If year == 0, diet data are averaged from suit_styr to suit_endyr If prey_age >= 0 diet data are diet proportion of prey-at-age in predator-at-age If prey_age < 0 diet data are diet proportion of prey-spp in predator-at-age (sum across prey ages) If prey_age < 0 and pred_age < 0, diet data are mean diet proportion of prey-spp in predator-spp (sum across prey ages and take mean across predator ages) If prey_age < 0 and pred_age < -500, diet data are weighted mean diet proportion of prey-spp in predator-spp (sum across prey ages and take weighted mean across predator ages)