Natural and human induced environmental changes affect populations at different time scales. If they occur in a spatial heterogeneous way, they cause spatial variation in abundance. In this thesis I addressed three topics, all related to the question, how environmental changes influence population dynamics.<br><br> In the first part, I analysed the effect of positive temporal autocorrelation in environmental noise on the extinction risk of a population, using a simple population model. The effect of autocorrelation depended on the magnitude of the effect of single catastrophic events of bad environmental conditions on a population. If a population was threatened by extinction only, when bad conditions occurred repeatedly, positive autocorrelation increased extinction risk. If a population could become extinct, even if bad conditions occurred only once, positive autocorrelation decreased extinction risk. These opposing effects could be explained by two features of an autocorrelated time series. On the one hand, positive autocorrelation increased the probability of series of bad environmental conditions, implying a negative effect on populations. On the other hand, aggregation of bad years also implied longer periods with relatively good conditions. Therefore, for a given time period, the overall probability of occurrence of at least one extremely bad year was reduced in autocorrelated noise. This can imply a positive effect on populations. The results could solve a contradiction in the literature, where opposing effects of autocorrelated noise were found in very similar population models.<br><br> In the second part, I compared two approaches, which are commonly used for predicting effects of climate change on future abundance and distribution of species: a "space for time approach", where predictions are based on the geographic pattern of current abundance in relation to climate, and a "population modelling approach" which is based on correlations between demographic parameters and the inter-annual variation of climate. In this case study, I compared the two approaches for predicting the effect of a shift in mean precipitation on a population of the sociable weaver <i>Philetairus socius</i>, a common colonially living passerine bird of semiarid savannahs of southern Africa. In the space for time approach, I compared abundance and population structure of the sociable weaver in two areas with highly different mean annual precipitation. The analysis showed no difference between the two populations. This result, as well as the wide distribution range of the species, would lead to the prediction of no sensitive response of the species to a slight shift in mean precipitation. In contrast, the population modelling approach, based on a correlation between reproductive success and rainfall, predicted a sensitive response in most model types. The inconsistency of predictions was confirmed in a cross-validation between the two approaches. I concluded that the inconsistency was caused, because the two approaches reflect different time scales. On a short time scale, the population may respond sensitively to rainfall. However, on a long time scale, or in a regional comparison, the response may be compensated or buffered by a variety of mechanisms. These may include behavioural or life history adaptations, shifts in the interactions with other species, or differences in the physical environment. The study implies that understanding, how such mechanisms work, and at what time scale they would follow climate change, is a crucial precondition for predicting ecological consequences of climate change.<br><br> In the third part of the thesis, I tested why colony sizes of the sociable weaver are highly variable. The high variation of colony sizes is surprising, as in studies on coloniality it is often assumed that an optimal colony size exists, in which individual bird fitness is maximized. Following this assumption, the pattern of bird dispersal should keep colony sizes near an optimum. However, I showed by analysing data on reproductive success and survival that for the sociable weaver fitness in relation to colony size did not follow an optimum curve. Instead, positive and negative effects of living in large colonies overlaid each other in a way that fitness was generally close to one, and density dependence was low. I showed in a population model, which included an evolutionary optimisation process of dispersal that this specific shape of the fitness function could lead to a dispersal strategy, where the variation of colony sizes was maintained. / Änderungen in der Umwelt - sowohl natürliche Variabilität als auch anthropogene Änderungen - beeinflussen Populationen auf verschiedenen Zeitskalen. Wenn sie räumlich heterogen wirken, verursachen sie räumliche Variabilität in der Abundanz. In dieser Dissertation habe ich drei Themen bearbeitet, die sich auf den Effekt von Änderungen in der Umwelt auf Populationsdynamiken beziehen.