Additions to the Odonata (Insecta) of Goa
Parag Rangnekar 1, Manoj Borkar 2 & Omkar Dharwadkar 3
1 Bldg 4, S-3, Technopark, Chogm Road, Alto-Porvorim, Goa 403001, Tamil Nadu
2 HoD, Department of Zoology, Carmel College for Women, Nuvem, Salcette, Goa, India
3 Flat No. F-2, First Floor, Kurtarkar Commercial Arcade, Kaziwada, Ponda, Goa 403401, India
Goa lies between latitudes 14053’-15048’N & 73045’-74024’E, covering an area of 3,701km2. Tucked between the Western Ghats and the Arabian Sea, it has a warm tropical climate with temperature ranging from 310C to 210C. Humidity throughout the year is high, the average being 86%. The southwest monsoons operate over the entire state registering an annual rainfall of around 300-400 cm.
The complete eastern stretch is under legal protection in the form of four wildlife sanctuaries and one national park. Serious taxonomic work to document the diversity of this small state though, has been found wanting. Sporadic efforts limited to certain taxa have been carried out by researchers and premier organizations like the Zoological Survey of India. Unfortunately, with the exception of Lepidoptera (Rhophalocera) and to some extent Odonata and Arachnida, other lesser known fauna have been neglected. For that matter, earlier studies on Odonata of the state were based on limited samples and does not cover the entire state and all seasons (Prasad 1995).
The Odonata diversity is well documented from the rest of the country after the pioneering work by Fraser (1936). The first peer reviewed work for the State of Goa was by Prasad (1995) wherein 22 species of Odonates were reported. The Fauna of Goa: State Fauna Series (2008) by Zoological Survey of India added another 17 species to the list by Prasad, thereby increasing the total species count to 39. In between these two reports Borkar et al. (2006) gave an account of Odonata in the campus of the Carmel College for Women in Salcette Taluka wherein 16 species not reported earlier were reported. This paper somehow did not figure in the compilation by the Zoological Survey of India, thereby ten species new to the state were not reported in the State Fauna Series, an anomaly that needs to be taken cognizance of for realistic assessment of status of odonate diversity.
A total of 499 species and subspecies of Odonata are known to occur in India (Prasad & Varshney 1995) out of which about 200 species are recorded from peninsular India, thereby highlighting the fact that the 39 species recorded for the state is an underestimate.
The present paper provides updated information on the diversity and distribution of Odonata of Goa, based on extensive surveys from May 2007 to December 2008. The need to address gaps in information on Odonate diversity of Goa has been highlighted in the Goa State Biodiversity Strategy Action Plan (GSBSAP)
Surveys were conducted throughout the state to cover varied habitats ranging from mountain streams, inland water bodies, paddy-field to marsh lands. The locations visited and the associated habitats are presented in Table 1. The survey locations are also marked on the state map for easy reference (Image 1).
A total of 38 surveys were conducted in these locations to document the Odonata diversity. Observations were done over three seasons: Monsoons (June - September), Winter (October - January) and Summer (February - May) in the year 2007-08. Individual specimens were photo-documented from various angles and these images were cross-checked with identification manuals for identification. Collection and killing was avoided for species which could be visually identified. For difficult species, specimens were caught using sweep nets and collected in paper envelopes. The specimens were kept alive to let them excrete and clear their gut before being treated in acetone solution at the end of the day. Larger species were treated for 10-12 hours while smaller species, especially damselflies were treated for 7-8 hours before drying in the shade and then preserved in air-tight plastic envelopes properly labeled with the name of collector, date of collection, habitat and in few instances the latitude and longitude co-ordinates. The collected specimens were identified using standard field guides (Fraser 1933, 1934, 1936; Subramanian 2005). Systematic arrangement of the species follows Subramanian (2009).
Occurrence frequency was calculated by plotting the occurrence of individual species at the each sampling locations. A presence-absence matrix gave an indication of the most abundant species over the sampling locations and over varied habitats.
