A proposed prioritization system for the management of invasive alien plants in South Africa
- Robertson, Mark P, Villet, Martin H, Fairbanks, Dean H K, Henderson, L, Higgins, Simon I, Hoffmann, John H, Le Maitre, David C, Palmer, Anthony R, Riggs, I, Shackleton, Charlie M, Zimmermann, Helmuth G
- Authors: Robertson, Mark P , Villet, Martin H , Fairbanks, Dean H K , Henderson, L , Higgins, Simon I , Hoffmann, John H , Le Maitre, David C , Palmer, Anthony R , Riggs, I , Shackleton, Charlie M , Zimmermann, Helmuth G
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6911 , http://hdl.handle.net/10962/d1011872
- Description: Every country has weed species whose presence conflicts in some way with human management objectives and needs. Resources for research and control are limited, so priority should be given to species that are the biggest problem. The prioritization system described in this article was designed to assess objectively research and control priorities of invasive alien plants at a national scale in South Africa. The evaluation consists of seventeen criteria, grouped into five modules, that assess invasiveness, spatial characteristics, potential impact, potential for control, and conflicts of interest for each plant species under consideration. Total prioritization scores, calculated from criterion and module scores, were used to assess a species' priority. Prioritization scores were calculated by combining independent assessments provided by several experts, thus increasing the reliability of the rankings. The total confidence score, a separate index, indicates the reliability and availability of data used to make an assessment. Candidate species for evaluation were identified and assessed by several experts using the prioritization system. The final ranking was made by combining two separate indices, the total prioritization score and the total confidence score. This approach integrates the plant's perceived priority with an index of data reliability. Of the 61 species assessed, those with the highest ranks (Lantana camara, Chromolaena odorata and Opuntia ficus-indica) had high prioritization and high confidence scores, and are thus of most concern. Those species with the lowest ranks, for example, Harrisia martinii, Opuntia spinulifera and Opuntia exaltata, had low prioritization scores and high confidence scores, and thus are of least concern. Our approach to ranking weeds offers several advantages over existing systems because it is designed for multiple assessors based on the Delphi decision-making technique, the criteria contribute equally to the total score, and the system can accommodate incomplete data on a species. Although the choice of criteria may be criticized and the system has certain limitations, it appears to have delivered credible results.
- Full Text:
- Date Issued: 2003
- Authors: Robertson, Mark P , Villet, Martin H , Fairbanks, Dean H K , Henderson, L , Higgins, Simon I , Hoffmann, John H , Le Maitre, David C , Palmer, Anthony R , Riggs, I , Shackleton, Charlie M , Zimmermann, Helmuth G
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6911 , http://hdl.handle.net/10962/d1011872
- Description: Every country has weed species whose presence conflicts in some way with human management objectives and needs. Resources for research and control are limited, so priority should be given to species that are the biggest problem. The prioritization system described in this article was designed to assess objectively research and control priorities of invasive alien plants at a national scale in South Africa. The evaluation consists of seventeen criteria, grouped into five modules, that assess invasiveness, spatial characteristics, potential impact, potential for control, and conflicts of interest for each plant species under consideration. Total prioritization scores, calculated from criterion and module scores, were used to assess a species' priority. Prioritization scores were calculated by combining independent assessments provided by several experts, thus increasing the reliability of the rankings. The total confidence score, a separate index, indicates the reliability and availability of data used to make an assessment. Candidate species for evaluation were identified and assessed by several experts using the prioritization system. The final ranking was made by combining two separate indices, the total prioritization score and the total confidence score. This approach integrates the plant's perceived priority with an index of data reliability. Of the 61 species assessed, those with the highest ranks (Lantana camara, Chromolaena odorata and Opuntia ficus-indica) had high prioritization and high confidence scores, and are thus of most concern. Those species with the lowest ranks, for example, Harrisia martinii, Opuntia spinulifera and Opuntia exaltata, had low prioritization scores and high confidence scores, and thus are of least concern. Our approach to ranking weeds offers several advantages over existing systems because it is designed for multiple assessors based on the Delphi decision-making technique, the criteria contribute equally to the total score, and the system can accommodate incomplete data on a species. Although the choice of criteria may be criticized and the system has certain limitations, it appears to have delivered credible results.
