Habitat preferences and niche breadth/overlap
Habitat represents one of the main niche dimension, which has often been
considered in community ecology studies (Morris, 1996). Nevertheless,
most studies conducted to date concerned communities in outdoor
environments, where habitats may differ according to several factors
like vegetation, soil, elevation, among others. Here, room type and
rooms characteristics were chosen as easy-to-describe proxies of habitat
/ microhabitat structure that may be relevant for commensal small
mammals. Indeed, the variables recorded here enable us to distinguish
between categories of domestic spaces, in terms of “privacy” (from
bedrooms to outdoor spaces or shops), type of activities hosted, hiding
places and food resources present. Also, the nature of construction
materials used for rooms can help to distinguish between traditional
(use of clay for floor and walls, and of straw for ceiling) and more
modern buildings (use of concrete for floor and walls, and of corrugated
iron for ceiling), the latter being expected in villages that are more
integrated in commercial networks and directly connected to large
cities, thus more prone to the introduction of exotic rodents (Diagne et
al. 2016, but see Lucaccioni et al. 2016).
Our analyses present M. musculus as more abundant in some room
types (kitchens and stores), especially when built with non-traditional
construction materials (cement and iron, particularly), similarly toM. natalensis in its area of occurrence. These habitat types
contrast with those where A. niloticus is found more often than
expected (granaries and outdoors), which is coherent with the ecology of
the latter species, more abundant in grassy habitats and grain fields in
outdoor environments (Granjon et al., 2013). Arvicanthis
niloticus also shows both the larger niche breadth and the lower mean
overlap with other species. These characteristics may represent
attributes of the “occasional commensal” category of Hulme-Beaman et
al. (2016), of which A. niloticus is probably the most extreme
representative. Interestingly, P. daltoni , which is regularly
found indoors in West Africa (Bryja et al., 2010), has the smallest
niche breadth – being often under-represented in the room types
sampled, and nearly only over-represented in bedrooms, mainly in the
extreme East of the country. This species may suffer from the arrival of
exotic invasive species, and be pushed back into the innermost rooms of
the houses until it is excluded. The only non-rodent species, i.e. the
shrew C. olivieri appears as very catholic in its habitat
preference, being found in all room types in numbers close to those
expected from their proportions in the overall sample. This also
translates in a relatively high value of niche breadth, and also high
niche overlap values with all rodent species. The wide range of habitats
occupied and adaptability of this species have already been underlined
(Churchfield & Hutterer, 2003). The habitat niche overlap with rodent
species here observed probably relates to the fact that this shrew does
not belong to the same ecological guild (sensu Simberloff &
Dayan, 1991) and as such, is probably not submitted to competitive
interactions with them likely to constrain its ecological distribution.
Here, another type of interaction may rather be at work between shrews
and rodents, namely a predator-prey relation: a preliminary
metabarcoding study of the gut and faeces content of C. olivi eri
individuals provides support for such a hypothesis, that would imply
active predation, possibly mostly on neonates or non-active unweaned
juveniles, directed primarily against M. musculus (Galan et al.
2023). Rattus rattus , which was very abundant in stock rooms
where it probably causes important damages to food stuff (see Dossou et
al., 2020 for an example in Cotonou, Benin), presents an average value
of niche breadth compared to other species, and high overlap values with
other species. Using telemetry in a rural area around Berega in
Tanzania, Monadjem et al. (2011) found that within the houses or
buildings they live in, black rats (also called roof rats) were located
in the roof (37% of fixes), in the bedroom (35%), kitchen (14%) and
in walls and windows (14%). Even if some R. rattus were caught
in traps set on top of furniture items or wall tops, we were not able to
quantify the three-dimensional activity of the species known to be at
home in the upper parts of dwellings (Granjon & Duplantier, 2009;
Monadjem et al., 2011). This vertical component of its spatial niche may
however participate to the ecological distribution of the species and
help its coexistence with the other ones. Its tolerance for quite
traditional and rural conditions also makes it a good candidate for
long-term persistence in relatively marginal areas, even in the absence
of intense and regular road traffic (Lucaccioni et al. 2016)
As precised by Colwell & Futuyama (1971), such raw measures of actual
niche breadth and overlap cannot per se give conclusive answers
on the potential competition between coexisting species from a
community. However, they can help formulate hypotheses to be tested via
experimental procedures. In between, co-occurrence analyses may also
help go further in the understanding of actual interspecific
relationships at various spatial scales.