Fluxo de energia em teias alimentares de ecossistemas aquáticos tropicais: das fontes autotróficas até os grandes consumidores ectotérmico

Food webs constitute one of the main research frameworks in ecology, and food web structure is considered one of the most fundamental attributes of ecosystems. Linkages among habitats and the flux of matter across ecosystem boundaries have important implications for biomass production of animals and plants, which is facilitated by trophic relations between consumers and their resources. It has been well documented that fish movements may transfer nutrients and aquatic production, but information on how this production contributes to individual energy allocation and reproductive investment is scarce. Furthermore, the trophic position of top predators in a food chain strongly influences food-web structure because it reflects the number of steps that energy takes from primary producers to tertiary consumers. Crocodilians are likely to influence the structure of food webs because of their pronounced ontogenetic shifts in diet. Some species of large crocodiles may be trophic links in diverse food webs throughout their lives, from freshwater, brackish, marine and adjacent terrestrial food webs. Amazonian crocodilians show interspecific differences in diet. However, it is unknown to what extent they differ in the primary sources of their diet and to what extent those differences are reflected in ontogenetic shifts in trophic position. It is also not well understood to what extent interspecific differences in diet are a reflection of foraging behavior or are a function of macrohabitat selection. We used a spatiotemporal context to trace the origins and the flux of energy by applying chemical tools, such as the natural ratio of carbon and nitrogen stable-isotopes and RNA:DNA. Within the tropical aquatic ecosystems we studied, we aimed to understand three aspects of food-web functioning: the seasonality and spatiality in the reproductive investment of diamond mullet (Liza alata) from the Northern Territory of Australia (Chapter 1); interspecific differences in the origins of energy sustaining the four species of Amazonian crocodilians within a spatial context (Chapter 2) and ontogenetic shifts in trophic position of these predators within the context of the food web (Chapter 3). The results show that reproductive investment of diamond mullet takes place during the dry season, when resources are limited and fish are in poor body condition. There is a strong trade-off between somatic and reproductive investment. This may be explained because diamond-mullet show a temporal uncoupling between resource acquisition from floodplains during the wet season, energy storage within lipid mesenteric bodies for some months and a subsequent reproductive allocation during the dry season. Because this fish undertakes spawning migrations across habitats, temporal and spatial uncoupling between energy acquisition and reproductive allocation have important implications for the preservation of natural hydrological regimes of water bodies. The maintenance of these hydrological regimes is important to enhance the capacity for fishes of this region to maintain viable populations. In the context of lotic ecosystems from central Amazonia, the results show evidence of differences in the basal resources sustaining the four species of Amazonian crocodilians. These differences result from behavioral divergences and foraging strategies in addition to macrohabitat selection. Furthermore, we found a positive relationship between crocodilian size and trophic position. However, there are interspecific differences in the shape of these relationships. Crocodilians occupy higher trophic levels than piscivorous fishes. This structure may create significant divergences in food-chain-length estimates because, traditionally, only fish have been considered as top predators in most food-chain-length studies. The information presented in this study brings novel insights about the biology and ecology of the studied consumers, depicting the trophic functioning of ecosystems where they occur in relation to the resources that sustain them.A estrutura das teias alimentares é considerada um dos atributos mais fundamentais dos ecossistemas. Além disso, as conexões entre hábitats e o fluxo de matéria através dos limites dos ecossistemas têm importantes implicações na produção de biomassa de animais e plantas, que é facilitada pelas relações tróficas entre consumidores e recursos. Migrações de peixes podem transferir nutrientes e produção de origem aquática, mas informações sobre como essa produção contribui para a alocação individual da energia e o investimento reprodutivo de animais é escasso. A posição trófica dos predadores de topo de cadeia influencia fortemente a estrutura das teias alimentares, pois reflete o número de passos que a energia atravessou a partir do produtores primários até os consumidores terciários. Os crocodilianos exercem uma forte influência em diversas teias alimentares ao longo das suas vidas, desde água doce, salobre, marinha e hábitats terrestres adjacentes. Os crocodilianos amazônicos apresentam diferenças interespecíficas na dieta. Porém, desconhece-se em que medida diferem nas fontes primárias dos recursos que consomem e até que ponto essas diferenças são refletidas em mudanças ontogenéticas na posição trófica. É também desconhecido em que medida as diferenças