Rediscovery of the “ extinct ” Pinatubo volcano mouse

In June 1991, Mount Pinatubo, a volcanic peak on the Philippine island of Luzon, literally blew up its peak. It was the second most powerful volcanic eruption of the 20th century, ten times stronger than Mount Saint Helens, and its effects were devastating. Lava and ash spread through the surrounding environment in the Zambales mountains, aggregating in layers up to 600 feet thick in the valleys. Following the eruption, powerful typhoons and monsoon rains triggered landslides and ash flows that continued for many months. Eight hundred people lost their lives and the lush forests that covered the mountain before the eruption were destroyed or severely damaged. In recent years, scientists have returned to the region to investigate surviving mammal populations, and in a new article in the Philippine Journal of Science, the team announced the rediscovery of a species of mouse that has long been feared to become extinct.

“When Pinatubo blew up, the last thing that probably worried someone was probably that a small mouse species lived only on this mountain and could have gone extinct as a result. What we learned afterwards really blew us away. Says Larry Heaney, the Negaunee curator of mammals at the Field Museum in Chicago and one of the authors of the article.

In early 2011 and again in 2012, twenty years after the eruption, Field Museum researcher Danilo (Danny) Balete visited Mt. Pinatubo to study its mammalian fauna. For several months, Balete and his team of field assistants (including local men from the Aeta tribe) investigated the mammals on the mountain, from the bottom to the top where the forest had been devastated by the eruption.

“Most of our fieldwork in Luzon and elsewhere in the Philippines has been done in natural forest habitats where mammals are most common,” says Eric Rickart, curator of vertebrates at the Natural History Museum of Utah and lead author of the paper. , “But Danny couldn’t ‘don’t miss an opportunity to see how the mammals fared on Mount Pinatubo. “

There have been no surveys of mammals on Mt. Pinatubo before the eruption. However, specimens in the United States National Museum of Natural History have provided records from low elevations around the mountain. “Most of these early records were of common bat species collected in the 1950s,” says Heaney, “but one specimen was particularly intriguing – a small rodent that became the type specimen, and the only example, of a new species described in 1962 as Apomys sacobianus, the Pinatubo volcano mouse. “

Conditions on Mt. The Pinatubo were very tough and the investigative work of Balete’s team was both grueling and dangerous. Even after 20 years, the evidence of the rash was everywhere. The landscape was very unstable due to the constant erosion of ash deposits and lahar which made working in steep terrain dangerous. It also significantly slowed down the process of plant succession. The vegetation was a sparse mixture of native and non-native plants, dense stands of grasses (including bamboo), shrubs, low-growing vines, and few trees – all characteristic of second-rate habitat. early stage growth. It was a far cry from the ancient rainforest that covered the mountain before the eruption.

Field studies of small non-flying mammals elsewhere in Luzon have revealed that ancient forests contain a wide variety of native species and few, if any, of non-native “pest” rat species. But in heavily disturbed second-growth habitats, especially areas close to cropland, the reverse is that non-native rats are most abundant and there are only a few hardy native species. “We thought the work on Pinatubo would confirm this general pattern, so we expected to see little or none of the native species,” says Rickart.

A specific motivation of the Pinatubo investigation was to discover the fate of Apomys sacobianus, the mouse of the Pinatubo volcano. “After the Pinatubo eruption, we looked for this mouse on other summits of the Zambales mountains, but we were unable to find it,” Heaney notes, “suggesting a very limited geographic distribution for the species. We thought the volcano might be the only place the mouse lived. “And based on the expectations of islands elsewhere, at the time, it seemed possible that the species may have been lost due to the eruption.

However, the investigation into Pinatubo produced some very surprising results: a total of 17 species have been documented, including eight bats, seven rodents (five native and two non-native), and even two large mammals (wild pig and deer. ). Contrary to expectations, non-native rats were not at all common and were limited to areas close to Aeta cropland where these agricultural pests are often most abundant. Despite the fact that all of the surveyed areas were home to sparse and scrubby second-growth vegetation rather than forests, native rodents were abundant everywhere.

Most surprising of all, the most abundant species was the volcanic mouse Apomys sacobianus. Far from being wiped out by the eruption, this species thrived in this heavily disturbed landscape along with other native species that also have a high tolerance to disturbance. “For some time now we have known that many small mammals in the Philippines can tolerate disturbance to their habitat, whether natural or man-made,” says Rickart, “but most of them are species. geographically widespread, and not locally endemic which are generally considered by conservation biologists to be highly vulnerable. “

Like Mt. Pinatubo recovers from damage from the eruption, forests will return and other mammal species will move in. “Mount Pinatubo could be a wonderful place to establish a long-term project to monitor habitat restoration and community reassembly after the eruption,” says Rickart, “such information would be useful in efforts to regenerate land. many areas that have been deforested by people.

After completing the Mt. Pinatubo Mammal Survey, Danny Balete returned to the Field Museum where he organized specimens and data from the survey, took some preliminary notes for possible publication, and then put them aside. to finish later. After his sudden death in 2017 at the age of 56, Rickart and Heaney say they have resumed and completed the study in tribute to Balete, who is now recognized as one of the most important figures in the science of Biodiversity in the Philippines for her vast contributions to research, mentoring younger colleagues and promoting the enjoyment of nature across the Philippines.

“Knowing that a species once thought to be vulnerable, if not feared to become extinct, is in fact flourishing is the finest tribute to Danny we can imagine,” Heaney adds.

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More information:
Eric A. Rickart et al. Mammals of Mt. Pinatubo, Luzon Island, Philippines: Extreme resilience following catastrophic disruption. Philippine Journal of Science, (2021)