Study of Butterfly Diversity in Chilkigarh, West Bengal (India)

INTRODUCTION

Faunal components of forest ecosystems play a crucial role in the maintenance and sustainability of that ecosystem, and ecological indicator species are used worldwide for assessing biodiversity. The effect of forest management on the structure and function of a forest ecosystem can be illustrated by studying bioindicators [1, 2]. Butterflies, among the insect groups, due to their short life history traits, host plant preferences, easily identifiable features (unique wing color patterns), high diversity, sensitivity to microclimate as well as environmental changes, themselves achieve such a status to be accepted as bioindicator [3]. Butterflies are primary consumers in the forest ecosystem and play an important role as herbivores in the stability of food webs [4, 5]. To maintain and improve community structure, they serve as pollinators [5-7], surrogate species for floral and faunal diversity [8], host of parasitoids [5, 9], and prey of predators [4, 5, 10]. Chilkigarh, a rural and tribal area situated on the bank of the Dulung River, is mostly surrounded by Sal Forest and has become a famous tourist destination for the presence of Chilkigarh Raj Palace and Kanak Durga Sacred Grove. In 2018, it received the status of Chilkigarh Kanak Durga Biodiversity Heritage Site from the Environment Department, Govt. of West Bengal, India. Altogether, 388 plant species, including 105 with medicinal values and 26 species of megafauna (vertebrates), have been reported [11]. Recently, 37 species of birds have been documented from different sites in Chilkigarh [12]. To elucidate the butterfly community of this area, a study has been done to gather knowledge about their diversity, dominant family group, species-to-genus ratio, legally protected species, etc., that will surely provide a route for future investigations regarding their nectar plants, host plants, seasonal fluctuations and ultimately planning for conservation.

MATERIALS AND METHODS

Study area

Chilkigarh (Figure 1) is a tribal area (latitudes 22°27′20′′ N and 22°56′50′′ N and longitudes 86°52′20′′ E and 86°53′10′′ E), having an average elevation of 60-85 m above the sea level [13], situated in Jamboni CD block, under Jhargram Subdivision of District Jhargram, West Bengal. The western boundary falls under the lower ranges of the Chhotanagpur Plateau, the northwest area is uninhabitable, and most of the areas are non-productive due to the nature of the lateritic soil. Dulung, a monsoon-nourished river, passes down across the village. Chilkigarh forest is situated on the eastern side of the bank of this river, comprising heterogeneous vegetation of semideciduous, deciduous, and evergreen trees [11]. This area can be classified under the category of “Tropical Moist Deciduous Forest” as huge Sal plants predominate. Different types of shrubs, herbs, climbers, and grasses provide resources to small to large creatures. Dulung river bank, Chilkigarh Kanak Durga Sacred Grove, Open grasslands, Chilkigarh Raj Palace, Sonajhuri garden, Sal forests, and Agricultural lands were selected for study.

Data collection

The study was carried out from 7:00 am to 10:00 am and 3:00 pm to 6:00 pm for 12 months (December 2021 to November 2022), adopting sampling techniques such as the Pollard walk method [14], Direct searching method [15], and Time Constrained method [16].

Identification & documentation of butterfly species

Photographic documentation was done by visiting different sites once or twice per month to capture photos from the best possible angles using a Canon IXUS 190 Digital camera and mobile phone camera – Redmi 6 Pro & Redmi Note 8. Species were identified using the following references [17-19] and further consulting the website of Butterflies of India [20].

Community analysis

To understand the structure of butterfly community α-diversity, i.e., the diversity of species within the community has been measured using the following diversity indices. All data were calculated using MS Excel 2019 software, and results were further verified using statistical software PAST version 4.03 [21].

Species richness

The Shannon-Wiener index, commonly known as the Shannon index of diversity [22], sometimes erroneously called the Shannon-Weaver index, was derived independently by Shannon and Wiener, which apply information theory to measure species diversity. Rare species with very few individuals can contribute some value to this index [23]. It is calculated considering Eq. (1) as follows:

Where H’ is the value of the Shannon index and pi is the proportion of individuals of ith species in the community. The value usually ranges between 1.5 to 3.5 and rarely exceeds 4.5. The value of H’ is related to species richness but is also influenced by underlying species abundance distribution.

Margalef’s index [24] is used to calculate species richness considering Eq. (2) as follows:

Where S is the total number of species and N is the total number of individuals in S species.

Species abundance

Simpson’s index [25] is the measure of the probability that two organisms picked at random from a community will belong to the same species. This index relates the contribution made by each species to the total number of individuals present. It can be calculated considering Eq. (3) as follows:

The value of D ranges between 0 to 1 and is inversely proportional to the wealth of species. As the value of Simpson’s index increases, the species diversity decreases. Therefore, the more the index value is inclined to 0, the more abundance will be in the community.

Simpson’s index of diversity = 1- the probability of picking two organisms that are the same species and calculated considering the following Eq. (4) as follows:

Where D is the value of Simpson’s index of diversity and pi is the proportion of individuals of the species in the community. Simpson’s index of diversity gives relatively little weightage to rare species and more weightage to common species. It ranges from 0 (low diversity) to a maximum of (1-1/S), where S is the total number of species.

Table 1. Family-wise checklist with common and scientific names along with relative abundance, dominant status, and WPA status of each butterfly species encountered at Chilkigarh.

*RA < 1 = Subrecedent (SR); 1.1-3.1 = Recedent (R); 3.2-10 = Subdominant (SD); 10.1-31.6 = Dominant (D) and > 31.7% = Eudominant

Species evenness

Pielou’s index [26] was used to measure species evenness. It was calculated considering Eq. (5) as follows:

Where H’ is the Shannon index and S is the total number of species. The value of e ranges from 0 to 1. The more the index value inclined towards 1, the more will be the evenness in the community.

The dominance status of each species was enumerated based on relative abundance following Engelmann’s scale [27]. Rank-abundance curve (Whittaker plot) is prepared, taking abundance rank on the X axis against relative abundance on the Y axis to graphically represent the relative species abundance [28].

RESULTS AND DISCUSSION

In our study, overall, 59 species of butterflies were recorded with a total count of 1583 individuals belonging to 45 genera under 6 families from Chilkigarh (Table 1; Figures 2 and 3). The family Nymphalidae appeared to be the most dominant (42.3% with 25 species), followed by Lycaenidae (20.3% with 12 species), Papilionidae (15.2% with 9 species), Pieridae (13.5% with 8 species), Hesperiidae (6.7% with 4 species) and Riodinidae (1.6% with 1 species) (Figure 4). Previous reports also support our findings that Nymphalidae is the dominant family in the neighboring districts: Purulia [29], Haldia [30], Midnapore [23, 30], and Howrah [31].