/view/178
- Description: Advances in information and communication technologies are enabling higher educa-tion institutions to build virtual partnerships with other institutions. Virtual partner-ships are defined here as collaborations between geographically dispersed institutions, where interaction between these institutions is enabled mainly by electronic modes of communication. This article reports on the participants’ experiences of the implemen-tation of one such partnership from the perspective of a partner in a developing con-text. It uses the SANTED Virtual Classroom Project (VCP), a virtual partnership initia-tive between the Departments of Computer Science at the University of Namibia (UNAM) and Rhodes University (RU), as a case study. In the VCP, the department at RU was tasked with building teaching and human resource capacity in the department at UNAM. The article focuses on the challenges experienced at UNAM during the first year of implementation of the VCP and lessons learned.
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- Date Issued: 2012
Characterization of 2,(3)-tetra-(4-oxo-benzamide) phthalocyaninato cobalt (II)—single walled carbon nanotube conjugate platforms and their use in electrocatalysis of amitrole
- Authors: Mugadza, Tawanda , Arslanoğlu, Yasin , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244382 , vital:51252 , xlink:href="https://doi.org/10.1016/j.electacta.2012.02.041"
- Description: In this paper we report on the use of carboxylic acid functionalized single walled carbon nanotubes (SWCNT) in the synthesis of 2,(3)-tetra-(4-oxo-benzamide)phthalocyaninato cobalt (II)–single walled carbon nanotube conjugates (CoTOBPc–SWCNT), their characterization and application in the electrocatalytic oxidation of amitrole. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were used for the detection of amitrole on the modified glassy carbon electrode. The catalytic rate constant was 1.6 × 103 M−1 s−1 and the apparent electron rate transfer constant was 1.5 × 10−5 cm s−1. The linear dynamic range was 1.0 × 10−6–3.0 × 10−5 M, with a sensitivity of ∼1.13 A mol−1 L cm−2.
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- Date Issued: 2012
Chieftainship succession and gender equality in Lesotho: negotiating the right to equality in a jungle of pluralism
- Authors: Juma, Laurence
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127067 , vital:35951 , https://heinonline.org/HOL/Page?handle=hein.journals/tjwl22amp;div=11amp;g_sent=1amp;casa_token=amp;collection=journals
- Description: Women constitute about 51% of Lesotho's population 1 and enjoy a higher literacy rate than men. 2 They are also the backbone of a society that for several hundreds of years provided male labor to South Africa's farms and gold mines.3 However, Basotho women are generally excluded from mainstream politics and are discriminated against in almost all spheres of socioeconomic life. This exclusion, marginalization, and discrimination have been largely blamed on patriarchy and entrenched traditional norms, both of which are sustained by a plural legal system that has seemingly remained insular to developments around the globe. 4
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- Date Issued: 2012
China-Africa relations: research approaches
- Authors: Simbao, Ruth K
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147503 , vital:38644 , https://doi.org/10.1162/afar.2012.45.2.1
- Description: About to board a plane in Johannesburg, I handed my temporary boarding pass to the flight attendant who exclaimed,“Simbao, you have a fong kong boarding pass!” Fong kong is a slang term used in South Africa meaning fake, cheap, or low quality and is often associated with Chinese imports. In this case, the term was used to refer to a temporary pass issued earlier on my journey that needed to be replaced with a new boarding pass in Johannesburg.
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- Date Issued: 2012
Civil society and state-centred struggles
- Authors: Helliker, Kirk D
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71231 , vital:29821 , https://doi.org/10.1080/02589001.2012.641723
- Description: This article is about civil society and state-centred struggles in contemporary Zimbabwe. I first identify and outline three current understandings of civil society. Two understandings (one Liberal, one Radical) are state-centric and exist firmly within the logic of state discourses and state politics. A third understanding, also Radical, is society-centric and speaks about politics existing at a distance from the state and possibly beyond the boundaries of civil society. This civil society-state discussion frames the second section of the article, which looks specifically at Zimbabwe. It details civil society as contested terrain (from the late 1990s onwards) within the context of a scholarly debate about agrarian transformation and political change. This debate, which reproduces (in theoretical garb) the key political society (or party) fault-lines within Zimbabwean society, has taken place primarily within the restricted confines of state-centred discourses.
