Rare mountain-dwelling Nilgiri tahr could lose 60% of habitat as climate warms

A new study paints a precarious picture for the rare Nilgiri tahr, an endangered goat-like species that lives in the mountains of the Western Ghats, a biodiversity hotspot in India.

Extreme global warming could slash by 60 percent the amount of available habitat that’s suitable for the tahr, researchers reported in the study published in Ecological Engineering. As a result, they’re calling for greater monitoring of the habitats and populations of the Nilgiri tahr that have been identified as most at risk.

The shy and elusive Nilgiri tahr (Nilgiritragus hylocrius) lives at altitudes of 1,100 to 2,700 meters (3,600 to 8,900 feet) in the mountainous grasslands and rocky cliffs of the southern portion of the Western Ghats, a range of peaks that run parallel to the western Indian coast and that host countless species found nowhere else.

The Nilgiri tahr once ranged over a larger area in the Western Ghats, the researchers say, but its distribution has shrunk considerably since 1950. Some 3,000 individuals are known to occur today in isolated groups, restricted to the states of Kerala and Tamil Nadu, covering less than 10 percent of their former range.

Modeling the Nilgiri tahr’s future

The study’s authors first identified 10 existing tahr habitats using previously published literature and by consulting scientists and forest officials from 2010 to 2011. The team then surveyed these habitats for the presence of the tahr to model its distribution under current climatic conditions.

Next, the researchers used models to predict how the distribution of suitable tahr habitat would change during three time periods: the 2030s (from 2021 to 2050); 2050s (2040 to 2069); and 2080s (2070 to 2099). They ran the models under two future global climate warming scenarios. The first scenario, which is more optimistic, assumes greenhouse gas emissions will peak in the 2040s and decline thereafter, with a surface temperature rise of 1.5 degrees Celsius (2.7 degrees Fahrenheit). The second scenario considers a case where emissions will continue to rise throughout the century, with a surface temperature rise of 2 degrees Celsius (3.6 degrees Fahrenheit).

The ecological niche model, which the team used, relies on the known distribution of species and the relationship between a species and its habitat, to identify potential species’ distributions at locations that have not been surveyed. Niche models are widely used to predict the impact of climate change on the distribution of species taking into account future changes in environmental conditions.

“A niche is nothing but a combination of environmental conditions which allows a species to survive,” said Kannambally M. Jayahari, a co-author of the study, who was a program officer at development NGO Winrock International India during the study and is now a consultant at the World Resources Institute.

The habitat suitable for the tahr currently spans 21,448 square kilometers (8,280 square miles). In all the future climate change scenarios, much of that habitat would become unsuitable for tahr, shrinking the range to less than 8,500 square kilometers (3,280 square miles). For the extreme scenario, the models predicted a maximum range loss of 61.2 percent, 61.4 percent and 63 percent of current habitats for 2030, 2050 and 2080 respectively.

Specifically, Kalakkad Mundanthurai Tiger Reserve and Srivilliputhur Wildlife Sanctuary in the state of Tamil Nadu, and the Peppara, Neyyar and Shendurney wildlife sanctuaries in Kerala are predicted to become unsuitable for the tahr in the future. Protected areas such as Peechi-Vazhani and Chinnar wildlife sanctuaries as well as Parambikulam Tiger Reserve and Silent Valley National Park in Kerala are predicted to become vulnerable under the extreme climate change scenario.

Image sourced from the study with permission from the authors.

Greater monitoring of tahr habitats

Jayahari said the study was merely flagging the level of climate risk and that in order to suggest any mitigation strategies, further studies were needed to understand how tahr habitats would become unsuitable — something that, at present, is unknown. “It is hard to predict how the niche unsuitability is going to be translated to on-the-ground scenarios,” Jayahari said. “It may work as increased susceptibility of the species to wildlife diseases, the grasslands may be taken over by other vegetation types, the food species of these species may get replaced by other species, etcetera.”

Jayahari and co-author Sandeep Sen, a doctoral student at the Bengaluru-based Ashoka Trust for Research in Ecology and the Environment (ATREE), said these models had limitations and that more detailed long-term ecological studies needed to be conducted to understand how climate change could affect tahr populations, in order to develop appropriate management strategies.

Wildlife biologist A.J.T. Johnsingh of Nature Conservation Foundation, an NGO based in the city of Mysuru, who also is an honorary scientific adviser to WWF-India, said that while the Nilgiri tahr could live in the lower altitudes of the Western Ghats, the increased heat waves caused by climate change could have a “disastrous effect on their habitats, particularly resulting in the drying up of the springs in summer, which could be detrimental to the overall tahr population.”

Sen suggested surveying outside of protected area networks to map small populations, which are more vulnerable to extinction than larger ones. He said small populations within the same landscape required habitat connectivity to ensure their survival.

“This will not only ensure the probability of the animals’ migration to suitable habitat in the future but can also help to curb the deleterious effects on these populations due to inbreeding,” Sen said.

He recommended greater monitoring of climate-vulnerable habitats and populations flagged by the study to improve connectivity and habitat quality in those areas.

Overall, more studies investigating the impact of climate change on tahr will help in predictions of future scenarios.

CITATION:

Sony R.K., Sen, S., Kumar, S., Sen. M., Jayahari, K.M. (2018). Niche models inform the effects of climate change on the endangered Nilgiri Tahr (Nilgiritragus hylocrius) populations in the southern Western Ghats. Ecological Engineering, 120, 355–363, doi.org/10.1016/j.ecoleng.2018.06.017

This story was first published on August 7, 2018, by Mongabay-India.