| Several factors may influence intraspecific niche differentiation, such as the different levels of resources or degrees of competition and predation organisms experience. Resource use polymorphism can lead to morphological differentiation and to the evolution of different life history traits. Trinidadian Guppies (Poecilia reticulata) inhabit streams where they experience high or low predation pressure. Guppies living in high (HP) and low predation (LP) sites have evolved different life history traits: HP guppies mature earlier, produce more and smaller offspring, and have higher overall fecundity and reproductive allotment than their LP counterparts.;The objective of this dissertation was to investigate the trophic ecology of guppies and its correlation with their life histories patterns. Three methodologies were employed: gut content analysis, gut length measurement, and stable isotope analysis. In the dry season, guppies in HP sites had a higher quality diet, which consisted of a greater proportion of invertebrates. Guppies in HP sites were more selective than guppies in LP sites, avoiding invertebrates of poor quality, as measured by a high carbon:nitrogen ratio. Gut morphology data confirmed these results, as guppies with lower quality diets (from LP sites) had longer guts. Comparisons between dry and wet seasons revealed that the diet of guppies shifted during the wet season, thereby eliminating dietary differences between HP and LP guppies found during the dry season.;A survey of HP and LP population pairs from six different rivers conducted in the wet season showed some similarity within stream types in their environmental and biological characteristics but with some differences between rivers. delta 15N and delta13C stable isotope analysis across the surveyed sites showed that LP guppies generally occupied a higher trophic position than HP guppies, but that this relationship was highly influenced by the river of origin. Stable isotopes also indicated that guppies assimilated invertebrates into their tissues more than other dietary items and that the variation in diet composition between sites was high.;The results of this dissertation help distinguish the mechanisms by which guppy phenotypes (HP vs. LP) affect their environment, improving the understanding of the feedback between evolutionary and ecological processes in nature. |
