The social association of the translocated elephants (excluding independent adult males) with conspecifics (both locals and translocated) decreased with time (random effects-mixed model: R=−0.56, n=385; ‘time’: F1,381=7.12, p=0.008; ), supporting the BSNE hypothesis. The translocated elephants associated with more conspecifics during the wet than dry seasons (‘season’: F1,380=28.63, p<0.0001; ). The random effect ‘elephant identity’ accounted for 15.7 per cent of the data's variance, suggesting that there was individual variation among the translocated elephants in the initial number of conspecifics they associated with.
Figure 1 Relationship between social association and time. The number of conspecifics (locals and translocated) that translocated elephants associated with decreased over time (R=−0.56, p=0.008). Shaded background denotes wet seasons and white background (more ...)
Body condition of the translocated elephants (excluding calves and adult males) positively correlated with the number of individuals with whom they associated and with time (random effects-mixed model: R=0.64, n=151; ‘association with conspecifics’: F1,147=7.48, p=0.007; ‘time’: F1,147=11.21, p=0.001), suggesting that elephants gain direct benefits from sociality. The random effect ‘elephant identity’ accounted for 23.9 per cent of the data's variance, suggesting that there was individual variation among the translocated elephants in their initial body condition.
The translocated elephants and the local Tsavo residents were socially segregated. The translocated elephants associated with one another throughout the study period (). Translocated family groups captured separately associated significantly more with one another than expected according to the permutation model and less than expected with local resident groups (Χ2 test: Χ42=680.45, p<0.001; ). Moreover, a significant negative correlation was found between the translocated elephants' association with the local elephants (AL) and their WD as a measure of their association with other translocated elephants (Pearson correlation coefficient test: R=−0.35, n=56, p=0.007). In other words, the more a translocated elephant associated with other translocated elephants, the less it associated with the local elephants and vice versa.
Figure 2 Social network of translocated elephants. Network nodes represent individual translocated elephants and connecting edges denote their social association (AI). Elephants captured together, as an intact social unit, are represented in the same colour. Node (more ...)
Figure 3 Bond group formation. Log of the ratio between the observed and expected (as computed by the permutation model) number of times translocated elephant groups were seen alone (T); translocated groups captured separately associated with one another (TT); (more ...)
The translocated elephants did not gain inclusive fitness benefits from forming bond groups with familiar conspecifics. Genetic relatedness between elephants captured together was on average, X
±s.e.=0.13±0.02, similar to the relatedness found within the family groups of undisturbed African elephant populations (Archie et al. 2006
). This finding supports our grouping method for the translocated elephants in the permutation model. By contrast, average genetic relatedness among the translocated elephants belonging to separate groups was X
±s.e.=−0.02±0.003. In relatedness analysis using microsatellite data, negative relatedness values indicate with high confidence that two individuals are unrelated (Konovalov & Heg 2008
). The difference between the relatedness of elephants captured together and those captured apart was statistically significant (Student's t
=0.002). In addition, the social association (AI) between the translocated elephants captured together correlated positively and significantly with their genetic relatedness (Pearson correlation coefficient test: R
=60 pairs, p
<0.001), as one might expect based on the previous work (Archie et al. 2006
). However, the social association (AI) between the translocated elephants belonging to separate family groups did not significantly correlate with their genetic relatedness (Pearson correlation coefficient test: R
=32 pairs, p
The social segregation between the translocated elephants and the local population did not persist over time. The average WD of the translocated elephants decreased significantly between the long dry season of 2005 and that of 2006 (Wilcoxon signed-rank test: T=101, n=80, p<0.0001; a). Furthermore, the association of the translocated elephants with the locals (AL) was more frequent during the long dry season of 2006 than that of 2005 (Wilcoxon signed-rank test: T=1.5, n=14, p=0.04; b). Thus, the translocated elephants transitioned from a closed immigrant enclave to integrating into an existing social structure.
Figure 4 Change in association with translocated and local elephants over time. (a) Average weighted degree (WD), as a measure of association among translocated elephants, was significantly higher during the long dry season of 2005 than that of 2006 (p<0.0001, (more ...)