A fuzzy classification technique for predicting species' distributions: applications using invasive alien plants and indigenous insects
- Authors: Robertson, Mark P , Villet, Martin H , Palmer, Anthony R
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6897 , http://hdl.handle.net/10962/d1011659 , http://dx.doi.org/10.1111/j.1366-9516.2004.00108.x
- Description: A new predictive modelling technique called the fuzzy envelope model (FEM) is introduced. The technique can be used to predict potential distributions of organisms using presence-only locality records and a set of environmental predictor variables. FEM uses fuzzy logic to classify a set of predictor variable maps based on the values associated with presence records and combines the results to produce a potential distribution map for a target species. This technique represents several refinements of the envelope approach used in the BIOCLIM modelling package. These refinements are related to the way in which FEMs deal with uncertainty, the way in which this uncertainty is represented in the resultant potential distribution maps, and the way that these maps can be interpreted and applied. To illustrate its potential use in biogeographical studies, FEM was applied to predicting the potential distribution of three invasive alien plant species (Lantana camara L., Ricinus communis L. and Solanum mauritianum Scop.), and three native cicada species (Capicada decora Germar, Platypleura deusta Thun. and P. capensis L.) in South Africa, Lesotho and Swaziland. These models were quantitatively compared with models produced by means of the algorithm used in the BIOCLIM modelling package, which is referred to as a crisp envelope model (the CEM design). The average performance of models of the FEM design was consistently higher than those of the CEM design. There were significant differences in model performance among species but there was no significant interaction between model design and species. The average maximum kappa value ranged from 0.70 to 0.90 for FEM design and from 0.57 to 0.89 for the CEM design, which can be described as 'good' to 'excellent' using published ranges of agreement for the kappa statistic. This technique can be used to predict species' potential distributions that could be used for identifying regions at risk from invasion by alien species. These predictions could also be used in conservation planning in the case of native species.
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Endothermy in African Platypleurine Cicadas: the influence of body size and habitat (Hemiptera: Cicadidae)
- Authors: Sanborn, Allen F , Villet, Martin H , Phillips, Polly K F
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6925 , http://hdl.handle.net/10962/d1011912
- Description: The platypleurine cicadas have a wide distribution across Africa and southern Asia. We investigate endothermy as a thermoregulatory strategy in 11 South African species from five genera, with comparisons to the lone ectothermic platypleurine we found, in an attempt to ascertain any influence that habitat and/or body size have on the expression of endothermy in the platypleurine cicadas. Field measurements of body temperature (Tb) show that these animals regulate Tb through endogenous heat production. Heat production in the laboratory elevated Tb to the same range as in animals active in the field. Maximum Tb measured during calling activity when there was no access to solar radiation ranged from 13.2° to 22.3°C above ambient temperature in the five species measured. The mean Tb during activity without access to solar radiation did not differ from the mean Tb during diurnal activity. All platypleurines exhibit a unique behavior for cicadas while warming endogenously, a temperature- dependent telescoping pulsation of the abdomen that probably functions in ventilation. Platypleurines generally call from trunks and branches within the canopy and appear to rely on endothermy even when the sun is available to elevate Tb, in contrast to the facultative endothermy exhibited by New World endothermic species. The two exceptions to this generalization we found within the platypleurines are Platypleura wahlbergi and Albanycada albigera, which were the smallest species studied. The small size of P. wahlbergi appears to have altered their thermoregulatory strategy to one of facultative endothermy, whereby they use the sun when it is available to facilitate increases in Tb. Albanycada albigera is the only ectothermic platypleurine we found. The habitat and host plant association of A. albigera appear to have influenced the choice of ectothermy as a thermoregulatory strategy, as the species possesses the metabolic machinery to elevate to the Tb range observed in the endothermic species. Therefore, size and habitat appear to influence the expression of thermoregulatory strategies in African platypleurine cicadas.
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Mechanisms generating biological diversity in the genus Platypleura Amyot & Serville, 1843 (Hemiptera: Cicadidae) in southern Africa: implications of a preliminary molecular phylogeny
- Authors: Villet, Martin H , Barker, Nigel P , Lunt, N
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6554 , http://hdl.handle.net/10962/d1006012
- Description: Truly understanding biological diversity requires a move from descriptive studies to mechanistic interpretations based on comparative biology and a thorough recognition of the natural history of the focal organisms. A useful step in such comparative studies is the generation of a phylogeny, so that one can assess the phylogenetic independence of the focal taxa and trace the evolutionary significance of their characteristics. As a preliminary to such studies on the platypleurine cicada genus Platypleura, we sequenced 498 bases of the cytochrome oxidase I (COI) gene from thirteen African species. To circumvent problems with outgroup selection, we also included sequences from representatives of the platypleurine genera Brevisiana, Capcicada, Munza, Oxypleura, Severiana, and Systophlochius, all of the subtribe Platypleuriti, and two species of the genus Ugada, of the subtribe Hainanosemiiti. The resulting phylogenies support the synonymization of the monotypic genus Systophlochius with the widespread, speciose genus Platypleura; confirm the placement of Platypleura sp. 7 in that genus; and confirm the independence of Capcicada and Platypleura. Although the preliminary phylogeny lacks strong support at many nodes, it suggests that three radiations of Platypleura have occurred in southern Africa and that there was progressive southward speciation of these radiations. A novel modification of the ancestral area analysis further suggests that the group has an ancestral association with acacias but there were five independent speciation events associated with host- switching. These insights can be summarized by a general hypothesis that the mechanisms underlying platypleurine biodiversity in southern Africa involve two ancient vicariance events and subsequent speciation by vicariance, switching of plant associations, and changes of habitat preferences. We offer this example to illustrate how analysis of preliminary data can help to generate hypotheticodeductive research hypotheses, to provoke interest in testing these hypotheses, and to illustrate the utility of phylogenies beyond systematics.
