3.1 Local dynamics
Ischnura elegans has increased its presence in central Spain over the last ten years. Currently, it is present in 32 provinces (in 8 provinces since at least 1900, in 21 since 1980, and in 32 since 2000; see Fig 1B), and although it is not yet a resident in 15 southern provinces, observations of I. elegans in the field are increasing also in these provinces.
The twelve populations from the Spanish hybrid region were sampled at least four times over a period of 4-10 years (north-central hybrid region) and a period of 4-5 years (north-west hybrid region). Data from this study, and available data from previous studies were compiled as documented in (Supplementary Table S2). In the north-central hybrid region, studied localities were frequently subjected to desiccation (and therefore recolonization) because of water is used for irrigation of neighbouring wine crops, or by management of invasive species (mainly American crab). Cañas, Perdiguero and Villar all periodically dry up, and a recolonization from nearby populations of both species is regularly happening. In fact, Cañas and Villar were emptied and recolonized a couple of years before we sampled them. During the studied 4 years, at least two recolonization events were recorded. In this region, species proportions were unstable, and the seven studied localities were sympatric (at different species proportions) at the end of the study in 2018 (see Table 2). However, although studied localities in the north-central hybrid region were also exposed to recolonization events, but in this case, by natural desiccation (evaporation) or by brought brackish water event (lagoon retro dune), species proportions were stable in the studied period (Table 2).