Using public surveys to reliably and rapidly estimate the distributions of multiple invasive species on the Andaman archipelago

Global trade and transport has brought with itself an exponential rise the in introduction of species to regions where they do not naturally occur (i.e., outside their native range). Those populations that manage to establish themselves in the new system and spread have been compared to military invasions of a new land, conferring upon them the tag of ‘biological invasions’. Such ‘invasive species’ can have a myriad of detrimental impact on the native species, by predation, competition and spreading diseases – a phenomenon widely recognized as a major threat to biodiversity.

Developing countries, which harbour a significant proportion of global biodiversity, lack in research and management of biological invasions. To effectively manage invasions, these countries must locate invading populations- rapidly, reliably, and at a large scale. Public surveys, banking on the observations of knowledgeable local inhabitants, can be used to generate such baselines. However, to account for potential species misidentification by the public, such information must be further ‘processed’ to ensure reliability. Using such an approach of including public survey information, we aimed to map the locations of three major human-associated invasive species on the Andaman archipelago – the Giant African snail, the House sparrow, and the Common myna. We interviewed 855 farmers, plantation workers, and aqua-culturists in 91 villages on all major inhabited islands of the archipelago. We asked the respondents to confirm or deny the presence of these species in their village, aiding them with photographs and local names. Simultaneously, we carried out field observations of our own to detect these species at a subset of surveyed villages. We combined both types of data and analysed them using the recently developed false-positive occupancy models. The Giant African snail was most ubiquitous with 90% occupied sites, followed by the myna (60%) and the sparrow (34%). If we had ignored the possibility of misidentifications, we would have over-predicted the geographic range of all three species. This cost-effective method seems appropriate to simultaneously assess the status of multiple invasive species rapidly and reliably over large areas.

Nitya Prakash Mohanty1,2
1 Andaman and Nicobar Islands’ Environmental Team, Wandoor, Andaman and Nicobar Islands, India
2 Centre for Invasion Biology (C.I.B), Stellenbosch University, Matieland X7602, South Africa