Effect of introduced spotted deer (Axis axis) on forest floor herpetofauna of Andaman Islands.
Wildlife Institute Of India
The study we carried out focused on the effect of introduced spotted deer (Axis axis) on the forest floor herpetofauna of Andaman Islands. We contrasted the densities of ground dwelling and semi-arboreal reptiles and amphibians in islands with and without the spotted deer. We tried to determine possible pathways of indirect interaction between a mammalian herbivore and insectivorous herpetofauna and the probable consequences of such an interaction.
We sampled the densities of ground dwelling and semi-arboreal herpetofauna in the islands using 31 bound quadrates. Factors that could possibly mediate the relationship between spotted deer and herpetofauna, such as, vegetation cover and arthropod abundance were quantified for each island using a densitometer and the bagging method respectively. The study was carried out for a period of 12 months.
The study showed a contrasting effect of herbivory by spotted deer on reptiles and on amphibians in the Islands during the dry season. Reptiles showed reduced density in the presence of deer (Mean = 7, S.E = 1.43) in comparison to island where deer was absent (Mean = 36.5, S.E = 6.28). Vegetation cover below the maximum browse height of deer (1.5 m) was found to be a mediator of this relationship between deer and reptiles. No such effect was observed in the case of amphibians.
The density of forest floor reptiles were found to be reduced in the presence of spotted deer and seemed to be mediated by a reduction in the understory vegetation cover due to herbivory by the deer. The study highlights the impact of an introduced mammalian herbivore on a starkly different taxonomic group and raises conservation concern about the capability of an introduced species to alter an island ecosystem drastically