What Is on the Menu When You Move Far Away? Realised Diet Niche in a Geographic‐Range‐Expanding Ant‐Eating Spider

ABSTRACT Aim Diet represents a fundamental dimension in a species' ecological niche, helping to define where it occurs over space. This is especially apparent in diet specialists, which can be restricted by the limited range of resources they are able to use. Specialists are therefore rarely involved in cases of geographic range expansion, although this may occur as exemplified by the myrmecophagous spider Zodarion rubidum Simon, 1914, which spread from southern France to the rest of Europe in a few decades. In this study, we assessed the trophic niche of this specialist predator over its range. Specifically, we investigated its realised diet niche on a broad spatial scale, using dietary metabarcoding on field‐collected individuals. Location Thirty‐seven localities throughout Europe and North America. Taxon Zodarion rubidum Simon, 1914 (Araneae: Zodariidae). Methods We first compared diet compositions between populations using an ordination method. We then interpolated the phylogenetic diversity of preyed items over space as a measure of diet niche breadth, as well as the probability of being preyed upon by Z. rubidum in the study area for the most consumed prey, using ordinary kriging. Finally, we tested for a spatial trend in diet breadth using a linear model. Results We found that Z. rubidum remains strictly myrmecophagous over space; its populations have similar diets; and its diet breadth is consistent across the distribution range. Interestingly, Z. rubidum tends to feed more on Myrmicinae ( Tetramorium ants) towards north‐eastern Europe, suggesting that it has a broader fundamental diet niche than expected. Main Conclusion Overall, Z. rubidum does not seem to be restricted by its diet specialisation along its geographic range expansion.