- Full Text:
- Date Issued: 2003
Comparing models for predicting species' potential distributions : a case study using correlative and mechanistic predictive modelling techniques
- Robertson, Mark P, Peter, Craig I, Villet, Martin H, Ripley, Bradley S
- Authors: Robertson, Mark P , Peter, Craig I , Villet, Martin H , Ripley, Bradley S
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6539 , http://hdl.handle.net/10962/d1005980 , http://dx.doi.org/10.1016/S0304-3800(03)00028-0
- Description: Models used to predict species’ potential distributions have been described as either correlative or mechanistic. We attempted to determine whether correlative models could perform as well as mechanistic models for predicting species potential distributions, using a case study. We compared potential distribution predictions made for a coastal dune plant (Scaevola plumieri) along the coast of South Africa, using a mechanistic model based on summer water balance (SWB), and two correlative models (a profile and a group discrimination technique). The profile technique was based on principal components analysis (PCA) and the group-discrimination technique was based on multiple logistic regression (LR). Kappa (κ) statistics were used to objectively assess model performance and model agreement. Model performance was calculated by measuring the levels of agreement (using κ) between a set of testing localities (distribution records not used for model building) and each of the model predictions. Using published interpretive guidelines for the kappa statistic, model performance was “excellent” for the SWB model (κ=0.852), perfect for the LR model (κ=1.000), and “very good” for the PCA model (κ=0.721). Model agreement was calculated by measuring the level of agreement between the mechanistic model and the two correlative models. There was “good” model agreement between the SWB and PCA models (κ=0.679) and “very good” agreement between the SWB and LR models (κ=0.786). The results suggest that correlative models can perform as well as or better than simple mechanistic models. The predictions generated from these three modelling designs are likely to generate different insights into the potential distribution and biology of the target organism and may be appropriate in different situations. The choice of model is likely to be influenced by the aims of the study, the biology of the target organism, the level of knowledge the target organism’s biology, and data quality.
- Full Text:
- Date Issued: 2003
- Authors: Robertson, Mark P , Peter, Craig I , Villet, Martin H , Ripley, Bradley S
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6539 , http://hdl.handle.net/10962/d1005980 , http://dx.doi.org/10.1016/S0304-3800(03)00028-0
- Description: Models used to predict species’ potential distributions have been described as either correlative or mechanistic. We attempted to determine whether correlative models could perform as well as mechanistic models for predicting species potential distributions, using a case study. We compared potential distribution predictions made for a coastal dune plant (Scaevola plumieri) along the coast of South Africa, using a mechanistic model based on summer water balance (SWB), and two correlative models (a profile and a group discrimination technique). The profile technique was based on principal components analysis (PCA) and the group-discrimination technique was based on multiple logistic regression (LR). Kappa (κ) statistics were used to objectively assess model performance and model agreement. Model performance was calculated by measuring the levels of agreement (using κ) between a set of testing localities (distribution records not used for model building) and each of the model predictions. Using published interpretive guidelines for the kappa statistic, model performance was “excellent” for the SWB model (κ=0.852), perfect for the LR model (κ=1.000), and “very good” for the PCA model (κ=0.721). Model agreement was calculated by measuring the level of agreement between the mechanistic model and the two correlative models. There was “good” model agreement between the SWB and PCA models (κ=0.679) and “very good” agreement between the SWB and LR models (κ=0.786). The results suggest that correlative models can perform as well as or better than simple mechanistic models. The predictions generated from these three modelling designs are likely to generate different insights into the potential distribution and biology of the target organism and may be appropriate in different situations. The choice of model is likely to be influenced by the aims of the study, the biology of the target organism, the level of knowledge the target organism’s biology, and data quality.
