Abstract: Background: Dragonflies and damsflies are one of the most diversified creatures on the earth. Materials and Methods: In the present study, Swanga-Vithoba lake was choosen to study Odonata diversity. This study was carried out in three seasons as: monsoon, winter and summer. Lake area was divided in four sites as: East, West, North and South. A total of 33 species representing 6 families were recorded from the multiple transect area of 1 km long and 5 m wide. Results: In summer, 88.89% indivuals were randomly distributed and 11.11% were aggregated, 89.65% were randomly distributed and 10.35% were aggregated in winter and 93.93% were randomly distributed and 6.06% were aggregated in monsoon. During monsoon, 650 flies were encountered which decreased to 424 individuals in winter and it was only 249 flies in summer. Brachythemis contaminata was the most abundant in monsoon. Lebellulidae was the dominant family with 19 species while other families were not as much diverse which could be due to their shorter life cycle and widespread distribution. Conclusion: Shannon diversity index indicated that winter is relatively diverse (1.357) followed by monsoon (1.342) and summer (1.319).
INTRODUCTION
Odonata belongs to one of the most ancient creatures on earth with fossil records dating back to the Permian era 230-280 million years ago with 5740 species/subspecies of Odonates belonging to 654 genera in 32 families are reported worldwide1,2. Order Odonata which includes dragonflies and damselflies is a small, well known order of insects which is widely distributed all over the world3. Pre-adult stages of Odonates are aquatic in nature and adjust themselves in both stagnant and running water4. Odonates may be taken as an indicator of ecosystem quality. In addition to their direct role as predators in ecosystem, they are also indicators of quality of the biotope5. They are often used as indicators for environmental health and conservation management6. Their sensitivity to structural habitat quality (e.g., forest cover, water chemistry) and amphibious habits make dragonflies well suited for use in evaluating environmental changes in the long term (biogeography, climatology) and in the short term (conservation biology), both above and below the water surface7-11. Dragonflies are often used in both fundamental and applied research because of the relative ease with which they can be observed and their broad array of behaviours. In many regions reliable identification literature is available, so species can be determined fairly easy.
There is no comprehensive account of Indian odonates after12 published during 1930’s. Large number of endemic odonates are being threatened due to large scale habitat destruction. Large scale habitat alterations such as damming channel diversion, sand mining and pollution are seriously threatening the survival of these species13.
Sawanga lake is situated at 20°49' 0" N, 77°53' 0" E, 23 km East to Amravati, Maharashtra; India set in hilly region with good forest cover. At mean water level, the surface area is 6,717 km2, the height from riverbed is 19 m, the largest length of the lake is 1,422 m and the volume is 481 m3. The lake is constructed for irrigation purpose and was started to use14 in 1972.
A seasonal study on Odonata fauna from different locations in Sawanga-Vithoba lake region is carried out. Seasonal diversity and abundance of species are studied. This report also emphasizes season wise family abundance of order Odonata.
MATERIALS AND METHODS
Sawanga-Vithoba lake area was divided into four sites as; East, West, North and South. Each site was surveyed in three seasons multiple times. For the observations of species, transects of 1 km long and 5 m wide was followed. Bi-weekly random survey carried out from June, 2011 to May, 2012 at Sawanga-Vithoba lake region. Odonates were photographed and identified. Surveys were conducted in all the seasons. All surveys were conducted in the afternoon till 3 pm.
Photography and identification: Odonates were photographed by the digital camera (Make-Sony model No. W-310) and identified using the keys of Andrew et al.13 and Subramanian15.
Statistical analysis: Species richness was calculated as:
where, D is the species richness, S is the No. of individuals of a particular species and N is the total No. of the individuals in collection.
Simpson’s index (λ): It was calculated by the following equation:
where, n is the No. of individuals or amount of each species and N is the total No. of individuals for a site.
Shannon-weiner index (H’): It was calculated as:
where, n is the No. of individuals or amount of each species and N is the total No. of individuals for a site and ln is natural log of the number.
