SUMMARY1 Life history characters (body size of adults, egg diameter, egg sac length and breadth) of nineteen species of central European cyclopoid copepods were measured and sexual size dimorphism (adult female length x adult male length−1), relative egg size (egg weight X body weight−1), weight of adult females and of eggs, egg sac shape (egg sac length x egg sac breadth−1), and reproductive effort (clutch weight produced per female weight per day) were calculated to detect trends in life history strategies.2 Typical planktonic species exhibited the lowest reproductive effort. Among planktonic species, the value for egg sac shape increased with clutch size.3 Large species and small species exhibited different trends in life history characters. Large species had larger clutches, larger eggs, and a greater sex size dimorphism than small species. However, small species had a greater relative egg size.4 Large species live in cold water and reproduce during the spring bloom of phytoplankton where the production of large clutches with relatively small eggs is advantageous. Reserves are unnecessary for juveniles because food is abundant. Small species generally are most abundant during the warm season, when conditions are less predictable, and relatively large eggs, possibly provided with reserves, are