Diversity, distribution pattern and seasonal variation in moth assemblages along altitudinal gradient in Gangotri landscape area, Western Himalaya, Uttarakhand, India
Abesh Kumar Sanyal 1, V.P. Uniyal 2, Kailash Chandra 3 & Manish Bhardwaj 4
1,2,4 Wildlife Institute of India, P.O. Box-18, Chandrabani, Dehra Dun, Uttarakhand 248001, India
3 Central Zone Regional Centre, Zoological Survey of India, 168-189 Vijaynagar, Jabalpur, Madhya Pradesh 482002, India
1 email@example.com, 2 firstname.lastname@example.org (corresponding author), 3 email@example.com, 4 firstname.lastname@example.org
An inventory of biodiversity is of primary importance as part of biodiversity conservation for sustainable development, particularly in threatened and fragmented landscapes like Western Himalaya that harbours unique assemblage of flora, fauna of considerable conservation importance. In comparison with higher plants and larger animals, the inventory of insects in Western Himalayan landscape is still fragmentary and incomplete.
Recent estimates reveal the report of over 127,000 species of moths from the world, of which over 12,000 species are recorded from India (Chandra 2007). The comprehensive work on moths of different regions of Western Himalaya within the Indian Territory was mostly carried out by Hampson (1892, 1894, 1895, 1896) and Bell & Scott (1937) in their “Fauna of British India” series and Cotes & Swinhoe (1886) in “A catalogue of moths of India”. Since then not much work has been carried out on moth fauna of Western Himalaya except Arora (1997, 2000) who had published some moth species from the Nanda Devi Biosphere Reserve, Garhwal Himalaya, Uttarakhand and Smetacek (2008) who published 887 species of moth from different elevations in Nainital District, Kumaon Himalaya, Uttarakhand. So far no comprehensive work on moth fauna in Gangotri landscape area which is an important wildlife refuge in high altitudes of Uttarakhand State has been done.
The study was conducted in two high altitude protected areas of Uttarakhand (Fig. 1) Gangotri National Park (30050’–31012’N & 78045’–79002’E) and Govind National Park (31002’–31020’N & 77055’–78040’E), which represents the biogeographical zone - 2B West Himalaya (Rodgers & Panwar 1988). They are situated in Uttarkashi District of the Uttarakhand State. The altitude varies from 1200–6000 m. The Gangotri NP covers an area of 2,390km2 harbouring the Goumukh Glacier, the origin of the river Ganges and Govind NP covers an area of 953.12km2 encompassing the upper catchment of river Tons. The climate of the area is typically Himalayan with medium rainfall during July–August at lower altitudes. The average rainfall is 1,500mm, extreme cold with three to four month snowfall in winter with permanent snowline in the higher reaches.
The vegetation pattern in the study area resembles the broad pattern of vegetational zones of northwestern Himalaya. The lower altitude represents montane subtropical type with Chir Pine (Pinus roxburghii Sarg. (Pinaceae) dominating with tree rhododendron (Rhododendron arboreum Smith (Ericaceae), Rohini (Mallotus philippensis Lam. (Euphorbiaceae), Alder (Alnus nepalensis D. Don (Betulaceae), Wild Pear (Pyrus pashia Buch.-Ham. (Rosaceae), Indian Laburnum (Cassia fistula Linn. (Caesalpiniaceae), Amla (Emblica officinalis Gaertn. Euphorbiaceae), Toon (Toona ciliata, M.J. Roem (Meliaceae). Shrub layer is dominated by Musk Rose (Rosa moschata Miller (Rosaceae), Raspberry (Rubus sp. (Rosaceae), Wig plant (Rhus sp. (Anacardiaceae), Dodonea viscosa Linn. (Sapindaceae), Colebrooka oppositifolia Smith (Labiatae), Pyracantha crenulata M. Roemer (Rosaceae), Ziziphus mauritiana Lam. (Rhamnaceae). The mid altitude regions were represented by montane moist and dry temperate type of vegetation. Moist temperate vegetation consists of Grey Oak (Quercus leucotrichophora A. Camus (Fagaceae), Blue Pine/kail (Pinus wallichiana A.B. Jackson (Pinaceae), Western Himalayan Fir (Abies pindrow Royle (Pinaceae), Deodar (Cedrus deodara G. Don (Pinaceae), Horse Chestnut (Aesculus indica Hook. (Hippocastanaceae), Himalayan Cypress (Cupressus torulosa D. Don (Cupressaceae), and Yew (Taxus baccata Pilger (Taxaceae). The shrub layer was dominated by Viburnum continifolium D. Don (Sambucaceae), Hippophae rhamnoides Rousi (Elaeagnaceae) and Berberis sp. (Berberidaceae). The montane dry temperate vegetation zone was predominantly coniferous along with broad-leaved trees like oak, ash, maple. There were also deodar, juniper, high level fir (Abies spectabilis Mirbel. (Pinaceae) and Silver Birch (Betula utilis D. Don (Betulaceae). The subalpine zone around 3000m had dense coniferous forest represented by the species like Pinus wallichiana A.B. Jackson), Himalayan Yew (Taxus wallichiana Pilger (Taxaceae)) with intermixed broad-leaved trees like Kharsu oak (Quercus semecarpifolia Smith (Fagaceae)). The common shrubs were Rosa webbiana Wallich (Rosaceae, Cotoneaster sp.(Rosaceae) and Berberis sp. etc. The herbaceous species like Delphinium sp.(Ranunculaceae), Swertia sp. (Gentianaceae) and Pedecularis sp. (Scrophulariaceae) were found common.