- Full Text:
- Date Issued: 2003
Seasonal phenology of the diamondback moth, Plutella xylostella (L.), (Lepidoptera: Plutellidae), and its parasitoids on canola, Brassica napus (L.), in Gauteng province, South Africa
- Mosiane, S M, Kfir, R, Villet, Martin H
- Authors: Mosiane, S M , Kfir, R , Villet, Martin H
- Date: 2003
- Language: English
- Type: text , Article
- Identifier: vital:6856 , http://hdl.handle.net/10962/d1011139
- Description: Canola, Brassica napus L. (Brassicaceae), is a relativelynewcrop in SouthAfrica. Several insect pests, including diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), that attack cruciferous vegetables, also attack canola. The aims of this study were to determine the seasonal phenology of P. xylostella populations on canola, and the composition, relative abundance and seasonal phenology of parasitoids attacking P. xylostella on this crop. Diamondback moth adults were monitored with synthetic sex-pheromone traps. Larval and pupal populations of P. xylostella were monitored weekly for three years at Bapsfontein and Rietondale in Gauteng province. Samples of diamondback moth larvae, pupae and parasitoid cocoons were collected and transported to the laboratory. Parasitoids that emerged were identified and their incidence recorded. Berlese funnel catches were used as an indicator of the accuracy of the visual counts. The infestation level of P. xylostella larvae was high from May to August at Rietondale, while at Bapsfontein it was high from September to December. There was a high correlation (r=0.79, P<0.001) between pheromone trap catches and subsequent larval infestations at Bapsfontein. The pheromone traps indicated that diamondback moth adults were present throughout the year. Berlese funnel catches indicated that a large number of larvae, especially first instars, were overlooked during visual plant scouting. Parasitism rates were often very high, reaching 90–100 %. The following parasitoids were recorded from field-collected P. xylostella: the larval parasitoids Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) and Apanteles halfordi Ullyett (Hymenoptera: Braconidae), the larval/pupal parasitoids Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae), the pupal parasitoid Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae), and the hyperparasitoids Mesochorus sp. (Hymenoptera: Ichneumonidae) and Pteromalus sp. (Hymenoptera: Pteromalidae). Cotesia plutellae was the most abundant parasitoid throughout the study.
- Full Text:
- Date Issued: 2003
- Authors: Mosiane, S M , Kfir, R , Villet, Martin H
- Date: 2003
- Language: English
- Type: text , Article
- Identifier: vital:6856 , http://hdl.handle.net/10962/d1011139
- Description: Canola, Brassica napus L. (Brassicaceae), is a relativelynewcrop in SouthAfrica. Several insect pests, including diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), that attack cruciferous vegetables, also attack canola. The aims of this study were to determine the seasonal phenology of P. xylostella populations on canola, and the composition, relative abundance and seasonal phenology of parasitoids attacking P. xylostella on this crop. Diamondback moth adults were monitored with synthetic sex-pheromone traps. Larval and pupal populations of P. xylostella were monitored weekly for three years at Bapsfontein and Rietondale in Gauteng province. Samples of diamondback moth larvae, pupae and parasitoid cocoons were collected and transported to the laboratory. Parasitoids that emerged were identified and their incidence recorded. Berlese funnel catches were used as an indicator of the accuracy of the visual counts. The infestation level of P. xylostella larvae was high from May to August at Rietondale, while at Bapsfontein it was high from September to December. There was a high correlation (r=0.79, P<0.001) between pheromone trap catches and subsequent larval infestations at Bapsfontein. The pheromone traps indicated that diamondback moth adults were present throughout the year. Berlese funnel catches indicated that a large number of larvae, especially first instars, were overlooked during visual plant scouting. Parasitism rates were often very high, reaching 90–100 %. The following parasitoids were recorded from field-collected P. xylostella: the larval parasitoids Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) and Apanteles halfordi Ullyett (Hymenoptera: Braconidae), the larval/pupal parasitoids Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae), the pupal parasitoid Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae), and the hyperparasitoids Mesochorus sp. (Hymenoptera: Ichneumonidae) and Pteromalus sp. (Hymenoptera: Pteromalidae). Cotesia plutellae was the most abundant parasitoid throughout the study.
