In this write up butterflies have been identified as the 'biotic-indicators' for the species richness monitoring system in an ecosystem and similarly for forecasting the climatic change impacts on biodiversity. It has already been found from the scientific experiments that, by using butterflies as indicators, increase of species richness and species assemblage have been augmented to 47% in a wild state. This wild state has been used as the healthy habitat for all kinds of animals
Use of butterflies as “indicators” is possible because they need three types of vegetation populations for their survival and distribution. This distribution is highly related with the phenological stages of the plants, the three types of plant population categories are larval food plants, nectar plants, and shade plants.
The butterflies use food-plants as egg laying supports. Butterfly species are very selective in plants for their egg laying activities. A female butterfly lays her egg only on a single plant on which its larva can develop by feeding on it; mainly by feeding on the leaves. These plants are so termed as food plants. Most butterflies can utilize a wide variety of flowers, including those of many cultivated varieties, as nectar sources. However, a more critical need is for the plants that provide food for the larval (caterpillar) stages, and most species will accept only one or a few species of plants at this stage.
Although the caterpillars feed on the leaves of these plants, the damage is usually minor and only temporary. It is estimated by experiments that, rather doing damage to the food-plants at the developmental stages, the butterfly adults do more benefit to the host plants by pollinating and gene-flowing activities leading to population increase of the plants. Caterpillars of some species feed on plants that are usually considered weeds.
Nectar plants are that by which butterflies can be attracted for their suitable flowers to nectar. Most butterflies can utilize a wide variety of flowers, these may be cultivated varieties or wild varieties, as nectar sources. But experiments showed that the butterflies are somewhat specific in selecting even the nectar plants as their family characters and many times as their generic characters. For the nectar-sac of the flower shall have to be within the range of proboscis capacity of the butterflies. All nectar-producing plants are not equally chosen / visited as they are not adaptable to the capability of all the butterflies equally. Butterflies seek nectar from many types of plants including ground covers, annuals, perennials, shrubs, trees etc.
Shade/ resting plants are mainly trees and hedges. It is revealed that, in the day time the butterflies take complete rest during afternoon 1:30 pm to 3.30-4.30 pm. The resting is not seen to occur on nectar plants or food plants. They take rest under/ on the leaves of hedges under a big shade tree. During this resting time butterflies do not move and do not feed on anything, but resting place need to be with high humidity and temperature comfortable for them. For this reason the butterfly park area especially the shade/resting area needs to be supported with water bodies.
Compared to the density of nectar plants and food plants area, the shade/ resting plant area must be more dense and with assemblage of high species composition. This means that species-richness of the plants (either related or not related to the butterflies) needs to be very high. Butterfly park directly and indirectly is very helpful for bio-diversity conservation and for establishment of species richness in an ecosystem.
Why butterflies are the best indicators?
Healthy presence of butterflies ensure the healthy status of a forest ecosystem. Butterflies have got reciprocal relations with the related plants. Because of that, they are distributed at all heights in the forest areas. The true/healthy forests provide three layers of vegetations in their status: vegetation at the ground level i.e. the grasses and the below man-height level vegetation; vegetation at man-height level i.e. the hedges and bushes; the canopy layers of vegetation i.e. the trees. The butterflies have got access to the plants of all heights at equal frequency. On the other hand, these plants are dependant on the butterflies for their pollination purposes and gene-flow activities.
Life cycle changes in the butterflies are deeply related with phenology of the host plants and other related plants. Butterfly wings and its entire body is covered with billions of dust particles which capable of absorbing quantum of light coming from the solar system; and the photons received by the dust particles produce (by prismic system) the beautiful colourations (combination of colours) on the genetically characteristic basis for each of the species differently. At the same time, these (arrangements of dust particles on the body) are very much sensitive to the climatic changes i.e. the changes in photoperiodism and thermoperiodism of the habitat where they are living.
For designating the butterflies as “biotic-indicators”, we have identified the research result in the way that, any climatic change is first perceived in the biosphere by plants and then by plant-phenology, but it does not appear visible to humans unless or until any organic damage is seen visually at drastic level. The butterflies have got serious sensitiveness to determine the phenological changes in the plants; and then in connection with the changes in plants, immediate changes in the life cycle and time-lag in butterflies are occurred. Then the population sustenance of butterflies gives them the “status of indicators” for forecasting impact of climatic changes and for the sustenance of biodiversity in an ecosystem.
Butterflies are very sensitive to the change of phenology of the plants in a forest ecosystem as they require plants of all heights for their life sustenance. Any climatic change affects phenological changes in plants. Any phenological, temporal and seasonal changes in plants affect the life cycle of the butterflies. Any abnormal change in the life cycle of buterflies affect the butterfly populations in an area. So, by seeing the population fluctuation visiually, 'climate change' forecasting can be measured.
The “Environmental Biology and Biodiversity Laboratory (EBBL)”, department of zoology, University of Dhaka has been conducting researches on the butterfly conservation and conservation of forest biodiversity since 1999. The EBBL conducted researches in the forest biodiversity of Bangladesh and has found very significant result on the question of utilizing butterflies as “biotic indicators” for monitoring climatic change impacts on biodiversity of forest ecosystems. In summary, the EBBL reports that all the south-eastern forest areas have been facing the question of climatic changes, especially in the status of providing biodiversity . The working areas of the EBBL are Anarsbari, Chautali, Phulbari, NoorJahan and Lawasara under Srlmanagal forest area; Rama-Kalenga and Satsaree under Habigang forest area; Karerhat, Mirsarai, Padua, Chunati, and Tangabati under Chittagong area; Fashiakhali, Eidgaon, Eidgar and Teknaf under Cox's Bazar area.
Of the experimenatl stations, the “butterfly indicators- experiments” showed that only Satsaree forest area has got less climatic change impacts on biodiversity and all other forests are affected. The most affected areas are under the Cox'sBazar forest region. In a study on the Fashiakhali forest it has been seen that the largest butterfly “bird wing” (Troides spp) are the most burning victim of the changes.
From 1999 to 2003 representative of the largest butterfly in the forest was found decreasing and from the year 2004 no trace of the “birdwing” in the forest is found. Reasons are accumulated in the EBBL lab. In abstract it could be said that the plants on which the “birdwings” depend (special vine: climbers) are very sensitive to climate change and human interference; their phenological changes have been occurred drastically and the dependant butterfly could not survive. But on the other hand, the same butterfly is still surviving in the Satsaree forset area. On the recorded data, the EBBL reports that biodiversity of all flora and fauna is in healthy condition in the Satsaree forest.
The EBBL has planned to extend its research areas as the following:
*Use butterflies as “biotic indicators” for monitoring/forecasting climatic change impacts on the biodiversity in the south-eastern forest ecosystems.
*Establishment of butterfly-colonization centres in experimental forest areas.
*Establishment of butterfly parks/ gardens for enhancing ecotourism and wildlife sanctuaries.
Establishment/materialization of the above programmes is the responsibility of the government. It is difficult for a lab. like the EBBL to materialize financially and administratively such large and national vital programmes. What the EBBL of Dhaka University can do is to do the scientific experiments and the researches to advance the programmes in perfect way. Though only the EBBL in the country has got vital experts in the line, but the laboratory intends to involve all other institutes like the forest department and other related organizations in the programmes.
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