Pollution's Impact: Butterflies' Plight And Survival

Butterflies are important indicators of a healthy environment and healthy ecosystems. However, they are extremely sensitive to environmental changes, and pollution is a key factor in their decline. Butterflies are affected by both direct and indirect effects of pollution, including haze smoke, nitrogen deposition, and heavy metal stress on local plants. These impacts can lead to increased mortality, longer development times, and smaller pupal weight, threatening the survival and development of butterflies.

Butterflies' nectar plants are sensitive to heavy metals

Butterflies are important indicators of a healthy environment and healthy ecosystems. Their fragility makes them quick to react to change, so their struggle to survive is a serious warning about our environment.

Plants growing in heavy-metal-rich soils can accumulate these metals into their nectar. Nectar chemical composition can alter the foraging behaviour of pollinators, including butterflies, and further affect plant reproductive fitness.

In a 2018 study, four heavy metals (zinc, copper, nickel, and lead) were experimentally manipulated in a native ornamental plant, Hosta ensata F. Maekawa, to investigate the effect of nectar metals on plant reproductive success. The study found that pollinators spent less time foraging on metal-treated flowers, but their visitation rate to metal-treated flowers was significantly higher than to control flowers. Moreover, pollinators removed less nectar from flowers treated with metals. The study concluded that heavy metals in nectar are capable of deterring nectar robbers and modifying pollinator foraging behaviour to enhance plant reproductive fitness.

Another study, conducted in 2013, found that nickel in nectar shortened the foraging time of bumblebees and discouraged bees from visiting nearby nickel-contaminated flowers.

In addition to altering the behaviour of pollinators, heavy metals in nectar can also have toxic effects on butterflies. A study on the impact of nitrogen deposition on butterflies found that nitrogen, coupled with warmer temperatures, allowed for much greater vegetation growth, leading to the loss of bare ground, very short turf, or dead plant material. These areas, known as hotspots, can reach temperatures of 30-35°C in the sunshine, while the adjacent grassland may only be around 10°C. This microclimate is essential for the survival of caterpillars, which need high temperatures to function properly and grow fast to avoid predators and disease.

Overall, the presence of heavy metals in nectar can have significant effects on the behaviour and survival of butterflies, highlighting the importance of conserving these fragile creatures and the ecosystems they inhabit.

Nitrogen deposition

Research has shown that butterflies dependent on dry, nutrient-poor habitats are more prone to extinction than those in nutrient-rich environments. Nitrogen, coupled with warmer temperatures, promotes vegetation growth, threatening the survival of caterpillars that depend on very warm microclimates. These microclimates, provided by bare ground, very short turf, or dead plant material, are essential for caterpillars to function properly and grow quickly to avoid predators and disease.

Several butterfly species that prefer open, sunny habitats, such as the Grayling, Wall, and Pearl-bordered Fritillaries, are experiencing further declines due to the impact of nitrogen pollution. Studies have also revealed negative effects on the development of caterpillars, with nitrogen enrichment leading to cooler, shadier, and damper conditions that are detrimental to their survival.

To mitigate the negative consequences of nitrogen deposition, policies and laws aimed at reducing air pollution are necessary. Additionally, technical improvements, buffer zones, and adapted landscape management can help reduce unwanted nitrogen input and protect sensitive habitats.

Haze smoke

The impact of haze smoke on butterflies

The smoke haze contains a mixture of gases and particles from forest fires, including carbon monoxide, carbon dioxide, sulphur dioxide, and methane, which have been found to negatively impact human health and local economies.

Similarly, haze smoke has been found to have a significant deleterious effect on butterflies, specifically the Squinting Bush Brown Butterfly (Bicyclus anynana). The haze smoke was found to increase the mortality of caterpillars, increase larval development time, and decrease pupal weight.

The mechanism of haze smoke's impact on butterflies

Insects breathe through spiracles, which are valve-like openings on the side of their bodies. These spiracles connect to internal tracheal tubes, which branch into finer tracheoles that eventually reach every cell inside the insect's body, where gas exchange occurs. This direct path to all internal organs makes insects extremely vulnerable to air quality.

The haze smoke was found to affect the butterflies in two ways. Firstly, the toxic chemicals in the smoke increased the mortality of caterpillars. Secondly, the haze smoke reduced the available food sources for the surviving caterpillars, either by damaging the plants they feed on or by preventing the caterpillars from locating them.

The implications of haze smoke on butterflies

The surviving caterpillars that were exposed to haze smoke took longer to reach the adult stage and turned into smaller adults, likely suffering from reduced potential for reproduction.

Butterflies are sensitive to environmental disturbances and are easy to identify and monitor, making them useful as bioindicators of the health of an ecosystem.

Insecticides and industrial pollution

A study monitoring the biodiversity of plants, adult butterflies, and leaf-mining larvae in a Dutch nature reserve over a period of six years (1994–1999) found that butterfly abundance decreased steadily over the period, indicating a negative diversity trend. The study hypothesized that the decline in butterflies was a secondary effect of heavy metal stress on local plants, which subsequently affected their pollinators.

Another study, which investigated the impact of haze smoke on the survival and development of butterflies, found that direct haze exposure significantly increased the mortality of caterpillars and decreased pupal weight. The study suggested that toxic smoke gases and toxic food, rather than particulate matter, were the main causes of the observed negative effects.

In addition to direct impacts, industrial pollution can also have indirect effects on butterflies. For example, nitrogen deposition, resulting from the burning of fossil fuels and intensive farming, can lead to habitat loss for butterflies.

Overall, insecticides and industrial pollution have been shown to have significant negative impacts on butterflies, contributing to their decline and extinction. These impacts can be direct, such as the toxic effects of haze smoke, or indirect, such as the loss of habitat due to nitrogen deposition.

Air pollution and climate change

One of the main ways air pollution affects butterflies is through the deposition of nitrogen in the atmosphere. Nitrogen levels have built up over time due to the burning of fossil fuels and intensive farming practices. Transport, power stations, industry, farm fertilisers, and livestock are all significant sources of nitrogen-based emissions. When deposited in the air and rain, nitrogen enriches the soil and creates acidic conditions that are damaging to the environment.

Research has shown that butterflies dependent on dry, nutrient-poor habitats are much more prone to extinction than those in nutrient-rich environments. Nitrogen, coupled with warmer temperatures, allows for greater vegetation growth, which can be detrimental to caterpillars that depend on very warm microclimates. These microclimates, provided by bare ground, very short turf, or dead plant material, can reach temperatures of 30-35°C, while the adjacent grassland may only be around 10°C. The loss of these warm habitats can have severe consequences for caterpillars, as they need high temperatures to function properly and grow fast enough to avoid predators and disease.

In addition to nitrogen deposition, heavy metal pollution has also been linked to the decline of butterfly populations. Studies have shown that the nectar plants of adult butterflies are much more sensitive to heavy metals than those of moths and other pollinating insects. It is hypothesized that the decline in butterfly populations is a secondary effect of heavy metal stress on local plants, which subsequently affects their pollinators.

Furthermore, haze smoke, which contains a mixture of gases and particles from forest fires, has been found to negatively impact the survival and development of butterflies. Exposure to haze smoke has been shown to increase caterpillar mortality, prolong larval development time, and decrease pupal weight. The toxic smoke gases and food sources affected by haze are believed to be the main contributors to these negative outcomes, rather than particulate matter.

The effects of air pollution and climate change on butterflies highlight the urgent need to address these issues. Conserving butterflies not only protects their intrinsic value but also improves the environment for other wildlife and enhances the lives of people now and in the future.

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