National Scientist Angel C. Alcala wrote that since the 1970s, frogs have been dropping dead in significant numbers around the world. These were recorded by scientists in western United States, Puerto Rico and Western Australia in the 1970s and in Costa Rica, Ecuador and Venezuela in the 1980s.
At first the events were believed to be just “normal variations in natural populations.” At other times the causes were linked to fungus attacks, as in five continents where 100 species were infected.
But as the declines grew even more widespread and more severe towards the 1990s and 2000s, the scientists concluded that these resulted from climate change—in addition to already known human-induced causes of habitat (forest) fragmentation and destruction and overexploitation.
“There is evidence for the link of global amphibian population declines and species extinctions to climate change during the decades of the 2000s,” wrote Alcala in the Philippine Journal of Science in 2012, together with co-authors Abner A. Bucol, Arvin C. Diesmos and Rafe M. Brown.
They cited a source that said in Sri Lanka, for example, 19 out of the 103 species of frogs became extinct, “and most of these were restricted to high elevations of 1,800 meters where average annual temperature increased by 1.3°C and average annual precipitation increased by up to 20 per cent during the period 1869 to 1995.”
In this connection, it would be of interest to find out if climate change has affected frog populations in the fragmented Philippine forests at higher elevations particularly in areas that were explored by Alcala and his research team in the 1950s-1990s.
In the Philippines, Alcala and his team assessed the vulnerability of amphibians to climate change. They considered five criteria in the assessment (and five grades per criteria), namely: status (alien or endemic), elevation (lowland to 500m and above), habitat (non-forest, ground forest, arboreal forest), mode of reproduction (tadpoles or direct layers on ground or trees) and rarity (common or rare).
Based on the scores, Alcala and his group concluded that almost one-fourth (24 per cent) of the total known 107 species of Philippine amphibians were Highly Vulnerable and almost half of all the species (48 per cent) were Moderately Vulnerable.
Since there are new species of Philippine amphibians yet to be described, and most of them live in forested mountain habitats, “ the percentages of vulnerable taxa are expected to climb sharply,” they added.
The Highly Vulnerable species could be affected by the drying up of their microhabitats in high elevation due to climate change. “They spend most of their lives in perpetually moist microhabitats and utilize as egg-laying sites leaf axils of screw pines, root masses of aerial ferns, moss growing on tree trunks, and top surfaces of broad leaves of forest shrubs. These microhabitats easily desiccate with decreases in atmospheric moisture.”
The Moderately Vulnerable group occupy forest floors and limestone caves and widely distributed on islands at various altitudes.
Both groups of species include “small amphibians that live on small islands that are susceptible to environmental and atmospheric disturbances and may be at risk of extinction.”
About 85 per cent of Philippine amphibians inhabit forested areas, and more than 78 per cent of them are endemic (or indigenous) species.
In a place where species richness and endemism are high but habitat destruction is rapid, as in the Philippines, species extinction is also high. This is why the Philippines is considered one of the four conservation “hotspots” in Southeast Asia and one of 25 hotspots around the world, the authors explained.
In addition, the Philippines is most vulnerable to climate change, with “high exposure frequencies of droughts, cyclonic storms, landslides, and floods, all of which are believed to be driven by changes in temperature and precipitation.”
Alcala et al. wrote that Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) projected that in 2020, annual temperature rise is between 0.9 °C and 1.4°C, and in 2050, 1.7°C and 2.4°C . The dry months of March to May will become drier and the wet months of June to November will become wetter.
They also wrote: “Reduction in rainfall in most parts of Mindanao for all seasons is predicted. Stronger southwest monsoon winds are also projected in Luzon and Visayas. Areas with increasing elevation in slope are more vulnerable to excessive rains, landslides, and flashfloods.” —Celia E. Acedo, SU Research and Environmental News Service
Featured image from El Nido Resorts: Environment and Sustainability