<br><br> Im ersten Teil untersuchte ich an einem einfachen Populationsmodell den Effekt von positiver zeitlicher Autokorrelation im Umweltrauschen auf das Extinktionsrisiko einer Population. Der Effekt der Autokorrelation hing davon ab, wie empfindlich eine Population gegenüber singulären, katastrophenähnlichen Ereignissen schlechter Umweltbedingungen war. War die Population nur dann direkt bedroht, wenn eine Serie von schlechten Umweltbedingungen auftrat, erhöhte positive Autokorrelation das Extinktionsrisiko. Konnte eine Population auch dann aussterben, wenn schlechte Umweltbedingungen einzeln auftraten, verringerte positive Autokorrelation das Extinktionsrisiko. Diese unterschiedlichen Effekte konnten durch zwei Eigenschaften autokorrelierter Zeitreihen erklärt werden. Einerseits erhöht positive Autokorrelation die Wahrscheinlichkeit, daß in einer Zeitreihe Serien von schlechten Bedingungen auftreten. Andererseits führt die Aggregation von schlechten Jahren auch zu langen Zeiträumen mit relativ guten Bedingungen. Deshalb ist die Wahrscheinlichkeit, daß innerhalb eines bestimmten Zeitraums zumindest ein extrem schlechtes Jahr auftritt, geringer unter positiver Autokorrelation. Die Ergebnisse konnten einen Widerspruch in der Literatur aufklären, in dem unterschiedliche Effekte von autokorreliertem Umweltrauschen auf das Extinktionsrisiko gefunden wurden, obwohl sehr ähnliche Modelle verwendet wurden.<br><br> Im zweiten Teil, verglich ich zwei Methoden, die häufig verwendet werden, um den Effekt von Klimawandel auf die zukünftige Verbreitung und Abundanz von Arten vorauszusagen: Ein "Raum-ersetzt-Zeit-Ansatz" ("space for time approach"), in dem Voraussagen aufgrund der aktuellen geographischen Verbreitung und Abundanz einer Art in Relation zum Klima getroffen werden, und ein "Populationsmodell-Ansatz", der auf Korrelationen zwischen demographischen Parametern und der jährlichen Variabilität im Klimas beruht. In einer Fallstudie verglich ich die beiden Methoden, um den Effekt einer Änderung im mittleren Niederschlag auf eine Population des Siedelwebers <i>Philetairus socius</i> vorauszusagen. Der Siedelweber ist eine häufige, koloniale Vogelart in semiariden Savannen im südlichen Afrika. Im "space for time approach" verglich ich zwei Populationen des Siedelwebers in Gebieten mit stark unterschiedlichem mittleren Niederschlag. Die Untersuchung zeigte keinen Unterschied zwischen den beiden Populationen. Sowohl dieses Ergebnis als auch das weite Verbreitungsgebiet des Siedelwebers implizieren keine sensitive Reaktion der Art auf eine geringfügige Änderung im mittleren Niederschlag. Im Unterschied dazu zeigte der "Populationsmodell-Ansatz", der auf einer Korrelation zwischen Niederschlag und dem Reproduktionserfolg des Siedlerwebers beruhte, eine sensitive Reaktion in den meisten der untersuchten Modelltypen. Die Inkonsistenz der Ergebnisse wurde in einer Kreuz-Validierung der beiden Ansätze bestätigt. Aus der Untersuchung folgerte ich, daß die unterschiedlichen Ergebnisse dadurch verursacht wurden, daß die beiden Methoden unterschiedliche Zeitskalen widerspiegeln. Auf einer kurzen Zeitskala reagiert die Population sensitiv auf Änderungen im Niederschlag. Auf einer großen Zeitskala oder im räumlichen Vergleich kann die sensitive Reaktion jedoch durch eine Reihe von Mechanismen gepuffert oder kompensiert werden. Diese Mechanismen können Anpassungen im Verhalten oder in der Lebensgeschichte ("life history"), Änderungen in den Interaktionen mit andern Arten oder Unterschiede in der physikalischen Umgebung beinhalten. Diese Studie zeigt, daß ein Verständnis, wie solche Mechanismen funktionieren, und auf welcher Zeitskala sie wirken, eine wesentliche Voraussetzung ist, um Prognosen über ökologische Effekte des Klimawandels treffen zu können. Im dritten Teil untersuchte ich, warum Kolonien des Siedelwebers so stark in ihrer Größe variieren. Die Variabilität der Koloniegrößen ist erstaunlich, da man in Untersuchungen zur Kolonialität bei Tieren oft davon ausgeht, daß eine optimale Koloniegröße besteht, bei der die individuelle Fitneß maximiert ist. Aufgrund dieser Annahme sollten Vögel sich so im Raum ausbreiten, daß die Koloniegrößen möglicht nahe am Optimum liegen. In dieser Arbeit konnte ich jedoch anhand von Daten zum Reproduktionserfolg und zur Überlebensrate in Relation zur Koloniegröße zeigen, daß die Funktion der Fitneß in Abhängigkeit von der Koloniegröße nicht einer Optimumskurve folgt. Statt dessen überlagern sich positive und negative Effekte der Koloniegröße so, daß die Populationswachstumsrate generell nahe eins ist, und die Dichteabhängigkeit gering ist. Auf diesen Ergebnissen aufbauend zeigte ich in einem Populationsmodell, das einen evolutionären Optimierungsprozeß der Dispersal-Strategie beinhaltet, daß die spezifische Form der Fitneßfunktion zu einer Dispersal-Strategie führen kann, bei der die hohe Variabilität der Koloniegrößen aufrecht erhalten wird.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Atualmente observa-se uma expressiva perda de biodiversidade global resultante de atividades antrópicas, sendo a introdução de espécies exóticas uma das mais impactantes. A jaqueira Artocarpus heterophyllus é uma espécie exótica introduzida no Brasil durante o período colonial, sendo considerada invasora em diversas localidades. Na Mata Atlântica invade áreas de mata aberta e de borda, habitualmente associadas a ambientes antrópicos. Na Ilha Grande é encontrada em grande abundância em decorrência do histórico de ocupação humana. Para compreender como a mastofauna responde a presença da jaqueira, o Laboratório de Ecologia de Mamíferos da Universidade do Estado do Rio de Janeiro (UERJ) vem desenvolvendo um estudo ao longo de seis anos nos arredores da Vila Dois