Impact of invasive spotted deer (Axis axis) on tropical island lizard communities in the Andaman archipelago

Introduced mammalian herbivores are known to be detrimental to native biodiversity and can alter ecosystem processes, by direct and indirect effects. Island systems, with inherently high rates of extinction are particularly susceptible to the impacts of such herbivores. The introduced spotted deer (Axis axis) is a potential threat to native forest floor and semi arboreal lizards in the Andaman Islands. We evaluated the nature and extent of this potential indirect effect on lizards from 2012 to 2014. We sampled for lizard abundance, arthropod abundance and understory vegetative cover on islands with varying intensity of spotted deer use. We inferred that, spotted deer depressed the abundance of forest floor and semi arboreal lizards approximately five fold, by reducing vegetative cover in the understory. The findings reveal a probable indirect effect of spotted deer on reptile abundance mediated by structural changes in the understory vegetation. The study provides evidence and the impetus for conservation of endemic reptiles in small tropical islands by mitigating the impacts of invasive spotted deer.