Diversity-invasibility in space and time
The relationship between native species richness and E. canadensis variation in space and time (hypothesis 1 ) was assessed using Pearson correlation coefficients. Correlations were assessed at both within- and among-lake scales for the contemporary data and at the within-lake scale for the palaeo-data. Since unvegetated sampling points could produce spurious positive correlations betweenE. canadensis abundance and native macrophytes at the within lake scale (Capers et al. 2007), we removed these from all analyses. Sampling points with native macrophytes but no E. canadensis or with onlyE. canadensis were retained. Negative correlations betweenE. canadensis abundance and speciose native assemblages would be supportive of hypothesis 1 (Beaury et al. 2019). Positive correlations would support hypotheses 2 and 3 by suggesting that coexistence of native and invasive species in space and time is mediated by habitat heterogeneity (Clark et al. 2013).