interespecíficas na dieta podem ser um reflexo de divergências no comportamento de forrageio, além de ser uma função do uso de hábitat. No presente estudo, utilizamos um contexto espaço-temporal para traçar as origens e o fluxo da energia utilizando ferramentas químicas, como a razão de isótopos estáveis de carbono e nitrogênio e RNA:DNA. Em relação ao funcionamento das teias alimentares dos ecossistemas aquáticos tropicais, buscamos entender três aspectos: A sazonalidade e espacialidade no investimento reprodutivo da tainha-diamante (Liza alata) do território Norte da Austrália (Capítulo 1); as diferenças interespecíficas nas origens da energia que sustenta as quatro espécies de crocodilianos amazônicos dentro de um contexto espacial (Capítulo 2); e as mudanças ontogenéticas na posição trófica desses predadores dentro do contexto das teias alimentares em que estão inseridos (Capítulo 3). Os resultados indicam que o investimento reprodutivo da tainha-diamante acontece durante a época seca, quando os recursos são limitados e os peixes mostram uma pobre condição corporal. Existe um forte compromisso entre o investimento somático e reprodutivo. Isso pode ser explicado porque a tainha-diamante mostra um desacoplamento temporal entre a ingestão de recursos nas planícies de inundação durante a época cheia, o estoque de energia por alguns meses em corpos lipídicos mesentéricos e a posterior alocação para reprodução durante a época seca. Devido às migrações entre hábitats desses peixes para desovar, o desacoplamento temporal e espacial entre a aquisição de energia e sua alocação para reprodução tem importantes implicações para a preservação dos regimes hidrológicos naturais das planícies de inundação. A manutenção desses regimes naturais é importante para garantir a capacidade dos peixes dessa região de manter populações viáveis. No contexto dos ecossistemas lóticos da Amazônia central, os resultados mostram evidências de que existem diferenças nos recursos basais que sustentam as quatro espécies de crocodilianos amazônicos. Essas diferenças resultam de divergências comportamentais e estratégias de forrageio além da seleção de macrohábitat. Encontramos também uma relação positiva entre o tamanho dos crocodilianos e a posição trófica que ocupam, mas existem diferenças interespecíficas na forma dessa relação. Os crocodilianos ocupam níveis tróficos mais altos do que peixes piscívoros. Essa estrutura pode gerar divergências significativas nas estimativas do comprimento das cadeias alimentares, pois tradicionalmente, apenas os peixes têm sido considerados como predadores de topo em estudos de comprimento das cadeias tróficas. As informações apresentadas nesse estudo trazem aspectos inovadores sobre a biologia e ecologia dos consumidores estudados, retratando o funcionamento trófico dos ecossistemas e as origens dos recursos que os sustentam

Fatores que influenciam a variação espacial e temporal nas fontes autotróficas de energia e nível trófico do Paracheirodon axelrodi (Osteichthyes, Characidae) num sistema interfluvial do médio rio Negro

Factors that influence the spatial and seasonal variations in the autotrophic energy sources and trophic level of the cardinal tetra (Paracheirodon axelrodi) were investigated in an interfluvial region of the middle Negro River. A secondary objective involved investigating mercury biomagnification in the cardinal food chain and the potential mechanisms controlling this process. Stomach content analyses were performed to determine the cardinal diet in these habitats. Carbon stable isotopes (δ 13 C) were utilized to trace organic carbon between the plants (tree/shrub leaves, aquatic emergent and submersed herbaceous plants and epiphytic and floating metaphytic algae), aquatic invertebrates and the cardinals. Nitrogen stable isotopes (δ 15 N) were used to indicate the trophic level of the cardinal in relation to the aquatic invertebrates and plants. A mass balance mixing model called IsoSource was used to determine the relative contributions of autotrophic energy sources for the aquatic invertebrates and fish. Total mercury concentrations and δ 15 N values of the plants, invertebrates and fish were used to examine trophic levels and mercury biomagnification along the food chain. Cardinals were collected in three streams and three interfluvial swamps during a period of 12 months. Water samples were collected at all sampling points to measure total suspended sediments (TSS), chlorophyll concentrations and δ 13 C and δ 15 N values of fine particulate organic matter (FPOM). Water physical-chemical parameters including dissolved oxygen, pH and water temperature were measured at all sampling points. Daily changes in water level and water temperature were recorded with Leveloggers (hydrostatic sensors) installed in two interfluvial swamps. Local precipitation was measured with rain gauges installed in the same areas as the Leveloggers. Daily primary productivity rates of epiphytic and floating metaphytic algae, tree and shrub leaf-fall, emergent herbaceous plants and phytoplankton were estimated and extrapolated over the area of influence in the interfluvial region utilizing a dual-season classification map for wetland habitats developed by Hess et al. (2003). Plant selectivity indexes were devised using the relative contributions of plant groups to fish and invertebrate carbon and nitrogen and the productivity of each plant group in relation to total