Let's make this clear: Spanish population only grows because of immigration. We have one of the lowest birth rates in the world (see https://worldpopulationreview.com/country-rankings/birth-rate-by-country), but allowing immigration has somewhat contained our population decline. Without immigration, our pension and health systems would be unsustainable, unable to cater an aging population. So we have immigration to thank for what you see in that image. Countries with low birth rates and low immigration (like Japan) are actually doomed.