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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Lions on small reserves : an evaluation of ecological impact and financial viability

Erasmus, Wayne Norman 31 July 2008 (has links)
A founder population of lion (Panthera Leo) was introduced into a 70 km² privately-owned, wildlife reserve in the Waterberg area of South Africa. The lion and prey species' populations were monitored between 2001 and 2004. In this period, 452 kills were recorded at a mean kill rate of one kill every 2.43 days. The lions killed 11 common prey species. Eland, warthog, kudu, wildebeest and zebra comprised 75 % of the lion's diet. The lions consumed an average of 8 % of the available common prey species population per annum. Initially, the mean ungulate population growth rate was 30.9 %, but this rate declined to -0.8 % during the study period. Significantly more animals were killed in open habitats than in closed habitats. The loss in game value for the study period was over one million Rand. A formula was compiled to quantify the cost versus return aspects of introducing lion. / Nature Conservation / M. Tech. (Nature Conservation)
102

La diminution des espaces ouverts en Israël depuis 1948 : exploration et discussion des facteurs contribuant à un problème de société

Gamache, Étienne 11 1900 (has links)
Le présent mémoire se penche sur la diminution des espaces ouverts en Israël, un problème environnemental considéré comme l’un des plus importants par les organisations environnementales de ce pays. La situation est particulièrement préoccupante depuis le début des années 1990 alors que la superficie occupée par ces espaces s’est réduite significativement. Les craintes liées à cette évolution se sont traduites par l’implantation de plans nationaux d’aménagement visant expressément à concentrer le développement futur du pays au sein des quatre principales régions métropolitaines (Tel-Aviv, Jérusalem, Haïfa, Beer-Sheva) de manière à préserver de façon optimale les espaces ouverts restants. Plusieurs facteurs sont responsables de cette perte d’espaces ouverts. Ainsi, l’un des objectifs cet ouvrage consiste à identifier ces facteurs de même qu’à analyser dans quelle mesure ils ont influé. Par ailleurs, ce mémoire fait le point sur l’évolution de la superficie des espaces ouverts au fil des années. Finalement, le dernier chapitre aborde les enjeux actuels quant à la conservation des espaces ouverts israéliens et souligne quelques solutions proposées afin d’accroître leur protection pour le futur. Afin de dresser un portrait complet de la situation, la période étudiée s’étend de 1948, année de fondation de l’État d’Israël, à 2010. / This research examines the loss of open space in Israel, one of the most acute environmental problems facing this country, according to several Israeli environmental organizations. This situation is peculiarly ominous since the beginning of the 1990s while the area occupied by open space has decreased significantly. Fears linked to the proliferation of built area have led to the implementation of national outline plans (NOP 31, NOP 35) which aim specifically to concentrate future development into the main metropolitan regions (Tel Aviv, Jerusalem, Haifa, Beersheba) to ensure that the remaining open spaces will be protected optimally. Several factors are responsible for the loss of open space in Israel. Thus, one of the research objectives is to identify and analyze how these factors have influenced the extent of open spaces. Furthermore, this research provides an update of the open spaces’ evolution over the years. Finally, the last chapter discusses the current issues regarding open space as well as some solutions to enhance its protection. In order to obtain a thorough picture of the situation, the temporal field of this study spans from 1948, founding year of the State of Israel, to 2010.
103

The determinants of government expenditure in South Africa

Maluleke, Glenda 11 1900 (has links)
This study empirically examines the determinants of government expenditure in South Africa using annual data for the period from 1970 to 2014; and provides an overview of the South African government expenditure. The Johansen-Juselius co-integration test established that there is a long-run relationship between government expenditure and its determinants. The error correction model was used to examine the key determinants. The results of this study show that urbanisation rate, national income, poverty reduction; trade openness lagged one period and the wage rate significantly influence the size of government expenditure. Therefore, the study recommend that government create job opportunities; increase its expenditure in developing rural areas; and find ways to manage the public sector wage bill. The study concludes that population growth, inflation and trade openness in current period are not important in determining government expenditure in South Africa / Economics / M. Com. (Economics)
104

The influence of lifestyle on demographic responses to climate change : the Alpine marmot as a case study / Influence du mode de vie sur les réponses démographiques au changement climatique : l'exemple de la marmotte alpine