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- Date Issued: 2012
Comparison of carbon screen-printed and disk electrodes in the detection of antioxidants using CoPc derivatives
- Authors: Matemadombo, Fungisai , Apetrei, Constantin , Nyokong, Tebello , Rodríguez-Méndez, María Luz , de Saja, José Antonio
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244371 , vital:51251 , xlink:href="https://doi.org/10.1016/j.snb.2012.02.088"
- Description: Cobalt phthalocyanine (CoPc) and cobalt phthalocyanine carboxylic derivatives (CoTCPc and CoOCPc) have been used as electrocatalysts for the detection of the antioxidants vanillic acid, caffeic acid, pyrogallol, and ascorbic acid on screen-printed carbon and disk electrode surfaces. The cobalt phthalocyanines were used to detect vanillic acid (with limit of detection ranging from 1.15 μM to 2.42 μM at potentials of 0.55–0.88 V vs. Ag|AgCl), caffeic acid (with limit of detection ranging from 1.17 μM to 2.20 μM at potentials of 0.30–0.81 V vs. Ag|AgCl), pyrogallol (with limit of detection ranging from 1.16 μM to 3.63 μM at potentials of 0.52–0.63 V vs. Ag|AgCl), and ascorbic acid (with limit of detection ranging from 1.16 μM to 1.58 μM at potentials of 0.34–0.46 V vs. Ag|AgCl). The kinetic studies also demonstrate diffusion-controlled processes at the electrode surface. The SPCE electrodes have better detection properties towards vanillic acid, caffeic acid, pyrogallol while the disk electrodes had better ascorbic acid detection properties as proven by kinetic studies. Both types CoPc-influenced electrodes show 100% discrimination of the antioxidants.
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- Date Issued: 2012
Comprehension and production of figurative language by Afrikaans-speaking children with and without specific language impairment
- Authors: van der Merwe, Kristin , Adendorff, Ralph
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123442 , vital:35438 , https://doi.org/10.2989/16073614.2012.693708
- Description: This article reports on the comprehension and production of figurative language, namely idioms and similes, in first language Afrikaans-speaking (AFR) boys, ages eight to 10 years, and first language Afrikaans-speaking boys with specific language impairment (SLI), also ages eight to 10. It draws on a larger study by Van der Merwe (2007; see also Van der Merwe & Southwood, 2008). Testing of the comprehension and production abilities of the children was conducted verbally and individually and elicited their understanding of 25 idioms and 25 similes. The idioms were first presented without context; if the child gave an incorrect interpretation, the idiom was placed in context. Raw scores show that the SLI group performed marginally more poorly than the AFR group, but there was no statistically significant difference between the comprehension of idioms by the two groups. The same can be said for the number of literal interpretations provided by the groups. Placing the idioms in context was beneficial to both groups. The simile completion task required the children to provide the last word of each simile. For both groups, the similes task proved to be easier than the idioms task but there was again no statistically significant difference found between the two groups. The results seem to imply that children at this developmental phase, aged eight to 10, whether language impaired or not, have not yet fully grasped figurative language as a concept and need explicit instructions on figurative language. The article ends with a reflection on the suitability of idioms and similes as particular categories of figurative language in studies of this nature.
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- Date Issued: 2012
Computer-aided identification of coelacanths, latimeria chalumnae, using scale patterns
- Authors: Thornycroft, Rosanne E , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124013 , vital:35526 , https://doi.10.1080/17451000.2011.628679
- Description: Despite coelacanths, Latimeria chalumnae, being listed as either endangered by CITES or critically endangered by the IUCN, their population size within South Africa is unknown and still needs to be estimated. Their conservation status unfortunately excludes the use of conventional tagging to mark individual animals for a possible mark-recapture experiment. This study shows that because coelacanths have a unique spot patterning it is possible to quickly and accurately identify specific individuals photographically using computer-aided identification software. Without any manual intervention by an operator, the software accurately identified between 56 and 92% of the individuals. Indentification success increased to 100% if the operator could also manually select from other potential matching photographs. It was also shown that fish exhibiting a yaw angle not exceeding 60˚ could be accurately identified in photographs, although the percentage of fish correctly identified without operator-intervention decreased rapidly with increasing yaw angle. Computer-aided identification should therefore facilitate future coelacanth research as it is both efficient and accurate while also reducing potential stress on the animals observed.
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- Date Issued: 2012
Cost-effective realisation of the Internet of Things
- Authors: Andersen, Michael , Irwin, Barry V W
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/427930 , vital:72474 , https://www.researchgate.net/profile/Barry-Irwin/publication/326225063_Cost-effec-tive_realisation_of_the_Internet_of_Things/links/5b3f2262a6fdcc8506ffe75e/Cost-effective-realisation-of-the-Internet-of-Things.pdf
- Description: A hardware and software platform, created to facilitate power usage and power quality measurements along with direct power line actuation is under development. Additional general purpose control and sensing interfaces have been integrated. Measurements are persistently stored on each node to allow asynchronous retrieval of data without the need for a central server. The device communicates using an IEEE 802.15. 4 radio transceiver to create a self-configuring mesh network. Users can interface with the mesh network by connecting to any node via USB and utilising the developed high level API and interactive environment.
