Modelling climate suitability across the UK
A total of 1331 lizard sightings (presence) data (76 from online portal, 52 from postcard returns, 1203 from visual surveys) were used to develop relative habitat suitability maps at the UK national extent using MaxEnt v3.3.3k software (Phillips, Anderson, & Schapire, 2006). Podarcis muralis has demonstrated rapid adaptive responses following introduction to cool climates, with ability to evolve broader thermal tolerance at dispersal fronts (Litmer & Murray, 2019), and prolonged embryo retention and faster embryonic growth at low temperatures - compared to ancestral states (While et al., 2015). For this reason, we only used P. muralis presence records from the introduced UK range in our MaxEnt model, as they best reflect the current climatic tolerance of the species, and, secondary introductions from established populations are the primary concern for the species extending its range in the UK. We focused on seasonal averages of six climatic variables (predictors) at 5km resolution (Met Office, 2018) that have most relevance to wall lizard biology and therefore likely to influence distribution (Wirga & Majtyka, 2015) (Table 1). These six variables were refined from an initial input of 13 climate variables through an iterative process of removal/retention to limit covariate correlation (Spearman’s rank correlation; correlated if rs ≥ 0.6) and maximise model performance (Glover-Kapfer, 2015). We kept parameter settings in MaxEnt the same for modelling at the national and local levels (see Appendix 1 for detailed method). The following Maxent parameters were used: Features used = Linear; Output format = logistic; Random Test % = 20; Regularization Multiplier = 2; Max number of background points = 10000; Replicates = 5; Replicated run type = Crossvalidate.