Rézouki, Célia 25 September 2018 (has links)
Comprendre la réponse des populations aux variations environnementales est un défi central en écologie et est devenu un enjeu indéniable ces dernières années avec le changement climatique. Dans ce contexte, nous pouvons nous attendre à ce que certaines caractéristiques écologiques propres aux espèces, comme le mode de vie, qui ont évolué en réponse à des contraintes environnementales et qui influencent les traits d'histoire de vie des espèces, puissent façonner la démographie des populations en environnement variable. Pourtant, cette influence du mode de vie sur la réponse démographique des populations demeure encore mal comprise. J'ai essayé de combler cette lacune au cours de ma thèse, principalement par l'analyse d'un jeu de données exceptionnel obtenu grâce à un suivi à long terme d'une population de marmottes alpines (Marmota marmota) dans les Alpes Françaises. La marmotte alpine présente un mode de vie très particulier. Les individus vivent au sein de groupes familiaux de taille variable, généralement composés d'un couple de dominants reproducteurs, de subordonnés et de juvéniles. Ils hibernent durant la moitié de l'année, et pratiquent l'élevage coopératif ; les subordonnés mâles participent activement à la survie des jeunes durant l'hibernation, et sont alors appelés helpers. J'ai d'abord étudié comment le mode de vie de la marmotte (qui allie hibernation et socialité) a influencé les effets des fluctuations météorologiques sur les variations de survie de chaque classe d'âge. Les résultats ont alors révélé une forte diminution de la survie des juvéniles au fil des ans, et cela du fait d'effets interactifs entre facteurs environnementaux (i.e., hivers de plus en plus rudes) et sociaux (i.e., diminution de la présence des helpers). Dans un deuxième temps, j'ai étudié la valeur adaptative de l'élevage coopératif au sein de cette population de marmottes alpines et j'ai pu montrer que les effets bénéfiques de la présence des helpers sur la survie des juvéniles tendaient à disparaître du fait du changement climatique. En conséquence de cela, la population de marmottes alpines semble être actuellement en déclin. Cependant, l'impact du changement climatique semble avoir été en partie limité par une plus grande probabilité d'accéder à la dominance pour les subordonnés au cours des dernières années, ce qui démontre une influence complexe de la socialité sur la réponse de cette espèce. Enfin, j'ai comparé la démographie de la population de marmottes alpines avec celle d'une population de chamois (Rupicapra rupicapra) soumise à des variations météorologiques similaires dans les Alpes. J'ai été en mesure de montrer que le mode de vie et la stratégie de reproduction de ces espèces ont façonné différemment leurs réponses démographiques aux variations environnementales, et ainsi au changement climatique / Understanding populations' response to environmental variation is a central issue of ecology, and has become a compelling goal in the last years due to climate change. In this broad context we could expect some species-specific ecological characteristics known to influence life history traits, such as lifestyle, to shape the demography of populations in variable environments as well as structure between-species differences in response to environmental change. Yet, the influence of species' lifestyle on population demographic responses to environmental variation is still poorly understood. During my PhD, I tried to fill this gap primarily through the analysis of an extensive data set of an Alpine marmot (Marmota marmota) population in the Alps. Alpine marmots present a particular lifestyle. 1ndividuals live in family groups of variable size, typically composed of one dominant breeding pair, of sexually mature and immature subordinates and of pups of the year. Half the year, they hibernate together in burrows and practise cooperative breeding with male subordinates acting as helpers for the pups, increasing their survival probability during hibernation. I first investigated how the marmot's lifestyle (hibernation and sociality) mediated the effects of weather fluctuations on age-specific survival variation. I found that juvenile survival strongly decreased over the years because of inter-related effects of harsher winter weather conditions and social factors (i.e., decrease in helpers' presence). In a second step, I studied the adaptive value of cooperative breeding in this Alpine marmot population, and showed that the positive influence of helpers' presence on juvenile survival was vanishing with climate change. The Alpine marmot population is currently decreasing accordingly. However, in parallel to the latter changes, I found a better access to dominance for subordinate individuals over the years, compensating in part this decrease, and highlighting a complex influence of sociality on marmot response to climate change. Finally, I compared the demography of the Alpine marmot population with that of an Alpine chamois (Rupicapra rupicapra) population, subjected to similar weather conditions in the Alps. I was able to show that the difference in lifestyle and reproductive tactic between these species shaped their demographic responses to environmental variation, providing them with differentresistance to current environmental change
105

La diminution des espaces ouverts en Israël depuis 1948 : exploration et discussion des facteurs contribuant à un problème de société

