Butterflies as nature’s early warning system

Butterfly species need to be conserved in real landscapes, not only because they deserve it in their own right but also because of their usefulness as sensitive indicators of environmental change and as an umbrella species whose targeted conservation benefits wider communities of lesser-known, threatened species.

A kaleidoscope of blue tiger butterflies.

IN the 21st century, India has had many large projects involving butterflies as tools for science, conservation and leisure. The use of butterflies as model systems in biological research has increased enormously over the past two decades, far more rapidly than any scientist of the 1980s could have foreseen. There has been a parallel advance in the priority global, national and voluntary conservation bodies have afforded butterflies, not just as objects worthy of greater conservation effort in their own right but also in recognition of their usefulness as sensitive indicators of environmental change and as an umbrella species whose targeted conservation benefits wider communities of lesser-known, threatened species.

Hand in hand with the increased use of butterflies in pure and applied biology, there has been a burgeoning popular interest in them as objects to be noticed and enjoyed. Today, butterfly gardening, watching and photography have largely replaced as leisure activities the more specialised and male-dominated hobby of butterfly collecting, and thanks to new technology, the beauty of butterflies has been captured in an unprecedented number of high-quality images, films and videos. Inevitably, this growing knowledge and interest and the availability of high-quality images have made butterflies increasingly useful tools in education.

Most ecosystems have been modified by man. Their preservation has become a major concern and is the aim of conservation biology. A better understanding of the peculiar life cycle of butterflies would directly contribute towards this important area of biology and help prevent the extinction of some species. It is not just a question of conserving humid zones and their incredible biodiversity but all natural habitats. Land management has become indispensable. In many cases, in-depth studies of various faunistic groups offer new conservation perspectives and foster fascinating challenges for multidisciplinary work teams.

Organised butterfly surveys have been carried out in different parts of the world since the 18th century. So far, a total of 19,238 butterfly species have been documented worldwide. Many researchers have carried out studies on butterfly ecology and conservation in various habitats of India in the past century, and butterfly fauna has been documented, particularly in the protected areas of central, northern and north-eastern parts of the country. Similar studies have been done in the Nilgiri Biosphere Reserve and the Eravikulam National Park in south India.

Butterflies are sensitive indicators of future change in vertebrates and plants because their reaction to environmental degradation or perturbations is amplified and rapid. Populations living at such sites are often subject to extreme fluctuations. Hence, butterflies (and by implication other insects) can be considered particularly sensitive bioindicators of environmental change compared with plants and vertebrates. The role of butterflies in assessing environmental quality in terrestrial ecosystems is crucial as their presence is a direct indicator of habitat quality and regional vegetation. Butterflies help in pollinating various plant species. Some butterfly species show migratory behaviour, which is seasonal, and are restricted to a selection of habitats, and this is an indication of the richness of the biodiversity of that region. Hence, butterflies are perfect candidates for biodiversity studies. Deforestation and loss of nectar resources and habitats for larvae and adults cause a decline in the population of several butterfly species as do hunting and forest fires. Various species of butterfly are threatened in natural ecosystems and in protected areas.

However, little information is available on butterflies in the southern protected regions of southern Tamil Nadu. Therefore, two surveys were undertaken in the Sathyamangalam Tiger Reserve in 2019-20 and 2020-21 to determine the trends in the composition of butterfly species and to identify their preferred host plants, adult food plants and distribution pattern. This information requires periodic updating in protected areas. The Sathyamangalam Wildlife Sanctuary and Tiger Reserve (STR) is a protected area along the Western Ghats in Erode district, which is in north-western Tamil Nadu. In 2008, it was declared a wildlife sanctuary, and in 2011 additional area was brought under its purview. The forest now covers an area of 1,411.6 sq km and is the largest wildlife sanctuary in Tamil Nadu. In 2013, it became the fourth tiger reserve in Tamil Nadu as part of Project Tiger.

In the context of significance, the Sathyamangalam forests act as a corridor in the Nilgiri Biosphere Reserve between the Western and Eastern Ghats that provides a genetic link between four other protected areas adjoining the STR: the Biligiriranganatha Swamy Temple Wildlife Sanctuary, the Sigur Plateau, the Mudumalai National Park and the Bandipur National Park. This protected area falls in the taluks of Sathyamangalam and Gobichettipalayam in Erode district.

Forest types in the ecoregion are predominantly tropical, dry forest, part of south Deccan vegetation and dry deciduous. In addition, this ecoregion has tropical evergreen (Shola), semi-evergreen, mixed deciduous and thorn forests. Evergreen forests are restricted to small patches in a few high-altitude areas (between 750 metres (2,460 ft) and 1,649 m (5,410 ft) of Sathyamangalam. Because the land-use pattern has changed towards hill agriculture and plantation crops, the semi-evergreen forests located in the high altitudes are under threat. The vegetation in the middle altitude slope comprises mixed and dry deciduous forests, while the foothills have the thorn forests. The dry deciduous forest present in the middle elevations is also under pressure of degradation. However, the protected area forest cover is about 65 per cent. The presence of mixed shrub land and grasslands leads to a good population of herbivores, the preferred prey of tigers.

