Naupliar and copepodite growth and survival of two freshwater calanoids at various food levels: Demographic contrasts, similarities, and food needs

Various demographic responses of Tropodiaptomus spectabilis and Metadiaptomus meridianus (Copepoda: Calanoida) were measured at 17°C at seven food levels of Cryptomonas (0.05–2.5 mg C liter−1). In both species, naupliar, copepodid, and total postembryonic durations declined monotonically, while survivorship, fecundity, and adult size increased asymptotically with rising food supply. M. meridianus matured faster than T. spectabilis up to ∼0.5 mg C liter−1, and its development responses were saturated at lower food levels (∼0.35 mg C liter−1). High naupliar mortality led to lower overall survival in M. meridianus (maximally 40%) than in T. spectabilis (90%). Survival asymptotes varied between ∼0.35 and 0.5 mg C liter−1. Clutch sizes were 5‐fold larger in M. meridianus than in T. spectabilis. Although respective regression estimates of food threshold levels for maturation (11 and 5), egg production (18 and 60), and population increase (46 and 79 µg C liter−1) in T. spectabilis and M. meridianus did not differ, the derived estimates of interspecific equivalence for egg production and population increase (82 and 165 µg C liter−1) suggest that T. spectabilis may be the better competitor below these food levels.