Seasonal species diversity and abundance of Butterflies around Mukutmanipur Dam and its surrounding areas of Bankura District, Bankura, West Bengal, India

Introduction:

Due to the unique ecology of Mukutmanipur, various types of plants and animals can be seen here. Although it is not a recognized biodiversity hotspot like the Himalayas or the Western Ghats. The large and beautiful water reservoir and the green forests surrounding it are habitats of various small and large aquatic and wild animals. They are essential for ecological balance and their existence depends on the abundance of host and nectar plants. As primary consumers in the food chain and masterful pollinators, they not only sustain biodiversity but also enhance plant fertilisation and boost the productivity of flourishing landscapes. The diversity and richness of butterflies within a region provide information regarding the health of the ecosystem and its functioning [1]. Plants in particular locations exhibit a close relationship with the life cycle of butterflies [4]. Environmental factors such as temperature, photoperiod, rainfall, humidity, food availability, and vegetation cover, including bushes and herbs, can be the root cause of seasonal variations. Certain species of butterflies depend on specific host plants to lay eggs and complete their life cycle. The population dynamics of various species were significantly impacted by environmental influences [4]. Approximately 90% of the world’s 19,238 butterfly species are found in tropical regions [1,3]. About 1,504 butterfly species can be observed on the Indian subcontinent; it has a diverse topography, climate, and vegetation [7].

The expansion of human settlements and urbanization has led to widespread habitat destruction to accommodate new infrastructure such as residential colonies, offices, roads, apartments, and market complexes. Consequently, green vegetation, open fields, and roadside bushes are frequently removed. The loss of natural habitats has an adverse impact on butterflies, various insects, and birds, ultimately reducing the area’s biodiversity. Mukutmanipur is a beautiful region in West Bengal, India, famous for its beautiful landscape, rich flora, and it is also India’s second-largest earthen dam. This place is not being recognized as a place of biodiversity hot spot, much like the Western Ghats. The rare ecology in this place provides a place for various plants and animals. Birds, butterflies, tiny creatures of many types are regularly seen in the forests, hills and lakes of this region. Its ecological balance is at risk due to increasing urbanisation and tourism; that’s why conservation measures are crucial for maintaining its biodiversity. Maintaining a list of the different species in this area is essential in the current situation. Assessing the diversity and abundance of butterfly species in Mukutmanipur and the surrounding area was the objective of the present study.

Materials and Methods:

Study area:

The Mukutmanipur Dam is an earthen gravity dam. It was constructed at the crossing point of the Kangsabati and Kumari rivers in the Bankura district of West Bengal, India. (Fig. 1) The approximate coordinates of this dam are 86.7818° E longitude and 22.9639° N latitude. Including dykes and hillocks, the dam spans 11.27 km (7 miles) in length and reaches to a maximum height of 41.15 meters (135 feet) above the riverbed. It encompasses a catchment area of 3,625 square kilometres (1,400 square miles). Mukutmanipur experiences a diverse range of temperatures throughout the year. During the Summer (March to June), temperatures are generally high. Average high temperatures in July are about 32°C (90°F), and average low temperatures are about 25°C (78°F). This period also sees significant humidity and precipitation. The cooler and more pleasant months are November to February. January is the coldest month, having an average high temperature of 24°C (75°F) and lows around 9°C (48°F). The study area is home to a variety of nectar and host plants that offer an ideal habitat to numerous pollinators. These nectar plants provide an adequate and regular supply of nectar, it attracted bees, butterflies, and other beneficial insects. The host plants that they feed on (which also provide them with an excellent habitat for egg laying) are therefore able to support a complete life cycle for butterflies and other species, not only supporting it but also maintaining the overall biodiversity thus making it an ideal place for them. Massive trees offer lots of shade and places for living, while the landscape is large, serene water basins surrounded by lush greenery offer an ideal place for butterflies. The entire ecological health of the region has improved, and this balanced environment supports biodiversity.

