Patterns of Diversity, Abundance and Species Richness of Butterfly Fauna in
Borajan-Bherjan-Podumani Wildlife Sanctuary, Assam

¹Nikita Das*

Department of Zoology, Sikkim Central University, Gangtok, Sikkim, India

*Corresponding author: nitunikita1903@gmail.com

Abstract

Butterflies are important pollinators and effective bioindicator species to assess habitat quality and environmental health. The present study, conducted from March to October 2024, documents the diversity, species richness, and abundance of butterflies in the Borajan -Bherjan- Podumani Wildlife Sanctuary, Tinsukia District, Assam. A total of 89 butterfly species belonging to six families were recorded, out of which 14 species are protected under various schedules of the Indian Wildlife (Protection) Act, 1972. Out of the six families, the Nymphalidae family was the most dominant with 43 species, followed by Pieridae (13), Lycaenidae and Hesperidae (12 each), Papillionidae (8) and Riodinidae (1). The highest Shannon–Wiener Diversity Index (H′=3.63) and Evenness (E=0.96) were of the Nymphalidae family, which has the maximum diversity index of 3.63 and Evenness (E) is 0.96 for the family Nymphalidae. The study area highlights that the sanctuary has a rich butterfly diversity and important habitat for butterflies, emphasising the need for more conservation-focused studies and robust management strategies.

Key words: Lepidoptera diversity; Conservation; Wildlife Sanctuary; Shannon-Weiner index

Introduction

Butterflies, an important pollinator in an ecosystem beyond their aesthetic values they play an important role in ecosystem functioning, particularly as a biodiversity indicator species [1], [2]. Their high sensitivity to any subtle changes in environmental gradients and habitat heterogeneity strongly influences their species composition in a particular area, making them reliable indicators of habitat quality [3], [4].

Butterflies are considered to be one of the best taxonomically studied and documented groups of insects [5]. The members of the order Lepidoptera are distinguished from their other insect relatives by the presence of minute scales covering their wings and a pair of clubbed shaped antenna. The diversity of this insect fauna is restricted to specific habitats as butterflies, and their caterpillars are contingent on specific host plants and food resources [6].

Lepidoptera is further divided into Rhopalocera and Heterocera and into two groups, namely Microlepidoptera and Macrolepidoptera. Microlepidoptera consists of small moths, whereas Macrolepidoptera consists of all large moths and butterflies. The two superfamilies of the order Lepidoptera are Hesperioidea and Papilionoidea [7] where Hesperioidea includes skippers, and Papilionoidea comprises the true butterflies. Superfamily Papilionoidae is divided into five families Papilionidae (Swallowtails), Pieridae (Whites and Yellows), Lycaenidae (Blues), Riodinidae (Judies and Punches), and Nymphalidae (Brush-footed butterflies) [8].

Butterflies are the ideal organisms for various ecological studies, and the loss of abundance and diversity adversely impacts the ecosystem functioning of an area [6]. The North-Eastern region of India is home to a rich butterfly diversity [9]. Assam, located in this biodiverse region of North East India, lies between the Eastern Himalayas and the Indo-Burmese hotspot. The state supports a vast array of species, yet deforestation and resource exploitation are gradually decreasing its diversity of flora and fauna [10].

The documentation of butterflies in the state of Assam goes back to the British Era. In the Eastern Himalayan region, the major account of butterflies was documented by Evans [11], who documented 96 endemic butterfly species, of which 45 species were from Assam. Similarly, Talukder and De [12] conducted comparative research on the diversity of butterflies in tropical semi-evergreen forest and disturbed habitats in Assam University Campus, Silchar, Assam. Another preliminary study carried out by Gogoi [13] documents 292 butterfly species from Jeypore-Dehing Forest, indicating high butterfly diversity in the semi-evergreen forest of upper Assam. Similar findings with abundance of swallowtail butterflies population in Dangori reserve forest in Tinsukia District of Assam also indicate high butterfly diversity in the region [14].

The Borajan-Bherjan-Podumani Wildlife sanctuary of Tinsukia district, Assam, is less explored in terms of studies on butterfly diversity, hence this present study was undertaken to document the diversity, abundance and species richness of butterfly fauna in this protected area with reference to their conservation status.

While many studies have documented diversity and identified many endemic species of the butterfly fauna in the Eastern Assam’s protected sites, yet many other protected areas, mainly on the easternmost part of the state, such as the Borajan-Bherjan-podumani Wildlife Sanctuary has not been completely documented. There is a need for proper documentation and regular monitoring of butterfly fauna from this wildlife Sanctuary which enables the reduction of human mismanagement and anthropogenic activities [15].

