Hummingbirds have long lifespans for organisms with such rapid metabolisms. Some differences include a highly conserved genome, sulfur and glycogen metabolisms and viral resistance. For this reason, folivorous animals tend to have long digestive tracts and slow metabolisms. Large aggregates can become anoxic which give rise to anaerobic metabolisms. The temporary slowing-down of their metabolisms also lengthens the animals' lifespans. The balance between respiration and fermentation metabolisms is strain specific. Typically anaerobic metabolisms are confined to areas where it is more energetically favorable. Microbial communities can coordinate in syntrophic metabolisms to shift reaction kinetics in their favor. The fish were kept alive in a laboratory and their aerobic metabolisms were measured. As the external temperature increases, ectotherm metabolisms increase as well, increasing their demands for oxygen. Their persistence ascribes to their competitive metabolisms and adaptation to this environment. These are some of the earliest known metabolisms (see methanogenesis).