Rios, localizada na face oceânica da Ilha Grande. A partir dos resultados prévios iniciou-se uma segunda etapa do estudo no mesmo local que buscou avaliar diferentes métodos de controle das jaqueiras. O presente estudo é uma continuação direta desses dois trabalhos anteriores e teve como objetivo acompanhar as respostas da comunidade de pequenos mamíferos no período imediatamente posterior ao controle. Durante 18 meses foram amostradas bimestralmente 18 grades, 10 aonde foi efetuado o controle das jaqueiras e 8 aonde não foi constatada a presença desta árvore. Em cada grade foram colocadas 11 armadilhas de captura viva sendo banana a isca utilizada. Os mamíferos capturados foram medidos e suas fezes coletadas. A quantidade de jacas em cada área também foi anotada bimensalmente. As fezes foram analisadas em laboratório e as sementes encontradas identificadas. Os resultados obtidos indicam que a influência de A. heterophyllus sobre a estrutura da comunidade de pequenos mamíferos foi menor após o tratamento de controle. A única espécie que parece ainda responder a abundância de jaqueiras é o roedor Trinomys dimidiatus, que apresentou densidades mais elevadas nas áreas em tratamento, porém mais próximas a resultados obtidos para espécies congêneres em áreas pouco antropizadas. Utilizando uma abordagem de redes complexas observamos que, embora T. dimidiatus seja a espécie mais abundante em termos de número de indivíduos, o gambá Didelphis aurita parece ser a espécie de mamífero mais importante para dispersão de sementes nativas, aparecendo como espécie com maior número de conexões com espécies de sementes nas redes contruídas para as áreas sem jaqueiras e com jaqueiras antes e após o tratamento. Finalmente, a partir dos dados obtidos criamos um modelo matemático para a população de T. dimidiatus dos arredores da Vila Dois Rios, baseado em um crescimento logístico. Os resultados do modelo proposto se mostraram correlacionados com os dados de abundância reais, de modo que ele parece ser um simulador adequado da população local. / Currently, the world is experiencing a severe loss of biodiversity as consequence of human activities. Of these, the introduction of exotic species is one of the most harmful. The jackfruit tree, Artocarpus heterophyllus, is considered an exotic species in Brazil, where it was introduced during colonial times. In the Brazilian Atlantic Rainforest, A. heterophyllus colonizes open canopy and edge areas, mostly associated with anthropic environments. In Ilha Grande it can be found in high densities as a result of the historical process of human occupation of the island. To better understand if and how the small mammalian fauna responded to the presence of A. heterophyllus, the Laboratory of Mammal Ecology of Universidade do Estado do Rio de Janeiro (UERJ) has been developing a study in the course of the last six years in the surroundings of Vila Dois Rios, located in the oceanic front of Ilha Grande. Based on previous results, a second phase of the study was implemented in the same local. This second study aimed to evaluate the best control method for the jackfruit trees (Moura 2011). The present study is a direct continuation of both studies, its main objective being to accompany the responses of mammalian community in the period immediately after the treatment of the jackfruit trees. During the course of 18 months 18 grids were sampled in a bimonthly basis, 10 where the jackfruit trees were treated and 8 where jackfruit trees were absent. In each grid 11 live traps were opened, and the bait was banana. The captured mammals were ear-tagged and measured and their feces collected. The number of jackfruits was also counted in each area bimonthly. The feces were analyzed in laboratory and the found seeds identified. Our results indicate that the community structure is being less influenced by A. heterophyllus abundances after the control treatment. The only species that still presented a response to the presence of A. heterophyllus was the spiny rat Trinomys dimidiatus. Even so, although the density of T. dimidiatus was high, it was lower than the density found previously, being more similar to results obtained for congeneric species in less anthropized sites. By using complex network analysis we observed that, although T. dimidiatus is the most abundant species in the study area, the opossum Didelphis aurita seems to be the most important species in terms of seed dispersal. D. aurita was the species with most connections in all built networks for areas without jackfruit trees and with jackfruit trees before and after the treatment. Finally, based on the obtained results we created a mathematical model for T. dimidiatus population of the surroundings of Vila Dois Rios, based on the logistic growth equation. The results of the proposed model were statistically correlated with our actual data, and so may be considered an adequate simulator for this particular population.