Measures of food quality as demographic-predictors in fresh-water copepods
Abstract:
This study examines the ability of a number of short-term measures of algal food quality to predict longer term demographic parameters for two species of freshwater calanoid copepods, Diaptomus minutus and Epischura lacustris. Food quality of two species of algae that are usually considered highly edible (Cryptomonas erosa var, reflexa and Chlamydomonas reinhardtii) are compared with respect to: (i) the biochemical constituents of the algae (total N, total C and protein); (ii) short-term foraging responses by D.minutus to either algal species (e.g. clearance, ingestion and assimilation rates); (iii) longer term demographic responses (e.g. survivorship and reproduction) by both D.minutus and E.lacustris fed a diet of either algal species. Demographic responses of the two copepod species indicate that C.erosa is a higher quality food. In fact, survival and reproduction of both copepod species fed C.reinhardtii were not different from starved treatments. Cryptomonas erosa treatments also had greater C, N and protein. However, D.minutus ingested five times more C.reinhardtii than C.erosa, indicative of 'compensatory feeding' in the presence of poor-quality food. Based upon these higher ingestion rates, individuals fed C.reinhardtii actually ingested greater amounts of C, N and protein. Hence, ingestion rates taken alone or coupled with biochemical parameters are not reliable predictors of consumer demographic response. Assimilation rate, which was positive for C.erosa and zero for C.reinhardtii, was the single best short-term predictor of food quality.
Chen CY, Folt CL, Journal of Plankton Research, 15 (11): 1247-1261 NOV 1993
This study examines the ability of a number of short-term measures of algal food quality to predict longer term demographic parameters for two species of freshwater calanoid copepods, Diaptomus minutus and Epischura lacustris. Food quality of two species of algae that are usually considered highly edible (Cryptomonas erosa var, reflexa and Chlamydomonas reinhardtii) are compared with respect to: (i) the biochemical constituents of the algae (total N, total C and protein); (ii) short-term foraging responses by D.minutus to either algal species (e.g. clearance, ingestion and assimilation rates); (iii) longer term demographic responses (e.g. survivorship and reproduction) by both D.minutus and E.lacustris fed a diet of either algal species. Demographic responses of the two copepod species indicate that C.erosa is a higher quality food. In fact, survival and reproduction of both copepod species fed C.reinhardtii were not different from starved treatments. Cryptomonas erosa treatments also had greater C, N and protein. However, D.minutus ingested five times more C.reinhardtii than C.erosa, indicative of 'compensatory feeding' in the presence of poor-quality food. Based upon these higher ingestion rates, individuals fed C.reinhardtii actually ingested greater amounts of C, N and protein. Hence, ingestion rates taken alone or coupled with biochemical parameters are not reliable predictors of consumer demographic response. Assimilation rate, which was positive for C.erosa and zero for C.reinhardtii, was the single best short-term predictor of food quality.
Chen CY, Folt CL, Journal of Plankton Research, 15 (11): 1247-1261 NOV 1993
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