Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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Thesis (M.I.N.C.) -- Lincoln University, 2008. / Also available via the World Wide Web.

Dans ce travail de thèse, nous avons analysé les résidus des plusieurs contaminants anthropiques dans des prédateurs de la chaîne alimentaire aquatique et des proies de la chaîne terrestre. En effet, la loutre, le grand cormoran et le silure sont prédateurs piscivores au sommet de la chaîne alimentaire, les pesticides organochlorés, les PCBs et les éléments traces métalliques (plomb, cadmium, cuivre et mercure) ont été détectés dans tous les foies de ces prédateurs prélevés dans les bassins de la Loire en France. Les PCBs sont les organochlorés les plus répandus dans les trois espèces, suivi des DDTs. Les valeurs maximales de PCBs ont atteint 1,61, 1,96 et 0,28 mg/kg de poids frais pour les cormorans, les loutres et les silures, respectivement. La concentration du mercure a dépassé la limite toxique pour plus de 40 % des cormorans analysés. L‘effet « cocktail » de ces contaminants sur les trois espèces n‘est pas étudié dans cette thèse. Cependant, Les concentrations des organochlorés et des éléments traces dans ces prédateurs sont généralement modestes ou faibles. Ainsi, Il nous semble que ces contaminants ne constituent pas une menace pour la conservation de ces espèces à court ou moyen terme. Par ailleurs, dans le réseau trophique terrestre, nous avons trouvé que trois rodenticides anticoagulants la chlorophacinone, la bromadiolone et le brodifacoum s‘accumulent dans les limaces de la manière rapide et stable au cours de temps, par contre aucune mortalité n‘a été observée chez les limaces. Le brodifacoum a été détecté dans plus de 90 % des limaces prélevées sur le terrain, et nous avons constaté que ces limaces représentaient un risque élevé d'empoisonnement secondaire pour trois de leurs prédateurs, le hérisson européen, la musaraigne commune et l'étourneau sansonnet. On pourrait donc confirmer que les invertébrés constituent une source non négligeable de rodenticides pour leurs prédateurs.L‘objectif de cette thèse est de montrer l‘influence du régime alimentaire sur la contamination des proies, des prédateurs et d‘évaluer les risques toxicologiques pour ces espèces / In this work, we analyzed the residues of several anthropogenic contaminants in predators of the aquatic food chain and prey of the terrestrial chain. The otter, the great cormorant and the catfish are piscivorous predators at the top of the food chain. Organochlorine pesticides, PCBs and trace elements (lead, cadmium, copper and mercury) were detected in all these predators collected from the basins of the Loire in France. Residue level of PCBs in these predators was the highest followed by DDTs and maximal PCB values reached 1.61, 1.96, and 0.28 mg/kg wet weight for cormorants, otters, and catfish, respectively. The concentration of mercury exceeded the toxic thresholds for more than 40% of the cormorants analyzed. The possible combined effect of these contaminants on the three species has not been studied in this thesis. However, the concentrations of organochlorines and trace elements are generally modest or low. Thus, it seems that these contaminants do not constitute a major threat to the conservation of these species for the short or medium term. Furthermore, in the terrestrial food chain, we found that three anticoagulant rodenticides chlorophacinone, bromadiolone and brodifacoum accumulate in slugs in a stable way over the time, whereas no mortality was observed in slugs. Brodifacoum was detected in more than 90% of the slugs collected in the field, and we found that these slugs represented a high risk of secondary poisoning for three of their predators, European hedgehog, common shrew and European starling. Therefore, it could be confirmed that invertebrates constitute a non-negligible source of rodenticides for their predators.The objective of this thesis is to show the influence of the diet on the contamination of prey, predators and to evaluate the toxicological risks for these species

Rodents cause damage in commercial forests by gnawing at the bark of the trees. It is currently estimated that rodent damage in commercial forestry costs the industry R50 million per annum. The species of rodents which cause the damage are not known, neither is the reason behind this behaviour. Through stomach analysis it has been established that 3 species are involved Otomys irroratus, Rhabdomys pumilio and Mastomys natalensis, however this behaviour is confined to the winter. Chemical analysis of the bark reveals that the percentage concentration of nitrogen varies seasonally. The period of high concentration correlates with periods when the natural food of the rodents is restricted and when bark gnawing is most prevalent. In the past the industry's response to the damage has been to treat the areas with rodenticides. Using standard CMR methods, the two commercially-licensed rodenticides and raptor perches were tested to examine their efficacy as rodent control strategies. It was found that at a lower application of I block of rodenticide every third tree there is little difference in the effectiveness of the rodenticide brands and there is also little reduction in the abundance of the rodents. At a higher application rate of I block per tree, the abundance of rodents is reduced but termination of the treatment results in the rodent numbers quickly recovering, indeed they surpassed their original population numbers within 4 months. Apart from the environmental dangers of applying such concentrations of poison, this is clearly an uneconomic solution. My results indicate that at first planting, the sites should be provisioned with raptor perches at a density of 16 ha⁻². Contrary to accepted policy the perches do not require cross pieces, which add to the expense and offer no advantage in raptor residency time. In areas of very high rodent abundance the provisioning of tree collars provide physical protection to the trees. An additional benefit of the collars is that the collars cause a beneficial microclimate around the tree which enhances its growth rate. When the tree is around 2 years old it should be pruned to a height of I ffi, the slash being left in the inter-row. Results show that trees treated in such a way experience no further attack and the rodents browse on the prunings. As the cost of the perches is reduced and the cost of pruning is non-recurring the recommendations provide an economical and environmentally sympathetic alternative to rodenticide application. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

MENVSC / Department of Ecology and Resource Management / Rodents can quickly respond to land use changes whether the change positively or negatively influences their life. In the case of positive influence, rodents exploit the additional food resources and increase their numbers to potential pest level, especially in the absence of predators. Such a population increase can potentially be harmful to humans due to the diseases that rodents carry and the costs due to damage to crops, stored foods and personal possessions that they may cause to small holder farmers. Small holder farmers live in a mixed landscape that is constantly changing. Such changes are changes in land use and they do not only affect rodent population dynamics and species composition, but also their ecosystem services and integrity. Understanding how rodents respond to these land use changes (crop, grazing and settlement) will not only improve the implementation of Ecologically Based Rodent Management (EBRM), but might also enable the monitoring of ecosystem integrity. Rodent trapping was conducted in two different study sites which experience different rainfalls during wet and dry season. A 70 m x 70 m grid was set in three different land uses (crops, grazing and settlement) per study site. A mark-recapture technique was applied and all captures were processed on a temporal station on site. In all grids at a distance of 30 m a line of 20 snap traps were set. With the tapping effort of 1470 trap nights per season for both seasons in this study we captured 839 rodents and 2 shrews, which represented 469 individual rodents and 1 individual shrew. At Vyeboom, cropping land use had the highest number capture (210) and the highest in species richness (9) rodent species and 1 shrew. The settlement land use was second at 144 captures for 8 rodent species and lastly the grazing land use at 80 captures with 7 rodent species. On the other hand, at Ka-Ndengeza also cropping land use had the highest capture (186) with highest richness at 7 rodent species. When it comes to settlement and grazing, settlement was second (129) to cropping in terms of the number of capture but last in terms of richness (5) whilst grazing was last in terms of number of captures 92 and second in terms of richness (6). Despite the high diversity of rodents, only Mastomys natalensis, Gerbilliscus leucogaster, Steatomys pratensis and Rattus rattus were captured in meaningful sample sizes to allow for robust density estimation. Similarly there were strong seasonal effects on rodent captures, with almost no captures during the wet season.