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Atualmente observa-se uma expressiva perda de biodiversidade global resultante de atividades antrópicas, sendo a introdução de espécies exóticas uma das mais impactantes. A jaqueira Artocarpus heterophyllus é uma espécie exótica introduzida no Brasil durante o período colonial, sendo considerada invasora em diversas localidades. Na Mata Atlântica invade áreas de mata aberta e de borda, habitualmente associadas a ambientes antrópicos. Na Ilha Grande é encontrada em grande abundância em decorrência do histórico de ocupação humana. Para compreender como a mastofauna responde a presença da jaqueira, o Laboratório de Ecologia de Mamíferos da Universidade do Estado do Rio de Janeiro (UERJ) vem desenvolvendo um estudo ao longo de seis anos nos arredores da Vila Dois Rios, localizada na face oceânica da Ilha Grande. A partir dos resultados prévios iniciou-se uma segunda etapa do estudo no mesmo local que buscou avaliar diferentes métodos de controle das jaqueiras. O presente estudo é uma continuação direta desses dois trabalhos anteriores e teve como objetivo acompanhar as respostas da comunidade de pequenos mamíferos no período imediatamente posterior ao controle. Durante 18 meses foram amostradas bimestralmente 18 grades, 10 aonde foi efetuado o controle das jaqueiras e 8 aonde não foi constatada a presença desta árvore. Em cada grade foram colocadas 11 armadilhas de captura viva sendo banana a isca utilizada. Os mamíferos capturados foram medidos e suas fezes coletadas. A quantidade de jacas em cada área também foi anotada bimensalmente. As fezes foram analisadas em laboratório e as sementes encontradas identificadas. Os resultados obtidos indicam que a influência de A. heterophyllus sobre a estrutura da comunidade de pequenos mamíferos foi menor após o tratamento de controle. A única espécie que parece ainda responder a abundância de jaqueiras é o roedor Trinomys dimidiatus, que apresentou densidades mais elevadas nas áreas em tratamento, porém mais próximas a resultados obtidos para espécies congêneres em áreas pouco antropizadas. Utilizando uma abordagem de redes complexas observamos que, embora T. dimidiatus seja a espécie mais abundante em termos de número de indivíduos, o gambá Didelphis aurita parece ser a espécie de mamífero mais importante para dispersão de sementes nativas, aparecendo como espécie com maior número de conexões com espécies de sementes nas redes contruídas para as áreas sem jaqueiras e com jaqueiras antes e após o tratamento. Finalmente, a partir dos dados obtidos criamos um modelo matemático para a população de T. dimidiatus dos arredores da Vila Dois Rios, baseado em um crescimento logístico. Os resultados do modelo proposto se mostraram correlacionados com os dados de abundância reais, de modo que ele parece ser um simulador adequado da população local. / Currently, the world is experiencing a severe loss of biodiversity as consequence of human activities. Of these, the introduction of exotic species is one of the most harmful. The jackfruit tree, Artocarpus heterophyllus, is considered an exotic species in Brazil, where it was introduced during colonial times. In the Brazilian Atlantic Rainforest, A. heterophyllus colonizes open canopy and edge areas, mostly associated with anthropic environments. In Ilha Grande it can be found in high densities as a result of the historical process of human occupation of the island. To better understand if and how the small mammalian fauna responded to the presence of A. heterophyllus, the Laboratory of Mammal Ecology of Universidade do Estado do Rio de Janeiro (UERJ) has been developing a study in the course of the last six years in the surroundings of Vila Dois Rios, located in the oceanic front of Ilha Grande. Based on previous results, a second phase of the study was implemented in the same local. This second study aimed to evaluate the best control method for the jackfruit trees (Moura 2011). The present study is a direct continuation of both studies, its main objective being to accompany the responses of mammalian community in the period immediately after the treatment of the jackfruit trees. During the course of 18 months 18 grids were sampled in a bimonthly basis, 10 where the jackfruit trees were treated and 8 where jackfruit trees were absent. In each grid 11 live traps were opened, and the bait was banana. The captured mammals were ear-tagged and measured and their feces collected. The number of jackfruits was also counted in each area bimonthly. The feces were analyzed in laboratory and the found seeds identified. Our results indicate that the community structure is being less influenced by A. heterophyllus abundances after the control treatment. The only species that still presented a response to the presence of A. heterophyllus was the spiny rat Trinomys dimidiatus. Even so, although the density of T. dimidiatus was high, it was lower than the density found previously, being more similar to results obtained for congeneric species in less anthropized sites. By using complex network analysis we observed that, although T. dimidiatus is the most abundant species in the study area, the opossum Didelphis aurita seems to be the most important species in terms of seed dispersal. D. aurita was the species with most connections in all built networks for areas without jackfruit trees and with jackfruit trees before and after the treatment. Finally, based on the obtained results we created a mathematical model for T. dimidiatus population of the surroundings of Vila Dois Rios, based on the logistic growth equation. The results of the proposed model were statistically correlated with our actual data, and so may be considered an adequate simulator for this particular population.

