Endemic Malabar Tree Toad populations may decline 68.7% due to climate change: Study

Climate change may decrease the distribution range of the Malabar Tree Toad (MTT) by up to 68.7 per cent of the current estimated distribution in India’s protected areas (PAs), according to a study conducted by a concerned group of citizens and scientists. 

The current estimated species distribution in PAs decreased its range to 68.7 per cent from 33.5 per cent between 2061 and 2080 in multiple models, if eight future climate change scenarios — including high emissions — were considered.

But in case of low emissions scenarios, the distribution range of the species increased from 1.9 per cent to 111.3 per cent in PAs, according to the study published recently in the Nature journal. 

MTT is endemic to India’s Western Ghats and the only species in the monotypic genus Pedostibes. Meaning, it is the only arboreal species in India, having the unique capability to climb trees and dwell unlike the majority of the toads in the region that are ground-dwelling. 

It was first discovered in 1876 and the species was not sighted for more than 100 years. 

It was later rediscovered in 1980 at Silent Valley National Park in Kerala. Scientists told Down To Earth (DTE) that very few sightings were noted until 2014, which led to studies that revealed the occupancy and extent of occurrence to be ‘nearly throughout the Western Ghats’.

The current study noted that an adversely changing climate has endangered a wide array of species in the Western Ghats, a global biodiversity hotspot.

The region hosts about 252 species of class amphibia, of which 17 are critically endangered while 40 are classified as ‘data deficient’.

Globally, 40.7 per cent of amphibians (8,011 species) are the most threatened taxa of vertebrates due to anthropogenic activities such as timber and plant harvesting, agriculture and infrastructure development. 

Habitat fragmentation, pollution, disease and morphological deformities with climate change has led to the decline of amphibian populations in the past 40 years. 

S Harikrishnan, project head of the Amphibian Recovery Project at non-profit Wildlife Trust of India, who was part of the study, remarked that the study is a first for India in that the distribution modelling of a species from the amphibian-reptile category and an endangered amphibian species has been conducted by including citizen science. 

“Previously, such estimates have been known to be done on birds,” he added.

Harikrishnan said PAs in the central Western Ghats are to lose most of their regions suitable for biodiversity, whereas habitats in the southern Western Ghats are predicted to be become more suited. The species distribution would shift accordingly. 

“Restricted and discontinuous distribution along with climate change can limit the dispersal and persistence of MTT populations, thus enhanced surveys of MTT habitats within and outside the PAs of the Western Ghats are an important step in safeguarding the persistence of MTT populations,” the study warned.

Meanwhile, Ravi Chellam, chief executive of Metastring Foundation & Coordinator, Biodiversity Collaborative said climate change is one of the major reasons for biodiversity loss and such distribution modelling can help understand the distribution of any species and help initiate effective conservation steps.

“Amphibians are one of the most sensitive groups to the impacts of climate change due to their unique ecology, habitat needs and limited thermal tolerance, giving them narrow dispersal abilities,” he said

Unprecedented study on Indian amphibians
The authors of the study used 655 observations of the toad from various citizen science platforms, and observations from published scientific papers between 1876 and June 27, 2022. 

 KV Gururaja, associate professor at the Srishti Manipal Institute of Art, Design and Technology and the corresponding author in the study said, “Based on the call phenology (the first call of the season), the entire citizen observations were divided into north and south populations. 

“We estimated that in future climate scenarios, the populations may see an increase in the Mhadei, Mookambika, Sharavathi Valley and Netravali wildlife sanctuaries. It will also show an increase in Mollem and Kudremukh National Parks. The Kalakad Mundanthurai Tiger Reserve and Brahmagiri Wildlife Sanctuary would, on the other hand, witness a decrease in the number of suitable habitats,” he said.

The study noted that the future distribution fell within evergreen forest by 63.6 per cent, some pockets in plantations by 14.23 per cent, in croplands by 6.75 per cent and in mixed forests by 8.41 per cent. 

Grasslands, water bodies and built-up lands showed losses by 2.97 per cent, 2.6 per cent and 1.56 per cent respectively, indicating the occurrence of the species in human-modified habitats. 

“Although MTT is a tree toad, it comes to the ground to breed in water pools at the edges of the streams generated during the monsoon, implying that precipitation and moisture provide the necessary conditions for MTT to breed,”the study noted.

Gururaja stated that forest-resident amphibians will lose their much needed microhabitats due to climate change as opposed to those inhabiting open areas, as per studies. Hence, the study becomes crucial for conservation and management of MTTs.

Harikrishnan pointed out that the drought situation experienced by toads and frogs of Karnataka in 2023 impacted their breeding and nesting habitats. “Such scenarios may occur more frequently and force shifting of their distribution range. Our results also show that annual precipitation influences species populations,” he added. 

“The northern populations get affected most, compared to southern populations in the future climatic scenarios,” he said. 

“Considering these insights of the MTT, an endemic toad of the Western Ghats, stemming from citizen science initiatives, a proposal has been submitted to the Government of Karnataka to declare it as the state amphibian,” Gururaja said.