Green, John D.Chapman, M. AnnGreenwood, Tracey2026-08-202026-08-201993https://hdl.handle.net/10289/18561The seasonal changes in the plankton communities, and the dynamics and life histories of the Cladocera of Lake Mangakaware, were studied over a period of 19 months, during which time populations were sampled at weekly or two weekly intervals. Lake Mangakaware, a small, polymictic lake in the North Island of New Zealand, is characterised by a high nutrient status, low Secchi transparencies, and an unstable thermal regime. In the algal community, small euchlorophycean genera and diatoms predominated. Peak abundances occurred in autumn and late spring and were due almost exclusively to Tetrastrum triangulare and Aulacosira distans respectively. The frequent mixing events precluded the prolonged abundance of any one species and species replacements were rapid. Small species (< 30 μm) predominated amongst the dominant class (Euchlorophyceae), but there were frequent occurrences of large, unpalatable and/or nutritionally poor genera (Aulacosira, Closterium, Trachelomonas). Amongst the zooplankton, the Copepoda and Rotifera predominated. The rotifer community exhibited a pattern of sharp sequential peaks in the abundance of different species. Maximum density occurred in summer (1989) due almost entirely to Keratella cochlearis. The Copepoda were generally low in abundance in winter, but increased in summer and autumn periods. The four cladoceran species: Bosmina meridionalis; Ceriodaphnia pulchella; C. dubia; and B. longirostris; exhibited disjunct population maxima, with peak abundances occurring in mid summer (1987), autumn (1988), spring (1988), and summer (1989). Only B. longirostris was perennially present. The Cladocera of Lake Mangakaware have life histories which predispose them to success at particular times of the year. All species exhibited low fecundities and lipid scores, indicating that resource availability was low and competitive interactions and starvation resistance were probably important in determining species success. Increases in body size in cooler seasons were correlated with higher egg volumes, but not with higher clutch sizes, giving further support for the view that available food was limited. B. longirostris appears to be the most successful planktonic cladoceran in Lake Mangakaware. It is a small species, but produces relatively large neonates which mature quickly. It appears able to maintain populations for prolonged periods with low fecundity, produces ephippia as a means of persistence, and is not particularly vulnerable to predation from Mesocyclops leuckarti. Its selective feeding mode is probably favoured in Lake Mangakaware, where palatable algal species are in low density or difficult to obtain. B. meridionalis is a less able competitor than its congener and is apparently disadvantaged by long development times at low temperatures. The seasonal success of each of the two species of Ceriodaphnia appears to be partly determined by temperature. C. pulchella was the more abundant species but was restricted to warmer seasons and, like B. meridionalis, has a prolonged development time at low temperature. In contrast C. dubia grows quickly at low temperature. The life history responses of C. pulchella and C. dubia to different food and temperature regimes were examined using two way ANOVA for the treatments: 23°C-high food; 23°C-low food; 13°C-high food; 13°C-low food. Growth, fecundity, and resource allocation were examined and the two species found to be different in critical aspects of their life history. At high resource levels, C. dubia had a higher fecundity than C. pulchella and increased its reproductive effort with age while maintaining a high growth rate. However, at low food levels, C. dubia lost most of this advantage and development times were also considerably prolonged. C. dubia neonates were larger than those of C. pulchella, yet possessed the same amount of lipid for any given regime. C. pulchella, although the smaller of the two species, with generally lower fecundity and longer development times, produced relatively larger neonates than C. dubia. C. pulchella was less responsive to low food level, curtailed growth after maturity, and maintained a rather constant clutch size regardless of food availability. Offspring were quite resistant to starvation and were able to reproduce without provided food, regardless of maternal history. The results suggest that subtle differences in life history can determine seasonal success and competitive outcome between similar species. Very large differences in life history strategy or selection pressure need not be invoked.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Thesis