As Unidades de Conservação (UCs) foram criadas para proteger e manter os remanescentes de ecossistemas naturais a fim de reduzir a perda da biodiversidade e garantir sua manutenção em longo prazo. Atualmente, muitas UCs se encontram na forma de pequenos fragmentos isolados e sob forte pressão antrópica, exigindo um manejo na forma de uma rede de fragmentos, visando reduzir as pressões das atividades do entorno. O presente trabalho teve como objetivo gerar subsídios para a criação de uma zona de amortecimento (ZA) comum para o Parque Estadual de Vassununga e para a Estação Ecológica de Jataí, visando reduzir as pressões antrópicas sobre as UCs e facilitar o fluxo biológico entre os fragmentos. Foi realizado o mapeamento da paisagem para identificar as principais formas de uso, as fontes de impactos ambientais e verificar o cumprimento da legislação de áreas de preservação permanente. Foram utilizadas métricas de paisagens para analisar a configuração espacial dos remanescentes de vegetação arbórea e selecionar fragmentos importantes para a facilitação do fluxo biológico. Foram utilizados modelos de previsão de riqueza e probabilidade de ocorrência de espécies-alvo de aves para selecionar áreas potencialmente importantes para a manutenção da biodiversidade. A paisagem da área de estudo apresenta menos de 30% de remanescentes de vegetação natural, distribuídos em pequenos fragmentos, imersos em uma matriz de cana-de-açúcar e eucalipto. O desrespeito à legislação e numerosas fontes de impacto ambiental contribuem para aumentar a pressão sobre os recursos naturais. O incremento da conectividade dos fragmentos, principalmente com a restauração das florestas ribeirinhas mostrou ser uma estratégia importante para restabelecer a conectividade funcional entre as UCs e entre os remanescentes da paisagem. Na região existem fragmentos com potencial para facilitar os fluxos biológicos, atuando como uma rede de fragmentos, e auxiliar na manutenção da biodiversidade. Porém, grande parte deles está localizada no interior de propriedades particulares, exigindo esforços para conscientização dos proprietários para proteção e incremento da conectividade destes fragmentos. / Natural reserves have been created to protect and maintain natural ecosystems remnants in order to reduce biodiversity loss and to ensure their maintenance in the long run. Nowadays, most of these reserves are small and isolated fragments under anthropogenic pressure. Such small remnants must be managed and protected as a fragment network to reduce the human pressure and to promote biological fluxes among fragments. This study aimed at producing information to help on the process of designing a common buffer zone for three public natural reserves: Vassununga State Park, Jataí Ecological Station and Luís Antônio Experimental Station. An up to date land cover/land use map was generated to identify the main activities and sources of anthropogenic impacts in the study area, their possible consequences to the environment, and also if and how much the environmental legislation is being followed. To select the most important natural fragments which could facilitate biological fluxes and maintain the regional biodiversity, two approaches were used: analysis of the spatial arrangement of the fragments in the landscape applying landscape metrics, and the use of models to predict bird species richness and occurrence. The studied area presently has less than 30% of remnant natural vegetation, spread as small fragments in a sugar cane and eucalyptus matrix. Environmental legislation is not being obeyed and, together with several sources of impact, produce negative pressures on the natural resources. The restoration of riparian forests would be a good strategy to reestablish the landscape functional connectivity. Fragments able to facilitate biological fluxes and to maintain biological diversity still exist in the region, but a great deal of them are located in private properties. Therefore, efforts to warn and educate the owners are needed to increase the landscape connectivity and to conserve the regional biodiversity.

No description available.

