Interview with Dr.Manju Siliwal, Etymologist on Spiders
Interview with Dr. Manju Siliwal
1. Which are the spider species affected by Climate change in India’s biodiversity Hotspots – North Eastern Himalayas and the Western Ghats? What are the factors threatening their survival?
Spiders that are habitat or niche specific, poor at dispersal and / or endemic to a region or an area are more likely to get affected by Climate Change. It includes spiders such as cave spiders, mygalomorph or burrowing spiders. These spiders are at higher risk of local extinction in both the biodiversity hotspots in India (the North Eastern Himalayas and the Western Ghats).
2. Which are the richest habitats for spiders world over? What kind of spiders inhabit these areas?
No specific habitat is designated as rich habitats but tropics and sub-tropics have been recognized as most complex habitat systems housing highest species diversity of all fauna, including spiders. Amongst Indian hotspots, North Eastern Himalayas is rich in spider diversity and densities as compared to the Western Ghats. But more endemism is found in the Western Ghats. The reason why the Western Ghats have endemics is that Indian landmass got cut off from the Gondwana landmass and remained as an island for millions of years before it collided with the Eurasian plate and formation of Himalayas took place. And when fauna remains isolated for a long time, the physiological and morphological changes in them take place, which is enough to categorise them into either new species or a subspecies. And these become endemic or unique to the area. Whereas, the Eastern Himalayas have undergone lot of geographical changes and have witnessed faunal exchanges from neighbouring countries or areas.
3. Please describe the endangered spiders and their habitats.
Endangered spiders are those which face threat of extinction (local or global) as a result of human induced or interference like habitat loss & fragmentation, trade for meat or for pet market, etc. Endemic spiders that are having small distribution range and/or are poor at dispersal are more threatened than other spiders, which can disperse through air (ballooning).
4. How does habitat destruction affect the endangered spiders?
Spiders like mygalomorphs are having low dispersal rates, high site fidelity, habitat specific, high endemicity, takes longer time to mature (2-4 years in case of Indian tarantulas) and are long lived (6 to 20 or 25 years in case of tarantulas) than other non-mygalomorph spiders and therefore, they are more endangered and face high risk of extinction and they need a contiguous habitat for their survival. Any alteration in their habitat can be detrimental for the spider.
5. How is their food chain, affected by Climate Change?
There are no specific studies on spider and their food chain. But as they are the top-predators amongst invertebrates, they face same challenges as other terrestrial predators.
Mygalomorphs are sit and wait kind of predators and therefore, if prey population goes down then their survival is difficult.
6. How is their natural history behaviour, affected by Climate Change?
Studies have also shown that climate change may induce changes in morphological characters such as body size and other life-history traits, enhancing the skew in sexual dimorphism. But, unfortunately the past studies on mygalomorphs or in general on spiders lacks natural history or behaviour notes and therefore, there is no data available to compare to infer the impact of climate change on web or burrow size, burrow depth, spider body size, number of egg laying or reproductive success, dispersal ranges, etc. Therefore, its difficult to comment on it.
7. How is their hunting behaviour affected by Climate Change?
Spiders in general is very poorly documented group of animals and majority of the studies in the past and recent past were restricted to description of the species. Behaviour studies on these spiders are totally neglected.
In general studies on arthropods have shown that overall changes in prey-predator relationships have been predicted to be impacted by climate change, by affecting the survivability and growth phases of either group.
8. How is their mating behaviour affected by Climate Change?
9. How are tarantulas and widows affected by Climate Change?
There are no specific studies on tarantulas or widow spiders but recently a paper published stated that tropical cyclones have proven to impact behavioural and reproductive processes in certain spiders. Climate change may aggravate occurrences of such cyclones, consequently affecting natural selection dynamics of target spider population and growth.
10. Are there tarantulas in the Indian subcontinent too? How re they affected by Climate Change?
Yes, tarantulas do occur in India and about 60 species have been reported from India, high level of endemism observed in this group. They have very habitat specific requirements and any alteration in their habitat can directly put them under the risk of local extinction. Reasons for habitat change could be either human included or climate change but the impact on spider is same. Climate change is a slower and long process than the human induced changes in the spider habitat. Thus, human induced alterations in the habitat are more detrimental on spiders.
11. Where are tarantulas found to occur in India? Please dwell on the ideal habitat for Indian tarantulas.
Tarantulas have been recorded from all parts of India except for higher ranges in Himalayas (above 2100m elevation). Tarantulas can be divided into two groups based on their habits, arboreal and ground burrowing tarantulas. Only one genus amongst the spiders in India is strictly arboreal in habit, vis., Poecilotheria, commonly known as ornamental spiders or tiger spiders or Parachute spiders. They occupy natural crevices or cavities on trees and are found in wooded areas in the peninsular India. Whereas, the ground burrowing spiders are found throughout the India and they make their burrows on mud-banks or on flat ground or on fallen wooden logs or old trees. Tarantulas in general are predominantly found in wooded areas like forest or plantations.
Interviewed by Malini Shankar,