How mice survived the Pinatubo eruption, extinction of dinosaurs

The mice that survived the Pinatubo eruption volcano in 1991 give us a clue about how small rodents occupied the gap left by the extinction of the dinosaurs.

Mice are known to be small but bully. An indigenous mouse species survived the violent eruption of the Mount Pinatubo volcano in 1991, and has since become the most abundant small mammal in the area. Their survival gives us clues as to how small rodents were able to survive after the mass extinction that took the dinosaurs 66 million years ago due to an asteroid impact.

Mount Pinatubo is an active 1,486-meter high volcano found on the island of Luzon, Philippines. On June 15, 1991, its last eruption took place after 500 years of inactivity. The surviving mouse is named Apomys sacobianus, the Pinatubo volcano mouse, and it was first captured in 1956.

A team of researchers from the Utah Museum of National History and the Chicago Natural History Museum, both in the United States, conducted surveys during 2011 and 2012 in different areas of Luzon Island and found that the mouse had become the king of the mountain. Their results have been published in the Phillipine Journal of Science.

What was the 1991 Pinatubo eruption like?

Three months before the great Pinatubo eruption of June 15, the citizens of Luzon experienced several periods of small earthquakes. The great eruption, which lasted approximately three hours, created a caldera 2.5 km in diameter, reducing the height of the mount by 250 meters (previously it had a height of 1,745 m).

The volcanic ash column reached 34 km in height and left the center of the island of Luzon dyed gray. The ashes reached Vietnam, Cambodia, Malaysia and Indonesia.

The large amount of ash reduced the sun’s rays reaching Earth. As a consequence, the global temperature dropped 0.5ºC for two years, and the sea level also dropped by six millimeters for one year.

The erosion was severe due to the volcanic fragments thrown (tephras) and the sediment and water flows that were mobilized from the slopes of the volcano (lahars). Currently the tree cover is still scarce in the area.

The large crater that was created after the eruption on the 15th became Lake Pinatubo, after the caldera landslides caused by monsoon rains.

How do you know how many mice are on Mount Pinatubo

Mount Pinatubo eruption of volcano

It is a common belief that mammals native to oceanic islands are susceptible to extinction after major ecological disturbance. However, the researchers knew from previous work that Luzon mammals had a great capacity to adapt to changes in the environment, both due to human and natural activity.

The researchers did not have exact information on the mammalian species present in the area before the eruption, but they did know of the existence of the Pinatubo mouse. They carried out samplings of small mammals with nets in five different places in the forest, between 300 and 1,100 m high. To position the traps, they enlisted help from the Aeta tribe, the indigenous people who live in the mountains of Luzon.

How did the Pinatubo mice survive after the volcanic eruption

In the sampling, 308 bats of eight different species were captured, three of them found in all locations, and also 329 rodents of seven different species, of which only two were “non-native”. In addition, they documented the presence of wild pigs and deer.

Species richness was similar in all locations and independent of the height at which they were captured. However, the Pinatubo mouse was the most abundant in four of the five locations, and accounted for 69% of the total captures.

The Pinatubo mouse was also the only one found only in the surroundings of Mount Pinatubo and not in the other locations, data that reveals that it is endemic to the area. Although the researchers point out that more sampling will have to be done throughout the island of Luzon to confirm this.

The most reasonable explanation given to the survival of the Pinatubo mouse is that it is an animal adapted to live both at low altitudes and at mid-elevation mountains, around 1,000 meters above sea level.

They are not the only surviving mice. After the eruption of Mount Saint Helena in Washington, United States, in 1980, the most catastrophic of the 20th century, the so-called Saint Helena mouse survived underground in devastated areas. In addition, it was fundamental for the regeneration of the soil and the repopulation with plants.

In addition to confirming the adaptability to changes of Luzon’s small mammals, the authors note, their results present opportunities to study how natural disturbances have shaped the evolution of Philippine biodiversity. With this information, it could help to regenerate deforested areas.

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