To answer your question, I would need to refer to the specific graph mentioned, which is not visible in this text format. However, typically, the initial population size of an invasive species can be found at the start point of the graph (when x = 0 or the first year of data collection).
If you provide the coordinates or any specific information regarding the graph, I can help with a more precise answer. Otherwise, you would look for the y-value corresponding to the x-value at the beginning of the data collection on the graph.