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Parasitoids associated with the diamondback moth, Plutella xylostella (L.), in the Eastern Cape, South Africa
- Authors: Smith, Tamara J , Villet, Martin H
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , conference
- Identifier: http://hdl.handle.net/10962/442795 , vital:74034 , ISBN , https://www.cabidigitallibrary.org/doi/full/10.5555/20093098381
- Description: Seasonal fluctuations of diamondback moth and its hymenopteran parasitoids were recorded weekly from April 1997 to November 1999 at four cabbage sites in the Grahamstown area of the Eastern Cape, South Africa. Two sites were commercial farms with active spraying programmes; the others were unsprayed. Infestation levels were highest during spring (September to November) and autumn (March to May), where 100% infestation of plants was reached at times. The highest infestation was found during the spring months, where 12 larvae/plant were found at the unsprayed sites and between 6 and 10 larvae at the sprayed sites. At the unsprayed sites abundance of diamondback moth larvae and parasitoids was high during 1997, but much lower during 1998 and 1999, indicating possible control by the parasitoids. Nine species of parasitoid were recorded from diamondback moth during this period and four (Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae), Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae), Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae)) showed potential as biological control agents. The highest rate of parasitism was found from mid-autumn to the beginning of winter (April to June) and from mid-spring to the beginning of summer (October to December). Percent parasitism varied throughout the year, ranging between 10% and 80%. Parasitism of 100% was observed when moth numbers were low. Different species of parasitoids were found to be dominant at different times of the year.
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Recent African derivation of Chrysomya putoria from C. chloropyga and mitochondrial DNA paraphyly of cytochrome oxidase subunit one in blowflies of forensic importance
- Authors: Wells, J D , Lunt, N , Villet, Martin H
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6888 , http://hdl.handle.net/10962/d1011648
- Description: Chrysomya chloropyga (Wiedemann) and C. putoria (Wiedemann) (Diptera: Calliphoridae) are closely related Afrotropical blowflies that breed in carrion and latrines, reaching high density in association with humans and spreading to other continents. In some cases of human death, Chyrsomya specimens provide forensic clues. Because the immature stages of such flies are often difficult to identify taxonomically, it is useful to develop DNA-based tests for specimen identification. Therefore we attempted to distinguish between C. chloropyga and C. putoria using mitochondrial DNA (mtDNA) sequence data from a 593-bp region of the gene for cytochrome oxidase subunit one (COI). Twelve specimens from each species yielded a total of five haplotypes, none being unique to C. putoria. Therefore it was not possible to distinguish between the two species using this locus. Maximum parsimony analysis indicated paraphyletic C. chloropyga mtDNA with C. putoria nested therein. Based on these and previously published data, we infer that C. putoria diverged very recently from C. chloropyga.
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Seasonal rates of parasitism of diamondback moth (Plutella xylostella) in subsistence cabbage crops in the Eastern Cape, South Africa
- Authors: Mkize, Nolwazi , Villet, Martin H
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/442807 , vital:74035 , ISBN , https://www.torrossa.com/en/resources/an/5063829#page=221
- Description: Smith's (personal communication) work in a continuous, commercial cabbage-growing area near Grahamstown showed that parasitism of diamondback moth averaged over 60% and could reach 100%. In many parts of the world cabbage crops are not under continuous cultivation, and periodic cropping Systems may demonstrate différent patterns of parasitism, especially in disrupted, patchy subsistence crops. Cabbage (Brassica oleracea) is the most commonly grown cruciferous crop in subsistence gardens in the suburbs of Grahamstown East. The subsistence farmers' crops are considered patchy because the cabbages are grown in small and relatively widely separated plots. Thèse gardens provided an opportunity to follow Talekar and Shelton's (1993) suggestion to investigate the population dynamics of P. xylostella (a useful model pest) and its rate of parasitism on cabbages of subsistence farmers where commercial pesticides are used less.
