It

H. ulvae

H. ventrosa

H. ulvae

H. ventrosa j_i_i_i_i_i_i_i_i_i_i_i_i_i_i_i_i_i_i_i_l

0.0 0.0 1.5 4.1 4.3 10.7 26.3 40.3 84.1 93.1 97.5 0.0 0.2 2.1 4.3 9.3 24.2 27.5 45.0 92.2 93.3 Percentage H. ventrosa

"S 60

0.0 0.0 1.5 4.1 4.3 10.7 26.3 40.3 84.1 93.1 97.5 0.0 0.2 2.1 4.3 9.3 24.2 27.5 45.0 92.2 93.3 Percentage H. ventrosa

"S 60

Location

population (Figure 8.26b). When the two-species site was cleared of T. repens only, the re-planted T. repens grew better than the transplanted clover-alone plants (treatments 1 and 4, respectively; P = 0.086, close to significance), suggesting that the transplanted plants were competing more with the resident L. perenne. Moreover, when L. perenne was also removed, this made no difference to the two-species T. repens (treatments 4 and 5; P > 0.9), but led to a large increase in the growth of the clover-alone plants (treatments 1 and 2; P < 0.005). Also, when L. perenne was removed, the clover-alone plants grew better than the two-species ones (treatments 2 and 5; P < 0.05) - all of which suggests that only the clover-alone plants were released from competition by the absence of L. perenne. Finally, at the clover-alone site, the two-species clover plants grew no better than they had at their

Figure 8.25 Character displacement in body size. (a) Mud snails in Finland (average lengths of Hydrobia ulvae and H. ventrosa, arranged in order of increasing percentage of H. ventrosa). (After Saloniemi, 1993.) (b) Giant rhinoceros beetles in southeast Asia (average lengths of Chalcosoma caucasus and C. atlas). (After Kawano, 2002.) In each case in allopatry, body sizes overlap broadly, but in sympatry body sizes are significantly different.

home site (treatments 4 and 6; P > 0.7), whereas the clover-alone plants grew far better than they had at the two-species site in the presence of the grass (treatments 1 and 3; P < 0.05). Thus, the clover from the two-species population hardly competes with the L. perenne with which it coexists, whereas the clover-alone population would do - and does so if transplanted to the two-species site.

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