primary production for the study area. Stomach content analyses demonstrated that the cardinal in the interfluvial region consumes predominantly a mix of microcrustaceans and insect larva; however no seasonal variations were observed. The relative contributions of autotrophic energy sources varied seasonally and spatially, with tree and shrub leaves and emergent herbaceous plants as the principal energy sources for the cardinals from the campos and streams, respectively, during the high water period. In the dry season, the principal energy sources were epiphytic algae for the cardinals from the campos and submerged herbaceous plants for the cardinals from the streams. The selectivity index results showed that the cardinal food chain was preferentially selecting energy from epiphytic algae in all seasons, although the production from this plant group was small in comparison to the flooded forest and herbaceous plants. δ 15 N results indicated that the cardinals were one trophic level above the aquatic invertebrates, who, in turn, were two levels above the plants. Total mercury concentrations in relation to δ 15 N values of shrimp and different fish species showed strong biomagnifications through the food chain. Higher mercury levels were encountered in cardinals from the low water period when production of epiphytic algae and herbaceous plants was highest. The selective incorporation of epiphytic algae and/or submerged herbaceous plants into the tissues of aquatic invertebrates and cardinals could be an important link in the biomagnification of mercury in this food chain. The high mercury levels encountered in cardinals and predators of the cardinal like Cichla sp. in a remote area far removed from anthopogenic mercury inputs shows additional supporting evidence for large, natural-occurring sources of mercury in the Negro River.Foram investigados os fatores que influenciam a variação espacial e temporal nas fontes autotróficas de energia e o nível trófico do cardinal (Paracheirodon axelrodi) num sistema interfluvial do médio rio Negro. Um objetivo secundário foi investigar a biomagnificação de mercúrio na cadeia alimentar do cardinal e os potenciais mecanismos que controlam este processo. Análises de conteúdo estomacal foram feitas para determinar a dieta desta espécie. O método dos isótopos estáveis de carbono foi utilizado para traçar o carbono orgânico entre as plantas (folhas de árvores/arbustos, herbáceas aquáticas emergentes e submersas, e algas epifíticas e metafíticas flutuantes), invertebrados aquáticos e os peixes. O método dos isótopos estáveis de nitrogênio foi utilizado para indicar o nível trófico do P. axelrodi em relação aos invertebrados aquáticos e às plantas na base da cadeia alimentar. O modelo de mistura de massa IsoSource foi utilizado para determinar as contribuições relativas de energia para os cardinais e invertebrados aquáticos. Concentrações de mercúrio total (THg) das plantas, invertebrados e peixes foram utilizadas com δ 15 N para indicar o nível trófico por meio da biomagnificação do mercúrio ao longo da cadeia trófica. Exemplares de cardinal foram coletados em três igarapés e três campos alagados na região interfluvial durante um período de 12 meses. Amostras de água foram coletadas para medir os sedimentos totais em suspensão (TSS), clorofila e o material orgânico particulado fino (FPOM). Os parâmetros físico-químicos da água (pH, oxigênio dissolvido e temperatura da água) foram medidos em cada ponto de coleta. Foram feitas medidas diárias de cota, temperatura da água e pluviosidade em duas áreas de campo alagado na região interfluvial. A produtividade das algas epifíticas, metafíticas flutuantes, fitoplanctônicas, herbáceas aquáticas emergentes e árvores/arbustos foi estimada e extrapolada utilizando o mapeamento da área alagável e, a classificação dos habitats alagáveis na região interfluvial para as épocas da cheia e seca. Índices de seletividade dos grupos de plantas foram determinados por meio das contribuições relativas de energia para os invertebrados aquáticos e cardinais e a produtividade de cada grupo de plantas em relação à produtividade total na região interfluvial. As análises do conteúdo estomacal demonstraram que o P. axelrodi consome principalmente microcrustáceos e larvas de inseto, com pouca variação sazonal. Na cheia, a floresta foi a principal fonte de energia para os cardinais dos campos, enquanto as herbáceas aquáticas emergentes foram a principal fonte de energia para os cardinais dos igarapés. Na seca, as algas epifíticas foram a maior fonte para os cardinais dos campos, enquanto as herbáceas aquáticas submersas foram a maior fonte para o Paracheirodon dos igarapés. Os índices de seletividade indicaram uma contribuição preferencial das algas epifíticas em relação à produtividade total. As análises de δ 15 N mostraram que esta espécie estava aproximadamente um nível trófico acima dos invertebrados aquáticos e dois níveis acima das plantas. As concentrações de mercúrio total dos juvenis de camarão e peixes, em relação aos valores de δ 15 N mostraram uma forte biomagnificação deste metal entre os níveis tróficos. Foram encontrados elevados níveis de mercúrio nos cardinais no período seco, quando a produção de algas epifíticas e herbáceas aquáticas submersas eram maiores. O consumo seletivo de algas epifíticas e herbáceas aquáticas por juvenis de camarão e outros invertebrados na cadeia trófica do cardinal pode ser um dos principais mecanismos responsáveis pela alta taxa de biomagnificação observada neste estudo. Os altos níveis de mercúrio encontrados no P. axelrodi e seus predadores, como Cichla spp., numa área longe de qualquer fonte antrópica de mercúrio, fornece evidência adicional para a existência de uma grande fonte natural de mercúrio nesta região