Results of the surveys

A total of 168 species of butterflies was reported in the surveys; six families and 102 genera were recorded. The Nymphalidae family was rich in terms of number of species, comprising 58 of them, followed by Lycaenidae with 51, Hesperiidae with 25, Pieridae with 21, Papilionidae with 12 and Riodinidae with just 1. Eleven of the 12 listed species from Papilionidae appear to be common and account for 6.5 per cent of the total number of species recorded in the STR. The Paris peacock ( Papilio paris ) is the one species that appeared to be very rare. All of the 21 species from Pieridae are common in the STR and account for 12.5 per cent of the total number of species recorded. Among the Nymphalidae, 45 of the 58 species recorded are very common in the STR and account for 26.8 per cent of the total number of species recorded; five species are rare and eight species are uncommon. Forty-six of the 51 species recorded from Lycaenidae are common in the STR and account for 27.4 per cent of the total number of species recorded. Three species appear to be rare and two species are uncommon. The single species recorded from Riodinidae is one of the commonest in the STR. Twenty-three of the 24 recorded species of Hesperiidae are common and account for 13.7 per cent of the total number of species recorded in the reserve. All in all, 18 species in the STR were found to be migratory: 2 species from Papilionidae, 3 from Pieridae, 12 from Nymphalidae and 1 from Lycaenidae. The recently declared Tamil Nadu State butterfly, Tamil yeoman ( Cirrochroa thais ), was recorded in the higher elevations of the STR, nearer to the Western Ghats of Nilgiris. To date, only one fifth of the estimated four to five million species of insects living in the world have been discovered and described. Of these, about 40 per cent are beetles, of which most are known from a single specimen or site. With such poor data on which to base priorities, conservationists have inevitably relied on extrapolations from a few well-recorded, conspicuous insect groups to assess change among invertebrates. Butterflies are the only practical group to use in most parts of the world, but are they representative of other taxa? Moreover, among butterflies, are the more specialist species particularly sensitive to environmental change and can they act like an early warning system, alerting us to changes that will eventually impact more generalist species?

It was recently suggested that the widespread use of butterflies as indicators of change is appropriate because butterflies had apparently experienced extinction rates earlier. It was pointed out that comparisons of the proportion of species believed to have become extinct in different taxonomic groups would be biased if the groups being compared had not been recorded at the same levels in the past. Butterflies require certain specific soil temperatures; this seems to be crucial for their presence. This takes the form of an along-latitude ecological compensation, which does not allow for generalisations or extrapolations relating to the ecology and habitat requirements of other species.

Species once regarded as single entities are increasingly being found to be ecologically and genetically diverse, with many displaying local adaptations and several containing cryptic species. Understanding variations within morpho-species is vital both for the preservation of genetic diversity and for practical conservation management. We believe that the observed trends are similar in other populations although the pattern formed by these behavioural trends depends strongly on the availability of host plant resources as butterflies lay more eggs on food plants with a high number of flowers, a food resource of larvae in the phase of early development.

Most species show rather static (or slowly shrinking) distributions over the landscape. However, occasionally rapid range expansion has been reported in recent years in several cases, which has been attributed to the effect of global warming. Dispersal has a fundamental effect on local population dynamics and the long-term persistence of a species at the metapopulation scale. Dispersal within habitat patches determines the spatial structure of local populations and describes the pattern of movement of individuals.The population dynamics of most butterfly species are believed to be predominantly affected by environmental variations, particularly in resources and weather patterns. The sizes of butterfly populations are mainly estimated in the adult stages. Nevertheless, preliminary stages may also be used in many cases. The knowledge of the egg population size is advantageous because it is the reproductive output of the population that will determine the next generation and might therefore be more relevant for some ecological studies.

Although butterflies provide society with multiple benefits, including “butterfly watching” and their role as pollinators and important contributors to biodiversity, their value has so far hardly been reflected in the management of their habitats. As a consequence, some species are declining and face local extinction owing to inappropriate habitat conditions of which human land use is the main driving force in cultural landscapes. Humans apply different land-use regimes (disturbance regimes, for example, mowing, grazing or tilling) on the patch level and thus create highly dynamic and variable spatio-temporal patterns on a larger scale. These spatio-temporal patterns and dynamics directly translate into patterns of resource availability for organisms living in the landscape.

Urgent action should be undertaken to counteract this by setting up a butterfly habitat at the STR, but the action should be rooted in a deep knowledge of species ecology in Sathyamangalam with a clear determination of negative trends. It will be a difficult challenge, considering that even obtaining knowledge comparable to that which we have about butterflies in Sathyamangalam is extremely time-consuming and laborious. Butterflies require active management that should be based on an understanding of population dynamics and be economically efficient. Management decisions should not be arbitrary and should be based on current knowledge, even if limited. To meet these requirements, an Internet-based decision-supporting tool needs to be developed. Active management of butterfly conservation is strongly needed to evaluate an existing conservation scheme. A deterministic community module has to be developed for butterflies. This model should be novel and made realistic by incorporating the life stage (seedling, juvenile, vegetative, reproductive and dormant) dynamics of butterfly larval food plants. Overall, we can conclude that conservation strategies for optimal management of butterfly species need to be conducted on a case-by-case basis.

Vaithianathan Kannan is former Wildlife Biologist, Sathyamangalam Tiger Conservation Foundation, Tamil Nadu Trust, Erode, Tamil Nadu.