The Asian toad, Duttaphrynus melanostictus, was accidentally introduced to Toamasina (Eastern Madagascar) around 2010, and since then has spread at a substantial rate across a larger area. This study documents the expansion of the invasive range of this species, calculates the invasion spread rate, and it further estimates the toad abundance and habitat preferences. Updates of the distribution range revealed a fivefold increase of the invaded area during three years, and a doubling of the rate of spread, showing a shift of the invasion towards the North-West, most probably because of the absence of ecological barriers. We used N-mixture models to estimate toad's abundance on the basis of repeated count data of six areas in Toamasina and its surrounding countryside. Toad distribution shows heterogeneous density across the distribution range, with an average abundance of 184 toads ha -1 (95% CI, 132-263). The toad's abundance was highest in sites with the presence of organic waste, and was negatively related to the density of road networks in the proximity of study sites. The rapid expansion of the Asian toad in the Toamasina region suggests that this toad is an increasing threat for Madagascar. We identify immediate management actions that could limit the spread of alien toads in this megadiverse country.

No abstract

No abstract

This is an open access article under the terms of the Creat ive Commo ns Attri butio n-NonCo mmerc ial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

The Asian common toad Duttaphrynus melanostictus has been introduced to the eastern province of Toamasina in Madagascar, where it is feared to be having devastating effects on native communities by poisoning frog-eating predators. So far it was unclear whether the toad can invade forest habitats, and empirical evidence of its impact on native predators was lacking. We used radio tracking to investigate the spatial behaviour of adult toads in a small parcel of lowland humid forest and we quantify the disruptive effects of toad poisoning on a native frog-eating snake, the Malagasy cateyed snake (Madagascarophis colubrinus). We used N-mixture models to estimate the population size of cat-eyed snakes, and used the mortality events recorded in the same area to obtain an estimate of monthly mortality rate of snakes due to toad poisoning.Our results point to severe mortality rate of snakes that, if constant through the year, could halve the predator population, with the potential risk of extirpation. We expect cat-eyed snake populations across rural and suburban areas of Toamasina to be severely affected by the toad invasion, and suggest that future research should investigate the effects of indirect facilitation of human-commensal rodents and the potential repercussions on human health and well-being.