Co-existence between Iberian lynx and Egyptian mongooses: estimating interaction strength by structural equation modelling and testing by an observational study

1. We used path analysis to investigate the causal relationships between Ib erian lynx and Egyptian mongoose track numbers, and to estimate the direct effect of the former on the latter in the Donana area (2750 km(2)), south-w estern Spain. Relative abundance of rabbits, shrub cover and protection lev el were also considered in the path analysis. 2. An observational study consisting of a repeated track survey with a spli t-plot design was also carried out between 1990 and 1996 to independently t est the results obtained by path analysis. 3. Maximum likelihood ratio tests of the goodness-of-fit of the model to th e data and other indices used all indicated that the proposed theoretical m odel depicting the relationships among variables was adequate. Egyptian mon gooses suffered a significant direct negative effect from lynx, and rabbits and protection level positively, and significantly affected lynx track abu ndance; rabbits were also significantly affected by shrub cover (all these standardized partial correlation coefficients ranged from 0.34 to 0.41). Sh rub cover did not directly affect either lynx or mongoose tracks. 4. Relatively important indirect effects were found between shrubs and lynx (0.12), and between rabbits and mongooses (-0.14), and protection and mong ooses (-0.17). The two latter non-intuitive indirect effects were through t he lynx path, as a consequence of the negative direct influence of lynx on mongooses. 5. The repeated track censuses confirmed that lynx presence significantly a ffects number of mongoose tracks. In areas without lynx, mean number of mon goose tracks were 3.6 times higher than in areas with lynx. 6. It remains an interesting question which of several proposed hypotheses explains co-existence of both species in south-western Spain.