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The identification and distribution of two species of Peromyscus in southeastern Ontario Lanko, Joyce Laurian

Abstract

One hundred and sixty-nine mice of Peromyscus leucopus noveboracensis and Peromyscus maniculatus gracilis were examined for characters to best separate them. Each species was obtained from an area in Ontario where it was known to be the only one present. An additional 12 mice of both species were obtained from an area of sympatry. The best characters found to separate them were, in order of importance: ear length, interparietal length, tail length, skull length, and rostral length. Although ear length and interparietal length separated most of the individuals, there were still individuals that could not be separated. The two species were found to be completely separable, using either one of two indices: Ear length X tall length X interparietal length skull length or, Ear length X tail length X interparietal length rostral length. With skull length, P. 1. noveboracensis has an index value of 2.57-4.09 and P. m. gracilis has an index value of 4.26-7.90. With rostral length, P. 1. noveboracensis has an index value of 7.39-12.50 and P. m. gracilis has an index value of 12.83-22.77. Six crossbreeding experiments were attempted between P. 1. noveboracensis and four subspecies of P. maniculatus. The animals were kept together for periods ranging from 71 days to over a year. No offspring resulted. Three pairs of P. leucopus and four pairs of P. maniculatus were kept for the same periods of time in the same room, as a control. One pair of leucopus produced two litters, another pair produced one, and the third pair, none. Two pairs of maniculatus produced one litter each and the two pairs, none. P. m. gracilis was not as excitable or nervous as P. 1. noveboracensis and was therefore easier to handle. Although the ranges of P. 1. noveboracensis and P. m. gracilis differ, the mice meet in a zone of overlap where they occur sympatrically. Correlations were made between the ranges of the mice and vegetation, food preference, temperature tolerance, water requirement, morphology, color of pelage, and behavior. P. m. gracilis was found to occur in coniferous and P. 1. noveboracensis in deciduous vegetation. No correlation was found between the ranges of the mice and food preference, temperature tolerance, water requirement, morphology, and color of pelage. Correlation between the ranges of the mice and their behavior was doubtful. Preliminary tests were made of the ability of one species to discriminate between its odor and that of the other species. Results showed that a mouse entered more often and stayed longer in a chamber containing the odor of its own species. A chamber containing odor of either species was preferred to the control chamber without odor.

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