While studies on butterfly diversity have been documented in different habitats across the state of Assam, such as semi- urban habitats [16] and urban-altered forest habitats [17]. However, forest fragments such as Borajan-Bherjan Podumani Wildlife Sanctuary in Tinsukia district, Assam, remain less explored. Hence, the present study was undertaken to document the diversity, abundance and species richness of butterfly fauna in this protected area with reference to their conservation status.

Material and Method

Study Area

The sampling was carried out in Borajan-Bherjan-Podumani Wildlife Sanctuary in Tinsukia district, a legally protected area covering 7.22 sq. km comprising three separate forest blocks, namely Borajan, Bherjan and Podumani in Tinsukia district [18]. This sanctuary is situated in the upper Brahmaputra valley between latitudes 27°31′30.89″N and longitudes 95°22′0.53″E and falls within a humid subtropical zone supporting diverse vegetation [19].

Despite its size, the sanctuary harbours a high biodiversity, including primates such as the western Hoolock gibbon (Hoolock hoolock) and Rhesus macaque (Macaca mulatta). The wildlife sanctuary also harbors ideal habitat for mammals, including Leopard (Panthera pardus), wild boar (Sus scrofa), as well as an avian community of more than 80 species, including woodland bird species such as kingfishers, hornbill, drongos, mynas and many other insect species, including butterflies, damselflies and dragonflies [20].

Sampling Method

Butterfly sampling was conducted from March to October 2024, twice per month following the Pollard Walk Method [21]. A transect of 1 km was established within the study site and is divided into 20 smaller sections, each 50 meters in length, across different locations in the study site. Each transect was surveyed by slowly walking at a constant pace within a fixed distance, and species from either side of the transect were recorded. Identification was done by sampling and by using the photographic guide provided in Kehimkar [8], and Evans [11], and photographs were captured in cases where the identification of the small species belonging to the Hesperidae family was not feasible, and were identified later using various resources, including ifoundbutterflies.org [22].

Data Analysis

Various community parameters such as species richness, abundance, Shannon-Weiner diversity index and evenness were calculated for the butterfly community of the study area. Species richness is the total number of species recorded in the study site during the sampling. Species richness is the basic and most commonly used measure of diversity calculation of any biological community. But there is a possibility of missing many species present in an area or habitat during the sampling. Hence, different non-parametric richness estimators were computed using the software Estimate S Version 9 [23]. Among the various non-parametric estimators Chao and Jackknife estimators based on their precision in estimating true richness were considered. Based on the observed and the estimated non-parametric estimators, the species accumulation curve was obtained to test whether the sampling effort was enough to encounter all the species that occur in the study area.

The diversity was calculated using the Shannon-Weiner diversity index [24] (H′) formula: H′ = − Σ Pi ln (Pi). Where, Pi = Proportion of total sample belonging to the ith species. Similarly, evenness (E or J) was calculated by using Pielou’s Evenness index [25] formula: J = H′ / Hmax or J = H′ / ln S, where H′ is the value of the Shannon-Weiner diversity, and lnS is the natural logarithm of the species richness.

Results

During this study, a total of 89 species of butterflies of 2,211 individuals of butterfly species belonging to six families were recorded after the completion of 20 transect counts. The species accumulation curve of butterflies in the habitat is presented based on the observed and estimated richness (Table 2). The species accumulation curve reached an asymptote, indicating that the sampling effort was complete and no further sampling is required (Fig. 1).

Butterflies belonging to six families, namely, Nymphalidae, Hesperidae, Papillionidae, Lycaenidae, Pieridae and Riodinidae (Fig. 4). Family Nymphalidae (48.31%) was the most dominant family with 43 species and 1,071 individuals, Pieridae (14.60%) with 380 individuals of 12 species; Lycaenidae (13.43%) with 295 individuals of 12 species, Hesperidae (13.48%) with 226 individuals of 12 species, Papillionidae (8.98%) with 213 individuals of eight species and family Riodinidae (1.12%) with 26 individuals of only one species (Table 3), (Fig. 2, Fig. 4 and Fig. 5).

The Shannon-Weiner diversity indices for the six families Hesperidae, Lycaenidae, Nymphalidae, Papillionidae, Pieridae and Riodinidae are 2.376737, 2.425171,3.639842, 2.042251, 2.50783 and 0, respectively. Similarly, Pileous evenness indices for these families are found between 0.95-0.97, indicating a good ecosystem condition (Table 1), (Fig. 3).