Polarimetric data for tropical forest monitoring : studies at the Colombian Amazon

An urgent need exists for accurate data on the actual tropical forest extent, deforestation, forest structure, regeneration and diversity. The availability of accurate land cover maps and tropical forest type maps, and the possibility to update these maps frequently, is of great importance for the development and success of monitoring systems. For areas like the Amazon the use of optical remote sensing systems as the source of information, is impeded by the permanent presence of clouds that affect the interpretation and the accuracy of the algorithms for classification and map production. The capabilities of radar systems to acquire cloud free images and the penetration of the radar waves into the forest canopy make radar systems suitable for monitoring activities and provide additional and complementary data to optical remote sensing systems. Information regarding forest structure, forest biomass, and vegetation cover and flooding can be associated with radar images because of the typical wave-object interaction properties of the radar systems.In this thesis new algorithms for the classification of radar images and the production of accurate maps are presented. The production of specific maps is studied by applying the developed algorithms to two different study areas in the Colombian Amazon. The first site, San José del Guaviare, is a colonisation area with active deforestation activities and dynamic land cover change. The second area is a pristine natural forest with high diversity of landscapes.A detailed statistical description of the polarimetric AirSAR data is made in terms of backscatter (gamma values), polarimetric phase difference and polarimetric correlation. This approach allows a better interpretation of physical backscatter mechanisms important for interpretation of images in relation to ground parameters. Theoretical cumulative probability density distributions (pdf) are used to describe the mean field values and the standard deviation for a class. A Gausian distribution is used to describe the field average gamma values; a circular Gausian distribution is used to describe the field average HH-VV phase difference and a Beta distribution is used to described the field average HH-VV phase correlation. The accuracy of the estimation of the field-averaged values depends on the level of speckle, i.e. number of independent looks. This effect is included in the calculation of the pdf's and therefore can be simulated.For the Guaviare site the classification algorithm is used to assess the AirSAR data in the production of a land cover type map. Classification accuracies are calculated for different combinations of bands and level of speckle. An accuracy of 98.7% was calculated for a map when combining L-HV and P-RR polarisations. Confusion between classes are studied to evaluate the use of radar bands for monitoring activities, e.g. loss of forest or detection of new deforested areas. In addition a biomass map is created by using the empirical relationship between the combination of the same radar bands and the biomass estimations from 28 plots as measured in the field. The agreement of the biomass map with the land cover map is used to evaluate the biomass classification.For the Araracuara site the classification algorithm is used to assess the use of polarimetric data for forest structural type mapping and indirect forest biophysical characterisation. 23 field-measured plots used for forest structural characterisation are used to assess the accuracy of the classification. A new SAR derived legend is more suitable for the SAR map allowing better physical interpretation of results. A method based on iterated conditional modes is introduced to create maps from the classified radar images, increasing in most of the cases the accuracy of the classification. The structural type map with 15 classes can be classified with accuracies ranging from 68% to 94% depending on the classification and the mapping approach. The relationship between forest structure and polarimetric signal properties is studied in detail by using a new decomposition of polarimetric coherence, based on a simple physical description of the wave-object interactions. The accuracy of the complex coherence is described using the complex Wishart distribution. In addition for the same area, a biomass map is created using the previous structural type characterisation as the basis for the classification, overcoming problems as the well know radar signal saturation.The possibilities and restrictions of creating biomass maps with AirSAR polarimetric images are deeply investigated. Two different approaches are proposed depending on the terrain conditions. A theoretical exploration on the physical limits for radar biomass inversion is made by using a new interface model, called LIFEFORM that describes the layered tropical forest in terms of scatterers. The UTARTCAN scattering model is used to analyse the effect of flooding, forest structure and terrain roughness in the biomass inversion