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Food webs of two Venezuelan clear-water streams with seasonal fluctuations in hydrology
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Two Venezuelan clear-water streams were sampled to describe resource use by fishes, community interactions, and the effects of seasonal environmental change and resource availability on food web structure. Previous studies that compiled food webs from published literature have been criticized for describing food web statistics from studies with varying methods. Patterns described may have been artifacts that arose from analyzing webs that varied in data quality. The criticisms of earlier studies needed to be addressed with standardized methodologies so that an accurate description of an ecosystems food web could be created. This study was conducted with methods similar to Winemiller (1990) in order to standardize food web methodologies and create data sets that could be used in future analyses of food web statistics. Morichal Charcote and Morichal Charcotico are tributaries of the Aguaro and Guariquito rivers, which flow to the Orinoco and define the boundaries of AguaroGuariquito National Park. Both sites are influenced by seasonal fluctuations in hydrology that create productive marshes during the wet season and isolated pools during the dry season. Fishes exploited seasonally available food resources at both sites and reproduction increased during the wet season. Dietary overlap was high during the wet season due to fishes consuming abundant invertebrate prey. As fish densities increased, and dietary overlap decreased for most species pairs. Piscivory was low during the wet season due to low fish densities and low capture efficiency. Piscivory increased during the dry season as fish densities increased. Morichal Charcotico appeared to have more allochthonous input than Morichal Charcotico, however food web diagrams showed allochthonous input to be of relatively little importance at both sites. Aquatic macrophytes and algae were the most important basal resources, and detritivory had little importance in the webs at either site. Web connectance was higher than values reported by Winemiller, but lower than values computed by other authors. The proportion of intermediate species in the food webs at both sites was larger than recorded by other studies, and the number of intermediate trophic level species in food webs indicated that omnivory was greater than published values.
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Includes bibliographical references: p. 131-143.
Issued also on microfiche from Lange Micrographics.
Peterson, Christopher Chase (1997). Food webs of two Venezuelan clear-water streams with seasonal fluctuations in hydrology. Master's thesis, Texas A&M University. Available electronically from
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