Table 1: Species richness in terms of number of species, abundance, Shannon-Weiner diversity index and Pielou’s Evenness of butterfly fauna in Borajan- Bherjan-Podumani Wildlife Sanctuary

During this study, 14 species among the total 89 species, viz. Pelopidas sinensis (Mabille) Schedule IV, Tagiades japetus (Stoll) Schedule II, Polytremis lubricans (Herrich-Schaffer) Schedule IV, Prosota aluta (Druce) Schedule II, Poritia hewitsoni (Moore) Schedule II, Prosotas nora (C. Felder) Schedule II, Lampides boeticus (Linnaeus) Schedule II, Athyma ranga (Moore) Schedule II, Discohora sondaica (Boisduval) Schedule I, Lexias dirtea (Fabricius) Schedule II, Lexias cyanipardus (Butler) Schedule II, Cynitia lepidea (Butler) Schedule II, Euploea radamanthus (Fabricius) Schedule IV, and Charaxes bernardus (Fabricius) Schedule II were found to be protected under different schedules of the Wildlife (Protection) Act, 1972 (Table 2 ).

Table 2: Butterfly species protected under different Schedules of Indian Wildlife (Protection) Act, 1972

Table 3: List of butterfly species along with the number of individuals observed during the sampling

Discussion

In this study, a total of 89 butterfly species belonging to six families were observed, which represents 23.77% among the total 375 species that occur in eastern Assam [19] and 9.25% of the 962 total butterflies in the entire state of Assam. This reveals that the study area has diverse habitats to support various butterfly species.

Species richness and diversity are high in the Borajan-Bherjan-Podumani wildlife sanctuary, similar to another research conducted by Gogoi et al. [26], Josi & Dhyani [27], where higher species richness in the Wildlife Sanctuary. It is because the wildlife sanctuary is comprised of undisturbed patch of vegetation with all trees and abundant flowering plants, which provide a favourable habitat to the butterflies [28].

Among the six observed families, the most dominant one with the highest species is the Nymphalidae. This is the usual trend in butterfly composition in almost all types of habitats. A similar pattern of dominance of Nymphalidae is also reported in other studies as well [27], [29], [30]. As supported by the result of this research, the highest species richness of the Nymphalidae family is due to their polyphagous nature and strong tolerance towards disturbance, which allows them to thrive across a wide range of habitats [28].

Different species of butterflies react differently to their surrounding landscapes due to the variations in the resources, tolerance level to any disturbance and according to their feeding (monophagous and polyphagous) nature as well. Additionally, the areas that consist of a higher density of tree species and abundance of resources such as flowering plant species and shrubs and provision of more light and space for basking and puddling, those areas attract more butterfly species. The wildlife sanctuary species, such as Common Duffer (Discohora sondaica), Common four-ring (Ypthima huebneri), Grey Pansy (Junonia atlites), Plain Tiger (Danaus chrysippus), Stripped Tiger (Danaus genutia), and Yellow Helen (Papilio nephelus), are some of the species that are common in most of the transects, showing that they are generalist species and have higher tolerance to any change in the environment.

The species that occurred only in a few transects in the Wildlife Sanctuary are Spotted Snow Flat (Tagiades menaka), Common Snow Flat (Tagiades japetus), Wax dart (Cupitha purreea), Common gem (Poritia hewitsoni), Suffused Snow Flat (Tagiades gana alica), Colour Sergeant (Athyma nefte inara), Commander (Moduza procris), and Knight (Lebadea martha). Such a pattern of varied occurrence indicates the degree of vegetation heterogeneity, abundance of trees, resource availability, and distribution pattern of butterflies [31].

Conclusion

The presence and absence, distribution and diversity pattern of butterflies in the Borajan- Bherjan-Podumani Wildlife Sanctuary establishes a correlation of butterfly abundance with the habitat of the region. The findings obtained from this study reflect the availability of diverse habitats, which overall facilitate favourable conditions for the survival of butterflies belonging to different families in the Borajan-Bherjan-Podumani Wildlife Sanctuary.

The study also reflects that intact and connected habitats such as wildlife sanctuaries and other protected areas are richer in terms of butterfly species [14], [32]. This emphasizes the importance of safeguarding forest fragments and the need for more effective conservation measures, such as a combination of scientific research, habitat management, protection of host and nectar plants, maintenance of habitat connectivity, and involvement of local communities in the management plans for the preservation of butterfly diversity and the overall integrity of the ecosystem [33]. High abundance of the Nymphalidae family and the presence of 14 species protected under different wildlife protection act has also proved that the area is highly diverse and has a beneficial ecological role, and should be explored more for conserving this unexplored wildlife sanctuary in the district. Despite its relatively small geographic area, the Borajan-Bherjan-Podumani Wildlife Sanctuary harbours a remarkably rich butterfly fauna, including the protected species. This sanctuary has been unexplored and undocumented in terms of studies on butterflies, and this current study represents the first systematic documentation on butterfly diversity from this area. Hence, the findings and results highlights need for further long-term monitoring and conservation planning and management strategies for this lesser-known but diversity-rich wildlife sanctuary.

Declarations

Conflict of interest: The author declares that there are no financial, personal, professional, or Institutional relationships that could be perceived as a conflict of interest or as having influenced the research or its interpretation in this manuscript.

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