- Full Text:
- Date Issued: 2003
Studying the impact of ocean eddies on the ecosystem of the Prince Edward Islands: DEIMEC ll
- Pakhomov, E A, Ansorge, Isabelle J, Kaehler, Sven, Vumazonke, Lukhanyiso U, Gulekana, K, Bushula, T, Balt, C, Paul, D, Hargey, N, Stewart, H, Chang, N, Furno, L, Mkatshwa, S, Visser, C, Lutjeharms, Johan R E, Hayes-Foley, P
- Authors: Pakhomov, E A , Ansorge, Isabelle J , Kaehler, Sven , Vumazonke, Lukhanyiso U , Gulekana, K , Bushula, T , Balt, C , Paul, D , Hargey, N , Stewart, H , Chang, N , Furno, L , Mkatshwa, S , Visser, C , Lutjeharms, Johan R E , Hayes-Foley, P
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6932 , http://hdl.handle.net/10962/d1011952
- Description: The Dynamics of Eddy Impacts on Marion’s Ecosystem Study (DEIMEC) programme was begun in 2002 with the aim of understanding the importance of the oceanic, upstream environment to the ecosystem of the Prince Edward Islands. This island group consists of two small volcanic islands and provides many opportunities for studying ecological and evolutionary processes, for monitoring ecological changes in relation to global climate change and for conserving a unique component of the planet’s biological diversity.
- Full Text:
- Date Issued: 2003
- Authors: Pakhomov, E A , Ansorge, Isabelle J , Kaehler, Sven , Vumazonke, Lukhanyiso U , Gulekana, K , Bushula, T , Balt, C , Paul, D , Hargey, N , Stewart, H , Chang, N , Furno, L , Mkatshwa, S , Visser, C , Lutjeharms, Johan R E , Hayes-Foley, P
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6932 , http://hdl.handle.net/10962/d1011952
- Description: The Dynamics of Eddy Impacts on Marion’s Ecosystem Study (DEIMEC) programme was begun in 2002 with the aim of understanding the importance of the oceanic, upstream environment to the ecosystem of the Prince Edward Islands. This island group consists of two small volcanic islands and provides many opportunities for studying ecological and evolutionary processes, for monitoring ecological changes in relation to global climate change and for conserving a unique component of the planet’s biological diversity.
- Full Text:
- Date Issued: 2003
Studying the impact of ocean eddies on the ecosystem of the Prince Edward Islands: DEIMEC ll
- Pakhomov, E A, Ansorge, Isabelle J, Kaehler, S
- Authors: Pakhomov, E A , Ansorge, Isabelle J , Kaehler, S
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:7132 , http://hdl.handle.net/10962/d1011774
- Description: The Dynamics of Eddy Impacts on Marion’s Ecosystem Study (DEIMEC) programme was begun in 2002 with the aim of understanding the importance of the oceanic, upstream environment to the ecosystem of the Prince Edward Islands. This island group consists of two small volcanic islands and provides many opportunities for studying ecological and evolutionary processes, for monitoring ecological changes in relation to global climate change and for conserving a unique component of the planet’s biological diversity.
- Full Text:
- Date Issued: 2003
- Authors: Pakhomov, E A , Ansorge, Isabelle J , Kaehler, S
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:7132 , http://hdl.handle.net/10962/d1011774
- Description: The Dynamics of Eddy Impacts on Marion’s Ecosystem Study (DEIMEC) programme was begun in 2002 with the aim of understanding the importance of the oceanic, upstream environment to the ecosystem of the Prince Edward Islands. This island group consists of two small volcanic islands and provides many opportunities for studying ecological and evolutionary processes, for monitoring ecological changes in relation to global climate change and for conserving a unique component of the planet’s biological diversity.