Gamache, Étienne 11 1900 (has links)
Le présent mémoire se penche sur la diminution des espaces ouverts en Israël, un problème environnemental considéré comme l’un des plus importants par les organisations environnementales de ce pays. La situation est particulièrement préoccupante depuis le début des années 1990 alors que la superficie occupée par ces espaces s’est réduite significativement. Les craintes liées à cette évolution se sont traduites par l’implantation de plans nationaux d’aménagement visant expressément à concentrer le développement futur du pays au sein des quatre principales régions métropolitaines (Tel-Aviv, Jérusalem, Haïfa, Beer-Sheva) de manière à préserver de façon optimale les espaces ouverts restants. Plusieurs facteurs sont responsables de cette perte d’espaces ouverts. Ainsi, l’un des objectifs cet ouvrage consiste à identifier ces facteurs de même qu’à analyser dans quelle mesure ils ont influé. Par ailleurs, ce mémoire fait le point sur l’évolution de la superficie des espaces ouverts au fil des années. Finalement, le dernier chapitre aborde les enjeux actuels quant à la conservation des espaces ouverts israéliens et souligne quelques solutions proposées afin d’accroître leur protection pour le futur. Afin de dresser un portrait complet de la situation, la période étudiée s’étend de 1948, année de fondation de l’État d’Israël, à 2010. / This research examines the loss of open space in Israel, one of the most acute environmental problems facing this country, according to several Israeli environmental organizations. This situation is peculiarly ominous since the beginning of the 1990s while the area occupied by open space has decreased significantly. Fears linked to the proliferation of built area have led to the implementation of national outline plans (NOP 31, NOP 35) which aim specifically to concentrate future development into the main metropolitan regions (Tel Aviv, Jerusalem, Haifa, Beersheba) to ensure that the remaining open spaces will be protected optimally. Several factors are responsible for the loss of open space in Israel. Thus, one of the research objectives is to identify and analyze how these factors have influenced the extent of open spaces. Furthermore, this research provides an update of the open spaces’ evolution over the years. Finally, the last chapter discusses the current issues regarding open space as well as some solutions to enhance its protection. In order to obtain a thorough picture of the situation, the temporal field of this study spans from 1948, founding year of the State of Israel, to 2010.
106

Atividade inseticida e de repelência de óleos essenciais de cravo e canela sobre o caruncho Acanthoscelides obtectus (Say) / Insecticidal effect of clove and cinnamon essential oils in controlling weevil Acanthoscelides obtectus (Say) in beans