Data Collection:

This butterfly survey was carried out over four seasons between February 2024 and January 2025 to understand how butterfly diversity changes throughout the year. The four seasons included in the study were Pre-monsoon (March–May), Monsoon (June–August), Post-monsoon (September–November), and Winter (December–February). To keep the conditions consistent and avoid environmental changes affecting the results, observations were done only on bright, sunny days. During these times, the average temperature was about 32°C, and the humidity was around 80%. These weather conditions are ideal for butterfly activity. To spot as many butterfly species as possible, field observations were planned during two key times of day. The first was in the morning, from 8:00 AM to 11:00 AM, when butterflies are most active because of the light and temperature. The second session was in the afternoon, from 1:00 PM to 3:00 PM, which is another time when many butterflies are still active. The survey was done in eight selected locations for 24 days using fixed paths known as linear transects. Observers used the modified Pollard Walk Technique [14], slowly walking along each route and noting every butterfly seen in an imaginary area of 5 × 5 × 5 metres. The preferred host plants of butterflies have also been documented using direct observation in the field and secondary data [5,6,11,17,18,19,21]. In the field, butterflies were systematically observed, identified, and counted. Photographic documentation was done using a Nikon D90 with a 72–300 mm lens. Preliminary identification was done on-site during the survey, generally by direct observation and photography and typically by manual collection, using conventional field guides. Common English names follow the conventions of Wynter-Blyth’s (1957) [20]. The scientific nomenclature used in this study aligns with Varshney’s (1983) [21]. Through precise and seasonally representative data collection, this strategy enhanced our understanding of the patterns of butterfly diversity in the year.

Statistical analysis:

1. Measurement of dominance-

In order to calculate the Importance Value Index (IVI), species dominance is measured through parameters such as density, relative density, abundance, relative abundance, frequency, and relative frequency [16].

Data interpretation:

Ecological indices data of four distinct seasons were compared through one-way ANOVA. Rarefaction analysis was done to assess the species richness in each season individually. The Jaccard similarity index was used for hierarchical classical clustering. PAST software (Version 4.03), developed by Øyvind Hammer at the Natural History Museum, University of Oslo, has been used for statistical analyses.

Result:

The present study is based on an extensive assessment of Mukutmanipur’s butterfly biodiversity. Ecological richness of this region was made apparent by the study’s impressive diversity, comprising 42 species representing 31 genera and five distinct families [1]. The butterflies are classified under 9 genera and 10 species of the Lycaenidae family, 10 Genera and 18 species of the Nymphalidae family, 2 genera and 3 species of the Papilionidae family, 6 genera and 7 species of the Pieridae family, and 4 genera and 4 species of the Hesperidae family. A total of 1097 butterflies were noted during four sampling seasons. With 378 individuals recorded, the Nymphalidae family exhibited the most abundance, peaking at 81 in a single monsoon sample. Also well-represented were the Lycaenidae and Pieridae families, with 328 and 294 butterflies, respectively. Hesperidae and Papilionidae were less abundant, with 36 and 61 individuals noticed, respectively. Compared to other seasons, most butterflies were found during the monsoon season [4]. A total of 382 individual butterflies and 39 species were recorded in Table 1. Fig. 2 illustrates the number of individual butterflies recorded for each family across different seasons.

Different ecological indices based on the observed butterfly species diversity are shown in Table 2. Eurema hecabe recorded the highest values, with a density of 4.4167, a relative density of 9.6624, an abundance of 4.4167, and the highest Importance Value Index (IVI) of 19.7674.

