Invasive insect colonisation shapes the population distribution of an island‐endemic scaly cricket

Abstract To what extent can island‐native insect populations be shaped by non‐native insects? The Ascension Island scaly cricket Discophallus ascension (Orthoptera: Mogoplistidae) of volcanic Ascension Island in the South Atlantic is abundant on young coastal lava flows. I aimed to assess whether non‐native insect colonisation modified the population distribution of this island‐endemic insect. I trapped insects across 12 sampling blocks/transects spanning coastal and inland sand and lava flows up to 534 000 years in age. I modelled the abundance of D. ascension and compared predicted population distributions with and without the presence of two significant invasive insect taxa: the tropical house cricket Gryllodes sigillatus (Orthoptera: Gryllidae) and ants (Hymenoptera: Formicidae). The invasive insect species disproportionately colonised older and inland lava flows. On flows <10,000 years in age and within 20 m of the coastline, D. ascension population size with invasive insect presence was predicted to be 48.7% relative to without. On flows >10,000 years in age or beyond 20 m inland, D. ascension population size with invasive insect presence was predicted to be just 12.1% relative to without. This suggested that the current D. ascension distribution is partly a result of habitat preference, but largely residual of invasive insect colonisation on older and inland flows. This study demonstrates that apparent habitat specialism of island‐endemic insects may instead indicate extirpation from other habitats by invasive species. Landscape heterogeneity can facilitate some degree of refuge from invasive species that may be slower or unable to colonise certain habitats.