Boots M, PJ Hudson, A Sasaki (2004). Large shifts in pathogen virulence relate to host population structure. Science 303: 842-845. 21. Burger R, A Gimelfarb (2004). The effects of intraspecific competition and stabilizing selection on a polygenic trait. Genetics 167: 1425-1443. Page 1 of 16 EFTA_R1_015