Evaluating range-expansion models for calculating nonnative species’ expansion rate

1. Species range shifts associated with environmental change or biological invasions are increasingly important study areas. However, quantifying range expansion rates may be heavily influenced by methodology and/or sampling bias. 2. We compared expansion rate estimates of Roesel’s bush-cricket (Metrioptera roeselii, Hagenbach 1822), a non-native species currently expanding its range in south-central Sweden, from range statistic models based on distance measures (mean, median, 95th gamma quantile, marginal mean, maximum and conditional maximum) and an area-based method (grid occupancy). We used sampling simulations to determine the sensitivity of the different methods to incomplete sampling across the species’ range. 3. For periods when we had comprehensive survey data, range expansion estimates clustered into two groups: (i) those calculated from range margin statistics (gamma, marginal mean, maximum and conditional maximum: ~3 km/yr), and (ii) those calculated from the central tendenc...