Rapid dung removal by beetles 185
TABLE 3 Summary of the full and optimal generalized linear models used for testing the effects of factors causing dung to disappear, season and dung pile diameter on dung survival time. Models were fitted with a gamma error distribution.
Explanatory variables
Main factor Beetles
Leaf cover Rainfall
Season
Minor wet Minor dry Major wet
Log(diameter)
Cephalophus spp. Intercept
Main factor Beetles
Leaf cover Rainfall
Season
Minor wet Minor dry Major wet
Log(diameter)
FIG. 4 Distribution of dung survival time for (a) the blue duiker and (b) red duikers by the main factors causing dung to disappear and by season. The horizontal bar and upper and lower box edges indicate the 50, 75 and 25% quantiles, respectively. The whiskers denote 1.5 times the inter-quartile range.
Dung beetles, the main factor responsible for the removal
of dung piles, preferred fresh dung (Table 2, Fig. 4). In all seasons, dung beetles removed high proportions of fresh dung piles within a few hours of deposition, and other dung piles remained until they disappeared as a result of other factors. This finding is consistent with studies that showed rapid removal of dung by beetles in Gabon (White, 1994; van Vliet et al., 2009) and Congo-Brazzaville (Breuer et al., 2009, 2021) (Supplementary Table 3). As van Vliet et al. (2009) argued, intense beetle activity can consis- tently hide duikers. Dung survival time for red duikers and for the blue dui-
ker was up to five and six times longer, respectively, in the major dry season than in the minor wet season. Even within each season, dung survival time was highly variable, ranging from a few hours to$5 weeks. In Gabon, White (1994)has also noted a wide range of dung survival time for red duikers (up to 2 months) in the dry season. However, our analysis withGLMs showed that dung sur- vival time was more directly influenced by beetle activity
Full model Optimal model Estimate ± SE Estimate ± SE
Philantomba monticola Intercept
2.01 ± 0.42 2.13 ± 0.25 t P 8.47 ˂ 0.001
−2.15 ± 0.26 −2.26 ± 0.27 −8.44 ˂ 0.001 −0.04 ± 0.34 −0.05 ± 0.35 −0.16 n.s. −0.75 ± 0.36 −1.00 ± 0.37 −2.69 ˂ 0.001
−0.47 ± 0.23 −0.48 ± 0.28
0.01 ± 0.23 0.11 ± 0.17
−0.53 ± 0.30 −0.51 ± 0.30 −1.73 n.s. −0.69 ± 0.24 −0.67 ± 0.23 −2.92 ˂ 0.005
−0.51 ± 0.20 −0.39 ± 0.19 −2.07 ˂ 0.05 −0.18 ± 0.22 0.03 ± 0.19
0.16 n.s.
−0.20 ± 0.19 −0.08 ± 0.18 −0.49 n.s. 0.24 ± 0.13
than by season or dung pile size. Therefore, as beetle abun- dance and activity are likely to vary between regions, the use of dung survival time calculated in a given locality to esti- mate duiker density in another locality may be inappropri- ate, even if a dung count survey is carried out in the same season as the estimation of dung survival time. Dung pile diameter had no significant effect on dung survival time, suggesting that beetles removed dung piles independently of their size. Dung survival time tended to be longer in the major dry
season, probably because the proportion of dung piles that beetles removed was significantly lower because of the rapid drying of dung pellets and the low abundance of beetles (Andresen, 1999; van Vliet et al., 2009). Conversely, during wet seasons, beetles were probably more abundant, dung moisture remained high for longer periods and therefore beetles removed dung piles of a wider age range (Fig. 4), re- sulting in a shorter dung survival time than in dry seasons. Some previous studies estimated mean survival time of 1–
4 days, even in the major dry season (Breuer et al., 2009; van Vliet et al., 2009). Our estimates for mean survival time in the major dry season were higher than this. There are three possible reasons. Firstly, beetles may have been more abun- dant and active even in the dry season in the areas where these previous studies were carried out, or the forest under- storey in south-east Cameroon is dryer than in these other
Oryx, 2023, 57(2), 180–187 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001599
1.81 ± 0.33 2.31 ± 0.19 12.21 ˂ 0.001 −2.01 ± 0.17 −2.04 ± 0.16 −12.56 ˂ 0.001
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