Changing environmental conditions often impose stressful growing conditions in plant communities. Until now, morphological plasticity, i.e. polymorphic growth physiognomies of plants, has not been sufficiently studied as a pivotal strategy for the whole ecosystem adaptation to environmental stress. We consider mangrove ecosystems as suitable models to provide insights on this subject. In the thesis, I investigate the ecological significance of tree morphological plasticity in the structural development and the dynamics of mangrove forests. I conducted field experiments in two regions located on both sides of the Amazon River mouths i.e. in French Guiana and North Brazil. Forest inventories were carried out in contrasting mangrove stands in both regions. The thesis combines empirical analysis of field data, terrestrial laser scanning (TLS), and mechanistic, individual-based computer simulations. We published results that proved the TLS-based analysis of individual tree structure useful for a better knowledge on biomass allocation between trunk and branches in tall and large Avicennia germinans mangrove trees reaching 45 m high and 125 cm of trunk diameter. Combining structural descriptions of A. germinans trees found in both sites, I highlighted the site-specific differences in tree allometries. The study suggests that regional differences in mangrove tree structure and function could be captured through better description of crown metrics, and that selected indicators of local morphological plasticity and consequent stand structure could generate a plus-value in the understanding of mangrove stand dynamics across contrasting coastal environments. Beyond the extension of allometric models to large Avicennia trees, we proposed new biomass equations with improved predictive power when crown metrics is taken into account. Additionally, we developed a novel software tool, named Lollymangrove, based on the AMAPStudio suite of software, with the objective of maximizing the potential of further field descriptions and modeling works. Lollymangrove allows standardized forest data capture, 3D visualization of structural data, aboveground biomass computations from a configurable module and export formats for forest dynamics and remote sensing models. Simulation experiments were conducted by means of the spatially explicit, individual-based stand model BETTINA_IBM. This model describes the important mechanism of water uptake limited by salt stress, and revealed insights into the relation between environmental conditions, allometric variations and biomass partitioning of mangrove trees, and stand characteristics. The simulation results suggest close matches with observed ecological patterns (e.g., tree allometries, mortality distributions, and self-thinning trajectories) under higher salinity. In low salinity conditions, however, the current parameterization underestimates the maximum tree height and diameter, and consequently, aboveground biomass and self-thinning trajectories of forest stands. This suggests that the morphology of trees under low levels of salinity are explained by further regulation mechanism(s) that still need to be addressed in a subsequent model improvement. Overall, this work has essentially pointed out the need to elucidate how morphological plasticity relates with structural development of forest stands. It establishes that TLS measurements and structural data analysis associated to efforts for integrative software and mechanistic modelling works could link mangrove dynamics to fast-changing coastal processes.

Using trap data the Hawdon, Poulter and South Branch valleys, a spatial distribution model was created for Stoats (Mustela erminea), Ship Rats (Rattus rattus) and Weasels (Mustela nivalis) in the North Branch of the Hurunui River. Ten spatial attributes were analysed in this thesis as potential spatial predictors of Stoats, Ship rats or Weasels; four of which were distance related measurements (distance from ecotonal edge, distance from river, distance from river tributary and distance from trapping edge); three were climate based variables (mean maximum temperature, mean minimum temperature and mean precipitation) and three were topographical based variables (elevation, aspect and slope). Relationships that existed between each spatial attribute and the number of Stoats, Ship Rats and Weasels caught were quantified by comparing the significance of the mean trapping rate with each spatial attribute and expressed spatially as maps in a Geographical Information System (GIS). Results from this thesis found elevation, aspect and distance from ecotonal edge as potential spatial predictors of Stoat populations. Elevation and aspect were found to be potential predictors of Ship rat and Weasel populations. GIS is able to predict the spatial distribution of pest species to a similar (or better) level compared to more formal associative models. The potential of GIS is however, restrained by the same limitations associated with these models. By using a larger trapping data set and identifying a number of social interactions between Stoats, Ship Rats and Weasels, one can improve the accuracy of spatially modelling each species within a Beech forest environment. Therefore, improve our understanding how landscapes influence the distribution of each pest species.

Using trap data the Hawdon, Poulter and South Branch valleys, a spatial distribution model was created for Stoats (Mustela erminea), Ship Rats (Rattus rattus) and Weasels (Mustela nivalis) in the North Branch of the Hurunui River. Ten spatial attributes were analysed in this thesis as potential spatial predictors of Stoats, Ship rats or Weasels; four of which were distance related measurements (distance from ecotonal edge, distance from river, distance from river tributary and distance from trapping edge); three were climate based variables (mean maximum temperature, mean minimum temperature and mean precipitation) and three were topographical based variables (elevation, aspect and slope). Relationships that existed between each spatial attribute and the number of Stoats, Ship Rats and Weasels caught were quantified by comparing the significance of the mean trapping rate with each spatial attribute and expressed spatially as maps in a Geographical Information System (GIS). Results from this thesis found elevation, aspect and distance from ecotonal edge as potential spatial predictors of Stoat populations. Elevation and aspect were found to be potential predictors of Ship rat and Weasel populations. GIS is able to predict the spatial distribution of pest species to a similar (or better) level compared to more formal associative models. The potential of GIS is however, restrained by the same limitations associated with these models. By using a larger trapping data set and identifying a number of social interactions between Stoats, Ship Rats and Weasels, one can improve the accuracy of spatially modelling each species within a Beech forest environment. Therefore, improve our understanding how landscapes influence the distribution of each pest species.

