Species range expansion constrains the ecological niches of resident butterflies

Abstract

Changes in community composition resulting from climate change entail modifications of biotic interactions and reshape local species distributions. Such changes are currently occurring in nettle-feeding butterflies in Sweden where Araschnia levana has recently expanded its range northward and is now likely to interact with the resident species (Aglais urticae and Aglais io). Butterfly occurrence data collected over years and across regions enabled us to investigate how a recent range expansion of A. levana may have a↵ected the environmental niche of resident species. • We focused on two regions of Sweden (Skåne and Norrström) where A. levanahas and has not established, and two time-periods (2001)(2002)(2003)(2004)(2005)(2006)(2009)(2010)(2011)(2012) corresponding to before and after its establishment.• We performed two distinct analyses in each region using the PCA-env and the framework described in Broennimann et al. (2012). We first described the main sources of variation in the environment. Second, we characterized, in each timeperiod and region, the realized niches of our focal species across topographic and land use gradients. Third, we quantified overlaps and di↵erences in realized niches between and within species over time.• We found indications of niche partitioning between native species, although niche di↵erentiation was not clearly associated to specific environmental factors. Looking over time, we found a larger shift in species distributions of the resident species in Skåne than in Norrström. These shifts showed a consistent pattern of avoiding overlap with the environmental space occupied by A. levana, and it was stronger for A. urticae than for A. io.• Interspecific interactions play a role in shaping species distributions. It seemed clear that the range expansion of A. levana modified local biotic interactions, and potentially induced shifts in resident species distribution. We suggest that parasite-driven apparent competition may mediate niche partitioning in this community.

Altered parasitism of a butterfly assemblage associated with a range-expanding species

“…levana and V. atalanta. Previous work on this study system hypothesized that a change in 408 the composition of this community, namely, the arrival of A. levana, would influence the 409 dynamics and spatial distribution of the resident butterflies through apparent competition 410(Audusseau et al, 2017). The association between host community composition and parasitism 411 of A. io and A. urticae is consistent with this prediction.…”

Climate change and local host availability drive the northern range boundary in the rapid northward expansion of the eastern giant swallowtail butterfly

“…Poleward range shifts in herbivorous insects, particularly butterflies, have been documented for a number of species (Parmesan et al , 1999;Warren et al , 2001;Pöyry et al , 2009;Breed et al , 2012) . Additionally, northward expansions of other butterfly species have been shown to have dramatic impacts on community composition through linked biotic interactions (Audusseau et al , 2017) , which could be happening in this system as well, but would require further examination to determine. While studies demonstrating range shifts in multiple taxa provide valuable insights into the magnitude and direction of shifts for different taxa, gaps in knowledge remain (Pöyry et al , 2009) .…”