Jumbo, Luis Oswaldo Viteri 13 December 2013 (has links)
Made available in DSpace on 2015-03-26T13:30:48Z (GMT). No. of bitstreams: 1 texto completo.pdf: 754859 bytes, checksum: b3501a3bf9aa715323fdceb139bc976d (MD5) Previous issue date: 2013-12-13 / Beans are the major source of protein in developing countries, and still the storage losses are estimated in 30% as a result of pests attack including Acanthoscelides obtectus (Say). Although chemical pesticides are effective to control these pests, their overuse can compromise the quality of food. Essential oils of vegetable origin are presented as an attractive alternative for the synthetic chemical insecticides to pest control, because they have little or no effect on grain quality, human health and environment. This study aimed evaluate the toxicity of the essential oils of Syzygium aromaticum (Myrtaceae) or clove and Cinnamomun zeylanicum (Laureaceae) known as cinnamon on A. obtectus in beans (Phaseolus vulgaris L.). We evaluated the instantaneous rate of increase (ri) of these insects exposed to time-lethal, developmental rate, repellency, persistence and loss of mass of the beans. The toxicity of the oils was evaluated by preliminary tests to estimate the lethal dose to 50 and 95% (DL50 and DL95) of adult insects. The experimental unit consisted of 0.8 L bottles containing 200 g of beans (Queen variety) treated with doses of 2,80; 5,54; 8,88; 14,22; 28,09 μL of clove oil, and 4,26; 6,93; 9,70; 13,60; 22,17 μL of cinnamon oil. Later were added 25 adult insects per vial (four replicates per dose), and insect mortality was assessed after 24 h. The instantaneous rate of increase (ri) of the oils of clove and cinnamon was determined using lethal doses (LD10, LD30, LD50, LD70 and LD90), obtained in the toxicity bioassay. After 45 days, the adult progeny was recorded; bottles with 200 g of beans and 25 adult insects, non-sexed 1-3 days old, and four replicates were used for LD. A similar procedure was done to assess the rate of development, with the difference that in this test the insects were removed from the flasks after 15 days they were introduced, and counting was performed every two days after the emergence of the first adult. The persistence was evaluated in beans treated with LD100 oils. The repellent activity of oils was tested with the LD10, LD50, LD90 doses for each oil. The results indicate that the toxicity LD50 and LD95 were 8.88 L and 38.94 L for clove essential oil, and 9.71 L and 27.97 L for cinnamon essential oil, respectively. Furthermore, with increased doses of essential oils and ri, development rate decreases significantly. Regarding the persistence of oil, was observed mortality reduction of A. obtectus with increasing time between the treatments of treated grains, keeping a higher mortality at 50% of the insects within 7 days after exposure. However, repellency of essential oil of cinnamon to this insect was observed only when using LD90; clove essential oil showed no repellency against A. obtectus at the tested doses. The loss of grain weight during 48 days was directly proportional to the number of emerged insects in each test. For beans treated with clove essential oil the average of mass loss was 6.6%, and 9.6% in the control, whereas for tests with essential oil of cinnamon the average of loss was 6.8% and 9.2% for the treatment and control, respectively. Thus, with the results obtained in this study, it can be concluded that the essential oils of clove and cinnamon have effect on mortality of A. obtectus by contact, as an alternative to the use of traditional insecticides. / O feijão representa uma das principais fontes de proteínas em países em desenvolvimento, ainda assim as perdas estimadas no armazenamento são de 30% em consequência do ataque de pragas, entre elas Acanthoscelides obtectus (Say). Embora os pesticidas químicos sejam eficazes para controlar essas pragas, seu uso excessivo pode comprometer a qualidade dos alimentos. Óleos essenciais de origem vegetal são apresentados como uma alternativa atrativa aos inseticidas químicos sintéticos para o controle de pragas, porque apresentam pouco ou nenhum efeito sobre a qualidade dos grãos, saúde humana e meio ambiente. Este trabalho teve como objetivo avaliar a toxicidade dos óleos essenciais de Syzygium aromaticum (Myrtaceae) ou cravo e Cinnamomum zeylanicum (Laureaceae) conhecida como canela sobre A. obtectus em grãos de feijão (Phaseolus vulgaris L.). Avaliou-se a taxa instantânea de crescimento populacional (ri) desses insetos expostos a tempos- letais, taxa de desenvolvimento, repelência, persistência e perda de massa do feijão. A toxicidade dos óleos foi avaliada através de testes preliminares para estimar a dose letal para 50 e 95% (DL50 e DL95) dos insetos adultos. As unidades experimentais foram constituídas por frascos de 0,8 L contendo 200 g de feijão (variedade rainha) tratados com doses de 2,80; 5,54; 8,88; 14,22; 28,09 μL de óleo de cravo, e 4,26; 6,93; 9,70; 13,60; 22,17 μL de óleo de canela. Posteriormente, foram acrescentados 25 insetos adultos em cada frasco (quatro repetições por dose), e a mortalidade dos insetos foi avaliada após 24 h. A taxa instantânea de crescimento (ri) dos insetos na presença dos óleos de cravo e canela foi determinada utilizando as doses letais (DL10, DL30, DL50, DL70 e DL90), obtidas no bioensaio de toxicidade. Foram utilizados frascos com 200 g de feijão e 25 insetos adultos, não-sexados com idade de 1-3 dias, e quatro repetições por DL; após 45 dias, a progênie adulta foi contabilizada. Procedimento similar foi feito para avaliar a taxa de desenvolvimento, com a diferença de, que neste teste, os insetos foram retirados dos frascos depois de 15 dias de terem sido introduzidos, e a contagem foi realizada a cada dois dias após a emergência do primeiro adulto. A persistência foi avaliada em grãos de feijão tratados com a DL100 dos óleos. A atividade repelente dos óleos foi testada com as doses DL10, DL50, DL90 para cada óleo. Os resultados de toxicidade indicaram que as DL50 e DL95 foram 8,88 L e 38,94 L para o óleo essencial de cravo, e 9,70 L e 27,97 L para o óleo essencial de canela, respectivamente. Além disso, com o aumento das doses dos óleos essenciais, a ri e a taxa de desenvolvimento decrescem significativamente. Com relação à persistência dos óleos, observou-se a redução na mortalidade de A. obtectus com o aumento do tempo entre o tratamento dos grãos tratados; mantendo uma mortalidade superior ao 50% dos insetos até 7 dias após a exposição. Entretanto, foi observada repelência do óleo essencial de canela para este inseto somente ao utilizar-se a DL90; o óleo essencial de cravo não apresentou repelência contra A. obtectus nas doses testadas. A perda de massa dos grãos no período de 48 dias foi diretamente proporcional ao número de insetos emergidos em cada teste. Para o feijão tratado com óleo essencial de cravo, a perda média da massa foi de 6,6%, e no controle de 9,6%; nos ensaios com óleo essencial de canela, a perda média foi de 6,8% e 9,2% para os tratamentos e controle, respetivamente. Assim, com os resultados obtidos nesta pesquisa, pode-se concluir que os óleos essenciais de cravo e de canela têm efeito por contato na mortalidade de A. obtectus, sendo uma alternativa ao uso de inseticidas tradicionais.
107

