They are called bellwether species, also known as sentinel species.
<span>Emilio Mola, a Nationalist Genral during the Spanish Civil War, told a journalist in 1936 that as his four columns of troops approached Madrid, a "fifth column" of supporters inside the city would support him and undermine the Republican government from within. The term was then widely used in Spain. Ernest Hemingway used it as the title of his only play, which he wrote in Madrid while the city was being bombarded, and published in 1938 in his book The Fifth Column and the First Forty-Nine Stories[1]</span><span>Some writers, mindful of the origin of the phrase, use it only in reference to military operations rather than the broader and less well defined range of activities that sympathizers might engage in to support an anticipated attack. Madeleine Albright for example, in a lengthy account of German sympathizers in Czechoslovakia in the first years of World War lI, reserves it for their possible response to a German invasion: "Many, perhaps most, of the Sudetens would have provided the enemy with a fifth column".<span>[2]</span>
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Answer:The fact that you "see" it is because you are having a flashbulb memory of where it was.
Explanation:
Flashbulb memory is memory in which we are able to recall something because we can see where it was before it passed.
In this case the lighting moves too fast for our eyes to see it but we can see the remnants of where it was before it passed .
Sample are the characteristics of the individuals of the population being studied