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Similarities and differences between rivers of the Kruger National Park
- Authors: Muller, Nikite W J , Villet, Martin H
- Date: 2004
- Language: English
- Type: text
- Identifier: vital:537 , http://hdl.handle.net/10962/d1009527
- Description: [From Introduction] Aquatic ecosystems play an important role in the maintenance of ecological diversity and ecosystem functioning at both local and regional scales (Roux et al, 1999). Effective management of riverine ecosystems requires an understanding of their ecosystem processes, hi order to understand ecosystem processes, and interactions between the landscape and riverine ecosystems, it is necessary to have both spatial and temporal data at both landscape and site-specific scales (Allan and Johnson, 1997). There are many tools available for the analysis of these data to provide insight and understanding of the data in order to understand influences on aquatic ecosystems. Increasingly complex computational tools allow analysis and modeling of data in order to explain river, and subsequent biological, processes from landscape (catchment) processes (Johnson and Gage, 1997), although the scale at which analysis and interpretation occurs is important. Science and management need to interact in order to truly succeed in effectively applying adaptive management and incorporate monitoring and assessment programmes in management processes (Rogers and Biggs, 1999). However, water resource management is often undertaken in the context of incomplete information and knowledge of functioning ecosystem processess and responses: this inevitably leads to uncertainty and unpredictability (Roux et al. 1999). One of the major challenges for managing rivers is to be able to monitor rivers effectively in order to detect changes as they occur, to identify the causes of the changes and to distinguish between natural and anthropogenic causes of change. Adaptive management is required to effectively manage rivers, but this does require that there is an understanding of, and information for, the rivers being managed. Rogers and Biggs (1999) highlighted the need to integrate monitoring programmes with indicators in order to undertake assessments of ecosystem health as part of the management plan of the rivers of the Kruger National Park in order to maintain, and restore, natural river ecosystem health and biodiversity (Rogers and Bestbier, 1997). One of the main aims of the Kruger National Park Rivers Research Programme (KNPRRP) was to contribute to the conservation of the natural environment by developing skills and methods to understand the ecological functioning of the natural environment and to predict responses of the river systems to natural and anthropogenic changes in order to effectively manage them (Breen, 1994, in van Rensburg and Dent, 1997). Classification systems are able to provide useful management information, but many have focussed on abiotic rather than biotic factors because resultant biotic patterns are likely to be correlated with abiotic components (Solomon et al., 1999). Much of the classification of the Kruger National Park has focussed on classification of land with little regard for rivers (these were incorporated into the two classification systems proposed by Venter and Gertenbach (in Solomon et al., 1999)). The objective of this project is to identify similarities and differences between the five major rivers of the Kruger National Park, towards the design and testing of a classification framework in order to aid management of the KNP rivers by contributing to effective monitoring. This will be achieved through the following: 1. collate available (current and historical) information concerning physical and biological variables for the Luvuvhu, Letaba, Olifants, Sabie and Crocodile Rivers, using a common dataset to establish the degree of similarities and differences between these five major rivers of the KNP; and 2. determine how different the rivers are, in order to optimize monitoring and management programmes for these differences. The aim of this project was not to classify the rivers of the KNP. The project rather aims to identify gaps in data availability which may result in inadequate and inappropriate management of the rivers. Results (in the form of a data matrix) emanating from this study could assist in establishing expected natural conditions and biota in the five major rivers of the KNP, and knowledge from data-rich rivers (e.g. Sabie River) could potentially be extrapolated to data-poor rivers, or sections of rivers. Invertebrates and fish are the main tools of aquatic species biodiversity monitoring, and require an understanding of the natural presence, absence and abundance patterns in aquatic ecosystems. This study contributes to this understanding by organising available information of biotic and abiotic information.
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Spiders (Arachnida: Araneae) from black cotton soil habitats of a highland savanna biome in Laikipia, central Kenya
- Authors: Warui, Charles M , Villet, Martin H , Young, Truman P
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442705 , vital:74025 , https://tpyoung.ucdavis.edu/sites/g/files/dgvnsk4821/files/inline-files/spiders%20in%20highlands.pdf
- Description: Spiders were sampled at Mpala Research Centre, Laikipia, Kenya using pitfall trapping and sweep netting. Sampling was conducted from May 2001 to July 2002. A total of 10,487 individuals from 132 species belonging to 30 families were recorded. The family Salticidae had the highest number of species (24), followed by Gnaphosidae (20), Araneidae and Lycosidae (15 each), Theridiidae and Thomisidae (8 each) and Zodariidae (4). Most of the other families had fewer than 4 species. Throughout the study period, species not previously sampled emerged after rainfall peaks. Many species are apparently undescribed, highlighting the inadequate documentation of these taxa in Kenya. We suggest that the spider fauna of black cotton soil habitats is rich and useful for environmental monitoring, that further surveys using other collecting methods are needed, and that support for the conservation of this ecosystem should be continued. The study once more reveals the urgent need for taxonomic studies on Kenyan invertebrates.
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