The measurement that tells the effective weight of an atom is atomic mass

atomic weight

metalic weight

nuclear mass

mass weight

True, for example a habitat that has been untouched by humansis suddenly found and an invasive germ or bug enters off of the humans. This germ or bug will disrupt the community as they have no defense and ultimately will reform but with a different configuration than before as the bug like lowered the population of the native species. Also in terms of a wildfire as it likely killed many native species and then the ecology that survived would have a different make-up than before as well.