Three species of Diaptomus (D. minutus. D. oregonensis and D. sanguineus, in order of increasing size) occur in Clarke Lake, Ontario. The following mechanisms have been suggested in the literature to explain the occurrence of congeneric Diaptomus species; vertical segregation, seasonal separation and size differences. In Clarke Lake D. minutus was found in the upper five metres, separated from D. sanguineus which occurred below the six metre level. A distinct size difference with no overlap was observed between D. minutus and D. sanguineus. D. minutus was also distinctly different from D. oregonensis in size. The seasonal maxima of these two species were distinct, that of D. minutus was in the spring, and of D. oregonensis in the summer months. D. oregonensis was separated seasonally from D. sanguineus. The latter species had a seasonal maximum in the spring. D. oregonensis was found above five metres and so was segregated vertically from D, sanguineus. A combination of two mechanisms seems to enable the coexistence of each of the three Diaptomus species-pairs in Clarke Lake. It is suggested that in general two or more mechanisms must be operative for the co-occurrence of Diaptomus species. / Science, Faculty of / Zoology, Department of / Graduate

Despite high densities in an upstream lake, the herbivorous calanoid copepod, Diaptomus leptopus, is extremely rare in oligotrophia Eunice Lake in the Coastal Range Mountains near Vancouver, British Columbia. In situ experiments conducted in 1979 and 1980 tested the hypothesis that competition from zooplankton species resident in Eunice Lake prevents immigrant D. leptopus from colonizing the lake. Polyethylene enclosures, each holding 29,000 1 of lake water, contained all experimental treatments. Experiments in 1979 exposed a standard density of D. leptopus to all Eunice Lake zooplankton species at lake densities (control), to all Eunice Lake species at reduced densities (low density), and to all Eunice Lake species except one of Daphnia rosea (Daphnia-removal), Diaptomus kenai (kenai-removal), or Diaptomus tyrelli (tyrelli-removal). Improved performances of D. leptopus in non-control treatments was evidence for competition in controls. Measures of performance included density, number of eggs per female, and adult size. Similarity between D. leptopus performances in control, Daphnia-removal, and kenai-removal treatments plus relatively high concentrations of D. leptopus nauplii in the tyrelli-removal treatment suggested that D. leptopus did not compete with species other than D. tyrelli. However, similarity between tyrelli-removal and low density treatments in concentrations of D. leptopus nauplii confounded competition between D. leptopus and D. tyrelli with diffuse competition from several Eunice Lake species combined. D. leptopus overlapped in vertical distribution and seasonal cycle more with D. tyrelli than with other species. Differences' among experimental treatments in algal size compositions did not conclusively show whether zooplankton partitioned food resources. Experiments in 1980, designed to separate D. tyrelli competition from diffuse competition, did not provide any evidence of interspecific interactions. By increasing zooplankton metabolic efficiencies, cool temperatures in 1980 may have virtually eliminated, competition for algal foods. / Science, Faculty of / Zoology, Department of / Graduate

Arctic charr are susceptible to cestodes like Diphyllobothrium dendriticum which are transmitted through the food web. Field studies investigating Arctic charr-Diphyllobothrium relationships often provide little data from which to fully understand Diphyllobothrium transmission or to assess their impact on copepod or fish hosts. Experimental studies may, therefore, be the only direct way to investigate these issues. The research goal of this thesis was to duplicate the D. dendriticum life cycle in the laboratory to investigate parasite development and host specificity, and to apply the experimental data to natural situations. Results indicated that at 10°C, D. dendriticum eggs develop slowly and 65 days are required for complete embryonation. In many Canadian Arctic lakes water temperatures rarely exceed 4°C, and this study has shown that at this temperature embryonation requires several months, necessitating more than one ice-free season for life cycle completion. The results also showed that embryos developed more rapidly and significantly more eggs hatched when incubated with light or aeration, results that were consistent for D. dendriticum originating from Canada and Norway. To continue the life cycle, coracidia must be consumed by suitable copepod hosts. This study showed that although D. dendriticum will infect the European copepods Cyclops scutifer and Eudiaptomus graciloides, prevalence was higher and procercoids developed more rapidly in E. graciloides. These results showed that E. graciloides is a better host for D. dendriticum than is C. scutifer, contradicting published literature. In North America, E. graciloides is not found in lakes containing D. dendriticum and no North American calanoid species have been tested to determine their host suitability to this cestode. This study identified two North American species, Diaptomus minutus and D. leptopus, which are suitable laboratory hosts. D. minutus is almost certainly a natural host for D. den

Copepods live in a nutritionally dilute environment, experiencing temporal and spatial variations in food supply which differ in magnitude and predictability. Understanding the mechanisms by which organisms deal with changes in their food is a primary concern in elucidating the nutritional ecology of zooplankton and the role of food in structuring zooplankton communities. In this thesis, I examine changes in behavior, morphology, and physiology of two species of calanoid copepods (Diaptomus kenai and D. leptopus) in response to variation in food composition and density. In Chapter Two, I present a study of population-level responses to variation in food composition and quality, using fertilization techniques to generate a range of phytoplankton communities in field enclosures. The phytoplankton assemblages studied supported copepod populations which differed in such attributes as population size, reproduction, and body size. The most striking finding of this study was the occurrence of two co-existing size classes of D. kenai, the abundance and clutch size of which varied among the enclosures, suggesting differences between the two classes in their ability to utilize the different phytoplankton communities. Chapter Three investigates patterns of lipid storage in response to changes in food supply. I concluded that lipid stores were affected by species composition of the phytoplankton food and the two copepod species differed in their sensitivity to differences in cell chemistry. Chapter Four investigates behavioral responses of the two size classes of D. kenai to changes in food composition and abundance. Subtle differences in feeding behavior suggest that the two sizes differ in their utilization of available food. These results demonstrate that D. kenai and D. leptopus are capable of responding to changes in their food supply through modifications of their behavior, morphology, and physiology over a range of magnitudes and time scales. There can be very subtle changes in feeding behavior or very pronounced changes in size structure. Responses occur over time scales ranging from hours to days to seasons. These results also bring into question the utility of models generated under laboratory conditions in predicting behaviors or dynamics of copepod populations and communities in nature. / Science, Faculty of / Zoology, Department of / Graduate

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