Fig. 3

The effect of within-trophic competition and trophic interactions on alewife morphological evolution and prey abundance in ecosystems with two (a) or three (b) prey clusters. A low eA value indicates a low intensity of within-trophic competition. A low eI value denotes strong trophic interactions. \(\bar {P(A)}\) was the mean frequency of the allele improving growth. \(\bar {P(B)}\) was the mean frequency of the allele increasing alewives’ gill-raker count. Reductions in alewives’ body size substantially improved the efficiency of their foraging for small prey (eb=0.125). Narrow gill-raker spacings did not reduce the efficiency of the alewives’ foraging for large prey (lp=0). Allele frequencies were recorded every 150 years in this figure