Dans le contexte des nouvelles exigences en termes de qualité des eaux du surface, les modèles hydro-écologiques s'avèrent être des outils indispensables pour compléter notre compréhension du fonctionnement du milieu ou prévoir l'impact sur la qualité de l'eau de nouvelles mesures. L'objectif de cette recherche est de tirer parti de l'outil de modélisation ProSe, et de le faire évaluer afin de compléter la compréhension du fonctionnement biogéochimique de la Seine. Dans une première étape, différents processus biogéochimiques sont implémentés, calibrés et validés indépendamment, grâce à des jeux de données disponibles sur un linéaire de 220 km (de Paris jusqu'à l'estuaire), à différents pas de temps, pour la période 2007-2012. Ces améliorations sont réalisées grâce à l'utilisation directe de résultats expérimentaux, à l'extrapolation de résultats de couplage entre expériences de laboratoire et modélisation biogéochimique, ou encore grâce à l'analyse de mesures haute fréquence in-situ. Le modèle ProSe est ensuite utilisé pour établir un bilan du fonctionnement biogéochimique de la Seine dans cette zone fortement anthropisée. L'effet des processus pélagiques et benthiques sur les différents cycles biogéochimiques (carbone, azote, phosphore) est quantifié, pour différentes conditions hydrologiques, en amont et en aval de la plus grosse station d'épuration de l'agglomération parisienne, qui traite les effluents de plus de 5 millions équivalent habitants. La précision spatio-temporelle du modèle est ensuite utilisée pour évaluer l'effet de la fréquence d'échantillonnage sur l'estimation des critères de qualité de l'eau au sens de la Directive Cadre sur l'Eau. Les résultats soulignent l'importance d'une représentation précise des processus physiques (hydrodynamique et processus hydro-sédimentaires) dans les modèles de qualité de l'eau pour parvenir à une simulation fiable des flux biogéochimiques dans le milieu et des échanges entre compartiment benthique et colonne d'eau. Ce travail illustre enfin toute l'utilité des modèles hydro-écologiques pour venir en appui au suivi du milieu dans le cadre des objectifs actuels d'amélioration de la qualité des milieux aquatiques. / Hydro-ecological models are essential to complete our knowledge of the functioning of aquatic systems. They can moreover be used to forecast the impact of new management strategies on the future water quality. The aim of this thesis is to use the hydro-ecological ProSe model to improve our understanding of the biogeochemical functioning of the Seine River downstream the Paris urban area. Simulated biogeochemical processes are first implemented, calibrated, and validated independently for the 2007-2012 period. For each one of these processes, appropriate methodologies are used. These methodologies include the direct use of experimentally obtained parameters, the upscaling of results from coupled laboratory experiments and stand-alone biogeochemical modelling, or the analysis of high frequency in-situ measurements. Different datasets, which are available at various time steps, allow the validation of these processes along the whole 220 km simulated stretch (from Paris to the entrance of the Seine River estuary). Once validated, the ProSe model is then used to assess the biogeochemical functioning of the Seine River along this highly anthropized stretch. The impact of pelagic and benthic processes on the different biogeochemical cycles (carbon, nitrogen, and phosphorus) is quantified for different hydrological conditions, up- and downstream the major waste water treatment plant of the Paris urban area, which treats the effluents of over 5 million population equivalent. The model is then used to assess the effect of the monitoring frequency on the estimation of the water quality as defined by the European Water Framework Directive. The results highlight the importance of a detailed representation of physical processes in hydro-ecological models for a reliable simulation of in-river biogeochemical fluxes and of exchanges at the sediment-water interface. Having in mind the present targets of the improvement of the quality of water bodies, this work illustrates the importance of hydro-ecological modelling as an essential complement to water quality monitoring strategies.