Results and Discussions
In the field study spanning 20 months, 66 species of odonates belonging to 12 families were documented from Goa. The results are presented in Table 2. In Zygoptera, the family Coenagrionidae dominated the list with 14 species followed by Calopterygidae (3), Platystictidae (3), Platycnemididae (2), Chlorocyphidae (2), Protoneuridae (1), Euphaeidae (2) and Lestidae (1) (Fig. 1). In Anisoptera, the family Libellulidae dominated the list with 32 species followed by Gomphidae (3), Aeshnidae (2) and Cordulidae (1) (Fig. 2). Of all the families, the maximum contribution to the species diversity was found in Libellulidae accounting to 47.76% followed by Coenagrionidae which contributed 20.89% of the total species. This is a general trend which can be attributed to the presence of habitat generalist species in the above families.
The most significant finding has been reports of 34 species and four families for the first time from the state of Goa. Three Species reported by Borkar et al (2006) but not reported by ZSI or documented during the present study have not been included since they were documented prior to the present investigation period and hence are beyond the scope of the present study, though it is felt that the findings have significant scientific value. The four new families viz., Platystictidae, Euphaeidae, Cordulidae, Aeshnidae include species which are mainly found in and around water bodies in areas with good forest cover. The absence of species representing these families in the previous studies suggests overlooking of such areas in the surveys, which is evident from the locations mentioned in the respective papers. The present study has resulted in a staggering increase of 47.30% in the number of species reported from the Goa to 74 from the existing 39. The new records are marked with an asterisk in Table 2.
Orthetrum sabina was the most abundant species with an occurrence frequency of 81.25% followed by Diplacodes trivialis & Pantala flavescens (75%). Orthetrum glaucum was a close fourth with an occurrence frequency of 50%. These results indicate a fairly well distributed population of the above species in the entire state and also in varied habitats. Seven species viz., Mortonagrion varalli, Agriocnemis splendidissima, Agriocnemis femina, Hylaeothemis indica, Idionyx saffronata, Neurothemis intermedia, Palpopleura sexmaculata were documented only once during the survey period. The details are shown in Table 2.
Table 1 indicates that the maximum diversity was observed at Bondla (25 species) followed by Paytale (23) and Derode (22). This could also be attributed to the survey effort since at all these sites maximum surveys were conducted (4 times). Paytale and the surrounding areas in Ponda Taluka are of conservation importance since the site not only holds a good diversity of odonates but two of the seven species documented only once during the period were documented from this site.
It was also observed that the maximum diversity was found during the monsoon season wherein 46 species were documented followed by winter (43) and summer (29). This is in accordance with the life history of odonates and their dependence on water bodies. Idionyx saffronta and Mortonagrion varalli were recorded only in the monsoons, Palpopleura sexmaculata was recorded only in winter, while Lathresticta asiatica was recorded only in summer. The Kerala Dartlet Agriocnemis cf. keralensis hitherto known and reported only from Kerala where it was considered endemic, has been documented from the state, thereby indirectly suggesting its presence in the states of Karnataka and Tamil Nadu. This species was identified in consultation with David Raju, Naturalist, Taj & CC Africa.
Except Aciagrion hisopa, Aciagrion pallidum, Agriocnemis lacteola, Enallagma parvum, Pseudagrion malabaricum, Ellatoneura tetrica and Lestes viridulus listed by Kulkarni & Talmale (2008) from the Fauna of Goa, all other species were recorded in the present study.
Though the present study covers varied habitats in the state of Goa, the authors are conscious of the fact that more extensive surveys are needed along the water bodies throughout the state and especially in the network of protected areas to understand seasonality and flight periods. Biodiversity surveys still largely focus on larger animals, especially vertebrates and even the biodiversity hotspot status of the Western Ghats is based largely on data pertaining to vertebrates and flowering plants, as data on invertebrates is insufficient or non-existent (Meyers et al. 2000). The present work is expected to be the foundation on which academicians and researchers will undertake more systematic surveys and studies on habitat requirement of these “indicator” species.
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