Date of Award


Publication Type

Master Thesis

Degree Name



Earth and Environmental Sciences

First Advisor

Aaron Fisk

Second Advisor

Trevor Pitcher




This dissertation demonstrates that diet discrimination factors (DDF) have a strong negative correlation with stable isotope values in food for d15N (slope=-0.59±0.02, r2=0.95) and d13C (slope =-0.56±0.02, r2=0.94). Based on these results, a reliable DDF was used to evaluate the influence of predation on the trophic ecology of wild guppy populations in Trinidad. The trophic position of the guppies was 2.7 and did not differ between high- and low-predation sites (p=0.77). Nevertheless, high-predation populations had significantly higher proportions of the fatty acids associated with algae than low-predation populations which had higher proportions of fatty acids associated with invertebrates (p= 0.005). Additionally, standard ellipse area, a measure of isotopic niche width, was greater at high-predation sites compared to low-predation sites within Quare (p<0.001), Turure (p=0.003) and Tacarigua/Tunapuna (p=0.016) but not Aripo (P=0.19). Therefore, low-predation guppy populations appear to have diets more specialized on invertebrates, while high-predation guppies consume resources more indiscriminately.