Light Pollution's Impact On Amphibians: Understanding The Threat

Light pollution is a growing problem, with 20% of land on Earth now affected by artificial light. This has a detrimental effect on amphibian populations, which are already in decline due to environmental stressors such as climate change, habitat loss, and pollution. As amphibians are sensitive to environmental changes, they are useful for studying the impact of light pollution on other species. Research has shown that light pollution can affect the growth, development, and activity of amphibians, as well as their breeding and foraging behaviour. For example, the calling behaviour of many frog species is disrupted, and red-backed salamanders from North America hide in the leaf litter rather than foraging under artificial light. Artificial light can also increase road mortality, as demonstrated by the American toad, which is attracted to street lighting and is therefore more likely to cross roads. The combination of light pollution with other stressors may have negative impacts on amphibian populations, and more research is needed to understand the full extent of this problem.

Light pollution affects the calling behaviour of many frog species

Light pollution has been shown to affect the calling behaviour of many frog species. Individuals call less frequently and move more often, which can reduce mating opportunities and negatively impact spawning success.

For example, a study on the impact of artificial light on male breeding-season behaviour in green frogs found that, when exposed to artificial light, frogs produced fewer advertisement calls and moved more frequently than under ambient light conditions. This has the potential to reduce recruitment rates and affect population dynamics.

Another study on wood frogs found that intensified daytime illuminance treatments and artificial light at night decreased hatching success in tadpoles.

The calling behaviour of túngara frogs also changed under different light conditions, suggesting that they felt safer under darker conditions.

Artificial light impacts the growth and development of larvae, juveniles and adults

Artificial light at night has been shown to have a detrimental impact on amphibians, affecting their growth, development, and activity at the larval, juvenile, and adult stages.

Larvae

Laboratory experiments have revealed that exposure to artificial light at night can disrupt the growth and development of amphibian larvae. For example, one study found that tadpoles exposed to constant light or light at night experienced reduced melatonin production, which affected their thyroid hormones, gonadal development, and reproductive behaviour. Another study found that increased levels of darkness contributed to a greater number of matured frogs, suggesting that light at night can delay metamorphosis. This delay could decrease the chances of tadpoles escaping a pond before it dries out or cools, increasing mortality rates.

Juveniles

Research on American toads has shown that artificial light at night can negatively impact juvenile amphibians. Juvenile toads exposed to artificial light were more active and had lower growth rates than those in dark conditions. This increased nocturnal activity resulted in higher energy expenditure, leading to reduced growth rates. These effects could have long-term consequences, including delayed reproductive maturity, lower fertility, and reduced survival, ultimately contributing to population declines.

Adults

Artificial light at night can also affect the behaviour and reproductive success of adult amphibians. For example, the calling behaviour of many frog species is disrupted, with individuals calling less frequently and moving more often, potentially reducing mating opportunities. Common toads exposed to artificial light during the breeding period decreased their activity levels and energy expenditure, which could negatively impact their reproduction and survival. Additionally, artificial light may increase road mortality, as seen in the American toad, which is attracted to streetlights and more likely to cross roads.

Light pollution can increase road mortality in amphibians

Light pollution can negatively impact amphibian populations in several ways, and one of the most pressing concerns is its potential contribution to increased road mortality.

Firstly, light pollution can disrupt the reproductive and calling behaviours of amphibians. For example, male green frogs exposed to artificial light call less frequently and move more often, potentially reducing their mating opportunities and subsequent spawning success. This disruption can have a ripple effect on population numbers over time.

Secondly, light pollution can directly influence amphibian behaviour in ways that make them more vulnerable to road traffic. The American toad (Bufo americanus), for instance, is attracted to street lighting and, as a result, is more likely to cross roads, leading to increased mortality rates.

Additionally, artificial light may impact the growth, development, and activity of amphibians at various life stages. Juvenile American toads under artificial light treatment exhibit increased nocturnal activity, which results in higher energy expenditure and reduced growth rates. This can have long-term consequences, such as delayed reproductive maturity, lower fertility, and decreased survival rates, further contributing to population declines.

Furthermore, light pollution can make amphibians more susceptible to other environmental stressors. For instance, tadpoles reared under artificial light at night are more sensitive to road salt pollution and tend to have higher parasite loads. The combination of light pollution with other stressors can have synergistic negative impacts on amphibian populations.

Overall, light pollution's effect on amphibian behaviour and physiology increases their vulnerability in human-altered landscapes, making them more susceptible to road-related mortality. This highlights the need for further research and the implementation of measures to mitigate the impacts of light pollution on these sensitive species.

Artificial light can cause stress and reduce energy expenditure in amphibians

Artificial light at night can have a detrimental effect on amphibians, causing stress and reducing energy expenditure.

Amphibians are highly sensitive to environmental changes, and artificial light at night is an increasingly common phenomenon due to industrialization, urban development, and suburban expansion. This type of light pollution can affect various aspects of amphibian life, including growth, development, and activity of larvae, juveniles, and adults, as well as reproduction and foraging behavior.

Research has shown that exposure to artificial light at night can decrease hatching success in tadpoles and make amphibians more susceptible to additional stressors such as road salt and parasites. For example, tadpoles reared under artificial light were found to be larger, less active, and more sensitive to pollutants. This increased sensitivity to stressors can have negative consequences for amphibian populations, especially when combined with other environmental factors such as climate change.

Artificial light can also impact the calling behavior of frogs, with individuals calling less frequently and moving more often, potentially reducing mating opportunities and affecting spawning success. Additionally, artificial light can disrupt the activity and energy allocation of amphibians during the breeding period, with male toads exhibiting decreased activity levels and reduced energy expenditure. This alteration in behavior could negatively impact reproduction and survival rates.

The effects of artificial light on amphibians vary depending on the species and their ecology. Some species, such as the cane toad, may benefit from street lights by foraging on the insects that congregate beneath them. In contrast, other species, like the red-backed salamander, may hide and forage less under artificial light. The impact of artificial light on amphibian populations is complex and requires further research to fully understand its long-term effects and possible interactions with other environmental stressors.

Light pollution may increase the detection of amphibians by predators

Amphibians are an important part of forest and aquatic ecosystems, and they are very sensitive to environmental changes. They are affected by chemical pollutants because of their skin. Frogs and toads can hibernate in winter and even inside mud because oxygen can pass through their skin. As such, they are important indicator species of the health of ecosystems. Their populations have been declining worldwide as a result of environmental stresses.

Artificial light at night (ALAN) has been shown to affect a range of animal taxa from mammals to birds, reptiles, and insects. The impacts of artificial light on amphibians appear to be varied, depending on the species and their ecology. For example, the calling behaviour of many frog species appears to be affected, with individuals calling less frequently and moving more often. This has the potential for decreasing mating opportunities and negatively impacting subsequent spawning success.

Indirect effects of artificial light may include increased detection by predators and subsequent mortality of amphibians. The American toad (Bufo americanus), for instance, is attracted to street lighting and is more likely to cross roads, leading to increased road mortality.

The ecological impact of light pollution on wildlife is a relatively new field of study, especially for taxa other than insects, sea turtles, and birds. More research is needed to assess the potential magnitude of such impacts on biological diversity and to understand how artificial lighting patterns may influence wildlife behaviour at a broad scale throughout urban areas.

Frequently asked questions