Table 3. Number of checkerboard units for all the sprawlers’ species pairs.

“Checkerboard units" is any submatrix of the form $\left(\begin{array}{cc}1& 0\\ 0& 1\end{array}\right)or\left(\begin{array}{cc}0& 1\\ 1& 0\end{array}\right)$ between all possible pairs of species occurring at least once in the matrix. Average CU ± Standard Deviation for every species: C.erythraea 59.250 ± 15.041, S. fonscolonbii 30.000 ±13.089, S. sanguineum 18.500 ± 21.763, S. striolatum 28.500 ± 28.618, S. meridionale 26.750 ± 35.845.

Species	S. fonscolonbii	S. sanguineum	S. striolatum	S. meridionale
C. erythraea	44	50	66	77
S. fonscolonbii		13	35	28
S. sanguineum			11	0
S. striolatum				2