. The Canadian field-naturalist. 1988 MACKIE and TOPPING: UNIONID FAUNA OF THE SYDENHAM RiVER 623 Lasmigona complanata L/W. 10 20 30 40 50 DISTANCE DOWNSTREAM Km 70 Figure 4. Relationship between length/width (L/W) and length/height (L/ H) of Lasmigona complanata and the distance downstream in Bear Creek. The stations used are given in Table 4, Station V being 0 and Station 9 being 65 km downstream. Vertical bars are standard errors of the estimated ratios. stations for all species. However, stepwise linear regression of the length/height ratio with distance downstream yields slopes significan
. The Canadian field-naturalist. 1988 MACKIE and TOPPING: UNIONID FAUNA OF THE SYDENHAM RiVER 623 Lasmigona complanata L/W. 10 20 30 40 50 DISTANCE DOWNSTREAM Km 70 Figure 4. Relationship between length/width (L/W) and length/height (L/ H) of Lasmigona complanata and the distance downstream in Bear Creek. The stations used are given in Table 4, Station V being 0 and Station 9 being 65 km downstream. Vertical bars are standard errors of the estimated ratios. stations for all species. However, stepwise linear regression of the length/height ratio with distance downstream yields slopes significantly different from zero for only A. plicata (Figure 2) and A. g. grandis (Figure 3); the length/height ratios of L. complanata do not correlate (P>) with distance downstream (Figure 4). The stepwise multiple linear regressions indicate that distance is not a highly significant variable in the shell length or width models of any of the three species studied (Table 5). Distance downstream is a significant (P < ) variable in the height models of both A. g. grandis and A. p. plicata from the Sydenham River and L. complanata from Bear Creek, but marginally significant (P = ) in the height model of A. g. grandis from Bear Creek; distance downstream only slightly improves ( P ) the models for length of A. p. plicata and the length and width of L. complanata (Table 5). Species diversity of both living specimens and empty shells in the Sydenham River tends to increase for 85 km downstream, reaching a maximum approximately 10 km southwest of Shetland, Ontario (Figure 5). However, significant variations within this 85 km reach are present. Discussion The Carolinian zone of southwestern Ontario, one of the five most threatened natural regions in Canada, has about one-third of Canada's endangered, threatened and rare species (World Wildlife Fund Canada 1984). The present study indicates that the four rare or endangered unionid I. Please note that these images are
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