Co-occurrence analyses
At the global level (i.e. with localities as sites), two significant
patterns of aggregation were revealed, both implying M.
erythroleucus : with C. olivieri (Z = -2.20, p = 0.0274 with
“fixed row–fixed column” [ff] randomization; Z = -2.32, p =
0.0202 with “fixed row-equiprobable column” [fe] randomization),
and with P. daltoni (Z = -2.01, p = 0.0440 with “fe”
randomization). Conversely, five segregation patterns were found
significant using at least one of the two randomization schemes. Four of
them are suspected to be biased by overall differences in spatial
distribution of the species involved, at the scale of southern Senegal:
between M. musculus and P. daltoni , between C.
olivieri and M. natalensis , between R. rattus andM. natalensis , and even more conspicuously between M.
musculus and M. natalensis , which distributions were completely
disjoint at the time of sampling (see Fig. 1). The last one, implyingM. erythroleucus and M. musculus (Z = 3.35, p = 0.00078285
with “ff” randomization, Z = 2.84, p = 0.0044 with “fe”
randomization) is less prone of being influenced by distribution range
differences.
At the locality level (i.e. with “houses” as sites within the 49
localities and districts of Kédougou and Tambacounda, see details in
Table S1), a total of 586 species pair associations were tested. Only 39
(27 with “fe” + 12 with “ff” randomization schemes, respectively) of
them (10.75%) proved to show a significant pattern of segregation or
aggregation, 33 (22 + 11) of which concerned the seven most abundant
species. They are detailed in Table 4. Mus musculus and R.
rattus were involved in most of the segregation cases (13 / 15). In the
large cities (where more than 50 sites were considered in co-occurrence
analyses), a significant segregation was observed between M.
musculus and R. rattus in Tambacounda as well as in two of its
districts, and between M. natalensis and both R. rattusand C. olivieri in Kédougou (where M. musculus is absent).
Conversely, M. musculus was never involved in aggregative
patterns, to the opposite of R. rattus which was regularly found
more often than expected to co-occur with C. olivieri andM. erythroleucus (for instance in Kédougou and Rufisque). Native
species of small mammals also show aggregative patterns in a number of
other localities.