NAUPLIAR AND COPEPODITE GROWTH AND SURVIVAL OF 2 FRESH-WATER CALANOIDS AT VARIOUS FOOD LEVELS - DEMOGRAPHIC CONTRASTS, SIMILARITIES, AND FOOD-NEEDS

Various demographic responses of Tropodiaptomus spectabilis and Metadi aptomus meridianus (Copepoda: Calanoida) were measured at 17 degrees C at seven food levels of Cryptomonas (0.05-2.5 mg C liter(-1)). In bot h species, naupliar, copepodid, and total postembryonic durations decl ined monotonically, while survivorship, fecundity, and adult size incr eased asymptotically with rising food supply. M. meridianus matured fa ster than T. spectabilis up to similar to 0.5 mg C liter(-1), and its development responses were saturated at lower food levels (similar to 0.35 mg C liter(-1)). High naupliar mortality led to lower overall sur vival in M. meridianus (maximally 40%) than in T. spectabilis (90%). S urvival asymptotes varied between similar to 0.35 and 0.5 mg C liter(- 1). Clutch sizes were 5-fold larger in M. meridianus than in T. specta bilis. Although respective regression estimates of food threshold leve ls for maturation (11 and 5), egg production (18 and 60), and populati on increase (46 and 79 mu g C liter(-1)) in T. spectabilis and M. meri dianus did not differ, the derived estimates of interspecific equivale nce for egg production and population increase (82 and 165 mu g C lite r(-1)) suggest that T. spectabilis may be the better competitor below these food levels.