O objetivo desta Tese foi avaliar o papel da macrófitas submersas em relação à qualidade da água, interações com o fitoplâncton e ciclagem biogeoquímica na Lagoa Mangueira, um grande lago raso subtropical, no sul do Brasil. Para alcançar estes objetivos, este trabalho conta com uma série de abordagens, como: levantamentos de campo, etapas experimentais e uso de modelos ecológicos para avaliar a influência de macrófitas sobre a dinâmica do ecossistema de estudo, cujas águas são intensamente exploradas para suprir a cultura de arroz em sua área de entorno. Ao longo de seus 200km de perímetro litorâneo, a Lagoa apresenta maciços estandes submersos de vegetação. A análise de qualidade da água e estrutura da comunidade fitoplanctônica ao longo de um gradiente de vegetação submersa, partindo da zona litorânea para a zona pelágica (sem vegetação), revelou menor disponilibidade de nutrientes como orto-fosfato (PO4) e menor concentração de clorofila-a (Clo-a), na área com vegetação submersa. Na zona pelágica, os maiores valores de Clo-a foram corroborados pela maior biomassa fitoplanctônica, sendo representada principalmente por espécies de cianobactérias. Tais evidências sugerem o efeito antagônico entre macrófitas e fitoplâncton, como a competição por nutrientes e alelopatia. Em laboratório, estes mecanismos puderam ser comprovados em experimentos de coexistência realizados em microcosmos com 4 espécies de macrófitas nativas e uma cepa da cianobactéria Microcystis aeruginosa. Os testes envolveram níveis distintos de intensidade luminosa e concentração de PO4 visando determinar limiares para a ocorrência de alelopatia. As espécies Cabomba caroliniana e Myriophyllum spicatum se demonstraram potencialmente alelopáticas enquanto que as espécies Ceratophyllum demersum e Egeria densa apresentaram elevada capacidade de absorção de PO4 (±0,35 mg.g-1d-1) reduzindo rapidamente a concentração deste nutriente a valores abaixo de 0,05 mg.L-1. Outra abordadem experimental foi conduzida para parametrizar a cinética da liberação de nutrientes e carbono de 5 espécies de macrófitas durante o processo de decomposição. Com o auxílio de modelos ecológicos, foi simulado o crescimento de macrófitas submersas em lagos subtropicais e temperados. Isto foi realizado visando avaliar a possibilidade de aumento da resilência do estado de dominância por macrófitas em lagos de baixa latidude devido ao crescimento contínuo da vegetação, ao contrário de lagos temperados, onde as plantas morrem sazonalmente em função do inverno rigoroso. Além disso, foram simulados cenários considerando a possibilidade de colapso da vegetação submersa na Lagoa Mangueira em função de intensa tomada da água da Lagoa para irrigação. Com base na modelagem, foi possível estimar limiares de eutrofização para a proliferação do fitoplâncton. Em suma, os resultados comprovaram os mecanismos de retroalimentação positiva de macrófitas submersas sobre a qualidade da água e importância de suas funções ecológicas para o estado trófico e gestão da Lagoa Mangueira. Além disso, este conjunto de informações constitui uma base teórico-prática para o manejo, restauração e conservação de lagos rasos subtropicais e tropicais. / The aim of this Thesis was to evaluate the role of the submerged macrophytes with respect to water quality and, interactions with phytoplankton and nutrient cycling in the large shallow subtropical Lake Mangueira, southern Brazil. To achieve these goals, this work counts with approaches in situ, in laboratory and aplication of ecological modelling to verifify the influence of the submerged vegetation over the dynamics of the ecosystem, whose water is intensively explored to irrigate rice crops around its surrounding area. Over the 200km of the lake littoral perimeter, several submerged macrophyte beds are established. The analysis of water quality and phytoplankton structure along a macrophyte-pelagic gradient revealed lower concentration of orto-phosphate (PO4) and chlorophyll-a (Chlo-a) in the vegetated area. At the pelagic zone, the higher Chlo-a values were corroborated by the higher biomass of phytoplankton, which was mostly composed by cyanobacteria species. Such evidences suggest the antagonistic relantionship between macrophytes and phytoplankton as nutrient competition and allelopathy. Experiments of coexistance, in microcosms, with 4 native submerged macrophytes and a toxic strain of the cyanobacteria Microcystis aeruginosa proved the occurrence of these mechanisms. The experiments included different levels of light intensity and orto-phosphate concentration (PO4) in the medium aiming to identify thresholds in which allelopathy is likely to occur. The macrophytes Cabomba caroliniana and Myriophyllum spicatum showed allelopathic potential while the species Ceratophyllum demersum and Egeria densa showed a high capacity for PO4 absorption (±0.35 mg.g-1d-1), being able to reduce this nutrient to lower levels than 0.05 mg.L-1. Another experimental approach was carried out to parameterize the leaching of nutrients and carbon from 5 macrophytes under decaying process. Moreover, ecological modelling was utilized to simulate the growth of submerged macrophytes in subtropical and temperate lakes. This was done aiming to evaluate the possibility of resilience enhancement of the clear water state in lakes of low latitude because the plants can grow continuously, in contrast with temperate lakes, where they die seasonally due to rigorous winter. In addition, simulation of scenarios considering the collapse of the vegetation in Lake Mangueira because of water uptake for rice crops were carried out in oder to provide elements for the ecosystem management. Through this approach, it was possible to forecast possible eutrophication thresholds for phytoplankton blomming. In conclusion, the results proved the the postive feed-back mechanisms exerted by the submerged macrophytes on the water quality and the importance of their ecological functions to the trophic state of Lake Mangueira. In addition, such information serve as theoretical and practical basis for the management, restoration and conservation of subtropical and tropical shallow lakes.