In Table 3, several ecological indices based on the diversity of butterfly species observed in the study area during the several seasons are shown. Of these, the post-monsoon period had the lowest value of the Margalef index (6.154), while the winter season had the highest species richness, as indicated by the highest Margalef index value (6.831). The monsoon season had the lowest dominance index (0.0435), indicating a more even distribution of species, whereas the winter had the highest dominance (0.0557). Similarly, the species dominance indicator, the Berger-Parker index, had a low value of 0.09492 in the post-monsoon and a maximum value of 0.12 in the winter. Diversity indices indicate a high butterfly density across the study area. The Simpson index ranged from 0.9565 in the monsoon to 0.9443 in winter. The Shannon index, a widely used diversity measure, varied between 3.376 (monsoon) and 3.236 (winter), showing rich but slightly fluctuating diversity throughout the seasons. The evenness (E) shows how evenly individuals are distributed. It is higher in the pre-monsoon season (0.7821) and lowest in the winter season (0.6692). The Brillouin index (HB) shows the lowest value of 2.975 in the winter and the highest value of 3.189 in the monsoon, indicating substantial variation. Lastly, the Menhinick index (DMn) shows that species richness in relation to individual count was lowest during the monsoon (1.995) and highest during the pre-monsoon (2.65). Together, these results highlight the study area’s dynamic and seasonally changing butterfly diversity [9]. These findings collectively underline the dynamic and seasonally shifting diversity of butterflies in the study area.

The values of Whittaker’s Beta Diversity Index are represented in Table 4. While the lowest value (0.10811) was between the Post-monsoon and Winter, indicating relatively less change in species composition between these seasons, the highest value (0.09589) was recorded between the Pre-monsoon and Post-monsoon seasons, indicating an increase in species turnover.

Table 5 shows the result of one-way ANOVA based on the season-wise variation of Brillouin index. It shows that the F value (9.78) is greater than the F crit value (6.59). It means the null hypothesis is rejected, indicating a statistically significant difference among the group means. At least one group of the Brillouin index is significantly different from the others.

In Table 6, the Tukey test result shows that there is a significant difference at three points: Monsoon and Pre-monsoon, Monsoon and Winter, and lastly Post-monsoon and Winter. This result indicates seasonal variation significantly affects the Brillouin diversity index between specific seasons. Other ecological indices like Simpson, Shannon, Dominance, etc., are accepting null hypothesis that clearly suggests seasonal variation is not significantly affecting those indices like the Brillouin index does.

The study site has trees, dense shrubs, and grasses that offer butterflies ideal shelter. There are various nectaring and host plants in the area (Table 7), resulting in it being a good habitat that is suitable for laying eggs and for a source of sufficient nectar [5,10]. The most commonly found host plants among them are Lantana, Imperata, and Calotropis, which attracted a wide variety of butterfly species to this area.

An Individual-based Rarefaction (IR) curve, which compares species richness across sample sizes, is shown in Figure 3. The Y-axis (Taxa ± 95% confidence) represents the number of taxa (species) expected for a given number of individuals, with 95% confidence intervals, and the X-axis (Individuals) represents the number of individuals sampled. Multiple coloured curves represent different seasons (Pre-monsoon, Monsoon, Post-monsoon, Winter). Each curve shows how species richness accumulates with the increasing number of individuals sampled in that season. Monsoon season (blue curve) has the highest species richness, reaching the highest point on the y-axis. Post-monsoon (green curve) has the lowest species richness among all the seasons.

Fig.4 is cluster analysis; the dendrogram is used to show the connections between various seasons. The vertical axis indicates the degree of similarity between the seasons. Higher values representing higher similarity. Seasons that are more similar to each other are joined together earlier in the dendrogram, making clusters. For instance, Post-monsoon and Monsoon are clustered together (~0.92), indicating a high degree of similarity between them. Post-monsoon and Monsoon joined at a higher point compared to the merge point of Pre-monsoon with this (Post-monsoon and Monsoon) cluster, showing that Post-monsoon and Monsoon are more similar to each other than Pre-monsoon. Winter is the most distinct season, as it joins at ~0.82 the rest of the cluster at the lowest similarity level [13].

