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Functional Response and Fitness in a Generalist Filter Feeder, Daphnia Magna (Cladocera: Crustacea)
Author(s) -
Porter K. G.,
Orcutt J. D.,
Gerritsen J.
Publication year - 1983
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1937196
Subject(s) - daphnia magna , biology , fecundity , functional response , cladocera , daphnia , parthenogenesis , reproduction , ecology , branchiopoda , population dynamics , population , zoology , survivorship curve , predation , zooplankton , predator , demography , embryo , fishery , genetics , chemistry , organic chemistry , toxicity , cancer , sociology
The functional response of an organism is often assumed to maximize its fitness. We examined the relationship between functional response and body growth, survivorship, and reproduction in Daphnia magna under controlled and comparable conditions. In a previous study we determined that D. magna exhibits a Holling Type II functional response with an asymptotic increase in ingestion rate with increasing food concentration to a maximum rate at an incipient limiting concentration of °10 4 Chlamydomonas reinhardi cells/cm 3 (measured as carbon, 0.2 mg/L) and that observed feeding activity does not follow the predictions of energy optimization models. In this study, we determined the fitness response for cohorts of D. magna (n = 20—30) at 0, 10 3 , 10 4 , 10 5 and 10 6 Chlamydomonas reinhardi cells/cm 3 using life table methods. Most parameters indicative of fitness (e.g., body growth, fecundity, survivorship, r, and R 0 ) were maximal at 10 5 cells/cm 3 (2.0 mg/L). The optimum food concentration for growth and reproduction remained at 10 5 cells/cm 3 when cohort life spans were truncated in a simulation of mass mortality due to predation or environmental deterioration. The fitness optimum occurred above the incipient limiting concentration and below the maximum food concentration encountered in nature. These appear to be "suboptimal" behavioral and reproductive responses. However, reproductive models of parthenogenesis and resting egg formation along with these feeding, growth, and reproductive responses suggest that Daphnia track the environment in that they are adapted for rapid population increase and for recovery from mass mortality in cyclical environments in conditions for optimal growth that can be expected to reoccur but are of highly variable duration.