Similarity index: Similarity index was calculated as:
RESULTS
Distribution of Odonates in different seasons at study area was assessed as 88.89% were randomly distributed and 11.11% were aggregated in summer, 89.65% were randomly distributed and 10.35% were aggregated in winter and 93.93% were randomly distributed and 6.06% were aggregated in monsoon. The aggregated distribution indicates seasonal preference, where random distribution indicates available resource use and suitability of season to survival.
In this study, the number of Odonates encountered during monsoon were 650, which decreased to 424 individuals in winter and it was only 249 individuals in summer. However, 33 species were recorded throughout the year. Few species of Odonates such as Diplacodes lefebvrii, Orthetrum glaucum, Tholymis tillarga, Aethriamanta brevipennis, Aciagrion pallidum and Lestes elatus were not observed in summer. Brachythemis contaminata was the most abundant in monsoon indicating polluted water16. Pantala flavescens was also abundant in monsoon. A total of 33 species representing 6 families were recorded from the multiple transect area. Lebellulidae was the dominant family with 19 species, followed by Coenagrionidae (10 species), Gomphidae (1 species), Aeshnidae (1 species), Platycnemididae (1 species) and Lestidae (1 species). Orthetrum was found to be the most species rich gen with 4 species. During the study, Shannon, Simpson and Hills indices were calculated as a measure of diversity in three different seasons of multiple use areas. The Shannon diversity index indicated that winter is relatively diverse (1.357) followed by monsoon (1.342) and summer (1.319).
Odonata diversity: Thirty three species of Odonata were observed at Sawanga-Vithoba lake area under six different families. Most of the species were common. Odonata species distribution at four sites at Sawanga-Vithoba lake is documented in Table 1.
| Table 1: | Documentation of Odonata species at Sawanga-Vithoba lake |
| Fig. 1: | Family distribution of Odonata at Sawanga-Vithoba lake area |
| Table 2: | Diversity indices of Odonata diversity and distribution at four sites at Sawanga-Vithoba lake area in monsoon |
Family diversity of Odonata: Six families of Odonata reside at Sawanga lake region. In the present study, 19 species of odonates belonging to family Libellulidae, 10 species of family Coenagrionidae and one species each of Ghomphidae, Ashnidae, Platycnemididae and Lestidae was found. Libellulidae is the most represented family with 19 species exploring 58% of species, family Coenagrionidae 30% species, families Ghomphidae, Ashnidae, Platycnemididae and Lestidae exhibit 3% of the species (Fig. 1).
Seasonal distribution of Odonata: In monsoon, total 650 individuals were observed at the lake region, 132 individuals at East site, 189 at West, 176 at North and 153 South sites. Trithemis festiva was not observed at site third (North). Brachythemis contaminata and Pantala flavescens were prevalent.
In winter, total 424 individuals of the Odonata were observed. One hundred and eleven at East site, 107 individuals at West site, 111 at North site and 95 at South site. Species Diplacodes lefebvrii, Rhyothemis variegate, Potamarcha congener, Aethriamanta brevipennis were not observed in winter.
In summer, total 249 individuals of the Odonata were observed, 66 at East site, 65 individuals at West site, 58 at North site and 60 individuals at South site were observed. Few species of Odonata such as Diplacodes lefebvrii, Orthetrum glaucum, Tholymis tillarga, Aethriamanta brevipennis, Aciagrion pallidum and Lestes elatus were not observed in summer. Most of the species were less in number in summer (Fig. 2).
Diversity indices in monsoon: Diversity indices show that the distribution and diversity of Odonata at four sites of Sawanga-Vithoba lake area are in good range. Similarity index (J) is in the range of 0.9 stating much similar species of Odonata at four sites of Sawanga-Vithoba lake area. Various indices of Odonata diversity are shown in Table 2 and 3.
Diversity indices for winter season: Diversity indices show that the distribution and diversity of Odonata at four sites of Sawanga-Vithoba lake area are in good range. Similarity index (J) in the range of 0.9 stating much similar species of Odonata at four sites of Sawanga-Vithoba lake area. Various indices of Odonata diversity are shown in Table 4 and Fig. 3.
