Models of N excretion (A; size-corrected and log-transformed), P excretion (B; size corrected and log-transformed), and excretion N:P (C; log-transformed).

All models include ‘river’ as a random effect, to account for differences between guppies from the Aripo and Guanapo Rivers in age, rearing environment, and background genetics. Variation in P excretion and excretion N:P suggests independent influences of diet and ancestral predation, while variation in N excretion suggests only an influence of predation. Model support for predation effects on N excretion was strong (removing predation LRT: df = 1, χ2 = 6.68, p = 0.01). Model support for diet and predation effects on P excretion was also strong (removing predation LRT: df = 1, χ2 = 10.2, p = 0.001; removing diet LRT: df = 1, χ2 = 22.7, p < 0.001). Model support for diet effects on excretion N:P was strong (LRT: df = 1, χ2 = 19.0, p < 0.001) but support for predation effects on excretion N:P was weak (LRT: df = 1, χ2 = 2.35, p = 0.13).