Temporal trends of the economic costs (US$, log) of invasive alien species in Spain using the robust data (reported, incurred and reliable costs). Each blue circle represents the cumulative cost for a given year, whereas its size is proportional to the number of estimates for that particular year. Average annual costs are calculated in 4-year periods and are represented by black dots and horizontal solid lines. Dashed lines connect the average annual costs for these 4-year periods.