Materials & Methods
The moths were collected using light trap running for four hours from 19:00–23:00 hr in the three seasons, viz, summer (April–May), monsoon (June–July), and post Monsoon (August–September). Wherever electricity was available, light traps were set by placing a 120W Tungsten filament bulb in front of a white 10’x 6’ cloth sheet hung between two vertical poles in a way that it touches the surface and extends forward over the ground slightly and the data collected by this method were used for the inventory purpose, not for diversity analysis. In higher areas of subalpine zone, light traps were set by solar powered lantern which had significantly low light intensity than tungsten filament bulb. After collecting, moths were killed by Benzene vapour in killing jar. The collected specimens were processed for pinning, setting and preserved in air-tight wooden boxes. First the specimens were sorted into morphospecies. Identifications were done with the help of available literature and also by comparing with the reference collection available at Zoological Survey of India. The classification used mainly follows Hampson (1892, 1894, 1895, 1896) and subsequent changes in the families based on Kristensen (1999).
Altitudinal distribution: Diversity of moth fauna in terms of morphospecies collected showed a decreasing trend along increasing altitude. For comparison between different nightly catches at different altitudes, species were collected in same season, weather condition and moon phase. The data provided in Table 1 shows the average number (total morphospecies collected/sampling night) of moth species collected in the four different altitudes with their respective broad vegetation type.
The four altitudinal zones sampled were categorized into three elevational ranges: The lower zone is represented by 500–1500 m which is characterized by montane subtropical and moist temperate type of forest. This zone came out as the most diverse zone (Fig. 2) in respect to moth species collected. The mid altitude zone is represented by 1500–2500 m, which is characterized by montane dry temperate type of forest. This zone had medium diversity. The higher altitude zone is represented by 2500–3500 m, which is characterized by subalpine vegetation. This zone contained significantly less diversity of moth species.
Seasonal variation: The data provided in Table 2 shows the total number of specimens collected in different seasons. For comparing the catch success in different season, the average value of catch success per night were used as a simple mean of total species collected by total trap nights.
Catch success was highest in summer months (April–May) followed by post monsoon (August–September) and monsoon (June–July) (Fig. 3).
Effect of moon phase: To observe whether the moon phase has any significant effect on catch success, a light trap was run on daily basis for one month period in the month of April at an altitude of 1440m from 20:00–24:00 hr. The result of the observed species catch and individual catch per day in a complete lunar cycle is shown in Fig. 4. Most species as well as individuals were attracted in and around no moon nights and declined as the ambient moon light started to increase and came to a minimum around full moon nights when the ambient moon light was at its best.
Species list: Although a total of 475 specimens were collected representing 436 morphospecies in different seasons, only 32 were identified up to species rank representing six superfamilies and nine families within the short span of study time. The identified species list with their collection locality (GVNP: Govind National Park, GTNP: Gangotri National Park) and altitude at which they were collected is given in Table 3. Current valid names are provided after consulting from LepIndex (Global Lepidoptera Species Database 2007 & The Natural History Museum, London).
In tropical or subtropical landscapes, two patterns of diversity are typically reported on altitudinal gradients: diversity either declines (linearly or nonlinearly) with increasing altitude, or, more commonly, unimodal patterns (mid-elevation peak) are found (Rahbek 1995, 2005; McClain et al. 2007). Our study result, although a preliminary one, has indicated the previous trend, i.e., moth diversity declining linearly with increasing altitude. As the study does not cover the entire elevational range, it is hard to predict the underlying cause of such pattern. The lower altitude zone represented by montane subtropical and moist temperate type of forest is in comparatively better condition than the upper reaches, which are under pressure from increasing human settlements and grazing-related problems. The sampling related issues may also have a significant effect on this pattern as setting up light traps in lower altitude zone was easier than the alpine areas due to availability of good logistic support like electricity. Whereas in lower areas the light trap was run by tungsten filament bulb run from main power source, for sub-alpine areas solar powered light was the only feasible option with much lower intensity.
Significant seasonal variation in catch success per night was observed with the highest catch success in summer time followed by post-monsoon season and the monsoon time which had significantly lowest success. High rainfall in monsoon months resulted in low catches, suspecting that flight may be restricted in such conditions. Post-monsoon months observed a significantly high moth abundance and species richness perhaps by increased availability of fresh plant material stimulated by rain. Summer (April–May) was the best season for sampling. Moon phase or the monthly lunar cycle had a significant effect on the light trap catch success. Yela & Holyoak (1997) from their study recommended to restrict the light trapping to periods without strong moonlight because moths are not attracted to artificial light in the presence of high ambient moonlight, though their activity remains at it’s peak. Our study documented the same phenomenon where maximum number of species as well as individuals were attracted to light traps in the beginning and end of lunar cycle, i.e. from 3rd to 6th day and 24th to 28th day when there was apparently no ambient moon light. Catch success eventually dropped as the ambient moon light started to increase and became almost zero in the full moon period from 14th to 18th day. One factor that masked this general pattern was the presence of cloud cover evident from the slightly increased catch success in 12th day when there was strong moon light but its effect was nullified by the clouds.
The present work gives an idea about previous and new distribution record of the 32 species mentioned (Table 3). Of these, nine species are first records from Uttarakhand State, viz., Goniorhynchus signatalis, Lista haraldusalis, Trichopterigia rufinotata, Psyra similaria, Nordstromia lilacina, Spilosoma obliqua, Diarsia albipennis, Cyana horsfieldi and Spilosoma strigulata.
As the area is under tremendous pressure from the threat of loss of biodiversity due to various anthropogenic activities like increasing human population, conversion of forested land to agricultural patch, shifting cultivation and livestock grazing of pastoral people, it is very important to know about the overall picture of diversity of an important indicator group like moth calling for the need of a more thorough investigation.
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