Current World Environment

Introduction

As one of the most widely recognized group of arthropods, spiders make up a diverse portion of the world’s invertebrates.¹ They are distributed on every continent except Antarctica and have adapted to all known ecological environments except air and open sea.² Spiders globally include about 47,099 described species in 4,073 genera and 113 families.³ They are unique among all organisms in their modes of silk production and usage and of reproduction.  Spiders are clearly an integral part of the global biodiversity since they play an important role in ecosystems as predators and source of food for other creatures.⁴ They primarily feed on insects, but also eat other arthropods, including other Araneae. They are suitable biological indicators of ecosystem changes and habitat modifications due to their small body size, short generation time, and high sensitivity to temperature and moisture changes.⁵

Spiders form one of the most diverse groups of organisms existing in India.  Previous conservation efforts in India have focused on the larger vertebrates while invertebrates were largely ignored. There is now a growing need to conserve all species and not only the larger vertebrates.⁶ Documentation of spider fauna is more important because they play a significant role in the regulation of insects and other invertebrate populations in most ecosystems.  A comprehensive data on diversity and distribution of spiders from Kerala region is sparse as compared to other regions of the country. India is having 1,686 species of spiders belonging to 60 families and 438 genera, which constitutes 3.6% of world’s spider population.⁷ Very little work has been done on spider diversity of Kerala.^{8, 9, 10} Joseph et al.¹¹ reported 20 species of spiders from Periyar Tiger Reserve. Patel B.H.¹² described 91 species of spiders from Parambikulam tiger reserve. Sudhikumar et al.,¹³ reported 75 species of spiders from Mannavan shola forest areas and Sunil et al.,¹⁴ reported 147 species of spiders from Parambikulam tiger reserve. Most recently Sudhikumar¹⁵ listed 210 species of spiders from Nelliyampathy hill ranges of Western Ghats. This is higher than the number recorded from any other regions surveyed in Kerala. The present study is carried out in Kavvayi River Basin, which is in Northern Kerala.  This region is abundantly blessed with rich flora and fauna. The only reported study from this area on spiders was Palot and Balakrishnan¹⁶ in which they reported 17 species from Madayipara, a lateritic hill of Northern Kerala. The aim of this study was to compile the first checklist of spiders of the Kavvayi river basin and to determine the percentage of species protected.

Materials and Methods

Study Area

We conducted our study in the Kavvayi river basin, located between 12⁰ 05’ to 12⁰ 15’ North latitude and 75⁰ 05’ to 75⁰ 20’ East longitude. It spread over an area of 164.76 km² spreads over nine local administrative bodies in the districts of Kannur and Kasaragode. The Kavvayi River emerges from the Cheemeni laterite hills at an elevation of 119 m. above MSL having a length of 31 Km and directly flows into the Kavvayi backwater. The river basin is topographically complex, biodiversity-rich, fragmented and densely populated cultural landscape. Even though the Kavvayi River is prominent among the 14 rivers originating in midland in Kerala there is no reserved forest patch in the river basin. According to land use or land cover pattern, the study area has major subdivisions such as Lateritic exposed area, Sacred Groves, Kaanams, Plantations and Agro-ecosystems, Mangrove or marsh (Figure-i).
 

Sampling

The study has been carried out during the month of January to December 2014 in the Kavvayi river basin of Kerala. Two surveys were conducted per month at selected areas of the river basin. Spider collection was done during the morning (7.00am to 11.00am) and evening (16.00pm to 18.00pm) time to maximize the species richness. An all out search method was used for spider collection and the collection was conducted mainly by handpicking and beating methods. Pitfall sampling was also employed for spider collection. Spider microhabitats like fallen logs and leaf litters were thoroughly checked for ground-dwelling spiders while leaves of trees and visible webs were searched for arboreal spiders. Smaller spiders were collected by leading them into tubes containing alcohol with the help of brush dipped in alcohol. Most of the spiders were photographed in the field itself with the help of SLR Camera Canon EOS 5D Mark-III. Identification was done at the Centre for Animal Taxonomy and Ecology (CATE), Dept. of Zoology, Christ College, Irinjalakuda. The specimens were preserved in 70% alcohols with proper labeling of locality, date of collection and other notes of importance. The mature specimens were identified up to the species level with the help of stereo zoom microscope (Magnus MSZ TR) and also with available literature.^{17,18,19,20,21}

