Habitat characteristics and species interference influence space use and nest‐site occupancy: implications for social variation in two sister species

Abstract

Nest‐site selection is an important component of species socio‐ecology, being a crucial factor in establishment of group living. Consequently, nest‐site characteristics together with space‐use proxies may reveal the social organization of species, which is critical when direct observation of social interactions is hindered in nature. Importantly, nest‐site choice is expected to be under strong selective pressures and the object of intra‐ and interspecific competition. Although the bulk of research on sociality focuses on its ecological drivers, our study introduces interspecific competition as a potential factor that could influence social evolution. We investigated the influence of habitat and interspecific competition on the social organization of two sister species of the African four striped mouse, Rhabdomys dilectus dilectus and Rhabdomys bechuanae, in a similar macroenvironment. These species diverged in allopatry and occupy distinct environmental niches. We radiotracked 140 adults to identify their nest‐sites, determine nest characteristics and record groups that shared nest‐sites. Group cohesion was estimated from nest‐site fidelity, group association strength, and home range overlap within versus between group members. We compared the two species in sympatry versus parapatry to determine the impact of species interference on sociality. In parapatry, the two species selected distinct nest‐site types, interpreted as different anti‐predator strategies: R. bechuanae selected fewer, spaced, less concealed nest‐sites whereas R. d. dilectus selected clumped and less visible nest‐sites. Rhabdomys bechuanae also showed more cohesive and stable social groups than R. d. dilectus. In sympatry, compared to R. bechuanae, R. d. dilectus occupied similar nest‐sites, however slightly more exposed and clumped, and displayed similar nest‐site fidelity and group association strength. We conclude that although habitat selection may be an important driver of social divergence in Rhabdomys, species interference, by limiting R. d. dilectus movements and forcing nest‐site sharing may induce new ecological pressures that could influence its social evolution.

An update on the distribution and diversification of Rhabdomys sp. (Muridae, Rodentia)

“…Still, we identified that R. d. dilectus occurring in South Africa (Castiglia et al 2011) had a discontinuous distribution, which also seems to characterise its other clades´ distribution in eastern Africa (Sabuni et al 2018). We also documented that some populations of R. (Dufour et al 2015(Dufour et al , 2019.…”

“…Long considered as an opportunistic and generalist genus, we know now that Rhabdomys taxa, having diversified in allopatry, occupy distinct environmental niches (du Toit et al 2012, Ganem et al 2012. Moreover, at least some of these taxa show distinct habitat and microhabitat preferences (Mackay 2011, Dufour et al 2015 and display distinct social behaviour (Schradin & Pillay 2005, Dufour et al 2019).…”

Variation in brain volume in nine populations and three taxa of the African striped mouse Rhabdomys

“…Alternatively, it is also possible that the broad scale of the regions analysed in this study may have masked relationships that are evident at a narrower scale. Recent studies have shown that social context can be more fluid in some populations of R. dilectus because of interference competition with R. bechuanae restricting its availability of nest sites, although group cohesion is weaker than in group‐living R. pumilio (Dufour et al, 2019). In addition, although female R. dilectus have the capacity to form groups in the laboratory, they show higher levels of stress (i.e., higher corticosterone levels) than groups of female R. pumilio (Rimbach et al, 2022).…”

“…Home ranges of female R. d. chakae are six times larger and home ranges of males are 10 times larger than R. pumilio females and males from the Succulent Karoo largely because of the scarcity of food (Schradin & Pillay, 2005). Social organisation is more fluid in R. dilectus ; populations occurring in sympatry with R. bechuanae have restricted availability to nesting sites because of interference competition (Dufour et al, 2019). Additionally, R. dilectus females have the capacity to form groups under laboratory conditions but show high measures of corticosterone than R. pumilio females (Rimbach et al, 2022).…”

African striped mice (Rhabdomys) mind the neighbors.

“…The authors suggest that the behavioral differences between R. pumilio and allopatric R. dilectus are driven primarily by habitat differences, but that the behavior of sympatric R. dilectus requires a different explanation. The authors suggest on the basis of previous findings (Dufour et al, 2015, 2019) that R. dilectus and R. bechuanae , when sympatric, both shift toward selecting microhabitats with greater cover, larger home range size, and higher group cohesion in both species.…”