The impact of the invasive tree Cedrela odorota on the Electric Blue Gecko (Lygodactylus williamsi) and its habitat (Pandanus rabaiensis) in Kimboza Forest Reserve, Tanzania

Abstract

Non-native plants are a major cause of habitat loss and fragmentation that lead to biodiversity loss. Geckos are particularly vulnerable to habitat alterations due to their small range and their restricted and specific terrestrial habits. However, our understanding of how introduced plants affect geckos, is poor. In this study, we investigate the potential effects of non-native and invasive neo-tropical tree Cedrela odorata on the critically endangered electric blue gecko, Lygodactylus williamsi, and its sole habitat, Pandanus rabaiensis. We used 107 square (10 m x 10 m) sample plots distributed systematically throughout the forest to assess the extent and effects of C. odorata on P. rabaiensis forest patches. We compared the abundance of L. williamsi on 125 P. rabaiensis trees growing in a mixture with C. odorata, native trees, and in pure stands and at three canopy cover categories (0–30%, >30–50%, and > 50%). We found an inverse relationship between the abundance of C. odorata trees (diameter at breast height (DBH)> 10 cm) and the abundance of P. rabaiensis. Spatially, the two trees dominated different parts of the forest. In contrast, the abundance of L. williamsi was not significantly affected by the presence of C. odorata. However, change in the canopy cover of the trees growing above the P. rabaiensis significantly affected the abundance of L. williamsi. The abundance of L. williamsi in a 0–30% cover was significantly higher than 30–50% and > 50% canopy covers. The findings of this study suggest that if left unmanaged, C. odorata could continue to take up the space that could be occupied by P. rabaiensis and other native plants, and thus limit the population size of an endangered species.