Table 2.

Occurrence of transitions according to substrate (number in parenthesis stands for the percentage of each case). (a,b) Tables showing the number of experiments showing no, one or both morphological transitions. (a) Table for granular substrate (n = 24). (b) Table for cohesive substrate (n = 25). (c) Tables (a,b) have been merged into one 2 × 2 contingency table (n = 49) to remove sampling zeroes and test with χ² analysis, the independence of presenting both transitions against the substrate (χ² = 11.038, d.f. = 1, p = 0.00089, occurrence of both transitions is not independent of substrate).

(a) granular
second transition	first transition
	yes	no
yes	12 (50%)	0 (0%)
no	5 (21%)	7 (29%)
(b) cohesive
	first transition
second transition	yes	no
yes	24 (96%)	0 (0%)
no	1 (4%)	0 (0%)
(c)
	transitions
substrate	both	else
sand	12 (50%)	12 (50%)
clay	24 (96%)	1 (4%)