The role of consumer-resource interactions in structuring a small-bodied Cladoceran community: Differential reproduction and survival of Bosmina, Ceriodaphnia, and Daphnia on individual species of phytoplankton.

Abstract

The importance of consumer-resource interactions to the seasonal succession of a resource-limited cladoceran community was investigated in Third Sister Lake, MI, from 1985 until 1987. Field populations revealed a correspondence between the species dynamics of the phytoplankton and zooplankton communities. Cladoceran species composition shifted from Daphnia parvula and Bosmina longirostris dominance to Ceriodaphnia reticulata and D. rosea. These shifts coincided with low particulate carbon concentrations and with a complete shift in algae species composition from chrysophytes and cryptophytes to chlorophytes. Birth rates and juvenile survivorship of B. longirostris and D. parvula were adversely affected by the shift in their phytoplankton resource-base. Ceriodaphnia reticulata responded positively to the changes in algae species composition. Grazing experiments determined that C. reticulata and D. parvula were selective feeders with similar diets. Spongiochloris lamellata, the mid-summer dominant alga, was more important in Ceriodaphnia's diet than in the diet of D. parvula. All cladocera readily consumed chrysophytes and cryptophytes, but B. longirostris had no measurable grazing rates on S. lamellata. In situ survivorship experiments determined that Bosmina juveniles had low mortality rates during the late-spring dominance of Cryptomonas and Chroomonas, but they had high mortality rates when the resource-base was dominated by S. lamellata. In contrast, Ceriodaphnia's survival was unaffected by the change in species composition of the algae. Population-level responses were tested in laboratory life table experiments. Ceriodaphnia and D. parvula were fed S. lamellata or C. ovata at either a high or low total carbon level. Ceriodaphnia demographic parameters were significantly affected by food level but not by food type. D. parvula responded to food level in a similar fashion when fed C. ovata, but had poorer performance on S. lamellata regardless of food level. Ceriodaphnia out-performed D. parvula on S. lamellata but not on C. ovata.