Diversity indices for summer season: Diversity indices show that the distribution and diversity of Odonata at four sites of Sawanga-Vithoba lake area is less as compared to winter and monsoon. Similarity index (J) is the range of 0.9 stating much similar species of Odonata at four sites of Sawanga-Vithoba lake area. Various indices of Odonata diversity are shown in Fig. 4.
| Fig. 2: | Pattern of species distribution of Odonata at Sawanga-Vithoba lake area in monsoon |
| Table 3: | Species distribution of Odonata at Sawanga-Vithoba lake region in monsoon |
| Fig. 3: | Pattern of species distribution of Odonata at Sawanga-Vithoba lake area in winter |
| Fig. 4: | Pattern of species distribution of Odonata at Sawanga-Vithoba lake area in summer |
| Table 4: | Diversity indices for Odonata diversity and distribution at four sites of Sawanga-Vithoba lake area in winter |
| Table 5: | Seasonal variation of Odonata interms of species richness at Sawanga-Vithoba lake area |
| Fig. 5: | Seasonal variation in family abundance of Odonata at Sawanga-Vithoba lake area, y-axis represents number of species |
Seasonal variation and family abundance: In all the three seasons family Lebellulidae and Coenagrionidae are the most represented families. The most abundant family is Lebellulidae with more number of species. Other four families Gomphidae, Ashnidae, Platycnemididae and Lestidae are distributed equally (Fig. 5, Table 5).
DISCUSSION
Distribution range of Odonata is from temporary to permanent water bodies6,17. Earlier 54 species of Odonata: Anisoptera (33) and Zygoptera (21) belonging to temporary water bodies were recorded from different parts of India12,18-24. Odonata are sensitive to the changes in the habitat and climate, which influence their distribution and abundance.
In the present study, Anisoptera (Dragonfly) were abundant than the Zygoptera (damselfly). However, Fraser12 and Subramanian15 stated that shade and aquatic vegetation could favour Zygoptera more than Anisoptera. Anisoptera are abundant in most of the water bodies might be due to their high dispersal ability25-28 and their adaptability to wide range of habitats29-31. Damselflies are less abundant might be due to their limited dispersal ability32, unstable and changing environment in the temporary water bodies26,28 and partial or absence of shade cover7. Species richness and diversity of Odonata also influenced by the size of the temporary water bodies7,28,33-37. Satisfactory species richness and abundance at Sawanga-Vithoba lake could be attributed to the size of the lake and less pollution.
Human disturbances (modification of habitat structure)9,34,38-43 contamination of water bodies44 and the presence of predators45,46 affect assemblage of Odonata species. The abundance of Libellulidae (Anisoptera) and Coenagrionidae (Zygoptera) in the present study could be due to their shorter life cycle and widespread distribution40 and tolerant to wide range of habitats47,48. Species richness was found to be similar for all the sites. In summer few species were totally absent. Patterns of species richness and community composition are found to be similar.
In odonates showing highly significant univariate relationships between community composition and locally measured habitat/vegetation structure variables. The importance of environmental variables in predicting the community similarity and odonates may be largely attributable to substantial similarity in the physical environment (e.g., vegetation structure) between various sites.
CONCLUSION
Thirty three species of Odonata under six different families were observed at Sawanga-Vithoba lake. Most of the species are evenly distributed at four sites of Sawanga-Vithoba lake area. Species richness of few species such as Trithemis pallidinervis, Brachythemis contaminata, Pantala flavescens, Ictinogomphus rapax and Ceriagrion coromandelianum is higher in all the seasons. Odonata season wise preference and available resources use was almost same at four sites. Diversity as determined by Shannon index was higher in winter as compared to summer due to reducing the level of water in summer and partial drying of lake at some places causing loss of feeding resources. Some families such as Libellulidae and Coenagrionidae were highly represented due to their shorter life span and wider distribution. Most of species were common at four station as determined by similarity index (J).
ACKNOWLEDGMENT
Authors acknowledge ISRO for financial support, Principal Chief Conservator of Forest (PCCF), Government of Maharastra for giving permission to conduct present study. BCUD, Savitribai Phule Pune university, DST-PURSE, DRDP and UGC-CAS are acknowledged for partial financial support.