Lions on small reserves : an evaluation of ecological impact and financial viability

Erasmus, Wayne Norman 31 July 2008 (has links)
A founder population of lion (Panthera Leo) was introduced into a 70 km² privately-owned, wildlife reserve in the Waterberg area of South Africa. The lion and prey species' populations were monitored between 2001 and 2004. In this period, 452 kills were recorded at a mean kill rate of one kill every 2.43 days. The lions killed 11 common prey species. Eland, warthog, kudu, wildebeest and zebra comprised 75 % of the lion's diet. The lions consumed an average of 8 % of the available common prey species population per annum. Initially, the mean ungulate population growth rate was 30.9 %, but this rate declined to -0.8 % during the study period. Significantly more animals were killed in open habitats than in closed habitats. The loss in game value for the study period was over one million Rand. A formula was compiled to quantify the cost versus return aspects of introducing lion. / Nature Conservation / M. Tech. (Nature Conservation)
108

Effect of food quantity and quality on population growth rate and digestive activity in planktonic rotifers. / Effect of food quantity and quality on population growth rate and digestive activity in planktonic rotifers.

ŠTROJSOVÁ, Martina January 2008 (has links)
As homeostatic organisms, rotifers have to use the mechanism to cope with nutrition unbalance in their food. The regulation of digestive enzyme activities as a possible physiological mechanism involved in maintaining of rotifer homeostasis was studied. This study further explored the effect of food quantity and quality on rotifer population growth rate and reproduction.
109

"Jedna si jedina moja domovina?" Etno-demografické proměny Bosny a Hercegoviny v letech 1945 - 2012 / "Are You the One and Only Homeland I have?" Ethnodemographic Changes in Bosnia and Herzegovina 1945-2012

Žíla, Ondřej January 2014 (has links)
ŽÍLA, Ondřej: "Are You the One and Only Homeland I have?" Ethno-demographic Changes in Bosnia and Herzegovina 1945-2012 Abstract Thesis on "Are You the One and Only Homeland I have?" Ethno-demographic Changes in Bosnia and Herzegovina 1945-2012 analyses population development of three constitutive nations of Bosnia and Herzegovina, transformation of ethnic proportional representation of Bosnian population due to differences in demographic behaviour and spatial impacts of forced migration on population distribution after the end of the civil conflict in the 1990s. The main focus is on comparing the development of the ethno-demographic structure of socialist Bosnia and Herzegovina with the condition of the country after the war. The current demographic characteristics of the population, and contemporary ethnic composition of the country remains fundamentally affected by events related to the conflict: the so called forced migration and ethnic cleansing. The thesis compiles two fundamental approaches, one of them being the top-down approach. It focuses on the characteristics of the role of Western powers in the post-war peace-building process, specifically the analysis of their principal objective - restoration of the original ethnic heterogeneity by means of controlled repatriation of refugees, and evaluation...
110

Efeitos de flora??es de cianobact?rias sobre os clad?ceros ceriodaphnia dubia e daphnia gessneri / Effects of cyanobacterial blooms on the cladocerans ceriodaphnia dubia and daphnia gessneri

