Extinction events are gauged by diversity loss, not population decline. The toll is measured in disappearance from the fossil record, not deaths, which are uncountable.
Ecological generalists – species with considerable tolerances to environmental changes – are the most successful migrants into new habitats. When invaded, generalists hang tougher than specialists, which are well-adapted to their niche but lack robustness in challenging times.
Specialists make the most of their habitat. Generalists fare better during rapid environmental changes, but there are fewer species of them. Owing to their inherent adaptability, generalists are less prone to speciation.