Results and Discussion

A total of 112 species of spiders belonging to 81 genera and 21 families were collected (Table 1) during the study period.  The genera such as Oxyopes and Neoscona show high species diversity. Out of the 438 genera reported from Indian region,⁷ 81 genera were collected from Kavvayi River Basin. Maximum generic diversity was found   in families including Salticidae (18), Araneidae(14), Theridiidae(9) and Thomisidae(8). Out of the 60 families recorded from the Indian region, 21 families were collected from Kavvayi river basins. This represents 35% of the total families reported from India. Araneidae was the most dominant family corresponding 24 species from 14 genera constituting 21.5% of total spider population. The second dominant family was Salticidae with 22 species from 18 genera constituting 19.5% of the total population. The relative species abundance of various families recorded during the study can be represented as    Salticidae > Theridiidae > Thomisidae > Tetragnathidae > Oxyopidae > Lycosidae =  Uloboridae  > Pholcidae =  Sparassidae = Pisauridae > Ctenidae = Gnaphosidae = Linyphiidae =  Eutichuridae = Scytodidae > Corinnidae = Eresidae = Hersilidae = Philodromidae = Theraphosidae (Figure-ii).. The spiders collected from the study area can be divided into seven functional groups or guilds based on the classification system proposed by Uetz et al.²²  Orb weavers was the dominant feeding guild with 32% of the total population, which was followed by stalkers with 28%, ambushers with 12%, space web builders with 12%, ground runners with 7% , foliage runners with 6%, wandering sheet weavers with 2% and sheet web weavers with 1% (Figure-iii).
 

The spider fauna of the entire regions of Kavvayi river basin has never been documented or summarized. The only reported study from this area on spiders was carried out by Palot and Balakrishnan,¹⁶ who listed 17 species of spiders from Madayipara, a typical lateritic biotope of Kavvayi river basin. The present study covers the entire ecosystems of Kavvayi river basin and it resulted in the documentation 112 species of spiders. The study emphasizes that the spider fauna of Kavvayi river basin is qualitatively rich. This area holds a wide range of unique habitats and these varied habitats provide a greater array of microhabitats, microclimatic features, alternative food sources, retreat sites and web attachment sites. The rich floral and faunal diversity is the key to building microhabitats for a variety of spiders. All of which probably favors the colonization and establishment of a high number of spider species in the study area. Many other studies also have demonstrated a correlation existed between the structural complexity of habitat and species diversity.²³ In 1991, Uetz²⁴ reported   that structurally more complex shrub can support a more diverse spider community.

At present, the study area is facing unprecedented levels of fragmentation. The changes in land use pattern led to over exploitation of ecologically important land classes like Laterite exposed area, mangrove – marsh lands, paddy cultivation, eco-groves, etc.., without considering its  importance.  Due to the scarcity of woody species or forest cover the lateritic exposed regions in the study area appear devoid of vegetation in remote sensing images and often considered as ‘wastelands' that’s why miners easily get the permission from the authorities for mining and reclamation of the area but, in reality, these landscape units having high biodiversity value and ecological significance.  At present only a small portion of the lateritic exposed area remains undisturbed. There is no reserve or protected forest in the study area that’s why no parts of the river basin other than some sacred groves got authorized protection, sacred groves got cultural or religious protection from the local people. Considering their ecological importance there is an urgent need to conserve the critical ecosystems in the river basin. Our study provides baseline information of spiders inhabiting in this ecosystem. The habitat destruction is at its peak, this type of valuable scientific information would help to create proper conservation and management strategies of this landscape.
 

Table 1: Checklist of spiders identified in Kavvayi river basin north Kerala

Conclusion

This was the first attempt to document spider diversity in a lateritic biotope of Southern India. The diversity both at ecosystem and microhabitat level supports large number spiders in the Kavvayi river basin. Since the study area is a human dominated landscape, they are facing threats like habitat loss, laterite mining, pollution and changes in land use pattern. Appropriate conservation strategies should be developed and implemented to conserve the faunal and floral diversity in the lateritic biotope of the region.

Acknowledgements

The authors are thankful to the Kerala State Council for Science, Technology and Environment, Government of Kerala for providing financial support. Thanks to Dr. A.V. Sudhikumar, for the help in confirming the identity of the spiders. We Acknowledge the support from Director, KFRI and thanks to Dr. K.V. Sankaran and Dr. P.S. Easa, former Directors of KFRI for their support and encouragement, Dhaneesh Bhasakar, Manjunatha H P and Prijo for assistance in field.

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