Comparisons of sympatric reptile species were used to assess the variation in niche overlap for food between potential competitors at different trophic levels. Omnivorous tortoises and carnivorous vipers inhabiting the rain-forest region of West Africa were used as study models. Food niche overlap between species increased with habitat alteration in both the independent study systems: tortoises (Kinixys homeana and Kinixys erosa) and vipers (Bitis gabonica and Bitis nasicornis) showed lower values of Pianka's niche overlap index in the pristine habitat than in the altered habitat, and these differences in overlap values did not depend on chance after Monte Carlo simulations. There were higher inter-habitat food niche overlaps within-species than between-species. Permutation tests (assessed after 5000 iterations) revealed that, for both study systems, the P-values became significantly smaller with fewer resource states, thus showing the niche overlap between species really increases after habitat alteration. The observed increases in food niche overlap between species accomplished with rain-forest habitat degradation in turn may be predicted to have cumulative effects on reducing the level of forest biodiversity.