Title: Species Range Expansion Constrains the Ecological Niches of Running Header: Range Expansion and Changes in Species Interactions

21 Aim Changes in community composition resulting from environmental changes modify biotic 22 interactions and affect the distribution and density of local populations. Such changes are currently 23 occurring in nettle-feeding butterflies in Sweden where Araschnia levana has recently expanded 24 its range northward and is now likely to interact with the resident species (Aglais urticae and Aglais 25 io). Butterfly occurrence data collected over years and across regions enabled us to investigate 26 how a recent range expansion of A. levana may have affected the environmental niche of resident 27 species. 28 Location We focused on two regions of Sweden (Skåne and Norrström) where A. levana has and 29 has not established, and two time-periods (2001-2006, 2009-2012) during its establishment in 30 Skåne. 31 Methods We performed two distinct analyses in each region using the PCA-env and the framework 32 described in Broennimann et al. (2012). First, we described the main sources of variation in the 33 environment. Second, in each time-period and region, we characterized the realized niches of our 34 focal species across topographic and land use gradients. Third, we quantified overlaps and 35 differences in realized niches between and within species over time. 36 Results In Skåne, A. levana has stabilized its distribution over time while the distribution of the 37 native species has shifted. These shifts depicted a consistent pattern of avoiding overlap between 38 the native species and the environmental space occupied by A. levana, and it was stronger for A. 39 urticae than for A. io. In both regions, we also found evidence of niche partitioning between native 40 species. 41 peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/026765 doi: bioRxiv preprint first posted online Sep. 14, 2015;