Silva, Leide Amara Pereira da 25 September 2012 (has links)
Made available in DSpace on 2014-12-17T14:33:08Z (GMT). No. of bitstreams: 1 LeideAPS_DISSERT.pdf: 986741 bytes, checksum: e18d4b42b9411720a51bd3f7786fa126 (MD5) Previous issue date: 2012-09-25 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Cyanobacterial blooms are common in eutrophic reservoirs in Brazilian northeastern semi-arid. Given this reality, the present study aimed to analyze the effect of potentially toxic cyanobacterial blooms in Gargalheiras reservoir (semi-arid) on the cladocerans Ceriodaphnia dubia and Daphnia gessneri. In vitro chronic bioassays were performed with reservoir water dilutions from August/2011 to May/2012 and the following effects were evaluated on: intrinsic rate of population growth (r), reproductive parameters (age of first reproduction and fecundity per capita) and cladocerans movements. Phytoplankton was dominated by Cylindrospermopsis raciborskii and Planktothrix agardhii and saxitoxin and microcystin were detected in reservoir water. In most months C. dubia showed differences in r between control (absence of cyanobacteria) and treatments, and has shown negative effects on reproductive parameters. In all months paralysis of swimming movements was observed in C. dubia when both C. raciborskii and saxitoxin (cyanotoxin neurotoxic) were present in water. While C. dubia was sensitive to the reservoir water containing cyanobacteria, D. gessneri showed less intense negative effects in r and reproductive parameters. Furthermore, D. gessneri showed no paralysis of swimming movements. These results support the hypothesis in the literature that D. gessneri is resistant to the Cylindrospermopsis effects. The clone‟s life history may be a key to understand the results. The C. dubia clone, isolated from eutrophicated environment, is in the lab for ten years and it is an exotic species in Brazil. D. gessneri is a common species in the country and this clone was isolated from the Gargalheiras reservoir (where there are constant blooms of potentially toxic cyanobacteria) a year ago. Perhaps the recent contact with cyanobacteria explain the higher resistance presented by this D. gessneri clone. In conclusion, the cladocerans studied have different levels of sensitivity to cyanobacteria, characterizing species-specific responses / Flora??es de cianobact?ras s?o frequentes em reservat?rios eutr?ficos do semi-?rido do nordeste brasileiro. Diante dessa realidade o presente trabalho objetivou analisar o efeito de flora??es de cianobact?rias potencialmente t?xicas do reservat?rio Gargalheiras (semi-?rido brasileiro) sobre os clad?ceros Ceriodaphnia dubia e Daphnia gessneri. Foram realizados ensaios cr?nicos in vitro com dilui??es de ?gua do reservat?rio de agosto/2011 a maio/2012 e foram avaliados efeitos sobre: taxa intr?nseca de crescimento populacional (r), par?metros reprodutivos (idade da primeira reprodu??o e fecundidade per capita) e movimenta??o dos clad?ceros. O fitopl?ncton foi dominado por Cylindrospermopsis raciborskii e Planktothrix agardhii e houve detec??o de saxitoxina e microcistina na ?gua do reservat?rio. Na maioria dos meses C. dubia apresentou diferen?a em r entre controle (aus?ncia de cianobact?rias) e tratamentos, al?m de ter apresentado efeitos negativos nos par?metros reprodutivos. Observou-se ainda um efeito de paralisia dos movimentos natat?rios de C. dubia em todos os meses, concomitante ? presen?a de C. raciborskii e saxitoxina (cianotoxina neurot?xica) na ?gua. Enquanto C. dubia apresentou-se sens?vel ? ?gua do reservat?rio contendo cianobact?rias, D. gessneri apresentou efeitos negativos menos intensos em r e nos par?metros reprodutivos. Al?m disso, esta esp?cie n?o teve os movimentos paralisados. Esses resultados apoiam a hip?tese levantada na literatura de que D. gessneri apresenta resist?ncia aos efeitos da Cylindrospermopsis. A hist?ria de vida dos clones pode ser uma chave para compreens?o dos resultados. O clone de C. dubia, isolado de ambiente eutrofizado, est? em laborat?rio h? dez anos e essa ? uma esp?cie ex?tica no Brasil. D. gessneri ? uma esp?cie comum no pa?s e este clone foi isolado h? um ano do reservat?rio Gargalheiras, onde h? constantes flora??es de cianobact?rias potencialmente t?xicas. A hip?tese mais prov?vel ? que o contato recente deste clone de D. gessneri com cianobact?rias tenha lhe conferido maior resist?ncia. Conclui-se que os clad?ceros estudados apresentam diferentes n?veis de sensibilidade ?s cianobact?rias, caracterizando respostas esp?cie-espec?ficas

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