Discussion:

This study on butterfly diversity in Mukutmanipur highlights its ecological wealth and butterfly seasonal dynamics. The fact that 42 species are documented under 31 genera and five families indicates the biological significance of the area. This study area has seasonal variation in butterfly diversity, thus giving an idea of habitat heterogeneity due to the presence of host and nectar plants all over the study area [12]. The most species-rich and abundant family was Nymphalidae, confirming findings of other tropical and subtropical ecosystems. Nymphalidae is a family that generally have high flexibility and wide ecological niches. Likewise, the Lycaenidae and Pieridae families were also well represented, most probably due to the availability of host plants and the right microhabitat for the taxon. However, the low abundance of the Hesperiidae and Papilionidae families could possibly be due to their tolerance of disturbance in the habitat, that are more specialised habitats, or that the host plant requirements demand too much from these families. Overall, this seasonal survey has revealed the highest diversity and abundance of butterflies at this time of year, with 382 individuals and 39 species being found, probably because the monsoon season has the most vegetation cover, the most floral abundance and the most favoured conditions for larval host plants and nectar resources. When compared to other seasons, winter has the highest Margalef index, which indicates high species richness, but at the same time the lowest evenness and the highest dominance values indicate that there was some species in the survey very much abundant at this time. Diversity indices further support the dynamic nature of butterfly communities. The Simpson and Shannon indices show overall high diversity, though they exhibited seasonal fluctuation. In winter, a relatively lower Simpson index (0.9443) and higher in monsoon (0.9565) indicate more equitable species distribution during the winter season. The highest level of Evenness (E) appears during the pre-monsoon season, representing a more uniform distribution of individuals within species during this period of transition. With the highest values for density, abundance, and relative density metrics, Eurema hecabe was clearly the most ecologically significant species based on the Importance Value Index (IVI). This suggests that populations may be able to withstand a range of environmental conditions. In Whittaker’s index-based beta diversity study, there was a great deal of seasonal variation in species composition, but the greatest change occurred between pre- and post-monsoon seasons, this could reflect changes in vegetation cover and the availability of resources. At the same time, winter and post-monsoon seasons showed little change, thus suggesting that community composition was rather stable between those two periods. The results of the ANOVA analysis show that ecological indices have less change between seasons despite the Brillouin index being significantly different with respect to the distribution of butterflies. These findings suggest that monitoring should be long-term, seasonal and stratified for biodiversity.

Conclusion:

Mukutmanipur is a very vibrant ecosystem with numerous seasonal and taxonomic variations, and this study brings forth the butterfly diversity at Mukutmanipur. The area has great riches. It also gets impacted due to seasonal changes in climate and availability of habitat, and hence has a lot of dynamic nature [4]. The monsoon season turned out to be the most productive one in terms of the number of individuals and species richness, with unique community characteristics during winter. Families like Nymphalidae, Lycaenidae and Pieridae being more abundant indicates their adaptability. However, the low utility of families like Papilionidae and Hesperiidae means the need for careful application of habitat management facilities. Ecological indices, rarefaction curves and cluster analysis together give a system in constant change with species turnover, evenness and dominance fluctuating with the seasons of this area [13], this provides a picture of a finely balanced ecosystem of this area. The statistically significant seasonal differences show that the monitoring needs to be continued with a seasonally inclusive approach to attain the full information about species diversity in Mukutmanipur. Butterflies are one of the important species of diversity in Mukutmanipur. They provide fantastic information on how the diversity of species changes with seasons [1]. Their results confirm the need for proper conservation management and more ecological research work especially during different seasons. These vulnerable but important pollinators are able to survive and continue to perform their natural role by protecting their habitat.

Abbreviations:

D-Density per Day                                          H-Shannon index              

RD-Relative Density                                      D-Simpson’s Index of Diversity

F%-Frequency (F%)                                       HB-Brillouin Index           

RF-Relative frequency                                   DBP-Berger-Parker index

A -Abundance                                                 DMg-Margalef index

RA-Relative Abundance                                DMn-Menhinick’s Index

IVI-Importance Value Index                           E-Evenness

ANOVA -Analysis of variance                      VC-Very Common

C-Common                                                     R-Rare

VR-Very Rare

Acknowledgements:

The authors like to express sincere gratitude to the Department of Zoology, Sidho Kanho Birsha University, Purulia, for the facilities provided. We also wish to acknowledge Assistant Professor Arijit Ganguly, Achhruram Memorial College, Jhalda, Department of Zoology, for his continuous guidance, insightful suggestions, and encouragement during the research programme. Special thanks to Abhik Rong for providing the study area map, which is instrumental to this study.

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