Using public surveys to rapidly profile biological invasions in hard-to-monitor areas

Understanding the impact and dynamics of invasive alien species (IAS) is essential for tailoring appropriate management plans. This information can be difficult to obtain in the short term, and intrinsic difficulties of monitoring hard-to-reach areas may hamper prompt estimation of IAS distributions. Using the case of the invasive Asian common toad (Duttaphrynus melanostictus) in Madagascar, we show how public surveys coupled with a multi-analytical approach can promptly provide accurate information on invasion dynamics and impacts. On the basis of key- informant responses, we built polynomial regressions to investigate the spatiotem- poral invasion patterns, false-positive occupancy models to estimate species occu- pancy, and mixed-effect models to evaluate the public perception and attitudes. The invasion followed a linear expansion of approx. 2 km year 1 , with human- mediated dispersal facilitating the spread of the species. Toad occupancy decreased towards the invasion front and increased in the southern portion of its range. Nega- tive perception decreased in urban areas, where people were less concerned by toad impacts on ecosystems, and in recently invaded localities, suggesting density- or time-dependent effects. We also identified 12 potential impacts, with “loss of domestic apiaries”, “poisoning of poultry” and “decline of snakes” standing out for prevalence and potential severity. Our results bring important insights into the inva- sion dynamics and the human-toad interactions in Madagascar, highlighting the versatility of public surveys to obtain essential information for invasion science and management, which can be especially useful in hard-to-monitor regions of the world with a low in-country capacity to counter invasive species.