- Full Text:
- Date Issued: 2003
The experience of being diagnosed with a psychiatric disorder: living the label
- Knight, Zelda G, Bradfield, Bruce
- Authors: Knight, Zelda G , Bradfield, Bruce
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6262 , http://hdl.handle.net/10962/d1007880
- Description: Informed by the investigative thrust of phenomenological inquiry and the 'phenomenology of intersubjectivity', the overarching aim of this article is to provide an accurate illumination of the experience of being diagnosed with a psychiatric disorder, and thus being 'a labelled individual'. This article is based on research that sought to understand the impact of the psychiatric label upon labelled individuals interpersonal and intersubjective presence as experienced outside the psychiatric institution. The principle question asked was: "What is the experience of being a labelled individual in the world?". It was discovered that psychiatric labelling unfolds as a disconnection and dislocation from co-existence with others. Moreover, labelling had the effect of robbing such individuals of their subjectivity, rendering them lonely, misunderstood and viewed as somehow defective, disabled and wrong.
- Full Text:
- Date Issued: 2003
- Authors: Knight, Zelda G , Bradfield, Bruce
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6262 , http://hdl.handle.net/10962/d1007880
- Description: Informed by the investigative thrust of phenomenological inquiry and the 'phenomenology of intersubjectivity', the overarching aim of this article is to provide an accurate illumination of the experience of being diagnosed with a psychiatric disorder, and thus being 'a labelled individual'. This article is based on research that sought to understand the impact of the psychiatric label upon labelled individuals interpersonal and intersubjective presence as experienced outside the psychiatric institution. The principle question asked was: "What is the experience of being a labelled individual in the world?". It was discovered that psychiatric labelling unfolds as a disconnection and dislocation from co-existence with others. Moreover, labelling had the effect of robbing such individuals of their subjectivity, rendering them lonely, misunderstood and viewed as somehow defective, disabled and wrong.
- Full Text:
- Date Issued: 2003
The vegetation of the habitat of the Brenton blue butterfly, Orachrysops niobe (Trimen), in the Western Cape, South Africa
- Lubke, Roy, Hoare, D, Victor, J, Ketelaar, R
- Authors: Lubke, Roy , Hoare, D , Victor, J , Ketelaar, R
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6524 , http://hdl.handle.net/10962/d1005957
- Description: The Brenton blue butterfly is known only from a small population in one hectare of asteraceous coastal fynbos at Brenton-on-Sea. This fynbos is characterized by a great diversity of shrubs, herbs and graminoids, with a successional gradient to thicket where Pterocelastrus tricuspidatus is dominant. The eggs of the butterfly are laid on the lower side of the leaves of Indigofera erecta, on which the larvae feed. Fifteen 1-m² quadrats containing plants of Indigofera erecta with and without eggs of the butterfly were distinguished and sampled separately from 15 1-m² quadrats containing plants of Indigofera erecta without eggs. No marked differences in total vegetation, shrub or herb cover between the sites with and without eggs were observed. There was a difference in abundance of the fern Pteridium aquilinum, with over 30% cover at sites with no eggs and only about 6% at sites with eggs present. This could reflect the absence of other plants where the ferns had such dense cover.
- Full Text:
- Date Issued: 2003
- Authors: Lubke, Roy , Hoare, D , Victor, J , Ketelaar, R
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6524 , http://hdl.handle.net/10962/d1005957
- Description: The Brenton blue butterfly is known only from a small population in one hectare of asteraceous coastal fynbos at Brenton-on-Sea. This fynbos is characterized by a great diversity of shrubs, herbs and graminoids, with a successional gradient to thicket where Pterocelastrus tricuspidatus is dominant. The eggs of the butterfly are laid on the lower side of the leaves of Indigofera erecta, on which the larvae feed. Fifteen 1-m² quadrats containing plants of Indigofera erecta with and without eggs of the butterfly were distinguished and sampled separately from 15 1-m² quadrats containing plants of Indigofera erecta without eggs. No marked differences in total vegetation, shrub or herb cover between the sites with and without eggs were observed. There was a difference in abundance of the fern Pteridium aquilinum, with over 30% cover at sites with no eggs and only about 6% at sites with eggs present. This could reflect the absence of other plants where the ferns had such dense cover.
- Full Text:
- Date Issued: 2003
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