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- Date Issued: 2012
Cutaneous myiasis: is Lucilia cuprina safe and acceptable for maggot debridement therapy?
- Authors: Kingu, Howard J , Kuria, Simon K , Villet, Martin H , Mkhize, Jane N , Dhaffala, Adupa , Iisa, John M
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442649 , vital:74018 , DOI:10.4236/jcdsa.2012.22018
- Description: Preservation of viable tissue is important in wound management. It is achieved by small, incremental removal of devitalised, necrotic and infected tissues. Maggot debridement therapy (MDT) is used in septic necrotic wounds that fail to respond to conventional modalities. MDT has relied on Lucilia cuprina, which consumes only necrotic tissues, as opposed to Lucilia cuprina, which devours both flesh and necrotic tissues. Recent findings have shown that L. cuprina consumes mainly necrotic and very small amounts of viable tissues and may be used in MDT where L. sericata is very rare or absent. Here we describe wound healing in a patient from rural South Africa with cutaneous myiasis. Our findings agree with workers who indicated that L. cuprina could be used in MDT.
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- Date Issued: 2012
Design of realistic hybrid marine resource management programs in Oceania
- Authors: Aswani, Shankar , Ruddle, Kenneth
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70615 , vital:29681 , https://doi.org/10.2984/67.3.11
- Description: This review article synthesizes the authors' several decades of multidisciplinary natural and social science and applied marine resource management experience in the Asia-Pacific region to examine the strengthening of coastal and marine resource management and conservation using alliances between local communities and external institutions. The objective is to assist the design of resource management and conservation programs that enhance the capacity of coastal communities in Oceania to confront both diminishing marine resources and the effects of climate change by providing guidelines for protecting marine biodiversity and vulnerable ecosystem functions. This article describes a management framework that hybridizes local beliefs and institutions expressed in customary management (CM) with such modern management concepts as marine protected areas (MPAs) and ecosystem-based management (EBM). Hybrid management accommodates the social, political, economic, and cultural contexts of Oceanic communities and, compared with recent or conventional management approaches, can therefore better address fundamental local concerns such as coastal degradation, climate change, sea level rise, weak governance, corruption, limited resources and staff to manage and monitor marine resources, and increasing poverty. Research on the hybridization of management systems demonstrates opportunities to establish context-appropriate EBM and/or other managerial arrangements that include terrestrial and adjacent coastal-marine ecosystems. Formal and informal CM systems are widespread in Oceania and in some parts of Southeast Asia, and if appropriate strategies are employed rapid progress toward hybrid CM-EBM could be enabled.
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- Date Issued: 2012
Detecting impacts of invasive non-native sharptooth catfish, Clarias gariepinus, within invaded and non-invaded rivers.
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124100 , vital:35539 , https://doi.10.1007/s10531-012-0291-5
- Description: In aquatic ecosystems, impacts by invasive introduced fish can be likened to press disturbances that persistently influence communities. This study examined invasion disturbances by determining the relationship between non-native sharptooth catfish Clarias gariepinus and aquatic macroinvertebrates in the Eastern Cape, South Africa. A Multiple Before–After Control–Impact (MBACI) experimental design was used to examine macroinvertebrate communities within two rivers: one with catfish and another one without catfish. Within the invaded river, macroinvertebrates showed little response to catfish presence, whereas predator exclusion appeared to benefit community structure. This suggests that the macroinvertebrate community within the invaded river was adapted to predation impact because of the dominance of resilient taxa, such as Hirudinea, Oligochaeta and Chironomidae that were abundant in the Impact treatment relative to the Control treatment. High macroinvertebrate diversity and richness that was observed in the Control treatment, which excluded the predator, relative to the Impact treatment suggests predator avoidance behaviour within the invaded river. By comparison, within the uninvaded river, catfish introduction into the Impact treatment plots indicated negative effects on macroinvertebrate community that was reflected by decrease in diversity, richness and biomass. A community level impact was also reflected in the multivariate analysis that indicated more variation in macroinvertebrate composition within the Impact treatment relative to the Control in the uninvaded river. Catfish impact within the uninvaded river suggests the dominance of vulnerable taxa, such as odonates that were less abundant in the Impact treatment plots after catfish introduction. From a disturbance perspective, this study revealed different macroinvertebrate responses to catfish impact, and suggests that within invaded habitats, macroinvertebrates were less responsive to catfish presence, whereas catfish introduction within uninvaded habitats demonstrated invasion impact that was shown by a decrease in the abundance of vulnerable taxa. The occurrence of non-native sharptooth catfish within many Eastern Cape rivers is a concern because of its predation impact and potential to influence trophic interrelationships, and efforts should be taken to protect uninvaded rivers, and, where possible, eradicate the invader.
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- Date Issued: 2012