Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Populations of the crayfish Cambarus bartoni from six lakes in Algonquin Provincial Park, Ontario were compared to evaluate the influence of an introduced predator, the smallmouth bass Micropterus dolomieui. Bass were introduced into lakes in the southern portion of the park in the late 1800's and early 1900's. Crayfish populations from three lakes containing bass were contrasted with populations from three lakes without bass.;Comparisons of relative abundances, patterns of habitat use and length-frequency distributions were compromised by seasonal changes in crayfish trappability and differences in crayfish species composition. Catches of C. bartoni in baited traps were lower in lakes containing bass and in lakes with greater numbers of co-occurring crayfish species. The presence of bass did not affect trap catches of C. bartoni from different habitats. Length-frequency distributions of trap catches varied among lakes with no consistent pattern associated with the presence of bass, but trap catches contained proportionately more large crayfish in lakes with more crayfish species.;Frequency of cheliped loss among populations of C. bartoni was highest in lakes with more crayfish species. Only females displayed increased incidences of claw loss in lakes with bass. Female C. bartoni in two lakes containing bass were characterized by a smaller size at sexual maturity. Females from the third lake with bass exhibited a size at maturity similar to populations from lakes without bass, yet smaller females produced proportionately more eggs than similarly sized females in any of the other lakes. Ovarian egg counts indicated that size-specific fecundity was higher among populations from lakes containing bass. However, the magnitude of the increase in fecundity ranged from 4 to 35% above values from populations in lakes without bass.;C. bartoni from lakes containing bass differed morphologically from crayfish in lakes without bass. Populations experiencing bass predation displayed a common form characterized by a more robust carapace, larger chelipeds and a smaller rostrum. The magnitude of sexual dimorphism was reduced in lakes with more crayfish species. However, the presence of bass reduced the influence of the number of crayfish species and enhanced sexual divergence in morphology.



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