Abstract
Climate change and invasive species threaten biodiversity, yet rigorous monitoring of their impact can be costly. Citizen science is increasingly used as a tool for monitoring exotic species, because citizens are geographically and temporally dispersed, whereas scientists tend to cluster in museums and at universities. Here we report on the establishment of the first exotic ant taxon (Tetramorium immigrans) in Denmark, which was discovered by children participating in The Ant Hunt. The Ant Hunt is a citizen science project for children that we ran in 2017 and 2018, with a pilot study in 2015. T. immigrans was discovered in the Botanical Garden of the Natural History Museum of Denmark in 2015 and confirmed as established in 2018. This finding extends the northern range boundary of T. immigrans by almost 460 km. Using climatic niche modelling, we compared the climatic niche of T. immigrans in Europe with that of T. caespitum based on confirmed observations from 2006 to 2019. T. immigrans and T. caespitum had a 13% niche overlap, with T. immigrans showing stronger occurrence in warmer and drier areas compared to T. caespitum. Mapping the environmental niches onto geographic space identified several, currently uninhabited, areas as climatically suitable for the establishment of T. immigrans. Tetramorium immigrans was sampled almost three times as often in areas with artificial surfaces compared to T. caespitum, suggesting that T. immigrans may not be native to all of Europe and is being accidentally introduced by humans. Overall, citizen scientists collected data on ants closer to cities and harbours than scientists did and had a stronger bias towards areas of human disturbance. This increased sampling effort in areas of likely introduction of exotic species naturally increases the likelihood of discovering species sooner, making citizen science an excellent tool for exotic species monitoring, as long as trained scientists are involved in the identification process.
Highlights
The introduction and establishment of new species outside of their native range, which go on to become invasive, threaten biodiversity (IPBES, 2019)
Tetramorium immigrans Tetramorium immigrans was first discovered in the Botanical Garden of the Natural History Museum of Denmark (55.69, 12.57) during a pilot run of the citizen science project in 2015 and was confirmed to be established and spreading in 2018 and 2019
Climatic niches of T. immigrans and T. caespitum Environmental niche overlap between T. immigrans and T. caespitum, measured as D, which compares the frequency of observations for each species within the chosen climatic categories, was 13% with only a slight difference of the niche centroid in environmental space (Fig. 3A)
Summary
The introduction and establishment of new species outside of their native range, which go on to become invasive, threaten biodiversity (IPBES, 2019). Citizen science can help to document introduced species in general, but in some of the habitats typically missed by traditional surveys. In Denmark, 80% of foreign trade goes through Danish industrial harbours (Danske Havne, 2017). Among other products, these ships carry agricultural products, fodder and fertilisers through which new species can be introduced. While general surveys in cities and harbours can be difficult, these are some of the habitats most available to citizen scientists
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