IENE 2016

Human-mediated dispersal acts as a vector for many exotic species, both at the introduction and secondary spread stages. The introduction stage is a consequence of human-mediated long distance dispersal and is known to happen at continental or global scales. Secondary spread occurs at smaller spatial and time scales (e.g. landscape), and can result from natural or human-mediated dispersal . Despite the importance of local goods and materials (e.g. for landscaping, construction, or road-building) transport for the spread of invasive species, few studies have investigated short distance human-mediated dispersal. This lack of consideration seems to be the consequence of multiple factors:

• human-mediated dispersal is generally considered as a long distance dispersal process, more important for invasive species introduction than for secondary spread,
• it is difficult to qualify and quantify this mode of dispersal because of the multiplicity of potentially involved human activities,
• for organisms that can disperse naturally, it is complicated to distinguish between natural and human-mediated dispersal, as they may occur at similar scales.

 Even though a range of methodologies are available for describing population spread by natural dispersal, only few models have been developed to describe and predict human-mediated dispersal consequences at small scales, and none of them take into account the topology of the transport infrastructure (roads, waterways).

Therefore, in order to fill this gap and provide new insights into invasion dynamics, we combined ecological (invasive species occurrence data) and geographical (transportation network topology) data and used a computer modeling and simulation approach to provide estimate frequencies and distances of materials transportations through landscapes.

In the present work, we studied the spreading pattern of Lasius neglectus, an invasive ant species originating from Turkey, which spread into Europe in the last decades. In this species, no mating or dispersal flights are performed, its spread is therefore solely ensured by the transport of soil materials in which individuals are present. We present a numerical model enabling the estimation of multiple human-mediated dispersal parameters, based on ground-truth sampling and a priori minimizing. The first step of this work was to build a model of the landscape-level spreading process taking explicitly into account the topology of the road network. Subsequently, initializing our model with field data, we localized the most probable sites of introduction, the number of jump events, as well as parameters of jump distances linked to the road network. Our model is also able to compute presence probability map, and can be used to calibrate sampling campaigns, explore invasion scenarios, and more generally perform invasion spread predictions. It could be applied to all the species that can be disseminated at local to regional scales by human activities through transportation networks.